Spatial and seasonal distribution of human schistosomiasis intermediate host snails and their interactions with other freshwater snails in 7 districts of KwaZulu-Natal province, South Africa.

The spatial and seasonal distribution, abundance, and infection rates of human schistosomiasis intermediate host snails and interactions with other freshwater snails, water physicochemical parameters, and climatic factors was determined in this study. A longitudinal malacology survey was conducted at seventy-nine sites in seven districts in KwaZulu-Natal province between September 2020 and August 2021. Snail sampling was done simultaneously by two trained personnel for fifteen minutes, once in three months. A total of 15,756 snails were collected during the study period. Eight freshwater snails were found: Bulinus globosus (n = 1396), Biomphalaria pfeifferi (n = 1130), Lymnaea natalensis (n = 1195), Bulinus tropicus (n = 1722), Bulinus forskalii (n = 195), Tarebia granifera (n = 8078), Physa acuta (n = 1579), and Bivalves (n = 461). The infection rates of B. globosus and B. pfeifferi are 3.5% and 0.9%, respectively. In our study, rainfall, pH, type of habitats, other freshwater snails and seasons influenced the distribution, abundance, and infection rates of human schistosomiasis intermediate host snails (p-value < 0.05). Our findings provide useful information which can be adopted in designing and implementing snail control strategies as part of schistosomiasis control in the study area.

Spatial distribution, abundance, and infection rates of human schistosome-transmitting snails and related physicochemical parameters in KwaZulu-Natal (KZN) province, South Africa.

This study investigated the spatial distribution, abundance, and infection rates of human schistosome-transmitting snails and related physicochemical parameters and environmental factors in 11 districts in KwaZulu-Natal (KZN) province, South Africa, from December 2020-February 2021. Snail sampling was carried out in 128 sites by two people for 15 min using scooping and handpicking methods. Geographical information system (GIS) was used to map surveyed sites. In situ measurements of physicochemical parameters were recorded, while remote sensing was used to obtain measurements for climatic factors required to achieve the study's objective. Cercarial shedding and snail-crushing methods were used to detect snail infections. Kruskal-Wallis test was used to test the differences in snail abundance among snail species, districts, and habitat types. A negative binomial generalized linear mixed model was used to identify the physicochemical parameters and environmental factors influencing the abundance of snail species. A total of 734 human schistosome-transmitting snails were collected. Bu. globosus were significantly more abundant (n = 488) and widely distributed (found in 27 sites) compared to B. pfeifferi (n = 246) found in 8 sites. Bu. globosus and B. pfeifferi had infection rates of 3.89% and 2.44%, respectively. Dissolved oxygen and normalized difference vegetation index showed a statistically positive relationship, while normalized difference wetness index showed a statistically negative relationship with the abundance of Bu. globosus. However, there was no statistically significant relationship between B. pfeifferi abundance, physicochemical parameters, and climatic factors. Our study described the current distribution, abundance, and infection status of human schistosome-transmitting snails in KZN province, which will contribute to informing control measure policies for schistosomiasis.

Systematic Review and Meta-Analysis on the Infection Rates of Schistosome Transmitting Snails in Southern Africa.

Efforts to interrupt and eliminate schistosomiasis as a public health problem have increased in several Southern African countries. A systematic review was carried out on the infection rates of snails that cause schistosomiasis in humans. The searches were conducted in PubMed, Web of Science, and Scopus databases, using the PRISMA guidelines from inception to 24 February 2022. The study quality was assessed by using the Joanna Briggs Institute prevalence critical appraisal checklist. Pooled infection rates were estimated by using an inverse variance heterogeneity model, while heterogeneity was determined by using Cochran's Q test and Higgins i2 statistics. A total of 572 articles were screened, but only 28 studies were eligible for inclusion based on predetermined criteria. In the selected studies, 82,471 Bulinus spp. and 16,784 Biomphalaria spp. snails were screened for cercariae. The pooled infectivity of schistosome intermediate host snails, Biomphalaria spp., and Bulinus spp. were 1%, 2%, and 1%, respectively. Snail infection rates were higher in the 1900s compared to the 2000s. A Luis Furuya-Kanamori index of 3.16 indicated publication bias, and a high level of heterogeneity was observed. Although snail infectivity in Southern Africa is relatively low, it falls within the interval of common snail infection rates, thus indicating the need for suitable snail control programs that could interrupt transmission and achieve elimination.

Challenges and Opportunities Presented by Current Techniques for Detecting Schistosome Infections in Intermediate Host Snails: A Scoping Review.

Schistosomiasis, a neglected tropical disease (NTD), causes morbidity and mortality in over 250 million people globally. And 700 million people are at risk of contracting it. It is caused by a parasite of the genus Schistosoma. Freshwater snails of the family Planorbidae are of public health significance as they are intermediate hosts of these highly infective flukes. Accurate diagnostic techniques to detect schistosome infections in intermediate host snails (IHS) and environmental surveillance are needed to institute measures for the interruption of transmission and eventual elimination. We carried out a systematic review of the literature to assess advantages and limitations of different diagnostic techniques for detecting schistosome infections in snails. Literature from Scopus, Web of Science, and PubMed databases from 2008 to 2020 were searched using combinations of predefined search terms with Boolean operators. The studies revealed that conventional diagnostics are widely used, although they are labor-intensive, have low specificity and sensitivity levels, and cannot detect prepatent infections. Whereas more advanced techniques such as immunological, nucleic-acid amplification, and eDNA diagnostics have high sensitivity and specificity levels, they are costly, hence, not suitable for field applications and large-scale surveys. Our review highlights the importance of designing and developing innovative diagnostics that are high in specificity and sensitivity as well as affordable and technically feasible for use in field laboratories and for large-scale surveys.