ANAPLASMOSIS Staying ahead of a costly problem for California’s cattle producers
by Gaby Maier, DVM, PhD, DACVPM, Extension Veterinarian for Beef Cattle Herd Health & Production, UC Davis and Josh Davy, UC Livestock/Range Advisor, Tehama, Glenn and Colusa counties Anaplasma marginale is a blood parasite that targets red blood cells of ruminants including cattle. Anaplasmosis is the disease caused by the organism, estimated to cost the U.S. cattle industry several hundred million dollars annually, and one of the most important cattle diseases throughout the world. The name Anaplasma stems from the Greek words an (“without”) and plasma (“shape”) describing an organism that appears to have little substance to it. “Marginale” means – you guessed it – marginal, so we are talking about a small organism living “on the edge”, in this case on the outer edge of red blood cells. It falls in the order Rickettsiae, which belong to the bacteria, but similar to viruses it needs other cells to live and can’t survive outside an animal for long. Transmission between cattle occurs via several species of ticks. In California, Dermacentor aka the dog tick is most commonly responsible for transmission. Mechanical transmission of small amounts of blood through instruments such as taggers, hypodermic needles, tattooers or through blood-sucking insects like biting flies is also possible. Once infected, disease in cattle develops within 7 to 60 days depending on the infective dose. The body recognizes the intruder and destroys infected red blood cells. This process causes fever, anemia, lethargy, abortion and death in cattle. The disease can easily be confused with respiratory disease because cattle may have a fever and breathe harder. Since red blood cells get destroyed during the disease, there are fewer of them picking up oxygen in the lungs, which cattle try to compensate for by breathing faster. It is like going from sea level to a 10,000-foot mountain and realizing the air is pretty thin and getting out of breath easily. Some telltales that cattle have the disease include the color of mucous membranes, like the inside of the mouth, that may appear pale or yellow, incoordination, and/or a cow’s behavior. With insufficient oxygen supply to the body including the brain, changes in behavior occur. Often cattle are simply found dead and a necropsy by a veterinarian will lead to diagnosis. Affected cattle can become aggressive and may attack an approaching person so proceed with caution if you suspect anaplasmosis in a cow or bull. Stress, such as a gather, can exacerbate the disease causing death. If anaplasmosis is suspected as the culprit causing aggression, it may be better to leave animals where they are. 54 California Cattleman September 2020
Although not BQA approved, antibiotic treatment with a dart gun may be less stressful than a long walk to the corral or roping in this particular instance. Besides cattle, blacktail and mule deer, water buffalo, American bison and bighorn sheep can also become infected and act as reservoirs although disease is most severe in cattle. Cattle that survive the infection likely stay infected for life, i.e. they eventually replenish their red blood cells, but the organism survives at low levels in their body. The good news is that recovered cattle are usually protected from future anaplasmosis disease; the bad news is that survivors can become quite debilitated with loss of body condition, decreased fertility and their calves can have reduced weaning weights. Age at infection determines the severity of disease where young animals less than six months of age rarely are affected by the infection, while older cattle, especially those over two years of age are much more likely to become very sick and die. Sick cattle can be treated with antibiotics or blood transfusions and may survive. However, treatment works best in the early phases of the disease and the stress of restraint can kill the animal once the disease has progressed. Anaplasma marginale does not cause disease in people, but there are other Rickettsiae that infect humans through tick bites, e.g. Rocky Mountain spotted fever. Removing ticks as soon as possible helps prevent tickborne disease in people.
HOW CAN YOU PROTECT YOUR HERD FROM ANAPLASMOSIS?
The herd status determines how Anaplasma should be managed. Herds that do not come into contact with infected ticks, infected wildlife or infected cattle, for example in the Central Valley on permanent pasture, have little risk for disease. For such naïve herds, the biggest risks for an anaplasmosis outbreak are either movement to an endemic area or introduction of a carrier animal. If such a herd needs to be moved to an area that is suspected to harbor Anaplasma, vaccination of all adult cattle before movement is the best option. For incoming cattle to a naïve herd, a negative blood test should be a prerequisite for introduction. Introducing a positive animal to a negative herd could start the spread of disease and could result in multiple losses.
