The Plague Is Still Around

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The Plague Is Still Around

Simply saying “the bubonic plague” brings visions of squalor, dirt, millions of rats scurrying about, and people falling over and dying in the middle of the street during the mid-14th century. Indeed, Europe’s population was decimated and approximately 50 million people died during that time. 

Nowadays, we think the horror is over and shudder at the thought of living back then. Unfortunately, cases of the plague still exist in several countries (including the United States) and major outbreaks in sub-Saharan Africa have happened recently.

The popular misconception is that fleas spread the plague by jumping off rats onto an unsuspecting victim and cause the telltale black spots. This could occur, but other scenarios of infection and transmission are possible.

First of all, more than one species of infected flea exists and generally the Oriental rat flea, gerbil flea, or the northern rat flea are the primary carriers of the plague. Predominantly, the most common fleas found on cats and dogs are usually the aptly named cat flea or dog flea, which are rare in climates conducive to the plague. However, that does not mean that a rat flea couldn’t jump onto a dog or cat.

Secondly, the plague carrier fleas have to be exposed to the specific bacterium causing the plague, Yersinia pestis. For instance, a study of New York City rats released in 2015 stated findings of the Oriental rat flea, but not the bacterium Yersinia pestis

So, where is the plague still seen in the United States? Currently, it is found in the West. But why do sporadic and small outbreaks occur in these regions? The outbreaks are small because we are hypervigilant to contain them and they are located in rural regions. Researchers believe that climate, rainfall, elevation, and land type are all factors. Those, in turn, affect both flea and rodent populations. In the United States, studies suggest that outbreaks occur during cooler summers that follow wet winters.  

As you may have noticed, I switched above here from saying rats to rodents. Indeed, great gerbils in Kazakhstan are studied for their population numbers and are actually believed to be the perpetuators of “The Black Death” in Europe due to the climate conditions at the time. In the United States, squirrels, rats, prairie dogs, chipmunks, mice, voles, and rabbits are considered the primary reservoirs.

When an outbreak occurs, we do not quarantine people or pets because of having fleas on their bodies. We quarantine them primarily to reduce the potential spread of pneumonic plague, one of the three plague forms.

  • Pneumonic plague – Pneumonic plague can be spread by breathing in Y. pestis suspended in respiratory droplets from an already infected person or animal. It generally requires direct and close contact. It can also be secondary to the bubonic or septicemic forms if they are left untreated. The pneumonic form of the plague is considered a “bioweapon”, too.
  • Bubonic plague – Buboes are swollen and painful lymph nodes. Literally, the lymph nodes stick out and look like goiter, but it is not a goiter. Bubonic plague is the most common form of the plague. This occurs when an infected flea bites a person or animal, or when materials or dead animals contaminated with the bacteria enter through a break in the skin.
  • Septicemic plague – Septicemic plague is the telltale blackened skin. Septicemia happens when the bacteria multiply in the blood. It can occur on its own or be secondary to either the pneumonic or bubonic forms of the plague. It is also spread the same way as bubonic plague.

Cats are particularly susceptible to the plague and usually develop the bubonic form. They are generally exposed either by a flea bite or by picking up or eating an infected animal. What is interesting is that an experiment showed that the majority of cats will develop enlarged lymph nodes at the site of exposure. So, if your cat picked up an infected mouse, the lymph nodes of the mouth and neck region enlarge. 

When an infection happens, cats usually develop bubonic plague and the incubation period is anywhere from 1-4 days. Cats with bubonic plague typically present with:

  • Fever
  • Anorexia
  • Lethargy
  • Enlarged lymph nodes that could abscess and drain
  • Diarrhea
  • Vomiting

Cats can also develop primary or secondary septicemic plague. However, primary pneumonic plague has not yet been documented in cats. Unfortunately, mortality rates are around 60%.

Dogs are less likely to develop clinical illness from the plague, but it has happened.

If caught early enough, certain antibiotics can be prescribed to fight the plague. However, the best thing to do is prevention. In fact, the federal Centers for Disease Control emphasizes that the most common way US Citizens are contracting the plague is from their pets who either bring in fleas or cough near the caregiver.

  • Don’t allow your companion dog or cat to roam freely. Keep your pet leashed and take them for walks.
  • Avoid sick or deceased animals. Report them to the public health authorities. In this part of the country, tularemia (rabbit fever) is prevalent as well. Tularemia is caused by a different bacterium and is also considered a bioweapon.
  • Rodent-proof your home. I don’t suggest putting out rat poison. However, just make sure home is kept sanitary and clear out piles of brush or rock that might make a nice habitat for a rodent.
  • If you are a camper, I would suggest the same as above. However, if you hear of an outbreak in your area, please revise your vacation camping plans.
  • You can use flea and tick preventative for your pet as well.
  • Before coming indoors, use a flea comb to check your dog or cat for fleas. 

W. Jean Dodds, DVM
Hemopet / NutriScan
11561 Salinaz Avenue
Garden Grove, CA 92843


Ettestad, Paul, DVM. “Overview of Plague.” Merck Veterinary Manual, Nov. 2013. Web. 06 Nov. 2016.

“Fleas That Could Potentially Carry Plague Found on New York City Rats.” Entomology Today. N.p., 2 Mar. 2015. Web. 06 Nov. 2016.

“Plague.” Centers for Disease Control and Prevention, 10 Sept. 2015. Web. 06 Nov. 2016.

Samiaa, Noelle I et al. “Dynamics of the Plague–wildlife–human System in Central Asia Are Controlled by Two Epidemiological Thresholds.” Proceedings of the National Academy of Sciences of the United States 103.35 (2011): n. pag. PNAS, 19 Aug. 2011. Web. 06 Nov. 2016.

Schmid, Boris V et al. “Climate-driven Introduction of the Black Death and Successive Plague Reintroductions into Europe.” Proceedings of the National Academy of Sciences of the United States 112.10 (2015): n. pag. PNAS, 23 Feb. 2015. Web. 06 Nov. 2016.

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