Controlling ticks to control anaplasmosis

In cattle, they are transmitters of anaplasmosis, a destructive and costly disease. Given the risk, they deserve our attention.

John Marks

Anaplasmosis has been spreading through the U.S. for the last few years, partially due to the movement of cattle from one area to another as carriers are brought into herds that were previously clean. Once there are carriers in the herd, anaplasmosis can be spread by horse flies, stable flies, deer flies, vaccination needles, ear tagging tools, castration knives, tattoo equipment and by ticks.

Anaplasmosis is a devastating disease both physically and economically. It is caused by a tiny blood parasite that attacks red blood cells, reducing the ability to carry oxygen through the body. Young animals seem to be able to produce enough new red blood cells to overcome the effects, but mature animals (2 years and older) cannot.

Affected cows become panicky from the lack of oxygen and can be hard to move or doctor, even dangerous to handle. Pregnant cows will normally abort their calves. The acute stage comes on quickly and often unnoticed until it is too late. By the time symptoms are seen, cattle are already in an anemic, oxygen-starved stage and can die when trying to move or doctor them.

Treatment with oxytetracycline has been effective when started early enough. With a Veterinary Feed Directive, chlortetracylines may be fed during the vector season to prevent the disease from progressing through the incubation stage. Regulations approve the use of chlortetracycline during an outbreak, but require daily hand-feeding of a mix containing chlortetracycline, or using an approved free-choice mineral formulation.

Recently, there have been reports of strains of anaplasmosis resistant to chlortetracycline, but it is still effective in most cases.

Although there are many ways the disease can be spread, ticks have been identified as the main reservoir. Most ticks go through four life stages, taking up to three years to complete. They require blood at each stage and can host on different animals. Rodents, birds, dogs, deer, coyotes and other animals can carry ticks at one stage, while cattle can be hosts at another stage.

Cattle pick up ticks as they move through the grass where ticks are hiding. Once they are on an animal, they move to an area where they can attach easily such as the ear or under the leg. When a tick draws blood from a host cow, if it is a carrier, anaplasmosis organisms will be taken in also.

These organisms are then carried and maintained in the salivary glands of male ticks for a long period of time. They inject a small amount of saliva when attaching and drawing blood, so the next host animal gets infected.

Biting flies, such as horse flies, transmit infected blood as they move from one animal to the next. In the same way, blood is transferred when vaccinating cattle if the same needle is used from one to the next. Any operation that transfers blood from one animal to another is a possible source of transmission.

Since ticks are a reservoir of disease, minimizing their numbers or their ability to feed on cattle is a major part of controlling anaplasmosis. Insecticides that protect the animal are available in several forms including sprays, pour-ons, dust bags and eartags.

Application must be timely so the insecticide is effective during the height of the vector season. The incubation period for anaplasmosis, until clinical signs are noticed, can be from three to eight weeks after infection, which means the source of infection is sometimes mistaken. Also, resistance to the current insecticides by ticks is becoming a concern.

Controlling tick populations in pasture is more difficult. Spraying is usually not practical or possible since it would mean covering large areas with an insecticide that would be approved for grazing. Best control is obtained in pastures by reducing the favorable tick habitat.

Ticks require a humid environment which tall grass and brush provide. Overgrown pastures with brushy areas along a creek are often prime areas for ticks. Heavy growth is also good habitat for rodents, which are one of the host animals for ticks. Mowing, grazing, and burning are all good ways to keep forage short and allow light and air to penetrate. Fencerows, tree lines and low, wet areas are hard to control and may need extra attention or to be fenced off.

A couple of newer ideas show promise as tick control measures. An experimental vaccine has been used to give cattle some resistance to ticks. Certain proteins, when formulated as a cattle vaccine, can interfere with tick function and reduce the number of ticks surviving on cattle. Vaccines are available or are being tested in some countries, but commercial use in the U.S. may be some time away.

Plant extracts have gained attention lately with the concern for continuous feeding of antibiotics. Field reports indicate good control of ticks on cattle in heavily infested pastures using a mineral formulation with cinnamon and garlic extracts. More research needs to be done in this area, as well as with vaccines, but both may prove effective and provide new tools for managing ticks.

Regardless of the preventative measures you choose, it’s critical they are preventative. What you do or don’t do to manage ticks proactively can be the difference between life and death for your cow herd.

PHOTO: Since ticks are a reservoir of disease, minimizing their numbers or their ability to feed on cattle is a major part of controlling anaplasmosis. Photo by Getty Images.