Malaria is carried by a few species of anopheline mosquitoes. Female mosquitoes feed on blood, and during feeding may acquire malaria from a person already infected with malaria parasites. A warm environment is needed for the parasite, a single celled organism like an amoeba, to survive and multiply in the mosquito. After 10 days the mosquito is infective to man.

Mature infected mosquitoes feed in the late evening and throughout the night, from around 1 0.00 pm to just before dawn. While they feed,parasites are injected into man and find their way to the liver, where they multiply. Some day later, the parasites invade the bloodstream and multiply further, parasitising increasing numbers of red cells'.

As the percentage of red blood cells parasitised increases, the patient begins to feel ill. In many people, without treatment, the parasite multiplication is not contained, and by the time 5% of the red cells are parasitised complications, of which the best known is cerebral malaria, develop. Should the parasite count be left to rise further, death may occur despite treatment. Note that cerebral malaria is not a special type of malaria, but often follows when Plasmodium falciparum infections proceed untreated.

During the tourist boom of the last 30 years, there has been no major change in malaria in East Africa apart from the evolution of chloroquine resistant strains of Plasmodium falciparum, which are widespread in Kenya and Tanzania and to a lesser extent in Uganda.

"Highland" malaria is epidemic malaria occurring above 5OOOft. Over 5000ft the environment is increasingly unsuitable for malaria parasites to multiply in the mosquito, so that transmission is halted. Seasonally, with warmer temperatures and provided humidity is high enough, conditions may be right for the malaria cycle to develop in the mosquito. Epidemics of malaria then occur in populations not normally exposed to malaria.

The other 3 malarias cause non fatal illnesses with characteristic fever patterns and the potential to relapse over a number of years. Plasmodium vivax and Plasmodium ovale cause tertian fever (fever every 48 hours) and Plasmodium malariae quartan fever (fever every 72 hrs). In East Africa all 3 are much less common than Plasmodium falciparum.

Anopheles gambiae and Anopheles funestus are the main vectors in East Africa

Malaria mathematics are determined by many variables. Put simply a single Plasmodium falciparum parasite (sporozoite) injected into a person will have developed in 6 days into a mature liver schizont capable on rupture of infecting 40,000 red blood cells. Each of these parasites develops in 48 hours into a mature blood schizont capable of infecting a further 32 red cells. With repeated multiplication, by 1 2 days after the bite 0.01 % of all red cells are parasitised. This level is around the fever threshold and the tourist begins to feel ill. Over the next 4 days the parasite count can rise to 10%, a desperate situation. Any further multiplication will almost inevitably be fatal.

Remember that this sequence of events may follow a single parasite injected by the mosquito. Often hundreds of parasites (sporozoites) are injected, with a corresponding acceleration of parasite population growth and shortening of illness development.

The benign malarias - vivax, ovale and malariae, multiply more slowly and their multiplication is contained by natural immunity, so that never more than 2% of red cells are parasitised.

ANTI MALARIA RULES FOR TOURISTS

Avoid mosquito bites.
All kinds of mosquitoes may bite during the day but in East Africa transmitters feed almost entirely at night, between 10.00 pm and dawn. Bed nets, especially if they are impregnated with an insecticide, are effective in preventing malaria. Rooms and tents should be thoroughly sprayed with an aerosol insecticide in the early evening. Danger periods are any time between 10.00 pm and 6.00 am spent outside your mosquito net or your mosquito proof room or tent, for example, late night arrival and departure from airports. Long sleeves and trousers/dresses will help. Light coloured clothing may be less attractive to mosquitoes. Repellents can be applied to exposed skin, and around the ankles. Mosquitoes bite through socks and stockings.

Prophylaxis.
While there is no drug which will guarantee total protection against malaria in East Africa, proguanil (Paludrine) is at present ICAA's first choice It is best taken after the evening meal so that blood levels are high during the time of maximum malaria mosquito activity and so that minor side effects are lost in sleep. There are no dangerous side effects. The adult nightly dose is 2 tablets of 100mg each. The drug is safe for children of all ages on a rough weight for weight basis. There is no need to start proguanil (Paludrine)until the day you arrive in the malarious area. It should then be taken regularly throughout your stay, and for 2 weeks after leaving the area of malaria transmission. It is especially important to take the tablets without missing a single day for the first 7 days after a potentially infective mosquito bite. It is during these days when the developing parasite is in the liver that proguanil is most effective and wher