Ticks are not biological vectors in Missouri. Horseflies and eye gnats are probably mechanical vectors, or hosts that transmit the disease-producing organism but are not required for its life cycle.
Horseflies are probably the major mechanical vector in Missouri.
Recent studies at Mississippi State show that anaplasmosis can be transmitted from infected calves to non-infected calves with as few as 10 horsefly bites and that horseflies can transmit the disease for at least 60 minutes after a meal of blood. In addition, blood-contaminated instruments such as needles and dehorners can transmit the organism from one animal to another. In the western United States, wildlife also appear to be reservoirs of infection. Anaplasmosis is a cyclical disease, with outbreaks every five to seven years. The cycles are caused by the gradual buildup of non-infected cattle, which then become infected, causing the visible outbreak and also reducing the number of unexposed cattle that can be infected in the next few years.