Biomphalaria camerunensis as a viable alternative intermediate host for Schistosoma mansoni in southern Cameroon

Abstract

BackgroundIntestinal schistosomiasis due to Schistosoma mansoni was mapped in Cameroon in the 1990s and preventive chemotherapy launched since 2005. A situation analysis conducted in 2011 revealed an increase in schistosomiasis transmission, especially in the equatorial part of the country, despite the fact that Biomphalaria pfeifferi, the main intermediate host of this parasite, is now scarce in many foci. Biomphalaria camerunensis, restricted to the equatorial part of the country, is considered as a less suitable host for S. mansoni due to it resistance to the parasite, although exhibiting a better survival than B. pfeifferi. In a context where human migration is quite frequent as a consequence of terrorism, war in neighboring countries, as well as development of hydraulic projects, it seems appropriate to evaluate the current epidemiological role of B. camerunensis to estimate the risk of extension of S. mansoni distribution in Cameroon. To do this, the susceptibility of three B. pfeifferi and five B. camerunensis populations to a strain of S. mansoni was assessed. Juvenile snails (G1) of each population were infected with S. mansoni miracidia, and prepatent period, infection and survival rates of infected snails, as well as cercarial production were recorded and compared between snail species and populations.ResultsCompatibility tests were performed on a total of 827 snails: 344 B. pfeifferi and 483 B. camerunensis. Infection rates were quite heterogeneous, higher in B. pfeifferi (61.5%) as compared to B. camerunensis (7.8%) (Chi-square test: χ2 = 258.88, df = 1, P < 0.0001). All the three B. pfeifferi-infected populations were susceptible to S. mansoni. However, among the five B. camerunensis populations tested, four were susceptible to S. mansoni, with 21.9% as the highest infection rate. The prepatent period was, on average, shorter in B. pfeifferi than in B. camerunensis (P < 0.0001), but the cercarial production was significantly higher in B. camerunensis as compared to B. pfeifferi (P < 0.001).ConclusionThese findings indicate that B. camerunensis populations might substantially contribute to S. mansoni transmission and dissemination in Cameroon, their low susceptibility being compensated by their high cercariae production. More attention and surveillance towards this species are required to achieve intestinal schistosomiasis elimination in Cameroon.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-2763-2) contains supplementary material, which is available to authorized users.

PCR-based molecular identification of two intermediate snail hosts of Schistosoma mansoni in Cameroon

“…As no intermediate profile was found between ribotypes, further investigation is needed to check their taxonomical status (subspecies or simple variant). The existence of intraspecific variation is in line with the observation of a high polymorphism in the susceptibility of B. camerunensis populations to S. mansoni [14]. This level of polymorphism is expected in an outbred species such as B. camerunensis [51].…”

“…1). Sites mentioned in previous studies were visited [13,14], while new sites were chosen in additional streams favourable to the survival of molluscs. Snails were collected using a long-handled dip net by systematically combing the aquatic vegetation and identified using morphological criteria previously described by Brown [37].…”

“…Conversely, B. camerunensis has until now only been reported under the 6° north latitude and appears to play a minor role in the transmission of S. mansoni [13]. However, recent compatibility studies highlighted a relatively high susceptibility and cercarial emission rate in some B. camerunensis populations as high as those observed among B. pfeifferi, suggesting that they might play a more important role in the transmission of S. mansoni [14].…”

Genomic analysis of a parasite invasion: Colonization of the Americas by the blood fluke Schistosoma mansoni

“…In Africa, S. mansoni use Biomphalaria alexandrina , B. camerunensis , B. choanomphala , B. pfeifferi , B. stanleyi and/or B. sudanica as the snail host, none of which are present in the Americas (Figure 1 ). Instead, these parasites have adapted to using different Biomphalaria hosts, including B. glabrata , B. straminea and B. tenagophila (Hailegebriel et al, 2020 ; Kengne‐Fokam et al, 2018 ; Vidigal et al, 2000 ). We examined exomic SNV data to identify genes and larger regions of the genome under selection at a finer scale and identified zero to five putative regions of selection from each of the major populations (Table 4 ).…”

Genomic analysis of a parasite invasion: colonization of the Americas by the blood fluke, Schistosoma mansoni

“…In Africa, S. mansoni use Biomphalaria alexandrina, camerunensis, choanomphala, pfeifferi, stanleyi, and / or sudanica as the snail host, none of which are present in the Americas. Instead, these parasites have adapted to using different Biomphalaria hosts, including B. glabrata, B. straminea, and B. tenagophila (Figure 2; Hailegebriel, Nibret, & Munshea, 2020;Kengne-Fokam, Nana-Djeunga, Bagayan, & Njiokou, 2018;Vidigal et al, 2000). We examined exomic SNV data to identify genes and larger regions of the genome under selection at a finer scale and identified 0-5 putative regions of selection from each of the major populations (Table 4).…”