Snail borne larval trematodes of the Okavango Delta, Botswana

[摘要] English: The Okavango Delta, situated in northwestern Botswana is one of the worlds largest inlanddelta systems formed by the Okavango River, flowing in a southeasterly direction fromAngola. The snail fauna comprises 20 species occurring in the Okavango Delta andsurrounding areas. The aim of this project was to determine what types of cercaria werefound infecting freshwater snails in the system as well as to determine whether humanschistosomiasis was present in the system. Snails are economically important because theyserve as the intermediate hosts for a number of parasitic diseases such as schistosomiasis inhumans and animals and paramphistomiasis in cattle. During two consecutive field trips tothe Okavango Delta in 1999 and 2000 freshwater snails were collected from various localitieswithin the delta. A total of eight different cercariae were shed from six different freshwatersnail species. Cercariae were described and placed into their respective families: Pilaoccidentalis shed a vivax cercaria belonging to the family Cyathocotylidae which arecommon parasites of birds, reptiles and mammals. Lanistes ovum shed a xiphidio cercariaebelonging to the family Plagiorchiidae and are known to parasitize amphibians and birds.Cleopatra elata shed a parapleurolophocercous cercaria belonging to the familyHeterophyidae which parasitize fish. Lymnaea natalensis shed two types of cercaria fromdifferent localities within the delta, the first type being a strigeid cercaria belonging to thefamily Diplostomidae and parasitising birds. The second type was a 27-echinostomatidcercaria 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 tothe family Schistosomatidae known to parasitise mammals and another strigeid cercariabelonging to the family Diplostomidae. Bulinus globosus shed a dark bodied amphistomecercaria belonging to the Family Paramphistomidae and are known to be parasites oflivestock. The prevalence of infection was higher in the 2000 survey than in the 1999 surveysince the localities that were sampled in 2000 were closer to human settlements. No snailswere found to be infected with larval trematodes, which could result in humanschistosomiasis. This study of snail borne larval trematodes provided insight into thedifferent kinds of larval trematodes that are present in this unique system and has laid thefoundation for further research of the different trematode life cycles occurring in theOkavango Delta.

[发布机构] University of the Free State