Environmental determinants of distribution of freshwater snails and trematode infection in the Omo Gibe River Basin, southwest Ethiopia

Abstract

BackgroundDetermination of infection rates of snail populations is one of the basic tools for epidemiological studies of snail borne diseases. In this study, we opted to determine the trematode infection of freshwater snails in the Omo-Gibe River Basin, southwest Ethiopia.MethodsWe collected snail samples from 130 observation sites in lakes, wetlands, rivers, reservoirs and irrigation canals surveyed during the dry season (March to May) in 2016. The snail samples were examined for trematode infections by cercarial shedding immediately after collection. Habitat conditions, water quality, human water contact practices and other human activities were assessed at each survey site. A redundancy analysis (RDA) was used to examine the relationship between cercarial infection and environmental variables. The statistical significance of eigenvalues and cercariae-environment correlations generated by the RDA were tested using Monte Carlo permutations at 499 permutations.ResultsA total of 3107 snails belonging to five species were collected. The most abundant species was Biomphalaria pfeifferi, representing 66% of the total collection. Overall, 109 (3.6%) of the snails were found infected with trematodes (cercariae). Biomphalaria pfeifferi was found to be the most highly infected, accounting 85% of all infected snails. A total of eight morphologically different types of cercariae were recorded, which included: Echinostoma cercariae, brevifurcate apharyngeate distome cercariae, amphistome cercariae, brevifurcate apharyngeate monostome cercariae, xiphidiocercariae, longifurcate pharyngeate distome cercariae, strigea cercariae and unidentified cercariae. Brevifurcate apharyngeate distome cercariae, and Echinostoma cercariae were the most abundant cercariae, accounting for 36 and 34% of all infection, respectively. The mean concentration of water conductivity and 5 days biological oxygen demand were higher in irrigation canals and lake sampling points. Human activities such as open field defecation, urination, livestock grazing, farming, and swimming were highly correlated with trematode infection.ConclusionsThe abundance, occurrence and infection rates of snail species were largely influenced by water physicochemical quality, sanitation and water contact behaviour of the inhabitants. Human activities, such as open field defecation and urination, livestock grazing, farming, and swimming were important predictors of the abundance of cercariae. Therefore, awareness creation should be implemented for proper containment of excreta (urine and faeces) and reducing human and animal contacts with surface waters to reduce snail-borne disease transmission.

Abundance and annual distribution of freshwater snails and some trematode cercariae at Damietta Governorate, Egypt

“…Our results showed a positive correlation between the distribution of gymnocephalus cercariae and the value of DO, while xiphidiocercariae distribution was negatively correlated with DO. Similar to our results, Mereta et al . (2019) reported a negative correlation between the prevalence of the xiphidiocercariae emerging from Lymnaea natalensis and water DO.…”

“…(2016) reported xiphidiocercariae as the most common type of cercariae (44.3 %) but from the snail Bulinus truncates at the irrigation canal in the East Nile, Khartoum, Sudan. In addition, Mereta et al . (2019) reported the highest infection rate of xiphidiocercariae (1.5 %) emerging from Lymnaea natalensis at wet land of Omo-Gibe River Basin, southwest Ethiopia.…”

“…(2019) reported the highest infection rate of xiphidiocercariae (1.5 %) emerging from Lymnaea natalensis at wet land of Omo-Gibe River Basin, southwest Ethiopia. According to Mereta et al . (2019) , human activities such as open field defecation, urination, livestock grazing, farming, and swimming were highly correlated with trematode infection.…”

A Cross Sectional Assessment on Distribution of Snail and Risk Factors of Schistosoma Mansoni Infection in Proximity to Water Contact Points in Gorgora Town, Western Dembia District, Northwest Ethiopia.

“…As assessed using morphological methods, 546(49.4%) of the snails collected were putatively identi ed as B. pfeifferi, whereas 310(28.1%), 101(9.1%), and 147(13.3%) were identi ed as Bulinus spp., Lymnaea and Bivalve, respectively. This result is consistent with the malacological survey conducted in freshwater bodies, in Sanja, Northwest Ethiopia, during January and April, where B. pfeifferi were 150(97.4%) and 180(81.4%), respectively and also B. forskalii and L. natalensis (29) (44). The main reason for the variation here may be an increase in organic matter will increase the concentration of detritus and possibly the proliferation of algae that forms the diet of planorbid and prosobranch snails and prevalence of Schistosoma spp.…”

Cercarial trematodes in freshwater snails from Bangkok, Thailand: prevalence, morphological and molecular studies and human parasite perspective

“…McKinney (2008) has suggested that diversities in species of invertebrates, amphibians, reptiles and mammals tend to be lower in extreme urbanization areas. Furthermore, the lack of certain anthropogenic activities, such as open-field defecation and urination, and a comparatively low proportion of livestock farming can lead to low trematode infection rates in freshwater snails (Mereta et al, 2019). Species diversity of snail faunas served as first-intermediate hosts may also reflect the low infection rate in this study.…”