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First record of Anopheles stephensi in Sri Lanka: a potential challenge for prevention of malaria reintroduction.

ABSTRACT: The major malaria vector in Sri Lanka is reported to be Anopheles culicifacies with Anopheles subpictus, Anopheles annularis, and Anopheles varuna considered as potential vectors. The occurrence of Anopheles stephensi, which is the key vector of urban malaria in India and the Middle East, had never been reported from Sri Lanka.A series of entomological investigations were carried out by the Anti Malaria Campaign, Ministry of Health, Sri Lanka during December 2016 to April 2017 in two localities of the Mannar District in the Northern Province of the country. Adult mosquito collections were done through indoor and outdoor resting collections, animal and human biting collections and emergence traps. Potential mosquito breeding sites were investigated through larval surveys. The larvae and adults of An. stephensi were initially identified using morphological keys, and subsequently confirmed by sequencing the barcode region of the cytochrome c oxidase I (COI) gene.This is the first report of the presence of An. stephensi in the island of Mannar in the Northern Province of Sri Lanka. Anopheles stephensi (36.65%) was the most abundant anopheline species in the larval habitats in Mannar. It was found breeding together with An. culicifacies (20.7%), An. subpictus (13.5%) and An. varuna (28.13%). Anopheles stephensi was found to be abundantly breeding in built wells used for domestic purposes. Adult females of An. stephensi were observed in emergence trap collections (93.9%), human landing catches all night (79.2%), pyrethrum spray sheet collections (38.6%), outdoor collections (8.3%), donkey-baited trap collections (14.3), and cattle-baited net trap collections (0.7%).Sri Lanka was certified as malaria-free by the WHO in September 2016, however, this new finding may pose a serious challenge to the efforts of the Ministry of Health to prevent the re-introduction of malaria transmission in the country, considering the role that An. stephensi could play in urban and high vulnerability areas of Sri Lanka.

SUBMITTER: Gayan Dharmasiri AG

PROVIDER: S-EPMC5553605 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature

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First record of Anopheles stephensi in Sri Lanka: a potential challenge for prevention of malaria reintroduction.

Gayan Dharmasiri A G AG Perera A Yashan AY Harishchandra Jeevanie J Herath Hemantha H Aravindan Kandasamy K Jayasooriya H T R HTR Ranawaka Gaya R GR Hewavitharane Mihirini M

Malaria journal 20170810 1

<h4>Background</h4>The major malaria vector in Sri Lanka is reported to be Anopheles culicifacies with Anopheles subpictus, Anopheles annularis, and Anopheles varuna considered as potential vectors. The occurrence of Anopheles stephensi, which is the key vector of urban malaria in India and the Middle East, had never been reported from Sri Lanka.<h4>Methods</h4>A series of entomological investigations were carried out by the Anti Malaria Campaign, Ministry of Health, Sri Lanka during December 20 ...[more]

PMID: 28797253

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Project description:BackgroundAlthough Sri Lanka is considered as a malaria-free nation, the threat of re-emergence of outbreaks still remains due to the high prevalence and abundance of malaria vectors. Analysis of population genetic structure of malaria vectors is considered to be one of the vital components in implementing successful vector control programmes. The present study was conducted to determine the population genetic structure of three abundant malaria vectors; Anopheles subpictus sensu lato (s.l.), Anopheles peditaneatus and Anopheles vagus from five administrative districts in two climatic zones; intermediate zone (Badulla and Kurunegala districts) and dry zone (Ampara, Batticoloa and Jaffna districts) of Sri Lanka using the mitochondrial gene, cytochrome c oxidase subunit I (COI).MethodsAdult mosquitoes of An. subpictus s.l., An. peditaeniatus, and An. vagus were collected from five study sites located in five districts using cattle baited traps and backpack aspirators. Representative samples of each species that were morphologically confirmed were selected from each locality in generating COI sequences (> 6 good quality sequences per species per locality).ResultsAnopheles subpictus s.l. specimens collected during the study belonged to two sibling species; An. subpictus 'A' (from all study sites except from Jaffna) and An. subpictus 'B' (only from Jaffna). The results of haplotype and nucleotide diversity indices showed that all the three species are having high genetic diversity. Although a high significant pairwise difference was observed between An. subpictus 'A' and 'B' (Fst> 0.950, p < 0.05), there were no significant genetic population structures within An. peditaeniatus, An. vagus and An. subpictus species A (p > 0.05), indicating possible gene flow between these populations.ConclusionsGene flow among the populations of An. peditaeniatus, An. vagus and An. subpictus species A was evident. Application of vector control measures against all mosquito species must be done with close monitoring since gene flow can assist the spread of insecticide resistance genes over a vast geographical area.

Project description:BackgroundAnopheles subpictus sensu lato, a widespread malaria vector in Asia, is reportedly composed of four sibling species A - D. Mosquitoes morphologically identified as belonging to the Subpictus complex were collected from different locations near the east coast of Sri Lanka, and specific ribosomal DNA sequences determined to validate their taxonomic status.MethodsAnopheles subpictus s.l. larvae and blood-fed adults were collected from different locations in the Eastern province and their sibling species status was determined based on published morphological characteristics. DNA sequences of the D3 domain of 28 S ribosomal DNA (rDNA) and the internal transcribed spacer -2 (ITS-2) of mosquitoes morphologically identified as An. subpictus sibling species A, B, C and D were determined.ResultsPhylogenetic analysis based on D3 domain of rDNA resulted in two clades: one clade with mosquitoes identified as An. subpictus species A, C, D and some mosquitoes identified as species B, and another clade with a majority of mosquitoes identified as species B with D3 sequences that were identical to Anopheles sundaicus cytotype D. Analysis of ITS-2 sequences confirmed a close relationship between a majority of mosquitoes identified as An. subpictus B with members of the An. sundaicus complex and others identified as An. subpictus B with An. subpictus s.l.ConclusionsThe study suggests that published morphological characteristics are not specific enough to identify some members of the Subpictus complex, particularly species B. The sequences of the ITS-2 and D3 domain of rDNA suggest that a majority that were identified morphologically as An. subpictus species B in the east coast of Sri Lanka, and some identified elsewhere in SE Asia as An. subpictus s.l., are in fact members of the Sundaicus complex based on genetic similarity to An. sundaicus s.l. In view of the well-known ability of An. sundaicus s.l. to breed in brackish and fresh water and its proven ability to transmit malaria in coastal areas of many Southeast Asian countries, the present findings have significant implications for malaria control in Sri Lanka and neighbouring countries.

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First record of Anopheles stephensi in Sri Lanka: a potential challenge for prevention of malaria reintroduction.

Publications

First record of Anopheles stephensi in Sri Lanka: a potential challenge for prevention of malaria reintroduction.

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