Malaria

Malaria is a serious human disease caused by a blood parasite (Plasmodium) and transmitted by the bite of an infected mosquito (Anopheles).

 

The Mosquito

The Anopheles mosquito mainly bites during the twilight hours, in other words dawn and dusk. Only a mosquito that has previously bitten a human infected with malaria acquires the malaria parasite, incubates it and subsequently transmits it to a new human.

Malaria occurs mainly in tropical and subtropical regions.

 

The Disease

There a four distinct types malaria disease, each type being caused by a different parasite species. For practical purposes these diseases are divided into two categories: "malignant" caused by the Plasmodium falciparium species, and "benign", caused by the Plasmodium vivax, P. ovale, and P. malariae species. In general, there is an incubation period after the bite of 7-14 days before the disease begins. With some types of malaria, the incubation period is as long as several months.  The disease has an acute onset with chills and fevers (usually 102-106 degrees F.), along with severe headaches, backaches, and muscles aches.  Symptoms such as diarrhea, vomiting and abdominal pain, difficulty breathing and chest tightness may occur and occasionally become the major symptoms of the illness.  Rashes almost never occur.  Fevers initially occur at irregular intervals of every few hours to every day or two and are followed by profound sweating and total exhaustion. Each episode of fever is usually several hours long. The individual is left profoundly weak and often incapacitated for hours or even days after the episode.  Untreated the episodes of fever recur for two or three weeks then resolve.

 The "malignant" form of the disease, caused by the P. falciparium, is often worse than the above description. The victim may have severe pulmonary congestion (pulmonary edema), kidney failure, hemorrhages, severe confusion and hallucinations, or even strokes. This form is fatal 5-10% of the time.  However, the disease spontaneously ceases after 2-3 weeks and does not recur, unless a new mosquito again transmits a new infection. Victims are left severely anemic and weakened for months afterwards.

The "benign" form of the disease is rarely fatal for healthy adults, and may be milder than the description above. It however has a tendency to recur every several months or as long as years later unless proper treatment is given. Both forms of malaria are very serious if they occur in a pregnant woman (they can rapidly lead to fetal death), or in a person with pre-existing cardiac disease.

Immunity to Malaria is species specific but incomplete. Second infections occur, but are usually milder than the first episode.  Chronic and recurrent infections are a contributory cause to chronic illness and premature mortality, especially in children in the developing world. 

Seek prompt treatment if you suspect you may have malaria. Treatment can be simple or complex depending on the type of malaria, duration of disease before treatment and any concurrent medical conditions.

 

Protection from malaria

1) Avoid mosquito bites by use of mosquito nets and dwelling screens.  Use insecticide impregnated clothing, and wear long sleeved shirts and long pants.  Apply insect repellents before going outdoors, and remain indoors during dawn and dusk.

2) Pretreatment with anti-malarial medications taken before, during and after the period of travel to the malarious area will prevent establishment of the disease.  It is vital anti-malarial medications be taken according to directions.  The specific medication and duration of treatment depends on the geographic area and the type of malaria being avoided.

Diagnosis

Since malaria is one of the most common causes of high fevers, over-diagnosis, especially by non-experts, is very common. It is frequently misdiagnosed in Africa and Southern Asia when a high fever occurs and specific diagnostic tools are not used.  This has led to over-treatment and the misperception that use of anti-malarials has not been effective.  Also, since other diseases can cause high fevers, incorrect non-diagnosis may occur, sometimes with tragic outcomes.

Specific diagnosis can only be made by one of two methods.1) Microscopic examination of blood smears by an experienced microscopist or an infectious disease expert. Finding the parasite may require only a few minutes or require repeated blood smear examinations over the course of several episodes of fevers. 2) Use of sensitive "dip stick" to detect the parasite antigen in the blood. This is newly developed method can be very sensitive, unfortunately it is not available the USA at this time for general use.

 

 

 

The Travel Medicine Clinic of Valley Infectious Disease Assoc.© 2010  
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