2000-12 Mosquito

2000-12 Mosquito In the past few years we have experienced a resurgence of mosquito-borne illness in the U.S., Central America and in tropical South America. The two illnesses of most concern to divers are malaria and dengue fever. Most of us are familiar with malaria, but the viral illness dengue fever is not as familiar and can cause severe illness. These mosquito-borne diseases are appearing in the U.S. as travelers bring the illness home, infecting hometown mos-quitos, which spread the disease locally.

When planning a diving holiday, pre-parations relating to equipment and travel are so much in mind that medical problems are usually not considered. Asking your family physician about diseases specific to the area you will be traveling should be on your pre-travel checklist.


There are many medical problems that can occur while on a dive trip. Malaria, a serious and potentially fatal disease, is still a major problem in many tropical areas of the world. In the early days of the U.S., malaria could be found in the southern states, but was eventually eradicated by mosquito control measures. However, two cases were reported in New Jersey several years ago that were due to mosquito-borne transmission from migrant workers on local farms to residents of a nearby town. There are an estimated 150 million new cases reported every year.

Malaria is transmitted by a specific type of mosquito called the Anopheles. You can recognize this nighttime mosquito by its resting posture, where the proboscis (mouth part), head and thorax (middle section) are held in a straight line, while the entire body is at an angle to the skin surface. It is this characteristic angled posture that distinguishes the Anopheles.

If a malaria-infected mosquito bites a human, malaria organisms carried by the mosquito are injected into the blood stream. The malaria organisms pass into the liver and grow silently during a latent period without any signs or symptoms of the disease. This latent period can last from 6 to 11 days, depending on the type of malaria parasite involved.

The malaria infection occurs in three phases, which are closely related to events occurring in the blood stream: viral growth, fever and sweating. When the organism has matured in the liver, it invades the red blood cells, grows and breaks out of the cells. This process causes a rapid rise in temperature associated with a feeling of intense cold and accompanied by 15 to 60 minutes of shivering severe enough to make the teeth chatter. Fever of 102-105 degrees, vomiting and headache are common symptoms. During the periods of high temperature, the malaria parasites just released from the red cells invade more red blood cells. The third phase is sweating that can be severe enough to cause large fluid loss. The temperature falls rapidly accompanied by severe sweating, and the victim may drop into a deep sleep. The victim will usually awake feeling well again. However the cycle repeats again and again at 48- or 72-hour intervals until the disease becomes chronic. The number of days between fevers is unique for the specific species of malaria parasite which caused the infection.

Treatment of malaria is often prolonged and difficult, while prevention is much easier with one pill a week. When going to the tropics, inquire about malaria protection and whether your dive site is in a high-risk area. In Central America, prevention is achieved with Chloraquine taken once a week starting two weeks before departure, continuing throughout the period of exposure and for four to six weeks after leaving the malaria area. In all other parts of the world, the malaria organism is resistant to Chloraquine and an alternative must be used. The best alternative is Mefloquin (Larium). It has side effects in 11 percent of the people who take it, including dizziness, which may affect dive safety. Be sure to try this medication before departing for your trip.

If any unexplained fevers occur, even weeks after a visit to a malarial area, alert your doctor.

Dengue Fever

Mosquitos carry another disease that is common in Central and South America called dengue fever. The dengue virus is similar to the West Nile virus that has caused mosquito-borne encephalitis in New York and New Jersey. Severe cases can cause bleeding, shock and death. The common form of dengue is called, "Break-bone fever" because of the severe bone and muscle pain. This illness begins with fever, chills and severe muscle pains. Symptoms are accompanied by a rash and a severe headache. After three days, the symptoms usually subside only to recur in two or three days. The second phase of the illness usually lasts three to five days. This is one of the viral illnesses in which aspirin should not be used because of the risk of Reye syndrome, a serious complication of aspirin use in severe viral infections.

Dengue is found throughout the coastal areas of Central America, in Puerto Rico, where it is a common illness, and in the northernmost countries of South America. Dengue is carried by the Aedes aegypti mosquito, a daytime mosquito that breeds in stagnant water. In countries with a high incidence of dengue, there are strong mosquito eradication programs. Dengue is also found along the Gulf Coast of the U.S., where cases have been reported in the past several years, as well as parts of Africa, India and the Indochina Peninsula, northeastern Australia and many of the islands in the Western Pacific.

Prevention of dengue fever begins with removal of any stagnant pools of water where mosquitoes can breed. In areas where dengue is particularly common during certain seasons, it is best to avoid the area during those times. No vaccine is available for this illness, and antibiotics are not useful since this is a viral disease. Treatment is usually bed rest, pain medication (not aspirin) and fluids. If the severe form of dengue develops, the victim should be hospitalized, and carefully monitored for bleeding, kidney and heart abnormalities.

When traveling to remote parts of the world, use of mosquito netting at night, insect repellent during the day and protective clothing will reduce the risk of any mosquito-borne disease. Before you travel to a tropical country, inquire about the local diseases from your physician or from the U.S. Centers for Disease Control at www.cdc.gov.