Revisiting malaria

Health Page
By Dr Walter Chin
Stabroek News
May 6, 2001

Malaria is a serious, sometimes fatal, disease caused by a parasite called plasmodia. It is, indeed, the world's most important parasitic disease, occurring in over 100 countries and territories. Every year more than 500 million people have an attack of malaria, and more than one million die from it. The majority of deaths from malaria are in children; malaria kills nearly four children somewhere in the world every minute. Malaria is also particularly dangerous during pregnancy. It causes severe anaemia, and is a major contributing factor to maternal deaths

Two and a half billion people, 40 per cent of the world's population, are at risk of catching the disease. Forty years ago, malaria was controlled in many of the countries, including Guyana, but malaria is still present and is now increasing at a substantial rate. Over the last decade, between 30 to 60 thousand cases have been diagnosed in Guyana every year.

There are four different types of malaria: P. vivax, P. falciparum (both of which are present in Guyana), P. malariae, and P. ovale. They are all spread by Anopheles mosquitoes.

The main malarial zones are in Africa, South-East Asia, the Indian sub-continent, Hispaniola (Haiti and the Dominican Republic) and Central and South America. Most of the deaths from malaria occur in Africa, where it is estimated that the disease costs the African economy over $2 billion a year. In many developing countries, malaria exacts an enormous toll in lives, in medical costs, and in days of labour lost.

Malaria is not only a danger to those living in the countries at risk. Each year 20 million tourists are at risk, and as international travel increases, so does the risk increase. Moreover, as global warming becomes more marked, the changes in the climate could result in malaria becoming endemic in countries not now affected.

Malaria is transmitted through the bite of a malaria-infected mosquito, the Anopheles. When the anopheles mosquito bites an infected person, it ingests the malarial parasites found in the person's blood. The malarial parasite then grows in the mosquito for a week or more before infection can be passed to someone else. If, after a week, the mosquito bites another person, the parasite goes from its mouth into that person's blood stream. The parasites then travel to the person's liver, enter the liver cells, grow and multiply. At this time while the parasites are in the liver, the person does not feel ill. The parasites then leave the liver and enter the red blood cells. Once inside the red cells, the parasites again grow and multiply. The red cells eventually burst, releasing the parasites which then attack other red cells. In addition to the parasites, toxins are also released causing the person to feel ill. Once in the blood stream, the parasites can now be ingested by a previously uninfected mosquito, with the cycle being repeated all over again.

The symptoms of malaria include fever, and flu-like illness, including shaking chills, headache, muscle aches, tiredness, generalized convulsions and coma. The main symptom of infection is the classic malarial ague (fever). The fever tends to have three stages: a cold stage of severe shivering (rigors), a hot stage in which the temperature can rise as high as 105 degrees F, and finally a sweating stage with a reduction in temperature. In many cases, the red blood cells with their parasites rupture at the same time in each cycle and the fever occurs cyclically, depending on the type of malaria. Nausea, vomiting, and diarrhoea may also occur. Malaria may cause anaemia and jaundice (a yellow discolouration of the eyes and skin) because of the destruction of the red blood cells. Infection with one type of malaria, P. falciparum, may cause kidney failure, seizures, mental confusion, coma, and death. P. falciparum infects red cells of all ages, whereas the other varieties attack only young or old cells. Falciparum malaria thus affects a greater proportion of the red blood cells and is therefore a more severe form of malaria.

For most people, symptoms begin ten days to four weeks after infection, although a person may feel ill as early as eight days or up to a year later. Two kinds of malaria, P. vivax and P. malariae can relapse; in the latter forms, some parasites can remain in the liver for several months or years after a person is bitten by an infected mosquito. When these parasites do eventually come out of hibernation and out of the liver, and invade the red blood cells, the infected person will become ill.

Malaria is diagnosed by looking under a microscope for the parasites in a drop of blood, where parasites at different stages of development can be seen inside the red cells. Their appearance can indicate what kind of malaria is present. There are now dipstick strip tests available which are simple to perform, and are just as reliable as the blood films.

Malaria is a curable disease although there is only a limited number of drugs available. The type of drugs and the length of treatment depend on the type of malaria. The two most important groups of drugs for malaria treatment are based on quinine or artemisinin. Chloroquinine is the usual treatment for vivax malaria. However, quinine or an artemisinin derivative is commonly used to treat falciparum malaria, which in many places throughout the world is chloroquine resistant. Patients suffering from vivax malaria must also take primaquine to eradicate any parasites present in the liver.

The prevention of malaria encompasses a variety of measures. Measures that protect against infection are directed against the mosquito. These include personal protection measures such as repellants or bednets, or community/population protection measures e.g., the use of insecticides. In the past, the use of DDT virtually eliminated malaria from the coastal region of Guyana. When the use of DDT was reduced between 1984 and 1991, the rate of the disease increased twelve-fold. Unfortunately, DDT has been banned in many countries of the world, but it probably still remains the most effective and least expensive way to combat malaria.

The development of an effective malaria vaccine has become an international health priority, but the construction of a successful vaccine has been hampered by the complexity of the parasite's life cycle. The parasite undergoes multiple changes within the host, either in the red blood cells or in the liver. The parasite's identity changes through each of these stages, and this presents a challenge to vaccine development. Many malarial vaccines have been tried, and found wanting. A new malarial vaccine designed to protect the host from each stage of the parasite's life cycle has shown promise in animal testing, but will require more tests before it can be tried in humans. There is no doubt that greater research efforts are required on a more intensive and urgent basis for the development of vaccines to help in the control of malaria worldwide. Unfortunately, the total global expenditure on malaria research remains puny (it was only about $84 million in the late 1980's) compared to $900 million for HIV. Malaria which has such an enormous impact on health especially in the developing countries, and is likely, with global warming, to have serious implications for non-tropical countries, certainly deserves greater research funding.