What is Anaplasmosis? This is a cattle disease caused by an organism called Anaplasma marginale. This organism is a rickettsia—halfway between the viruses and the bacteria. It cannot grow without living cells (like a virus) but is susceptible to tetracyclines (like the bacteria). The disease, anaplasmosis, is caused when the infected cattle react to the agent and remove their own infected red blood cells. This reaction causes a severe anemia and often death.
What breeds are susceptible? All cattle are susceptible to infection by A. marginale. Also, deer, elk, and other wild ruminants are susceptible to becoming infected and can act as natural reservoirs of the agent. Cattle of any age can become infected; however, young cattle do not become ill, as will be explained later.
How do cattle become infected? A number of ruminants such as cattle, deer, and elk can be carriers of the anaplasmosis agent. These species can carry the agent all or most of their lives and serve as a reservoir for infection of other animals. The transfer of the agent from a carrier animal to a susceptible animal can occur by a number of routes. One of the most common ways is via ticks. In California, we have a number of ticks that transmit the anaplasmosis agent and are extremely effective at passing the agent to new, susceptible hosts. Additionally, transmission of a small amount of blood from a carrier animal to a susceptible animal can transmit anaplasmosis. So insects such as horse flies are capable of transmission. Even larger culprits in this type of transmission are humans. Ear-tagging instruments, tattoo tools, needles, ear implant tools, castrating instruments, dehorning instruments, etc., can all easily transmit the agent. So we can also be important in the spread of this disease.
What happens when an animal becomes infected? If the animal is a calf under the age of 12 months, virtually nothing is noticed. The calf undergoes an incubation period of about 45 to 90 days, has a very mild illness, which is rarely noticed, and becomes a carrier for life. Cattle that become infected between 1 and 2 years of age become ill after the incubation period, with severity increasing with age. Cattle over 2 years of age become very ill and approximately 50 percent die unless treated. The older the animal and the better shape they are in--the sicker they get! Usually, once the cattle become infected, and if they survive, they stay infected for life. They are "immune carriers"-they do not get sick; but, act a reservoir for other susceptible animals. Therefore, being an infected carrier protects the animal from becoming sick if re-infected by ticks or other means.