Bull. Org. mond. Sante 1956, 15, 635-649 Bull. Wld Hlth Org.

SPLEENS AND HOLOENDEMIC IN WEST NEW GUINEA D. METSELAAR, M.B., D.T.M. & H. Head of the Malaria Division, Department of Public Health, Netherlands New Guinea

SYNOPSIS The author describes the results obtained in recent malaria surveys in West New Guinea, where what is essentially holoendemic malaria prevails. However, the spleen-rate in adults differs markedly from what is regarded as normal under holoendemic conditions according to the definition put forward at the Malaria Conference in Equatorial Africa in 1950. The author therefore concludes that that definition is not properly applicable to New Guinea.

The Malaria Conference in Equatorial Africa held in 1950 at Kampala, Uganda, proposed a working classification for malaria endemicity which, for the sake of simplicity, is based only on the spleen-rate in relation to age.39 According to this classification, malaria is labelled " " when the spleen-rate in children aged 2-10 years is constantly over 50% and that in adults is high. "Holoendemic" areas are those where the spleen-rate in children is constantly over 75 % but "low " in adults. From the report of the conference it appears, moreover, that holo- malaria is supposed to be accompanied by an absolute parasite- rate approaching 100% early in the second year of life and then declining throughout life, while the parasite density declines rapidly between the second and fifth year and then more slowly. The decline of all these malar- iological rates in the older age-groups is explained by growing immunity. The Wilsons were among the first to draw attention to this peculiar course of the various malariological indices.35, 36, 38 Their observations concerned the Digo-Bantu, a tribe in Tanganyika of about 600 people, who were investigated every two months for a period of 21 months. At first, Swellengrebel 30 did not accept that the spleen-rate in holo- endemic areas necessarily also declines with growing age. Considering it not impossible that there might be racial differences in the reactions of spleens, he expected to find in New Guinea a degree of malaria comparable to that in highly malarious areas of Africa but not accompanied by a declining spleen-rate. However, a visit to this island caused him to accept the views of the Wilsons. The spleen-rate in the areas investigated by

529 - 635 636 D. METSELAAR him in New Guinea 31 declined more than he expected them to do, while the heavy -rate was lower than that in the Digo-Bantu, which, in Swellengrebel's opinion, made it unjustifiable to attempt comparison with malaria conditions in Tanganyika. However, since Swellengrebel's visit, the Malaria Division of the Nether- lands New Guinea Department of Public Health has surveyed a new area in which the malariological data appear to be such that one wonders whether the previous views of Swellengrebel do not deserve renewed con- sideration, without, however, dogmatically accepting the influence of race.

New Observations in Netherlands New Guinea The newly surveyed area is the centre of the Nimboran valley, which is situated at about 140° E. and 2.50 S., 40 miles (about 60 km) south-west of Hollandia. The vectors are members of the Anopheles punctulatus group: A. punctulatus, A. farauti, and A. koliensis. Rain is perennial, with a total ofalmost 2600 mm, a maximum of 357 mm in January and a minimum of 127 mm in June (average of 17 years). Trans- mission occurs, therefore, the whole year round. The inhabitants are Papuans, a Melanesian race. Antimalarial drugs are administered in a dispensary and by the nurse of a recently opened infant welfare clinic, but it can be accepted that a complete course of treat- ment is seldom, if ever, taken. A number of villages were selected for observation, and spleen and parasite surveys were done in May 1953, February 1954, July 1954, and July 1955. Each survey included between 730 and 1000 people, all ages being well represented. In addition, children up to the age of 12 months in October 1954, of 2 years in February 1955, and of 11 years in May 1955 were investigated for malaria. The results of these surveys were very much alike. Birth-dates of practically all the infants and of many of the older children could be obtained from the books of the Mission. Absolute parasite-rate On an average, the absolute parasite-rate was 38 % in the age-group 0-2 months, 75 % in the age-group 3-5 months, 82% in the age-group 6-8 months, 89 % in the age-group 9-11 months, and 34 % in adults of 25 years and over. In Table I the average of the surveys is compared with the findings in two African tribes in Tanganyika.10 35 Heavy infection-rate and parasite counts Our heavy infection index is not completely comparable with that of the Wilsons. They counted parasites against leucocytes. We regarded blood HOLOENDEMIC MALARIA IN WEST NEW GUINEA 637

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, 0-co 0 D C0 .0 E20 X * D Ml 0 CF 0 co 000§ S U) -I 4. -. co O0 C C C C -c U).c co "_ a) 0c 0 0 0 0 co co cm . . E U) U) a) a) «0l >C> (0>1 a-a@ 2(D C') o4 LO Co 2 Cli >1 I- _ Cli C; (6 a) CO UD a) 0 0 638 D. METSELAAR as being heavily parasitized when every microscopic field of the thick film was positive; for the type of film we make, this means a density of about 500 or more parasites per cubic millimetre of blood. The heavy infection- rate is the percentage of these heavy against the total number examined. For the July 1955 survey only, we had an opportunity to count parasites against leucocytes. The averages of the heavy infection-rate of the surveys mentioned above and the infestation index of the July 1955 survey are compared with the infestation index in the Digo-Bantu in Table II, from which it is clear that differences do exist. The figure for the Digo- Bantu is highest in the age-group under 1 year old, and for the Nimboran Papuans in the 1-year group. Though the rise is not significant in Papuans, it is not improbable that their parasite counts really show a maximum in the second year of life. After this, the decline with age is constant from the 1-year-old group up to and including the 12-14-year group. The maximum parasite count in Nimboran Papuans is about half as high as that which Wilson found in the Digo-Bantu. Without being able to calculate it, I accept that this big difference is really significant. An ex- planation of this discrepancy is not likely to be found in a smaller infection risk, which will be discussed later. One possible explanation can be found when the ratio between the species of malaria parasites is considered (Table III). In Digo-Bantu infants the more abundant Plasmodium falci- parum appears to be prevalent, and P. vivax in Nimboran babies. Another factor to be considered is the difference in the state of nutrition. In the area referred to by Wilson 35 there was considerable malnutrition, and from the age of a few weeks breast-feeding had to be supplemented by starchy foods. Nimboran mothers are, as a rule, able to breast-feed their babies completely for six months and longer. The opinion that breast-feeding may have a limiting influence on the number of parasites was expressed by Trowell 33 and is supported by recent findings of the influence of a diet of cow's milk on P. berghei in rats and mice22 and on P. cynomolgi in monkeys.4 Results of quite a different sort of experiment by Bruce-Chwatt 7 indicate that in rats humoral immunity to infection with P. berghei can be transmitted through the milk of immune mother rats. Innate immunity in children born of immune mothers has been observed by many authorities, e.g., Hackett,16 Garnham, 14 Swellengrebel,32 and Bruce-Chwatt.6 Taking into account what has been observed and what is known from experiments, it may be concluded that, as a rule, the breast-fed Nimboran Papuan infants also succeed in limiting the number of their malaria para- sites. They do so to even lower numbers than do the malnourished Digo- Bantu babies. This points to the possibility of nutritional influences, and the present investigations tend to stress the evidence that one or another of the mechanisms mentioned above as working in animal malaria may operate in Nimboran Papuan infants also. HOLOENDEMIC MALARIA IN WEST NEW GUINEA 639

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When passive immunity wanes and supplementary food is provided, active immunity is in most cases apparently strong enough in the Nimboran infant to prevent casualties, though the number of parasites rises to a maximum in the second year of life. This rise was not seen in the Digo- Bantu examined by Wilson, nor in the people in Tanganyika more recently seen by Davidson & Draper.10 Mackerras & Aberdeen 21 found the highest parasite counts in Papuans of Wewak to occur in the first year of life as well. However, the infants in their survey were born of war-refugees who, shortly before the survey, had been suffering from malnutrition and disease.

Sickness Our observations of the infants examined in our surveys do not point to much sickness from malaria as long as they are breast-fed, and it was not often necessary to provide them with anti-malarial drugs.

FIG. 1. AVERAGE WEIGHTS OF 51 NIMBORAN PAPUAN CHILDREN

Grams Grams 9000 9000

8000 8000

7000 7000

6000 6000

5000 5000

4000 4000

3000 3000

2000. 2000 0-1 1 2 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Weeks Months 1et 6t23

In the July 1955 survey, 69 infants were investigated and 44 were found positive, of which only 3 had 20 000 parasites or more per mm3 of blood. Gain in weight is as a rule constant as long as the infants get sufficient milk from their mothers. A total of 578 weighings of 51 children who regularly attended the infant welfare clinic were averaged by Miss S. Mal- colm, nutritionist of the South Pacific Commission. These averages are shown in Fig. 1, from which it can be seen that, apart from an initial fall, the curve shows a fall for one month only-at the age of 10 months- followed by a slight rise. Most infants show a reasonable or perfectly healthy appearance for the first 7 or 8 months, while apparent ill-health can

19* 642 D. METSELAAR

often be attributed to diseases other than malaria. By the end of the first and during the second year of life, their weight-gain is less rapid; some protein deficiency is most likely; they often look more anaemic; and they probably suffer more from their parasite burden than before. With increasing age, the average parasite count falls off again. In adults, even mild attacks of malaria are very rare. In the July 1955 survey, 20 000 or more parasites per mm3 of blood were seen only 10 times, apart from those in infants, the oldest with this high number being a child of 5 years. I do not pretend to claim that infants are not influenced at all by their malaria infections. We have no idea how many children directly or indirectly die of malaria. Infant mortality is high in New Guinea, varying between 30% and 50%. One cannot escape the impression that malaria has some- thing to do with it, as it probably has also with the general lassitude and lack of energy which can be observed in adults.

Ratio between species ofmalaria parasites There is also a difference in the ratios of the three species of malaria parasites between Nimboran Papuans on the one hand, and the Digo- Bantu on the other (Table III). In the Digo-Bantu P. falciparum prevails markedly over the other species, while immunity is developed more rapidly against the latter than against the first, resulting in a more rapid decline with age of the ofP. vivax and P. malariae. It is supposed that the most " strong " and dangerous parasite is able to push back the others, a phenomenon also found with P. cynomolgi and P. inui in monkeys.'7' 29 These tendencies are less apparent in Nimboran Papuans, in whom P.falci- parum just significantly prevails over P. vivax between 1 and 24 years of age only. Over 24, the difference is not significant. In the youngest age- group, P. vivax is the predominant species. Moreover, the rapidity of decline with age is almost equal for both species, resulting in a practically equal representation in adults. Many of these tendencies were also observed in a Papuan tribe near Wewak.21 There too, P. vivax was predominant in infants only. In older age-groups, the predominance of P. falciparum was more marked than in the Nimboran, but a number of the children investigated had been recently exposed to conditions. The course of P. malariae in Nimboran Papuans shows less divergences from what is usually found,28 though this species also is still well repre- sented at the adult age. Coatney and co-workers 8, 9 revealed that one of the characteristics of the Chesson strain of P. vivax, which originates from New Guinea, is the frequency ofits relapses, an interval ofsix weeks beingthe rule. Fairley 12 had noticed this too, and this quality is also well known to clinicians in HOLOENDEMIC MALARIA IN WEST NEW GUINEA 643

New Guinea. New Guinea strains of P. vivax are apparently not easy to suppress, while the frequency of relapses in itself must result in frequent findings during surveys. On the other hand, Lambert18 iS of the opinion that Melanesian malign tertian malaria, both in Europeans and in natives, is less often fatal and less severe than the Costa Rican variety. This might imply that New Guinea strains of falciparum parasites are less " strong " and less capable of suppressing relatively " strong " and virulent vivax strains (Fairley 12 cited by Manson Bahr 23). When comparing the relative incidence of both species of parasites in different races, one has also to keep in mind the high degree of resistance to infections with P. vivax often observed in Negroes.40

Infection risk The basic factor which determines the degree of endemicity ofan area is certainly the number of infective mosquito bites per inhabitant per year. Wilson, Garnham & Swellengrebel 37 estimate that, for holoendemic malaria this has to amount to about 30, well distributed over the year. We have tried to learn the number of infective bites by direct measure- ment. From January to July 1955, a total of 81 whole-night catches were organized in a number of villages in the Nimboran area. Two native laboratory assistants caught mosquitos from sunset to midnight; two others from midnight to dawn. They followed the habits of the local people, sitting outside the house during the evening and collecting indoors when the people went inside to sleep. They were instructed to catch mosquitos on their own legs only. Months of heavy and moderate rainfall were represented in the period of this experiment, and the number of anopheline mosquitos varied accordingly. At the height of the rainy season, not all the mosquitos could be caught. On an average, 34 anophelines per person per night were actually collected. The glands of 497 could be dissected, eight of which contained sporozoites (1.6 % ± 0.6). Before this experiment, in the course of 1954, 2555 vector anophelines, collected in the area, had been dissected by the Sergent method, and 27 positives (1 %±0.2) had been found. Taking 1 %-1 /2 % positives as normal, and a mean of 34 anopheline bites per night as representative for the whole year, then a Nimboran Papuan is infected about 150 times per year. Most probably this figure should, in fact, be higher. The same problem as that encountered in other highly endemic regions- namely, the discrepancy between this high number of infections and the relatively slow rate at which infants are infected-is met in the Nimboran valley. Exposure to a risk of more than 2 infections per week ought to result in a parasite rate of 100% much earlier than is in fact the case. Muirhead Thomson 26 observed that older children and adults are more attractive to anophelines than are infants and toddlers, but this can only partly explain the 644 D. METSELAAR

discrepancy. Davidson & Draper 10 and Bruce-Chwatt5 look for an explanation to the passive immunity obtained from the immune mother. So far, our observations are much in accordance with those made in other regions which are qualified as holoendemic. However, an important difference will become apparent when comparing the spleen-rates of Nim- boran Papuans with the rates in these holoendemic areas.

Spleens The average spleen-rate of five surveys of Nimboran Papuans, based on 3636 palpations, is compared in Table IV with the spleen-rates of two African tribes in Tanganyika. The high rates in the older age-groups of the Papuans are striking. The differences between Papuans and Africans are significant in the 5-10-year age-groups and older. The average enlarged spleen declines in the Digo-Bantu from a maximum of 3.6 to 0.8 (Schiiffner classification) at the age of 25 years. These figures are 3.2 and 1.9 in

TABLE IV. COMPARISON OF THE SPLEEN-RATES IN NIMBORAN PAPUANS WITH THOSE IN TWO AFRICAN TRIBES

Nimboran Papuans Digo-Bantu a 1 Sigri Valley, Tanganyika b

spleen (years) W aspleera age-(ears)ge (years) spleen-ratespenrtage (years) |

Under 1 80 + 2.6 Under 1 89 + 2.8 Under 1 51 ± 3.2 1- 5 95 ± 0.7 1- 5 93 1.2 1- 4 89 2.5 6-11 97 ± 0.6 6-10 77 + 2.1 5-10 73 i 3.2 12-24 .87 ± 1.3 11-20 44 2.4 11-14 53 +5.7 Over 24 78 ± 1.2 Over 20 39 1.2 Over 14 26 4.8

a Data derived from Wilson 35 b Data derived from Davidson & Draper 10

Nimboran Papuans. Thus, in New Guinea we find that the spleens ofPapuans remain constantly and considerably enlarged throughout their lifetime in spite of endemic conditions, which in other regions could lead to a marked decrease in the spleen-rate and in the size of spleen in adulthood. We made still another observation in New Guinea which points to the fact that Papuan spleens do not readily retract below the costal margin, once they have been enlarged for some time by malaria. A total of 49 Papuan -pupils of a boarding-school, aged 13-19 years, were given 25 mg of Dara- prim once weekly during a period of 15 months ; 49 others served as con- HOLOENDEMIC MALARIA IN WEST NEW GUINEA 645 trols. The boys can be regarded as semi-immunes. Before the experiment started, both groups experienced malaria attacks, with positive blood findings. In the run of the experiment, positive blood-slides were found regularly in the control group only. Nevertheless, the spleen-rate of the Daraprim-treated group fell from 79% ± 5.8 % to 63 % ± 6.9 % only, which is not a significant fall. The rate of the control group changed from 73 % ± 6.3 % to 77% + 6.0%. That a spleen-rate should not fall signi- ficantly after 15 months of prophylactic drug-intake is very unusual, and deviates from the experience elsewhere. 13, 15, 24, 25, 27 Moreover, in the Sentani Lake area in New Guinea, where the houses were sprayed with insecticides, the parasite-rate declined considerably one year after the first spraying, but the spleen-rate remained almost the same. The most probable explanation of these facts is loss of elasticity by excessive spleen fibrosis. In view of the experience with Daraprim in school- boys, this supposed excessive fibrosis must start at an early age. Comparative anatomical investigations by a pathologist will be necessary to find out whether these suppositions are true. If they appear to be so, then it may be asked why this phenomenon is seen in Papuans only and not in Africans. There is still another peculiarity of Papuan spleens. The absolute parasite-rate in infants, which is 38 % in the first quarter-year of life, rises through 75 % and 82 % to 89 % in the fourth quarter (Table I). The spleen- rate is 75 %, 87 %, 95 %, and 100 % respectively for the four quarters. The spleen-rate thus rises well ahead of the parasite-rate, which means that spleens in Nimboran infants are to a certain extent enlarged independently of malaria. The same was observed earlier in the Sentani Lake area and was confirmed there after spraying. In that area, during a period of 20 months, 2085 spleen-palpations were performed on 432 children born after spraying and free of malaria. A spleen-rate of about 19 % was found in the first month of life. Then it rose to a maximum of 69.5 %+3.8 % at the age of 6 months, after which the percentage fell again to 14 %±7.4 % at the age of 17 months. A rise in the last 2 months of observations was not signi- ficant and was probably due to the small figures for these two months. The palpable spleens were soft, and only a few large ones were seen. The ave- rage enlarged spleen did not exceed Schiiffner 1.3. Palpable spleens are not pathological in infants, but this high number seems unusual. Mackerras & Aberdeen 21 observed large numbers of enor- mous spleens in very young children at Wewak in New Guinea and speak of a " suggestion that many infants may be born with large spleens ". These spleens were firm and sometimes extended into the right iliac fossa. Whether their findings represent an extreme state of the same peculiarity as we found or whether they have a completely different cause remains an open question. 646 D. METSELAAR

Discussion Viswanathan34 recently introduced a new classification of malaria, in which " superendemicity" is distinguished from " holoendemicity ". In superendemic malaria, the highest degree of tolerance in adults is represented. It should be present only in races, such as the oldest tribes in India, for centuries exposed to frequent malaria infections, as a result of which a natural selective tendency towards a very high degree of tolerance has developed. The main characteristics of this superendemic malaria are: firstly, very little sickness in infants ; secondly, high parasite counts in these infants because, as a result of little sickness, the development of antibodies against the parasites is reduced; and thirdly, the practical absence of symptoms of malaria in adults, in whom tolerance is accompanied by a low spleen-rate. In Viswanathan's type of holoendemic malaria, which is developed in races that have been exposed to malaria for a limited number of genera- tions only, the parasite counts in infants are low and the spleen-rates in adults high. I do not think it necessary to accept Viswanathan's views as applicable to New Guinea conditions. For the relatively small average parasite counts in Nimboran infants and the high spleen-rate in adults other explanations than lack of racially determined immunity could be brought forward. Apart from this, Papuans must by now have been exposed to malaria infections for many centuries. Moreover, the experiments by Fabiana & Orfila "I indicate that in mice fed on a milk diet the combination of little sickness, low parasite counts and development of anti-parasitic immunity seems possible. In relation to the problem under consideration, one wonders whether the protection which the sickle-cell trait gives against malaria 1 has some- thing to do with the small spleens at adult agesL It occurs both in Africans and in the aboriginal tribes of southern India."' This needs investigation. Should a relationship become apparent between the sickle-cell trait and small spleens at adult ages in really holoendemic areas, one would be almost compelled to the conclusion that the Papuan spleen-rate represents the "normal" reaction of spleens in a population exposed to a high malaria- infection risk. The low parasite counts in Nimboran infants are not in disagreement with the characteristics of holoendemic malaria as given at the Kampala conference,39 and the absolute parasite-rate found in Nimboran Papuans agrees very well with them. The basic factor which determines the degree of endemicity-namely, the number of infections per year-can, as we have seen, be estimated in Nimboran Papuans at 150 or more per adult, well distributed over the year. HOLOENDEMIC MALARIA IN WEST NEW GUINEA 64*7

This, too, is well within the definition of holoendemic malaria. Only the spleen-rate runs a peculiar course: both in infants and in adults it is higher than that suggested for holoendemicity in the Kampala conference classi- fication. With regard to the high spleen-rate in infants, this appears to be independent of malaria and therefore cannot be used as a yardstick of . There remains the high spleen-rate in adults. The observations on Papuan schoolboys who took suppressive drugs and those on a population of an area sprayed with insecticides almost compel one to the conclusion that in some areas of New Guinea Papuan spleens simply cannot retract below the costal margin because they have lost most of their elasticity. The spleen-rate is only secondary to the number of infections and to the parasite-rate. When the latter two fit the definition of holoendemicity but the first does not, then it seems illogical to use the first as a yardstick of endemicity. I think I have made it clear that the Nimboran valley is one of the regions with the highest possible degree of endemicity. But the determination of the spleen-rate is not the way to assess this. On the other hand, the Kampala standard of holoendemicity can be applied rightly to the spleen-rates found in some islands east of New Guinea, but where the conditions differ radically from those encountered in Africa.2, 3, 20 Therefore, in reply to the invitation of the Kampala conference to test its proposals in the field, it must be concluded that these proposals do not suit New Guinea and the adjacent islands.

RJtSUMI! La Conference du paludisme en Afrique equatoriale, reunie a Kampala en 1950 etablissait une classification de l'endemie paludeenne et considerait comme zones d'holo- endemicite celles dans lesquelles l'indice splenique des enfants etait superieur a 75 %, de faqon constante, et se maintenait faible chez les adultes. D'apres le rapport de cette conference, l'holoendemicite serait caract6ris6e encore par un indice parasitaire absolu voisin de 100 % au debut de la deuxi6me ann6e de l'enfance, qui diminue ensuite au cours de la vie, tandis que la densit6 parasitaire d6croit rapidement entre la deuxieme et la cinquieme annee, ensuite plus lentement. Cette baisse des indices paludometriques au long de la vie s'explique par le developpement de l'immunit6. Ces conclusions avaient et6 etablies a la suite d'6tudes effectuees dans la tribu des Digo-Bantu, au Tanganyika, o'u 600 personnes environ avaient ete suivies pendant 21 mois. Cette baisse des indices paludometriques au cours de la vie ne fut pas accept6e par tous les auteurs comme critere d'holoend6micite. Certains d'entre eux avaient constat6 en effet, en Nouvelle-Guinee, un degre d'end6micit6 analogue a celui des r6gions fortement impaludees de l'Afrique, qui n'6tait pas accompagn6 d'une baisse de l'indice spl6nique a partir de l'enfance. Des recherches furent entreprises en Nouvelle-Guin6e, dans le centre de la vall6e de Nimbora habitee par des Papous, dans une zone ou l'end6micite rappelait celle de l'Afrique 648 D. METSELAAR

(pluie annuelle 2600 mm, transmission toute l'annee, vecteurs du groupe A. punctulatus). Dans les villages choisis pour cette etude, on a etabli les indices spl6niques et parasi- taires en mai 1953, f6vrier 1954, juillet 1954 et juillet 1955. Chaque enquete portait sur 700-1000 personnes, representant tous les groupes d'age. D'autre part, on a examine pour paludisme, au cours de ces diverses enquetes, des enfants de 12 mois, 2 ans et 11 ans. Apres avoir signale les diff6rences entre les donnees recueillies au Tanganyika et en Nouvelle-Guinee relatives A l'indice parasitaire absolu, aux especes de parasites en cause, A la morbidit6 et au risque d'infection, l'auteur developpe la question de l'indice splenique. Lorsque l'on compare les donnees des deux groupes, on est frappe par l'indice splenique 6leve chez les Papous adultes. Chez les Africains, la rate hypertrophi6e moyenne passe d'un maximum de 3,6 A un minimum de 0,8 A l'age de 25 ans; chez les Papous, ces chiffres sont respectivement 3,2 et 1,9. Les Papous conservent toute la vie une rate hypertrophiee, alors qu'ailleurs, dans les memes conditions d'end6micite, l'indice spl6nique baisse avec l'age. En outre, et contrairement a ce que l'on observe ailleurs, la chimioprophylaxie (en l'occurrence le Daraprim) n'a pu, en 15 mois, faire baisser l'indice splenique de fa9on significative. De plus, alors que les pulverisations d'insecticides avaient pour consequence de faire baisser l'indice parasitaire une ann6e apres leur application, elles n'affectaient pas l'indice splenique. Ces faits pourraient s'expliquer par une perte d'elasticite des tissus spl6niques, due A une fibrose excessive qui debuterait des le plus jeune age. II sera neces- saire de proceder A des recherches histologiques comparees afin d'etablir si ce phenomene est caracteristique des Papous ou s'il s'observe aussi chez les Africains. L'indice splenique, d'autre part, s'eleve plus rapidement que l'indice parasitaire durant la premiere annee de vie. En d'autres mots, l'hypertrophie splenique chez les nourrissons papous est, dans une certaine mesure, independante de l'infection paludique. Le nombre elev6 de rates palpables parmi les nourrissons est surprenant. L'auteur conclut que, dans la region impaludee qu'il a etudiee, l'indice splenique ne peut etre utilise comme critere d'holoendemicite. Les normes proposees par la conference de Kampala pour definir ce degre d'endemicite sont donc inapplicables en Nouvelle- Guinee et dans les iles avoisinantes.

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