Chapter 32: Vectorborne and Soilborne Bacterial and Viral Diseases

Many of these diseases are zoonotic infections in which humans become accidental hosts after exposure to infected animals or vectors. Animal transmitted viral diseases include rabies, a nearly always fatal neurological infection caused by rabies virus and transmitted through the saliva of infected mammals, and hantavirus infections that spread through inhalation of aerosolized rodent excreta and can produce severe respiratory or renal disease. Arthropod borne pathogens are transmitted by vectors such as mosquitoes and ticks and include rickettsial diseases like typhus and Rocky Mountain spotted fever, as well as ehrlichiosis and anaplasmosis. Lyme disease, caused by the spirochete Borrelia burgdorferi, is the most common tickborne infection in the United States and produces characteristic bull’s-eye skin lesions followed by systemic complications if untreated. Mosquito transmitted viral diseases represent another major category of vectorborne infections and include yellow fever, dengue fever, Zika virus disease, chikungunya, and West Nile fever, all of which circulate in animal reservoirs and are transmitted to humans during mosquito feeding. These arboviral infections range from mild febrile illness to severe hemorrhagic disease, neurological damage, or congenital abnormalities. The chapter also discusses soilborne bacterial diseases caused by endospore forming pathogens such as Bacillus anthracis, the agent of anthrax, and Clostridium tetani, which produces the neurotoxin responsible for tetanus and causes rigid muscle paralysis following wound contamination. Gas gangrene represents another severe soil associated infection produced by Clostridium species that generate tissue destroying toxins and gases in anaerobic wounds. Together these examples demonstrate how environmental reservoirs, animal hosts, and arthropod vectors enable microbial pathogens to persist in nature and occasionally infect humans, producing diseases with diverse transmission pathways, virulence mechanisms, and public health impacts.