Anaplasmosis remains one of the most persistent and frustrating vector-borne diseases affecting U.S. cattle herds. Caused by intraerythrocytic bacterium of the Anaplasma genus, usually A. marginale in cattle, this disease leads to hemolytic anemia and decreased performance, and it carries serious implications for herd health and production.
Whether you’re working with dairy or beef operations, maintaining awareness of anaplasmosis is important: Its distribution is broad, diagnostic interpretation is often challenging and management requires coordinated vet-client vigilance.
Anaplasmosis spreads through both biological and mechanical routes, making its transmission highly efficient in a range of production systems. The primary biological vectors are ticks in which the bacterium lives, as Dr. Bob Larson from Kansas State University describes.
“Anaplasmosis is one of those diseases that’s quite frustrating because it is transmitted by ticks primarily,” he says. “Anything that moves blood from one animal to another can [transmit it], but ticks fill an important role in that the organism can multiply inside ticks. So not only is it physically moving blood from one animal to another, it actually injects a bigger dose than what it took in.”
Expanding Geography and Shifting Risks
Anaplasmosis remains especially enzootic in southern Atlantic, Gulf Coast and south-central states; however, reports of infection now span most of the country. A 2020/21 survey of Ohio beef herds found a statewide Anaplasma spp. prevalence of 38.5%, with some farms testing over 50% positive. Older cattle were significantly more likely to be infected.
As tick ranges expand with shifting climates, anaplasmosis affects greater numbers of naive cattle, which can lead to big problems. Larson explains that the disease is fairly common in southeastern U.S., therefore the cattle there have more resistance and are less affected. However, a recent expansion of the tick range in Kansas had a big impact on herds.
“In the southeast and eastern portions of the state, anaplasmosis has been present long enough that a lot of the cattle have some immunity, and we don’t see the big health problems. You certainly see an occasional animal gets pretty sick, but you don’t see the big health problems,” he says. “A few years ago, the disease moved into more of the central and a little bit farther west into the state, and those herds were really susceptible. We saw some pretty bad disease outbreaks and animal deaths.”
Control of these ticks is also challenging. These pests are very tough to kill, and the existing tools for tick population management aren’t quite what we wish they were.
“Some insecticides work, but only usually for a short period of time,” Larson says. “Things like burning pastures and burning areas where ticks congregate help a little, but they’ve just not given us the tools to really drive the population of ticks down in a pasture where we know we have problems.”
Mechanical transmission remains equally important. Even in areas with low tick pressure, proper use of equipment to minimize contamination is imperative.
“As you’re working with cows, if you’re castrating, dehorning, anything where you’ve got metal instruments on syringes involved where you’re potentially transferring blood from one animal to the next, is a very effective way to spread anaplasmosis,” says Mark Johnson, Ohio State University Extension specialist. “Swapping needles animal to animal, making sure we don’t do anything to permit that blood from moving from one animal to the next, is a very important step in controlling anaplasmosis.”
Working With Infected Animals
There are some key considerations when working with cattle suffering from anaplasmosis.
- Severely anemic cattle could be unsafe to handle.
With lower red blood cell counts, there is a lower amount of oxygen being delivered to the brain. This can cause animals to become aggressive.
- Exercise can be dangerous or fatal.
Walking an anemic cow long distances can precipitate collapse and death.
“If I identify some animals that are affected, I don’t necessarily want to walk a mile to a squeeze chute. I really have to be cognizant of the fact that exercise is not a good thing at this point,” says Dr. Fred Gingrich, executive director of the American Association of Bovine Practitioners.
- Treatment is helpful, but not necessarily curative.
Long-acting tetracycline antibiotics are the primary therapeutic option and can improve clinical signs and survival. However, treated cattle often remain lifelong carriers — an important point for herd-level planning.
“The sooner we identify [an affected animal], the more effective the treatment is,” Gingrich says. “The treatment, I will say, is not curative. It’s not going to get rid of anaplasmosis. It may take care of some clinical signs, but that animal is going to have to rebuild its blood cells.”
Managing Anaplasmosis
Because anaplasmosis spreads in multiple ways and can be hard to control once established, a good vet-client relationship and helping producers stay ahead of the disease is essential. This starts with assessing the herd’s risk, screening new or high-value cattle before they move and setting up biosecurity steps that limit both tick exposure and mechanical transmission. Good communication around handling practices, instrument sanitation and seasonal vector activity helps prevent problems before they start.
