No one knows how many mosquitoes live in Bermuda but every week Government Vector Control Officers manually count the number of eggs laid by one type of mosquito — the Aedes Aegypti.

This pest can carry the virus that causes Dengue Fever. Although the mosquito is here, the virus is not and so we are safe. Safe for now that is, because the virus could get here. Recognising the health risk, Government monitors the situation very closely.

Twice a week Vector Control Officers check the 600 Ovi Traps at locations across the Island. Every trap covers a 500-foot radius and many overlap ensuring every bit of land is included.

“We are having a problem where some people are removing the traps,” said Chief Vector Control Foreman Ross Furbert. Mr. Furbert believes people remove the traps because they don’t know what they are. “I think if the public understood the importance of the traps our problem could be solved,” he said.

The traps are how the officers monitor the potentially dangerous mosquito. Each trap is a dark brown or black glass bottle, one half to three-quarters full of water with a strip of Masonite, called a paddle. Masonite is hardboard siding, smooth on one side and slightly perforated on the other.

Each paddle is labelled with the date and location and changed each week by area officers. The foreman for each of the three areas views each paddle under the microscope and counts and records the number of Aegypti eggs on it.

“Only one female will lay her eggs on a paddle,” said General Foreman Graham Vanderpool, “and one paddle may have hundreds of eggs on it.”

Paddles with very high egg counts are kept and sent once a year to the Caribbean Epidemiology Centre.

In the Vector Control Office the three area foremen record the Ovi Trap counts in a computerised database. The figures are also plugged into a map of the Island, so that an overall picture of mosquito infestation on the Island can be gleaned at a glance. The Arc View programme used also provides a detailed look at any specific area.

Every Friday an overall map of the Island is produced that shows exactly where they are breeding. Separate detailed area maps of those breeding areas are also run. These maps are used to isolate the source of specific breeding places. If the infestations are on private property, the owner or tenant of the property is contacted and asked to rectify the problem. Typically this means the removal of standing water, perhaps a bucket or small pond. In the case of a small pond or swimming pool, the water can be treated with granules to kill the mosquito larvae. Sometimes guppies (a small fresh water fish) can be used to eat up all the larvae.

Mr. Vanderpool said most people heed officers’ requests straight away, but a written caution is given at this stage. Ten days later officers check the site again and if nothing has been done, a written warning is issued. Ten days later the site is re-checked and if still nothing has been done a sample is collected in a vial and placed in a sealed evidence bag. This equips the officers to prosecute.

“We take them to court as a last resort,” said Mr. Vanderpool. While the majority of residents comply with vector officers’ requests there are a few who don’t. “About 20 to 30 people totally disregard warnings and reach the prosecution stage every year,” he said. “And it tends to be the same people year after year.”

“Prosecution is the most annoying part of our job,” he said. “It’s very frustrating. The public needs to see that mosquitoes transmitting disease could be very dangerous. The Dengue Fever mosquito is here already.”

Some problems

The Aegypti mosquito is very well adapted to survive. Well meaning residents who are cautioned may respond quickly and appropriately yet find the mosquito breeding returns just a few days later.

“It can be a tricky thing,” said Mr. Vanderpool. “We may caution a man who has some paint buckets around the house where breeding has started. He may empty the buckets but a few days later it rains. The rain water collects in the bucket and eggs that were there before now find ideal conditions and hatch,” he said.

How does this happen? Although the man threw out the standing water the first time, he did not wash the bucket and eggs deposited on the side will have remained. Once water collected again, ideal conditions for the hatching of the larvae will have returned and the bucket will again become a rich breeding ground. “It is important to wash the inside of containers to ensure eggs are not stuck to its sides,” said Mr. Vanderpool.

In a case such as the one described where a person is issued a caution, given a clean slate after ten days but then found to have breeding mosquitoes in the same location ten days later, the Vector Control Officer would issue the man a second caution and follow up as before.

Unlike many other types of mosquitoes, Aegypti can breed in fresh water.