Snail borne larval trematodes of the Okavango Delta, Botswana

Abstract

English: The Okavango Delta, situated in northwestern Botswana is one of the worlds largest inland delta systems formed by the Okavango River, flowing in a southeasterly direction from Angola. The snail fauna comprises 20 species occurring in the Okavango Delta and surrounding areas. The aim of this project was to determine what types of cercaria were found infecting freshwater snails in the system as well as to determine whether human schistosomiasis was present in the system. Snails are economically important because they serve as the intermediate hosts for a number of parasitic diseases such as schistosomiasis in humans and animals and paramphistomiasis in cattle. During two consecutive field trips to the Okavango Delta in 1999 and 2000 freshwater snails were collected from various localities within the delta. A total of eight different cercariae were shed from six different freshwater snail species. Cercariae were described and placed into their respective families: Pila occidentalis shed a vivax cercaria belonging to the family Cyathocotylidae which are common parasites of birds, reptiles and mammals. Lanistes ovum shed a xiphidio cercariae belonging to the family Plagiorchiidae and are known to parasitize amphibians and birds. Cleopatra elata shed a parapleurolophocercous cercaria belonging to the family Heterophyidae which parasitize fish. Lymnaea natalensis shed two types of cercaria from different localities within the delta, the first type being a strigeid cercaria belonging to the family Diplostomidae and parasitising birds. The second type was a 27-echinostomatid cercaria belonging to the family Echinostomatidae and are known to be parasites of birds. Biomphalaria pfeifferi also shed two types of cercariae, a schistosome cercaria belonging to the family Schistosomatidae known to parasitise mammals and another strigeid cercaria belonging to the family Diplostomidae. Bulinus globosus shed a dark bodied amphistome cercaria belonging to the Family Paramphistomidae and are known to be parasites of livestock. The prevalence of infection was higher in the 2000 survey than in the 1999 survey since the localities that were sampled in 2000 were closer to human settlements. No snails were found to be infected with larval trematodes, which could result in human schistosomiasis. This study of snail borne larval trematodes provided insight into the different kinds of larval trematodes that are present in this unique system and has laid the foundation for further research of the different trematode life cycles occurring in the Okavango Delta.

Afrikaans: Die Okavango Delta is een van die wêreld se grootste binnelandse deltas. Die Okavango Rivier het sy oorsprong in die hooglande van Angola en vloei in 'n suid oostelike rigting na Botswana. Die varswaterslak fauna van die Okavango Delta en omgewing bestaan uit 20 spesies. Die doel van hierdie projek wat om vas te stel watter tipe serkarieë infekteer varswaterslakke en of menslike schistosomiasis in hierdie stelsel teenwoordig is. Siakke is van ekonomiese belang aangesien dit as tussengasheer vir 'n verskeidenheid van parasitiese siektes dien, bv. schistosomiasis by mens en dier en paramphistomiasis by beeste. Tydens twee geleenthede, in 1999 en 2000, is veldwerk die Okavango Delta uitgevoer waar varswaterslakke by verskillende lokaliteite versamel is. 'n Totaal van agt verskillende serkarieë is deur ses verskillende slak spesies afgeskei. Serkarieë is beskryf en tot familie vlak geidentifiseer: Pila occidentalis het 'n vivax serkarie afgeskei wat aan die familie Cyathocotylidae behoort en wat 'n algemene parasiet by voëls, reptiele en soogdiere is. Lanistes ovum het 'n xiphidio serkarie afgeskei wat aan die familie Plagiorchiidae behoort en daarvoor bekend is dat dit arnfibieë en voëls parasiteer. Cleopatra elata het 'n serkarie afgeskei wat aan die familie Heterophyidae behoort en waarskynlik visse parasiteer. Lymnaea natalensis het twee tipes serkarieë afgeskei, die eerste hiervan behoort aan die familie Diplostomidae en parasiteer voëls. Die tweede, , n 27-stekel serkarie behoort aan die familie Echistomatidae en parasiteer ook voëls. Biomphalaria pfeifferi het ook twee tipes serkarieë afgeskei, een behoortende aan die familie Schistosomatidae parasiteer waarskynlik soogdiere, die ander serkarie van die familie Diplostomidae parasiteer voëls. Bu/inus globosus het 'n donker gekleurde serkarie van die familie Paramphistomidae afgeskei. Hierdie parasiet is bekend daarvoor dat dit plaasdiere infekteer. Die persentasie besmetting van slakke tydens die 2000 opname was hoër as gedurende die 1999 opname. Geén slakke is aangetref wat besmet was met larwale trematode wat die mens kan infekteer nie. Hierdie studie het die grondslag vir verdere navorsing oor lewenssiklusse van parasitiese platwurms in die Okavango Delta gelê.