By Sarah Nardi
As an invasive tick species spreads westward across the U.S., so does the threat of a new disease in cattle. Researchers are sounding the alarm.
Since the Asian longhorned tick was first discovered in the United States in New Jersey in 2017, it’s been detected in more than a dozen states and migrated as far west as Kansas.
A big concern is that the tick is the primary vector for theileria, a disease that causes severe anemia in cows that eventually leads to death.
And as the tick has carved a path westward, so has theileria. Cattle in Pennsylvania, West Virginia, North Carolina, Tennessee, Kentucky and Kansas have tested positive for the disease.
When a case was first detected in a herd in Tennessee in July of last year, the state veterinarian issued a statement to warn cattle producers that the threat of theileria was growing.
“We know it’s already taken hold in several other Tennessee counties and will continue to spread,” Samantha Beaty said at the time.
Then, in August, the Kentucky Department of Agriculture announced two cases in unassociated herds.
State veterinarian Katie Flynn said Kentucky is working with producers to learn the clinical signs of theileria so that they can protect their herds. Those signs can be difficult to distinguish because symptoms of theileria are easily confused with another disease common to cattle called anaplasmosis.
Both diseases affect the red blood cells, causing cows to become anemic and lethargic. Theileria and anaplasmosis share symptoms like “pale mucous membranes and rapid respirations and pulse rates,” Flynn said.
When producers submit samples from sick cows that test negative for anaplasmosis, Flynn said the state recommends testing for theileria. She hopes that kind of surveillance testing can help catch new cases before they spread.
There is no approved treatment for the disease in the U.S., so the most effective method of protection is educating cattle producers on tick control, Flynn said.
“Because most of the animals that we see, by the time they are confirmed positive, they're euthanized or have died due to the severity of the condition,” she said.
Part of the reason theileria is so devastating to cattle is because it’s new to the U.S., said Cassandra Olds, a microbiologist at Kansas State University who studies the relationships between pathogens and hosts.
U.S. cows are naïve to the disease, Olds explained, meaning the animals have never been exposed to the pathogen. Without prior experience, their immune systems have no knowledge of how to contend with the disease.
“Outbreaks are always going to be the most severe when something is introduced to an environment,” Olds said. And at this point, only a statistically negligible portion of the U.S. cattle population has been infected with theileria.
But those numbers will continue to grow, along with the list of states in which the disease has been detected.
“It's eventually going to spread. You can't keep it away 100%” said Teresa Steckler, a commercial agriculture researcher with the University of Illinois Extension who specializes in the beef industry.
“I figure in southern Illinois, it’s a matter of a year-and-a-half to two years before we have it,” she said.
And because younger pregnant cows seem to be the most susceptible to the disease, Steckler said it could have “potentially devastating effects” on herd numbers.
“Because if you're losing pregnant females, you know, you're losing the calf as well as that female,” she said.
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