Enhanced surveillance of mosquitoes and vector-borne diseases in the Maltese Islands: Molecular species identification, insecticide resistance monitoring, and risk assessment for vector-borne infections (2018)

  • Vector-borne
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Over the last decade, the combined influence of global travel, climate change, human migration and the spread of vector-borne infections like chikungunya, dengue, West Nile Virus (WNV) and malaria in Europe and North Africa, has made the spread of vector mosquitoes in Malta an urgent public health priority. We sought to identify competent vectors for infectious diseases in the Maltese islands, in order to inform public health response.

Entomological surveillance was conducted from July 2018 to February 2019 across Gozo and Malta with larvae, pupae and adult mosquitoes collected in 23 sites. From July to November 2018, egg density was measured weekly in 32 sites using ovitraps. Species were identified via morphological and molecular analyses. Insecticide resistance mutations were analysed in a partner laboratory in Greece. We analysed national surveillance data on vector-borne infections in Malta from 1990 to 2018.

The species most frequently found were Culiseta longiareolata (9 sites), Culex pipiens s.s (8 sites), including the hybrid Cx. pipiens pipiens/molestus biotype (2 sites) and Aedes albopictus (4 sites). Neither Anopheles nor Ae. aegypti mosquitoes were detected. Mutations relevant for pyrethroid-based insecticide resistance were detected among 53% Culex (n=37) and 15% Aedes albopictus (n=17). No Diflubenzuron-resistant mutations were recorded. From January 1990 to December 2018, 103 malaria, 7 dengue, one chikungunya and no WNV cases were reported in Malta; with the exception of one cryptic Plasmodium falciparum infection reported in October 2018, all other mosquito-borne infections were travel-related.

This is the first molecular species identification and insecticide resistance analysis of mosquitoes from Malta. We demonstrated the presence and establishment across the Maltese islands of competent mosquito vectors for artoviruses such as West Nile Virus, Chikungunya or Dengue. The sustained presence of competent vectors for arboviruses prompted the implementation of vector-control strategies including community information campaigns to reduce breeding sites, controlled insecticide use by environmental health authorities, and enhanced surveillance to monitor the arrival and spread of mosquito species, and the emergence of insecticide-resistant mutations.

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