The Iowa Department of Agriculture and Land Stewardship said the state’s first case of Theileria orientalis Ikeda was confirmed in a cattle herd in Van Buren County in the southeast corner of the state.
The protozoan parasite infects the red and white blood cells of cattle, causing anemia and sometimes death. It’s carried by the Asian longhorned tick, which has spread to over 20 states since it was first detected in New Jersey in 2017. Iowa and Michigan are the latest to join the growing list.
“We haven’t had this parasite in Iowa before, that we know of, and we haven't had the tick before, and so we've got some pretty susceptible cattle right now,” said Grant Dewell, Iowa State University Extension and Outreach beef veterinarian and associate professor.
The case in Iowa includes heifers and bulls on pasture, according to Dewell. Roughly 20 have died out of a 100-head herd.
Dewell said anemia caused by the parasite is often exacerbated by an infestation of Asian longhorned ticks. The adults are smaller than a sesame seed but swell to the size of a pea when engorged with blood.
The females can lay 1,000-2,000 eggs without a male to reproduce.
“We don't normally see 1,000 ticks on an animal, except for this Asian longhorned tick, where we can get just a massive amount,” Dewell said.
Since there’s no approved treatments for the parasite in the U.S., livestock health experts say the best way to protect cattle is through tick control methods. Additional biosecurity can also help prevent the spread of the disease.
Dewell said producers should check their cattle for tick infestations often, especially in southern Iowa. Signs of the parasite include lethargy and difficulty breathing, and they may develop into jaundice, ventral edemas and abortions.
Veterinarians who see clinical signs should submit samples to the Iowa State University Veterinary Diagnostic Laboratory for diagnosis.
What about risks to other animals and people?
Asian longhorned ticks can feed on birds and a wide range of mammals, including dogs and cats. But Dewell said their preferred hosts are ungulates, which include cattle, horses, sheep, goats and deer.
The first known human bite in the U.S. was recorded in New York in 2018. While the individual did not become sick, some infectious disease experts are concerned. Pathogens carried by the tick have caused people in other countries to become seriously ill.
The Centers for Disease Control and Prevention (CDC) stated, “It is likely that some ticks will be found to contain pathogens that can be harmful to people. However, we do not yet know if and how often these ticks are able to pass these pathogens along to people and make them ill.”
An experimental study found the Asian longhorned tick likely does not spread Lyme disease. A separate laboratory study found it has the ability to transmit Rocky Mountain spotted fever, but this has not been found in nature.
The CDC said research is ongoing.
