Veterinarians are concerned that anaplasmosis, a noninfectious disease in cattle, is reemerging throughout the U.S. The initial cause is the transmission of bacteria from ticks and horseflies, especially during heavy tick and fly seasons. Beef producers may control the disease with strategic pest control methods, good husbandry practices and antibiotics.
How ticks and horseflies infect cattle
“When ticks consume a blood meal from an infected animal, they pick up the bacteria Anaplasma marginale,” says Craig Payne, beef cattle extension veterinarian at the University of Missouri. “That organism infects the tick gut, completing part of its life cycle. Over time, the bacteria infect the tick’s salivary glands, introducing it through bites to other animals, such as cattle.”
Biting horseflies feed on infected livestock, contaminating their mouthparts. Studies suggest horseflies can transmit anaplasmosis up to two hours after they feed on an infected animal.
The second way this infection escalates is when producers use blood-contaminated equipment. Finally, an infected dam may infect her fetus via transplacental transmission in the second or third trimester. Payne reports that 10%-16% of calves born to infected dams carry the anaplasma bacteria.
Symptoms begin three to six weeks after the parasite is introduced into the bloodstream. The animal’s immune system recognizes infected red blood cells, which carry oxygen throughout the body, and removes them, resulting in anemia. In mild cases of anemia, animals may have a fever, show signs of depression, be off feed or stand away from the herd. Mucous membranes may be pale.
“In severe cases [in adults], we see jaundice, the yellowing of mucous membranes, around the eyes, gums and vulva,” Payne reveals. “In light-colored cattle, we may see yellowing in the teats and udder. When oxygen-deprived, even docile animals may become aggressive. The worst outcome is death.”
Clinical symptoms rarely appear in young, growing animals. Researchers believe this is because they regenerate red blood cells more quickly than adults, so anemia is not as severe. They may display fever and increased breathing rates.
The most commonly used antibiotics used for treatment are the long-acting injectable oxytetracyclines. These products require a veterinary prescription.
Should producers keep or cull carriers? Payne says that depends on the objectives and location of the operation. Chronic carriers will not show clinical signs of anaplasmosis unless immune compromised. However, they are a source of infection for uninfected animals.
“If a producer tries to create an anaplasmosis-free herd in a state like Missouri, where the disease is endemic, 100 percent of the animals are at risk for clinical disease if the organism is reintroduced in the operation,” Payne concludes. “In other parts of the U.S., where anaplasmosis is rare, those operations may look at that differently. They want to remove the chronic animal from the herd.”
Clean your equipment between each animal
Angie McDaniel, clinical associate professor at the University of Georgia College of Veterinary Medicine, says operators accidentally spread anaplasmosis.
“Be super clean, especially if you have a herd that tests positive for anaplasmosis,” McDaniel advises. “Make sure when vaccinating to change needles between every animal. Producers may be reluctant to change needles between animals due to increased cost, but the advantage may be decreased transmission of disease between animals on that farm.”
She continues, “Clean castration equipment and other bloody tools. Disinfect them in chlorhexidine or Betadine between each castration, and wash to remove manure, blood or organic tissue. Definitely change gloves after each cow when palpating during a pregnancy check. Anything that transfers blood can transmit the anaplasma organism to a healthy animal.”
McDaniel also recommends using only a disinfectant labeled safe for animals and warns: “Producers must be more careful with an anaplasmosis herd."
Prevention is a critical aspect of controlling anaplasmosis. The strategic control and management of ticks and horseflies is essential. Chemical applications provide the best tick control. Consult local extension agents who know which ticks and flies are emerging and the products that best control them.
Closely monitor an anaplasmosis-infected herd. If a rancher has an unexpected animal death, they should have a necropsy done.
“Keep a close eye on your cattle during tick season,” McDaniel advises. “Veterinarians have found that oxytetracycline won’t clear a carrier animal. If you identify anaplasmosis in your herd, use oxytetracycline to slow down or control the clinical disease. Add chlortetracycline to minerals or feed. I recommend adding it to minerals so you don’t have to feed cattle daily. It requires a Veterinary Feed Directive (VFD).”
Implement good husbandry practices and be proactive
Clint Roof, assistant professor of veterinary practice at the Texas Tech School of Veterinary Medicine, says one possible reason for increased anaplasmosis cases is the practice of shipping cattle infected with the disease across state lines to feedyards and backgrounding operations. Infected wildlife may also spread the disease.
Blood tests indicate anaplasmosis has infected an individual animal, although it can appear throughout the herd. Animals are often anorexic and weak due to anemia. An infected animal’s behavior may be confused with an aggressive form of rabies when oxygen-deprived animals chase producers or workers.
“Infected cattle can have increased urination, which isn’t uncommon with many diseases,” Roof explains. “They’ll have yellow or dark yellow urine. They won’t have blood-tinged urine, which is associated with redwater disease, caused by bacteria.”
Providing tetracyclines to infected animals is an indicated treatment. If animals are in the early stages, the disease should clear, but it can require many doses over some time.
“When giving injectable antibiotics, we tend to give one dose and three days later give another, for four treatments,” Roof reports. “I recommend adding tetracycline to feed or the water supply for up to 10 weeks with a VFD. Chlortetracycline is the only antibiotic approved to control anaplasmosis and may be fed for months.”
Roof says anaplasmosis is not going away unless ranchers and farmers take steps to prevent its circulation.
“That makes the onus on us as producers and stewards of cattle,” Roof warns. “We can mitigate and decrease the spread with good practices, such as changing gloves and keeping equipment clean. We can dip dehorning equipment in chlorhexidine or scrub emasculators between [animals] to slow the potential spread of disease.”
When implementing pour-on tick and fly control, Roof encourages producers to follow the product labels exactly so animals receive appropriate doses for their size to limit tick and horsefly populations. Unfortunately, sometimes animals are underdosed as a means to save money per head, or their weights are unintentionally estimated to be lower, affecting the success of the products.
Infected cattle may be harvested for food. According to Roof, carrier animals that do not show severe clinical signs are the easiest to treat. Cattle showing clinical signs over the age of two typically do not have a good prognosis. In 2021, it cost around $793 per head to treat.
“Infected animals may not be able to reach an appropriate weight before slaughter,” Roof concludes. “We can have abortion loss. These situations affect the rancher’s bottom line. Producers want to promote positive welfare in their herds. They want profitable operations and a healthy product for consumers. We can do that by practicing good husbandry. We must be active, not passive. We can’t hope anaplasmosis will just go away.”
