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Squirrels and The Bubonic Plague

Squirrels can and do spread the plague.

This article covers what the CDC told me about avoiding infection, what the dangers are, how the disease is spread and potential symptoms.


From the recent San Jose Mercury News article: "Plague-infested squirrel closes campgrounds" http://www.mercurynews.com/bay-area-living/ci_23738526/plague-infested-squirrel-prompts-angeles-national-forest-campground Photo credit: Walt Mancini.

From the recent San Jose Mercury News article:
“Plague-infested squirrel closes campgrounds”
Photo credit: Walt Mancini.


Yes, THE plague:

  • The bubonic plague
  • Black Death!
  • The pandemic disease that killed half of the people living in Europe during the middle Ages.
Illustration of the Black Death from the Toggenburg Bible (1411). Image credit wikipedia

Illustration of the Black Death from the Toggenburg Bible (1411). Image credit wikipedia


Squirrels and the plague!  No squirrels allowed:

  • Weather or not you think they look cute, squirrels can be very destructive;  they will tear your yard apart, chew through irrigation lines, eat your trees and now they can actually kill you!
  • I don’t want plague infected squirrels running around my yard.
  • Frankly, I don’t want healthy squirrels running around my place either.
  • I suspect that you probably feel the same way too…  Please read on.
  • August 7, 2015 update: A child was just diagnosed with the plague after visiting Yosemite National Park.  Here is the latest news from USA Today reports Officials: Child camping in Yosemite National Park contracts plague.  If you prefer a different angle, The Guardian reports California child diagnosed with plague after camping at Yosemite.
This pic is from the Huffington post article: "Squirrel Vandalized Bikes At Iowa College" http://www.huffingtonpost.com/2013/10/25/squirrel-vandalized-bikes_n_4164957.html

This picture is from the Huffington post article: “Squirrel Vandalized Bikes At Iowa College” http://www.huffingtonpost.com/2013/10/25/squirrel-vandalized-bikes_n_4164957.html

Catch 22:

  • Most methods of getting rid of squirrels involve coming in close contact with them.
  • Unfortunately, close contact with live squirrels, (or dead squirrels) puts you at risk.
  • In fact, even coming in proximity to where they live can potentially get you infected as well.
  • But if you do nothing to get rid of the squirrels, the population will likely rise and they will take over your area (I have seen this happen).
  • That overpopulation not only increases an individual squirrel’s risk of getting infected with the plague… it also means that your odds of getting infected also increase.


So now what?

  • As a result of all of this, I started looking around for an official recommendation regarding how to safely address the danger.
  • To my surprise, the CDC (Center for Disease Control) has no available published information on how to safely remove these pests.



Next step:

  • As a result, I decided to put my tax money to work and I wrote the CDC about my concern.
  • In the same letter, I also decided to ask a similar question about a different disease known as Relapsing Fever.
  • (see below)


My letter to the CDC:


Dear CDC

I am a medical doctor living in Southern California.

As you know, there are several serious zoonotic disease spread by parasites living on California ground squirrels.  For example, The Plague-Yersinia pestis and Relapsing Fever-Borrelia hermsii/turicatae. These diseases can be spread by close contact with the dens of these animals, as well as direct contact with the living or recently deceased animals.

Therefore, I was wondering if the CDC had a policy or suggestion regarding specific types of barrier protection for people trying to remove these pests from an area.

Thank you very much for your time.


Thomas Osborne, MD 


Response letter from the CDC:


Dear Dr. Osborne,


Thank you for your inquiry.  We have a number of recommendations for preventing plague:

Reduce rodent habitat around your home, work place, and recreational areas. Remove brush, rock piles, junk, cluttered firewood, and possible rodent food supplies, such as pet and wild animal food. Make your home and outbuildings rodent-proof.

Wear gloves if you are handling or skinning potentially infected animals to prevent contact between your skin and the plague bacteria. Contact your local health department if you have questions about disposal of dead animals.

Use repellent if you think you could be exposed to rodent fleas during activities such as camping, hiking, or working outdoors. Products containing DEET can be applied to the skin as well as clothing and products containing permethrin can be applied to clothing (always follow instructions on the label).
Keep fleas off of your pets by applying flea control products. Animals that roam freely are more likely to come in contact with plague infected animals or fleas and could bring them into homes. If your pet becomes sick, seek care from a veterinarian as soon as possible.

Do not allow dogs or cats that roam free in endemic areas to sleep on your bed.

Our recommendations for preventing relapsing fever differ somewhat.  Most people don’t acquire this disease in their own home, but rather on vacation.  Vacationers can avoid sleeping in rodent-infested buildings or wear repellents. People who maintain vacation rentals should:

Rodent-proof buildings in areas where the disease is known to occur.

Consult a licensed pest control specialist who can safely:Identify and remove any rodent nesting material from walls, attics, crawl spaces, and floors.

Treat “cracks and crevices” in the walls with pesticide.

Provide additional pesticide treatments as necessary to effectively rid the building of the soft ticks.

Homeowners in your area may wish to consult a pest control company so they don’t accidentally infect themselves with Hantavirus during the clean-up process. Activities that put you in contact with deer mouse droppings, urine, saliva, or nesting materials can place people at risk for infection with Hantavirus Pulmonary Syndrome (HPS), a potentially fatal condition.

Please let us know if you have additional questions, or consult www.cdc.gov/rodents.

Thank you,

Centers for Disease Control and Prevention

Division of Vector-Borne Diseases | Bacterial Diseases Branch

Fort Collins, Colorado

email: dvbid@cdc.gov 


FYI correspondence:

  • Below is a ‘screen shot’ of the actual email correspondence between myself and the CDC.
  • You can click on the image below to enlarge if you want to see the actual email exchange.  However, it is basically the same info that you can read directly above.

CDC tells me about how to avoid the Plague


Bubonic plague infection/transmission:

  • Yersinia pestis is the name of the bacteria that causes the plague.
  • This bacteria is usually spread between different animals by a flea.
  • (The specific flea that carries the plague bacteria is the rat flea. Scientific name = Xenopsylla cheopis).
  • The fleas carry the plague bacteria around in their stomach without being bothered by it.
  • However, when a flea bites an animal, it regurgitates some of that plague bacteria, which then allows those nasty bacteria to get out into the flesh of whatever animal the flea just took a bite of.
  • Then the plague bacteria (Yersinia pestis) travels through the lymphatics of the animal that it just entered, destroying tissue in its path.

Picture of Xenopsylla cheopis. Photo credit wikipedia


Avoid these fleas:

  • So since the disease is usually spread by fleas, you obviously want to avoid the fleas.
  • That’s why the CDC recommends the use of protective barriers and DEET bug repellent and/or permethrin
  • Note, in this regard, a dead squirrel could be even more dangerous than a live one.
  • This is because the flea’s on that dead squirrel are going to be very hungry and really looking to jump ship.  You don’t want to be that fleas rescue ship.
Photo credit: http://forums.steves-digicams.com/biweekly-shoot-out/201082-animals-ca-ground-squirrel.html#b

Photo credit: http://forums.steves-digicams.com/biweekly-shoot-out/201082-animals-ca-ground-squirrel.html#b


Get rid of squirrels:

  • There are a lot of different methods available to get rid of ground squirrels, each with their own pluses and minuses.
  • In my next article I will highlight some methods of getting rid of them.
  • Please see the article, How to get rid of squirrels.



Where are plague infected squirrels found:

  • Unfortunately, squirrels are all over the place… and it can be very difficult to tell which ones are infected just by looking at them.
  • In addition, squirrels are not the only animals that carry and spread the plague.
  • For example, prairie dogs, chipmunks, mice, voles, and rabbits (to name a few) can all be infected by the plague. Wild carnivores can become infected by eating other infected animals.  Unfortunately, your cat or dog can also pick up infected fleas from rodents and then bring them home to you!
Squirrels love to live under large rocks and structures. The one in this picture moved into an opossum den under a building. http://www.nhm.org/nature/nature_blog_archive/2012

Squirrels love to live under things such as large rocks and structures. The one in this picture moved into an opossum den under a building.


You can click the image below to enlarge.

Plague lifecycle in the US. via the CDC

Plague lifecycle in the US. via the CDC-big picture


Where are people getting infected?

  • The CDC map below shows recently recorded cases of human plague in the USA.
  • As you can see, human infections seem to be recorded west of the Mississippi.
  • Side note; Rodent infection in the US started in 1900 when infected rats were brought over by steamships. Since that time, infection has spread to multiple different species of rodents.
USA Plague map via the CDC

USA Plague map via the CDC


  • Internationally, Africa is a hot spot for human plague infection..
World Plague map

World Plague map via the CDC



The 3 Types of plague:

Forms of the plague. Pictures from the CDC

Forms of the plague. Pictures from the CDC


Bubonic plague:

  • The bubonic plague is also the most common type of the plague and it is the one that we have been talking about so far.
  • As we discussed, you get the bubonic plague from a tick bite and the infection travels through your bodies lymphatic system.
An inguinal bubo on the upper thigh of a person infected with bubonic plague. Swollen lymph glands (buboes) often occur in the neck, armpit and groin (inguinal) regions of plague victims.Photo credit wikipedia.

An inguinal bubo on the upper thigh of a person infected with bubonic plague. Swollen lymph glands (buboes) often occur in the neck, armpit and groin (inguinal) regions of plague victims. Photo credit wikipedia.


Pneumonic plague:

  • This is a form of severe pneumonia.
  • You can get this form of the disease by inhaling infected respiratory droplets expelled from the lungs of another person/animal with pneumonic plague.
  • Pneumonic plague may also result of secondary infection of the lungs following infection from another part of the body.


Septicemic plague:

  • This is infection of the blood.
  • This may develop as a result of any of the other two types of plague mentioned above.  It basically means that the bacteria is in the bloodstream.  Once the plague bacteria is in the blood, it can progress to infect every part of the body and typically results in severe shock.
A hand showing how acral gangrene of the fingers due to bubonic plague causes the skin and flesh to die and turn black. Photo credit wikipedia.

A hand showing how acral gangrene of the fingers due to bubonic plague causes the skin and flesh to die and turn black. Photo credit wikipedia.


Plague Symptoms: 

My personal experience with the plague:

When I was younger and backpacking through Asia Minor, I met a really lovely English woman in a remote town.  We hit it off rather quickly and she told me that she was working as a teacher in this small town for about a year.   She took me around the town, showed me the school where she taught, and introduced me to her students.

As the day progressed, we went deeper into the details of our lives.  When I shared with her that I was starting medical school in a few months, her persona totally shifted to intense.  This type of thing actually happens quite a bit and is one of the reasons why I tried to keep this information to myself before I got married.

However, her intensity was more of desperate concern.  As I listened, she told me about the nearly overnight onset of painful large lumps involving the right side of her upper leg.

Now at this point I have to admit, I was a little taken back.  As she described her problem, I tried to play it cool, as if this was a normal conversation for me to have.  However, having a discussion about issues in someone’s inner thigh was not something I was use to at this point in my life… Especially with a stranger that happened to be an attractive woman.   But then again, I was not a doctor at this point either.

As I listened I quickly felt that I was in over my head, the best I could do was to tell her that it sounds like it could be an issue with her lymph nodes, and then she allow me to change the subject… at least for a while.

Not too long after that, she insisted on making me lunch, and like any normal backpacker I graciously accepted.  While she was prepping the food, she told me about how isolated she felt and how difficult it was to find support or any kind of reputable health care.  As you can imagine, this conversation brought us back to the lymph node discussion.

As we talked, without prompting, she adjusted her clothing and showed me exactly where the problem was.   When she did this I was so startled that I really had trouble seeing anything.  Up to this point in my life, I had tried to avoid staring at a woman like this, and now I was being asked to.

When I regained my focus, I was able to see what she was talking about.  There was what looked like a conglomeration of several large lymph nodes that were clearly bulging outward and measured about 10 to 15 cm in total length, along the crease of her right groin.  She showed me her other leg/groin as well which looked normal.

As much as I wanted to tell her exactly what the problem was, I couldn’t.  I just didn’t have the medical knowledge yet.   However, I did let her know that the rapid onset of her symptoms really concerned me and I urged her to go to a nearby city or back to England for immediate medical care.

At first she was very reluctant to leave this small town for fear of missing any of her classes.  However, after after additional discussion we agreed that it was likely time to take a trip back to England anyhow.  After we devised the plan, I wished her the best and I was back on the road.

Many months later, after I had flown back to the US to start Med School, I received a grateful letter from that same woman.  In her note, she told me that immediately after I left, she booked a flight back to England.  Adding she wouldn’t have done this if we hadn’t met.

Fortunately, when she arrived back home, she was quickly treated for what turned out to be a Plague infection.   In that letter, she also said that acting swiftly and flying back home to get treated was a move that saved her life.

The moral of the story; dont mess with the plague. If you are at all concerned that you might have gotten infected, have things checked out ASAP. Early detection & treatment is critical and could save your life.

More on plague symptoms:


Plague is a serious illness. If you are experiencing symptoms that you think could be the plague, seek immediate medical attention. Prompt treatment with the correct medications is critical to prevent complications or death.


About Thomas Osborne, MD

Dr. Osborne is a Harvard trained Radiologist and Neuroradiologist who loves to share his insight about medicine and gardening.


  1. I was deeply moved by this article describing your experience. You were a hero for saving the stranger’s life. I re-read the article because we were plagued by Gophers but having gotten rid of them, they were replaced by an even more determined pest: Squirrels. Not only do they dig holes like the Gophers all over the yard, but they steal all my cherries, peaches, apples, pomegranates, figs, oranges, tomatoes, and the only thing they dont steal are my lemons & limes. So once again I have launched a war campaign against them but they have multiplied so fast, that they have over-run our whole neighborhood. I had used traps, and have 2 BB guns but my Grandkids scream at me if they see me shoot the blighters. Several of us have hired Pest Control services at a cost of several hundreds of dollars because they have taken up residence in several attics ;-( Very Bad News! Is there anything else you can suggest to get rid of them?

    • Thomas Osborne, MD

      Thank you for your kind comments Sateesh.
      It was a moving experience to you can have that kind of impact on someones life.
      However, as I am sure you would agree, we all have the potential to have a profound positive impact on the people around us if there is good intent.

      Now the gophers and squirrels on the other hand…
      I try to be patient with them but it is not an easy task.
      They just take to much.

      Unfortunately, I don’t have a silver bullet for the vermin.
      It seems that (for me) the best solution is a multi-pronged approach.

      Four main strategies I use:
      1. Harassment. I started throwing half bars of “Irish Spring” down the squirrel holes (like grenades). I know they dont like the smell because they either abandon the holes (evidence by spiderwebs at the hole entrance) or they try to push the soap out. I have also tried chili power, etc, which also works but not as much. Then there is always the constant filling their holes and destroying their tunnels.

      2. Physically remove the vermin (choose your own adventure).

      3. Remove their food. I often try to pick fruit just before it is on their ripeness radar. Let it finish ripening in your kitchen. We def need to remove any fallen fruit. This is just a a gateway for the freeloaders.

      4. Scare them away anything bright and flashy such as tinfoil, scare tape, pinwheels, auto water sprayers. Anything! Just put it out near the tree that is starting to produce the ripe fruit and remove when done so they dont get too useto it.

      Good luck!

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