by Bill Halfman
Those following beef news feeds may be reading about anaplasmosis and the dilemma of increasing resistance to the parasiticides used to kill the ticks that vector this disease. For cattle in Wisconsin however, transmission of Anaplasma is not so much about the tick or biting insects as it is about our husbandry and biosecurity practices. Contaminated needles are a common source of infection for this potentially devastating disease.
Cattle (both beef and dairy) are reservoirs of the bacteria Anaplsama marginale. The bacteria survive within bovine red blood cells and are transferred as blood is passed between cattle. These bacteria do not survive in the absence of blood. Bovine immunity fails to clear the infection. Even with treatment, those infected become lifelong carriers and serve as the source of infection for their herd mates.
Anaplasmosis is not contagious. It is transferred as blood is passed between animals. In Wisconsin, our husbandry practices serve to transfer Anaplasma from carrier to naïve cattle. Those potentially bloody practices where un-disinfected equipment is re-used between cattle include knife castration, dehorning, ear-tagging, implanting, re-using needles when vaccinating and using the same rectal palpation sleeve during multiple reproductive examinations.
High fever is the first inflammatory response that develops when the older animal becomes infected. Red blood cells are destroyed as the immune system kills the bacteria. The animal develops anemia and oxygen carrying capacity declines as red blood cells are lysed; the animal’s heart rate and respiratory rate increases, and the animal becomes exercise intolerant. Production suffers as the animal weakens.
The older the animal is when first infected, the more severe the clinical signs are. Fatalities may occur in cattle who are over two years of age when first infected. Youngstock who are less than one year of age when first infected may develop a mild case of anaplasmosis and then appear to get better, but they are infected for life. Carriers rarely become ill with anaplasmosis a second time and it’s the unidentified carriers that serve as the source of infection for the herd.
Biting flies, mosquitoes and ticks may also transfer Anaplasma. Some ticks are biological vectors of Anaplasma, which means the bacteria replicate in the tick and are passed between the tick’s life stages. Dermacenter andersoni (the Rocky Mountain wood tick) is a biological vector supporting endemic Anaplasma within southeast, central and southwest geographic areas of the United States. Dermacenter andersoni is not currently found in Wisconsin.
Replacement heifers sent to be raised in endemic areas (a frequent practice for many dairy farms) may return as infected carriers and biting flies and ticks may next transfer infected red blood cells across
Wisconsin fence lines. Purchasing beef bulls or replacement heifers from endemic states is the more likely scenario for introducing Anaplasma into a Wisconsin beef herd.
Cattle are not required to be tested for Anaplasma prior to entry into Wisconsin. Nevertheless, it is extremely important to test cattle from endemic areas. Devise an anaplasmosis and other disease prevention plan with your veterinarian.
Anaplasmosis is a reportable disease in Wisconsin. Veterinarians have ten days to report the case to the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP). DATCP is not reporting an increase in Anaplasma cases at this time.