Weather conditions may contribute to the incidence of animal diseases via their effect on fodder and therefore on nutrition and the general resistance of animals to disease. They may also contribute directly to produce a favourable environment for the growth of spores and parasites which cause disease, or to the spread of viruses and bacterial spores. In addition weather factors affect the proliferation of the intermediate hosts, such as flies and mosquitoes. Seasonal considerations can account for animal infertility.
Extreme heat or extreme cold adversely affect animal resistance to disease and may lead to undernourishment through lack of fodder. Extreme cold is the more harmful. Weather factors affecting the growth of spores and parasites and the incidence of viral or bacterial infection include wet weather, wind, rainfall followed by hot weather, hot dry weather, and drought. Mosquitoes and flies tend to proliferate during the rainy season where intermittent rainfall is followed by summer temperatures. Diseases affected by the weather include anthrax, African horse sickness, foot-and-mouth disease, fowlpest, and coccidiosis.