Veterinarians serve family-health role in suspected zoonoses

To test or not to test; that is the question

February 10, 2012 (published)
By Edie Lau; Bill Enfield

Photo by Dr. Radford Davis
Dr. Radford Davis, an authority in zoonoses, is not particularly worried about catching any diseases from his dog, Midnight.
Three young pet birds died one after the other within five months. The girl who owned them landed in the hospital soon after with a mysterious malady. Her family wondered: Might the birds hold a clue to the girl’s illness?

It was a natural question, their veterinarian, Dr. J.C. Burcham, said: “Three birds died, now the girl is sick, they all shared the same room. What’s wrong?”

The trouble is, no one knew what ailed the birds. Each died abruptly not long after undergoing a wellness exam that revealed no problem. A necropsy of the third bird failed to identify a cause of death.

When their owner, a young teenager in Kansas, ended up in the hospital with septic shock, her father phoned the veterinarian to ask whether she thought the girl’s illness might be connected to the birds’ deaths. Burcham racked her brain, fretted over what to do, then put the question to colleagues on the Veterinary Information Network (VIN), an online community for the profession.

“Should I call the state vet, even though I have no diagnostic results indicative of a human health concern?” she asked.

One of the veterinarians who responded was Dr. Radford Davis, an associate professor of public health at Iowa State University’s College of Veterinary Medicine and an authority in diseases that can transmit to people from animals. His answer was no. “Guessing about a zoonosis is really just an academic exercise unless the physicians work to diagnose the human patient,” he said.

Davis’s stance was consistent with answers he’s given over the years to similar inquiries. A VIN consultant on zoonoses and public health, Davis estimates that such questions pop up weekly on the organization’s message boards. In Burcham’s case, the series of bird deaths and their owner’s illness raised a logical question, but many times, veterinarians are asked to test apparently healthy animals — even if the human patient doesn’t have a definitive diagnosis.

“That’s really jumping the gun,” Davis said. “We don’t even know the exact disease in the person, let alone whether the (animal) could have transmitted it. Those kinds of questions really put the vet in a predicament.”

To help veterinarians respond to general requests for testing, Davis recently posted a commentary on VIN elaborating on his belief that, in many instances, testing should be discouraged.

“Testing of healthy animals for zoonoses is not indicated in most instances unless there is a high potential for the animal to infect others or in outbreak situations where a source is sought,” he wrote. “Some diseases in humans and animal populations are reportable at the state and national level (as well as international level), which also might require the testing of healthy animals to identify the source. Testing requires time, money, effort, and results may not correlate to risk of pathogen transmission or risk to human health. Depending on the type of testing done, testing may identify other zoonotic pathogens, which then creates problems in addressing their true risk to human health. False positive and false negative results can occur with some testing, and shedding of pathogens is often intermittent, so samples might be negative at any given point. Also, it should be noted that tests results from the animal will not change the course of treatment in the human.

“When testing an animal, the veterinarian should ask herself/himself: What will I do if the test is positive? What will I do if it is negative? What is the cost ... in terms of money, time, effort, actionable answers, emotion and health to all involved? Is the quest more academic, or is there a real need to test and find a source? If the animal is negative, where will the physician and/or veterinarian turn to next to find the source? ...

“A positive test in a healthy animal might mean euthanasia for that animal, or repeat cycles of testing and treatment, despite a low risk for future transmission. The animal may no longer be shedding, yet have evidence of past infection. A negative test might not truly be negative, giving a false impression of risk and a false sense of safety to owners. A false positive test result can lead to unnecessary outcomes: more testing, a greater financial input by owners, unnecessary treatments (creation of antibiotic resistance), and perhaps rehoming or euthanasia of the animal.

“Most zoonoses acquired directly from animals can be avoided by such measures as washing hands for 20 seconds after animal contact, washing hands after handling pet foods, avoiding contact with the animal's nose and anal regions, keeping the animal in good health, good husbandry practices, wearing gloves when contacting feces/litter, preventing pets from hunting/scavenging, regular fecal exams and regular veterinary visits...”

Perspectives differ

Davis’s stance against liberal testing is appreciated but not fully shared by experts on the human medical side. For instance, Dr. Cheryl Scott, an RN and DVM who heads the Calvin Schwabe One Health Project at the University of California, Davis, School of Veterinary Medicine, finds value in testing for “academic” reasons in some cases.

“If you don’t look, you’re not going to know,” Scott said. “You’re just going to keep these blinders on.”

As a general example of when looking and testing were productive, Scott pointed to the discovery that Lyme disease lurks in Northern California. Spread by ticks, Lyme disease was first identified in the Northeast, where it is most prevalent.

“Years ago when I first got out in practice, we never looked for tick-borne diseases,” Scott recalled. “When I started looking for things in my practice in Solano County (in California), sure enough, I started finding Lyme disease everywhere. Nobody thought it was out here. Well, it’s out here ... and it’s causing problems. It’s making dogs sick and it’s making people sick.”

Likewise, Dr. Carol Glaser, an MD and DVM in the California Department of Health Services, said she agrees with almost all of Davis’s comments, with some caveats.

“I don’t think it’s a simple yes or no (whether to test),” Glaser said. “It’s going to be highly dependent on which disease is being considered, how sick the human patient is, is it more than one patient, what type of animal is involved and the health status of the animal.”

Underscoring the need to examine seemingly unrelated events in animal and human health, Glaser pointed to the baffling set of circumstances in New York City that led to the discovery in 1999 of West Nile virus in the United States.

“There were dead birds on the lawn, people sick and zoo animals sick,” she recounted. “Nobody knew they were aligned. We didn’t even know West Nile virus was here. Having data from veterinary groups helped the people who deal with human medicine put it all together.”

In her role as chief of the encephalitis and special investigation section of the communicable disease emergency response branch in California’s Department of Health Services, Glaser said she has at times gone to great lengths to sleuth the source of a disease.

One such case occurred last May. An 8-year-old girl contracted rabies, and no one knew how. Her family owned a horse that died five months earlier, presumably of colonic torsion. “We actually had the horse dug up and tested,” Glaser said. Unfortunately, the “brain tissue was not ideal for testing,” according to an account in the U.S. Center for Disease Control’s Morbidity and Mortality Weekly Report, and the source of infection remained unknown. Remarkably, the girl survived.

While public health threats such as rabies call for aggressive action, Glaser said, other diseases don’t warrant the same level of response.

“Say you have a child with diarrhea and the dog also has diarrhea,” Glaser said. “You might know it’s Salmonella in the child; should you explore the dog? In those circumstances, I’d say probably not, for a number of reasons. Even if ... the dog had been the source, by the time you do the testing, the organism may be gone, so you’ve wasted the money and time. (And) if it’s positive, how do you know the kid got it from the dog? Maybe both ate (contaminated) chicken.”

But sometimes testing that’s not medically or scientifically necessary could be useful in educating patients or their families, said Dr. Larry Pickering, a professor of pediatrics at Emory University School of Medicine and a senior advisor to the director of the CDC’s National Center for Immunization and Respiratory Diseases.

For example, if a 6-month-old baby on a formula-only diet, living in a home with a turtle, came down with Salmonella sepsis, Pickering said, chances are that the baby contracted the pathogen from the turtle.

Some doctors might forgo testing, figuring by inference that the turtle is to blame. But Pickering said he would opt to test the turtle, if only to help the baby’s parents understand the hazards of keeping such a pet. “Some parents want evidence,” he said.

Cats and toxoplasmosis: a conundrum

In some situations, Glaser said testing is “absolutely not warranted.” For instance? To allay concerns about toxoplasmosis.

As most women who’ve ever been pregnant know, cats may shed the parasite Toxoplasma gondii in their feces. Healthy people may pick up and harbor the parasite with no problem, but a first-time exposure in a pregnant woman potentially is devastating to her fetus.

However, Glaser said, infected cats typically shed the parasite for only a short period — one to two weeks — and never again. Chances are much greater that a person will become infected by eating unwashed contaminated vegetables or undercooked meat, she said.

In fact, the CDC calls toxoplasmosis “the leading cause of death attributed to foodborne illness in the United States.”

While cats play an important role in the spread of the parasite — they are its only known definitive host — targeting the household pet is not justified, Glaser and others say.

Yet women widely believe that keeping a cat while pregnant is a significant risk. Dr. Michele Gaspar, a feline specialist in Chicago, said she once worked at a large animal shelter in which she saw “sobbing women bringing in their cats to give up” because of their fear of toxoplasmosis.

Pickering explained the thinking of physicians who advise pregnant patients not to keep cats: “If you get rid of the cat, you won’t get any diseases from the cat; that’s 100 percent,” he said.

“If you don’t get rid of the cat, make sure it’s immunized, make sure it’s dewormed, get rid of its fleas," he said, naming precautions that generally keep cats healthy, "and don’t clean the litter box." 

Pickering added: “If the obstetrician says ‘get rid of the cat,’ I’d support him or her. If you’ve seen a baby die of a disease that may have been acquired from a cat, that changes how you approach it.”

He acknowledged, at the same time, that cats may contribute to an expectant woman’s well-being. He personally witnessed this. “When my wife was pregnant with our baby, she had to be down (in bed) for three months. The cat was a lifesaver. It was with her all the time,” Pickering remembered.

“I think with the appropriate precautions, things can be handled well,” Pickering concluded. “We don’t want to go too far to the left or the right.”

Better communication needed

On one point veterinarians and physicians firmly are in agreement: they should talk to each other more.

“If there’s (a) question that (a) pet might be a source of infection to somebody who’s under medical care and the client is talking to the vet about this, then the vet could say, ‘If you give me permission, I’d be happy to talk to your doctor,’ ” Davis suggested.

Davis said he recommends this to colleagues all the time, but doesn’t believe such consultations happen frequently. “We (veterinarians and MDs) don’t really communicate too well,” he said.

Pickering agreed. The problem isn’t lack of desire, he said, but lack of time. “It’s another step in another process and we have so many steps and so many processes (already),” he said.

Whether in concert with physicians or not, veterinarians are playing a more prominent part in human health. The expanding role for small-animal veterinarians, in particular, in protecting public health was the topic of a 2007 commentary in the Journal of the American Veterinary Medicine Association

The authors, Drs. James S. Wohl and Kenneth F. Nusbaum, stated that small-animal veterinarians have assumed the job of primary educators “in the risks of emerging diseases such as West Nile virus infection and avian influenza for pets and pet owners; and the risks of animal contact for immunocompromised people.”  

They noted that “many Americans have more contact with their veterinarian than with their physicians.” 

Gaspar agreed. “Fact of the matter is that veterinarians are really at the forefront of public health,” she said. “We are not only the doctor for the pet; we have a role in the health of the family.”


In the case of the three dead birds and sick teenager in Kansas, the mystery has remained unsolved, although the girl reportedly has recovered.

“It was all so weird that you wanted there to be an explanation for it,” said Burcham, the veterinarian who had seen the two cockatiels and one green cheek conure. “The three birds dying back-to-back seemed like a red flag for something but ... it’s a reminder that just because there are animals dying doesn’t mean that is why the human is sick.”

VIN News Service commentaries are opinion pieces presenting insights, personal experiences and/or perspectives on topical issues by members of the veterinary community. To submit a commentary for consideration, email

Information and opinions expressed in letters to the editor are those of the author and are independent of the VIN News Service. Letters may be edited for style. We do not verify their content for accuracy.