Growing Beef Newsletter
November 2025, Volume 16, Issue 5
Keep an eye out for anaplasmosis this fall
Chris Clark, ISU Extension and Outreach beef specialist
With Thanksgiving just around the corner, vector-borne diseases like anaplasmosis are probably not top of mind for midwestern producers. However, it is important to keep an eye out for anaplasmosis yet this fall, especially considering how warm the fall weather has been. Anaplasmosis cases are often diagnosed in the fall or early winter following external parasite season. The longer warm weather persists in the fall, the longer external parasites are active, and the deeper into the fall and winter anaplasmosis cases may occur.
Anaplasmosis is an infectious, tick-borne disease of cattle caused by the bacterial organism Anaplasma marginale. Considered endemic in much of the U.S., anaplasmosis has been estimated to cost the U.S. beef industry $300 million annually. The disease is more prevalent in the southern U.S., but has been reported in nearly every U.S. state and can be found routinely in Iowa. Anaplasma marginale infects red blood cells, and as a natural response, the animal’s immune system attacks and destroys the infected red blood cells, causing anemia. This anemia causes decreased oxygen-carrying capacity in the blood and leads to a variety of clinical signs.
Here are five things you need to know about anaplasmosis:
- Clinical signs can be subtle and vague, making identification and diagnosis challenging. Often, the first sign of infection in a herd is simply finding a mature cow dead. Clinical signs of cattle with anaplasmosis include fever, weakness, poor appetite, constipation, pale or yellow mucous membranes, nervousness, and abortion of pregnant females. Younger animals are more resistant to disease, and most severe cases and deaths are seen in older animals.
- The pathogen is commonly transmitted from animal to animal by biological vectors and mechanical transmission. Biological vectors, such as some species of ticks, serve as additional hosts for the bacteria, allowing survival for a longer period and even multiplication within the vector organism. The bacteria are then transmitted to cattle when bitten by these biological vectors. Mechanical transmission can occur through the mouthparts of biting insects such as horse flies, stable flies, and horn flies. Mechanical transmission can also be iatrogenic, meaning it is caused by medical treatment. Iatrogenic transmission of anaplasmosis can occur through use of contaminated needles, dehorners, castration knives, implant guns, ear taggers, and OB sleeves. When processing cattle this fall and winter, use Beef Quality Assurance principles, including good hygiene and frequent needle changes, to minimize the risk of transmission.
- Handling severely anemic or hypoxic cattle is challenging. Infected animals are often nervous and agitated, and thus dangerous to handle. Handling animals with limited oxygen supplies can sometimes lead to death just from over-exertion and increased oxygen demand in this compromised state. Use caution to ensure personal safety and strive to use low-stress handling principles to minimize exertion of affected animals.
- There are management practices that can be utilized to protect your herd. Strive to control ticks and other external parasites. Change needles frequently and disinfect tools and instruments between each use. Utilize biosecurity practices such as quarantining new animals, obtaining health papers when purchasing new animals, buying from reputable sources, maintaining closed herds, etc.
- Management and control within infected herds can be complicated. Upon diagnosis, tetracyclines are the antibiotics of choice. In addition to antibiotic therapy, severe cases may require supportive therapy, and in cases of severe anemia, even with supportive therapy, prognosis can be poor. Other big challenges are the long-term carrier status of animals and the risk of reinfection in endemic areas. Recovered animals often become persistent carriers of the organism. These carrier animals have long-term immunity and rarely show clinical signs again, but they can serve as reservoirs of the pathogen within the herd. There are antibiotic protocols that can be used to attempt complete clearance of the organism from infected cattle, but cattle completely cleared of the pathogen will likely be susceptible to reinfection. In endemic areas with a high likelihood of reinfection, it can be challenging to determine how to most effectively manage this disease. Veterinary guidance is critical to most effectively prevent and control anaplasmosis. If you suspect you might have an anaplasmosis case or want more information about disease prevalence in your area, contact your local veterinarian.
Although winter weather can cause headaches, it can also help break the cycle of external parasites and biological vectors that transmit this disease. In the meantime, be vigilant in watching for clinical signs and in practicing biosecurity and effective management practices to protect your herd.
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