Mosquito surveillance must include non-residential urban environments

Mosquito surveillance must include non-residential urban environments

Subject: Science and technology

Section: Health

Context:

• A longitudinal study in Bengaluru city has found how urbanisation affects mosquito ecology and how mosquito species diversity and abundance change across macro and microhabitats.

Study findings:

• The study found that the quality of breeding sites determines the abundance and distribution of mosquito species, specifically the ones that cause dengue.
• The way mosquitoes interact with larval habitats in different macrohabitats did play an important role in determining mosquito diversity and abundance.
• Six macrohabitats were studied:
  • Barren lands, lakes and their surroundings, plantations, and high dense, medium dense, and low dense urban areas.
• Whereas plantations, owing to diverse habitat types, proved to have high mosquito species diversity and richness compared with high-density populated areas in the city, even barren lands did have microhabitats conducive for breeding.
• Aedes aegypti was the most dominant species (55%), followed by Aedes albopictus (28%).
  • Habitat preference by the two Aedes species appeared to be driven at the microhabitat level.
• Man-made artificial containers accounted for over 90% of larval habitats. Water storage containers came out as the most common breeding habitat for Ae. aegypti.
• Discarded grinding stones showed a high prevalence of Ae. aegypti and Ae. albopictus larvae. But the prevalence in stagnant water was less as these are open water bodies and more polluted.
• The body size of these mosquitoes varies according to the microhabitat. The wing length varies. The study found that when both Aedes species co-existed in a microhabitat, Ae. albopictus always ended up with reduced wing length.

Preventive steps: Neighbourhood surveillance:

• WHO protocols are restricted to door-to-door larval surveillance and looking for mosquito larvae in containers.
• The study has demonstrated that urban environments with non-residential locations too harbour ideal breeding sites.
• Any programme aimed at reducing dengue transmission should also factor in neighbourhood surveillance to prevent and control the rising threat of Aedes species.
• Wolbachia method:
  • The World Mosquito Program’s innovative Wolbachia method is helping communities around the world prevent the spread of mosquito-borne disease.
  • Wolbachia are extremely common bacteria that occur naturally in 50 per cent of insect species, including some mosquitoes, fruit flies, moths, dragonflies and butterflies.
  • Aedes aegypti mosquitoes don’t normally carry Wolbachia, however many other mosquitoes do.
  • When Aedes aegypti mosquitoes carry Wolbachia (by gene-editing), the bacteria compete with viruses like dengue, Zika, chikungunya and yellow fever.
  • This makes it harder for viruses to reproduce inside the mosquitoes. And the mosquitoes are much less likely to spread viruses from person to person.