April 6, 2020
It’s been said that reproductive losses are the single most important barrier to a profitable ranch. Certainly, controlling input costs is important. But here’s the bottom line: You can’t sell a calf that’s never born.
Indeed, anaplasmosis — or “anaplaz,” as it’s commonly called — may have been a forgotten disease. Not any more. It’s found in 48 states and is a growing animal health problem.
More to the point: There’s a pretty good chance you have it in your herd — especially if you live in warmer, more temperate climates.
“We hear about it a lot more,” says Kathryn Reif, assistant professor in the Department of Diagnostic Medicine/Pathobiology in the College of Veterinary Medicine at Kansas State University.
“We don’t have a lot of great records from the last several decades on the prevalence, but we’ve been hearing a lot from producers that they’re experiencing more deaths [in severely infected adult cattle] or more open rates, loss of calves [due to abortions].”
And the results of testing show anaplasmosis is prevalent. “So it seems it’s more in the producer mind sphere right now as a possibility.”
In fact, her lab cooperated with the K-State Veterinary Diagnostic Laboratory on a statewide survey from 2016-17, testing samples from 925 cow-calf operations across the state.
“We found that 47% of beef cattle herds in Kansas are actively infected with anaplaz. In the eastern half of the state, that jumps to about 80%,” she says.
“And that’s just at the herd level. So within a herd it could range from 10% to 100%, just depending on management practices at that particular operation.”
In addition to the Kansas study, several other anaplaz surveillance studies have recently been done, or are currently going on, in other states.
Studies looking at animals going to harvest found around 30% infection in individual animals in Mississippi. Reif is assisting with a survey in Arkansas that’s finding about 50% infection prevalence in individual animals there.
What’s the cause?
Anaplasmosis is a bacterial pathogen that lives within the red blood cells of cattle and is spread by Dermacentor species ticks. Ranchers will know them by their common names, the American dog tick and the Rocky Mountain wood tick. While calves can become infected, it’s generally adult animals 2 years old and older where the disease is more apt to show itself.
“That first wave of bacteremia, the bacteria level gets really high, and the animal’s spleen starts clearing out those infected red blood cells. And if it clears out too many of them, that animal becomes anemic pretty quickly,” Reif says.
The loss of red blood cells leads to a decreased oxygen-carrying ability, which leads to clinical signs of anemia, says A.J. Tarpoff, K-State Extension veterinarian. The problem is, the first clinical sign a beef producer sees is often a dead animal. But early signs can be lethargy — or on the flip side, acting wild or crazy.
For most animals, however, their immune system kicks in, takes care of the rising bacteria levels and controls the infection. “But the immune system doesn’t eliminate the infection,” Reif says. “So that animal now becomes a persistent carrier and reservoir for subsequent transmission events.”
Over time, those animals will likely be culled because they’ll have a greater potential for reproductive problems. But once you get it in your herd — unless you’re actively screening and removing infected animals — it’s extremely difficult to get rid of.
Tick transmission is the main way the bacteria are transmitted from one animal to another. The larvae and nymph, the first two stages of the tick life cycle, live in the environment and feed on rodents and other small animals. It’s the adult ticks that are associated with transmission, because this is the life stage that likes to feed on large animals like cattle, Reif says.
The ticks are uninfected in the environment. However, the adult ticks will seek out larger animals like cattle to feed on. In the case of anaplasmosis, it’s the male tick that’s the perpetrator.
If the male tick takes a blood meal from a persistently infected cow, he acquires the bacteria, which then amplifies in the tick’s salivary glands. “Now he’s looking for a female tick to mate with,” Reif says. After mating, the male tick reattaches and introduces the bacteria into the blood of the animal. If the animal the female tick is on is naïve for anaplasmosis, that animal is now exposed to the pathogen. One infected tick is sufficient to transmit this pathogen.
If the male tick finds a female on the same cow, her immune system is already fighting the infection, and clinical signs won’t reappear. But if the male tick moves from one cow to another through physical contact of the animals, and that cow is naïve, infection can occur.
Control is possible
While the disease is difficult to eliminate once it infects your herd, it can be controlled. Having a strong veterinary-client-patient relationship is extremely important when developing a control plan, Tarpoff says.
“My first suggestion is, know the status of your herd,” Reif says. “That doesn’t mean test all your animals, but test a subset; and then, based on the results, come up with a management strategy, choosing where you’re essentially willing to assume the costs of having an anaplasmosis-positive herd.”
That’s where your vet comes in. “A local veterinarian can help establish risk of infection and determine the realistic cost of the disease to an operation,” Tarpoff says. “A true estimation of costs should at least include diagnosed deaths and abortions. Then consider any control strategies you may want to employ.”
The most obvious is to control the tick. Given the duration of efficacy for many products, however, Reif says obtaining season-long tick control for the species of tick that transmits anaplaz can be difficult. While dusters and oilers can help, controlling these particular ticks can be tough, she says, especially for a pasture or range operation where the cattle aren’t handled again after turnout.
The Dermacentor ticks that spread anaplasmosis have a long life cycle. The larvae and nymph stages live in the pasture and find small rodents as hosts. It’s when they become adults that they seek out larger animals, like cattle.
If you’re not in an endemic area, your herd is clean and you want to keep it that way, a robust biosecurity program is essential. That’s because cattle can travel many miles as commerce takes place, and infected animals can end up just about anywhere.
Quarantine any animals you bring into your herd until you know their health status. Buy your bulls from a seedstock supplier who can guarantee anaplasmosis-free status.
If you’re in an endemic area, you can control the disease as best you can, or simply accept that it’s there and you’ll likely sustain some anaplasmosis-related losses.
In fact, Reif suggests that if you are in an endemic area and know your herd is infected, consider buying bulls from an infected seedstock herd. It’s a tough pill to swallow to lay down a big wad of money on a naïve bull, bring him home and then he dies from the disease.
The bacteria can also spread from equipment. “Hypodermic needles are very efficient at spreading the disease,” Tarpoff says.
“A 2010 study showed that six of 10 ‘clean’ animals became infected after needle injections following a positive animal. Changing needles between each animal not only eliminates the transmission, but also helps curb other bloodborne diseases,” he says.
Any instrument or tool that comes in contact with blood should be cleaned and disinfected after each animal. In addition to needles, consider ear taggers, dehorning tools, castration knives and any other tool that might come in contact with blood.
“Chlortetracycline also can be fed to cattle during the transmission period to help control anaplasmosis,” Tarpoff says. But keep in mind that an antibiotic won’t eliminate the pathogen, but can reduce the likelihood of a clinical case, he says.
Reif adds that medicated feed falls under the veterinary feed directive, so you’ll need a prescription from your vet. And the efficacy of the antibiotic may be reduced if the bacteria has developed resistance.
What about vaccines?
Currently, there is no commercially available vaccine to control anaplasmosis. There is an experimental vaccine that has no published data on its efficacy and requires permission from your state veterinarian to use, Tarpoff says. Since it’s a killed vaccine, it requires two shots the first year it’s used and annually thereafter.
However, hope is on the horizon. Reif and the folks in her lab are working to develop a vaccine that works on multiple strains of anaplasmosis, as well as reevaluating the efficacy of the antibiotics currently approved to control anaplasmosis.
Also, researchers at K-State and Iowa State University have recently collaborated on a new implant delivery platform to provide long-lasting protection against anaplasmosis infections. Iowa State holds the patent on the implant platform. The K-State Manhattan Innovation Center is exploring a partnership with Iowa State to further develop the technology.
A new vaccine with demonstrated efficacy will take time, but perhaps a long-term solution will someday be available.
Until then, beef producers will need to watch closely, manage carefully and work with their veterinarian to keep a lid on what was once a forgotten disease.
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