Anaplasmosis

You can't afford dead cattle.

Anaplasmosis, which appears most often in the fall months, can occur at any time of the year and can devastate herds if not treated properly or in a timely manner. Anaplamosis is in the Midwest states; it is said to be in 40 states in the US. 

Transmission of Anaplasmosis

Anaplasma marginale is an infectious parasitic organism that is transmitted through blood transfer by biting insects and ticks, and surgical instruments such as needles, dehorners, ear taggers, castrating knives, and tattoo instruments. Once in the tick, the parasite can remain active throughout the lifecycle of the tick and can be transmitted several months later.

The infection is also infrequently passed from an infected cow to her unborn calf. Although colostrum ingestion and absorption is essential for new calves, colostral antibodies do not increase the natural resistance calves have against the disease.

Anaplasma marginale has been shown, at least experimentally, to infect such wildlife species as American bison, mule deer, white-tailed deer, black-tailed deer, elk, pronghorns, and bighorn sheep. With the exception of the black-tailed deer in California, none of the wildlife species studied show severe signs of illness when they are infected. They probably become infected from their association with cattle and do not pose a threat as reservoirs of infection for susceptible cattle as previously believed. In fact, blood taken from experimentally-infected deer actually served as an effective vaccine to protect cattle.

Course of the Disease

Once susceptible cattle are infected with Anaplasma, the organism multiplies in the bloodstream and attaches to the animal’s red blood cells. The animal’s immune system destroys the infected red blood cells in an attempt to fight off the infection. Unfortunately, uninfected blood cells are also destroyed. When the number of blood cells being destroyed exceeds the number of blood cells that the body can produce, the animal becomes anemic. It takes 3 to 6 weeks for clinical signs to appear after the animal is infected.

Anaplasmosis is unusual because the clinical signs are most severe in adult animals. Calves less than a year old that are infected with A. marginale usually do not show clinical signs of the disease, but will become carriers. Carrier animals have immunity against anaplasmosis, so even if they are infected later in life, they will generally not get sick. Cattle 1 to 3 years old will show increasingly more severe clinical signs. Newly infected adult cattle over 3 years will show the most severe clinical signs, and 30 to 50% will die if they are not treated early.

After an animal survives a natural case of anaplasmosis, its immune system will protect against the organism for the life of the animal. Cattle that recover from anaplasmosis, however, are carriers that can spread the disease to susceptible cows.

Symptoms of Anaplasmosis

Unless cattle are being watched carefully, dead cows are frequently the first thing noticed with an anaplasmosis outbreak. If cattle are carefully observed, weakness may be the first clinical sign that is observed.

  • Infected cattle will fall behind the rest of the herd and will not eat or drink.
  • Cows with light skin will initially look pale around the eyes and muzzle, but later this can change to a yellowish color (jaundice). This jaundice is due to the destruction of the blood cells and their contents being released into the blood stream.
  • Weight loss is rapid.
  • Cattle can become extremely aggressive if they are oxygen deprived due to the severe anemia.
  • Oxygen deprivation can also result in abortions in pregnant cows.
  • Constipation, high fever, and labored breathing can also be seen.

The most critical period is the first 4 to 9 days after clinical signs appear. Cows that survive this period have an increased chance of survival.

Treatment for Anaplasmosis

Treatment of anaplasmosis is most effective if given in the early stage of the disease. Oxytetracycline is given to symptomatic cattle; I know of several different treatments regimes from 1 to 3 injections so consult your herd veterinarian. Animals in later stages of the disease may be so anemic that the stress of handling them will kill them. There is also evidence that antibiotics at this stage are not effective.

All affected animals should be provided with easy access to food and water and a low-stress environment. It may take surviving animals up to 3 months to completely recover from the disease. Animals treated with a single dose of antibiotics and those not treated at all will both become carrier animals.

Chlortetracycline also known as CTC can reduce the risk of anaplasmosis. A consistent intake of the correct amount of mineral is crucial to a anaplasmosis prevention program. CTC is available in medicated feed, free choice salt-mineral mixes or medicated blocks.

Only one killed vaccine is available in the United States. Cattle at Dixon Springs Ag Center have been vaccinated for several years; since then fewer cows show signs of anaplasmosis each year than before the vaccination program started. The U.S. Department of Agriculture allows its sale as an experimental product that can be sold only to licensed veterinarians and is available in 24 states, including Illinois, Missouri, Kentucky, and Arkansas.

Be vigilant, and if you suspect anaplasmosis on your farm, contact your herd veterinarian. This will allow a positive diagnosis of anaplasmosis to be made and the best course of treatment implemented.

This article also appeared in Mid-America Farmer Grower, July 7, 2015

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