Justin Talley, Oklahoma State University Extension Livestock Entomologist
Anaplasmosis is a common disease in cattle and Oklahoma is considered an endemic state. This means that anaplasmosis will occur every year within Oklahoma with some variation on the intensity of this disease usually based on the strain of Anaplasma marginale. A. marginale is a bacteria that infects red blood cells and once an animal becomes infected they are infected for life. This bacteria does not harm the red blood cells directly but the cow’s immune response recognizes it when it reaches certain levels which then causes anemia due to the immune system killing the red blood cells that are infected. This will limit the amount of oxygen that is transported throughout the animal’s blood, which can then lead to aggressive behaviors exhibited by normally docile cows or bulls. Other clinical signs that animals are infected with the bacteria are extreme lethargy, yellowing of the mucous membranes, abortions, weight loss, and difficulty breathing. Most producers will not know they have an anaplasmosis problem until they see dead cows or bulls that are older than 2-years of age. This is why this disease can be so devastating because it targets some of the older stock in the herd, which have significant investment towards these animals.
First and most important is to consult with your local veterinarian so that they can develop a comprehensive plan to limit the impact of anaplasmosis. This relationship is important because the most commonly utilized control plan is to administer tetracycline antibiotics through mineral supplements or feed and the only access to this preventative treatment is to obtain a Veterinary Feed Directive (VFD) through your veterinarian. More severe infections can be treated with injectable antibiotics via an intramuscular injection of oxytetracycline administered multiple days and should be given under a veterinarian’s directions. A vaccine is available in some states and Oklahoma is approved for this vaccine. This vaccine does not prevent infection but anecdotal evidence demonstrates a reduction in clinical signs.
Now for the “People” component for anaplasmosis prevention, one of the most prevalent ways the bacteria is spread is through contaminated needles used to administer pharmaceutical drugs to cattle. In fact, a study conducted by Kansas State University demonstrated that six out of 10 uninfected animals became infected with anaplasmosis after treating one infected animal due to not changing needles between animals. Also, any instrument that penetrates the skin or comes into contact with blood will serve as a fomite and transfer the bacteria from infected to uninfected animals. These can include dehorning tools, tattoo tools, castration equipment and ear tagging tools.
Ticks are probably the next most common source of maintaining the bacteria in the environment. The reason for this is that ticks are considered a biological vector of anaplasmosis, which means that the bacteria can multiply within the tick, and when the tick feeds on a different animal, they are exposing that animal to higher levels of the bacteria. In addition, the main ticks involved are Dermacentor ticks that go unnoticed due to their preferred feeding locations in between the legs. Producers will have to put their animals through a chute to accurately determine if they have a Dermacentor tick problem by conducting tick scratches which is time consuming and stressful to the animals especially when the heat index is above 90°F. The male Dermacentor ticks are more involved in the transmission of anaplasmosis due to the more interrupted feeding patterns exhibited by male ticks to receive a complete blood meal. The male ticks will feed on more animals to receive their blood meal, which increases the risk of transmission.
Tick control can be difficult due the life cycle of the Dermacentor ticks that require more than one host to reach the adult stage. This means some of the ticks are on alternative hosts such as wildlife and control programs will have to be developed based on history of tick problems in certain pastures. Burning pastures in the spring will reduce tick populations for a period but the burning frequency would need to be yearly or at least utilized in a patch burning system where different parts of the pasture are burned each year to affect tick populations. The most successful means of tick control is the combination of pasture rotation usually in August away from pastures with historical tick issues and the use of a systemic products such as an ivomec or moxidectin type products.
Certain biting flies are also involved in anaplasmosis transmission but not all flies are involved in moving this disease from animal to animal. The two main biting flies that are implicated in anaplasmosis are horse / deer flies and stable flies. Horse and deer flies visit multiple animals to receive a complete blood meal because their bite is very painful and will cause animals to react quickly when bitten. This causes the feeding by these flies to be interrupted so they visit multiple animals that increases the transmission risk. Similarly, stable flies cause significant pain when feeding on the legs of the animals that will cause the animals to react that then interrupts feeding by this fly. The difference between ticks and flies related to anaplasmosis is that biting flies are mechanical vectors of anaplasmosis. This means that the bacteria does not replicate within the fly and the survival on the exterior of the mouthparts of the fly is very short. When these flies are involved in the transmission of anaplasmosis this usually means that there are infected animals present either within your herd or located very close. Flies are not efficient carriers of the bacteria but can certainly transmit it from an infected animal to a nearby uninfected animal.
Fly control for horse / deer flies is very difficult because only the females visit the animals and are only on the animal for short periods. The most effective means to limit the impact of these type of flies is to apply a pyrethroid spray in combination with using commercially available traps located in areas where the cattle are congregating throughout the day. The pyrethroid spray will act as a repellent and the traps will attract the flies away from the animals. This is not completely effective during outbreaks of large populations of horse / deer flies. Stable fly control can be achieved by managing old hay feeding areas because stable flies utilize these old hay feeding areas as breeding sites. The goal is to dry out the area underneath the initial hay layer because that is where the stable flies are developing as maggots. This is achieved by dragging an implement through the hay feeding area so that the area under the hay is exposed to allow drying. Stable flies will be active in early fall which coincides with fall infection patterns of anaplasmosis in Oklahoma herds.
Whether it is people, ticks or flies that are involved in anaplasmosis, the main concern is preventing the spread of this devastating disease. Working with your veterinarian is the most important aspect in managing this disease because in Oklahoma it is not a matter of “if” but rather a matter of “when” anaplasmosis will impact your cattle herd.