As an outbreak of severe, sometimes fatal, upper respiratory infections in dogs continues in Bozeman, Montana, veterinarians elsewhere in the state and beyond say they, too, are seeing serious cases of canine coughing.

Reports from practitioners in Georgia, Missouri, Wyoming, and Billings, Montana, posted on a message board of the Veterinary Information Network, suggest the problem is not confined to Bozeman — although whether the multi-state outbreaks are related is undetermined.

The Montana Department of Agriculture stated last week that it had received reports of dogs with coughs, fevers and difficulty breathing in Butte, Livingston, Red Lodge and Roundup, as well as in Billings and Bozeman. Practitioners in Bozeman told the VIN News Service this week that transmission appears to be slowing but isn't over.

"Our caseload is decreasing in numbers but we are still seeing cases," said Dr. Loni Odenbeck, co-owner of 360 Pet Medical and of Pet Emergency and Trauma Services. "We have seen six to eight cases this week. Prior to last week, we were seeing four to eight cases a day."

Odenbeck said the Bozeman outbreak, which began in late spring, has afflicted at least 1,000 dogs in a region known as the Gallatin Valley. She said three deaths are confirmed. Practitioners have engaged several diagnostic laboratories and pharmaceutical company laboratories in trying to identify the culprit or culprits, but answers are elusive.

"We are frantically trying to identify the source — it is not the flu (influenza H3N2 or H3N8 or any other type A influenza strain)," Dr. Christian Leutenegger, director of molecular diagnostics at Idexx Laboratories, Inc., told the VIN News Service by email. "We did find some other pathogens, but they are not really frequent enough to make them responsible for the outbreak."

Dr. Amy Glaser, director of molecular diagnostics at Cornell University Animal Health Diagnostic Center, concurs with the preliminary assessment that flu is not the cause. "No one has identified H3N2 virus in any of those dogs," she said. "There's no evidence that influenza is currently circulating, but we are trying to determine what is going on in the area."

Glaser added: "There's all kinds of stuff emerging in dogs. And there's always the possibility that it is something new."

Canine influenza is, however, circulating elsewhere in the country. A map maintained by Cornell shows the flu in Florida, Kentucky, Texas and Minnesota.

In other regions, it's not clear what pathogen is to blame for coughing, sneezing, feverish dogs.

In early August, Georgia practitioner Dr. Whadzen Carrasquillo, reacting to an article about the Bozeman outbreak, commented on VIN:

"We're seeing a fast spreading cough in the North Atlanta suburbs also. But it's not as bad as the one described in this article. Our respiratory PCR's [diagnostic tests employing a technique called polymerase chain reaction] are also coming up negative. Severe cough with phlegm spit-up, but dogs are alert and eating otherwise. Seems to take about a week for recovery. All kennel facilities around us are being affected. Curious."

By email this week, Carrasquillo said the outbreak in his region began during the third week of July. He estimated seeing 45 cases, one of which was in the past week. He said his patients "[r]esponded very well to anti-tussives and most pets felt otherwise OK during the disease. Most recovered within five days, with some taking a week or two for the cough to resolve completely."

Dr. Ben Leavens, a veterinarian in Joplin, Missouri, reported seeing 150 to 175 cases between mid-May and early July. Waves of respiratory cases a few times a year are not uncommon, Leavens said, but the latest stood out.

"This round has been unusual because of the secondary pneumonia after the often very mild initial symptoms," he posted on VIN. "Four deceased due to pneumonia, only one we were allowed to post[mortem] grew large amounts of beta hemolytic strep and enterobacter. Septic/toxic shock secondary to that was the cause of death, which occurred in less than eight hours."

In Billings, Montana, Dr. Dell Bertino, owner of Shiloh Animal Hospital, said her practice has seen "tons of coughing dogs" — more than 100 cases since May. Unlike in Bozeman, which is 145 miles west, none of the patients developed pneumonia.

Bertino said the hospital sent nasal and throat swabs from three cases for laboratory analysis. One was positive for Mycoplasma and one had mixed results for Bordetella — positive by PCR but negative by culture. The third case was not positive for anything tested.

Bertino said this isn't the first summer to bring a round of coughing in dogs. "Seems like [it's happened] the last few years every summer," she said by email. She recalled that last year, tests turned up coronavirus and parainfluenza.

In many of this summer's cases in Montana, dogs have tested negative for every suspect usually responsible for respiratory illness. Idexx's standard panel encompasses 11 agents: Bordetella bronchiseptica, canine adenovirus type 2, canine distemper virus (using Quant test), canine herpesvirus, canine parainfluenza virus, canine pneumovirus, canine respiratory coronavirus, H3N2 canine influenza virus, influenza virus A (H1N1, H3N8, N7N2), Mycoplasma cynos and Streptococcus equi subspecies zooepidemicus.

Cornell's panel is largely the same, except that it screens for canine adenovirus type 1 and not canine herpesvirus. The lab has newly added Streptococcus equi subspecies zooepidemicus.

Idexx's Leutenegger said that as the Bozeman outbreak began, "We immediately had phone calls into our consulting line asking why our respiratory panels were coming up negative. That immediately was suspicious to us, [suggesting] that we have a new entity, most likely a new virus, circulating in that population."

Delving further, Idexx ran samples submitted in May, June and July from Montana through a screening panel of 11 other, more exotic and lesser-known pathogens, Leutenegger said.

Still, no clear picture has emerged.

In cases in which patients test negative in the two sets of tests, Idexx is soliciting from practitioners fresh swab samples to submit to its virus discovery program, a research-and-development collaboration with investigators at the University of California, Davis, and University of California, San Francisco. Idexx is covering the expense of the further analyses.

"Nobody benefits from seeing these outbreaks and not being able to figure out what causes the problem," Leutenegger said. "This is one way we can improve our diagnostic offering."

The laboratory at Cornell, too, is putting out a call for more samples from acutely ill animals, meaning those that have been sick for fewer than two days. The lab seeks nasal and pharyngeal swabs sent by overnight delivery, and a blood sample 10 to 14 days later. During disease outbreaks, the Cornell lab performs additional testing at no additional charge to clients.