MOSQUITO INFORMATION - CT Mosquito Control

MOSQUITO INFORMATION

Mosquitoes are insects belonging to the order Diptera, the True Flies. Like all True Flies, they have two wings, but unlike other flies, mosquito wings have scales. Female mosquitoes' mouthparts form a long piercing-sucking proboscis. Males differ from females by having feathery antennae and mouthparts not suitable for piercing skin.

Mosquitoes can be an annoying, serious problem in human domain. They interfere with work and spoil hours of leisure time. Their attacks on farm animals can cause loss of weight and decreased milk production. Some mosquitoes are capable of transmitting diseases such as malaria, yellow fever, dengue, filariasis and encephalitis [St. Louis encephalitis (SLE), Western Equine encephalitis (WEE), LaCrosse encephalitis (LAC), Japanese encephalitis (JE), Eastern Equine encephalitis (EEE) and West Nile virus (WNV)] to humans and animals.

Mosquito Borne Diseases

Mosquitoes cause more human suffering than any other organism -- over one million people die from mosquito-borne diseases every year. Not only can mosquitoes carry diseases that afflict humans, they also transmit several diseases and parasites to which dogs and horses are very susceptible. These include dog heartworm, West Nile virus (WNV) and Eastern equine encephalitis (EEE). In addition, mosquito bites can cause severe skin irritation through an allergic reaction to the mosquito's saliva - this is what causes the red bump and itching. Mosquito vectored diseases include protozoan diseases, i.e., malaria, filarial diseases such as dog heartworm, and viruses such as dengue, encephalitis and yellow fever.

Dog Heartworm: Dog heartworm (Dirofilaria immitis) can be a life-threatening disease for canines. The disease is caused by a roundworm. Dogs and sometimes other animals such as cats, foxes and raccoons are infected with the worm through the bite of a mosquito carrying the larvae of the worm. It is dependent on both the mammal and the mosquito to fulfill its lifecycle. The young worms circulate in the blood stream of the dog. These worms must infect a mosquito in order to complete their lifecycle. Mosquitoes become infected when they blood feed on the sick dog. Once inside the mosquito the young worms leave the gut of the mosquito and live in the body of the insect, where they develop for 2-3 weeks. After transforming twice in one mosquito the third stage infective larvae move to the mosquito's mouthparts, where they will be able to infect an animal. When the mosquito blood feeds, the infective larvae are deposited on the surface of the victums skin. The larvae enter the skin through the wound caused by the mosquito bite. The worms burrow into the skin where they remain for 3-4 months. If the worms have infected an unsuitable host such as a human, the worms usually die. The disease in dogs and cats cannot be eliminated but it can be controlled or prevented with pills and/or injections. Some risk is present when treating dogs infected with heartworms but death is rare; still prevention is best. Of course good residual mosquito control practices reduce the treat of mosquito transmission. Until the late sixties, the disease was restricted to southern and eastern coastal regions of the United States. Now, however, cases have been reported in all 50 states and in several provinces of Canada.

EEE: EEE is spread to horses and humans by infected mosquitoes. It is among the most serious of a group of mosquito-borne arboviruses that can affect the central nervous system and cause severe complications and even death. EEE is found in North America, Central and South America, and the Caribbean. It has a complex life cycle involving birds and a specific type of mosquitoes. These mosquitoes feed on infected birds and become carriers of the disease and then feed on humans, horses and other mammals. Symptoms may range from none at all to a mild flu-like illness with fever, headache, and sore throat. More serious infections of the central nervous system lead to a sudden fever and severe headache followed quickly by seizures and coma. About half of these patients die from the disease. Of those who survive, many suffer permanent brain damage and require lifetime institutional care. There is no specific treatment. A vaccine is available for horses, but not humans.

WNV: Since its introduction into the United States in 1999, West Nile virus has spread at an alarming pace, with a total of almost 15,700 human cases and 650 fatalities as of 24 September, 2004. Approximately 20% of human West Nile cases develop West Nile Fever, whose symptoms include fever, headache, tiredness, and body aches, occasionally with a skin rash (on the trunk of the body) and swollen lymph glands. This condition can last anywhere from a few days up to several weeks. Almost 30% of symptomatic human West Nile cases develop a more severe form of neuroinvasive disease characterized by headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. The neuroinvasive form occurs most often in people over age 50 and some immuno-compromised persons (for example, transplant patients), but can occur at any age in healthy individuals.

The 2002 outbreak of West Nile Virus constituted the largest documented outbreak of mosquito-borne meningoencephalitis in the history of the western hemisphere. West Nile Virus has wrought havoc with wildlife as well. More than 200 avian species and 30 mammalian species have been found infected. Although accurate counts of absolute numbers of birds and mammals fatally infected are problematic, the toll for corvids (crows, jays, etc.) is estimated to be in the millions. Horses suffer a 40% mortality rate from infection with this virus. The cost to the horse industry in vaccinations, medical costs, prevention/control measures, and mortality is estimated to exceed one billion dollars.

The transmission cycle of West Nile Virus involves birds as a reservoir of infection and means of spread through migration, avian-feeding species of mosquitoes amplifying the virus among bird populations, and bridging species of mosquitoes that feed upon both birds and mammals transmitting the virus to humans and equines. At present, 60 of the 174 species of mosquitoes currently recognized in the United States have tested positive for the virus. Of these, generally one species is primarily responsible for transmitting the disease in a particular area. Each species utilizes preferred aquatic habitats within which to breed. These habitats vary widely, from salt marshes to used car tires. Virtually any collection of stagnant water is fair game, with some species successfully utilizing even soda bottle caps. Factors favoring choice of breeding habitat depend upon the mosquito species involved, topography, climate and human use patterns.

West Nile Virus Transmission Cycle

Above Graphic Courtesy of AMCA.

Mosquito Control

Control ultimately consists of reducing the contact between the vector mosquito and humans. This is accomplished through removing, modifying or treating larval habitats; modification or removal of adult mosquito resting areas, adulticide treatments and the use of repellents and chemical control.

Mosquitoes can be controlled in the larval stage through the adult stage. The best treatment will vary depending on the stage of the life cycle of the mosquito, habitat conditions and environmental factors.

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