Malaria

By Dr. Mark Wise

Key Points || Prevention Measures || Antimalarial Medications || Malaria Myths

Also see the Center for Disease Control recommendations for travelers on the CDC website: SE Asia, E Asia.

KEY POINTS
Malaria is a serious parasitic infection of the bloodstream. It is the most important infectious threat to travellers to the tropics. The factors which will affect your risk of acquiring malaria include:

• your destination
• the duration of your stay
• the time of year
• the precautions you take
• ....... and once again luck!

It is transmitted through the bite of the female anopheles mosquito. The symptoms of malaria may occur in as little as 10 days after infection, but sometimes may not occur for several weeks or months after exposure.

Malaria resembles the flu, and may in fact mimic many illnesses. The classical symptoms include headache, chills, feeling hot and cold and muscle aches and pains. The most important sign of malaria is FEVER. Classically the fever recurs every 48 hours, but this is not always the case.

There is a fair bit of controversy and misinformation regarding both malaria and its prevention. Here are the facts!

• There are four strains, and only four strains, of human malaria.

• Plasmodium falciparum is the most serious strain, and the only one which may be fatal. This same strain is the one responsible for most of the drug resistance around the world. Drug-resistant malaria is not a new thing. It has been around since the 60's, but its distribution has been expanding. Chloroquine-resistant malaria is now found in all malarious areas of the world with the exception of The Middle East, Haiti and Central America.

• Personal measures such as DEET- containing repellents and mosquito nets are extremely important in preventing malaria.

• Malaria is often misdiagosed and mistreated in travellers who return home.

• Malaria is a treatable infection, as long as it is treated promptly and properly (sort of like a heart attack).

• It is a myth that once you have malaria, you have it for life. There are two strains of malaria which may persist in the liver and recur, Plasmodium vivax and Plasmodium ovale. However, this "dormant" stage can be eradicated with the drug primaquine.

• Malaria is usually a preventable infection. There are good drugs to prevent malaria. Unfortunately, there are no perfect ones.

• Many people say that antimalarials are worse than the disease. Ask someone who has had cerebral malaria!

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PERSONAL PREVENTIVE MEASURES
Antimalarial infections do not prevent your infection. They only suppress it. But with personal measures, the risk of infection can be greatly reduced. Consider the following:

• Reduce your outdoor exposure between dusk and dawn. This is when the female anopheles mosquito bites.
• Wear long sleeves and other protective clothing.
• Use an insect net at night. These may be impregnated with pyrmethrin, which further increases their efficacy.
• Use a repellent containing DEET. This is the most effective repellent. DEET-containing repellents are available in different concentrations, ranging from about 6% to 95%. It is probably best to use a concentration less than 35%. The higher the concentration the longer its duration of protection. 95% DEET provides about 8 hours of protection.
• DEET should be used cautiously in small children, as it may be absorbed through the skin. Use a low concentration, and wash it off when you return indoors.
• Other preparations, such as Skin-so-soft and citronella candles and coils are probably of some use. Buzzers, garlic and reruns of I Love Lucy are likely less effective!
• If you are in an area where there is also Dengue Fever, take precautions during the day as well.

ANTIMALARIAL MEDICATIONS

MEFLOQUINE
It was first developed in the 60’s during the Vietnam War because of the emergence of chloroquine-resistant falciparum malaria. Mefloquine is taken weekly, also beginning the week before travel, weekly while away, and for foour weeks after travel. It must be taken with food, preferably in the evening, and preferably not with a bucket of alcohol.

Minor side effects occur in up to 15% of people. These include stomach upset, dizziness, vivid (good, bad, erotic and otherwise) dreams, insomnia and anxiety. More serious side effects, such as seizures and psychosis, are relatively rare. These side effects are usually transient, and may dissipate with time. Remember, most side effects do not occur in most people most of the time. Many of the same adverse effects are reported with chloroquine.

Mefloquine should not be used in those with a history of epilepsy, depression, cardiac rhythm abnormalities, or perhaps those who have had a problem on it in the past. It is safe in children, and may also be used in pregnant women who have no choice but to travel to malarious areas. Mefloquine is a touch expensive ($5.30 in Canada, up to $10.00 in the USA), so some people may chose a cheaper alternative. It may often be purchased for less in tropical countries.

DOXYCYLINE (Vibramycin)
Doxycycline is an antibiotic, which is quite effective in preventing chloroquine-resistant falciparum malaria. It can be used in those who can not take mefloquine, and those who do not want to take mefloquine. It must be taken on a daily basis, starting the day before entering the malarious area, daily while away, and for four weeks after departure.

It must be taken with lots of water, or it may irritate the esophagus. As it can cause photosensitivity, sun precautions must be used. It will also predispose women to yeast infections. It is contraindicated in pregnancy and children under the age of 7, as it can cause staining of the teeth.

PROGUANIL (Paludrine)
This medication may be used in plaxce of chloroquine in chloroquine-sensitive areas. Most often, it is used in combination with chloroquine in resistant areas. This regimen is slightly less effective than mefloquine.

Proguanil must be taken on a daily basis. It is available in Canada (not the USA) and is much more expensive here than in tropical countries. It must be taken on a daily basis, beginning at the time of exposure, daily while away, and for four weeks after departure from the tropics. Its most common side effect is mouth ulcers. It is safe in pregnancy.

There are other medications, and combinations of medications, available in the tropics. Remember, none are perfect!

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MALARIA MYTHS

Malaria is now a greater threat to travellers than ever before. Drug resistant falciparum malaria is spreading, and unfortunately, there is no effective vaccine on the horizon. Several myths regarding this infection seem to persist amongst both medical and non-medical personnel alike. Let's try to dispel the most popular ones. 

Once you have malaria... you have it for life

Not true. While I have seen numerous patients who are convinced that they have suffered relapses on a yearly basis since World War II, this is rarely the case. There are two strains of malaria, P. vivax and P. ovale, which may persist in the liver as hypnozoites for months and even years and cause such recurrences, but they can easily be eradicated by the use of the drug primaquine. This is usually administered following a course of chloroquine. Having said that, there are now some interesting strains of P. vivax in Irian Jaya and Papua New Guinea which are displaying varying degrees of resistance in both chloroquine and primaquine.

There is no longer an effective antimalarial.

Not true. While there is no perfect antimalarial, drugs such as mefloquine, doxycycline and combinations such as chloroquine plus proguanil still offer excellent protection if used properly.
When combined with personal measures such as insect repellents and mosquito netting, the risk of malaria to most travellers is very small. While we do see cases of malaria due to drug failure, the great majority of patients who develop malaria do so because they have either stopped their antimalarial, or are on the wrong one.

Taking antimalarials only masks the disease.

Not exactly a myth, but a misunderstanding. In fact, it is true. Antimalarials do not prevent infection following a mosquito bite. Rather, they kill the parasites as they enter our red blood cells. This prevents them from multiplying, invading other red blood cells, and clogging arteries to our brain and other vital organs. As a result we don't suffer the fevers, chills, headaches and other joys of malaria. We continue our antimalarials for four weeks after leaving a malarious area in the hope that they will continue to mask, or suppress any symptoms until the risk of disease has likely passed.

The drugs are worse than the disease.

Tell that to someone who has almost died of malaria. Antimalarials do have side effects…in some people, some of the lime. All drugs do. Between 15-20% of travellers will experience stomach upset, dizziness, vivid dreams or emotional symptoms such as anxiety while taking mefloquine, the most commonly prescribed antimalarial. That means that 80-85% of people will be fine. The side effects are usually transient and tolerable. Serious adverse reactions such as psychosis or seizures are rare. Compare that to the real thing, which may be fatal. No contest!

I am immune to malaria.

Usually not true. People who grew up in malarious areas such as in tropical Africa do develop a relative immunity to the parasite. This does not mean that they don't get infected. Rather, their symptoms of malaria maybe milder than a non-immune person or they may even have circulating parasites in the absence of any symptoms. However this immunity is mostly lost after living through several Stanley Cup playoffs in Canada due to the lack of constant exposure to the parasite. Therefore, most Canadians returning to their native countries are quite susceptible to malaria, and in fact account for the majority of our imported cases.

If I take antimalarials, there will be nothing left to treat me if I do get malaria.

Wrong again. There are several drugs used to treat malaria, including quinine, halofantrine (Halfan), pyrimethamine / sulfadoxine (Fansidar) and derivatives of artemesinin. The drug of choice may depend upon where you are, i.e. downtown Toronto versus Timbuktu, and how sick you are. Sometimes a drug such as quinine or halofantrine will have to be used with extra caution if the patient has recently been on mefloquine, as all can have cardiac side effects. But having been on an antimalarial certainly doesn't leave a malaria sufferer without additional treatment options. Malaria is a treatable disease when treated quickly and correctly. When travellers die of malaria, it is usually because of delayed or inadequate treatment.

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© Copyright 2000 Dr. Mark Wise

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