Mapping freshwater snails in north-western Angola: distribution, identity and molecular diversity of medically important taxa

Abstract

BackgroundThis 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.MethodsSnails 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.ResultsIn 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.ConclusionsVarious 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.Electronic supplementary materialThe online version of this article (10.1186/s13071-017-2395-y) contains supplementary material, which is available to authorized users.

Prevalence of Schistosoma mansoni and S. haematobium in Snail Intermediate Hosts in Africa: A Systematic Review and Meta-analysis

“…The eligible articles were obtained from 17 African countries: Angola [ 18 ], Benin [ 19 ], Burkina Faso [ 20 ], Burundi [ 21 ], Chad [ 22 ], Côte d'Ivoire [ 23 , 24 ], Egypt [ 25 – 30 ], Ethiopia [ 31 – 36 ], Kenya [ 37 – 39 ], Mali [ 40 , 41 ], Niger [ 42 , 43 ], Nigeria [ 44 – 54 ], Senegal [ 55 , 56 ], Sudan [ 57 ], Tanzania [ 58 – 63 ], Uganda [ 64 – 67 ], and Zimbabwe [ 68 ]. Unfortunately, there were no studies from other African countries that fulfilled the inclusion criteria.…”

Phylogeography of Bulinus truncatus (Audouin, 1827) (Gastropoda: Planorbidae) in Selected African Countries

“…With the increasing global call that effective schistosomiasis control programmes should target snail control, there is a need to prioritize snail studies for effective mapping of schistosomiasis transmission [38], as well as to strengthen surveillance strategies.…”

Snail-Related Contributions from the Schistosomiasis Consortium for Operational Research and Evaluation Program Including Xenomonitoring, Focal Mollusciciding, Biological Control, and Modeling

“…Molecular identification methods such as cytochrome c oxidase 1 mitochondrial gene ( Cox1 ) sequences are available for numerous freshwater snails (e.g., Refs. 16 – 18 ), and reference data are available in online databases such as GenBank and barcode of life data system (BOLD). 19 As the same Cox1 region has been sequenced within and between species, this is a good comparison gene for general species identification.…”

“…The difficulty of obtaining schistosomes other than highly bottlenecked/inbred laboratory strains has made the SCAN collection very attractive to global research groups working on comparative genomics, with a number of studies in high-profile journals already published using specimens from SCORE and other programs archived in SCAN. 66 – 68 Schistosomiasis Collections at the Natural History Museum has also been available to support other projects working in schistosomiasis-endemic regions 16 , 69 and to facilitate secondary usage of collections. Although SCAN continues to be a very successful extension of the SCORE program, complications related to implementation of the Nagoya Protocol to the Convention on Biological Diversity may make sharing of genetic samples more challenging in the future, and ways need to be found to facilitate the best research outcomes toward disease elimination at all times, not only during pandemic emergencies.…”