Diving and Malaria

By Dr. Sawatzky

Malaria is a disease caused by infection with a parasite called Plasmodia. It causes recurring periods of chills, fever, sweating, anemia and splenomegaly (enlarged spleen). Malaria is very common in Africa, much of South and Southeast Asia, Central America and Northern South America. It used to be common in the USA but has been virtually eliminated. However, the anopheles mosquitoes that transmit the disease between people still exists. There have been small outbreaks in New York City, California and Florida where a traveller has been infected abroad and then spread the disease via local mosquitoes after they have returned home.

Malaria infects approximately 300 million people annually, resulting in three million deaths. It is the number one killer in Africa (followed by HIV). In 1998, there were approximately 1,000 cases of Malaria in the USA and another 1,000 cases in Canada. As the population of Canada is ten times less than the USA, the incidence of Malaria is 10 times higher in Canada than in the USA. Each year, 30,000 travellers from Europe and North America acquire Malaria.

There are four different species of Plasmodium that cause Malaria in humans. These are falciparum, vivax, ovale and malariae. Falciparum and vivax are often resistant to the common antimalarial drugs. The life cycle of all four species is the same. A female anopheles mosquito sucks blood containing malaria gametocytes from a person with malaria. Over the next one to two weeks, the gametocytes reproduce inside the mosquito and develop into infective sporozoites. When the mosquito next feeds on a human, the sporozoites are injected into the person where they quickly infect the cells of the liver. In the liver, they transform into merozoites that invade red blood cells (RBCs) where they change again into trophozoites that appear as rings in stained blood smears (this is how malaria is diagnosed in the lab). The liver infection does not cause any signs or symptoms but as the RBCs rupture, the fever, chills, and other symptoms typical of malaria occur. At the same time, gametocytes are being formed in the RBCs. These do not cause problems in the person but infect the next female anopheline mosquito to feed on them, thereby spreading the infection to other humans.

After being bitten by the malaria carrying mosquito, the person usually does not have any symptoms for the first two to four weeks. They then develop the fever, chills, etc. In some cases, they may not develop any symptoms for up to a year after being infected. People who have taken chemoprophylaxis (drugs that try to prevent being infected with malaria) may develop unusual symptoms like headache, backache, and irregular fever. Diagnosis is by blood smears but because the parasite is intermittently in the RBCs, several smears may have to be done before the diagnosis can be made. Malaria due to Plasmodium falciparum is the most serious, resulting in death in four percent of cases.

Prevention is the key to malaria but no drugs or measures are completely effective in preventing infection. Experimental vaccines are being evaluated but are not yet available to the general public. Children less than five, pregnant women and people
who have not been exposed to malaria before (most Canadians) are at increased risk of serious disease.

Prevention of Malaria is centred in two areas, avoiding being bitten by the mosquitoes and preventing the infection if you are bitten. Anopheles mosquitoes only fly at night (mosquitoes carrying Dengue Fever fly during the day) and therefore, night protection is paramount. In high risk areas, you should use bed netting impregnated with pyrethrum (mosquito repellent), spray buildings with pyrethrum-containing residual insecticide, wear protective clothing (long sleeves, long pants, socks, NB dusk to dawn), and use DEET (N,N-diethyl-metatoluamide) containing insect sprays.

Chemoprophylaxis should begin one to two weeks before entering a malaria risk area and continue for four weeks after leaving the area. The original drug used was chloroquine. Unfortunately, in may parts of the world, malaria is now resistant to this drug (still effective some places so check with a travel medicine expert before travelling). Mefloquine is a highly effective drug for malaria prophylaxis. However, it has some particularly nasty side effects. It can cause paranoia, depression, hallucinations, nightmares, and definitely interferes with sleep. How frequently it causes these problems is the subject of ongoing debate. Nevertheless, many dive resorts are now forbidding anyone taking mefloquine from diving. As the drug is taken only once per week, it will take approximately a month for the drug to be cleared from the body after the last dose.

Fortunately, an alternative exists for divers. Doxycycline (a tetracycline) 100 mg daily is highly effective. Unfortunately, it can cause stomach upset and sun-related rash in some people. Nevertheless, it is still the recommended drug for use in travelling divers. Divers who can not tolerate doxycycline (should not be taken by children and pregnant women) might want to restrict their diving to areas with low risk of malaria. Several newer drugs are becoming available but there is very limited experience with them. Treatment of malaria is sometimes very difficult and a tropical disease expert should always be consulted.

As can be seen from the previous discussion, malaria is a common and potentially very serious disease. It is widespread and drug resistance is a serious problem. The best advice that can be given about malaria is that there is no standard chemoprophylaxis, and no antimalarial drug guarantees protection. Advice from travellers and overseas health care providers should be ignored. Personal protective measures are very important. Any fever within a year of travel to a malaria area should be considered malaria until proved otherwise. The bottom line is that if malaria is a risk in the area you plan to travel to, you should check with a travel medicine clinic well in advance of your trip.