What is this new tick disease?

– Dr. Michelle Arnold, UK Veterinary Diagnostic Laboratory

Office of the State Veterinarian is warning beef producers to look for signs of Theileria infection (“theileriosis”) in cattle, with two confirmed cases in beef cattle recently reported in Kentucky. Theileria orientalis Ikeda is a microscopic protozoan parasite that infects the red blood cells of cattle, causing anemia. The disease is primarily transmitted by the bite of an infected Asian Longhorned Tick (Haemaphysalis longicornis) or by blood transfer through the use of contaminated needles and equipment. The tick can feed on many animal species, including humans, but the blood parasite only affects cattle. Once a cow is infected, it may take 1-8 weeks before she shows symptoms of disease.

Figure 1: Three life stages of the Asian Longhorned tick sized relative to the head of an insect pin. Nymphs and adults can transmit Theileria to cattle. Photo used with permission from Dr. Matt Bartone, NC State

There is a spring peak in disease incidence in March-April and a fall peak in September-October. There is no effective treatment for sick cattle or vaccine to prevent infections. However, once infected, cattle become carriers and are protected from new infections. There are no recognized long-term health or production effects from persistent infection. Theileria is not a public health concern and contact with affected cattle doesn’t pose a human health risk or food safety risk.

What to look for

  • The majority of infected cattle have limited or mild clinical signs. The symptoms are very similar to anaplasmosis, another tick-borne cattle disease that causes anemia.
  • Affected cattle show signs of anemia including lethargy, pale or jaundiced (yellow) mucous membranes, and increased respiratory and heart rates. Labored breathing may be mistaken for pneumonia, especially in young stock.
  • Affected cattle may be exercise intolerant and lag behind the rest of the herd or be off by themselves.
  • Affected cows may be off feed, have a fever, and sudden weight loss.
  • May see sudden death, especially in late pregnant and early lactation cows.
  • Late term abortions may occur due to lack of oxygen to the fetus with subsequent death of the calf. Metritis in the cow can follow. Breeding bulls may have decreased libido for 1-1.5 months.
  • Calves, especially 6-8 weeks of age but up to 6 months of age, may show symptoms.

What to do if cows show signs of anemia

  • Contact your vet. Theileriosis and anaplasmosis look almost identical so treatment with an approved antibiotic (LA-300 or Baytril 100-CA1) for treatment of anaplasmosis is recommended. However, if Theileria is the cause, there will be no response to the antibiotic therapy.
  • Stress and movement of affected animals should be minimized, as their reduced number of red blood cells lowers their ability to transport oxygen around the body. This can lead to collapse and death. Affected animals should be rested, given high quality feed and water, and handled only when necessary.
  • There is no treatment available for Theileria infection other than supportive care. Blood transfusions may be used for valuable animals. Recovery may take 1-2 months depending on the severity of the anemia.

Prevention and control of Theileria infection

  • Inspect cattle for presence of ticks: Routinely inspect livestock, pets, and humans for the Asian Longhorned tick (ALT). Parthenogenetic strains exist in the USA, meaning male ticks are not required to produce eggs and viable larvae. A female can produce 1,000-2,000 offspring without mating. A single cow can quickly become host to thousands of tick offspring that may cause death due to blood loss without a blood-borne parasite infection. The ticks are light brown and often smaller than a sesame seed. The adult female is about the size of a pea when full of blood (see Figure 1 above). All 3 life stages (larva, nymph and adult) may be present at the same time (see Figure 2). In cattle, check the head, neck, ears, flanks, armpit, groin, udder and under the tail (areas where the skin is thinner). Cattle that seem lethargic or unthrifty should be closely inspected for ticks.

    Fig. 2: Asian longhorned ticks on the ear of a cow that died due to anemia from the massive tick infestation (Photo courtesy of the UKVDL).

  • Manage the tick population on Cattle: The eradication or removal of ticks from a farm is virtually impossible. Ticks spend most of the time, nearly 90%, in the environment. Even though only a small proportion of the tick population is on livestock at any one time, treating cattle with a tick repellent will reduce the numbers that feed and develop into the next stage of the tick lifecycle. This will have an impact on the numbers of eggs that eventually get deposited in the pasture and helps manage the disease spread. Currently there are no acaricides labeled for use against the ALT. The use of pesticide impregnated ear tags, pour-ons, sprays, and back rubs that control the American dog tick and the Lonestar tick should provide beneficial tick control. There are field reports of success with macrocyclic lactone dewormers such as Cydectin® Pour-on and Dectomax® Injectable products.
  • Environmental Control to Reduce Contact with Ticks: This involves mowing pastures, especially shaded areas, and fencing cattle from wooded areas. Perimeter fencing of a minimum of 20 feet from wooded areas will reduce the number of ticks on the grazing area. All stages of the tick like warm, damp conditions and long grass. Avoiding long rank pasture that has not been grazed such as around the edge of crops and brushy areas will reduce the likelihood of animals picking up ticks. Keep in mind that wildlife can serve as tick hosts and move the ticks to new areas. Virginia Cooperative Extension has produced a fact sheet entitled “Managing the Asian Longhorned Tick: Checklist for Best Management Practices for Cattle Producers” that covers animal inspection, chemical control, and herd management options. It may be downloaded at https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/ENTO/ento-382/ENTO-382.pdf
  • Ease any underlying disease or stress: Cows in late pregnancy, early lactation and young calves (2-3 months old) are more susceptible to severe disease. Pay close attention to cows around calving, avoid trace mineral deficiencies, and vaccinate cattle against the immunosuppressive BVD virus.
  • Treat “new” animals: Treat cattle for ticks as they arrive to the farm and before moving cattle from one property to another to avoid movement of infected ticks.
  • Young stock: Calves should be closely inspected for ticks and signs of anemia, too.

If you suspect a case of Theileria infection, contact your veterinarian for advice. A blood test is available to test for this disease.