Ecology, identification and genetic diversity of intermediate hosts of Fasciola species in South Africa.

Abstract

Lymnaeid snails are known to transmit Fasciola spp. Moreover, the five lymnaeid snail species known to transmit Fasciola spp. have been reported in South Africa. However, there is paucity of information on the epidemiological role, ecology and distribution of these snails in South Africa. This study systematically assessed the prevalence of Fasciola spp. infections in lymnaeids and the geographical distribution of P. columella and its implications in the transmission of fasciolosis. Furthermore, the study aimed to determine the distribution, ecology, and identity of lymnaeids in South Africa and their potential species of infection. The susceptibility of lymnaeid snails to Fasciola spp. results showed that the infection rate was higher in experimental infections 50% (95% CI: 42-58%) compared to natural infections of field-collected snails 6% (95% CI: 0-22%). A systematic review showed that the wide ngeographical distribution of P. columella was related to its ability to adapt to and inhabit a vast array of freshwater bodies including thermal lakes and ditches with acidic soils. Freshwater snail survey was conducted in selected localities from six provinces of South Africa. One thousand and fifty-nine lymnaeid snails were collected, and only Pseudosuccinea columella and Radix natalensis were identified based on the 16S and COI genes, and the former species was shown to have a wider geographical distribution than R. natalensis which was restricted to Limpopo and Mpumalanga provinces. Furthermore, molecular analysis showed that P. columella populations lacked genetic variability, whilst R. natalensis formed two distinct sub-clades, showing genetic variations between Mpumalanga and Limpopo provinces. This was further supported by a moderate haplotype diversity of (16S: 0.618 and COI: 0.467) and a low nucleotide diversity (16S: 0.00685 and COI: 0.014) were recorded and a positive but non-significant Tajima’s D (16S: 0.64672 and 1.4948; p > 0.10), which indicated allele deficiency, which may be due to recent population bottleneck. Radix natalensis was more abundant (n = 649) and cohabitated with P. columella in 2/3 (66.7 %) of the habitats and both species showed preference to perennial habitats. The 28S gene detected Orientocreadium spp. And Trichobilharzia ocellata DNA in R. natalensis and P. columella. No Fasciola DNA was detected in these Lymnaeidae snails. Results highlighted and emphasised the need for designing species specific Fasciola spp. primers that will detect and differentiate between species especially in the IHs. This will be crucial for detection of natural infections of Fasciola spp. and identifying habitats with circulating infections in surveys to better understand the geographical extension of fasciolosis and areas with potential high risk of infections to both animals and human.