For all of our medical progress, the exploits of today’s circumnavigators are still fraught with many of the same diseases that laid claim to the crews of Drake and Magellan. And, of all the illnesses noted in the annals of medical history, probably none is so well documented as malaria. Historically, it stands as the great leveler, decimating the ranks of invading armies and damning many of the early voyages of exploration to failure. It has, in general, taken more lives than any other disease that a modern ocean sailor might encounter.
Fortunately, malaria is preventable and treatable. A wise captain will plan on encountering it during any prolonged voyage through the tropics.
Originally thought to be a poison in the local atmosphere, we now understand that malaria is a parasitic microorganism carried by the Anopheles mosquito, an insect found worldwide. There are four different kinds of parasite, all members of the genus plasmodium: P. vivax, P. ovale, P. malariae, and P. falciparum (also known as black water fever).
The organism needs both the mosquito and a healthy carrier (in our case, a human) to complete its life cycle. When a malaria-carrying mosquito bites us, we become infected with one form of the parasite, the sporozoite. Once in the bloodstream, it makes its home in the liver, happily thriving thanks to a brisk blood supply and the nutrients being absorbed from the stomach and intestines.
Once ensconced, the parasite begins an active replication to a new form and is released into the general circulation to mature and replicate again. The new form, the trophozoite, is the source of our symptoms as it replicates in our red blood cells and releases its progeny into the circulation to gum up the capillary blood flow to our brain, kidneys, joints, muscles, etc. The parasite is also programmed to become a hibernation form in the liver (a hyponozoite) if conditions are not favorable to active replication. Thus, we can be afflicted by a relapse of malaria at any point in our lives after just a single bout from years ago. The parasite completes its life cycle when a mosquito draws blood from a person with active malaria. Ingesting the merozoites (the progeny of the trophozoite), the parasite changes its identity again to accommodate to life in the mosquito. The mosquito bites again, transmitting the parasite to a new victim, and the cycle starts anew.What are the symptoms?
Unrelenting cyclical fevers followed by drenching sweats are the hallmark of malaria. The periods of time between fevers will depend on the species. Then there is also pain. When the merozoites find themselves in our circulation during the active replication phase, they have a hard time transiting our capillaries. As a result they tend to impede the normal circulation. In the brain this impedance results in a terrible headache. In the muscles, it results in diffuse muscle pain, especially a stiff neck. In the kidneys, it can result in blood and excessive hemoglobin in the urine (hence the "black water" in black water fever). The hemoglobin results from all the red blood cells that have been ripped open in the course of circulating through the spleen (the job of the spleen being to remove abnormal red blood cells). In the liver and spleen, this impedance to circulation can result in a vague dull right and left upper abdominal pain.
Carried by the blood, the parasite can go anywhere in the body with a panoply of symptoms as a result. Fortunately, most of the time our spleen and elements of our immune system can bring the infection under control before it kills us, but the effort is herculean. Little children and senior citizens sometimes cannot claim victory. In fact, falciparum malaria, the worst of the four species, is one of the most common causes of death among the older Caucasian citizens of East Africa.
Focus on prevention
There are essentially two ways to prevent contracting malaria, and both should be employed while living in areas with malaria. Both center on interrupting the life cycle of the parasite. The first is fairly straightforward: limit exposure to mosquitoes. Do this by installing durable screens on all hatches and ports, douse lights early when at anchor, and wear protective clothing. The best protective clothing is long sleeves, long pants, and a hat. This is not always possible in the tropics given the heat and humidity. A second line of defense is mosquito repellent. The best is DEET (N,N-diethyl-meta-toluamide), a potent chemical compound that mosquitoes dislike. The downside of DEET is that it is not entirely safe for use in small children, especially when it is applied all over. Many people I have run across in the developing world use a burning cigarette to repel mosquitoes. I cannot in good conscience recommend this, but personal experience has shown it to be effective for the length of time that the cigarette burns. It is certainly not a long-term solution. A citronella candle is probably at least as effective.
A less toxic mosquito repellent is permethrin, a naturally occurring compound that kills mosquitoes on contact. Personnel in high mosquito/malarial areas are well advised to apply permethrin to both their outer clothes and skin. It is safe for children.
It should be noted here that simple anti-mosquito measures such as these are also very effective in preventing many other mosquito-borne diseases, especially yellow fever and dengue (pronounced den-gee) fever, Japanese encephalitis, sleeping sickness, and others.
The second way to prevent contracting malaria is to take medication that interrupts the malarial parasite’s replication process. There are several medications to choose from. Listed here are the ones most well known. It is highly advisable to seek the services of a certified travel medicine clinic before committing to any one course of medication.
All of these anti-malaria drugs have potentially serious side-effects. They should only be taken under the direction of a doctor.
Chloroquine. This was the original antimalarial, derived from quinine, also known as Aralen. It has been used the world over. Taken as directed, it is generally safe. Even moderate overdoses, though, can lead to significant toxicity, so care should be taken to take the correct dose based on your body weight. As a preventive, it can be taken once weekly. Unfortunately, chloroquine-resistant malaria has developed the world over. The preventive dose for adults is 500 mg, once a week. Side-effects include blurry vision, dizziness, reduced coordination, and confusion.
Mefloquin. The heir to chloroquine, mefloquin, also known as Larium, is safe and effective in preventing malaria. It is the drug of choice for people traveling to areas where there is resistance to chloroquine. It is expensive compared to chloroquine.
The dose for prevention in adults is 250 mg once a week. Side-effects of mefloquin are similar to those observed for chloroquine. Some resistance to mefloquin has been reported in Cambodia and Myanmar.
Proguanil. This medication is also known as Paludrine. I took it while residing in Kenya. It is safe and effective and has limited side-effects. The preventive dose is 200 mg per day for adults. It is usually combined with a weekly dose of chloroquine 500 mg.
Doxycycline. A hybrid of the common antibiotic tetracycline. It has the unfortunate side effect of sun phototoxicity: a potentially severe rash over sun-exposed areas of skin. The preventive dose is 100 mg per day for adults. It is not recommended for small children or pregnant women. It is relatively inexpensive compared to the other antimalarials.
Your choice of which antimalarial to take should be based on where you are traveling and how long you plan to stay. In general, short-term stays in areas immediately adjacent to the ocean are at low risk for malaria transmission. Effective screening and personal protection may be all that is needed. It is strongly advised that you seek professional guidance if you plan on visiting countries where malaria is present.
You can call the travel medicine service at any major academic medical center or find one by contacting the CDC in Atlanta or visiting their web page (http://www.cdc.gov/travel/travel. html). Another excellent trip planning medical resource can be found at http:///www.tripprep.com. Take advantage of the free and effective information found at these places. It will make your voyage planning a great deal easier.
Common destinations and malaria
The Caribbean is generally free of malaria. The only exceptions are Haiti, The Dominican Republic, and southwest Trinidad. Chloroquine prophylaxis is generally recommended for any prolonged stays to these countries. Most presumed cases of malaria in the Caribbean are actually cases of dengue fever, which is found throughout the area.
Mexico and Central America both harbor malaria in mountainous areas. Rural western Mexico and rural Central America are the areas of highest concentration. Of interest, Panama has been identified as harboring chloroquine-resistant malaria. Visitors are advised to take mefloquin or similar preventive if they plan on staying for any length of time.
Chloroquine-resistant malaria has been identified in Papua New Guinea, the Solomon Islands, and Vanuatu in the South Pacific. Mefloquin is recommended except in New Guinea where doxycycline is the best choice. There is no risk for malaria in Australia, New Zealand, or the other islands of Melanesia, Polynesia, or Micronesia.
Malaria need not be a problem for the ocean sailor unless he or she plans on more than a short coastal stay in an area with malaria. Simple measures like limiting your exposure to mosquitoes and planning in advance for medication will render your voyage safe and enjoyable. Like almost everything in ocean sailing, planning and forethought will determine your success.