According to Brooks Hays of UPI.com, Arizona health officials became concerned when a large number of prairie dogs were found to be dying or dead. Several burrows were tested and were found to be infested with fleas that tested positive for Yersinia pestis. “Nearby burrows are now being cleared and disinfected, in an effort to stem any possible outbreak of the disease,” said UPI. The article went on to report that it’s actually not a new occurrence. “The plague isn't new to Arizona. The disease has been firmly established in the Grand Canyon State, as well as Colorado and New Mexico, for some time now. Every year, a handful of people are infected with the disease.” Still, with plague headlines in the news, you may well be wondering if your pet is at risk.
What causes the plague?
Yersnia pestis, the bacteria that causes plague, is commonly carried by small rodents such as ground squirrels, rats, mice and even rabbits. Unfortunately, small rodents and rabbits not only can carry Yersnia pestis, but can also become affected by it. Prairie dogs are very vulnerable to plague due to their social nature, and outbreaks can decimate the population.
This naturally occurring bacteria survives due to a cycle between rodents and fleas1. Plague is found in upland forests and grasslands in rural to semi-rural areas of the western part of the United States (especially the southwest regions)1. There is a higher incidence of plague during cooler summers that follow wet winters1, during the months of May to October. Wherever you expect rodents to live, that’s where this bacteria can survive. The more exposure to rodents or fleas, the higher the risk of exposure to Yersnia.
How can the plague spread to dogs and cats?
Rarely, dogs, cats and humans can be infected. The CDC says this may happen one of three ways:
So, is your dog or cat at risk from the plague?
Guardians should be especially cognizant of plague if they live in the Southwest, have indoor/outdoor pets that hunt, have pets with flea infestations, or live in an environment where their pets may be exposed to rodents. Keep in mind that outdoor cats are most at risk for being exposed to Yersnia, due to rodent hunting (another great reason to keep your cat indoors). Male cats may be at increased risk due to their roaming tendencies (and secondary exposure).
In dogs and cats, clinical signs of plague include:
When in doubt, if you notice any of these signs in your pet, get to a veterinarian immediately. Also, if you notice any clinical signs yourself, make sure to contact your medical doctor immediately for medical attention. The sooner you notice a problem, the sooner plague can be treated with the appropriate antibiotic and supportive care.
Tips to keep you and your pets safe from the plague
While Yersnia is rare, pet guardians should know of this potentially life-threatening bacterial infection that can be spread to pets and people.
If you have any questions or concerns, you should always visit or call your veterinarian -- they are your best resource to ensure the health and well-being of your pets.
A tularemia outbreak, caused by Francisella tularensis type B, occurred among wild-caught, commercially traded prairie dogs. F. tularensis microagglutination titers in one exposed person indicated recent infection. These findings represent the first evidence for prairie-dog-to-human tularemia transmission and demonstrate potential human health risks of the exotic pet trade.
Tularemia is a zoonosis affecting more than 150 wildlife species, including prairie dogs, squirrels, cats, and humans (1–3). Tularemia is caused by the bacterium Francisella tularensis, which exists in two main types. Type A is found almost exclusively in North America and is highly virulent in humans. Type B exists throughout North America, Asia, and Europe and is less virulent in humans (4). Tularemia vaccines have been used to protect military and laboratory personnel at high risk for exposure but are not available for the general population (5).
Humans can acquire tularemia through contact with infected animals (2,3,6). Although not previously documented, prairie dog–to-human-transmission is a concern because thousands of wild prairie dogs are captured annually in the United States and sold as exotic pets worldwide (7).
Figure 1. Black-tailed prairie dogs (Cynomys ludovicianus).
In mid-July 2002, a die-off began among wild-caught, black-tailed prairie dogs (Cynomys ludovicianus) (Figure 1) at a commercial exotic pet distributorship in Texas (facility A). On July 29, one of the dead prairie dogs tested positive for F. tularensis (8). Hundreds of potentially infected prairie dogs had already been distributed to other states and exported internationally. Epidemiologic and microbiologic investigations were initiated on August 1. We report on the epidemiologic findings the microbiologic investigation is reported separately (9).
Facility A’s purchasing and shipping records were reviewed and the staff interviewed. All involved states and countries were notified of the outbreak, asked to identify the status of prairie dogs from the suspected shipments, and submit tissue samples for testing.
All prairie dogs at facility A, prairie dogs distributed within Texas from facility A since June 2002, and other dead and free-roaming exotic species at facility A were retrieved live animals were euthanized, and all were tested for F. tularensis by direct fluorescence assay (DFA) and culture on cysteine heart agar with 9% chocolatized blood media (9). All recovered isolates were subtyped by using a polymerase chain reaction (PCR) assay (9).
Trappers who supplied prairie dogs to facility A in May and June 2002 were interviewed, and prairie dogs from their respective facilities in Texas and South Dakota were euthanized and tested for tularemia. South Dakota trapping sites suspected to be a potential source of the outbreak were also investigated.
Investigation of facility A on August 2 indicated a variety of exotic species crowded within a 2,500 square foot building. We found 163 remaining prairie dogs in four groups: sick and dying prairie dogs (bin 1), healthy-appearing prairie dogs (bin 2 and cages), prairie dog carcasses (frozen), and escaped prairie dogs roaming free around the facility. The bins were metal, uncovered, 2.5 feet tall and 5 feet in diameter, with 50–100 prairie dogs per bin. In addition, several other exotic animals were found roaming free or dead.
Figure 2. Weekly prairie-dog deaths at facility A, Texas, April–August, 2002. a Arrows represent prairie dog shipments arriving at facility A from Texas (TX) and South Dakota (SD). b No data are available for.
According to shipping records, approximately 3,600 prairie dogs passed through facility A during January through July 2002. In July, an estimated 250 prairie dog deaths occurred compared with approximately 25 deaths over the previous 6 months (Figure 2). On August 1, shipments to and from facility A were halted.
Necropsies on all 163 prairie dogs remaining in facility A indicated clinical signs of oropharyngeal tularemia in all the dead and most of the euthanized sick animals, suggesting transmission through ingestion. Many of the dead animals had been cannibalized. F. tularensis was isolated from 61 animals (Table 1). Of these, 60 isolates came from prairie dogs remaining in facility A, including one prairie dog roaming free in the facility, and one isolate came from a privately owned prairie dog purchased from a Texas pet shop supplied by facility A. All of the isolates were identified as type B.
During June through July 2002, more than 1,000 prairie dogs were distributed from facility A to locations in 10 U.S. states and 7 other countries (Table 2). By early August, 100 prairie dogs, those shipped to the Czech Republic, remained unsold: of these, approximately 30 were dead on arrival, 30 were ill, and evidence of cannibalism had been noted within the shipment. All living animals were euthanized.
Of the prairie dogs distributed from facility A to other U.S. states, specimens were received from two prairie dogs sent to Michigan serum samples from both tested negative for tularemia (Table 1). The Netherlands and Belgium retrieved 4 and 10 prairie dogs, respectively, for serologic testing and culture of tissue samples all were reported to be negative. The Czech Republic tested six prairie dogs for tularemia: one was positive by isolation of F. tularensis in culture, and five were presumptively positive by polymerase chain reaction (PCR). The Czech F. tularensis isolate was identified as type B, indistinguishable from the Texas isolates by restriction fragment length polymorphism analysis (9).
All healthy-appearing prairie dogs in bin 2 and cages, as well as other exotic animals roaming free or found dead in facility A tested negative for tularemia, demonstrating that outbreak propagation required direct contact with infected prairie dogs. Prairie dogs collected from Texas trappers, South Dakota trappers, and trapping sites all tested negative.
A human case was defined as a fourfold change in serial F. tularensis antibody titers from serum samples obtained at least 14 days apart, with at least one titer ≥1:128, in an exposed person. Paired serum samples were tested with an F. tularensis microagglutination assay. Anyone who transported, handled, bought, or cleaned the cages of prairie dogs from facility A since June 2002 was considered exposed. Exposed persons in Texas and other U.S. states were given a standardized questionnaire to assess infection risk factors and symptoms during the 2 weeks after their exposure. To enhance case finding, periodic follow-up was maintained with health authorities in involved U.S. states and foreign countries.
Twenty-two exposed persons were identified in Texas: 5 worked at facility A, 13 worked at other Texas facilities supplied by facility A, 3 worked at a veterinary care center and necropsied a prairie dog originating from facility A, and 1 privately owned an infected prairie dog originating from facility A. In interviews with 20 of 22 exposed persons, 6 (32%) reported recent prairie-dog bites, 7 (37%) ate or drank without handwashing after contact with prairie dogs, and 13 (67%) handled prairie dogs or cleaned cages barehanded. Although gloves and soap were available to employees, none of the involved Texas facilities had formal written policies enforcing proper handwashing, wearing gloves, or prohibiting eating or drinking in animal care areas.
During their exposure interval, 14 of 20 exposed persons interviewed reported having > 2 nonspecific symptoms that can be consistent with tularemia: headache, sore throat, myalgias, stiff neck, fever, chills, cough, and swollen glands. Initial serologic testing on blood samples obtained 1 week to 2 months after initial exposure from 19 of 22 persons in Texas identified a positive F. tularensis titer of 1:128 in a 24-year-old man, who was an animal handler at facility A. All other persons tested negative, and no new positive titers were identified from follow-up samples obtained 1–2 months later from 9 of 19 persons. Except for the animal handler, other symptomatic persons had spontaneous resolution of symptoms or other diagnoses for their symptoms. The animal handler’s 1-month follow-up titer persisted at 1:128 however, a fourfold decline in titer, from 1:128 to 1:32, was documented for samples obtained 4 and 6 months after the initial titer, indicating recent exposure to F. tularensis. The animal handler had begun working at facility A in June 2002 and had handled dead and dying prairie dogs barehanded. He denied prior potential tularemia exposures, such as hunting, having tick bites, or owning a pet. Additionally, he denied having received a tularemia vaccine, which could have explained the elevated titer. During our investigation, the animal handler reported having an afebrile upper respiratory infection-like illness atypical of tularemia, with sore throat, cough productive of green sputum, and mild chest discomfort but no interruption of work or leisure activities. His symptoms began 12 days after the last prairie dog shipment arrived at facility A and 1 week before the die-off, and they resolved after oral fluoroquinolone therapy.
Health authorities in other states and countries reported no illness in exposed persons. Six months after the outbreak occurred, follow-up calls to health authorities in the involved U.S. states indicated no new human cases. No serologic testing was performed on exposed persons outside of Texas.
Our investigation demonstrated the first evidence that prairie dogs can transmit tularemia to humans. The animal handler’s atypical symptoms and unclear route of infection might be because he was exposed to the less virulent subspecies type B. Studies have documented higher rates of F. tularensis seropositivity among animal trappers from tularemia-endemic areas, and many of the trappers were asymptomatic (10).
This outbreak highlights health risks to humans who handle wild-caught animals and underscores the speed with which exotic species and virulent pathogens can be transported worldwide (11). A number of public health risks associated with the exotic pet trade were observed at facility A. Prairie dogs were crowded in large bins, allowing unnaturally close contact and propagation of the outbreak through cannibalism. A variety of wild-caught and captive-bred exotic animals were also held in close quarters, providing opportunity for diseases to jump species. This risk for disease transmission between species was heightened because several exotic animals were able to roam free and comingle.
Until recently in the United States, no federal regulations existed to protect humans from the domestic distribution and sale of infected, wild-caught animals a ban against transport and sale of prairie dogs and certain other rodent species was implemented on June 11, 2003, in response to a monkeypox outbreak in the Midwest (12). Many states forbid capture and sale of native wildlife species, including prairie dogs however, states that do permit trapping and sale do not have regulations to address the human risk of acquiring zoonoses.
This incident and others, such as transmission to humans of plague from prairie dogs, monkeypox from prairie dogs, and salmonellosis from African pygmy hedgehogs, highlight the importance of developing strategies to reduce human risk from the domestic and international sale of infected, wild-caught animals (13–16). Strategies might include educating the public, standardizing exotic animal husbandry practices, restricting trade to animals bred in captivity, or banning sale of wild-caught animals. As a result of this investigation, Japan banned prairie dog importation as of March 2003. We recommend that U.S. states and other countries review and strengthen their regulations governing the transport and sale of prairie dogs and other exotic pets.
Dr. Avashia is an internist and pediatrician working as an Epidemic Intelligence Service Officer with the Centers for Disease Control and Prevention assigned to the Texas Department of Health. Her research interests include infectious disease epidemiology.
We thank the following persons: Valerie Carson Tim Kram Beverlee Nix Angi Bridges Marta Guerra Rachel Barwick Julie Magri R.G Herbes H. Verburg, and colleagues and public health authorities in Michigan, Arkansas, Florida, Mississippi, West Virginia, Nevada, Washington, Ohio, Illinois, Virginia, Kentucky, and North Carolina.
Please use the form below to submit correspondence to the authors or contact them at the following address:
Swati Avashia, Texas Department of Health, Infectious Disease Epidemiology and Surveillance Division, T-801, 1100 W. 49th Street, Austin, TX 78756, USA fax: 512-458-7616
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The flea that feeds on prairie dogs and other mammals serves as the vector for transmission of sylvatic plague to the new host, primarily through flea bites, or contact with contaminated fluids or tissue, through predation or scavenging. Humans can contract plague from wildlife through flea bites and handling animal carcasses. 
Yersinia pestis circulates in rodent reservoirs on all continents except Australia. Sylvatic plague affects over 50 species of rodents worldwide. It is vectored by a variety of flea species. Non-rodent animals susceptible to the disease include shrews, lagomorphs, ferrets, badgers, skunks, weasels, coyotes, domestic dogs and cats, bobcats, cougars, camels, goats, sheep, pigs, deer, and primates, including humans. Birds are not known to be susceptible. 
Sylvatic plague is normally enzootic, meaning it occurs at regular, predictable rates in populations and specific areas. At unpredictable times, it becomes epizootic in unexpected places. It is during these epizootic outbreaks that transmission to humans is most common.
Factors that predispose to epizootic cycles include dense populations of rodents, multiple species of rodents in a particular area, and multiple rodent species in diverse habitats. 
Prairie dog colonies reach nearly 100% mortality rates during outbreaks. Prairie dogs are a keystone species and play a vital role as the primary prey of black-footed ferrets. Developing methods to control plague is of high concern for preserving ferrets and the conservation of Western prairie and grassland ecosystems. 
Prairie dogs evolved over 3,000,000 years ago, and have been surviving sylvatic plague as a species for a long time. In the absence of understanding the natural prairie dog/plague cycles, dusting rodent dens with pesticides to kill fleas is currently the main method of controlling sylvatic plague in the wild, with some interest in using vaccines developing. 
FLAGSTAFF, Ariz., April 6 (UPI) -- Arizona health officials and wildlife managers are monitoring flea infestations more closely after several specimens in Picture Canyon, near Flagstaff, tested positive for Yersinia pestis, the bacteria that causes the disease known as the bubonic plague.
Officials grew concerned when they were alerted to a prairie dog den that appeared to features an unusually large number of dead or dying prairie dogs. Several surrounding burrows were tested, revealing the culprit to be the plague.
"It looked like something that could be associated with death due to plague," Randy Philips, division manager of the local health services district, told the Arizona Daily Sun.
Nearby burrows are now being cleared and disinfected, in an effort to stem any possible outbreak of the disease. Late last week, following the positive test, officials returned to test a much broader area for the dangerous bacteria. Those results are due back later this week.
The plague isn't new to Arizona. The disease has been firmly established in the Grand Canyon State, as well as Colorado and New Mexico, for some time now. Every year, a handful of people are infected with the disease -- the vast majority in one of those three states. Instances occasionally occur in other parts of the West.
As the Arizona Department of Health Services explains: "Plague activity in nature has been known to wax and wane over time, and this is influenced largely by climate conditions and rodent and flea populations."
The disease-causing bacteria is carried by rabbits and small rodents, including prairie dogs, ground squirrels, rats and mice. Prairie dogs are especially vulnerable to the disease due to their social nature. Outbreaks can quickly wipe out 90 percent of a local prairie dog population.
"If you normally see prairie dogs then next day they're gone, there is a good chance plague is coming," said Dave Engelthaler, programming director with pathogen research nonprofit TGen North.
Officials have posted signs at trailheads in Picture Canyon, warning visitors of the plague's presence. It's best to avoid close or direct contact with rodents and their living quarters. Dogs who come in contact with or feed on infested rodents can also carry the infected fleas or the disease itself.
Plague symptoms typically manifest themselves within six days of infection and include fever, chills, headache, weakness, muscle aches and swollen lymph nodes. While the disease can occasionally prove deadly -- it carries a roughly 10 percent mortality rate -- it is usually treatable with antibiotics when caught early enough.
In 2012, an Oregon man was infected when his cat bit him as he tried to dislodge a partially-eaten mouse from the feline's throat. He lost several fingers and toes to the infection before the antibiotics kicked in.
Bubonic and septicemic forms of plague are quite treatable with a variety of antibiotics, but successful treatment hinges on early diagnosis. Pneumonic plague is more resistant to treatment, so it is especially important to catch it early.
People need to be aware if they are in or have visited an area that is known to have plague so they can take proper precautions. Similarly, if you feel ill or you notice that your dog is acting sick or has a swelling below the jaw or behind a front leg and you have been in an area where plague is known to exist, go the doctor right away and let them know the area you have visited.