Malaria

Written by Dr Charlie Easmon, specialist adviser in travel medicine

What is malaria?

Malaria is a potentially fatal tropical disease that is caused by a parasite known as Plasmodium. It is spread through the bite of an infected female mosquito.

The infected person may have feverish attacks, influenza-like symptoms, tiredness, diarrhoea or a whole range of other symptoms. Malaria should always be suspected if these symptoms occur within the first year of return from an infected area; a test should be carried out to exclude the possibility of malaria as soon as possible.

Malaria is one of the leading causes of disease and death in the world. It is estimated that there are 300-500 million new cases every year, with 1.5 to 2.7 million deaths worldwide.

Malaria occurs extensively in tropical and subtropical regions. It used to exist in the UK, but fortunately no longer. Each year 2,000 to 2,500 people return to Britain with malaria, which they have contracted abroad, and, of these, an average of 12 die. For this reason it is important to prevent malaria in those travelling to and from the tropics.

What causes malaria?

The malaria parasite, Plasmodium, is a small, single-cell organism (protozoan), which lives as a parasite in man and a specific species of mosquito (Anopheles).

There are four different types of malaria parasite: Plasmodium falciparum is the cause of malignant malaria, while Plasmodium vivax, Plasmodium ovale and Plasmodium malariae cause more benign types of malaria. Malignant malaria can kill, but the other forms are much less likely to prove fatal.

There are several stages in the life cycle of the parasite and by and large these are the same for all four types.

How do you catch malaria?

Malaria is passed on by the Anopheles mosquito biting a person who has malaria parasites in their blood.

The parasites develop in the intestine and salivary glands of the mosquito and can be passed on to other people the next time the mosquito bites.

In man, the parasite travels to the liver via the blood and then out into the bloodstream again where it invades the red blood corpuscles (the cells which carry oxygen in the blood). Malaria can also be passed on by blood transfusions and the use of infected needles.

Where does malaria occur?

Malaria occurs where the Anopheles mosquito lives - ie particularly in hot, humid climates. Plasmodium falciparum is by far the most important malaria parasite in Africa.

There are also areas in Latin America, Asia, and Oceania, where malignant malaria still occurs. Plasmodium vivax is the most common in Asia and Latin America, including Central America.

What are the symptoms of the disease?

Normally, 10 to 15 days go by between being infected and the onset of the disease, but it may be longer if the patient has taken a preventive medicine.

On a purely practical level, the most malignant (P. falciparum) cases develop within three months of leaving the malaria region, while the forms transmitted by P. vivax and P. ovale may not appear until three years later.

Malaria malariae (a rare, benign form) can survive in man for up to 30 years, luckily without causing much discomfort. This form can also be treated, provided you get the right medication.

The actual attacks of malaria develop when the red blood corpuscles burst, releasing a mass of parasites into the blood. The attacks do not begin until a sufficient number of blood corpuscles have been infected with parasites.

What are the characteristics of a malaria attack?

Fever and shivering. The attack begins with fever, with the temperature rising as high as 40ºC and falling again over a period of several hours.

A poor general condition, feeling unwell and having headaches like influenza.

Diarrhoea, nausea and vomiting often occur as well.

When the temperature drops, the patient often sweats profusely and feels much better. Then the same day, or one to two days later, further attacks occur with feeling generally unwell, high temperature and so on.

The attacks diminish in the course of a number of weeks if the patient develops the ability to resist the malaria parasite. But if proper treatment is given, the fever and parasites can disappear within a few days.

It is rare that a Briton becomes entirely immune to malaria, because this requires repeated bites from malaria-carrying mosquitoes, practically every night for several years. In the worst affected areas, children who live to the age of five years become immune.

In malignant malaria the illness may evolve with a number of complications:

low blood pressure (hypotension)

kidney failure

possible haemorrhage (bleeding)

effects on the liver (eg infectious jaundice)

shock and coma may also develop

the condition may prove fatal.

Cerebral malaria

Malignant malaria can affect the brain and the rest of the central nervous system. It is characterised by changes in the level of consciousness, convulsions and paralysis.

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