Schistosomes of small mammals from the Lake Victoria Basin, Kenya: new species, familiar species, and implications for schistosomiasis control

Abstract

Recent schistosomiasis control efforts in sub-Saharan Africa have focused nearly exclusively on treatment of humans with praziquantel. However, the extent to which wild mammals act as reservoirs for Schistosoma mansoni and therefore as sources of renewed transmission following control efforts is poorly understood. With the objective to study the role of small mammals as reservoir hosts, 480 animals belonging to 9 rodent and 1 insectivore species were examined for infection with schistosomes in Kisumu, in the Lake Victoria Basin, Kenya. Animals were collected from 2 sites: near the lakeshore and from Nyabera Marsh draining into the lake. A total of 6.0% of the animals captured, including 5 murid rodent species and 1 species of shrew (Crocidura olivieri) were infected with schistosomes. Four schistosome species were recovered and identified using cox1 DNA barcoding: S. mansoni, S. bovis, S. rodhaini and S. kisumuensis, the latter of which was recently described from Nyabera Marsh. Schistosoma mansoni and S. rodhaini were found infecting the same host individual (Lophuromys flavopunctatus), suggesting that this host species could be responsible for the production of hybrid schistosomes found in the area. Although the prevalence of S. mansoni infection in these reservoir populations was low (1.5%), given their potentially vast population size, their impact on transmission needs further study. Reservoir hosts could perpetuate snail infections and favour renewed transmission to humans once control programmes have ceased.

The Role of Wild Rodents in the Transmission of Schistosoma mansoni in Brazil

“…They concluded that those rodents participate in the schistosomiasis transmission, but the human population is the main source of infection. Recently, Hanelt et al (2010) examined the extent to which wild mammals acted as reservoirs of S. mansoni in Kenya. They found five murids and one shrew species infected with schistosomes (S. manoni, S. bovi, S. rodhaini and S. kisumuensis).…”

Out of Animals and Back Again: Schistosomiasis as a Zoonosis in Africa

“…Schistosoma bovis and S. mattheei are both principally parasites of domestic cattle; S. bovis is located throughout Africa but primarily north of 10 south, and it is replaced by S. mattheei south of this latitude (Nelson et al, 1962). In addition to domestic cattle, both S. bovis and S. mattheei have been naturally found in a variety of other artiodactylids as well as horses, zebras and rodents (Hanelt et al, 2010, Pitchford, 1977. There are even reports of these species from humans and baboons, although usually alongside a mixed infection with either S. mansoni or S. haematobium.…”

“…Schistosoma rodhaini, on the other hand, is primarily an infection of rodents, although there are past reports of dogs and even a serval cat being naturally infected in Central Africa (Pitchford, 1977, Schwetz, 1954. More recently, insectivore species around Lake Victoria have also been observed to be infected with S. rodhaini (Hanelt et al, 2010); baboons have been successfully experimentally infected, but only when also co-infected with S. mansoni (Nelson and Teesdale, 1965). The literature only mentions one reported case of a natural infection of S. rodhaini in a human, from what is now DR Congo (D'haenens and Santele, 1955); however, given the age of the reference and its isolation in the literature, it may be suggested that it is a case of false diagnosis of S. mansoni.…”

DNA Barcoding of Schistosome Cercariae Reveals a Novel Sub-Lineage within Schistosoma rodhaini From Ngamba Island Chimpanzee Sanctuary, Lake Victoria

“…Schistosoma rodhaini is commonly considered primarily an infection of rodents and insectivores (Hanelt et al, 2010). The species has a very patchy distribution in East Africa, where it co-occurs alongside the more widely spread S. mansoni; in areas of overlap, S. mansoni has been observed to be much more abundant, suggesting ecological dominance (Steinauer, Hanelt et al, 2008).…”

“…The species has a very patchy distribution in East Africa, where it co-occurs alongside the more widely spread S. mansoni; in areas of overlap, S. mansoni has been observed to be much more abundant, suggesting ecological dominance (Steinauer, Hanelt et al, 2008). This is perhaps due to the greater susceptibility of human hosts to S. mansoni compared with small mammals and S. rodhaini, which, for the latter, tend to have lower infection intensities (Steinauer, Mwangi et al, 2008;Hanelt et al, 2010). Intriguingly, at a single site in the Lake Victoria basin, genetic introgression between S. mansoni and S. rodhaini has been observed (Steinauer, Hanelt et al, 2008); several snails collected from this region near Kisumu in Kenya were co-infected with both species of schistosome (Steinauer, Mwangi et al, 2008).…”