As producers buy and sell cows this year, anaplasmosis is becoming an all-too-common term. This serious disease is a major concern right now with Texas veterinarians in particular hoping to prevent a train wreck as ranchers repopulate herds devastated by drought.
Anaplasmosis is a disease caused by a protozoan parasite (Anaplasma marginale) transmitted through the blood of infected animals (carriers) to non-infected (naive) animals. Anaplasmosis is usually transmitted through biting insects and surgical instruments contaminated by infected blood.
Horseflies, stable flies, mosquitoes and ticks are confirmed insect vectors. Dehorners, ear taggers and other instruments that come into contact with blood also have the potential to spread the disease quickly, causing severe outbreaks.
Symptoms of anaplasmosis include anemia, overall weakness and jaundice. Unfortunately, beef cows are often down or even dead before producers notice problems. Many cows recover from mild cases of anaplasmosis without anyone having ever known they were ill. These seemingly healthy cows become carriers, spreading the disease to other members of the herd.
The prevalence of anaplasmosis can vary greatly within states. A recent Texas A&M University survey found a disease prevalence of 15% across the state, with a rate of 30% to 38% west of Interstate 35 and a lower prevalence of 5% to 20% east of I-35. The higher rate west of I-35 may be connected with large populations of winter ticks that transmit the disease.
As producers buy and transport cows to rebuild herds, Texas veterinarians are worried naive cows will be brought into herds with high numbers of carrier animals. On the other hand, carriers can be brought into clean herds and expose large numbers of naive cows. Either way, the chances of an outbreak are especially high if needles aren't changed and surgical instruments aren't carefully cleaned between treatment of each animal.
"One of the worst wrecks I saw as a practicing veterinarian was caused by a producer working a bunch of cows through the processing chute without changing needles and cleaning surgical instruments between animals," said Thomas Hairgrove, DVM, of Texas A&M.
Since a good beef cow is worth on average $1,500, and needles cost less than 20 cents each, the veterinarian recommends changing needles between each animal. He also recommends washing blood off dehorners and ear taggers with a disinfectant and wiping instruments with clean towels between animals.
"If you work some new animals and then you see cows going down and dying 35 to 40 days after a trip through the processing chute, there's a good chance anaplasmosis was transmitted from carriers to naive cows in the herd," Hairgrove said.
In addition to the effect this disease has on cows, anaplasmosis can hit bulls hard, too, causing sterility. Calves can also be infected and show signs of illness when under stress. In order to determine if anaplasmosis is the cause of the illness, a veterinarian will usually send a blood sample from the suspected animal to a diagnostic laboratory.
Because of its connection with biting flies and ticks, anaplasmosis has traditionally been considered a bigger problem in southern states with long insect seasons. However, the disease has gained a strong foothold in places like southern Iowa, as well.
"In the last two years, we've seen an increased number of anaplasmosis cases based on submissions to the Iowa State University [Veterinary] Diagnostic Laboratory," said Extension veterinarian Grant Dewell. In Iowa, anaplasmosis is seen most often in late summer at the height of horsefly and tick season.
As a rule of thumb, if an outbreak occurs during fly season, the source of infection is probably an insect vector. If the outbreak occurs three to six weeks after cattle are processed, anaplasmosis was more likely transferred from infected animals' blood on surgical instruments.
Tetracycline is the drug of choice to treat clinical anaplasmosis. A single dose of long-acting oxytetracycline is usually sufficient to help a cow recover.
While anaplasmosis affects cattle of all ages, naive adult cattle are the most severely affected and show the following signs:
- depression, lethargy and loss of appetite
- fever, muscle tremors and weakness
- reduced milk production
- pale gums, dry muzzle and labored breathing.
TREATING AN OUTBREAK
Gary Warner, DVM, of Elgin, Texas, grew up in an area of Louisiana where anaplasmosis was widespread. Unfortunately, he's still encountering the disease regularly in his Texas practice.
"If I'm called to a cow herd where there are a couple of dead animals and a couple more are sick, there will probably be 20 to 30 more cows incubating the disease," Warner said.
In this situation, the veterinarian has to first decide if it's wise to treat the sick cows with long-acting antibiotics. In many cases, the stress of giving a weakened cow an injection will kill her. Some cows with anaplasmosis recover on their own but continue to be carriers.
After dealing with the obviously sick cows, Warner treats the herd. He usually recommends two treatments with a long-acting tetracycline product.
"I strongly recommend consulting with a veterinarian before attempting to treat your cattle for anaplasmosis. Without the advice of an animal professional, you could have a major wreck."
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