Growing Beef Newsletter
September 2025, Volume 16, Issue 3
Theileria and ALHT update
Grant Dewell, ISU extension beef veterinarian
Since Theileria [and the Asian longhorned tick (ALHT)] was identified in Iowa at the beginning of June, there has been a steady increase in the number of herds and counties that have become positive. Although the identification of new positive herds is not racing across Iowa, it is still prudent to be knowledgeable of the issue and vigilant with your herd. At the end of July, there were 7 positive herds in 5 counties, which had increased at the end of August to 11 herds in 8 counties. Although initially the positive herds were located in southeast Iowa, it has expanded to include South Central Iowa. Positive counties are Clarke, Davis, Decatur, Marion, Monroe, Van Buren, Wapello, and Warren. Counties in southern Iowa are definitely more at risk as the tick moves from Illinois and Missouri. Although southeast Iowa has good habitat for the ALHT, the tick is capable of surviving in other habitats, so it can spread to Central and Northern Iowa over time due to movement of cattle, deer, and birds.
Theileria is a protozoan parasite that infects red and white blood cells, leading to anemia and death in some cases. The parasite is carried by Asian Longhorned Ticks (ALHT), which amplify the disease as the parasite goes through a life stage in the digestive tract of the tick. Typically, cattle affected by Theileriosis will show signs of lethargy, anemia, and difficulty breathing. They may develop ventral edema, exercise intolerant, jaundice, and abortions.
For fall, southern Iowa should be aggressive at tick control. Fall-calving cows are susceptible to late-term abortions and stillbirths as well as clinical disease as they near the end of gestation. Young calves are also at risk as colostral immunity plays out and calves are stressed around weaning. Backrubbers or sprays will be most effective at keeping ticks under control in the fall. Cows should be in a good plane of nutrition with access to a good trace mineral supplement and receive a basic herd health program. If you suspect either Theileria or ALHT, have your veterinarian collect appropriate samples and submit them to the ISU Veterinary Diagnostic Lab.
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