by Sandy Johnson, extension beef specialist, Colby and A.J. Tarpoff, DVM, beef extension veterinarian
A 2017 survey of herds across Kansas found Anaplasmosis positive herds in all reporting districts. See the May 2018 Beef Tips for a summary. It has been a more common problem in the eastern third of the state where prevalence is still higher, but increasingly noted across the state. The disease is caused by the Anaplama marginale bacterium which lives in the red blood cells of infected animals. Once an animal becomes infected, the body’s own immune system recognizes the abnormal red blood cells and removes the infected cells from the body. When the normal creation of new red bloods cells can’t keep up with the loss of the infected ones, the animal becomes anemic. The loss of red blood cells leads to a decrease oxygen carrying ability which results in clinical signs of disease. It usually takes about a month from time of infection to clinical disease but the range is 6-70 days. Although this disease can be spread during any time of year, clinical cases are most common during the late summer and early fall when transmission threats increase.
Transmission occurs by biting insects or equipment such as a needle or other veterinary instruments. Hypodermic needles are very efficient at transmitting this disease. A 2010 study showed that 6 out of 10 naïve animals became infected after needle injections following a positive animal. Changing needles between each animal not only eliminates this transmission, but also helps curb other blood borne diseases such as Bovine Leukemia Virus. Cleaning and disinfection between each animal should also be conducted with routine instruments such as ear taggers, tattoo pliers, castration equipment, or any other tool that comes in contact with blood. Certain tick species, mostly Dermacentor species (American Dog Tick), can amplify the pathogen in their salivary gland. After amplification, they expose the next cow to a large amount of pathogen. This is why we refer to these tick species as a biologic vector. Stable flies, deer flies, and horse flies can all mechanically transmit the Anaplasma organism from one animal to another.
As more herds become impacted by anaplasmosis, the first experience may be finding one or more dead mature cows or bulls. Anaplasmosis-infected cows become weak and lag behind the herd due to the lack of oxygen. If forced to move, cows may become excited, mean and fight to keep from moving. Movement of animals with severe clinical cases can even cause death. This change in behavior can occur in normally docile cows and increased awareness is need to prevent human injuries. Unlike most disease processes, clinical signs usually only occur in adults greater than 2 years of age. This is because younger animals have a greater ability to replace damaged red blood cells.
Control of Anaplasmosis is complex. Managing external parasites that transmit this blood parasite from one animal to another should always be at the top of the list of control measures. Season long control typically involves both environmental control and parasiticide use. Proper manure and feeding management that reduces decomposing feed will help decrease the breeding ground of some of these pests. Parasisticides are also targeted to specific pests during certain times of the year. Applications have many different modes including pour-ons, sprays, dust bags, ear tags, rubs, feed through IGR or larvicides, and environmental application. A mixture of two or more of these methods is often indicated to obtain season long protection. Many veterinarians recommend the use of feed-based chlortetracycline during critical times of the year to help control this disease. Feed-based use of antimicrobials now falls under the Veterinary Feed Directive. Questions have been raised on how effective the dosing is when feeding Chlortetracycline (CTC) to help control Anaplasmosis. A study conducted by K-State Research and Extension compared CTC administered by body weight daily to cows either in a capsule form or in medicated mineral in a small amount of grain supplement and individually hand fed to a non-medicated mineral also hand fed. A separate phase of the study provided medicated mineral free choice. The concentration of CTC in blood was similar when administered in a gel capsule or individually hand-fed. This indicates that hand fed formations in a feed are a reliable way to administer this product. When delivered in a free choice mineral (daily allocation for all cows provided each day), serum CTC concentrations were much more variable, which agrees with other studies that have measured and shown variation in daily intake of a free choice mineral. The full manuscript can be viewed here.
There is not a fully USDA licensed vaccine on the market for anaplasmosis. There is, however, an experimental vaccine that producers may be able to utilize in some states. Use of this vaccine does need approval from the state veterinarian where the animals are located. While the vaccine does not prevent infection, anecdotal reports show a reduction of clinical signs of at risk animals when proper label instructions are followed. Continued research is currently being conducted to potentially create new vaccine alternatives.
An example of the challenges of dealing with anaplasmosis are evidenced by one fall calving herd in central KS with over 50% of the herd positive. In the past, cows have been found dead at calving as the added stress of calving magnifies the anemia and lack of oxygen. This year, the producer has opted to feed cows in a drylot so CTC can be included in the daily ration to achieve more uniform intake and hopefully avoid these calving related deaths. Anecdotally, the owner’s spring calving herd has a much lower infection rate and uses a summer pasture with few trees in contrast to the more wooded pasture of the fall calving herd. Tick populations may be playing a key role in the transmission of disease within this herd.
Treatment of active infections with clinical signs has been a challenge for producers. Treatment has also been limited to the use of Oxytetracycline injectable formulations for decades. There has been a growing concern if some of these strains of Anaplasma marginale have developed resistance, or if treatment efficacy has been reducing. Recently another antimicrobial has been granted conditional approval for treatment of clinical anaplasmosis cases. Enrofloxicin (Baytril 100-CA1) is a prescription medication that can be used in replacement dairy heifers under 20 months of age, as well as all classes of beef cattle except those under 2 months of age and beef bulls intended for breeding. It is important to note that federal law prohibits any extra label use of this class of antimicrobial.
Producers should be aware of symptoms of anaplasmosis to identify the issue as soon as possible if it occurs and to avoid the unaccustomed and potentially dangerous behavior of a clinically ill animal. If anaplasmosis is confirmed in a herd, your veterinarian can help devise a management plan appropriate to the situation. Establishing and maintaining a strong Veterinary-Client-Patient-Relationship with a local veterinarian is extremely important when managing this disease. For more information on anaplasmosis see the videos from the 2016 Anaplasmosis Symposium or this fact sheet.