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Malaria: its causes, treatment and methods of prevention

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VOL: 101, ISSUE: 20, PAGE NO: 43

Joyce Skeet, MSC Travel Medicine, RGN, is practice nurse, Holbrook Surgery, Horsham, West Sussex, and a member of BTHA, ISTM, and the RCN Travel Health Forum

The World Health Organisation (WHO) estimates that there are between 350 and 500 million cases of acute malaria each year, causing at least one million deaths, mainly of children under five years of age living in sub-Saharan Africa (World Health Organization and the United Nations Children’s Fund, 2005). 

Children who survive may have learning difficulties, while pregnant women are particularly vulnerable, and may develop maternal anaemia and miscarry. Perinatal mortality is a further risk.

Travellers and tourists visiting countries where malaria is endemic are also at risk. Malaria is preventable but many of those who contract the condition abroad have not taken a prophylactic, have not completed the course or have taken prophylaxis that is unsuitable for the area they were visiting.

What is malaria?

Malaria is a serious tropical disease affecting people in Africa, South and Central America, parts of the Middle East and Asia (Fig 1). It is transmitted by the bite of a female anopheles mosquito that has been infected with a malaria parasite. The mosquito usually bites between sunset and sunrise, but in Asia and Latin America the peak of transmission is around midnight (Kassianos, 2001). Humans contract malaria when sporozoites present in the saliva of an infected mosquito are injected into their bloodstream by a mosquito biting to take a blood meal. The sporozoites infect the liver cells (hepatocytes) and develop in them over the next six to 11 days, becoming schizonts. When they are mature, the schizonts burst and release merozoites into the circulation, which multiply by asexual fission, some of which then invade the red blood cells. Each release coincides with fever.

After entering the red blood cells, the merozoites feed on the contents of the cells and some develop into male and female gametocytes. The life cycle is completed when a mosquito takes a blood meal from an infected person who has both male and female gametocytes in the bloodstream, which initiates sexual reproduction of the parasites in the mosquito’s gut (Steffan and DuPont, 2001) (Fig 2).

The cause of malaria

Malaria is caused by parasitic plasmodium species that are carried by the female of an anopheles mosquito and introduced into the bloodstream of humans by an infected mosquito:

- Plasmodium falciparum;

- Plasmodium malariae;

- Plasmodium ovale;

- Plasmodium vivax.

The four species are sometimes referred to as being one of two main forms: benign or malignant. The malignant form is the more serious and is caused by P. falciparum. It accounts for the majority of infections and is potentially life-threatening (Bell, 1999). Malaria caused by the other three plasmodium organisms is generally not life-threatening except in the very young, the very old, people with immunodeficiencies (Payling, 1995).

Breeding patterns of the mosquito

Changes in climate will affect the breeding pattern of mosquitoes. They require unpolluted water and warmth to reproduce and have a life expectancy of around 50 days. They can fly 1-2 kilometres, and although they rest on warm walls in the evening, they usually fly close to the ground (Martin, 1997).

During the wet season in tropical areas there is an increase in the number of breeding sites for the mosquitoes and an increase in humidity. Their number increases after heavy rainfall, especially if humidity is above 60 per cent, therefore the peak incidence of malaria occurs at this time. Transmission can occur throughout the year but if the temperature is under 20 degsC breeding is reduced. When cases of malaria occur in western countries they are usually in travellers who have returned from an area where malaria is endemic.

Incubation period

Malaria can develop weeks, months or years after a traveller has been bitten depending on the species of parasite causing the infection. The time lapse between being bitten by an infected mosquito and the appearance of the parasite in the blood varies from seven to 30 days with P. falciparum, but is usually around 10 days. With P. vivax, P. ovale, and P. malariae it may be longer. The incubation period from the time of being bitten to the appearance of clinical symptoms varies according to the species of mosquito: around 14 days for P. vivax and P. ovale, 12 days for P. falciparum and 30 days for P. malariae (Bell, 1999).

Signs and symptoms

Malaria is sometimes misdiagnosed as influenza because of the symptoms of fever, headache and generalised aches and pains. A pyrexia is common, and some patients complain of nausea and vomiting, diarrhoea and abdominal cramps. Children may present with a high temperature, cough and tachypnoea (rapid breathing) (Kassianos, 2001). The liver and spleen may be palpable and the condition may develop very rapidly; it often proves fatal in those infected by P. falciparum.

The other malarial infections - P. malariae, P. ovale and P. vivax - present with malaise, a slowly rising temperature with sweating over several days, a headache and nausea. This cycle may be repeated daily or every couple of days. An untreated attack will vary in length and relapses are common. Relapses can occur at irregular intervals for up to five years.

Diagnosis

Early diagnosis and treatment is lifesaving. Nearly all of the million malaria deaths that occur each year worldwide are from P. falciparum, and 90 per cent of deaths from malaria occur in Africa south of the Sahara, mostly among young children: malaria kills an African child every 30 seconds (Bell, 1999). Diagnosis is based on clinical signs and symptoms and confirmed by examining blood films in the laboratory.

At-risk groups

Children and babies are a very vulnerable group as they depend on their parents to adopt precautions to prevent insect bites. Mosquito nets should be used for children’s beds and cot nets for babies. There are insect repellents available that can be used for children.

Travel to areas where malaria is endemic is best avoided with babies and young children if at all possible (Chiodini, 2000).

Pregnant women should be advised that malaria could increase the risk of premature labour and birth, miscarriage and stillbirth. Because malaria is such a serious illness in pregnancy and because no chemoprophylactic regimen is completely effective, women who are pregnant or likely to become pregnant should be advised to avoid travel to a malaria-risk area. If a woman must travel she should be advised to use insect repellents sparingly and sleep under a mosquito net. It is safer to take malaria prophylaxis than to contract malaria (Kassianos, 2001).

Asplenic patients (without a spleen) are at particular risk from malaria. They must be aware of the need to use insect repellents to prevent bites and concur with the prophylaxis recommended.

Prevention

Prevention is described using the ABCD rule (Box 2) (Chiodini, 1999).

Mosquitoes bite between dawn and dusk so travellers should be advised to:

- Wear long-sleeve clothing, long trousers or skirts and limit the amount of exposed skin;

- Avoid dark colours - mosquitoes are not attracted to light colours;

- Impregnate clothing with permethrin solution. This should be carried out using a bucket or plastic bag according to the manufacturer’s instructions. Mosquito nets can also be treated in this way (Auerbach et al, 1999). This treatment works well with cotton clothing and it can be washed up to five times after being impregnated with the solution. It is recommended that the clothing is not worn in direct contact with the skin (Caumes, 2000);

- Use a spray containing permethrin on clothing. Clothes should be sprayed inside and out for 30-60 seconds and allowed to dry for two to four hours before being worn (Caumes, 2000);

- Apply insect repellents regularly in cream, spray or gel form that contain diethyltoluamide (DEET);

- Sleep under a net impregnated with permethrin;

- Use coils and mats impregnated with insecticide in closed rooms to repel the mosquitoes.

Malaria prophylaxis

Information about antimalarial drugs is listed in the British National Formulary and in manufacturers’ product information. Full details of all drugs should be checked before prescribing. Guidelines are also available to health professionals working in travel health clinics (see footnote).

Medical advice should be sought as soon as possible if there are side-effects from the prescribed prophylaxis, especially if it has been necessary to discontinue the medication. Travellers should be advised and informed about what symptoms to expect if they contract malaria. On return to the UK they should be seen in a travel clinic or by their GP.

It must be remembered that people who have lived in the UK for some years, those who frequently go to areas where malaria is endemic or immigrants who return to those areas to visit friends and relatives, will have no immunity and must use chemoprophylaxis.

Conclusion

Health professionals must be able to assess, advise and educate travellers about the potential risks to which they may be exposed when they visit countries where malaria is endemic. The travel health consultation should be used as a health promotion exercise. If travellers understand the need to avoid being bitten by mosquitoes and the importance of chemoprophylaxis they will be more likely to take the appropriate precautions and return well to plan their next trip abroad.

FURTHER READING

World Health Organization (2005)What is Malaria. Fact Sheet. Geneva: WHO. Available on: www.mosquito.who.int/cmc_upload/0/000/015/372/RBMInfosheet_1.htm

GUIDELINES FOR HEALTH PROFESSIONALS

Guidelines for Malaria Prevention in Travellers from the United Kingdom, 2003(D. G. Bradley, B. Bannister, on behalf of the Health Protection Agency Advisory Committee on Malaria Prevention for UK Travellers). Available on: www.hpa.org.uk/infections/topics_az/malaria/guidelines.htm.

Health Protection Agency (2004)Update to Guidelines for Malaria Prevention in Travellers from the United Kingdom for 2003. Available on: www.hpa.org.uk/infections/topics_az/malaria/menu.htm.

USEFUL WEBSITES

Health Protection Agency:www.hpa.org.uk

National Center for infectious diseases:www.cdc.gov/travel/diseases.htm#malaria.

National Travel Health Network and Centre:www.nathnac.org

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