Management versus elimination of anaplasmosis

Dr. Jared Taylor explained the effectiveness of chlortetracycline, or CTC, in mineral for anaplasmosis protection versus disease eradication at the recent Oklahoma State University Beef Conference.

Taylor is an associate professor at the OSU Center for Veterinary Health Sciences. He teaches epidemiology and his research includes the molecular epidemiology of bacterial species involved in bovine respiratory and other diseases.

Anaplasmosis is a disease caused by bacteria named anaplasma marginale. The bacteria infects the red blood cells, or the oxygen carrying cells, within the blood stream. The body then destroys the red blood cells in an effort to eradicate the infection.

“When you destroy a large amount of red blood cells, you get anemia,” Taylor said. “The bacteria is actually relatively slow in proliferating disease so we’ll see a range of 14 to 45 days after exposure to this organism before we see clinical signs. With such a wide variation of days it becomes difficult to determine when the exposure occurred and how we can control it.”

Taylor says anemic animals with the infection tend to display symptoms of lethargy, not moving around, exercise intolerance, lack of appetite, weight loss, constipation, jaundice, rapid breathing, loss of breath or sudden death. Occasionally at the end stages of disease, animals can become aggressive due to hypoxia, or lack of oxygen, in the brain.

“If you don’t catch the first signs of infection and the cow lives through them you might see abortion and maybe something of an abortion storm in the herd,” Taylor said.

Anaplasmosis is a blood-borne disease so infected red blood cells must come into contact with the red blood cells of an uninfected animal to be transmitted. Biting insects such as ticks and flies are common disseminators but needles, tattoo and implant guns, as well as horn nippers, can also spread the infection.

“Anytime we have an instrument that draws blood from one animal and then goes into another, we have the possibility of transmitting anaplasmosis as well as other diseases,” Taylor said. “It’s important to adopt a biosecurity approach for keeping your operation safe.”

In terms of understanding the disease, it is important to recognize that once infected, the animal will remain infected with that organism as long as it is alive. If the animal recovers from the symptoms, there will be a back and forth going on between the bacteria and the animal’s body. The animal is able to control it enough that you will not see clinical signs.

“Generally speaking, the good thing is the animal is not going to be susceptible to the disease again because their body has learned to keep that organism, and even other strains, at bay,” Taylor explained. “The bad thing is persistently infected animals can serve as a source of infection for others for the rest of their lives.”

Understanding the effect of anaplasmosis

Oklahoma is in the endemic region and if you have cattle in the state, you are going to have to learn to deal with anaplasmosis. Taylor says there is a vaccine that has not been approved in all states but it has been approved in Oklahoma. However, it is not something you can purchase at just any farm store.

“You will have to work with your veterinarian and see whether or not they recommend it and there are some hoops you have to jump through,” he said. “The vaccine is not 100 percent and it’s expensive, so it’s not something that myself and other vets will recommend as an addition everyone should incorporate into their vaccine protocol.”

Young animals have a more robust ability to respond to the anemia. Pre-weaned calves are generally not going to show clinical signs. Taylor says they have a lot of bone marrow reserve capacity and produce enough red blood cells to replace the ones the body destroys. Yearlings may show modest clinical signs, but the main targets of the disease are adult animals that can suffer abortions, severe disease and sudden death.

Newly introduced naïve adults that have been added to an endemic herd are at great risk of contracting the infection. Adults already in a naïve herd are at risk if a carrier is introduced.

“If you have an overall infected herd, that doesn’t mean every one of the animals has the infection. So any of the adults that have escaped the disease up until this point are at risk of developing clinical signs,” Taylor said. “If you see clinical signs it’s important to treat the others as well because there is such a wide span for when animals can start showing indicators. Other infected animals may be many days down the road from showing signs and if we can get the drugs on board maybe they can avoid the symptoms.”

When an outbreak is detected, uninfected animals should be treated subcutaneously or intramuscularly with an oxytetracycline formulation. Clinically infected animals should probably be treated as well, but understand stressing those animals can lead to death so often times this is a judgment call producers and veterinarians must make.

“To be clear, if we’re treating with these parenteral products we will not be clearing infection from those animals that already have the organism,” Taylor said. “We’ll be trying to avoid clinical signs in any more animals.”

This means once you have the first case and you treat all the animals, the pasture needs to be assumed positive. It is an infected herd at that point because you did not eliminate it based upon this treatment. It is possible to cure animals of anaplasmosis symptoms, it just comes with hazards.

The best treatment for the situation

“Our understanding of getting rid of anaplasmosis has evolved a great deal with improvements in diagnostics,” Taylor said. “We used to think it was easier to clear infection than we understand it to be now. Treating an animal two or even three times, three to five days apart doesn’t clear infection. It’s not about how much drug you get into them, it’s about duration of treatment–a long exposure of this organism to the drug.”

If you manage to clear a previously infected animal of the disease, they can become susceptible again. Preventing reintroduction can be challenging because your neighbor’s flies cannot be convinced to stay on his side of the fence. If you want to eradicate it, you are going to have to do testing to figure out the prevalence within your herd to know where to focus your efforts. The only way they can remain resistant to clinical signs is if they are a carrier and their body stays on guard against the infection all the time.

“This organism is very effective at evading immunity and the animal’s immune system is not going to be able to prepare for it and prevent it from coming back if we’ve eliminated that carrier status, and that comes at a risk,” Taylor explained. “It requires at least four weeks of treatment with antibiotics at the expected interval. You can probably eliminate infection with use of oral antimicrobials as well such as CTC in the mineral. There is a probability of being able to do that but it takes a very long time–probably 80 to 90 or maybe even 120 days. We achieve a relatively low dose of the drug in the animal. It’s not enough to prevent infection but it is enough to prevent clinical signs in a carrier.”

Many people aspire to manage anaplasmosis symptoms, but remember, 90 days of oral treatment has the potential for clearing the infection so you have to be careful if you are trying to control it with mineral rather than eliminate it. Taylor recommends feeding the mineral for 30 to 45 days on and then maybe 30 days off. He says this will avoid clearing the infection from those animals, and will keep the symptoms away.

Additionally, just because mineral was fed for 90 days doesn’t mean the infection has been eliminated. It can only be presumed that those animals had sufficient mineral intake, so further testing is needed to know they are clear. Factors to consider

Taylor warns even if you do everything right, efficacy is not guaranteed. Intakes are independent and variable. Cattle may not have been supplied with enough mineral or bully cows may have pushed the others out. CTC is an important tool for managing anaplasmosis but obviously comes with some challenges.

“If you’re in an endemic area and or on a budget and certainly if you are a terminal producer, you may want to live with it and mass medicate your herd with a long lasting oxytetracycline when you have an outbreak. Then you want to feed the CTC 30 to 45 days on and 30 days off. Your ultimate goal is to maintain indemnity. If in contrast you’re in the Dakotas, Nebraska or Montana with a non-endemic herd and or have a higher budget or you are a seed stock producer then you still want to mass medicate and treat but also try to feed CTC continuously for 90 days or longer to clear the infection.”

Lacey Newlin can be reached at [email protected].