Climate change affects mosquito behavior. This could make ending malaria in South Africa difficult

Changes in climate factors – such as higher temperatures and increased rainfall – affect the development, behavior and distribution patterns of insects such as mosquitoes. These changes have serious implications for the effective control of insect-borne diseases such as malaria.

Worryingly, temperatures in southern Africa are predicted to rise by at least 0.8⁰C by 2035.

Malaria is currently present in three South African provinces: Limpopo, Mpumalanga and KwaZulu-Natal. Limpopo reports 62% of local cases and KwaZulu-Natal only 6%.

Over the past 50 years, annual temperatures in South Africa have increased significantly faster than the global average. Increases have been most extreme in Limpopo, where temperatures have risen by an average of 0.12⁰C per decade. Small annual changes have a big impact. This high temperature increases the risk of malaria. This is because the malaria mosquito and parasite are happiest at temperatures between 17⁰C and 35⁰C.

Warmer weather means vector mosquitoes can grow faster, invade new areas and spread vector-borne diseases.

In addition, increased precipitation will potentially increase the number of breeding sites for mosquito vectors. Vector mosquitoes, such as those that transmit malaria, breed in stagnant and temporary bodies of water. Research in Limpopo has shown that heavy rains in spring are usually associated with increased malaria cases in the summer months.

The effects of climate change on mosquitoes are very clear. However, its effect on malaria transmission is still unclear. Some theoretical mathematical modeling studies predict that the number of malaria cases will increase due to climate change. But other models suggest that climate change will not affect malaria. More information is needed to see which model is correct. This is because the effect is difficult to test in the laboratory.

Whether climate change will create another challenge to achieving malaria elimination is yet to be confirmed. Our research group is currently working to address this knowledge gap.

What we know The relationship between climate change and malaria is complex. But four things are clear: As the Earth warms, malaria vectors will evolve faster, allowing them to multiply faster, bite more often, and move into previously unsuitable habitats.

This means that mosquito larvae will grow faster. The faster the female bites, the faster she can transmit the disease. If it bites more often, it will spread more diseases.

The development of the malaria parasite in the mosquito is highly dependent on temperature. At temperatures below 17⁰C and above 35⁰C, the parasite’s life cycle inside the mosquito cannot be completed. This stops the malaria from progressing.

The mosquito’s transformation from larva to free-flying adult generally occurs at temperatures between 22⁰C and 34⁰C. Interestingly, studies have shown that mosquitoes can change their behavior to spend most of their time resting in cool places. In this way, they can survive when the ambient temperature increases. This behavior of the mosquito may help it survive at temperatures that would stop the development of the parasite.

Different changes in seasons have been noted mainly due to climate change. The Southern African region experiences more extreme hot days and less extreme cool days.

Therefore, winters are very warm, allowing mosquitoes to multiply and transmit malaria more. The summer months are also getting warmer. In some cases, summers can be too hot for mosquitoes and parasites to grow, preventing the spread of malaria. Climate change may cause the malaria transmission season to shift from the summer months to the traditionally colder fall and winter months.

Rainfall also plays a major role in the spread of malaria. In general, malaria cases decrease during El Niño (warmer but drier) years and increase during La Niña (colder but wetter) years. This is particularly true in countries such as South Africa, where the adaptable malaria vector Anopheles arabiensis is the dominant transmission vector. South Africa is currently in a La Nina period, so the upcoming malaria season (October-February) could be potentially significant given the more favorable conditions for malaria transmission and the easing of all COVID-related movement restrictions.

The situation in South Africa Our research team, based at the National Institute of Infectious Diseases and the Malaria Research Institute of the University of the Witwatersrand, was involved in identifying the mosquitoes behind the malaria epidemic in 2000. This outbreak coincided with severe flooding in southern Mozambique. A dramatic increase in available breeding grounds has allowed the insecticide-resistant mosquito Anopheles funestus from Mozambique to re-invade KwaZulu-Natal, increasing the number of malaria cases.

Since this outbreak, our group has been conducting intensive surveillance in the endemic provinces of South Africa. We have also been involved in research to understand the impact of climate change on the spread of malaria in South Africa.

Research in our vector laboratories has shown that a warmer world will reduce the effectiveness of insecticides used for indoor residual spraying. In addition, insecticide-resistant mosquitoes are better adapted to survive in warmer conditions than insecticide-susceptible mosquitoes.

Modeling experiments suggest that humidity levels will also affect malaria transmission in South Africa. However, this needs to be confirmed in laboratory conditions using live mosquitoes.

What should be done? Clearly, the relationship between climate change and malaria is complex. More work needs to be done to understand this relationship so that effective control measures can be implemented. Importantly, to understand the role of microclimate in malaria transmission, malaria hotspots must be targeted for control. Microclimate is a set of local climatic conditions that may differ from the general climate.

There is currently no evidence of an expansion of malaria risk zones in South Africa. However, regardless of the climate or whether you’re traveling this summer, it’s important to think about malaria when it comes to unexplained fevers. Know what the symptoms of malaria are, how to reduce the risk of infection and what to do if you suspect malaria.

(This story was not edited by Devdiscourse staff and was automatically generated from a syndicated feed.)

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