Bilharzia in Lake Malaŵi - What Are the Facts?

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Bilharzia in Lake Malaŵi - What are the facts?

Henry Madsen, Jay R. Stauffer Jr., Peter Makaula, Paul Bloch, Adrianus Konings & Jeremy Likongwe 2006 Funding for this brochure was provided by the NSF/NIH joint program in Ecology of Infectious Diseases (DEB-0224958) and the work is conducted in collaboration with University of Malaŵi, Malaŵi Fisheries Department, and Malaŵi National Parks and Wildlife. Bilharzia in Lake Malaŵi What are the facts?

Madsen, H.1, Stauffer, J.R. Jr.2, Makaula, P.3, Bloch, P.1, Konings, A.4 & Likongwe, J.S.5 1) DBL Institute for Health Research and Development , Jaegersborg Allé 1D, DK2920 Charlottenlund, Denmark 2) School of Forest Resources, Penn State University, University Park, PA 16802, USA 3) Department of Community Health, Mangochi, Malaŵi, Africa 4) Cichlid Press, P.O. Box 13608, El Paso, TX 79913, USA 5) Bunda College of Agriculture, Aquaculture and Fisheries Science Department, University of Malaŵi, P.O. Box 219, Lilongwe, Malaŵi

Summary The open shores (Fig. 1) of Lake Malaŵi were considered free from schistosomiasis (=bilharzia, bilharziasis, or snail fever) transmission until the mid-1980’s, but transmission is now occurring along shores in the southern part of the lake (Nankumba Peninsula), and this may be related in part to over-ﬁshing. Several ﬁsh species including those that primarily feed on freshwater snails have declined in abundance. In addition to constituting a major health problem for people along the lakeshore, the increased transmission also affects tourism in Malaŵi. This brochure is meant to summarize current knowledge about bilharzia transmission in Lake Malaŵi so as to enable visitors and inhabitants to better judge the risks without creating unnecessary concern. Focus is on Nankumba Peninula, which has been most intensively studied but there are many other important foci around the Lake. There is a risk of infection but by following simple guidelines the risk can be minimized. Views expressed in the document are those of the authors entirely.

Fig. 1. Open beach at Chembe where transmission occurs.

1 Introduction Schistosomiasis (for further de- were considered free from schisto- tails see page 12) is a disease caused some transmission and only within by parasites (flukes of the genus Schi- relatively protected areas of the lake stosoma) and is widely spread in with presence of aquatic plants and many tropical and subtropical parts areas around inflowing rivers would of the world. The parasite requires transmission take place. The inter- two hosts during the course of its life mediate host snail, Bulinus globosus, cycle. In the intermediate host (cer- primarily is found in such habitats. tain species of freshwater snails), it During the mid-1980’s, reports that undergoes asexual reproduction and transmission took place in the lake the infective larval stage (cercariae) started to appear. In fact one of the are released from the freshwater snail authors (JRS) became heavily in- into the water; cercariae penetrate the fected in 1987 by SCUBA diving in skin of the final host (humans) with water contact, and sexual reproduction occurs. Although bilharzia or schistosomiasis, primarily the urinary form (caused by S. haematobium), has been a major public health problem for many years in many lakeshore communities all around Lake Malaŵi, there is evidence that transmission has increased in certain areas within the last 20 years. Investigations in Chem- be in 1999 showed that 87.5% of school chil- dren and 57.7% of the entire population was infected by the parasite. Previously, the Lake’s Fig. 2. Map of Lake Malawi showing stations men- open shores (Fig. 1) tioned in this report.

2 Fig. 3. Shells of the two intermediate host species for Schistosoma haematobium at Nankumba Peninsula, Bulinus globosus and B. nyassanus, and shell of Melanoides species which is the most common snail in the lake. the Lake and it is now evident that at tourists every year. Unfortunately, least in the southern part of the Lake many visitors become infected with (Nankumba Peninsula, Fig. 2) trans- schistosomes and some health orga- mission also takes place along open nizations such the American Centers shorelines with a sandy bottom (Fig. for Disease Control and Prevention 1). In this habitat, one of the authors (CDC) warn against visiting Lake (HM) discovered that another snail Malaŵi. The cause of the changed species, Bulinus nyassanus (Fig. 3), transmission pattern probably may is the intermediate host. In addition be found in the increased ﬁshing to causing a major health problem pressure resulting from the increased for local people, the disease also af- population density around Chembe fects an important source of income Village. It is well documented that a for the country, namely tourism. The number of cichlid species, including area around Cape Maclear is a World those that prey on freshwater snails, Heritage Site and is visited by many have declined in population density

3 Fig. 4. Sheltered bay at Same Bay (Chizumulu) where transmission takes place through Bulinus globosus, which is common among the stones and in other parts with vegetation. due to over-ﬁshing. Apparently this further elucidate the relationship be- has allowed the intermediate host tween over-ﬁshing, snail population snails to increase in density, thereby density, and schistosome transmis- creating the basis for increased dis- sion. ease transmission. We will try to

Fig. 5. Bernard searches for Bulinus globosus in habitat at Chembe Village.

4 Fig. 6. Bulinus globosus habitat at Msaka.

Schistosomiasis in Lake Malaŵi There are two species of Bulinus plants or stones that can function as that are documented to be interme- shelter against wave action and pos- diate hosts for Schistosoma haema- sibly predators. Bulinus nyassanus, tobium in Lake Malaŵi, B. globosus which is endemic to Lake Malaŵi, is and B. nyassanus. Bulinus globosus is found along open shores with sandy the most important intermediate host or gravel sediment. Transmission in for S. haematobium in Africa south the Lake occurs either in relatively of the Sahara and its role in the area well protected areas, harbors or pro- around Lake Malaŵi has been known tected bays (Fig. 4), where B. glo- for a long time. The role of B. nyas- bosus is intermediate host or along sanus as intermediate host, however, open shorelines with sand or gravel is a rather new discovery. In Lake bottoms (Fig. 1) with B. nyassanus as Malaŵi, B. globosus is primarily intermediate host. For transmission to found in protected areas with aquatic occur, there must be considerable human water contact, such that schistosome eggs are introduced and miracidia can find an intermediate host and cercariae can find a final host. In addition, transmission can occur by cercariae that en- ter the lake via streams or rivers. This form of transmission occurs primarily during the rainy season Fig. 7. Showing very high density of B. globosus in the and shortly after the rainy stream shown in Fig. 6. season most streams will

5 be isolated from the Lake and will visiting Lake Malaŵi. Transmission form pools on the shore. These pools is mainly restricted to areas with constitute important transmission considerable human water contact sites as well, because they may con- and therefore, if water contact in ar- tain water through a large part of the eas close to villages, protected areas dry season and they constitute an im- with aquatic plants and areas around portant habitat for B. globosus (Figs. stream or river inﬂows is avoided, 5-7). This form of transmission may the risk of infection is considerably occur in many areas around the Lake. reduced although not eliminated. Furthermore, human water contact Swimming and diving at open rocky may be signiﬁcant in these pools. In shores and around islands with little areas around the Lake, there may be human water contact is associated other habitats that could constitute with a minimal risk of infection. important transmission sites. The risk of infection is probably also For tourism, transmission along reduced if one avoids water contact the open shorelines is probably most between 11:00-14:00 hr, when most important, because tourists primar- cercariae are shed. ily would have water contact in such The snail fauna in the Lake sites (bathing, swimming and div- (Fig. 9) is composed of several spe- ing) and this is the form of transmis- cies but is dominated by species of sion that is a new development in Lake Malaŵi. To date, this form of transmission has been documented only in the southern part of the Lake (Nankum- ba Peninsula). In this part of the Lake, B. nyassanus (Fig. 8) occurs in relatively shallow water (from about 0.5 m deep). In spite of the transmission, one should Fig. 8. Bulinus nyassanus shedding cercariae of Schisto- not desist from soma haematobium.

6 Fig. 9. Shells of Lake Malawi.

Melanoides (Figs. 3 & 9, 10) that in These ﬁgures are obviously subject numbers constitute about 90% of the to a lot of variation from site to site. snail fauna. Bulinus nyassanus usu- Bulinus nyassanus lives primarily on ally constitutes less than about 5%. sand or gravel sediment and it usu-

7 Fig. 10. Live Melanoides tuberculata; very common in the Lake but has no impor- tance for schistosome transmission.

Fig. 12. Egg mass of Bulinus nyassanus Fig. 11. Bulinus nyassanus on sediment. on sediment. Usually it will dig into the top sediment and is therefore often not seen. ally digs slightly into the sediment sediment and movements in the sedi- (Fig. 11), where it feeds on various ment during storms. The snail lays organic materials. The species has a egg masses that are jelly-like (Fig. very strong shell compared to other 12) so they can attach to loose sedi- species of Bulinus and it probably ment. The eggs will hatch after 6-8 functions as protection against the days.

Fish fauna in the near-shore areas of Lake Malaŵi

The ﬁsh fauna in Lake Malaŵi is lier, transmission occurs along open unique with more than 850 species. shorelines with sandy or gravel sedi- Many cichlid species occur in the ment. In this habitat, several species near-shore areas and most of these of snail eating cichlid ﬁshes exist, are endemic. As mentioned ear- one of the most important of these is

8 Trematocranus placodon (Fig. 13). species, for example Metriaclima Although T. placodon feeds on many lanisticola, that also feed on snails different snail species, it prefers B. including B. nyassanus, do not crush nyassanus. The species has highly the shells, but suck and pull out as specialized pharyngeal jaws that en- much of the soft parts as possible. able it to crush snail shells. Other

Fig. 13. A male of the snail eating cichlid, Trematocranus placodon

Fig. 14. Stomach content of Trematocranus placodon. There are many shell frag- ments of Melanoides species and some almost intact shells of Bulinus nyassanus.

9 Fig. 15. Trematocranus placodon has special teeth on the pharyngeal bones that enable it to chrush snail shells. The problem to address The near-shore areas of Lake There may be other factors in- Malaŵi are the areas where the juve- volved and we are trying to address niles of many fishes find refuge; thus, those as well. For example, why has fishing within a zone less than 100 m B. nyassanus become important in from the shore is prohibited within the transmission in the southern part Lake Malaŵi National Park. In fact, of Lake Malaŵi? Is it possible that very fine-meshed (mosquito-net) the population density of B. nyas- seine nets are used directly from the sanus possibly because of over fish- shoreline. Clearly such practice will ing or other environmental changes remove a large amount of juvenile brought about by the increased hu- fishes and therefore seriously affects man population, has reached a level recruitment into the fish population. where it effectively transmits S. At the moment, we are conduct- haematobium? Or is it possible that ing a research project (funded by the visitors to the area have introduced NSF/NIH program in Ecology of In- another strain of the parasite that can fectious Diseases), where we have utilize B. nyassanus as an intermedi- discovered that the reduction in fish ate host? populations is highly correlated with Since transmission along the open the increased schistosome infection shorelines may be linked to reduced in Lake Malaŵi and we predict that fish numbers, we should be able to transmission can be reduced again if reverse the situation by protecting fish management is implemented. the fish population. At the moment,

10 we have been following ﬁsh and snail quired to mobilise people to imple- populations for 3 years and Chembe ment the ban are coordinated by one Village is now trying to ban ﬁshing of us (PM) with help of extension in the near-shore area. Activities re- workers in the area.

Fig. 16. Beach seining at Msaka.

Recommendations for visitors to Lake Malaŵi Adhering to the following simple season, avoid water contact close guidelines will minimise (but not to villages, as most will have such necessarily eliminate) the risk of streams in their vicinity. schistosome infection. Following Swimming and diving in the visits to Lake Malaŵi, be aware of Lake 200 m (and probably even 100 fatigue or ﬂu-like symptoms, and m) away from the shore would result consult a medical doctor for an ex- in minimal risk of attracting schisto- amination. some infection, even outside village Avoid water contact in harbour areas where transmission occurs. areas and other protected areas of the Along isolated shorelines, swimming Lake where local people have water and diving from the shore should not contact. result in exposure to schistosome Avoid contact with water in cercariae. streams and ponds behind the shore- Have a medical examination for line, as these habitats are potential schistosome infection performed high-risk transmission sites (as they about 2 months after visiting Lake are in most other African countries). Malaŵi. A schistosome infection Avoid water contact close to in- should not remain untreated. ﬂowing streams. During the rainy

11 Appendix

Human Schistosomiasis

Life cycle and distribution tions this process will take about 4-5 Schistosomiasis (=bilharziasis, weeks. Cercariae are liberated from =snail fever) is a disease caused by the snail and they should, within parasites of the genus Schistosoma a few hours, find and infect a final and is widely spread in many coun- host; otherwise they will die. Upon tries in Southeast Asia, Middle East, penetration of the final host the cer- Africa, and South America. The carium looses its tail and becomes a World Health Organization estimates schistosomulum, which will find its that about 200 million people are in- way to the lymph system, lungs and fected worldwide. its final position in the blood vessels The parasite changes hosts during around the intestine or urinary blad- the course of its life cycle, i.e. be- der (depending on species). tween the final host (humans), where the sexual reproduction occurs and the intermediate host (certain species of freshwater snails), where the asexual reproduction occurs. The adult parasites live in the blood vessels of the final host where they lay charac- teristic eggs (Fig. 18) which penetrate the wall of the blood vessels and make their way into either the intestine or the bladder depending on the schistosome species. If the egg enters freshwater they hatch to a miracidium which within a few hours should lo- cate and infect a suitable intermediate host snail. Within the snail, it produc- es a mother sporocyst which in turn starts to produce daughter sporocysts and these will migrate to the digestive organ of the intermediate host, where they will start to produce the infective larval stage, cercariae (Fig. 17). Fig. 17. Schistosome cercarium (about Under optimal temperature condi- 0.4 mm long).

12 Fig. 18. Life cycle Schistosoma haematobium and S. mansoni.

There are ﬁve species that infect mansoni utilizes different species of man and each uses certain species Biomphalaria as intermediate hosts of freshwater snails as intermedi- and S. haematobium uses certain ate host. In Africa, the most widely species of Bulinus as intermediate distributed species are Schistosoma hosts. Schistosoma mansoni is found mansoni that causes intestinal schis- also in South America and some of tosomiasis and S. haematobium, uri- the Caribbean islands. In Asia, S. ja- nary schistosomiasis. Schistosoma ponicum is the most distributed spe-

13 cies and it uses various subspecies of (vena portae). The body compensates Oncomelania hupensis as intermedi- for this by a gradual dilation of the ate hosts. minor blood vessels in the liver (col- lateral circulation). Similar changes Disease and symptoms will occur in the blood circulation of The disease (with clear morbid- the spleen. The parasite’s eggs can be ity) only develops in people that are carried by the blood stream to other heavily infected and is rarely seen in organs such as the lungs and the cen- tourists or other short-term visitors tral nervous system. to endemic areas. The clinical symp- For infections with S. haemato- toms are related to the parasite life bium, accumulation of eggs in the cycle. Within 24 h after the parasite’s wall of the ureter and the urinary penetration of the skin, patients can bladder is often associated with in- develop rashes and itching which flammation, granuloma formation, can last for 2-3 days. During parasite fibrosis and loss of elasticity of the migration through the host tissue, bladder wall and an increased pres- symptoms such as fever, diarrhea, sure in the ureter and kidneys. Pain coughing and swollen lymph nodes in connection with urination is com- often develop. These reactions are mon and cancer in the bladder wall acute and often start 2-3 weeks af- can develop. ter the initial infection and can last A common and clear symptom for 1-2 months. However, it it is the of infection with S. haematobium is host’s response against the schisto- bloody urine. Similarly, bloody stool some eggs that causes the most seri- is a common symptom of infection ous complications, and these are di- with S. mansoni and other intestinal rectly related to the level of infection schistosome species. Other symp- (number of worm pairs). toms may be an enlarged liver and For infection with S. mansoni, spleen resulting from the increased bloody wounds in the stomach and blood pressure in these organs. intestinal system caused by histolytic enzymes liberated by the eggs, often Epidemiology develops. In the liver, eggs trapped in People become infected when in the capillaries will cause an inflam- contact with water in which cercariae matory reaction due to the forma- are found. Transmission is often very tion of blood cell containing tissue focal and primarily occurs in places (granulomes) around individual eggs with intense human water contact. and the subsequent development of In areas with an abundance of good connective tissue, obstruction of the snail habitats and high human popu- blood vessel and increase in blood lation density, such as for example pressure in the big liver blood vessel irrigation schemes, transmission

14 can be very intense, but also natural parasite and it is given either as a habitats (streams, ponds, lakes) with single dose or split into halves given intense human water contact can be 6 hours apart. Medical treatment not important. The intermediate hosts only reduces the worm load dramati- are not normally found in fast ﬂow- cally but also results in a signiﬁcant ing water but in areas with human reduction in morbidity suffered from water contact suitable microhabitats the infection. In endemic areas, for the host snails may be found. people quickly become re-infected, although morbidity takes longer to Treatment reappear, and therefore it is desirable There is today an effective medi- to supplement with other means of cal treatment for schistosomiasis. reducing transmission such as con- The treatment is by 40-60 mg pra- trol of the intermediate hosts, infor- ziquantel per kg body weight de- mation campaigns, and improved pending on age and species of the water supply and sanitation.