Mosquito
Mosquito-borne diseases are currently most prevalent in East Africa, Latin America,  Southeast Asia, and India; however, emergence of vector-borne diseases in Europe have recently been observed. A weighted risk analysis demonstrated associations to climate for 49% of infectious diseases in Europe including all transmission routes. One statistical model predicts by 2030, the climate of southern Great Britain will be climatically-suitable for malaria transmission "Plasmodium vivax" malaria for 2 months of the year. By 2080 it is predicted that the same will be true for southern Scotland.
Karl Friedrich Meyer
Meyer also investigated what are called arbovirus diseases, among them equine encephalitis. Several diseases transmitted from animals to humans are due to a group of viruses carried by mosquitoes. Mosquitoes belong to the ‘animal family’ (technically a ‘phylum’) called arthropods; hence the viruses carried by them are "ar"thropod-"bo"rne. Different arboviruses may cause diverse diseases. Here, we summarize examples of Meyer’s outstanding discoveries in this area. 
In the early 1930s, thousands of horses in California suffered and died from a paralytic disease, later called western equine encephalitis. Meyer proved that it was of viral origin. Later it became clear that the virus can also infect humans causing encephalitis, sometimes with deadly complications. – Meyer and his colleagues at the Hooper later demonstrated that mosquitoes pick up the virus from chicken and (migratory) birds and transfer it to man and to horses. It also became clear that the disease is common near irrigated fields where mosquitoes abound. Meyer therefore qualified encephalitis as a man-made disease. Subsequently, a vaccine for horses was developed. And it turned out that the isolation of the virus by Meyer led to the discovery of similar kinds causing other types of encephalitis in man. (Other microbiologists found related types of viruses in other animals than horses.) – Effective mosquito control was the key to minimizing this problem.