During this period, the animal remains healthy and shows no signs of being infected. Finally, after the parasite has reproduced many times and established itself in the red blood cells, the body attempts to destroy the parasite.
Developmental
Clinical (observable) signs begin to be expressed about halfway through this phase. As the infected animal’s body destroys the parasite, red blood cells are destroyed as well. When a substantial loss of red blood cells has occurred, the animal will show signs of clinical anemia. Body temperature will rise to a point of 104 to 107º Fahrenheit, and a rapid decrease in milk production will occur in lactating cows.
Convalescent
Cattle that survive the clinical disease lose weight, abort calves and recover slowly over a two- or three-month period. This stage lasts until normal blood values return. The convalescent state is differentiated from the developmental stage by an increase in the production of red blood cells. Death losses normally occur during the late development stage or early convalescent stage.
Carrier
Cattle that recover from anaplasmosis remain reservoirs (carriers) of the disease for the rest of their lives. During the carrier stage, an animal will not exhibit any clinical signs associated with the persistent low-level A. marginale infection; nevertheless, the blood from these recovered animals will cause anaplasmosis if introduced into susceptible cattle.
Carriers very rarely become ill with anaplasmosis a second time. Unidentified carriers in a herd are the most likely source of infection for future outbreaks of the disease.
—Taken from the 59th Annual Texas A&M Beef Cattle Short Course proceedings
