Many Virginia farmers may not realize it, but a new tick-borne disease is threatening their cattle and dairy animals, livestock experts say.
A hemoprotozoa, a single-celled microorganism, is infecting herds in at least 21 Virginia counties, including Madison, Fauquier, Orange, Greene and Louisa.
If Culpeper farmers spot its symptoms, one local expert—Dr. Amanda Weakley-Scott, a Madision veterinarian specializing in livestock—asks them to contact her.
The first case in Virginia was discovered in 2017 in Crozet, Albermarle County, and confirmed by Dr. Kevin Lahmers at the Virginia-Maryland College of Veterinary Medicine, said Weakley-Scott, a graduate of that school.
When two farmers in Rockbridge County lost cattle in 2018 to a mysterious disease, veterinarians confirmed the cattle had perished from a tick-borne protozoa, states an article to be published in Cattlemen magazine. Researchers believe the protozoal parasite, named Theileria orientalis (Ikeda genotype), is transmitted through the saliva of the Asian Longhorned tick after the blood-sucker has been attached to its host for two to three days.
Infected animals usually take one to three weeks to display acute signs, so the disease can spread in a herd for that time before any cattle show symptoms—jaundice, anemia, lethargy, labored breathing, fever, diarrhea, anorexia, weight loss and foamy nasal discharge.
Infected cattle typically die at a rate of 1 to 5 percent, but mortality can be as high as 50 percent, writes author Sarah Vest, a master’s student at Virginia Tech’s College of Agriculture and Life Sciences.
“These cows sure go down in a hurry,” said C.S. Fitzgerald, a Rockbridge farmer who lost three cattle to T. orientalis last fall. “They look fine one day, and then the next day, they’re dead.”
Hard to detect
Fitzgerald’s point is important, Vest wrote: By the time the disease’s symptoms surface, it may be too late to save the infected animal.
The disease may cause abortions or still births in pregnant cows, and can reduce milk production in lactating cows, Vest wrote.
“Cattle that are pregnant or recently calved seem to be particularly susceptible because they are under a lot of stress, and stress alone can make symptoms a lot worse,” reported Dr. Katie Clevenger of Blue Ridge Animal Clinic in Lexington.
Cattle that have recovered from the disease may relapse and display symptoms again when they’re under great stress, Vest wrote.
T. orientalis was probably responsible for four to five Virginia cases in 2018, 2019 and earlier, but went undiagnosed as producers and veterinarians suspected other causes, Dr. Weakley-Scott said in an interview.
“We didn’t know to test for it,” she said. “It has been a learning curve.”
As for the disease in Virginia, experts have no idea how the infected tick got here, whether it traveled on a bird, a suitcase or another vector, she said.
“It’s hard to say for sure where it came from,” said Weakley-Scott, who owns and cares for a cattle herd in Madison with her husband, Roger.
Last September, T. orientalis infected a group of cows in Madison that she cared for, Weakley-Scott said. It caused a big “abortion storm” in the animals, causing the herd of 40 adults to lose 24 calves, she said. Six cows died.
“That was devastating,” she said. “For a producer to lose half their calves, that’s the only income they may have.”
Experts tested for the normal things—bacteria, and a protozoa carried by coyotes, mice and cats, Weakley-Scott said. But no dice.
Then a veterinarian in Harrisonburg said, why not check for T. orientalis?
A sample sent to Dr. Lahmers at Virginia Tech proved positive, she said. When cattle are necropsied, signs of the disease on internal organs look yellow, like jaundice.
“Word about this disease has spread like wildfire among producers,” Weakley-Scott said. “They want to know more.”
Similarly, veterinarians and other researchers are eager to learn more. “If anybody here catches wind of it, we want to know about it,” Weakley-Scott said.
Weakley-Scott said she thinks producers will be OK once they and researchers improve their understanding of the disease. Its acute phase lasts about two weeks, but animals that survive will be chronically infected, she said.
“A lot of things are in the works,” Weakley-Scott said.
When Virginia veterinarians gather in a few weeks for their annual conference, T. orientalis will be the topic of one of their formal discussions, she said.
The disease is most widespread when the tick population grows in February to early June and again from late September to mid-November. It is hard to detect in the autumn, when weather routinely causes cattle to lose conditioning.
No oral or injectable medications exist for T. orientalis, nor has a vaccine been developed. A semi-effective New Zealand drug hasn’t been approved for use in the United States, and it can cause “meat withdawal”—keeping animals off the market—for up to 18 months.
To encourage recovery, it may help to give infected beef and dairy animals Vitamin B, intramuscular iron dextran, intravaneous fluids and blood transfusions, Vest wrote.
To reduce risk of infection, farmers are encouraged to regularly apply topical treatment for ticks, deter wildlife such as deer, and avoid sharing needles between cattle.
The parasite was first found in Asia, Australia and New Zealand and has caused major economic issues for livestock producers there, wrote the authors of a September 2019 research paper in the Emerging Infectious Diseases journal of the federal Centers for Disease Control. Authors at Virginia Tech and the Virginia Department of Agriculture, including Dr. Lahmers, contributed to the article.
“At this point, we don’t have solutions, but we’re working to develop them,” Lahmers told Vest for her article. “Supportive care is the best bet if cattle in your herd have been infected, as well as separating out symptomatic animals and minimizing their stress to help them recover as quickly as possible.”
“As if farmers are not challenged enough, Mother Nature has set up yet another obstacle for cattle producers to overcome,” said Carl C. Stafford, senior agent in the Virginia Cooperative Extension’s Culpeper office who is an animal-science expert. “And they will figure out a way.”