Bovine theileriosis (Tie-lir-ee-OH-suhs) is a tick-borne disease caused by a protozoan blood parasite, Theileriosis orientalis. (Malaria is another disease caused by a protozoan blood parasite, but it is mosquito-borne.) It is often referred to as bovine anemia due to the chronic anemia that it can cause in cattle, and it affects many different species of cattle, buffalo and small ruminants like sheep and goats (Brandt, 2009). Signs in cattle include fever, lethargy, anemia, jaundice and diarrhea, but often animals can carry the disease and show no signs of infection (Iowa State University, 2019). Late term abortions and stillborn calves are common with this disease (Swilks et al., 2017).
There are a few different parasite species that cause bovine theileriosis worldwide. East Coast fever (T. parva) and tropical theileriosis (T. annulata) cause significant mortality, but neither organism is present in the United States (Morrison, 2015). All of these parasites are carried by ticks. For this article, the focus is on the T. orientalis species and its effect on cattle in the United States.
Infection Pathways for Bovine Theileriosis
The main infection pathway for bovine theileriosis is through ticks, such as the Asian longhorned tick. This tick is an invasive pest that was identified in the United States in 2017, but later found to have been present in the U.S. since 2010 (Oakes et al., 2019). It is important to manage this invasive tick species and other members of the “hard tick” family to prevent bovine theileriosis (Nicholson et al., 2019). The brown dog tick—native to the United States—is also a hard tick and can carry bovine theileriosis (CDC, 2020).
Depending on climatic conditions, these ticks can live in pastures for up to two years, but the disease is not present without the ticks (OIE, 2020). Besides tick bites, bovine theileriosis can also be transmitted via contaminated needles and other veterinary supplies, but is not spread via direct contact between animals, such as contact with urine, feces or saliva. However, calves can contract the disease from their mothers in utero and are particularly susceptible to it (Swilks et al., 2017).
According to the USDA’s Asian Longhorned Tick Situation Report and the CDC, the Asian longhorned tick has been found in the following states as of February 2020:
- North Carolina
- New Jersey
- New York
- West Virginia
The Ohio Department of Agriculture confirmed that an Asian longhorned tick was found on a stray dog last month, so the updated range of the tick also includes Ohio.
If a farmer suspects the presence of Asian longhorned ticks in their pastures, it should be taken as a serious threat to both animal and human health. It is described as an “aggressive biter,” and can collect in massive groups on a single host, causing significant distress and blood loss. Furthermore, the female Asian longhorned tick is able to reproduce without a mate, which allows just a single tick to easily start an infestation in a new environment (USDA APHIS, 2020).
Diagnosing Bovine Theileriosis
A diagnosis of bovine theileriosis is usually based on clinical signs and/or looking at stained blood smears under a microscope. In a 2015 study, PCR, a molecular diagnostic tool, was found to be more sensitive than other conventional methods used to detect bovine theileriosis (Khatoon et al., 2015). However, because many cows with this disease show no signs of infection, it can be hard to identify it in a herd.
Currently, there are no approved treatments for the T. orientalis strain of the disease, so prevention is key.
Prevention Strategies for Bovine Theileriosis
Prevention for bovine theileriosis includes appropriate quarantine and protocols for movement of cattle, as well as pest management. Where bovine theileriosis is endemic, adult cattle are generally immune. However, when cattle have been moved into these areas from places where it is not endemic, their health may be at risk because they lack immunity to the disease (Iowa State University, 2019).
When moving cattle from areas where bovine theileriosis is endemic to areas where it is not, it is important to quarantine those animals because they may be carrying the disease. Because infection can occur via blood to blood contact, needles and other veterinary supplies should not be reused between animals (Iowa State University, 2019). Moving animals is always a risk, and producers are urged to visit the Healthy Farms Healthy Agriculture’s Assessment page to determine what risks come with introducing new animals to a herd and what precautions should be taken.
Tick Control to Prevent Bovine Theileriosis
Managing bovine theileriosis includes the application of insecticides specifically for ticks in pasture settings (Iowa State University, 2019). Other control methods such as cattle sprays, ear tags and dips are also effective. Pasture rotation, keeping weeds mowed down in pastures, and allowing poultry to eat adult ticks in pastures before livestock are moved into the area are recommended as well (Cornell University). Producers who have found these ticks or are concerned about them should consult their veterinarian to make a tick control plan that works for their situation.
While humans cannot contract bovine theileriosis, samples of Asian longhorned ticks in Asia have been found to carry pathogens that are similar to anaplasmosis and other diseases (NEVBD, 2020). If one has found an Asian longhorned tick on themselves or their animals, it is important to safely remove it, and place it in a sealed bag. Contact a state health department, a veterinarian, or the state agricultural department for help with prevention, identification and more resources (CDC, 2020).
The Asian longhorned tick is a vector that can cause bovine theileriosis in livestock. It is important to recognize that management of this invasive tick species has a vital role in managing outbreaks of the disease, particularly because cattle often don’t show signs of an infection. While there is no approved treatment available for bovine theileriosis, prevention of the disease via pest control is crucial. Because of the severity of Asian longhorned tick infestations, their ability to reproduce without a mate, and the painful bites they produce, producers must take these pests seriously and develop strict protocols with their veterinarian for pest control. For more information about general biosecurity recommendations, visit HFHA’s Beef Cow Biosecurity Overview’s Pest Control section.
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Ohio Department of Agriculture (2020, July 31). Asian Longhorned Tick Confirmed in Gallia County. Retrieved from https://agri.ohio.gov/wps/portal/gov/oda/divisions/animal-health/news-and-events/07312020%20-%20Asian%20-Longhorned-Tick
Swilks, E., Fell, S. A., Hammer, J. F., Sales, N., Krebs, G. L., Jenkins, C. (2017). Transplacental transmission of Theileria orientalis occurs at a low rate in field-affected cattle: infection in utero does not appear to be a major cause of abortion. Parasites & Vectors. Retrieved from https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-017-2166-9
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