Although you can't catch your cat's sniffles, your pet can give you the plague. We're talking Black Death-style bubonic plague. But kitty isn't evil -- it's just a passive carrier, or vector, of disease like many other animals. HIV passed to humans through chimpanzees and severe acute respiratory syndrome, or SARS, started in China from infected badgers and palm civets.
But how could your cat catch the plague? If you live in Arizona, New Mexico or Colorado -- states which historically have the highest incidence of bubonic plague in the United States -- your cat could possibly ingest the plague bacterium by eating an infected prairie dog.
Before settlers expanded to the American West, hundreds of millions of prairie dogs ranged across nearly 100 million acres (40 million hectares) [source: U.S. Fish and Wildlife Service]. In spite of their name, prairie dogs belong to the squirrel family, and look like plump chipmunks, standing 14 to 17 inches (35 to 43 centimeters) tall and weighing between 2 and 3 pounds (0.91 and 1.4 kilograms). Native to the United States, the tan-colored prairie dogs are highly social, amassing in large groups called colonies. Colonies live in interconnected underground burrows that may span 100 acres (40 hectares). From there, the colony divides into smaller groupings, or wards. Wards are made up of coteries, or individual family units. One male, one to four females and their offspring compose a coterie. Individuals communicate through whistles and chirps, greeting each other by touching teeth as though kissing.
Sounds adorable, right? Not so much to livestock ranchers in the dogs' Western habitat. Since they tunnel underground and eat grasses aboveground, some ranchers consider them competition for grazing land. Also, mounded burrow entrances may trip cattle and cause injuries. In response, the federal government has authorized controlled prairie dog poisonings around certain areas of privately owned land.
As a result of this acrimony and the effects of plague bacteria, the prairie dog population has plummeted an estimated 98 percent [source: National Zoo]. In addition to the prairie dog plague, their range has shrunk as well, with less than 2 million acres remaining (809,371 hectares) [source: U.S. Fish and Wildlife Service]. The remaining population size of 10 to 20 million prairie dogs still leaves them out of the running to be classified as an endangered species. Nevertheless, ecologists classify prairie dogs as a keystone species, which means the livelihood of many nonrelated flora and fauna rely on their well-being. For example, the black-footed ferret depends on prairie dogs as its main prey, and the species has drifted toward extinction partially from lack of food.
But shouldn't we breathe a sigh of relief about this population decrease since these rodents can carry bubonic plague?
Plague Kills Prairie Dogs
Plague is the common name for the bacterium Yersinia pestis. Bubonic plague arrived in North America around 1900, most likely from Chinese cargo ships [source: Hoogland]. At least 76 wild mammals are known to carry plague [source: U.S. Fish and Wildlife Service]. Rats harbor the bacterium particularly well, making them the probable source in North America. After that, the first known rodent in the United States discovered with plague was a California ground squirrel in 1908 [source: Hoogland].
Plague-infected blood is transmitted between animals through fleas. When plague passes between rodents, such as squirrels and prairie dogs, it's referred to as sylvatic plague. Plague within a rodent species can potentially cross into the human population, most often through flea bites. Fleas deliver the plague bacterium when they feed on a new host. The bacterium clogs the flea's digestive system, causing it to regurgitate bacteria into the host's bloodstream when it attempts to feed. Prairie dogs are particularly susceptible to plague. When the bacterium enters a colony, it rapidly turns into an epidemic, or a fast-spreading virus. If this happens, the plague mortality rate is almost 100 percent [source: U.S. Fish and Wildlife Service].
That high mortality rate and the speed with which plague kills prairie dogs are the principal reasons that humans generally don't catch plague from them [source: Johnsgard]. Also, North Americans rarely come in close contact with prairie dogs for direct transmission to occur. From 1959 to 1999, only 8 percent of reported plague cases in the United States could be traced back to prairie dog contact [source: U.S. Fish and Wildlife Service].
According to the Centers for Disease Control and Prevention (CDC), people usually contract plague from infected fleas. The CDC also reports that ground squirrels and wood rats are the most prevalent plague vectors, or carriers, in the country. Likewise, an examination of plague cases in Colorado from 1947 to 1999 found that you were more likely to catch plague from a domestic cat than a prairie dog [source: Denver Animal Control]. For example, a house cat infected with bubonic plague was recently diagnosed and quarantined in Nebraska.
Thanks to improved sanitation practices, pesticides and antibiotics, incidences of plague in the United States are relatively uncommon with 46 confirmed cases from 2000 to 2007 [source: O'Connor]. Today, 90 percent of plague cases occur in Africa [source: Stenseth et al]. The World Health Organization estimates between 1,000 and 5,000 cases of plague are reported across the globe each year, resulting in 100 to 200 deaths [source: Stenseth et al]. Squalid living conditions and proximity to rodents are the greatest contributors to the bacterium's persistence.
Different plague classifications exist, depending on the way you catch it. If the bacterium enters from a flea bite or through open skin, that's called bubonic plague. Bubonic plague is the most common type of plague, so named for the lumps, or buboes, that form around your glands. Pneumonic plague denotes plague bacterium that you inhale. If you catch plague from a cat, it would likely be pneumonic. Finally, the most fatal type of plague is septicemic plague, in which the bacteria directly enters your bloodstream and overwhelms your immune system. For a detailed look at plague symptoms, you can read How Plague Works. All forms of plague are medically treatable with antibiotics, but if left untreated, plague has a 30 to 60 percent mortality rate [source: World Health Organization].
Since the entire rodent population is so great across the world, plague will likely continue to rear its ugly head for a long time. It may be wise to keep your distance from prairie dogs, but you're more likely to catch the disease from the indiscernible bite of a much smaller courier.
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More Great Links
- "Black-Tailed Prairie Dog." National Zoo. (Aug. 28, 2008)http://nationalzoo.si.edu/Animals/NorthAmerica/Facts/fact-pdog.cfm
- Grady, Denise and Altman, Lawrence K. "Beyond Cute: Exotic Pets Come Bearing Exotic Germs." The New York Times. June 17, 2003. (Aug. 28, 2008)http://query.nytimes.com/gst/fullpage.html?res=9400E7DF1238F934A25755C0A9659C8B63
- Hoogland, John L. "Conservation of the Black-Tailed Prairie Dog." Island Press. 2006. (Aug. 27, 2008)http://books.google.com/books?id=WL23Po48YeEC
- Johnsgard, Paul A. "Prairie Dog Empire." University of Nebraska Press. 2005. (Aug. 28, 2008)http://books.google.com/books?id=v1DKQL0OBigC
- O'Connor, Michael. "Bubonic plague reported in Scotts Bluff County." Omaha World-Herald. Aug. 5, 2008. (Aug. 27, 2008)http://www.omaha.com/index.php?u_page=1219&u_sid=10398657
- Ostfeld, Richard S.; Keesing, Felicia; and Eviner, Valerie T. "Infectious Disease Ecology." Princeton University Press. 2008. (Aug. 28, 2008)http://books.google.com/books?id=rm3yD35ExvsC
- "Plague." World Health Organization. Revised February 2005. (Aug. 28, 2008)http://www.who.int/mediacentre/factsheets/fs267/en/
- "Plague and Black-Tailed Prairie Dogs." U.S. Fish and Wildlife Service. March 23, 1999. (Aug. 28, 2008)http://www.fws.gov/mountain-prairie/species/mammals/btprairiedog/plague.htm
- "Plague Fact Sheet." Centers for Disease Control and Prevention. Jan. 7, 2005. (Aug. 28, 2008)http://www.cdc.gov/ncidod/dvbid/plague/resources/plagueFactSheet.pdf
- "Plague in the United States." Denver Animal Control. Denvergov.com. (Aug. 28, 2008)http://www.denvergov.com/AnimalControl/VectorControl/VectorControl12/tabid/377839/Default.aspx
- "Plague Training." Centers for Disease Control and Prevention. Updated Sept. 7, 2004. (Aug. 28, 2008)http://emergency.cdc.gov/agent/plague/trainingmodule/1/
- Stenseth, Nils Chr.; Atshabar, Bakyt B.; Begon, Mike; Belmain, Steven R.; Bertherat, Eric; Carniel, Elisabeth; Gage, Kenneth L..; Leirs, Herwig; and Rahalison, Lila. "Plague: Past, Present, and Future." Public Library of Science Medicine. Jan. 15, 2008. (Aug. 28, 2008)http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0050003&ct=1
- "Sylvatic Plague Immunization in Black-footed Ferrets and Prairie Dogs." National Wildlife Health Center. USGS. Updated Aug. 11, 2008. (Aug. 28, 2008)http://www.nwhc.usgs.gov/disease_information/sylvatic_plague/index.jsp