Animal diseases linked to weather, climate changes

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Windhoek

With Namibia now in the grip of another outbreak of Foot-and-Mouth Disease (FMD), it is critical to remember that many important animal diseases are affected directly or indirectly by weather and climate.

Many important animal diseases are affected directly or indirectly by weather and climate. Climate can affect distribution of a disease as well as the timing of an outbreak or the intensity of it. Many animal diseases of significant impact in Namibia are influenced by climate. Such influences are not the sole preserve of vector-borne diseases; certain directly transmitted food/waterborne and aerosol transmitted diseases are also affected. A common feature of non-vector-borne diseases affected by climate is that the pathogen or parasite spends a period of time outside the host, subject to environmental influence.

Climate appears to be more frequently associated with the seasonal occurrence of non–vector borne diseases than their spatial distribution. A second host-related effect is genetic resistance to disease. Many animals have evolved a level of genetic resistance to some of the diseases to which they are commonly exposed. It seems unlikely that climate change will directly affect genetic or immunologic resistance to disease in livestock. But with significant shifts in disease distributions driven by climate change, naive populations may, in some cases, be particularly susceptible to the new diseases facing them.

To explain this further, certain diseases show a phenomenon called endemic stability, which occurs when the disease is less severe in younger than older animals, when the infection is common or endemic and when there is lifelong immunity after infection. Under these conditions most infected individuals are young, and experience relatively mild disease. Certain tick-borne diseases, such as anaplasmosis, babesiosis and cowdriosis, show a degree of endemic stability (Eisler et al. 2003). If climate change drives such diseases to new-areas, non-immune individuals of all ages in these regions will be newly exposed, and outbreaks of severe diseases could follow. Climate can affect distribution of a disease as well as the timing of an outbreak or the intensity of it. Many animal diseases of significant impact in Namibia are influenced by climate. Such influences are not the sole preserve of vector-borne diseases; certain directly transmitted food/waterborne and aerosol transmitted diseases are also affected. A common feature of non-vector-borne diseases affected by climate is that the pathogen or parasite spends a period of time outside the host, subject to environmental influence.

Climate appears to be more frequently associated with the seasonal occurrence of non–vector borne diseases than their spatial distribution. A second host-related effect is genetic resistance to disease. Many animals have evolved a level of genetic resistance to some of the diseases to which they are commonly exposed. It seems unlikely that climate change will directly affect genetic or immunologic resistance to disease in livestock. But with significant shifts in disease distributions driven by climate change, naive populations may, in some cases, be particularly susceptible to the new diseases facing them. To explain this further certain diseases show a phenomenon called endemic stability which occurs when the disease is less severe in younger than older animals, when the infection is common or endemic and when there is lifelong immunity after infection. Under these conditions most infected individuals are young, and experience relatively mild disease. Certain tick-borne diseases, such as anaplasmosis, babesiosis and cowdriosis, show a degree of endemic stability since 2003.

If climate change drives such diseases to new-areas, non-immune individuals of all ages in these regions will be newly exposed, and outbreaks of severe diseases could follow.

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