Malaria Host Range

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QUESTION

What is a malaria host range?

ANSWER

Usually, a malaria host range refers to the natural geographical range of one of the hosts of a particular species of malaria. So, for example, Plasmodium reichenowi normally only infects chimpanzees. Chimpanzees live mainly in central and western Africa, so this would determine the host range for P. reichenowi. Other species of malaria, such as those that infect humans, have much larger host ranges, since humans live practically everywhere on the planet. In these cases, it is more likely that the range of that species of malaria is limited by climatic variables (malaria parasites require certain temperature ranges in which they are able to develop and mature) or the distribution of a suitable vector mosquito species, which also have climatic constraints.

Areas Where Malaria Occurs

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QUESTION

Can you please tell me the high, low and no risk areas for malaria.

ANSWER

Malaria requires certain climatic conditions, both for its own development as well as for the survival of its vector mosquitoes. As such, malaria transmission is concentrated in lowland areas of the tropics, where there is sufficient freshwater for mosquito breeding. However, malaria can also seasonably be transmitted in areas away from the tropics. Similarly, some tropical and sub-tropical areas have implemented successful control programs which has significantly reduced or even eliminated transmission.

Currently, high risk areas for malaria transmission include most of sub-Saharan Africa (except for the highlands of Ethiopia, Tanzania, Kenya and Eritrea – areas over 1800 meters of altitude tend to have less malaria), most of northern South America (except areas over 2000m, and many urban cities are also free of malaria), parts of Central America, some Caribbean islands, India, south-east Asia (again, apart from highland areas) and Oceania. Low risk areas include parts of southern Africa (i.e. northern South Africa), parts of Central America (including most of Mexico, though some parts of the south may be considered higher risk), parts of the Middle East and parts of China. There is no known malaria in North America, Europe, most of North Africa, Australia, New Zealand, Japan, the eastern coastal regions of Brazil, most of southern South America and northern Asia. For a detailed and up to date map of malaria risk around the world, please see the Malaria Map

Malaria Socio-Economic Issues

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QUESTION

What are the socio-economic issues on the spread of malaria?

ANSWER

Malaria transmission requires the presence of Anopheles mosquitoes; as such, conditions which favor the growth and persistence of these mosquitoes will also be hotspots for malaria transmission, provided the climate is also sufficiently warm for the development of the parasite within the mosquito.

Rural areas without sophisticated water and sanitation systems often utilize streams or ponds for everyday water needs; if these produce stagnant patches of water, they can be an ideal location for the development of mosquito larvae.

Similarly, if rural farmers dig canals or ditches to irrigate their fields, these can become breeding areas. Urban areas tend to have less standing water, apart from cisterns, so in many cases transmission is less prevalent in urbanized locations.

As a further socio-economic factor, preventing mosquitoes from entering the house and biting people is  key way to prevent infection. Rich people in malarial areas may be more able to have fully screened houses, possibly even with air-conditioning, which will prevent mosquitoes from establishing in the house. They may also be more likely to have access to a long-lasting insecticide treated bednet, which further reduces mosquito bites, and also access to accurate diagnostic screening and treatment, if they do happen to get infected.

All of these factors contribute to making malaria burden highest in some of the world’s poorest areas, with the highest levels of mortality in sub-Saharan Africa.

Malaria Host Range

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QUESTION

What are the Host range?

ANSWER

Malaria is caused by a parasite,  of the genus Plasmodium, which requires two organisms for the completion of its life cycle—an insect, which is usually referred to as the “vector,” in which sexual reproduction occurs, and a vertebrate “host,” in which asexual multiplication occurs.

Different species of Plasmodium infects a large range of vertebrate hosts, including many birds, reptiles, and dozens of different mammals, specifically primates (including humans) and rodents. These different types of Plasmodium are found all over the world; Plasmodium species that infect birds, for example, are found in much colder climates than human malaria.

The five species of Plasmodium that infect humans are found mainly in the tropics, and seasonally in the sub-tropics. Four of the species mainly infect humans only, but can also be found occasionally in other primates, such as chimpanzees and gorillas; the fifth species, P. knowlesi, is mainly considered a malaria of macaque monkeys in south-east Asia, but can also infect humans. As such, the host range of these malaria species extends wherever humans live throughout the world. However, in reality, the distribution of malaria is constrained to warmer, wetter climates based on the developmental needs of the parasite and also the vector.

For mammalian malaria, these vectors are all mosquitoes of the genus Anopheles, which breed in stagnant freshwater and also have temperature requirements, above or below which they will not develop. However, these mosquitoes are still found in many parts of the world, from far northern latitudes of Canada and Siberia in the summer to similar latitudes in the southern hemisphere and also throughout the tropics.

Distribution of Malaria

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QUESTION

Where does malaria mostly take place?

ANSWER

Malaria is mainly transmitted in tropical regions of the world; while some transmission does occur outside of the tropics, it tends to be seasonal in these areas (i.e. usually only during periods of high temperature/high rainfall). Within the tropics, malaria is found on all continents, though the highest number of cases is in Africa, which is also where over 90% of deaths due to malaria occur (of these, most are children under the age of 5). Outside Africa, the next highest levels of malaria are in India and south-east Asia and the western Pacific (such as Papua New Guinea).