source: Bovine Vet Online
An invasive tick carries a disease troubling to researchers because it slows animal growth while often going undetected. Its spread is only beginning to be understood.
The Ikeda strain of Theileria orientalis is known to be carried by the Asian longhorned tick (Haemaphysalis longicornis) in Australia and New Zealand, producing symptoms of anemia and jaundice similar to Anaplasma marginale, says Dr. Kevin Lahmers, DVM, a veterinary pathologist at Virginia Tech. The tick arrived in the U.S. as early as 2010, and outbreaks of T. orientalis in 13 Virginia counties are also counties where the tick has been found.
“It’s not like some foreign animal diseases, which have a massive mortality and morbidity that is going to cripple the industry,” Lahmers says. “It’s more insidious. In addition to death loss, it’s going to have potential impacts on growth rates and milk production that are going to cut into the bottom line and may not kill enough cows to reach national attention.”
Symptoms of anemia appear one to eight weeks after exposure, and while cattle typically appear to recover within another week or two, they remain chronically infected. Parturition and stress bring risk for recrudescence, and Lahmers is especially concerned about long-term slowed growth.
“Historically, if you had something that looked like Anaplasma, that’s what it was,” Lahmers says. “Now, there’s the potential it’s something else. Further workup could potentially be helpful.”
Asian longhorned ticks reproduce by parthenogenesis, enabling them to spread more quickly than typical tick species waiting on an opposite-sexed mate to also arrive in the area. Lahmers says the region east of the Mississippi River and as far north as Pennsylvania and Indiana is most at risk. However, the tick has also been identified in northwest Arkansas.
“It’s here, and it’s here to stay,” Lahmers says.
Carolynn Bissett, DVM, works with the Virginia Department of Agriculture and Consumer Services (VDACS). She says the agency first received a report of T. orientalis from a private practitioner veterinarian concerned about a cattleman losing 10% of his herd. The Asian longhorned tick was later identified on the same property.
“Since then, we’ve been doing a lot of outreach with producers and with veterinarians,” Bissett says.
Lahmers says he encourages veterinarians suspecting A. marginale to also test for T. orientalis. The test he developed is available from the Virginia Tech Animal Laboratory Services (ViTALS).
Testing can alert state agencies to the disease’s spread while also giving insight on treatment, Lahmers says. While A. marginale may respond well to tetracycline, there is no approved treatment for T. orientalis in the U.S.
“It’s almost worse to work the cattle,” says Lahmers, who encourages minimizing stress. “Make sure they have shade, food and water for a couple of days.”
In Australia, the disease causes high calf mortality. While this has not been commonly observed in the U.S., infrequent reporting may be due to lack of awareness. Therefore, monitoring slow-growing calves and pregnant cows is important.
Bissett has led outreach through the publication of several newsletters to veterinarians and producer groups. However, her primary goals are to monitor the disease’s spread to hopefully raise other researchers’ concern.
“We are just now beginning to know what it all means, and no one has clear answers at this point,” Bissett says.
VDACS livestock inspectors sample five cattle per week from each of Virginia’s 33 livestock markets, and samples are sent to Lahmers’ lab, she says. Right now, few researchers are considering the disease, and Bissett hopes documentation of its spread will change that.
Lahmers adds while Virginia officials and researchers are closely monitoring T. orientalis spread, other states and practitioners may want to become more proactive.
“They would need to monitor it repeatedly,” Lahmers says. “They might not have it now, but next year they may have it. Someone may have imported something.”
Readers seeking additional information may find these scientific reports on the potential spatial distribution of the Asian longhorned tick and a description of T. orientalis Ikeda strain in Virginia may be helpful. In addition, check out these past Bovine Veterinarian articles on tick control: