The Michigan Department of Agriculture and Rural Development (MDARD) reported April 7 that a fourth horse in that state has tested positive for equine herpesvirus-1 (EHV-1). The Saginaw County horse is the second to be found positive on a single quarantined farm.
On March 21, veterinarians euthanized an 8-year-old Quarter Horse gelding from Livingston County that tested positive for EHV-1 after attending a barrel racing event in Barry County in early March. A second horse from Livingston County and another from Saginaw County subsequently tested positive for the virus.
The two Saginaw County horses and the remaining Livingston County horse are under veterinary care.
"The MDARD continues to follow up on all horses potentially exposed to the first Michigan EHV-1 positive horse reported on March 19," the department said in a statement. "At this time, we consider all horses that attended a March 7 event in Barry County to be at the highest risk of exposure.
"We know from the progression of this outbreak that a secondary transmission is occurring," the statement continued. "In other words, horses that attended the March 7 event may have been infected, shown only minimal signs of disease (fever, possibly a runny nose), and spread the disease to another horse. If you have a horse that attended the March 7 event in Barry County and brought your horse home where there are other horses, those other horses are still at risk for getting and spreading disease."