The best dive spots in the world are located in tropical regions. However, staying in such regions leaves one open to mosquito-borne illnesses such as malaria and dengue fever. Several tips on how to avoid contracting these illnesses are presented.

When planning a diving holiday, preparations relating to equipment and travel are so much in mind that medical problems are often not considered. On your diving checklist should be a reminder to ask your family physician about diseases specific to the area where you will be traveling. Tropical regions are often the location of common mosquito-borne illnesses. Two you should avoid are malaria and dengue fever.

MALARIA

Malaria is a serious and potentially fatal disease that is still a major problem in many tropical areas. In the early days of the United States, malaria could be found in the southern states but was eventually eradicated by mosquito control measures. However, it can still occur in the U.S. Two cases were reported in New Jersey recently that were owing to mosquito-borne transmission from migrant workers on local farms. Malaria is well known in tropical latitudes and remains the most common of all tropical diseases, with an estimated 150 million new cases occurring every year.

Malaria has been known since antiquity and, in spite of massive efforts at eradication and control, is still a major problem. Malaria is transmitted by a specific type of mosquito called Anopheles. In the resting posture Anopheles holds its proboscis, head and thorax in a straight line, while the entire body is at an angle to the resting surface. It is this characteristic, angled posture that distinguishes Anopheles. It is the only mosquito species that assumes such a posture.

If an infected mosquito bites a human, malaria organisms are injected directly into the blood stream. A serious chain of events is then started. The malaria organisms pass into the liver and grow silently during a latent period, without any signs or symptoms. This latent period can last from 6 to 11 days, depending on the type of parasite involved,

The malaria infection occurs in three stages, closely related to events occurring in the blood stream. 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. A fever of 39 to 40oC (102 to 105oF), vomiting and headache are common. During the high temperature, the malaria parasites just released from the red cells invade more red blood cells. The third phase, which occurs several hours later, is sweating, which can be severe enough to cause a 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 one of four species of malaria parasite that has caused the infection.

This is a serious illness that is best avoided. When going to the tropics, you should inquire about malaria protection and whether your destination is in a high risk area. Prevention is achieved with medication, 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. Sometimes the illness will occur after a several week delay. If any unexpected illness occurs even weeks after a visit to a malaria area, let your doctor know you visited a country or region that has a malaria risk. There are special blood tests that can be used to detect the parasite.

In some areas malaria parasites are resistant to certain medications and alternatives should be used. All malaria medications should be prescribed by your physician. The entire Indo-Pacific area, most of Africa and some areas of Central America, including the Western Caribbean, should be regarded as malaria areas. The U.S. Center for Disease Control in Atlanta gives updated information on areas of the world where malaria is a problem.

General measures to protect against mosquitoes are the first line of defense against malaria and are definitely worthwhile. The following are recommended: long sleeved shirts and trousers or slacks and mosquito repellent used on any exposed skin surfaces. The effect of some repellents may not last long enough to give protection at dawn if applied the night before and reapplication is one solution to this problem. Mosquitoes are most active at dawn and dusk. Unless sleeping in a mosquito proof building, mosquito nets should be used at night; insecticide sprays are also useful. Incidentally, filariasis and encephalitis can also be transmitted by the Anopheles mosquito. These are more reasons for avoiding contact with these insects.

The malaria infection lasts variable periods of time, depending on the type of parasite. One type of infection may last for many years, others will disappear in two to three years without treatment. Treatment of malaria is often prolonged and difficult, prevention is much easier. Efforts at eradicating malaria in high risk areas have been frustrated by the need to take medication continuously. Tests of vaccines, mosquito control measures and education about avoiding mosquito bites are all part of a worldwide effort to control malaria infections.

DENGUE FEVER

Mosquitoes can carry another disease, common in Central and South America, called dengue fever. This is a short viral illness. 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 pain. These 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.

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. The Aedes aegypti mosquito breeds in stagnant water and the incidence of dengue rises after periods of heavy rainfall. In countries with a high incidence of dengue there are strong mosquito eradication programs. Dengue is also found along the gulf coast of the United States, in 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. Avoid areas where dengue is particularly common during certain seasons. Use of mosquito netting at night, insect repellent during the day and protective clothing will reduce the risk of any mosquito-borne disease. Staying indoors at night to avoid exposure to mosquitoes is also an effective way to avoid dengue fever. No vaccine is available for this illness and antibiotics are not useful since it 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 function.

Travel to remote parts of the world is now common for sport divers. Many of these areas harbor diseases not found in the United States, which can cause severe illness. A traveler returning to the United States may appear with an uncommon illness that might confound the physician if a history of recent travel is not revealed.

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