Trematode–gastropod associations in nine non-lacustrine habitats in the Mwanza region of Tanzania

Abstract

SUMMARYBetween August 1978 and July 1979, freshwater gastropods were collected at monthly intervals from 9 different non-lacustrine habitats in the Mwanza region of Tanzania. Of a total of 11 708 gastropods representing 14 species, 1748 (14'9 %) were infected with trematode sporocysts and/or rediae. Altogether 38 morphologically distinguishable' species' of cercariae were recovered (13 furcocercous, 10 xiphidiocercaria, 6 echinostome, 4 cystophorous, 3 gymnocephalous and 2 amphistome species), 22 of which did not conform to previously described African species. The majority (63'8 %) of all mature infections were xiphidiocercariae. Biomphalaria pfeifferi, B. sudanica and Ceratophallus natalensis each yielded 11 species of cercariae. Lymnaea natalensis had the highest overall prevalence of infection (36'9 %). Cercaria guttera from L. natalensis accounted for 20·4 % of all recovered trematode infections and C. blukwa from Biomphalaria accounted for 18'4 % of all infections; the high prevalence of these two xiphidiocercariae may alter the transmission patterns of Fasciola gigantica and Schistosoma mansoni, respectively. S. mansoni was recovered from both B. sudanica (22 of 2393 infected) and B. pfeifferi (79 of 1913 infected); S. haematobium (or related species) was recovered from Bulinus (Physopsis) nasutus (50 of 1503 infected) and to a lesser extent from B. (P.) africanus (6 of 186 infected). The findings are discussed in relation to the biological control of trematode diseases in Tanzania.

Schistosoma mansoni and other larval trematodes in Biomphalaria tenagophila (Planorbidae) from Guarulhos, São Paulo State, Brazil

“…Results indicate a low overall infection rate of snails with larval trematodes. This is in line with findings from other studies 2,7,21,27 . The low infection prevalence could be attributed to a direct consequence of high rates of parasite-induced mortality or resistance to infection acquired by host 34 .…”

“…In Brazil six to eight million people are infected and 26 million are at risk of Schistosoma mansoni infection. Currently, transmission occurs in 19 states and Federal District It is known that some trematodes may act as regulators of snail populations 21,24 . Studies on larval trematodes can also reveal the possible existence of certain trematode species that could be manipulated to achieve biological control of snail-transmitted diseases 9,12 .…”

Spatial heterogeneity in recruitment of larval trematodes to snail intermediate hosts

“…Like most freeliving organisms, such as marine invertebrates and reef fish, the recruitment of parasites to host populations is variable in space and time (Martin 1955;Robson and Williams 1970;Loker et al 1981;Sousa 1983Sousa , 1990Kuris 1990;Williams and Esch 1991;Kuris and Lafferty 1994;Lafferty et al 1994;Stevens 1996). This spatial and temporal variation may result from a variety of factors such as host movement, density, life history, susceptibility to infection; and parasite dispersal and behavior (Wakelin 1978;Anderson and Gordon 1982;Blower and Roughgarden 1989;Williams and Esch 1991;Sousa 1993;Grosholz 1994;Kuris and Lafferty 1994).…”

Structure and temporal variation of trematode and gastropod communities in a freshwater ecosystem

“…However, the species richness of the trematode collection in the whole gastropod community (10 species of cercariae) was not very high compared with other studies, e.g. nine cercarial species for seven gastropod species in the Albufera Natural Park (Spain) (Toledo et al, 1998), means of 12.3 trematode and six gastropod species in nine nonlacustrine habitats in Tanzania (Loker et al, 1981). Among the infected snails, prepatent infections were rare (8.1 %), probably due to the shorter duration of prepatency (a few weeks) versus patency (several months depending on the life-time of the snail), even if larval trematodes generally increased the mortality of their host.…”