April 2002 Surveillance At South Walton Mosquito Control, we conduct two types of surveillance, one to determine the mosquito population levels, changes, and specie makeup and the other to detect the presence, types and level of mosquito-borne viruses.
Mosquito surveillance is an essential activity for an effective, efficient, and environmentally sound mosquito control program. Surveillance is used to determine the nature and extent of a mosquito problem and to gauge the effectiveness of control efforts on a daily basis. Surveillance provides the data needed to comply with state rules and regulations, which require justification when applying pesticides and also provides a basis for evaluating the potential of disease transmission by mosquitoes.
In South Walton, we use several surveillance techniques to get a grasp on what the mosquito population is doing. We use 17 light traps, checked five times per week, with each collection counted and identified to specie. We conduct “landing rate counts” just prior to spraying to verify mosquito activity in certain situations and areas. We conduct “larval dips” in standing water to verify the presence of larvae prior to larviciding. And we use “citizen complaints” to alert us to specific problem areas and inspect such complaints to determine if the complaint is actually caused by mosquitoes or is a “container breeding” mosquito problem that can only be solved by the elimination of the container. If our surveillance indicates that mosquito populations have increased and are at a level that justifies the use of pesticides, we will treat the situation, weather conditions permitting.
Mosquito control is just that, mosquito control. Our activities will never eradicate or eliminate mosquitoes. Authorities tried to do that in the 1950s with DDT. It didn’t work. Mosquitoes like other insects, developed resistance. The objective of mosquito control is to keep their numbers low enough so as not to cause a major nuisance, affect the economy of an area, and to minimize the possibility of mosquito-borne diseases.
Arbovirus (arthropod/mosquito-borne disease) surveillance in South Walton is done using sentinel birds. There are 14 coops with four birds each located with our light traps in each spray route within our District. Eastern Equine Encephalitis (EEE) and West Nile Virus (WNV) are bird diseases. Wild birds reservoir or maintain these diseases, with certain mosquitoes transmitting the disease from bird to bird. These diseases are not usually fatal to birds. They get sick, develop an antibody and recover. We use chickens and pigeons as our sentinel birds. Both have proven to be effective at converting (developing antibodies) when exposed to mosquito-borne viruses. A blood sample is taken once a week from each bird and tested for the presence of antibodies to these viruses. A conversion (detection of antibodies) now and again is normal. These viruses are always circulating in bird populations. If, however, we get one or two conversions one week and four or five the next, it alerts us to step up our mosquito control activities. Disease transmission by mosquitoes is a numbers game. For example, a horse, outdoors may get bitten 50 times per day with low mosquito populations, with low or no conversions in our sentinel flocks, the chance of that horse picking up disease is very low. If, however, vector or disease transmitting mosquito populations are high and conversion rates in our sentinel birds is high, then that horse may get bitten 1,000 times a day, greatly increasing the possibility of infection. This is where mosquito control comes in. Our surveillance efforts will alert us to step up our control activities before mosquito populations become large enough to favor disease transmission. Controlling the vector, the mosquitoes transmitting the diseases, minimizes the possibility of infection by breaking the disease transmission cycle.
Weather conditions, mosquito abundance, species makeup, the level of infection in natural hosts, and the exposure of animals and humans to the mosquito vectors will determine the potential for disease transmission. Surveillance activities provide us with the information we need to act. Whether it is the need to treat or not to treat, to alert the public so they can take measures to minimize their exposure or to remind them to vaccinate their animals; surveillance is an essential activity for the proper and effective operation of any insect control program. |