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Written by Dr Charlie Easmon, specialist adviser in travel medicine
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What is malaria?
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| Talk to your doctor or pharmacist about prevention drugs
before you go abroad. |
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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?
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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.
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A poor general condition, feeling unwell and having headaches
like influenza.
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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:
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low blood pressure (hypotension)
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kidney failure
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possible haemorrhage (bleeding)
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effects on the liver (eg infectious jaundice)
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shock and coma may also develop
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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.
Blackwater-fever
In malignant malaria a large number of the red blood corpuscles
are destroyed. Haemoglobin (the red pigment) from the blood corpuscles is
excreted in the urine, which therefore is dark and almost the colour of
cola.
Late complications
If someone with a benign form of malaria is untreated, anaemia
and an enlarged spleen may develop after days or weeks.
Ability to resist malaria attacks
Immunity to malaria develops very slowly and is quickly lost.
Children living in endemic regions (where the disease occurs naturally all year
round) develop their own protection against the disease over four to five years
if they survive. On average one child dies every 30 seconds from malaria in
these countries.
Britons neither have nor develop immunity unless they have been
exposed to malaria with no protection.
It is important to remember that nationals from malarious areas
who return home for holidays need the same malaria protection as ordinary
travellers, because immunity develops slowly and is rapidly lost.
What can you do yourself?
There is no risk of catching malaria in the UK, but if you visit
tropical and subtropical countries it is important to investigate the chances
of catching malaria.
Because the situation can change rapidly, you should talk to a
doctor or pharmacist before planning your trip, both as regards to products for
malaria prevention and also for expert advice on avoiding other dangers and
diseases.
Prevention of malaria
is important. If you travel to a region where malaria is prevalent, you should
take preventive medication against the parasite and take whatever steps you can
to avoid being bitten.
How is the disease diagnosed?
The symptoms of malaria are similar to those of many other
feverish diseases and infections, which can upset the stomach. Therefore you
should always tell your doctor if you have been abroad, especially if you have
been to the tropics in the last 12 months.
The actual diagnosis is made by detecting the parasite in the
blood. This is done using a special product mixed with one to two drops of the
patient's blood and spreading it on a microscope slide. This is then
stained and examined carefully under a microscope.
The examination may have to be repeated if the fever has only
just begun and/or preventive medication is to some extent keeping the numbers
of the malaria parasite low.
Treatment
The treatment of malaria normally calls for admission to
hospital, because it may be malignant malaria, which can have a fatal outcome
in only a few days.
In addition, there is an increasing level of resistance of the
malaria parasite, particularly P. falciparum, to several
of the known antimalarial products.
Outpatient treatment, or worse still, self-treatment of malaria,
is something only to be undertaken when no qualified medical help is available,
ie if you develop malaria in a remote area.
The same antimalarial agents may be used to treat malaria as to
prevent it, but if you have caught malaria in spite of using the correct
preventive medication, a different product should be used to combat the
possibility of resistant parasites.
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Last updated 01.04.2005
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