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Viruses
A virus is a very small germ. Viruses that are carried by mosquitoes are called arboviruses. Many arboviruses cause encephalitis, a swelling of the brain. St. Louis encephalitis (SLE) virus is the most common cause of encephalitis in Florida. During most years, one to 10 people are found to have the SLE virus. During the last 30 years, several large outbreaks with as many as 200 cases have occurred in Florida. Other arboviruses that cause encephalitis in Florida are eastern equine encephalitis (EEE) virus and West Nile (WN) virus. Usually no more than five people in Florida are found to have EEE each year. WN virus was first identified in Florida during 2001. Twelve people were found to have WN virus encephalitis during 2001, and 28 were found in 2002.

Symptoms
Many people infected with an arbovirus may not even get sick. For the small number who do become ill, it may take from two to 15 days after the bite of an infected mosquito before they become sick. Symptoms may include high fever, headache, fatigue, dizziness, weakness, and confusion. WN may also cause rash or muscle weakness. People 50 and older are more likely to develop brain swelling from SLE or WN virus infections. Anyone infected with EEE virus may develop brain swelling. People with fever and a bad or strange headache should see a doctor as soon as possible. The doctor may need to order laboratory testing to see if an arbovirus caused the illness. Although there is no cure for arboviruses, symptoms can be treated. Treatment is important. People with a severe arbovirus illness might go into a coma or die because of brain swelling.

Prevention
At this time, there are no vaccines available to protect people from arboviruses. The best way to reduce the risk of getting ill is to avoid getting mosquito bites.

If you must be outdoors when mosquitoes are active, cover up. Wear shoes, socks, long pants, and a long-sleeved shirt.

Use a mosquito repellent. You get the best protection by using repellents containing DEET:N,N-diethyl-meta-toluamide, or N,Ndiethyl-3-methylbenzamide. The more DEET a repellent contains the longer time it gives protection from mosquito bites. Repellents with greater than 30 percent DEET do not give you more protection and may increase your chances of suffering side effects. You can add to your protection by applying a permethrin repellent directly to your clothing. Always read the manufacturer's directions carefully before you put on repellent.

It is important to remember that DEET is not recommended for children younger than two months old. Instead, avoid exposing your baby to mosquitoes. If you have to take your baby outside, dress him or her in protective clothing and cover the stroller with mosquito netting.

Transmission and Surveillance
SLE, EEE, and WN viruses pass back and forth between birds and mosquitoes. State and local agencies keep a close watch on mosquito populations. In many areas, mosquito control agencies and county health departments also keep chicken flocks, called sentinel chickens. The blood of these chickens is sampled for signs of arboviruses. Chickens make good sentinels because they do not get sick from arboviruses. People cannot catch an arbovirus from the chickens.

Horses can get encephalitis from the EEE and WN virus. Sick horses are often the first indicator that an arbovirus is in an area.

Malaria
Malaria accounts for over 2 million deaths each year around the world, making it the single leading cause of death in undeveloped countries. Its life cycle is one that is dependent on human hosts to continue the cycle, unlike most other mosquito borne diseases which require a local wild animal host when not infecting human populations.

Malaria in the United States has been virtually eliminated for this reason, in conjunction with enforced standards in building code and readily available window screens. The advent of air conditioning has also significantly reduced human exposure to mosquitoes and therefore greatly impacted the likelihood of malaria transmission.

Since the micro-organism has no way to survive in the wild unless it has a human host to sustain it, its presence in the United States decreased dramatically over the last century. However, other parts of the world are not so fortunate, and visitors from those parts of the world frequently have a history of malaria infection.

The key to malaria's survival is that it infects an individual for life, only periodically appearing in the bloodstream, which can then be taken up by a mosquito biting that individual. This individual is now considered to be infectious for malaria. These periodic infectious episodes or re-occurrences can happen at any time, with as little as 48 hours or as long as 30 years in between.

If such an individual should become infectious while in this country, malaria transmission is likely to occur if that individual is exposed to the appropriate type of mosquito. Since this disease is dependent on human initiation, your local mosquito control program has little control over its reintroduction into Palm Beach County. Our local populations of mosquitoes known to be effective hosts for malaria are significantly lower than those populations involved with other types of mosquito borne diseases and, more importantly, those populations which create the greatest demand for mosquito abatement services, the nuisance mosquitoes.

Extenuating circumstances can occur that allow for an infected individual to be exposed to long periods of mosquito bites. This extended exposure can overcome the decreased likelihood of malaria transmission due to low mosquito populations, even when those species that can carry malaria are in exceedingly low numbers.

Palm Beach County is riddled with drainage ditches and canals, which are prime habitat for the types of mosquitoes involved in malaria transmission. This type of mosquito does not occur in large enough numbers to be a nuisance problem, and thus do not generate demand for mosquito abatement services. Most ditches and canals are kept relatively free of aquatic weeds, which shelter the mosquito larval stage in the water, keeping them safe from predation by fish.

When these ditches become clogged with aquatic weeds, they produce greater amounts of mosquitoes, and in turn increase the chance that if an individual currently infectious for malaria is in the vicinity and is exposed to extended periods of mosquito bites, malaria can get into the mosquito population. Once this happens, it's simply a matter of time before an uninfected individual is bitten by an infected mosquito, giving that person malaria.

Since the residents of Palm Beach County are not routinely exposed to malaria, they have a reaction to the disease more severe than residents of countries that regularly experience malaria outbreaks. In parts of the world that routinely experience malaria, residents may think no more of malaria than you or I may think of the common flu. They often self-medicate using folk remedies, and when they visit Palm Beach County may do the same utilizing local sources of such remedies. The medical community is thus unaware of many cases of malaria due to this reason. Usually this is not an issue because, as mentioned above, our typically low levels of malaria host mosquitoes. However, if an infectious individual is exposed for an extended period of time to those mosquitoes, either through outdoor recreational activities or simply being homeless, the potential for malaria transmission increases.

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