<unk> s are<unk> s that are prevalent in or unique to<unk>  and subtropical regions. The<unk> s are less prevalent in temperate climates, due in part to the occurrence of a cold season, which controls the insect population by forcing hibernation. However, many were present in northern Europe and northern America in the 17th and 18th centuries before modern understanding of<unk>  causation. The initial impetus for<unk>  medicine was to protect the health of colonial settlers, notably in India under the British Raj. Insects such as mosquitoes and flies are by far the most common<unk>  carrier, or vector. These insects may carry a parasite, bacterium or virus that is infectious to humans and animals. Most often<unk>  is transmitted by an insect "bite", which causes transmission of the infectious agent through subcutaneous blood exchange. Vaccines are not available for most of the<unk> s listed here, and many do not have cures. Human exploration of<unk>  rainforests, deforestation, rising immigration and increased international air travel and other tourism to<unk>  regions has led to an increased incidence of such<unk> s to non-tropical countries.
Tropical disease
Feline zoonosis
Virgin soil epidemic
Polymer fume fever
Kyphosis
Kyphosis 
Infodemic
Cocoliztli epidemics