Surendran et al. Parasites Vectors (2020) 13:156 https://doi.org/10.1186/s13071-020-04037-x Parasites & Vectors RESEARCH Open Access Anopheline bionomics, insecticide resistance and transnational dispersion in the context of controlling a possible recurrence of malaria transmission in Jafna city in northern Sri Lanka Sinnathamby N. Surendran1* , Tibutius T. P. Jayadas1, Annathurai Tharsan1, Vaikunthavasan Thiruchenthooran1, Sharanga Santhirasegaram1, Kokila Sivabalakrishnan1, Selvarajah Raveendran2 and Ranjan Ramasamy3* Abstract Background: Malaria was eliminated from Sri Lanka in 2013. However, the infux of infected travelers and the pres- ence of potent anopheline vectors can re-initiate transmission in Jafna city, which is separated by a narrow strait from the malaria-endemic Indian state of Tamil Nadu. Methods: Anopheline larvae were collected from diferent habitats in Jafna city and the susceptibility of emergent adults to DDT, malathion and deltamethrin investigated. Results: Anopheline larvae were found in wells, surface-exposed drains, ponds, water puddles and water storage tanks, with many containing polluted, alkaline and brackish water. Anopheles culicifacies, An. subpictus, An. stephensi and An. varuna were identifed in the collections. Adults of the four anopheline species were resistant to DDT. Anopheles subpictus and An. stephensi were resistant while An. culicifacies and An. varuna were possibly resistant to deltamethrin. Anopheles stephensi was resistant, An. subpictus possibly resistant while An. varuna and An. culicifacies were susceptible to malathion. DNA sequencing showed a L1014F (TTA to TTC) mutation in the IIS6 transmembrane segment of the voltage-gated sodium channel protein in deltamethrin-resistant An. subpictus—a mutation previously observed in India but not Sri Lanka. Conclusion: Anopheles subpictus in Jafna, like An. stephensi, may have recently originated in coastal Tamil Nadu. Besides infected overseas travelers, wind- and boat-borne carriage of Plasmodium-infected anophelines across the Palk Strait can potentially reintroduce malaria transmission to Jafna city. Adaptation to diverse larval habitats and resistance to common insecticides in anophelines are identifed as potential problems for vector control should this happen. Keywords: Anopheles malaria vectors, Insecticide resistance, kdr mutation, Jafna, Larval habitats, Malaria control, Mosquito range expansion, Sri Lanka, Tamil Nadu, Transnational mosquito migration *Correspondence: [email protected]; [email protected] 1 Department of Zoology, Faculty of Science, University of Jafna, Jafna, Sri Lanka 3 ID-FISH Technology, Milpitas, CA, USA Full list of author information is available at the end of the article © The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creat iveco mmons .org/licen ses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/publi cdoma in/ zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Surendran et al. Parasites Vectors (2020) 13:156 Page 2 of 9 Background Lanka [6]. Anopheles subpictus species A and An. sun- Malaria remains a global health problem with an esti- daicus along with An. annularis functioned as secondary mated 228 million cases and 405,000 deaths worldwide in vectors in Sri Lanka together with several minor vectors 2018 [1]. Although the global malaria burden has shown including An. varuna [7–12]. Anopheles stephensi (sensu a decreasing trend, and a number of countries have elimi- stricto) (type-form), the potent urban vector of malaria nated malaria or are approaching elimination, increasing in India, was frst detected in Sri Lanka in 2017 [13, 14]. resistance of vector populations to insecticides in many Te expansion of its range to Sri Lanka occurred after its countries is a cause for concern [1]. Malaria, which had spread to South India as well as Djibouti, Ethiopia and the been endemic in Sri Lanka for centuries, was eliminated Sudan in Northeast Africa [15, 16]. Tis range expansion from the island in 2013. However, the approximately was attributed to human migration [15] as well as the 100 travelers with malaria who arrive every year from adaptation of An. stephensi to develop in cement wells endemic countries, and the prevalence of potent anophe- and water storage tanks associated with human dwell- line vectors throughout the island, pose the risk of reini- ings, a process exemplifying what was previously termed tiating local malaria transmission [2]. Indeed, an instance as the anthropogenically-induced adaptation to invade in of local malaria transmission from a malaria-infected mosquito vectors [17]. Indian national to a Sri Lankan resident was documented Te coastal city of Jafna (population ~ 100,000, area 2 in late 2018 [3]. 10.5 km ) is located in the Jafna Peninsula (population 2 Te principal malaria vector Anopheles culicifacies ~ 600,000, area 1130 km ) and is the largest city in the exists as a species complex in Sri Lanka [4]. Among the Northern Province of Sri Lanka. Te Jafna Peninsula is two sibling species B and E of the Culicifacies complex, separated by the 64–137 km wide Palk Strait from Tamil species E was previously considered to be the major vec- Nadu state in India (Fig. 1a, b). Numerous small inhab- tor of malaria in the island [5]. Molecular characteriza- ited and uninhabited islands lie between the peninsula tion of An. subpictus complex revealed the presence of and Tamil Nadu. Malaria remains endemic in proximal species A and the morphologically similar An. sundaicus coastal areas of Tamil Nadu [18, 19]. Te Jafna Pen- (previously classifed as An. subpictus species B) in Sri insula is located within the dry zone of Sri Lanka, has Fig. 1 a Location of Sri Lanka in the Indian Ocean. Northern Sri Lanka is separated from South India by narrow Palk Strait. Solid white arrows show wind direction during the Southwest monsoon in the Palk Strait. b Jafna city is located in the Jafna Peninsula of northern Sri Lanka in close proximity to South India. The Jafna mainland and associated islands are separate by a narrow strip of Jafna lagoon. c Sample collection locations in Jafna urban area. Green solid circles indicate the four sampled locations viz: 1, Kurunagar (9°39′17.5″N, 80°127.05″E); 2, Navanthurai (9°40′16.3″N, 80°029.6″E); 3, Aryalai (9°39′39.9″N, 80°3′1.5″E); and 4, Nallur (9°39′59.99″N, 80°01′60.00″E) Surendran et al. Parasites Vectors (2020) 13:156 Page 3 of 9 a limestone geology and is undergoing rapid saliniza- emerging from the collected larvae to common insecti- tion of its ground water resources [20, 21]. Te saliniza- cides was undertaken to assess the potential for malaria tion is caused by unsustainable rates of water extraction transmission re-establishing itself in the city. from freshwater aquifers and is exacerbated by rising sea levels. Adaptation of freshwater disease vectors to salin- Methods ity in coastal areas heightens the potential for transmit- Larval collection and rearing ting vector-borne diseases as previously described [22]. Larval sampling was done and water quality in lar- Malaria control eforts were severely hampered in the val habitats determined fortnightly, at four locations Jafna Peninsula during the civil war of 1983–2009 and in Jafna city (Fig. 1c) during the period April 2018 to malaria vector surveys have not been performed lately August 2019. Samples were collected from Kurunagar in Jafna city. Anopheles species identifed recently in (9°39′17.5″N, 80°127.05″E), Navanthurai (9°40′16.3″N, the Jafna peninsula and associated islands include An. 80°0′29.6″E), Aryalai (9°39′39.9″N, 80°3’1.5″E) and Nallur varuna [23, 24], An. culicifacies [23, 24], An. barbirostris (9°39′59.99″N, 80°01′60.00″E). Anopheline larvae were [23, 25], An. subpictus [6, 23, 26], An. sundaicus [6, 12, collected from deep wells using string-connected conical 15, 26, 27] as well as An. stephensi [14, 15]. Anopheles ste- drop nets with 15 cm diameter and 10 cm depth. Stand- phensi, the dominant urban malaria vector in India, was ard 350 ml dippers were used to collect larvae from pud- frst detected in Mannar island in the Northern Province dles, ponds, open surface drains, water storage tanks and of Sri Lanka in 2017 (Fig. 1a) [13–15] and subsequently shallow wells (Fig. 2) with an average of 10 dips per habi- in domestic wells and water storage tanks in Jafna city in tat. Te pH, salinity, dissolved oxygen (DO), total dis- 2018, with a genotype consistent with an origin in Tamil solved solids (TDS), and electrical conductivity in water Nadu [15]. Indigenous malaria transmission re-emerg- collections with anopheline larvae were measured with ing in Jafna city and the Jafna Peninsula remains pos- a Multi Parameter Probe (Hanna Instruments, Leighton sible because of the proximity to malaria-endemic areas Buzzard, UK). Larval density for each species was calcu- of Tamil Nadu. Tere is presently no form of authorized lated as the number of larvae per liter for every collection sea travel between Jafna and India but the movement of site.