(CNS): The Mosquito Research and Control Unit is carrying out a full-scale attack on the Aedes aegypti in an effort to keep the numbers of the disease-carrying mosquito down and contain the current Zika threat. Dr Bill Petrie, the unit’s director, said there had been an “unprecedented number of requests” for yard spraying, especially in George Town and from women who are expecting babies. Meanwhile, public health officials remained tight-lipped about the exact areas of local transmission.
Acting Medical Officer of Health Dr Samuel Williams-Rodriguez said the patients live in different areas of the capital with no obvious clustering, so the virus could be anywhere.
He said it would serve no purpose to identify specific transmission locations as it may give a false feeling of security. He pointed out that in most cases, Zika is virtually asymptomatic and healthy people who are infected may have no idea they have caught it, which means many more people are likely to have already caught the virus but they have not been formally counted.
Over the last week alone 77 requests have been made to the MRCU and 61 of those locations have now been treated, as staff work around the clock to meet requests. The unit is also spraying the specific address where patients who have reported having the virus are staying, as well as community-wide measures, including truck fogging and aerial spraying.
Speaking at a press meeting on Tuesday, Petrie explained that the MRCU had been inundated with questions and concerns from residents about Zika, but it was going after the disease-spreading bug with all of the larvae and insecticides it has at its disposal and deploying a variety of techniques.
As well as regular aerial spraying over inhabited areas of the island in the day, with insecticides that target the adult Aedes aegypti, the unit is using the fogging trucks to spray urban areas. In addition, it is using a barrier treatment, which is a liquid insecticide sprayed at walls that protects sites from more mosquitoes entering a given area and has been used on all of the islands’ pre-schools as a precautionary measure.
Teams from the MRCU on the ground are also using larvaesides to cut the next generation in yards, as well as thermal fogging to kill adult mosquitoes.
Responding to requests from the public, the teams use whatever techniques they feel are appropriate for the given location in an effort to deal with the immediate threat of the Zika virus, despite the increasing resistance of this mosquito to the current generation of larvae and insecticides.
Cayman is experiencing a bad year for all mosquitoes, including the native swamp species, and while these local bugs are certainly a pest, they do not carry disease. Zika is carried by the invasive Aedes aegypti, which only bites in the day and not, as is the case with the native varieties, after sunset and before sunrise.
But with five confirmed cases of locally transmitted Zika and significant concerns that the virus is connected to birth defects, the pressure is on for the MRCU to do whatever it can to exterminate the mosquito.
Just two months into an 18-month budget, Petrie said his unit was well-funded at present but if he felt there was a need to increase the resources he needs to combat Zika, he was prepared to go to government for more cash.
However, the genetically modified mosquito project can offer little hope to residents of George Town, where the local transmissions have occurred, as the project is limited to the district of West Bay as a result of legal and administrative issues.
Petrie also explained that the GM technique is a future, long-term solution and not one that can be used to react to an immediate disease threat as it takes several months for the genetically modified males to make any kind of dent in the adult biting female numbers.
But there is no doubt, he said, that the current insecticides are not good enough to eradicate or even reduce the numbers of Aedes aegypti to completely prevent disease transmission. However, Dr Petrie said that as imperfect as the current insecticides are against the bug, the onslaught from the unit is the best hope in the short-term of reducing the spread of Zika and other diseases related to this particular mosquito.
The Public Health Department has created a fact sheet on Zika for pregnant women, which in light of reports regarding various birth defects is the greatest concern about the virus, which is generally mild in healthy adults. The health services authority has also developed a Zika test for any patient not meeting the WHO guidelines which costs $100.