Anaplasmosis in Virginia

Livestock Update, December 2000

Dr. W. Dee Whittier, Extension Veterinarian, Cattle, VA-MD Regional College of Veterinary Medicine

A policy of testing bulls for Anaplasmosis in Virginia has recently been adopted for BCIA sales to prevent infected bulls from carrying the disease to non-infected herds. Anaplasmosis is an infectious disease that causes sickness and death in adult cattle. The disease is spread in several ways including by certain ticks, by horsefly bites and by infected needles or any other item that takes fresh blood from one animal to the next.

Anaplasmosis is an interesting disease in that the reaction to an infection is different depending on the age at which the infection occurs. Cattle less than 1 year of age usually show no signs of the infection. As cattle get older they show progressively more signs of the disease if they become newly infected. Adult cattle typically become very ill and often die from Anaplasmosis.

A second important characteristic of anaplasmosis is that once cattle become infected, they stay infected for life unless treated. The infection can be detected by a blood test. Cattle that have been infected for long periods are immune and so do not develop disease. They are a potential source of the infection for other cattle that are not immune.

A vaccine is available, but the animals must be vaccinated at least two weeks before the insect season. One dose is given followed by a second dose four weeks later. Thus, to be protected, the animals must receive the first dose six weeks before the insect season. The manufacturer recommends annual re vaccination. Some reports suggest that while vaccination will reduce clinical disease or the visible signs of the disease, animals can still become infected and become carriers.

There is not a good survey of the incidence of Anaplasmosis in the Virginia. Veterinarians report seeing the disease and having positive test results throughout the piedmont area in central Virginia. The disease is only occasionally diagnosed west of the Blue Ridge, probably because the ticks that are the carriers are not present in this part of the state. The state can be divided into three categories for Anaplasmosis:

1. Areas where nearly all cattle are infected and little disease is seen because calves become infected early in life so cattle are immune and continually infected.
2. Areas where infections only occur only during some years. In these areas some cattle are immune infected carriers but others reach adulthood without becoming infected. Adult cattle then develop disease during those years that conditions are right for spread. The most common tool being used in these areas is the feeding of tetracycline in the minerals throughout the insect season. Feeding the tetracycline at the low levels possible through the minerals prevents disease but not infections from occurring.
3. Areas where almost no cattle are infected and disease occurs only when an infected animal enters the herd and there is spread of the organism.

The major goal of Anaplasmosis testing is to prevent the introduction of an infected animal. Since the bull is the most common animal to enter many Virginia herds from outside the immediate area having non-infected bulls is very important. Our evidence suggests that cow deaths in Virginia have resulted from the introduction of an infected bull into a free herd and then the spread of the organism to susceptible cows by horseflies or needles.

The situation with various areas of infection creates a significant challenge for purebred producers operating in areas where there is Anaplasmosis. Such producers probably want to maintain cows with infections or initiate a vaccination program to assure that they don't loose cows when previously non-immune adults become infected. But there is the need to produce animals that can be sold free of the disease and negative to tests. Generally there are three approaches to attempt keeping young animals from becoming infected if they are in an area where other cattle are infected and there are ticks or horseflies that can spread the disease:

1. Injection of whole herd with 3-5 mg/lb. of tetracycline; repeat at 28-day intervals.
2. Vaccination.
3. Feeding low levels of tetracycline (0.5 mg/lb.) during the season of spread (May through November)

Vaccination is probably not a good idea for cattle that will be sold, as they will have positive test results that cannot be distinguished form reactions due to infection. There is also some possibility that vaccinated animals can become infected but not develop the disease.

Infected animals can be treated with tetracyclines and cleared of their infection. The tetracyclines can either be fed for a period of time or given as a series of injections (4 injections at 3-day intervals). Higher levels of tetracyclines must be fed than cattle will consume in minerals so mixing tetracycline with feed is required. Animals that have been cleared of the infection by treatment will continue to have a positive blood test for several months.

Producers who have animals that test positive to Anaplasmosis should test their herds to find out what the level of infection is. Local veterinarians will also be able to supply information about the likelihood that a neighboring herd will have infections that could be spread back to the herd. If the herd test shows a significant percentage of cows are infected a decision to vaccinate, treat to clear infections or live with an infected cow herd must be made. Local veterinarians can help in making this decision.

Increasing the attention to Anaplasmosis in Virginia will certainly bring inconvenience to some producers. Since it will also protect uninfected cow herds, it is an inconvenience that is worth the effort.

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