American dog tick larva (Dermacentor variabilis). Light micrograph (LM). This species, also known as the wood tick, is known to carry bacteria responsible for several diseases in humans, including Rocky Mountain spotted fever (RMSF) and tularemia. RMSF is a potentially fatal rickettsial disease of dogs and humans caused by the intracellular bacterium Rickettsia rickettsii. The pathogen has been reported throughout the USA, Central and South America. Diseases are spread when the tick sucks blood from the host. It can then take several days for the host to experience some symptoms. It usually takes 3 months to 3 years for American Dog Ticks to complete a life cycle. Magnification: x30 when printed at 10cm wide.