Researchers: Circovirus not primary cause of Midwest mystery illness
To steal a phrase from election night fodder, the canine illness reported first in Ohio and now in Michigan is still too close to call. Right now, researchers know what it isn’t. The primary cause is not canine circovirus. However, that doesn’t rule out testing for circovirus and possible coinfections in the hunt for a diagnosis.
The April release of a paper focused on canine circovirus published in Emerging Infectious Diseases and subsequent reports of an undiagnosed illness in Ohio dogs possibly related to circo prompted the Diagnostic Center for Population and Animal Health at Michigan State University College of Veterinary Medicine in Lansing, Mich., to take steps to add canine circovirus to its testing catalog. While Thomas Mullaney, MVB, MS, PhD, director of the Diagnostic Center, had predicted the need for a canine circovirus test, he could not have anticipated how quickly he would need it or the media attention that would surround it.
In early October, private practitioner Lindsay Ruland, DVM, went public with cases from her Ann Arbor, Mich., Emergency Veterinary Hospital that she believes are similar to the Ohio cases. Major media coverage ensued, and the Diagnostic Center was inundated with calls. Veterinarians wanted more information and to know how to submit samples.
Tony Forshey, DVM, state veterinarian at the Ohio Department of Agriculture, said in a recent podcast that the original samples from infected dogs in Ohio were being tested at the University of California-Davis, where authors of the Emerging Infectious Diseases paper are doing circovirus research. “We share our samples—we split them and share them—so that everybody can be working on this to get a diagnosis as quickly as possible,” Forshey says. “We’re still uncertain of what the primary cause is.”
Still in the very early stages of testing, Mullaney says as of Oct. 7 that canine circovirus has been found in two dogs in Michigan. But really, he says, a positive test tells investigators nothing. In the study published in Emerging Infectious Diseases, both healthy and ill dogs tested positive for circo. In fact, out of four ill dogs in Ohio, only one tested positive for circovirus; the second through the fourth dogs tested negative.
Presently, the only consistent clinical signs associated with the recent illness are vomiting and bloody diarrhea, which could have a wide range of contributing factors. Researchers are first working to rule out common causes. Forshey says they’ve done that with the Ohio cases. “Not many gut lesions, intestinal tract lesions, just the bloody diarrhea,” he says of the afflicted dogs. “We don’t think there’s a lot of gut damage being done.”
It’s a primary cause that is eluding them. “At this point in time we’re actually looking at the possibility—a very distinct possibility—that this is a coinfection, not just one organism. It may be viruses, it may be bacteria, those sorts of things, but one thing that is unique is this vasculitis,” Forshey says. “For example, one of the dogs actually had serum oozing through the gum tissue. It was very severe damage to the vascular system.
“One of the other dogs also had skin loss along the top of the loin area along the vorasic vertebrae back into the lumbar vertebrae due to lack of blood supply due to this vasculitis,” he continues. However, some dogs have had the vasculitis and some have not.
A spokesperson for the Ohio Department of Agriculture says that despite present uncertainty around the illness, canine circovirus has been ruled out as the primary contributor of the illness or as the cause of death in four dogs in the state.
Mullaney says all they can say about the role of canine circovirus at this point is that “it potentially might have been involved.” He says the bigger question is, does circovirus play a role in the illness when circo-positive dogs also test positive for another infection?
The authors of the UC-Davis paper only went so far as to conclude that “circovirus, alone or in co-infection with other pathogens, might contribute to illness and death in dogs.” Both samples testing positive for circovirus at the Diagnostic Center in Michigan also tested positive for coinfection. Mullaney says one case tested positive for parvo and circo.
Matti Kiupel, section chief for the Diagnostic Center’s pathology laboratory, encourages veterinarians to do a full diagnostic workup on the samples they submit—not just a circovirus test. “In order to link circovirus to the cause of a disease process, a full diagnostic workup (including a postmortem in the case of deceased animals) is essential,” Kiupel says in a release. “This also allows diagnosticians and pathologists to identify the full spectrum of infections and/or diseases that are present in a specific case.”
The Diagnostic Center is currently working on an in situ hybridization (ISH) technique researchers consider the next step in isolating a cause. ISH is a method that uses DNA or RNA probes to detect virus in microscopic lesions. “What we’re looking for in some of the lesions—is there something comparable?” Mullaney says. They are looking for evidence of vasculitis, evidence of necropsy in lymph node tissue, or infection of lymph nodes, for example. They are looking for any connection to porcine circovirus. “Anything that looks like that would be key for us,” he says.
In the meantime, he doesn’t want veterinarians to let pet owners panic. “The number one thing they really need to do is calm their clients,” he says. Like his colleague, Mullaney encourages veterinarians to do a thorough environmental and diagnostic workup on patients exhibiting clinical signs possibly linked to the illness. “Investigate all of the common causes—of which there are many—so you are not missing the common things,” he says. If the case still calls for testing, then submit it to the Diagnostic Center, he says.
Mullaney and the Ohio Department of Agriculture say there is no indication the illness is spreading. At the same time, he acknowledges that what they know now may change in the next few weeks, months or even years. “Our whole impression of circovirus in dogs may seem different than what we see today,” he says. “We’re in the very initial stages.”
Mullaney is confident that a diagnosis will be found soon. “My guess is we’ll get to the bottom of this in a matter of weeks.”