Theileria Ikeda Confirmed in New York Cattle Herd

By Blake Jackson

The Animal Health Diagnostic Center (AHDC) has confirmed the presence of Theileria orientalis, genotype Ikeda, in several cows and bulls from a New York State (NYS) cow-calf operation.

The affected herd had a history of acquiring cattle from various parts of the state and country, raising concerns about disease introduction through animal movement.

Theileria orientalis, a tick-borne hemoparasite, is the cause of bovine infectious anemia an emerging concern for the U.S. cattle industry. This parasite can trigger a range of clinical signs in cattle, including hemolytic anemia, fever, jaundice, lethargy, weight loss, reproductive failure, and even death.

All age groups of cattle are susceptible. There are three major genotypes found in the U.S.: Ikeda, which is highly pathogenic; Chitose, which may produce mild or no symptoms; and Buffeli, which is typically benign.

Once infected, cattle remain carriers for life, and the economic consequences can be significant. Infected animals may suffer from reduced milk production, increased health complications, and reproductive issues.

Mortality rates vary, with naïve herds experiencing up to 90% losses, though the average is around 5%. Regions where the disease is endemic tend to see lower mortality.

The Asian longhorned tick (Haemaphysalis longicornis), first reported in the U.S. in 2017, is the primary vector. However, the disease may also spread mechanically through biting flies, lice, or contaminated equipment like reused needles.

Diagnosis is typically confirmed through PCR testing on EDTA blood samples or spleen tissue in deceased animals. Genotyping can also be done via PCR, while blood smear examinations may detect the parasite but are less sensitive and cannot differentiate genotypes.

Coinfections with Anaplasma marginale and bovine leukosis virus (BLV) are frequently observed in affected cattle.

Theileria orientalis is a reportable disease in NYS. Currently, there is no approved treatment or vaccine for use in food-producing animals in the U.S., and vector control remains challenging.

The most effective prevention method is pre-movement testing to avoid introducing the parasite into disease-free herds.

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