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. 2017 Oct 10;10(1):460.
doi: 10.1186/s13071-017-2395-y.

Mapping Freshwater Snails in North-Western Angola: Distribution, Identity and Molecular Diversity of Medically Important Taxa

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Free PMC article

Mapping Freshwater Snails in North-Western Angola: Distribution, Identity and Molecular Diversity of Medically Important Taxa

Fiona Allan et al. Parasit Vectors. .
Free PMC article

Abstract

Background: This study was designed to determine the distribution and identity of potential intermediate snail hosts of Schistosoma spp. in Bengo, Luanda, Kwanza Norte and Malanje Provinces in north-western Angola. This is an area where infection with Schistosoma haematobium, causing urogenital schistosomiasis, is common but little is yet known about transmission of the disease. Angola has had a varied past with regard to disease control and is revitalising efforts to combat neglected tropical diseases.

Methods: Snails were sampled from 60 water-contact points. Specimens of the genera Bulinus, Biomphalaria or Lymnaea were screened for trematode infections by inducing cercarial shedding. Snails were initially identified using shell morphology; subsequently a cytochrome c oxidase subunit 1 (cox1) gene fragment was amplified from a subset of snails from each site, for molecular identification. Cercariae were captured onto FTA cards for molecular analysis. Specimens of Bulinus angolensis collected from the original locality of the type specimen have been characterised and comparisons made with snails collected in 1957 held at the Natural History Museum, London, UK.

Results: In total snails of nine genera were identified using morphological characteristics: Biomphalaria, Bulinus, Gyraulus, Lanistes, Lentorbis, Lymnaea, Melanoides, Physa and Succinea. Significant for schistosomiasis transmission, was the discovery of Bulinus globosus, B. canescens, B. angolensis, B. crystallinus and Biomphalaria salinarum in their type-localities and elsewhere. Bulinus globosus and B. angolensis occurred in two distinct geographical areas. The cox1 sequence for B. globosus differed markedly from those from specimens of this species collected from other countries. Bulinus angolensis is more closely related to B. globosus than originally documented and should be included in the B. africanus group. Schistosoma haematobium cercariae were recovered from B. globosus from two locations: Cabungo, Bengo (20 snails) and Calandula, Malanje (5 snails). Schistosoma haematobium cercariae were identified as group 1 cox1 corresponding to the type common throughout the African mainland.

Conclusions: Various freshwater bodies in north-western Angola harbour potential intermediate snail hosts for urogenital schistosomiasis, highlighting the need to map the rest of the country to identify areas where transmission can occur and where control efforts should be targeted. The molecular phylogeny generated from the samples confirmed that considerable variation exists in B. globosus, which is the primary snail host for S. haematobium in many regions of Africa.

Keywords: Angola; Biomphalaria spp.; Bulinus globosus; Schistosoma haematobium; Schistosomiasis transmission.

Conflict of interest statement

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Competing interests

The authors declare that they have no competing interests.

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Figures

Fig. 1
Fig. 1
Site location maps. a All sites visited in this study. b-e Sites where the following species were found: b Bulinus gobosus; c Bulinus truncatus; d Bulinus canescens (star), Bulinus crystallinus (triangle) and Bulinus angolensis (circle); e Biomphalaria salinarum
Fig. 2
Fig. 2
Maximum Likelihood tree for Bulinus globosus and B. angolensis based on cox1 sequences. Maximum likelihood tree of a 613 bp fragment of the cytochrome c oxidase subunit 1 (cox1) gene for B. globosus and B. angolensis collected in this study, with additional previously published sequences [13]. B. forskalii was selected as the outgroup. Numbers at the nodes indicate bootstrap support (1000 pseudoreplications). The scale-bar indicates substitutions per nucleotide site
Fig. 3
Fig. 3
Maximum Likelihood tree for Bulinus forskalii, B. crystallinus and B. canescens based on cox1 sequences. Maximum likelihood tree of a 590 bp fragment of the cytochrome c oxidase subunit 1 (cox1) gene for Bulinus forskalii, B. crystallinus and B. canescens collected in this study, with additional previously published sequences. B. truncatus was selected as the outgroup. Numbers at the nodes indicate bootstrap support (1000 replications). The scale-bar indicates substitutions per nucleotide site

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