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Bubonic Plague: The Role of Dogs in the Spread of Plague

Dogs may carry fleas with plague to people or cats.

Throughout history, few diseases have caused as much fear in humans as plague, with good reason. It caused around 50 million deaths in the 1300's, and it became known as the Black Death. The disease carries a 30-60% fatality rate in humans if it isn't treated.

What is Plague?

Plague is a serious illness caused by the bacteria Yersinia pestis. This bacteria is zoonotic, meaning that it is passed to humans from animals. In the case of plague, transmission occurs when humans are exposed to infected small animals or their fleas, or when the bacteria is inhaled. The most common animals to spread plague to humans are mice, rats, squirrels, prairie dogs, and rabbits.

Types of Plague

There are three types of plague infection, depending on how the bacteria is acquired by the victim:

  • Bubonic plague occurs when the infection is transmitted through a flea bite. This is the most common type of plague. The lymph node closest to the transmitting flea bite becomes painful and enlarged. This is known as a bubo, and it can eventually abscess and become a draining sore.
  • Septicemic plague occurs when the infection multiplies in the bloodstream rather than the lymphatic system. This can occur from transmission through flea bites or from direct contact with the infection through cracks in the skin.
  • Pneumonic plague is the most dangerous of plague's forms, but it is the least common. It either occurs when the infection spreads to the lungs late in one of the other plague disease processes, or when one person or animal with pneumonic plague coughs, releasing infected droplets into the air that another person or animal breathes in.

Do Dogs Get Plague?

Dogs are highly resistant to plague bacteria. When they do become infected, the disease is usually mild and self-limiting, meaning that it resolves on its own. Signs of dogs with plague, if they develop any signs at all, include:

  • Fever
  • Lethargy
  • Enlarged lymph nodes
  • Cough

Dogs Can Help Transmit Plague to Humans or Cats

Because dogs aren't very susceptible to developing plague infection, their role in an outbreak is often that of carrier. Dogs can pick up fleas that are infected with Yersinia pestis in rodent-infested areas and carry them to humans or cats, where they can bite and transmit plague.

When there is an outbreak of plague in a rodent population, the prairie dogs, mice, rats, or rabbits in that population often die off fairly quickly. This leaves all of their infected fleas looking for a host to feed from. They are eager to jump on a passing dog.

Cats are very susceptible to developing plague. Find out the signs of plague in cats here.

Is There Plague in the United States?

There have been cases of plague in some western states, especially New Mexico, Arizona, and Colorado. Plague usually occurs in rural areas. There are an average of 7 human cases per year in the US, mostly in the form of bubonic plague. Most cases in the US occur between late spring and early fall.

How Treatable is Plague?

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.

Current Events (April, 2015): Plague Found Near Flagstaff, Arizona

At the time of this writing, there is a warning in place for the people in and around Flagstaff, Arizona. Authorities there noticed the dying off of a large number of prairie dogs in a colony in the Picture Canyon trail area. They tested fleas found in the prairie dogs' burrows and confirmed that they were carrying Yersinia pestis.

Authorities have sprayed the area with insecticides aimed at killing the fleas. They are asking hikers to wear long pants and socks and to check themselves for fleas before getting back into their cars.

It is also extremely important that people make sure their dogs are current on flea preventative. Local veterinarians can recommend the best products for the area.

General Tips for Plague Prevention

  • Flea control for all pets in your home is an essential component to plague prevention in areas where it occurs.
  • Remove areas around your home that make good homes for rodents, rabbits, or squirrels such as brush piles, rock congregations, and logs.
  • Do your best to rodent-proof your home.
  • Wear long pants, socks, and shoes when hiking, and check your ankles for fleas before getting back into your vehicle.
  • Use gloves and a mask if you must handle dead wildlife.

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