Mosquito unit tackling dengue mosquitoes

With two recent imported cases of dengue fever in the Cayman Islands, the Mosquito Research and Control Unit is keeping an eye on the Aedes aegypti mosquito that spreads the virus from human to human.

Alan Wheeler, assistant director of the Mosquito Research and Control Unit, said the unit was aware of the recent cases and had sprayed the areas of the patients’ home and cleared any bodies of standing water nearby.

The unit is constantly on the alert for dengue cases, he said, as “we are surrounded by dengue in the Caribbean, most places have it. There’s nothing we can do to stop people returning to the Islands with dengue. We spray continually anyway and have crews going out there”.

In the two cases of imported dengue – the first to be reported in Cayman this year – both patients had returned from travelling overseas where it is believed they contracted the virus.

The Aedes aegypti mosquito spreads the virus. If it bites a person who has dengue fever, the insect can then spread the virus to another person. The virus does not spread from human to human.

According to the Caribbean Epidemiology Centre, as of August this year, Belize, Guyana, Suriname, Jamaica and Curacao accounted for about 87 per cent of 1,500 cases reported in the Caribbean region this year and that 17 of 23 countries in the region had confirmed cases of dengue fever, which is also known as break bone fever.

“We’re continually at risk from people bringing in the virus,” said Mr. Wheeler, adding that control unit teams carry out continuous yard-to-yard checks.

Mr. Wheeler said the Aedes aegypti is not the most common mosquito in Cayman, but it’s probably the one that most people encounter as it lives in and around people’s homes.

The Aedes aegypti mosquito, also known as the Yellow Fever Mosquito, breeds in standing water in containers often found around the home, like water drums, guttering, tyres, buckets and discarded trash. It can be controlled by simply clearing up any water holding containers or making sure that water is not allowed to stand for more than a couple of days, for example, in bird baths, pet water bowls or plant pots.

The mosquito can be identified by its distinctive black and white colour. It bites mostly in the daytime or late afternoon.

As well as being a carrier for dengue fever, as its name implies, the Aedes aegypti mosquito can also carry yellow fever, as well as the West Nile and chikungunya viruses.

The Black Salt-Marsh mosquito is the most common mosquito in the Cayman Islands, but lives mostly in swamps, with its numbers peaking in the rainy season. They are active around sunrise and sunset.

The biggest mosquitos are the Psorphora ciliata and Psorophora columbiae, which breed mainly in standing water in pasture land. They are black in colour and can be easily identified by their size.

The Southern House Mosquito, a small brown insect, can often also be found in people’s houses, as can the Asian Tiger Mosquito, a small black and white mosquito with a distinctive stripe across the thorax. The Asian Tiger Mosquito, or Aedes albopictus, which is found in relatively small numbers in Grand Cayman, also is a carrier of the dengue, yellow fever and chikungunya viruses.

A report published in the Nature Biotechnology this month showed that there had been an 80 per cent reduction in the numbers of Aedes aegypti mosquitoes in a section of East End in Grand Cayman after the introduction of genetically modified mosquitoes into the environment as a control measure.

Mr. Wheeler said this statistic only referred to a “very small sample and very limited area” and that the main control against this breed of mosquito was the “labour-intensive” inspection and eradication of mosquitos in people’s yards by control 
unit crews.

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