The Mosquito and Research Control Unit (MRCU), beginning on Monday 1 February, 2016, commenced its plan of action in destroying the breeding sites of the Aedes aegypti mosquito and preventing the potential threat of Zika virus to the Cayman Islands.

The Director of MRCU, Dr. William Petrie said his staff launched the first of two phases in combatting the mosquito population with aerial spraying and a full fleet of vehicle-mounted fogging machines at the ground level.

In explaining the two phases of the MRCU’s contingency plan, Dr. Petrie said that phase one will deal with the situation prior to the virus being introduced while phase two will be enacted only if Zika is detected locally.

“There will be twice-weekly aerial applications, mainly West Bay and George Town targeting South Sound and out to Red Bay because these are areas that we know have the highest concentrations of Aedes aegypti,” he said “We will treat the eastern districts as well but with less frequency.”

Phase two is essentially an intensified version of what is outlined in the first phase with the additional use of new laboratory equipment.

“The lab equipment will allow MRCU to determine in less than an hour whether or not a suspected patient tests positive for the virus. This in turn means we can immediately conduct spraying operations in the vicinity of the patient’s residence, rather than waiting for the return of results from overseas. This timing is critical as we need to disrupt the life cycle of the mosquito, which can be less than a week, in order to break the cycle of transmission. In addition, this equipment will enable us to look for presence of the virus in mosquito populations,” said Dr. Petrie.

Additionally, thermal fogging will be carried out on an individual basis and in more concentrated areas.

At a televised press conference on Tuesday, 2 February, Dr. Petrie acknowledged challenges in dealing with Aedes aegypti as it is a fast developing mosquito, “This is potentially a much more serious public health threat than we have seen previously but we do have the expertise and we have the necessary equipment and trained staff,” he said.

“The good news is that we have experience in dealing with this type of thing from the previous dengue and chikungunya outbreaks in the region.”

Dr. Petrie also thanked government for its pledge to provide additional funding needed to deal with any potential threat on a local level.

“We also have a commitment from government; from the Premier that we will be provided with the resources that we need,” he said.

Premier Alden McLaughlin offered his thanks to MRCU and the Public Health Department for the work that has been done over the course of several months since the virus’s presence was reported to have reached the Caribbean region.

“A tremendous amount of effort goes into getting us into a state of readiness in the event we face a situation like this,” the Hon Premier added.

MRCU and health authorities are urging the public to assist in combatting this disease by deterring any mosquito breeding sites. “Aedes aegypti only breeds around the home; around houses and yards,” said Dr. Petrie. “It does not breed in mangroves, swamps or bush; it likes fresh water. It’s a container breeder, so we are talking about buckets and drums, containers the size of a drinking water glass are favoured by Aedes aegypti. We are encouraging residents to have a look around your home twice a week, it just takes 10 minutes to go around your yard; turn up buckets, cover drums, fix your screens and drain water from plant pots and discarded tyres.”

Dr. Petrie also urged residents to check and clear roof guttering, and offered the help of MRCU staff to anyone who may need assistance in carrying out these relevant checks.

Zika was first detected in the 1940s in parts of Africa, Southeast Asia and the Pacific Islands. It reemerged in 2013, spreading extensively in South and Central America last year. According to the Public Health Department, the virus is reported as causing mild to no symptoms in the majority of patients, although it has been associated with serious birth defects such as microcephaly (shrunken head and brain) if contracted while pregnant.

Below is information and guidelines supplied to the Ministry of Health by the Pan American Health Organization (PAHO) in conjunction with the World Health Organization (WHO).

The vector:

• Aedes aegypti is the vector that poses the greatest risk for the transmission of arboviruses in the Americas and is present in almost all countries in the Hemisphere (except Canada and continental Chile). It is a domestic mosquito (living in and near homes) that reproduces in any artificial or natural recipient containing water.
• The mosquito can complete its life cycle, from egg to adult, in 7-10 days; adult mosquitos generally live 4-6 weeks.
• The female Aedes aegypti is responsible for transmission of these diseases because it needs human blood, mainly for the development of its eggs and for its regular metabolism. The male does not feed on blood.
• Female Aedes aegypti feeds every 3-4 days; however, if they fail to extract sufficient blood, they continue to feed every moment they can.
• The mosquito is most active in the early morning and mid-to-late afternoon, making these the periods of highest risk for bites. However, females that need to continue feeding will look for a blood source at other times.
• Aedes aegypti has a short range and does not usually fly more than 25 meters, provided that food is available in dwellings near its breeding sites. However, mosquitoes have been observed to fly as far as 400 meters in search of food.
• After feeding, Aedes aegypti lays its eggs every 3-4 days in different containers, ensuring that some of its offspring will survive predators and making the mosquito more difficult to control. This indicates the importance of disposing of unused containers in and around the home, and protecting useful containers that store water (sealing them or treating them with chemical or biological products).
• Aedes aegypti prefers to lay its eggs in artificial recipients that contain water (drums, barrels, and tires, mainly) in and around houses, schools, and workplaces.
• Females can lay some 400 eggs in the course of their lives. The number of eggs laid each time depends on the age of the female and the amount of blood extracted.
• Aedes aegypti eggs can resist dry environmental conditions for more than a year: in fact, this is one of the most important strategies the species employs to survive and spread. Properly cleaning the surfaces of drums and barrels is more effective than using chemical or biological products, since cleaning also destroys the eggs, which are always attached to surfaces in breeding sites.

 

Vector control

• The risk of transmission of these diseases resides primarily in the presence of mosquito vectors, Aedes aegypti being the leading transmitter in the Americas. If there were no mosquitoes, none of these diseases would be transmitted.
• Patients, other household members, and the community need to be educated about the risk of transmission and about measures to reduce both the amount of mosquitoes and contact between the vector and people.
• Measures to physically control the mosquito’s breeding sites are the most effective, with the greatest impact on vector populations. Physical control of mosquito breeding sites inside and around dwellings, and in public and/or private places, should be a responsibility shared by everyone––authorities, public sector, private sector, NGOs, families, and individuals––not just the public authorities or the health sector.
• Mosquito control operations are necessary and essential for reducing the risk of transmission of these diseases, but they cannot solve the problem entirely. The elimination of breeding sites should be the main control measure, since it is both the most effective and most sustainable one.
• To eliminate mosquitoes the following actions are recommended: avoid the collection of water in outdoor containers (pots, bottles, or other containers that can collect water) so that they do not become breeding sites for mosquitoes; keep tanks and water deposits covered to keep out mosquitoes; avoid accumulating trash, throw trash in closed plastic bags, and place in closed containers; and unclog drains that may leave standing water.
• Considering the hours when the vector is most active, it is recommended that actions aimed at controlling adult mosquitoes outside the home should be carried out at dawn and dusk. It is therefore essential that people/families be informed some days beforehand regarding the schedules in their neighborhoods, so that they can keep their doors and windows open to allow the insecticide into their homes.
• PAHO/WHO-recommended insecticides for adult mosquitoes and larvae are safe and effective for public health use, provided that the technical standards for application are followed (WHO/CDS/WHOPES/GCDPP/2006.1).
• It is important to minimize contact between the vector and patients infected with dengue, chikungunya, or Zika virus. This helps to prevent the spread of the virus and the disease. Patients suspected of having dengue, chikungunya, Zika, and other arbovirus diseases should rest under mosquito bed nets, as long as they remain sick.
• As additional measures, people can wear appropriate clothing that minimizes skin exposure (trousers and long-sleeved shirts) and install screens in doors and windows. They can also can use repellents authorized for human use, such as those containing DEET (N, N-Diethyl-3-methylbenzamide), IR3535 (3-[N-acetyl-Nbutyl]-ester ethyl acid aminopropionic) or Icaridin (acid-1 piperidinecarboxylic, 2-(2 – hydroxyethyl) – 1-methylpropylester), which can be applied to exposed skin or clothes and should be used in strict accordance with the instructions on the product label. There is no evidence to suggest restricting the use of these repellents in pregnant women, provided that the instructions on the product label are followed.
• To date, despite all efforts, there is no vaccine against these diseases and no new strategies or technologies (transgenic mosquitoes, Wolbachia, lethal traps, new insecticides or larvicides, etc.) that have been fully evaluated and validated by sufficient evidence to be recommended by PAHO/WHO.

References

1. Pan American Health Organization. Nelson Mj, 1986. Aedes aegytpti Biology and Ecology. Washington, D.C: PAHO/WHO.
2. Pan American Health Organization. Estrada JG, Craig. Biology, 1995. Disease Relationships, and Control of Aedes albopictus. Washington, D.C: PAHO/WHO; (Technical paper No. 42).
3. Dengue – Guidelines for diagnosis, treatment, prevention and control. World Health Organization. WHO/HTM/NTD/DEN/2009.1
4. Koren G, Matsui D and Bailey B. DEET-based insect repellants: safety implications for children and pregnant and lactating women. Canadian Medical Association Journal 2003;169(3):209-12
5. United States Centers for Disease Control and Prevention (CDC). Insect Repellent Use & Safety. Available at: http://www.cdc.gov/westnile/faq/repellent.html (accessed 18 December 2015).
6. Pesticides and their aplication for the control of vectors and pests of public health importance. Geneva, World Health Organization, 2006.

Photo Caption: (GIS)

Photo 1: Dr William Petrie, Director of the Mosquito Control and Research Unit

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