The Parasite

Plasmodium Falciparum is responsible for the majority of infections in Southern Africa. Drug resistance towards chloroquine appears to be growing in the region, Botswana, Malawi, South Africa and Tanzania use Sulphadoxine-Pyrimethamine as their first line drug. Mozambique, Zambia and Zimbabwe are currently reviewing their drug policy with continued monitoring of drug resistance.

The Vector
Three species, Anopheles Arabiensis, Anopheles Gambiae and Anopheles Funestus transmit malaria in Southern Africa.

Anopheles Merus plays a secondary role in some countries.

An. Arabiensis is the predominant vector. Particularly in the epidemic prone countries.

An. Gambiae is the main vector in places where malaria is more stable.

An. Funestus also plays an important role in areas of high malaria endemicity.

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Transmission
In Southern Africa the intensity of malaria transmission varies considerably and areas can be classified into three main groups:

· Malaria free

· Unstable transmission

· Stable transmission

In malaria-free areas transmission does not occur

In unstable transmission areas malaria is highly seasonal and occurs for only part of the year (usually less than 6 months). These areas are often prone to malaria epidemics which can result in high levels of morbidity and mortality if not prevented or contained.

In stable transmission areas malaria occurs throughout the whole year and there is relatively little seasonal variation. Malaria morbidity and mortality is greatest in these areas.

In Southern Africa, an arc can be drawn from South Africa in the south-east through Botswana and to Namibia which shows the border between malaria-free areas and unstable transmission areas. The Highveld of Zimbabwe and a few isolated upland areas (>2000m) principally in Tanzania, are also malaria-free. The division between unstable and stable transmission areas runs north along the South Africa-Mozambique and Zimbabwe-Mozambique borders and then along the northern borders of Zimbabwe, Botswana and Namibia. To the north of this line, there are also areas of unstable transmission, such as the Northern and Southern Highlands of Tanzania, and large towns and cities. Intensity of Malaria transmission by province.A number of factors affect malaria transmission in the sub-region. The chief determinant is climate which affects both the life of the anopheles mosquito and the development of malaria parasites. The development of the malaria parasite is greatly retarded below 20 Celsius and ceases to develop below 16 Celsius. In addition, relative humidity of over 80% lengthens the life of the mosquito enabling it to transmit the infection.

There are also a number of human factors that affect malaria transmission. Vector control efforts, particularly insectiside house spraying programmes and source reduction in urban areas have made previously malarious districts malaria-free. Equally the breakdown of vector control has resulted in formerly malaria free areas becoming malarious again, e.g. the Zambian Copperbelt. Forced and voluntary population movements also adversely effect malaria transmission . Man-made changes to the environment also alter malaria transmission levels. For example, planned urbanisation leads to source reduction. While dam building _ particularly in semi-arid areas can create foci of malaria transmission.

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Summary of peak malaria transmission and risk periods.

Peak Malaria Peak Malaria High Risk Malaria Transmission Period Epidemic Period Epidemic Districts

Angola
October - April May - June No information

Botswana
October - April February _ April
Okavango, Ngami, Chobe, Boteti, Tutume, Ghanzi

Malawi
November - May April -May No information

Mozambique
November - April Jan - April No information Namibia February to April February to April Caprivi, Omusati, Kavango

Tanzania
Two Seasons: Kyela, Mpwapwa, Babati, October _ January
March - April Mvumi, Lushoto, Korogwe, Muleba,
March _ May Hanang, Karagwe

South Africa
November - May January to May
Messina, Mutale, Phalaborwa, Tonga, with a peak in march Shongwe, Barberton, Ingwavuma, Ubumbo

Swaziland
December _ May March - April
Lubombo

Zambia
November - April November _ April
Livingstone, Kalomo, Choma, Namwala, Monze, Mazabuka, Kafue, Lusaka, Senanga, Sesheke

Zimbabwe
November _ April March _ April
Hwange, Kariba, Hurungwe, Lupane, Binga, Tsholotsho, Chipinge, Mutasa

Southern African Malaria Control Review

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