Finding a dead cow on a farm is very alarming. A farmer needs to know why, because there are many causes that result in a cow dying. In this particular case, a call to the veterinarian and some diagnostic tests determined that the cow had anaplasmosis. Anaplasmosis is a bacterial infection of concern to cattle producers because they might lose animals, or face restrictions when moving them across state lines (Purdue University, 2015).
While not all cattle infected with anaplasmosis die, it is important to identify and treat an outbreak before that happens. Anaplasmosis in cattle is caused by the bacterium Anaplasma marginale; it is infectious but not contagious between animals. It is transmitted by insect vectors, namely ticks and biting flies, as well as from infected animals to healthy ones via reused needles or contaminated livestock instruments. Once infected, the animal’s red blood cells are destroyed by the bacterium. Red blood cells are responsible for carrying oxygen, so when they are destroyed the animal is unable to properly circulate oxygen throughout the body. Without treatment, anaplasmosis causes severe anemia and subsequent death. The severity of disease is directly related to the animal’s age, as older cattle are more susceptible to disease than younger animals (Tabor, 2015).
Signs of anaplasmosis include:
- Weight loss
- Loss of appetite
- Severe anemia and resulting aggression
- High fever
- Labored breathing
Originally, anaplasmosis was considered a disease of only ruminant animals, such as cattle, goats, buffalo, and sheep. However, there are many bacteria in the Anaplasma genus that can also infect dogs, humans and horses. Human anaplasmosis is transmitted via tick vectors but can also be transferred in blood transfusions or via organ transplants. Hunters can contract the disease from butchering infected white tailed deer, so gloves should always be worn when doing so (Pennsylvania Game Division, n.d.).
Transmission and Diagnosis
Ticks and biting flies (vectors) are the most common forms of transmission of anaplasmosis. The blacklegged tick (eastern & central U.S.), which also carries Lyme disease, and the western blacklegged tick (west of the Rocky Mountains) can carry anaplasmosis (CDC, 2019) and infect an animal via tick bites. Blood-contaminated dehorners, needles, ear taggers and other livestock instruments can also spread the disease (Whittier et al., n.d.), when they are not cleaned and disinfected after each use (or when needles are reused).
Veterinarians can diagnose anaplasmosis from clinical signs and via stained blood smears, which are cheaper but less sensitive than PCR (a molecular diagnostic tool). After taking a blood sample, the vet may also run a packed cell volume blood test. This test is a measure of how much of the blood is made up of blood cells versus other materials (plasma). Measuring the packed cell volume allows the veterinarian to assess how far the anemia has progressed in the animal (Ward & Powell, n.d.). This is helpful to determine how likely the animal is to survive and what treatment regimen would best fit the herd.
In early stages of anaplasmosis infection, tetracycline drugs are effective. In more severe cases, blood transfusions can be helpful to increase survivability (Tabor, 2015). Tetracycline drugs do not outright kill the anaplasmosis organism, as they just stop the disease from progressing, and instead rely on the animal’s immune system. The animal’s overall fitness must be in good standing to overcome the infection, but this poses a problem for immunocompromised animals, and animals that have progressed to the severe stage (Payne, n.d.).
Infected animals also require supportive care including rest and close access to food and water, because the resulting anemia from the infection can make cattle very weak. Producers might choose to treat with medicated (chlortetracycline) feed to avoid stressing the animals (Ward & Powell, n.d.). It can take three months for cattle to recover from an infection (Whittier et al., n.d.).
Cattle that recover from anaplasmosis do not clear the infection but become lifelong carriers. It comes with pros and cons; the cow(s) will most likely not become sick with anaplasmosis. However, the animals will become a reservoir for infection within the herd, increasing the likelihood of transmission to uninfected animals (Payne, n.d.). Producers must consider this when deciding to move animals on and off their farms, and practice preventative measures on the farm even after an outbreak has passed.
Identifying an Anaplasmosis Outbreak
Anaplasmosis outbreaks occur when there is some combination of carrier animals, vectors (ticks, biting flies) and susceptible animals. In areas where anaplasmosis is not endemic, take note of any cattle that have died from unknown causes and have them examined by a veterinarian, as the first sign of an anaplasmosis outbreak is usually an unexpected dead cow (Whittier et al., n.d.). During an outbreak, producers should pay attention to the circumstances surrounding it to determine where the weaknesses are in their biosecurity protocols.
Seasonal outbreaks occur when biting flies and ticks are active, so they can be suspected as a source of transmission. Biting insects usually cause a first and second wave of infection. The first wave generally has a small number of cases, but the second wave can be more severe because the biting insects are feeding on the weak cattle from the first wave, and then transmit anaplasmosis to uninfected cattle. Sick cattle are perfect hosts for biting insects because they are unable to fight them off. The insects generally transmit anaplasmosis between animals within a short period of time, so the disease is most likely to spread when animals are close together, such as being clumped together in pastures. In cases where insects are the most likely cause of the outbreak, pest control and antibiotic use are usually the best defense.
In winter, when insect transmission is unlikely, stress can cause signs of infection in cattle that were infected previously. Stress in cattle should be managed closely and minimized as much as possible. Possible sources of stress could be nutritional or environmental, such as an unbalanced ration or a drafty barn. Similar to how humans get sick when we are run down by stress, the same can happen to cattle.
When transmission of anaplasmosis is due to reusing livestock instruments without cleaning and disinfecting them properly, the pattern of infection is different. While transmission via biting flies may produce staggered cases, transmission via livestock instruments causes many animals in the herd to be infected all at once. Infection usually occurs four to six weeks after a procedure with contaminated instruments, such as vaccination, dehorning, tattooing and castration (Carpenter, n.d.).
Preventing and Managing an Outbreak
When an outbreak and the cause have been identified, the next step is containing and managing it. The herd should be tested for anaplasmosis and separated into carriers and non-carriers. Those groups can be maintained separately, or one can be culled for easier management. Depending on the phase of infection they are in, carriers can be treated with tetracyclines.
If a lot of animals are carriers, producers may decide to have a 100 percent carrier herd. However, this decision comes with a lot of considerations, as carrier animals cannot be moved between some states, and if susceptible cattle are introduced into the herd, they could become extremely sick. If susceptible cattle are introduced into a carrier herd, they can be treated with tetracycline drugs to hopefully make the inevitable infection less severe.
During seasons when biting flies and ticks are abundant, entire herds can be systematically treated with tetracycline drugs. Chlortetracycline in the form of medicated feeds can be given at any time of year (Carpenter, n.d.).
It is obvious to see that most of the solutions to managing an outbreak involve the use of antibiotics on a large, even entire herd, scale. However, antibiotics should not be considered risk free, and liberal use of them can have consequences. Firstly, antibiotic treatments should not be used on animals that are in the later, more severe stages of anaplasmosis infection because they will be ineffective at that stage, and the additional stress of administering medication may worsen the animal’s condition (Carpenter, n.d.).
The overuse of tetracycline drugs contributes to widespread antibiotic resistance. When tetracycline drugs are used on a widespread basis, they can leach into the environment via manure and can contaminate surface water and soil (Granados-Chinchilla & Rodríguez, 2017). This is especially true with the use of medicated feeds. Because of this, using tetracycline antibiotics should not be taken lightly or considered a long-term solution.
Preventing an anaplasmosis outbreak involves limiting exposure to insect vectors. While it is impossible to completely eliminate the presence of biting flies, the application of insecticides (dust bags, insecticide ear tags, animal sprays, etc.) is helpful to limit exposure. Producers can also rotate pasture use so that cattle graze in areas that have lower fly populations during the vector season (Carpenter, n.d.).
Wildlife biosecurity measures should also be investigated to minimize risk. Wildlife and livestock can be reservoirs for infection. Deer and elk can be infected with A. marginale, so wildlife management in an agricultural setting should be considered. Some solutions would be to put up fencing to keep deer out, or planting unpalatable, “deer resistant” plants around the perimeter of a pasture to deter them.
To prevent transmission via contaminated instruments, they should be changed out or cleaned and disinfected between uses. While this takes additional time and can be tedious when producers are working many cattle, it can prevent losing cattle later.
While anaplasmosis is a bacterial infection that can turn deadly, there are many ways to prevent an outbreak or manage one if it happens. As outlined above, anaplasmosis can be transmitted via insects or contaminated instruments, so pest control and disinfecting livestock instruments are vital to preventing outbreaks. For other general biosecurity recommendations, see Healthy Farms Healthy Agriculture recommendations.
Carpenter, Z. L. (n.d.) Anaplasmosis in Beef Cattle. Retrieved from https://agrilifeextension.tamu.edu/library/ranching/anaplasmosis-in-beef-cattle/
CDC. (2019). Anaplasmosis Transmission. Retrieved from https://www.cdc.gov/anaplasmosis/transmission/index.html
Granados-Chinchilla, F., & Rodríguez, C. (2017). Tetracyclines in Food and Feedingstuffs: From Regulation to Analytical Methods, Bacterial Resistance, and Environmental and Health Implications. Journal of analytical methods in chemistry, 2017, 1315497. https://doi.org/10.1155/2017/1315497
Payne, C. (n.d.). Control of Anaplasmosis in Missouri. University of Missouri Extension. Retrieved from https://extension2.missouri.edu/g7705
Pennsylvania Game Division (n.d.). Anaplasmosis. Retrieved from https://www.pgc.pa.gov/Wildlife/WildlifeHealth/Pages/Anaplasmosis.aspx
Purdue University. (2015). Purdue vet: Cattle farmers should watch for anaplasmosis. Retrieved from https://www.purdue.edu/newsroom/releases/2015/Q4/purdue-vet-cattle-farmers-should-watch-for-anaplasmosis.html
Tabor, A. E. (2015). Anaplasmosis. Retrieved from https://www.merckvetmanual.com/circulatory-system/blood-parasites/anaplasmosis
Ward, H., Powell, J. (n.d.). Livestock Health Series: Anaplasmosis. [PDF]. Retrieved from https://www.uaex.uada.edu/publications/PDF/FSA-3081.pdf
Whittier, D., Currin, N., Currin, J. F. (n.d.). Anaplasmosis in Beef Cattle. [PDF]. Retrieved from https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/400/400-465/400-465_pdf.pdf
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