Animal diseases spread by ticks and mosquitoes could become an even bigger problem with climate change

Changes in rainfall and temperature might allow disease-carrying organisms, also called vectors, to spread to new areas on the African continent. Many vectors cause serious diseases in livestock, so their spread would impact food security and the livelihoods of farmers in many countries.

The researchers in this study were interested in how climate change could affect the spread of two types of diseases. The first, called Rift Valley Fever, is transmitted by mosquitoes, and causes abortions and death in animals like sheep, goats, and cattle. The second is a group of diseases carried by ticks that can cause animals to lose weight, become paralysed, or even die.

In both cases, the life cycle of the vectors is likely to be influenced by climate change, and this could mean that the diseases spread to new areas or become more common in areas where they already occur.

To better understand this problem, researchers reviewed other scientific studies that focused on these diseases, especially in relation to changes in rainfall and temperature.

What they found was that Rift Valley Fever outbreaks often occurred in areas where a higher-than-normal amount of rain has fallen, because this means there are more pools of water for mosquitoes to breed in. Because climate change is expected to increase rainfall in places like East Africa, the disease could spread and get worse as a result.

Meanwhile, the researchers say that diseases carried by ticks could become more common in countries like Botswana, Zambia, and South Africa as warmer temperatures allow the ticks to survive in new areas. They add that climate change also makes it likely that ticks can move further north, and that there is already evidence that this is happening in Russia and Sweden.

Overall, the findings show that climate change will make it possible for vectors to survive in areas that they previously couldn’t, expanding the range of many serious diseases. 

The researchers state that this could also have impacts on the strategies used to control vectors. For example, pesticides used to kill ticks might need to be applied more regularly than they currently are in areas where tick populations have increased.

They add that in the future it is important for more research to be done on how disease and vector control strategies are affected by climate change. They also say that animal health should be monitored on an ongoing basis, using tools like citizen science, so that outbreaks of disease can be predicted and controlled.

The study was a collaboration between scientists based in Kenya and Sweden, and forms part of a book on the effects of climate change on agriculture in Africa.

Abstract

Climate change influences the occurrence and transmission of a wide range of livestock diseases through multiple pathways. Diseases caused by pathogens that spent part of their life cycle outside the host (e.g. in vectors or the environment) are more sensitive in this regard, compared to those caused by obligate pathogens. In this chapter, we use two well-studied vector-borne diseases—Rift Valley fever (RVF) and tick-borne diseases (TBDs)—as case studies to describe direct pathways through which climate change influences infectious disease-risk in East and southern Africa. The first case study demonstrates that changes in the distribution and frequency of above-normal precipitation increases the frequency of RVF epidemics. The second case study suggests that an increase in temperature would cause shifts in the spatial distribution of TBDs, with cooler and wetter areas expected to experience heightened risk with climate change. These diseases already cause severe losses in agricultural productivity, food security and socio-economic development wherever they occur, and an increase in their incidence or geographical coverage would intensify these losses. We further illustrate some of the control measures that can be used to manage these diseases and recommend that more research should be done to better understand the impacts of climate change on livestock diseases as well as on the effectiveness of the available intervention measures.

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