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

Nwoko, Onyekachi Esther; Manyangadze, Tawanda; Chimbari, Moses John

doi:10.1016/j.heliyon.2022.e12463

Cited by 9 publications

(9 citation statements)

References 32 publications

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“…In most previous studies, increasing vegetation (higher NDVI) is shown to have a positive association on snails found due to vegetation providing more suitable breeding sites, whereas our study suggests a negative association [31]- [33]. This difference in result is likely due to our focus on Lake Malawi where molluscivorous fish may be present, as opposed to a more general area taking into account smaller bodies of stagnant water, which typically lack such predatory fish.…”

Section: {Figure 7 Place Around Here}contrasting

confidence: 75%

“…Firstly this result could be due to the water flow increasing and spreading to new locations, disrupting freshwater snail habitats [32]. Secondarily, an increase in rainfall has been reported to increase turbidity of water and in turn decrease the presence of snails (through disrupting their habitat) [32,33]. Lastly, increases in rainfall and water flow have also been reported to cause rapid changes in temperature causing thermal shock and reduced egglaying of the freshwater snails, causing an overall reduction in snail abundance [35].…”

Section: {Figure 7 Place Around Here}mentioning

confidence: 99%

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A geospatial analysis of local intermediate snail host distributions provides insight into schistosomiasis risk within under-sampled areas of southern Lake Malawi

Reed,

Al-Harbi,

Makaulai

et al. 2024

Preprint

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Background: Along the southern shoreline of Lake Malawi, the incidence of schistosomiasis is increasing with snails of the genera Bulinus and Biomphalaria transmitting urogenital and intestinal schistosomiasis, respectively. Since the underlying distribution of snails is partially known, often being focal, developing pragmatic spatial models that interpolate snail information across under-sampled regions is required to understand and assess current and future risk of schistosomiasis. Methods: A secondary geospatial analysis of recently collected malacological and environmental survey data was undertaken. Using a Bayesian Poisson latent Gaussian process model, abundance data were fitted for Bulinus and Biomphalaria. Interpolating the abundance of snails along the shoreline (given their relative distance along the shoreline) was achieved by smoothing, using extracted environmental rainfall, land surface temperature (LST), evapotranspiration, normalised difference vegetation index (NDVI) and soil type covariate data for all predicted locations. Our adopted model used a combination of two-dimensional (2D) and one dimensional (1D) mapping. Results: A significant association between normalised difference vegetation index (NDVI) and abundance of Bulinus spp. was detected [log risk ratio -0.83, 95% CI: -1.57, -0.09]. A qualitatively similar association was found between NDVI and Biomphalaria spp. but was not statistically significant [log risk ratio -1.42, 95% CI:-3.09, 0.10]. Analyses of all other environmental data were considered non-significant. Conclusions: The spatial range in which interpolation of snail distributions is possible appears less than 10km, owing to fine-scale biotic and abiotic heterogeneities. The forthcoming challenge is to refine geospatial sampling frameworks with future opportunities to map schistosomiasis within actual or predicted snail distributions. In so doing, this would better reveal local environmental transmission possibilities.

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Section: {Figure 7 Place Around Here}contrasting

confidence: 75%

Section: {Figure 7 Place Around Here}mentioning

confidence: 99%

A geospatial analysis of local intermediate snail host distributions provides insight into schistosomiasis risk within under-sampled areas of southern Lake Malawi

Reed,

Al-Harbi,

Makaulai

et al. 2024

Preprint

View full text Add to dashboard Cite

show abstract

“…In most previous studies, more vegetation (NDVI) is shown to have a positive association of snails found due to vegetation providing suitable breeding sites whereas, our study suggests a negative association [31]- [33]. This difference in result is likely due to our focus on the Lake Malawi, as opposed to a more general area taking into account smaller bodies of stagnant water.…”

Section: {Figure 7 Place Around Here}contrasting

confidence: 62%

A geospatial analysis of local intermediate snail host distributions provides insight into schistosomiasis risk within under-sampled areas of southern Lake Malawi

Reed,

Al-Harbi,

Makaulai

et al. 2024

Preprint

View full text Add to dashboard Cite

Background: Along the southern shoreline of Lake Malawi, the incidence of schistosomiasis is increasing with snails of the genera Bulinus and Biomphalaria transmitting urogenital and intestinal schistosomiasis, respectively. Since the underlying distribution of snails is partially known, often being focal, developing pragmatic spatial models that interpolate snail information across under-sampled regions is required to understand and assess current and future risk of schistosomiasis. Methods: A secondary geospatial analysis of recently collected malacological and environmental survey data was undertaken. Using a Bayesian Poisson latent Gaussian process model abundance data were fitted for Bulinus and Biomphalaria. Interpolating the abundance of snails along the shoreline (given their relative distance along the shoreline ∼x km) was achieved by smoothing, using extracted environmental rainfall, land surface temperature (LST), evapotranspiration, normalised difference vegetation index (NDVI) and soil type covariate data for all predicted locations. Our adopted model used a combination of two-dimensional (2D) and one dimensional (1D) mapping. Results: A significant association between normalised difference vegetation index (NDVI) and abundance of Bulinus spp. was detected [log risk ratio -0.83, 95% CI: -1.57, -0.09]. A qualitatively similar association was found between NDVI and Biomphalaria spp. but was not statistically significant [log risk ratio -1.42, 95% CI:-3.09, 0.10]. All other environmental data considered were non-significant. Conclusions: The spatial range in which interpolation of snail distributions is possible appears less than y km, owing to fine-scale biotic and abiotic heterogeneities. The forthcoming challenge is to refine geospatial sampling frameworks with future opportunities to map schistosomiasis within actual or predicted snail distributions which might better reveal the environmental transmission possibilities.

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“…Summary statistics including tables and graphs were used to describe freshwater snails’ abundance, distribution, and infection rates. Kruskal Wallis test is a non-parametric test that was used to statistically compare the difference in the snail abundance and infection rates of freshwater snails among districts 17 , 18 . The negative binomial generalized linear mixed effect model in the ‘glmmTMB’ package 19 was used to model the abundance and shedding of B. globosus and B. pfeifferi snails in relation to climatic factors, water physicochemical properties, habitat types, seasons and other freshwater snails.…”

Section: Methodsmentioning

confidence: 99%

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

Nwoko

Manyangadze

Chimbari

2023

Sci Rep

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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.

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

Cited by 9 publications

References 32 publications

A geospatial analysis of local intermediate snail host distributions provides insight into schistosomiasis risk within under-sampled areas of southern Lake Malawi

A geospatial analysis of local intermediate snail host distributions provides insight into schistosomiasis risk within under-sampled areas of southern Lake Malawi

A geospatial analysis of local intermediate snail host distributions provides insight into schistosomiasis risk within under-sampled areas of southern Lake Malawi

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

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