Plasmodium vivax
Plasmodium vivax is a protozoal parasite and a human pathogen. This parasite is the most frequent and widely distributed cause of recurring (Benign tertian) malaria, "P. vivax" is one of the five species of malaria parasites that commonly infect humans. Although it is less virulent than "Plasmodium falciparum", the deadliest of the five human malaria parasites, "P. vivax" malaria infections can lead to severe disease and death, often due to splenomegaly (a pathologically enlarged spleen). "P. vivax" is carried by the female "Anopheles" mosquito; the males do not bite.
White-tailed deer
Another issue that exists with high deer density is the spreading of infectious diseases. Increased deer populations lead to increased transmission of tick-borne diseases, which pose a threat to human health, to livestock, and to other deer. Deer are the primary host and vector for the adult black-legged tick, which transmits the Lyme disease bacterium to humans. Lyme disease is the most common vector-borne disease in the country and is found in twelve states in Eastern America. In 2009, it affected more than 38,000 people. Furthermore, the incidence of Lyme disease seems to reflect deer density in the eastern United States, which suggests a strong correlation. White-tailed deer also serve as intermediate hosts for many diseases that infect humans through ticks, such as Rocky Mountain spotted fever.
Newer evidence suggests the white footed mouse is the most significant vector. https://phys.org/news/2018-04-reveals-high-infection-white-footed-mice.html