MAP 1

E 718' F 8I2' G 86° H K 1 L 6 2° 90 94 98° 02° DISTRIBUTION OF FILARIAL INFECTION ,(based on examination of thick blood smears) Areas with filarial infection After Megaw & Gupta 1927. ASH4iR ± revised Acton & Rao 1931. `i I R ,-H

11 M. M U 9 MAP of UDHAMRUR 32 32 ( SHOWING PROVINCES AND DISTRICTS ).

REFERENCE.

Boundanes- International demarcated, undemarcated ZHOB

I , - Do, Province or State Do, Do

Do,. -- ..District and minor State

LaRALAi1

'GARNWAL S,q N CNAGAI E ALMO.

BUNOR.I= NAINIT/L-,1, a maputra R 28

TRACT

0 LARN'NA A I TRACT BALIPAM FRONTIER BRITT ÂN L

MTITLYINA

RIGA MILLS

- C.HAaiP

HYDERABAD; 24 AR

RAINA

i ÓI o CuTCH 6HWEB0; r' ¢! HIL

i1 LOWENCNINOWIÑI ,. NO

wLITNwAIfN AHAN SNAN STf P TRACTS.,

HANDESN

ABTAB 2 EpHANDESH Ml"BU ,) YAM ETNINi MADWE 11

DAMAN YAURPTM (POPTUGLI ESE

REFERENCES THAT

ORISSA (0.) COORG (C.) ANOLN', A I tlAu \) v 1 ANGUL 1 NORTH GOORO YjJ dávarl-ßL PUNJAB STATES (P. S.) 2 SOUTH COORG 1 RAPL,RTHALA BOMBAY (Bo.) AMABAO( NARiMNAGAR 2 NABHA MEHWAS A ] MALEP NOTLA 2 BROACH R RANCH NAHALB LOHARu ] OAMAN (Po,tuµw) èI 6 BILASPUR BOMBAY SUBURBAN S PATIALA O F 5 AHMAONAGAR U) T JiND SHOLAPUR 16 1 PUNJAB 0,1 T AHMADABAD I DUJANA A L 8 SURAT N (I 2 PATAUDI GWALIOR (G.) B ) FEROZEPORE 1 GIRO GWALIOR HISSAR REFERENCES UNITED PROVINCES 5 LUDHIANA (U. P)

6 ...LEM BENARES STATE EASTERN STATES (E. S.) BARODA (Be.) CENTRAL INDIA (C. I.) I SAMINELA 8NNARSAWAN 15 NHANDPARA AMRELI 151TAMAU 2 NAWARDHA NIMBI 16 NAYAGARN 2 NAVSARI 2 ) SANTI 10 ATHGARH 17 NAHPUR 3 6ARAHGARN 11 TIOIRIA 18 ATNMALLIN RfLJPUTANA (R.) AEI- RAJPUR 5 RHAIHAGARN 1) BARAMBA Iv TALCHER

I NISHANOARH S SAMTHAB 6 NANOGAON 1) HiNOOL a0 PAL Lama.

HHm, AN I. N RNNOL 2 TONTIBGARN T PAR. LINDA STATES OF WESTERN INDIA (S.W. I.) A N D BANTA 5 JASO weSTERN RITNIAWAR AGENCY 6 wADNwAN kMAN NATN11w1R DECCAN STATES (D. S.) 9 CHAR.:RI E Ew6TERN AGENCY a PAL1TANA BABAR BARTHA AGENCY N D B GUJARAT STATES (G. S.) LIMBDI 1 ANALNOT ISL RAOMANPUR 9 BNAUNDAR 2 SANGEI 1 SURGANA L ONRANOUNRA f0 VIJAYAMADAR 2 JAWNAR A C C A D ) JATN I V E (B.) BOLHAPIJR d HowRAH MADRAS(M.) ] JAMNNANDI PONDICHERRY NISTNA S (FRENCH) 6 MODHOL I L A N D S MA)1E MADRAS STATES (M. S.) (FRENC W NUMNDVAD C SAVANOR fl YNGANPALLE 9 RAMBLING liARIKAL PUBURNOTTA1 (PRENCN) ,0 6AVANTVA01 1 = 160 Miles. BOGN,N Scale Inch 11 MIRY (UAW Juni°,/ Miles BURMA (Bu.) 100 320 480 12 AUNOH mike 100 120 80 40 1] !MALIAN NANTHAWADOY BAL)JCHIST/LN (B.)

1BOLAN PASS 15 BHOR 0 94 98' 8 2H 8 6° 9 o' G 6° 7 0 74 HELIOZINCOGRAPHED AT THE SURVEY OF INDIA OFFICES. CALCUTTA.

RES No 1966. D 3,750 -- 500 -2, 000'29 -2,000 -400- 1,000'30- 1,500'34 -150 -400'38. 15.--1,000 -6,250'26 G. B 9tard, K.C.S.I., R.E., F.R.S., Surueyor General of India. Published under the direction of Colonel Sir S. COPYRIGHT RESERVED. (dawn 1915; 2nd 1930, 3rd 1934: 41h 1936. 1. III Copies of this map Can be obtained from the Map RecorO a Issue 011150. 13 Wood Street. Calcutta. Price: -Eight Anna.: with boundaries coloured One Rupee. Thesis for degree of Doctor of Medicine, University of Edinburgh :-

FILARIASIS IN ASSA(, WITH SPECIAL REFERENCE

TO THAT ASSOCIATED WITH MICROFILARIA

MALAYI (BRUG).

By

G. Fraser, M.B., Ch.B., (Ellin).

INTRODUCTION.

Most of the more important diseases that are

to be found in Assam have been very thoroughly investi-

gated, and the part they play and their distribution

have been well assessed. Notable examples have been

Kala -Azar, Malaria, Cholera, Hookworm disease, Yaws,

and, of late Nutritional diseases, the Anaemias and

Tropical Ulcer. A disease which has received very scant attention, and the degree and distribution of which has not been studied is Filariasis.

Filariasis itself in India as elsewhere has become more complex on account of the comparatively recent recognition of Mf.malayi, Brug. It is probable

that when its recognition and differentiation from Mf. bancrofti becomes better established it will be found

to have a much wider incidence than at present supposed.

It is proposed in this paper to discuss the

incidence of filarial infection in general in the

province of Assam, and in particular the occurrence of

Mf. malayi Brug; the mosquitoes which play the part of 2

vector of M Zf.malayi and the biological factors which

operate in the case of these vectors. The results of

the author's own investigation are given, and the

discussion is based mainly on these findings.

ASSAM. - Geography, physiography, climatology and population.

The administered area of Assam is nearly

70,000 square miles, as large as England & '.,Tales and a

third of Scotland. The population is a little over 9

raillions. It is situated in north east India bordered

on the "`est by Bengal, in the South by State

and the Chittagong Hill Tracts, on the East by the

Lushai Hills, State and Naga Hills contiguous lith Burma, on the North by Bhutan, and the lower eastern end of the Himalaya range. Except on the T','est, then, where it borders Bengal,it is surrounded by hills and mountains.It is divided into two valleys,separated by the North Cachar Hills, and the Khasia & Jaintia

Hills running practically East and Test,the upper being the Assam or Brahmaputra Valley, and the lower the Surma

Valley. In the Assam Valley the main river is the great

Brahmaputra winding from the north east corner along the northern part of the Valley to the north

estern corner where it abruptly turns South and then

South East through Eastern Bengal to empty into the

Bay of Bengal, in a delta on which stands the port of 3 -

Chittagong. The plains districts of the Surma Valley are two, Cachar in the Fast, Sylhet in the West bordering East Bengal; the main river is the Barak or

"urina rising in Manipur State, pursuing a very tortuous

course from East to Test through Cachar and Sylhet, finally emptying into the Brahmaputra in East Bengal.

In both valleys there are innumerable smaller rivers, in the hilly districts shift and moderately straight, in the plains slow and tortuous except at flood time.

The plains occupying the central part of each Valley, are very lot°: -lying - from about 300 ft. above sea level in the upper part of the Assam Valley to 70 ft.

in the Surma Valley at rice -land level. They form an alluvial tract of clay, sand and vegetable matter,and are freely cultivated for rice. In the Upper Valley there are large stretches of low flat plateau on which

tea is cultivated, but the Surma Valley is more broken up by isolated hillocks and small plateaus on which

the tea is grown. In both valleys swamps and stagnant water areas abound.

The annual rainfall in the Upper Valley

varies from 80 inches in certain districts to 125

inches in others. In Lakhimpur it is 120 inches. In

the Surma Valley it averages 130 inches, Sylhet being

a little more than Cachar. 7inor floods are common

\+ith occasional major floods in both valleys. The

range of temperature is from 80° to 95 °F. or higher 4 -

in the hot weather and rains, and 45° to 60 °F. in the cold weather, and the higher range continues roughly from April to October. The humidity in the plains of both valleys is from 70 to 100 per cent for about 7 months of the year. Finally, Cachar and Sylhet are about 180 miles distant from the sea (Chittagong),

Tezpur 300, and Dibrugarh in Lakhimpur is 400 miles distant (Map 2).

PRESENT VIEWS ON THE INCIDENCE OF FILAHIASIS IN AbSAM.

It is generally agreed filarial infection seldom to any degree occurs above 2000 ft., so that the hilly area of Assam is ruled out of consideration.

But the plains, apart from their low -lying situation, fulfill the requirements generally postulated for the occurrence of the infection : those are a range of temp. between 75° and 90 °F., and a humidity of over

60 per cent, for. 6. or 7 months of the year, the appro- priate carrier mosquitoes, and the infective human reservoirs. At the same time, in India, endemic areas are generally found either along the sea coast or in the neighbourhood of rivers. In this respect the plains of Assam are very similar to Bengal, especially Fast

Bengal,except that Assam has got no sea -board although on the other hand it has got a very large system of rivers. Bengal as a whole is one of the most MAP 2

O SAUn A

ñIeKUlA DIBRU G ARA

A. N U `` P " JORIIAT:1

N KAMRUP OWGONGr''' NOWGONG P PUT R A

o KORIMAi¡ GARO HILLS;' $HILLONG .. TURA KHASI &JAINTOA HILLS Q- Ir G MANIPUR 7 STATE `J SILCHAR O SYLHET 1MPHAL

O SYLHET MYMENSINGH SRIMANGAL 'T O

AIJAL DACCA LUSHP,I HILLS 0 9 o P P 92

tr"

2^^ O BARISAL Z O CHITTAGONG r

BAY I EIAL

MAP OF ASSAM SCALE 50 mYL ES TO ONE /NCH 5

heavily infected provinces of India, but Fast Bengal

lying adjacent to Assam, mainly the Sylhet district of

Assam, has an infection rate of less than 5; (Rao 1937).

Rao explains this as being due to the efficient drainage

by the river system of Fast Bengal preventing water-

logging. There appears to be a general impression

outside the province that Assam has also got a fairly

intensive filarial infection and Megaw & Gupta (1927)

and later Acton & Rao (1931) in their map of India

showing filarial distribution and intensity,mark Assam

as considerably infected. Rao also in a recent very

useful summary of the distribution of filarial infection

in India (1937) says that infection is present in most

districts; that districts lying on the banks of the

Brahmaputra show a fair amount of infection; and that

low -lying areas such as Sylhet, Tezpur and Jorhat on the banks of the Brahmaputra show heavier infection than

others in Assam. On page 8, however, he says that Assam

like the Central Provinces is a slightly endemic area.

On the other hand, the opinion held by most

medical men in the province is that filarial infection

must be very slight or absent in most districts. On

account of the few cases of filarial disease encountered

and from their experience they consider that the few

cases of infection or disease known never lead to

'endemic spread but rather die out.Such a keen observer las pr. G. C. Ramsay, the Principal of the Ross - F -

Institute in India, who has travelled extensively in

Assam and visited practically all tea estates advising on malaria control measures, and has seen considerable numbers of the estate population at spleen examination musters, was of the opinion that the incidence of filarial infection must be very slight to judge by the numbers exhibiting clinical signs, and that in most districts it appeared to be absent except for an occasional isolated case generally imported with the condition. He could refer to only one apparently ende- mic area and that was in Lakhimpur in the extreme north east of the Province (personal communication).

In this part of Cachar the writer has seen in a period of 10 years 4 cases of infection with what was diagnosed as M '.bancrofti. These cases ultimately ceased to show any microfilaria in the blood,and at the same time there was no evidence that they had started endemic spread. This was also the experience of his predecessor Dr. G.C. Ramsay. Other Medical Officers in the Surma Valley have remarked on the failure of the disease to take a hold in the low -lying plains districts of the Valley, and when this opinion was taken with special reference to Sylhet which is adjacent to Bengal, it became particularly interesting. 7

FILARIAL INFECTION IN SOUTH EAST CACHAR.

In the writer's medical practice, then,

filarial infection was practically non- existent,until

a few years ago supervision extended to a further

group of estates, separated from the original group by

a fairly large river, the Barak. Part of that area

( map3) was found to have numerous cases of elephan-

tiasis amongst its population, of which rumours had

previously been heard. It was obviously an endemic

area of filariasis. It was puzzling to understand how

the filariasis occurred in such active form in this

restricted area, and not elsewhere. Certainly the

terrain was low -lying and swampy but not more so than

innumerable other places of habitation throughout the district, further, the disease was of a very mild typey namely moderate elephantiasis of the extremities, generally the lower, and usually involving only one limb. A single case of mild elephantiasis of one arm was detected. It was found that genital elephantiasis, hydrocele, or chyluria, did not occur. Numerous cases of 1ymphangitis occurred. These features - the strict- ly local (but nevertheless fairly rapid) spread, and the mildness of the physical signs roused suspicions that the infection might be Mf.malayi. At that time,

Dr.J.J .C.Buckley from the London School of Hygiene &

Tropical Medicine arrived to study helminthological /n/KG ® e DOL/ LINES L A RA 4 G. CENT L HDSP ÁL Ó ;Fier MAP CACHAR DIST RIOT, 3

0 0 LABAKPA RO .C_',-!) ^'U Q 7TARAPUR T G. o , A/LA , , CHANO/aAPURóC O C C-/ J ALIPj(R !GHAL ITA 6 G'I` -} 3 - 3 . . NANDONkANON T. G. ° ° NA(`a.40UI/J/ a ° JIiNGLE

LAL PAN/ a ° ° ° " e Jrrishar [ JIRIGHAT T.G. ó0 é

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¡ DAL //DRAM PADDyLAND.._, LOWER JIRI RESERVED FOREST "_° -aa :r .: :_. N/ A°UPAI BÁLf PADDY LA 0 a °Q à: :v' UHUNBE PAW DA BU.YT Y CHHOTI MAMDH ,r o i 1 eCOOLIt f_/NE.' .°BARA /yAMDHA T Q PA4Dy L AND 4>"). o' n GOOLIS LI :: ON .á0, ° ró r-TOOLISLIN DUPE/0, RY e¡O 111

0. 10 PA=9USTy 0/4100USH G. J, .. r. L' I(A ALNI T.&. -4- .- ti.1. _121 ..iv ° NAI DAL LOWER JIM RESERVED FOREST J

11, Y

r< STATE Do .o MANIPUR r ae ALIACH.ÉkR/y RAUR , ' INN-04 as KANO/ T.6. -_ .1ö v, u .Y s e i h . , ... a a . e J O o`\ .. a , Coolie 4Ir¢S c I - @ e b e N...., °

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SCALE 1 INCH TO A MILE'

f{EFERENCES r

ROADS g FOOTPATH ------_

TROLLY LINE - - - - - o- girP RIYYER NA LL $ WATER COL/ SE ------BIL _ ,,,, °1 31L WITH OCCAS/NAL lvATER - - - BUIL OING -. tom:! ms es: HOlY1ESTEAD Coo LIE L /NE FACTORY &

_ 8 -

problems in the district and at the writer1s request examined the night bloods of the infected, and identified the microfilaria as '.Rf.malayi Brug. The infection rate in one set of lines was found to be over 305. Anopheles hyrcanus var nigerrimus ('ied.) was incriminated, although it was suspected that species of mansonioides w6 ld also be vectors. At that time however, the study of culicines had not been

undertaken at the writer t s laboratory.

Later, the writer himself investigated the area thoroughly with the following results :- TABLE I. Infection and Disease rates in the populations of Naidal, Rabipur, Alicherra, Tilkah T.E., Bhubonber and Powda Busty, in South East Cachar.

«Total Number Microfilaria Number with Mf. rate examined.in blood. . NAIDAL. Elephantiasis, etc. 9 1 11.11 No physical signs. 106 34 32.07 Total 115 35 30.43

RAB IPUR . Elephantiasis, etc. 2 1 50.'0 No physical signs 43 7' 16.27 Total 45 8 17.77

ALICHERRA. Elephantiasis, etc. 16 3 18.75 No physical signs. 380 43 11.31 Total 396 46 11.61 Total Number Number with Mf. Microfilaria examined. in blood. rate. %. TILKAH T.E.

Elephantiasis, etc. 9 -

No physical signs. 272 20 7.35 Total 281 20 7.11.

BHUBONBER.

Elephantiasis, etc. 4 - - No physical signs. 235 17 7.23 Total 239 17 7.11

POWDA BUSTY.

Elephantiasis, etc. 3 No physical signs. 505 27 5.34 Total 508 27 5.31

GRAND TOTAL.

Elephantiasis, etc. 43 5 11.62 No physical signs. 1541 148 9.60 Total 1584 153 9.65 TABLE II.

TYPES OF FILARIAL DISEASE. Ali- Naidol.Tilkah.Bhubon - Powda Rabi- Total.Percen- cherra. ber. Busty. mur. tage.

Elephantiasis of one leg 10 8 8 4 2 2 :S4 79.06

n both legs 1 - 1 - 1 - 3 6.97

n n rr n and one arm. - ï - - - - 1 2.32

Filarial lymphangitis 5 - - - - - 5 11.62

Total 16 9 9 4 3 2 43

Disease rate = 2.7%.

FILARIAL ENDEMICITY RnTE.

Number with signs of filarial disease .. 43 ) 191. 11 no signs but with microfilaria )

in blood .. 148 )

Total number examined .. 1584.

e Filarial endemicity rate 12%. Fig. i

I 2

1. Microfilari . malati. Brug ( Sheath noi shown.) 2. Of bancrofiL. Cobbold » 41

S l-a;.ti.Q,d, i'i ,Tei»-Ls d., MICROFILi RIA IALAYI BRUG . Description and Distribution as at resent known.

A brief description of Mf.malayi Brug 192'4and its differentiation from Mf.bancrofti Cobbold 1877, with a note on its vior1d distribution as far as it is at present known may be conveniently interposed here.

The microfilaria is on the whole rather shorter than Mf.bancrofti but its length varies considerably. It has been variously stated as 165 to

263p., 187 to 265pt (Brug 1927) , 220 to 260p (Manson Bahr

1935), and 145 to 1851u(Rao 1936). Mf.bancrofti on the other hand is 260 to 301.. The difference in breadth is insignificant. The cephalic space, that is, the anterior extremity devoid of nuclei, is about tl,ice as long as the breadth of the head in Mf.malayi and only equal to the breadth of the head in ]Tf.bancrofti. The nuclei are large, coarse, overlapping and hardly

countable in Mf.malayi; vhereas in Mf.bancrofti they

are neatly arranged, smaller, distinct, and countable.

The anal pore is more anteriorly placed in Mf.malayi,

at about 1/5 of the length from the tip of the tail.

It makes a clear indentation in the nuclear column and

is oval and deep, and very noticeable, whereas in

Mf.bancrofti it is faintly marked, situated to the

side of the nuclear column without breaking it, and

difficult to see. The tail is more tapering in

Mf.malayi, and in the majority of specimens one, two - 12 -

or three, but generally two, nuclei are seen, particularly one at the extremity, and one at the thicker (proximal) part of what is described as tail.

They generally stain much more deeply than the other nuclei, are conspicuous, and stain well with Giemsa.

They appear elongated in correspondence with the length of the microfilaria. In Mf.bancrofti, of course, the tail portion is devoid of nuclei. Transverse striation of the cuticle in Mf.malayi is not so obvious as in

Mf.bancrofti, but this is not a reliable feature. In thick films the disposition of the curves in Mf.malayi are irregular, coarse, with superimposed secondary waves in contradistinction to the long, smooth and graceful curves of Mf.bancrofti. On the whole, especially with Giemsa staining, Mf.malayi presents an appearance of being coarse, blurred, and dark staining, compared to the longer, apparently thinner on account of greater length, brighter staining and etched appearance presented by Mf.bancrofti and if the two are seen together in the same film or, better, in the same field of the film, the contrast is striking, and causes surprise that these differences remained so long undetected.

Both microfilariae are sheathed and have a nocturnal periodicity. Graphs of periodicity .( ?íg.12) of

M.2f.malayi in the Cachar endemic area are shown; it is interesting to note that Yen and Chang (1935) found P.M I A.M P.M A.M P.M A.M P.M A.M P.M ] A.M 6 3 912 3 9 12 2Oo 3 6 9 12 3 9 12. 6 912 3 6 6 9 i2 3 6 9 12 3 6 12 3 6 912 1000 3 6 9 3 6 912

J

160 800 2 Z

175

Ó O ,+4 600

ó H

é 400

Lk.

40 200

CASE No.1 CASE No.2 CASE No.3 CASE No. 4 CASE No.3

Fzg 12

3y courtesy of Dr. J.J.C. Buckley. -13 -

the peak concentration of larvae in the blood rather

later than these demonstrate.

Mf.malayi was first studied in Sumatra in

1926 by Lichtenstein (Lichtenstein 1927) who thought

he was dealing with Mf.bancrofti on account of the

sheath and periodicity. He became uncertain when he

found that culex fatigans :!Tied. could practically not be infected, and was in further doubt when he

found that the clinical signs of the disease were only

elephantiasis of the extremities even in heavily

infected areas with an infection rate of 30- 50%.There-

after Brug took up the study of the microfilariae from

these cases and deciding it was a new species called

it Mf.malayi. It was found to occur in Sumatra,

Java, the Celebes, New Guinea, and other islands

of the Malay Archipelago (Brug 1928; Monchtar 1929;

Van Gulik 1929; de Rook 1930; van Slee 1930;

Jurgens 1932; Rodenwaldt 1931, 1934; Scheepe 1935;

Vander Heijde 1937). At first it was thought not to

spread farther east than the lesser Sunda Islands and

the Molucca Islands, but it has since been found to be

common in China especially in Chekiang Province. Feng

(1933, 1934, 1935); Yen & Chang (1935). It has been

found in Malaya in Province Wellesley North (Strachan

& Morris, 1934), and in the States of Selangor, Perak

and Pahang (Hodgkin & Buckley, 1936). It has now - 14 -

been found by H.F.Carter in Ceylon where it appears to

be the main form of filariasis (Manson-Bahr 1935) .

In India the first to discover Mf.malayi

7,as Korke (1929) which he reported as the "atypical variety of bancrofti" in the sea -coast district of

Balasore in Orissa. This "atypical variety" would

appear to be the same as was reported by him from

"uzaffarpur in 2 years previously (1927). He

.:ould not agree that it was a new species, but argued

that as atypical forms, they might be adaptations of

the type species Mf.bancrofti to the culicine carriers

in the area.

Iyengar (1932) next reported Mf.malayi from

an endemic area with the heavy infection rate of 27.4 per cent in North in the south west of

India, and Rao (1936) found, during a survey in 1933,

Mf.malayi to be the sole microfilaria associated with

endemic filariasis in Patnagarh in Orissa, a small

rural town about 500 ft. above sea level.

The most recent discovery of it in India has now been that found in the endemic focus in south east

Cachar, identified by Buckley in 1934, as reported by

the :triter in his Presidential address to the Assam

Branch British Medical Association in 1936 (Fraser 1936),

this being the first ciscovery of Mf.malayi in the

province of Assam. - 15 -

A point which raises a major difficulty in

referring to this filarial infection, and the parti-

cular disease signs associated with it, is the fact that the parental forms of the worm have not yet been found, and so the generic name Filaria is not strictly

admissible. This fact excuses those who feel diffidence

in applying names to apparently new forms of micro - filaria.

::10S rUITO FAUNA IN THE CACHAR EPIDEMIC AdLA ANL VECTORS OF 11F. MALAY'.

The author continued the investigation of the original endemic area in and attention was first directed to the more thorough identification of the vectors. A.hyrcanus having previously been

satisfactorily proved to be a carrier in the area and other likely anopheles such as A.barbirostris shown to be insusceptible to infection by Dr. Buckley,

attention was turned to the culicines. The first

collection of identified specimens of the common

culicines of the area with the numbers of each caught

showing roughly the order of their frequency of occurrence was as follows :-

Mansonia (Mansonioides) uniformis Theo. 93 w

ti 11 indiana Edw. 44 n

Aedes (Aedimorphus) vexans Meigen. 42 - 16-

Culex (Culex) fuscocephalus Theo. 31 n

n ++ bitaeniorhynchus Giles. 10 + TT it tritaeniorhynchus Giles. 3 n tt tt fuscitarsus Barraud. y

II 11 cornutus Edwards. y

Subseuent collections showed also :-

Mansonia ('ansonioides) annulifera Theo.

Culex (Culex) vishnui Theo.

Mansonia (Coquillittidia) crassipes Van der ; "ulp.

The procedure adopted for discovering mosquitoes which were likely to be adequate as well as natural carriers was to take a heavily infected human host, place him in, or immediately in front of his house, in the evening, and capture alive all the mosquitoes which fed on him after they had been allowed to have a sufficient blood meal.

Experimental infection in the laboratory does not take account of the natural feeding habits of the

insects and t +naturaltt infection rates of mosquitoes based on dissections of random collections from human habitations frequently involve more labour than can be afforded, and the procedure causes resentment and opposition. The method adopted in this case is a

useful compromise and largely eliminates the

objections of the other two methods. The captured - 17 -

mosquitoes, then, were taken to the laboratory and

dissected some time after ten days. The results

were as follows ;- TABLE III. Number Humber Percen- dissec- oosi- tage. ted. tive.

nsonia (Mansonioides) uniformis 44 34 77.27

indiana 75 58 77.33

TT annulifera 14 9 64.28

Culex (Culex) vishnui 87 - -

t tt bitaeniorhynchus 25

Total 245 101

This agrees with the almost universal incrimi-

nation of three species of Mansonioides as being

important if not the main carriersof Mf.malayi - in

this case apparently in company with A.hyrcanus var

nigerrimus. The work of identifying the various

culicine fauna of the locality and the infectivity

investigations were carried in 1935 and 1936.

THE BIOLOGY OF THE MANSONIOIDES SUBGENUS.

Iyengar (1933, 1935, 1937), particularly, has drawn attention to the fact that the species of

Mansonioides lay their eggs on the under surface of

the leaves of the water plant Pistia stratiotes, and

that the larvae and pupae attach themselves to the

roots of Pistia by means of horn -like and strongly - 18 -

chitinised structures at the tip of the modified breathing syphons; these piercing structures penetrate the root tissue, and by this means the larvae obtain their oxygen needs from the air cavities of the root.

The larvae and pupae remain stationary there and do not come to the surface for air in those stages. Tn nature, :.ccording to Iyengar, eggs are found on the leaves of Pistia only, and the presence of Pistia is an essential factor for oviposition of riansoni_oides, furthermore Pistia is the only plant to which the larvae í:i11 attach themselves, and when Pistia is removed from a breeding place, the larvae also dis- appear from the breeding place although other. water

?plants may be present in the pond. Rodenwaldt (1934) also mentions the correlation of the plant Pistia stratiotes v,ith vectors of TRf.malayi.

PLANT HObTS OF id NSONIOIDES IN CaCW h.

In the endemic area in Cachar under discussion Pistia stratiotes does occur in patches of moderate quantity, and it occurs quite widely through- out the swamps, stagnant -water areas, and tanks of

Cachar plains generally. At the same time, at one spot in the area where infection Yas consiaerable, there was no Pistia within one to two miles. Mansonioides larvae were found breeding on their plant host

Pistia where it occurred, out it also was found as abundantly if not more so on the root of other aquatic - 19 -

plants, namely water hyacinth Eichhornia Crassipes, and "Doll, grass which is the local (Bengali) name for a coarse aquatic grass, whose botanical name would appear to be Sacciolepis interrupta Stapf,(syn.Panicum interruptum according to the authorities of the Royal Botanical Garden, Calcutta. (personal comminucation). This grass forms a weed partly aquatic and partly amphibious, growing in swamps,water logged areas and moist low lying lands. These three plants all have a similar type of root although that of Pistia appears the finest, and 'Toll' grass the coarsest. It is possible that there are other plants serving the same purpose. The larvae found in large numbers on these two plants and identified were

M.annulifera and M.uniformis or indiana, the last two being indistinguishable in their larval stage.

M.uniformis adults also were hatched out in large numbers. Other adults hatched out from these larvae were M.annulifera, and M.longipalpis. Species of

Coguillettidia, - the other subgenus of Mansonia, were also found numerously in the larval stage, on both hyacinth and "Dol" grass; these likewise have the syphonal valves mocified for piercing the tissues of aquatic plants.

In other parts of Cachar, it has been possible to find 1;:'ith ease the species of Mansonioides developing in the manner described on the three water - 20 -

plants, water hyacinth, "Dol" grass and pistia, and it

should here be pointed out that these three plants are

found growing profusely throughput the plains of the

Surma Valley in low lying water- logged areas, and that

":iansonioides species are amongst the most abundant

culicine mosquitoes encountered. Two more observations' are necessary, before leaving the subject of the mosquito fauna in Cachar, - one is the fact that

1..hyrcanus var: nicerrimus while of course not having the same life history as Mansonioides selects the same type of breeding place as happens to be suitable for fansonioides, i.e., swamps, and undrainable watery areas in low lying country and also tanks and borrow - pits. The other is the failure to find Culex fatigans in this part of Cachar. The writer has been on the look -out for this mosquito continuously for almost a year, and has had numerous catchers and surveyors

searching for the larva or adult in or around all the likely breeding places and adjacent habitations over a wide area in his district but without success.

Furthermore there is apparently no actual record of its presence in the districts of Cachar and Sylhet.

This is remarkable considering that it is described as the common house mosquito of the tropics and supposed

to be well -nigh universal. The possible significance of these observations will be discussed later. - 21 -

LAKIiIMPUR.

It was decided in 1937 to investigate the area in Lakhimpur in the north -east part of the Assam

Valley, \here a focus of endemic filariasis was suspected to exist. This was located on the south side of the small, tortuous and slow flowing Dibru river,

,;which flows from East to Test and empties at right angles into the Brahmaputra. It involved a tea estate

,nd the surrounding villages, 16 miles east of Dibrugarh town. On reference to the Medical Officer of the Tea

"states in that area it was definitely established that tea estates to a certain extent, and the villages in the vicinity to a greater extent, were affected with a gross degree of elephantiasis and other forms of filarial disease. The area was about 350 ft. above sea -level, and was intersected with slow- flowing,almost semi- stagnant streams and drains, and was dotted about lAth swamps, tanks and undrained collections of water.

The origin of the disease is obscure, it not being clear whether it started in the estate or adjacent villages as they are situated so close together. It is believed to have existed there for the last 50 or 60 years. It was soon found on examination of the night bloods of the inhabitants that both Mf.bancrofti and and Mf.malayi were present, one predominating more in one set of lines or village, and the other in another set of lines or village, .-.ith both infections occurring MAP 4 LAKNIMPUR DISTRICT & SADiYA FRONTIER-1ACT

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SCALE I ONE INCH TO A MILE

REFERENCES

ROADS á FOOTPATH - - - - TROLLY LINE - - - _ - _ - _ _ R / YE R , NALLA & OYATER COURSE _ - ß/L ------sC_%f° B/L kY /TH O OCAS /NAL IYATER _ - J', JU- HOMESTEAD, COOL /EL /NE, FACTORY do 8U/LD /NG- r. SsyAnT P _ _ MAP 5 $ ALIJAN SOUTH. T. F. (DISTRICT LAI4HIMPUR) WITH 'TIANLINE & NEPHAPHOO BUSTY ,3 g = one RAISED LAND . - ROADS WATERY PL ACES

OF WATER c+ c 0 POOLS 8. SMALL COLLECTION

Ea, 41. 4 BUNGALOWS pRAJAN op o C7 o HUMAN HABITATION KP o F CULER FATIGANS 0 J -.JUNGLE P/P9 LAND o o \4 A ----- 1.= IL

R InC E L A N

SWAMps/ V P I 1 - -- -- ,!` // .. - O --" _-- ö A PIS'TIq --- I STI A R

-r t E A IPF A

A 9 z p

ct T E A T E A T E

r O Ora O OCO a c or= u o 0 r oo TUKRA T E A OLD LINE LI NE T E A

T 0 o E A Ho PITAL ,4)

ol

RICE LAN: 1

- 22 -

siée by side in each locality and similarly a fair

number of dual infections in individuals.

Tables are given of the incidence of each

infection'in the various sets of lines and villages,

both individually and collectively for the whole area,

also giving the incidence of filarial disease infection

rate, and the endemicity rate. It will be seen that

though genital elephantiasis and the more severe forms

of the disease are not marked, nevertheless the

frequency of elephantiasis is more pronounced.

TABLE IV.

Infection arid disease and endemicity rates in the popu- lations of Christian Line Pathar, Nephaphoo Busty (Assamese), Nephaphoo Busty (Coolies), Tukra Line, Old Line and Ganjam Line.

Number P O S I T I V E. % CHRISTIAN LINE PATHAR. examined. Bancrofti ó ?:Zalayi ó Mixed ,G Total

Elephantiasis, etc. 12 2 16.66 1 8.33 - - 3 25.0

No physical signs. 140 14 10.0 22 15.71 2 1.42 38 27.14 Total 152 16 10.52 23 15.13 2 1.1 41 26.97

NEPHAPHOO BUSTY(ASSAMLSE)

Elephantiasis, etc. 6 - - 1 16.66 - - 1 16.66

No physical signs. 60 2 3.33 4 6.66 3 5.0 9 15.0 Total 66 2 3.03 5 7.57 4.54 10 15.15 dumber P 0 8 I T I V E.

; ralayi % Mixed NEPHAPHOO BUSTY(COOLIESgxamined. Bancrofti. % Total %

Elephantiasis, etc. 8 1 12.5 - - - - 1 12.5

No physical signs. 44 2 4.54 5 11.36 1 2.27 8 18.18 Total 52 3 5.76 5 9.61 1 1.92 9 17.3

TUKRA LINE.

Flephantiasis, etc. 4

No physical signs. 46 6 13.04 3 6.52 3 6.52 12 26.08 Total 50 6 12.0 3 6.0 3 6.0 12 24.0

III LINE. Elephantiasis, etc. 8 1 12.5 - 1 1.5

No physical signs. 113 11 9.73 4.42 4 3.53 20 17.69 Total 121 12 9.91 5 4.13 4 3.3 21 17.35

GANJAM LINE.

Elephantiasis, etc. 6

No physical signs. 65 8 12.3 4 6.15 2 3.07 14 21.53

Total 71' 8 11.22 4 5.63 2 2.81 14 1,-).71

GRAND T0TJ,L.

Elephantiasis, etc. 44 4 9.09 2 4.54 - - 6 13.63

No physical signs. 468 43 9.18 43 9.18 15 4.2 L01 21.58

Total 512 47 9.17 45 8.78 15 2.92 107 20.89 TABLE V.

TYPES OF FILARIAL DISEASE.

Christian Nephaphoo Bust . Tukra Old Ganjam Total.Per- Line --TASSA- (COOLLaS). Line. Line. Line. cen-

Pathar LiLJE) . tage.

Elephantiasis of one leg 7 3 5 2 5 4 26 59.00

" " both legs 2 3 3 2 2 2 14 31.81

n n ft and one arm. 1 - - - 1 - 2 4.54

of scrotum 1 - - - - - 1 2.27

" 1T and one leg. 1 1 2.27

Total 12 6 8 4 8 6 44

Both the scrotum cases came from Doomka district (Bihar recruiting depot.) v,ith elephantiasis about 15 years ago. No microfilaria found in their blood.

Disease rate = 8.6,°1

FILARIAL ENDELICITY RATE.

Number with signs of filarial disease .. 44 145. t " no signs but with microfilaria ) in blood .. 101 )

Total number examined ,., ., 512

Filarial endemicity rate 28.3°7

The mosquito factor yeas then studied and Table

gives the identification of a large number of culicine mosquitoes

captured in human dwellings, not in cow- sheds, before infectivity

experiments were undertaken. Particular attention was being paid

to culicines. - 25 -

TABLE VI.

Culicine mosquitoes caught in Lakhimpur, Assam Valley, showing relative frequency.

Name of species. Number caught. Percentage. Remarks.

IJiansonia (Mansonioides) uniforr.a.is 402 31.16

11 il indi ana 382 29.61 All were caught n ti annulifera 90 6. 97 from human habi- tations, not from Culex (Culex) fatigans 108 8. 37 cow-sheds.

II ti vishnui 308 23.87

Total 1290 OP-

Infection of mosquitoes was then taken up with

a view to finding the vectors. The particular method

desdribed for Cachar was used. It should be pointed

out that as the writer's particular interest was

Mf.malayi,, only cases of pure malayi infections were

used for feeding purposes, hence results refer only to

this microfilaria. These are shown in Table VII.

TABLE VII (See over). - 26 -

TABLE VII.

Mosquitoes dissected at Balijan T.E. (Assam) .

Number Number Name of species. dissected. positive. Percentage. Remarks.

Mansonia (Mansonioides. uniformis 32 27 84.37

indiana 28 27 96.42

annulifera 10 10 100.0

Culex (Culexl fatigans 16

u u vishnui 46

A.ahilippinensis 10 - -

" hyrcanus var niggerimus 9 7 77.77

" vaals 1 - -

Total 152 71

Nearly all mosquitoes which have proved

susceptible to Mf.malayi infection were dissected

within 14 days and showed mature or nearly mature

development of the filaria larvae at that time.

Examples of earlier mature development up to the

stage of labium involvement for the Lakhimpur

endemic area were as follows :-

TABLE VIII (See over). - 27 -

TABLE VIII.

Mosquitoes dissected at Balijan T.E. (Assam), about 10 days after feeding.

Labium stage of infection.

M.indiana. M.uniformis .

4 after 10 days 4 after 10 days

3 u 9 n 4 u 9 It

11 " 2 11 " Total 8 Total 10

M.annulifera. A.hyrcanus.

2 after 10 days. 3 after 9 days.

1 II 9 "

Total 3 Total 3

The three species of Mansonioides play their

part in the dissemination of filarial infection asso-

ciated with Mf. malayi in the human being, but

M.uniformis and M.indiana are probably more important

on account of their numerical superiority; M.annulifera

is a potent intermediate host, but it does not appear

to occur with nearly such great frequency as the other

two. This is comparable to what was found in Cachar. - 28 -

THE OCCURRENCE OF PLANT HOSTS OF THE MANSONIOIDES SPECIES IN THE LAKHIMPUR ENDEMIC AREA.

Pistia was found in a few places in a slugg- ish semi -obstructed waterway, and in a few swampy and stagnant water areas in the vicinity. The obstructed waterway was full of "Dol" grass however, and this grass grew luxuriantly in this type of terrain on all sides. Water hyacinth however, was absent from the area under investigation. (See map 5.).

THE INCIDENCE OF CULEX FATIGANS.

Culex fatigans adults were found in fair numbers in the human habitations of this area, as may be seen from Table VI At the same time numerous breeding places with larvae of C.fatigans were found in pools associated with stand pipes in the lines, in odd barrels and receptacles, and in borrow pits, and such excavations containing water. These are marked

"F" on Map 5. It was planned to carry out more extensive investigations in Lakhimpur particularly confirming the fact which is at present assumed, that

C.fatigans is the carrier of bancroftian infection, in conformity with its role elsewhere in India, and also a more extensive infectivity survey of the mos- quito fauna. It was also desired to explore the extent of this endemic area of filariasis of the two types, but further efforts had to be abandoned owing to opposition by the inhabitants, especially the Assamese -29-

villagers, and other difficulties. The coolie or villager in Cachar is generally much more amenable

and co- operative than his Assam brother. Enough

information however, has been collected to show that

an endemic area exists in Lakhimpur, that it involves

infection with Mf.bancrofti and Mf.malayi almost

equally, that the infection rate for the combined

types is very high, and might be classed as hyper- endemic.

QUESTIONNAIRE ON FILARIASIS IN ASSAM, AND THE COTúCLU- SIONS FROM REPLIES THERETO.

In view of the fact that Assam had been credit- ed with having a fair degree of filarial infection,

(Megaw & Gupta; Acton & Rao; Rao; loc. cit.), a questionnaire was sent to all Civil Surgeons of districts, and nearly all Medical Officers of Tea

Estates in the Province. Replies were received from

all the former except one and as this concerned a hill tract it did not matter; two Medical Officers of

Estates did not reply. The questionnaire was as

follows :-

(1) Taking elephantiasis and other evidence of fila- rial disease as an indication, is there any fila- ri asi s in -

(1) Tea Estates under your jurisdiction.

(2) Villages in your area - to the best of your knowledge.

If so,

(2) To what degree does it occur - sporadic & rare cases, numerous and fairly general, or a restricted endemic focus 7 - 30 -

(3) In your opinion, were these cases imported with filariasis ?

If imported - can you give approximate date ?

(4) Have you any idea from where it was imported ?

(Filariasis malavi commonly comes from Patnagarh, !`uzaffarpur, Balasore,and other parts of Bihar & Orissa).

(5) Is filariasis increasing noticeably ?

(6) What is the nature of the filarial disease seen ? Moderate elephantiasis of the lower extremity, especially if only of one leg; very occasionally mild swelling of arm, would seem to indicate Mf.malayi when this mild degree is common to a number of persons in the same area; gross elephantiasis of various parts including scrotum, hydrocele, and chyluria are more associated with F.bancrofti.

The replies received indicated on the whole that cases occurred very rarely and that endemic conditions did not exist, except in the two areas previously regarded as endemic and now described here.

Cachar and Sylhet replies including that of the Civil

Surgeon, Sylhet, were emphatic in stating that cases of filarial disease were extremely seldom seen. Similar- ly, replies representing Jorhat and Tezpur indicated only the odd cases of filarial disease. On one large central group of gardens representing 20,000 labour population in Jorhat district, Sibsagar, not more than

12 cases of elephantiasis were known to exist, over a long period. There is however, one garden near

Dhansirimukh on the Brahmaputra where eleven cases of elephantiasis were known; there was no increase of - 31 -

cases apparent within many years but neverthelesss this

might prove a minor endemic focus. The information

given by the Civil Surgeon, Lakhimpur, regarding

records of hospital admissions to Dibrugarh Civil Hos-

pital in the last years is interesting.

"Taking hydrocele, elephantiasis and unexplained chronic oedema as evidence of Filariasis we had in the last 3 years -

Cases of Hydrocele (Definitely imported .. 115 (Probably .. 13 128

" of Elephantiasis (Definitely imported) .. 9

Case of unexplained chronic oedema. 1

138

It is probable that many of these hydrocele

cases were due to F.bancrofti, and the evidence in view

of what has been proved in the vicinity of the Dibru

river which is only 16 miles distant from Dibrugarh,

suggests that Lakhimpur contains to a greater or less

degree the only real endemic focus in Assam. The

Medical Officer in that area is of the opinion that the

endemic conditions radiate to a distance amongst the

villages, beyond the field investigated and described here.In other parts of Lakhimpur however, the Medical

Officers are definite in their views that filarial dis-

ease does not occur, except the occasional sporadic case.

It is, of course, realised that infection may

exist without clinical signs and symptoms, but where this is at all extensive as in an endemic area there

should be a noticeable degree of gross disease. Solitary - 32 -

cases of elephantiasis are everywhere met amongst un-

infected population. It is well -known that a great

number of those brought the conditions with them as

immigrants, many years ago, but these are not regard-

ed as being of any epidemiological significance.

Degree of filarial disease then is regarded as a

sufficiently useful primary indication of the endemi-

city of the disease in any area, and no centre can be

endemic for long without this gross evidence.

DISCUSSION.

Taking the results of the questionnaire first

of all, then, it would seem that with the exception of

the two endemic areas described, of which the extent

of the Lakhimpur one is not fully known, filarial

infection is not endemic in Assam. Occasional,

usually burnt out cases of elephantiasis and gross

filarial disease occur sporadically throughout the

province, but these do not appear to spread the

infection. This is in marked contrast to the neighbouring provinces of Bengal, Bihar and Orissa,

which are heavily infected provinces. It is the more

surprising when it is considered that these three

provinces pour vast numbers of emigrants into Assam;

Bengal sending cultivators, fishermen and forest

workers admittedly mainly from East Bengal where the

infection is much lower than the west side, and Bihar - 33 -

and Orissa providing by far the greatest number of

tea garden coolie labourers for the estates. As has

been shown, the atmospheric conditions would appear

optimum in the plains of Assam for the propagation of

the disease and likewise the physiographical ones, and

therefore it seems difficult to believe that in the

last 5 or 6 decades or more, sufficient human carriers

of the disease have not been imported from the neigh-

bouring provinces to spread the disease extensively.

So far as is at present known the main type is due to

F.bancrofti of which the chief efficient intermediate host in India is C.fatigans, and in a large part of

Cachar it has been shown that this mosquito is not

found and if it occurs must be very scarce. If this holds good to any great extent it would account for

the absence of bancroftian filariasis without further

consideration, but more extensive surveys are required before this point can be ascertained. It is believed however, that its absence accounts for the failure of bancroftian filari asis to take a hold in Cachar and

Sylhet. On the other hand where it has been found in

Lakhimpur, there also was endemic F.bancrofti infec- tion.

Mf. malayi.

Iyengar (loc.cit.) has pointed out the signi-

ficance of Pistia stratiotes, an aquatic plant,in

sub - serving the part of plant host to the metamor- photic stages of Mansonioides species, which are - 34 - successful carriers of Mf. malayi. At the same time he (1937) ,and Sweet and Pillai (1937) show how under the Government of Travancore an endemic area of

Mf.malayi infection was controlled successfully over

25 miles by "species sanitation ", directed against

Mansonioides by biological measures. These biological measures were the destruction of Pistia stratiotes over the area mentioned. This was carried on for 3 or 4 years, with absence of infection in the young children of the biologically controlled area in contrast to an unchanged rate in the young children of the neighbour- ing uncontrolled area. Iyengar stated that in N.

Travancore only Pistia acted as host for Mansonioides; it was indispensable and its removal involved the death and disappearance of Mansonioides larvae although other aquatic plants were still left in the pond. He also commended this control work to other areas with similar conditions. In this he is justified, but the writer has found in Assam that Pistia is by no means the only, or even the most important, water plant acting as an essential host to Mansonioides; two others which are known are water hyacinth and "dol" grass, a kind of sedge with similar roots, common and abundant.Compared to these two, particularly the latter, Pistia is only fairly common, and in the case of one infected area, does not exist within a radius of over a mile. Pistia then is not the whole story and it would be unfortunate - 35 -

to give the impression that it is everywhere the only

problem in this connection. In some low lying parts

in Assam, water hyacinth is not always found, but "dol"

grass is very widespread in its occurrence. The removal

of these three water weeds then (and there may be

others) is required as a biological means of species

control of Mansonioides which actually is rather a

forbidding proposition akin to the formidable one of

cleariñg water hyacinth from waterways for traffic

and other purposes. (See Plate 5.).

While on the subject of "Dol" grass it is

interesting to note that only a few years ago the

writer was concerned to preserve it as a biological

measure in the control of malaria. The object was to

get sufficient denseness of the grass above the surface

of the water to cover it, and provide shade to dis-

courage the breeding of A.minimus.

The control of the spread of Mf.malayi in

Assam is difficult; Mansonioides are very common rural

mosquitoes, with their type of breeding place in abun-

dance nearly everywhere in the plains. At the same time

there is A.hyrcanus var nigerrimus to be considered.

It breeds very largely, though not altogether, in the

same type of place as Mansonioides; it does not how-

ever feed freely on human blood but largely on animal blood, nevertheless it would require control, and biological measures adopted for eradication of

IVlansonioides will not simultaneously suffice for -36-

A.hyrcanus, as it does not depend on the plant factor;

oil or paris green would therefore be required which,

under the circumstances, would not be feasible.

To limit the spread of the infection is the most that can be done, and it should be possible to

confine it to its existing area. in Cachar it is

spreading readily from the original central area,

amongst the small villages and lines, helped by inter - marriage, out it appears so far to be restricted by the Barak river. This river, within a bend of which it is confined, with a high range of hills behind, acts as a natural barrier in the matter of comnunication and intercourse with places farther afield.

An obvious precaution is that Estates else- where should not accept transfer of coolies from the endemic area, either for labour, or in the course of marriage agreements,without having the night -blood of the individual examined. At the same time, Estates in the endemic area should make it known at the time of any transfer of the possible risk of introducing this infection from their area. If more attention had been paid to this infection at the medical inspections at the recruiting depots in the recruiting districts, especially Bihar and Orissa, Filariasis might have been kept out of Assam. It has always been the practice to examine recruits for other infectious diseases before passing them for migration. At the - 37 - same time Estates should make a point of themselves examining new arrivals for the presence of microfilaria, especially as so many have a good medical organisation.

It is nearly certain that in the Cachar endemic area the disease was originally introduced by one or more coolies recruited from Doomka recruiting district in

Bihar about 25 years ago. The people of the area point to one coolie woman with filariasis,still living in Naidal village, the central and most highly infect- ed village, who is regarded as having introduced the disease.

The question of preventive precautions in the case of immigration into villages is more difficult, and is a matter for the Public Health authorities.

Such im igrants are generally from Bengal, and of the cultivator class, and of late years such settlers have been very numerous. On the evidence so far avail- able, the form of filariasis such people might introduce from Bengal, would be bancroftian, which, as the writer believes, does not readily become established.

It is interesting to speculate where Mf.malayi infection in the human being originally arose. It occurs in Bihar and Orissa - was it introduced there by returned labour from Malaya, and disseminated to

Assam therefrom ? There would seem to be a possible connection between the Ceylon and Travancore infections through labour movements. -3s-

If these assumptions could be accepted it would appear as if Mf. malayi infection was compara- tively new in India, but until the occurrence of the two infections throughout India is re- examined in the light of our fresh knowledge, that is difficult to say.

Then again was Mf.malayi introduced from China to Malaya and the Malay Archipelago ?

The whole question opens up an interesting field of speculation and inquiry.

SUMARY AND CONCLUSIONS.

It is concluded that Filariasic is less common in the province of Assam than has been main- tained by previous writers.

There are nevertheless two well -marked epidemic foci - one in Cachar district in the Surma.

Valley, and one in Lakhimpur district in the Assam

Valley.

In both these areas Mf.malayi infections were discovered, solely in the Cachar focus, and mixed with

Mf.bancrofti in the Lakhimpur district.

The mosquito vectors of Lif.malayi in both cases were M.(Mansonioides) uniformis Theo.,

M.(Mansonioides) indiana Edw., M.(Mansonioidesl

annuli,fera Theo . , and. A.hyrcanus var nigerrimus (Wied) .

The plant hosts of the Mansonioid.es species in Assam have been shown to be Pistia stratiotes, -0Q-

Eichhornia crassipes (water hyacinth), and Sacciolepis interrupta staff ( "Dol ") grass.

These last two constitute new observations.

It is considered that "species sanitation" directed against the Mansonioides species by the removal of these aquatic plants is impracticable, and

A.hyrcanus presents an additional difficulty.

A search for almost a year in an area of 400 square miles around the Cachar focus failed to reveal the presence of Culex fatigans. If this is general it would account for the apparent rarity of bancroftian

Filariasis in the Surma Valley, and possibly, in a large part of the Assam Valley.

Culex fatigans, on the other hand, was found breeding freely in the endemic area of mixed infection in the Assam Valley.

Autopsy on three cases of malayi Filariasis in Cachar failed to reveal the parent worms.

The source and origin of Mf.malayi Filariasis and the route by which it has spread is discussed. - 40 -

List of references to filariasis, especially concerning Mf.malayi Frug, with concentrated abstracts of each.

1. Megaw, J.W.D., and Gupta, J.C., 1927 -"The Geographical Distribution of some of the diseases of India." Ind. Med. Gaz. Vol.LVTI T.299.

2. Brug, S.L., 1927 - "Een nieuwe Filaria -soort (Filaria malayi), parasiteer -ende bij den Mensch (voorloopige mededeeling)." Geneesk. Tijdschr. v. Nederl.- Indie. 67 (51t 750 -754.

M.malayi described as different from M.bancrofti. Scattered nuclei in tail and forward position of anal pore distinguishin; characters.

3. Korke, V., 1928 - 0bservations on the atypical variety of bancrofti and its significance. Part IV. Ind. J. Med. Res. 1928 -29, 161 1023-1031.

4. Brug, S.L., 1928 - " Filariasis in Ned.- Indie." Geneesk. Tijdschr. v. Nederl.- Indie. 69 (5) 681 -704.

Detailed description of M.malayi. Distribution of filariasis in D. E. Indies tabulated. Outline of problems waiting to be soly( in light of new discovery of M.malayi as a separate species.

5. Idem 1929 -t(Filaria malai n. sp. parasitic in man in the Malay Archipelago." Trans. Far Fast. Assn. Trop. Med. (India 192.7) 3. 279 -298.

6. Mochtar, A. 1929 - "Filaria- inderzoek te Benkoelen en Omstreken ". Geneesk. Tijdschr. v. Nederl.- Indie, 69 C10), 967 -974.

12.3% of 1051 cases positive for M.malayi in Benkoelen (Sumatra), Nocturnal habit of Mf. observed. No symptoms. Aedes aegypti founc negative experimentally.

7. Gulik, P.J. van. 1929 - "Microfilariasis in de Ketaunolakte." Geneesk. Tijdschr. v. Nederl.- Indie. 69 (12), 1141 -1148.

People of villages below 2,300 ft. in Ketaun (1''est Sumatra) are slightly infected with M.malayi. None found infected above this :;.;, altitude. 2015 people examined. Blood taken at 10 p.m. -41-

8. Rook, H. de. 1930 - "Filariasis onder de Papoeats aan den Boven- Pigoel' Geneesk. Tijdschr. v. Nederl.- Indie, 70 (8), 739 -745.

M.bancrofti common in Dutch New Guinea. ".malayi only in carriers imported from elsewhere.

9. Slee, W. van, 1930 - "Onderzoek naar het voorkomen van filaria to Mamedjoe ". Geneesk. Tijd. v. Nederl.- Indie, 70(5),444 -450.

24.7% of 1024 infected with N.malayi (and a few M.bancrofti) in Namedjoe (W. coast Celebes. Periodicity of M.malayi exclusively nocturnal (15.1 at night to 1 during day). (Clinical symptoms said to be same as F.bancrofti).

10. Brug, S.L., & Rook, H. de., 1930 - "Filariasis in Ned.- Indie. II. De overbrenging van Filaria malayi." Geneesk. Tijdschr. v. Neder1.- Indie. 70(5), 451 -472.

Ta.eniorhynchus Mansonioides annuli es and T. (M.) annulatus

experimental vectors of F.malayi. 93 , and 83% respectively. Natural infection 1.2' 1.9p. Probably T. (M.) uniformis and annuliferus will prove to be vectors also.

11. ,";cton, 7.1 %, & Rao, S.S., 1931 - The Diagnosis of Lymphatic obstruc- tion of filarial origin. Ind. Med. Gaz. No.1, Jan.1931 - -with a revised edition of Megaw & Gupta s 1927 map of filarial distribution in India.

12. Brug, S.L., 1931 - "Filariasis in Nederlandsch- Indie. III ". Geneesk. Tijdschr. v. Nederl.- Indie, 71 (3), 210 -239.

13. Idem '1931 - "Filariasis in the Dutch Fast Indies ". Proc. Roy. Soc. Med. 24 (6), 663 -673.

Repetition of previous papers. Periodicity of ^M.malayi 1 to 15 and 1 to 20, noon to night numbers, compared with 1 to 100 for M.bancrofti. Periodicity was reversed in a night worker. Atypical form descr bed by Korke said to be identical with M.malayi.

14. Brug, S.L., 1932 - Filariasis en elephantiasis. Geneesk. Tijdschr. v. Nederl.-Indie 76 2772-2776. -42-

15. Iyengar, M.O.T., 1932 - "Filariasis in North Travancore ".

Indian J. Med. Res. t 20 (2) , 671 -672.

Filarial infection resembling M.malayi. Did not develop in A.fatigans but readily did so in Mansonia annulifera. Natural infection 26% of 900.

16. Jurgens, A.L., 1932 - "De overbrending van Filaria malaya in de onderafdeeling Mamoedjoe". Geneesk. Ti'dschr. v. Nederl. -Indie 72 (15 953 -959.

In Mamoedjoe (west coast of Celebes) F.malayi is principally carried by A.barbirostris. Fxperimental infection 83%, natural infection 8.9% Human infection 37%. A.barbirostris scarce compared with T.annulipes. Aedes failed to be infected.

1.7. Brug, S.J., & Rook, H. de., 1933 - "Filariasis in Nederlandsch- Indie ". Geneesk. Ti'dschr. v. Nederl.- Indie. 73 5) 264 -279.

Mainly on epidemiology of F.bancrofti and F.malayi in E. Indies.

18. Feng, L.C., 1933 - "Household mosquitoes and human filariasis in Amoy, South China ". China Med. J., 47 (2), 168 -178.

C.fatigans is the only mosquito found naturally infected with filaria larva in Amoy. Low incidence of human filariasis due to scarcity of A.hyrcanus v. sinensis which is a better carrier.

19. Idem 1933 - "A comparative study of the anatomy of M.malayi Brug, 1927 and M.bancrofti Cobbold, 1877 ". China Med. J., 47 (11/12) , 1214 -1246.

20. Rodenwaldt, E., 1933 - "Microfilaria malaya im delta des Serajoe. I." Meded. Dienst. Volks :ezondh Ned. - Indie 22 (1 44 -54.

M.malayi and elephantiasis cruris common in Serajoe (Java). 41% and 3.25 respectively in some Villages. Taeniorhynchus annuliferus, T.uniformis, F.indianus and A.hyrcanus said to be chief vectors.

21. Idem 1933 - "Zur Morphologie van Microfilaria malayi ". Md. Dienst. Volk. Ned. -Indie 22 (1 54 -60.

22. n.n,T., 1933 - Iyengar, "Ovinosition in mosquitoes of the sub genus , !lansonioides:" Ind. J. Med. Res. 21 (1) July 1933. -43-

23. Feng, L., 1934 - "Intermediate hosts of microfilaria malayi in Chekiang, China ". Proc. Soc. exp. Biology, N.Y., 32 (3), 494 -496.

M.malayi transmitted by A.hyrcanus v. sinensis in Chekiang. Larva reaches infectivity in 6 days in July & August. Also develops in M.(Mansonioides) uniformis but in small numbers. Culex p1piens, Aedes albopictus and Armigeres obturbans negative.

24. Rodenwaldt, E., 1934 - " Filaria malayi under ihre Uebertrager ". Med. Melt, 8 (39), 1369 -1371.

Mentions correlation of plant Pistia stratiotes with vectors of M.malayi.

25. Strachan, J. H., & Norris, V.H., 1934 - "Notes on the incidence of filariasis in Province Wellesley North."

Elephantiasis and filariasis common in province wellesley North (Malaya). Microfilaria said to have a slight nocturnal periodicity Ìdentified as M.malayi.

26. Rodenwaldt, E., 1934 - " Filaria malayi im Delta des Serajoe. II ". Meded. Dienst Volks'ezondh. Ned. -Indie 23 (1 21 -43.

Eggs of ¡'lansonia spp. (carriers of M.malayi) are laid on the under side of leaves of the aquatic plant Pistia stratiotes. Infection rate of mosquitoes caught on human beings (stage of infection not stated). mansonia annuliferus 73.65 of 91. M.uniformis 66.6v of 12, M.indiana 71.4 of 7, and A.hyrcanus 88.9% of 18.

27. Idem 1934 - "Filaria malayi im Delta des Serajoe. III." Meded. Dienst Volks ezondh. Ned. -Indie, 23 (4I, 194 -212.

Suggests that.F.malayi might be controlled by eradicating Pistia from swamps. Injection of antigen made from Dirofilaria immitis into elephantiasis cases without microfilariae in their blood and persons with M.malayi in their blood gave equally strong reactions in each group.

28. Tyengar, M.O.T., 1935 - "Biology of Indian mosquito larvae that attach themselves to the roots of water plants.

Proc. Ro . Fntom. Soc. London Vol. X. .9.

`. Manson Bahr,- 1935 - "Manson's Tropical Diseases;' 10th Ed. 883, Cassell & Co.,Ltd. 30. Scheepe, F.L., 1935 - "De verspreiding der Filariasis in Indragiri (Residentie Riouw en Onderhoorigheden)." Geneesk. Tijdschr. v. Nederl.- Indie, 75 (15). 1197-1201.

M.ma:layi recorded in large territory on the Indragiri R.(Sumatrai 187, of 5,000 persons infected.

31. Feng, L.C., 1935 - "Some experiments v,ith mosquitos and Microfilaria malayi in Huchow (Chekiang, China)." Trans. Far -East.Ass. Trop. Med.(9th Congress),1, 491 -494.

Fengts experiments show A.hyrcanus v. sinensis most important carrier (probably) of r:T.malayi in Huchow area, but Mansonia uniformis may also participate.

32, Feng, L.C., & Yao, K.F., 1935 - "Observation on Filariasis in Huchow, Chekiang, China." Chinese Medical Journal Vol. 49, pp. 797 -801.

33. Yen, C.H., & Chang, T.L., 1935 - "The periodicity of Microfilaria malayi Brug as observed from a case in the Lester Chinese Hospital, Shanghai." Lingnan Sci. J., 14 (3). 399- 402.(Abstracted in T.D.B.

with graph) .

34. Hodgkin, E.P., & Buckley, J.J.C., 1936 - " Filariasis in the Sabak Bernam Peninsula ". Annual Report of the Institute for Medical Research. F.M.S., P. 87 -90.

Filarial survey in parts of Sabak Bernam Perak, F.M.S., revealed M.malayi. Experimental infection of mosquitos gave following results - A.barbirostris 1 out of 19 fed, A.hyrcanus v. nigerrimus 3 out of 57, (A.hyrcanus v. sinensis 0 out of 19), Mansonia annuliferus 129 out of 182, M. indigna 2 out of 10,

' :.uniformis 11 out of 11.

35. Fraser, G.11936-7 In`Presidential Address to the Assam Branch British Medical Association. Proceedings of the Assam Branch, March 1936. - 45 -

38. Iyengar, M.O.T., 1936 - "Entry of Filaria larvae into the body cavity of the Mosquito." Parasitology, 28 (2) 190 -194.

Mf. of bancrofti and malayi penetrate gut wall of C.fatigans and Mansonia annuliferus near or in proventriculus and escape into perivisceral cavity of thorax. Penetration occurs within two hours, in some cases 20 minutes.

37. Teng, L.C., 1936 - "The development of Microfilaria malajri in A.hyrcanus var. sinensis rTied." Chinese Med. J. Supplement. No.1 345 -367.

Development in mosquito described in detail. Cellular changes in each stage. Correlation of structures in microfilaria and infective larva.

38. Rao, S.S., 1936 - " Filariasis in Patnagarh (Orissa Feudatory State) ". Indian J. Med. Ties., 23 (4L, 871 -879.

Filariasis in Patnagarh entirely due to F.malayi. Mansonia (Mansonioides) annuliferus the commonest mosquito, found to be principal carrier. 23 of 110 natural infection.

39. Idem 1937 - "Distribution of Filarial Infection in India ". The Antiseptics XXXI V. (2) L p. 234 -242.

40. Heijde, C.G., van der, 1937 - "Samenvatting van een onderzoek naar microfilariadragers onder de Chineeschen arbeider bij de Bankatinwinning op Banka ". Geneesk. Tildschr. v. Nederl.- Indie, 77(21), 1288 -1297.

2.5% of coolies in Banka tin mines have M.mala i. No obvious pathological effect and no detriment to work.

41. Iyengar, M.O.T., 1937 - "Public health aspects of filariasis in India'. Indian Med. Gaz., 72 (5), 300 -307.

Points out that distribution of filariasis is not well known in India, though known to be widespread. Differential distribution of bancrofti and malayi not well known. -46-

42. Brug, S.L., 1937 - "De overbrenging van Filaria mala)ri te Kalawara (o.a. Paloe, Res. ',4anado) ". Geneesk. Tijdschr. v. Nederl.- Indie. 77 (24),1460 -1470.

In Kalawara (Celebes) F.malayi is carried chiefly by A.barbirostris which rarely attacks man elsewhere in the Archipelago. experimental infection 99% (6.5 - 8.5 days). Natural infection 8.1 %.

43. Sweet, & Pillai, V.M., 1937 - "Clearance of Pistia stratiotes as a control measure for F.malayi infection ". Indian Med. Gaz., 72 (12), 730 -734. PLATE 1 - Naidal village. Heavily infected lines showing typical breeding areas for Mansonioides & A.hyrcanus in the vicinity. Plate. 2

PLstta straiiotes -r PLate. 4

Water hyacinth

Eichhorni . Crasstpes r ii /Q t . , > ' ...7,,,,2,4'..., *4,,_' ~ ì _ , e , Y : , , ,w N ` - -,10.--; ,v al,r-:-.%-- I. ,:"3. r i7'it7 r .^,. i .I C. A; /j.,,j/M4(/. . 3+?":.` it,-0-.. w ,! .4. F '. . r7r, ;.1 A ya , ,` . . . ! i ,v ,>. . . i , 19 t4i í-`?ai_ ?, axr <,., i -1'. I, fr -,.'i .t e ,' , /} Lv1 e . .- .1 . 2, r';= ` . ,- .../ Z° > , . Tw-,,,(/'l -`C,. , `.a _fl' ,; }. %, ..¿ s + /' ..L.i x°` s .T.. '. r i °.í.' r ^ ti f' i. '/T. .G _ t\ ''' -4-.* PLATE 5 Swamp with water hyacinth and 11Dol" grass. 'DOL" grass Sacciolepis interru Pta stapf (Syn-Panicum interruP-turn willd. ) PLA^'L. 7 - 3w. )y area with 'ID°liT grass. PLai e 8

Egg cluster of Mansonioides on Leaf of aquatic plant water hyacinth (as seen under low povier magnification) . FLe. 2

S1S y:+a+.} : Zßc7:F,'.3 .. °. xew.cccccet >?>a:.» s Q 44rr,.r,>y% YriC}; . StÍKTee "'r: ir;yIrrSAPifg áFaí.:di t4u

Mansonioides unìformis (Theo) Fig. 3

Mansonioides uniformis (Theo) ( Larva) Fig. 4

Mansonioides indiana. (Edw) Flg. 5

Mansonioides indiana (Edw) ( Larva.) RE. 6

,s.7., A: , ---4"--4-".";if"--r-z--,

pao-Ty:- . ig.: 1V z4;1/ZgWargAo. ..,

i. 41 V q ..0,

VI

Mansonioides unnutifera. (Theo) FLg. ri

Mansonioides annulifera (Theo) (Larva.) Ftg. 8

Anopheles hyrcanus var nigerrirnus (Wied) Fi,g. 9

Anopheles hYrcanus var nigerrimus(Wi.ed.) ( L2:t,rva ) Fig. 10

Culex fatigans ( \rhea) Fig. 11

Culex fatigarts (Wìed) ( Larva )