Malaria in Summer

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QUESTION

Does malaria only occur during summer season?

ANSWER

That depends on where you are. The transmission of malaria depends on the presence of the mosquitoes which are required to transmit the disease (they do this when they bite you).

Many kinds of mosquito transmit malaria, though all are of the genus Anopheles. These different species have different climatic requirements, but all lay their eggs in pools of stagnant water, and the larve likewise live in this stagnant water until they develop into adults. As such, malaria is only transmitted when there are suitable pools of standing, stagnant water available for mosquitoes to breed, and also when the temperature is suitable for mosquito development (optimum temperature for mosquitoes is 25-27 degrees C—the malaria parasite develops most rapidly around this temperature as well, though can survive in temperatures about ten degrees cooler as well).

In some regions of the world, this combination of conditions is only met in the summer time, which means that malaria transmission only occurs during this season. In other parts of the world, such as coastal West Africa, conditions are suitable for mosquito breeding and malaria development all year round, which means that malaria transmission occurs throughout the year.

Malaria in KwaZulu Natal

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QUESTION

How many people are infected by malaria in KZN?

ANSWER

By “KNZ” I assume you mean KwaZulu Natal (for the benefit of other readers, this is a region of South Africa, in the north-eastern portion of the country). KZN is one of the few parts of South Africa that experiences malaria transmission, though effective control measures have reduced its impact as a public health threat.

Up until 1996, South African policy had been to use DDT (even though it was a banned substance) to control mosquito populations, and malaria levels had correspondingly been low. However, after cessation of spraying with DDT, the number of malaria cases increased, to a high of over 40,000 cases in the 1999/2000 malaria season (in KZN, malaria is most commonly transmitted during the wet summer months, from November to May). Since then, the use of DDT as an insecticide has been reintroduced (along with other public health measures, such as switching to artemisinin-based combination therapies for first-line malaria treatment), and the burden of malaria has plummeted.

The most recent data I could find reported less than 3500 cases for the 2001/2002 malaria season, and zero cases in 2002/2003 (though the data I found were only up to February 2003). Efforts to coordinate malaria control between South Africa, Mozambique and Swaziland have also contributed to the success of reducing malaria transmission in the region.

Where is malaria found?

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QUESTION

Where is malaria found?

ANSWER

Malaria is found throughout the world’s tropical and sub-tropical areas, and mainly in Central and South America, Africa, Asia and the Indo-Pacific region. It is most common in tropical regions, where transmission occurs year-round; in sub-tropical and temperate areas, transmission may only occur during seasons that have appropriate climatic conditions. This includes sufficiently high temperature and water availability for the growth and development of the mosquito, which transmits the disease. Currently, the greatest burden of the disease is felt in sub-Saharan Africa, where over 90% of deaths due to malaria occur. The map below shows the estimated risk for malaria across the world, courtesy of the World Health Organisation.

Global_Malaria_2010_WHO

Map of the global distribution of malaria, courtesy of WHO (www.who.org)

Malaria in Africa

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QUESTION

What percent of Africa has malaria?

ANSWER

That is very difficult to measure, but maps of malaria transmission potential show that malaria is potentially present across most of the continent, excluding the heart of the Sahara and Kalahari deserts, and the highlands of Ethiopia, Lesotho and Uganda/Rwanda. Other parts of the continent, such as the coastline of North Africa (along the Mediterranean) and much of South Africa and Zimbabwe likely only experiences seasonal transmission of malaria, with some parts of the year too cold and/or dry to support transmission. The below map shows the distribution of malaria throughout Africa, and should give you some idea of the percentage landcover that is affected.

Distribution of endemic malaria

Distribution of endemic malaria in Africa. Picture courtesy of http://siteresources.worldbank.org/NEWS/Images/malaria-map.jpg

In What Countries is Malaria Found?

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QUESTION

What countries can malaria be found in?

ANSWER

Malaria is found on every continent of the world except Antartica—however, regular transmission every year mainly only occurs in Central and South America, Africa, parts of the Middle East, Asia and parts of Oceania/the Pacific Islands.

The world’s highest areas of malaria prevalence and transmission occur in sub-Saharan Africa, followed by India, south-east Asia (especially the Indo-Pacific islands, such as Papua New Guinea) and parts of Central America and northern South America.

Based on the latest available data, the top five countries reporting the most annual malaria deaths were Kenya, the Democratic Republic of Congo, Cote d’Ivoire and Burkina Faso. However, the top five countries with the highest number of malaria cases per 100,000 members of the population were Guinea, Botswana, Burundi, Zambia and Malawi.

The Solomon Islands have the highest number of malaria cases per 100,000 outside of Africa, followed by Yemen. Note that these statistics are highly dependent on quality of diagnosis, treatment and reporting!

Malaria Deaths in the Tropics

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QUESTION

What’s the difference of malaria deaths between the subtropical and tropical regions and all the other regions?

ANSWER

I am assuming you are asking about the distribution of deaths caused by malaria between the tropics/sub-tropics and the rest of the world.

95% percent of all fatal malaria cases occur in sub-Saharan Africa, which lies entirely in the sub-tropics and tropics. Additionally, most of the deaths occur in Central, West and Eastern Africa (North Africa and South Africa have more advanced malaria prevention and control initiatives to the rest of the continent, and transmission is also less severe), and the other 5% of malaria deaths are mostly found in India and south-east Asia, so you could say that virtually all deaths due to malaria occur in tropical regions alone.

Indeed, there is almost no malaria in non-tropical or sub-tropical regions; the few cases each year in North America and Europe are usually due to imported cases from people who have traveled to tropical or sub-tropical regions.