Zoonoses: Diseases that pass from animals to humans

We’ve all heard of COVID-19 by now and watched the negative effects that it’s had on our entire world — fear, anger, sadness, and the outright panic.  It has been well established that the disease originated in bats and potentially passed through a creature called a pangolin.

What you might not realize is that we deal with diseases every day that now routinely pass from animals to humans.  These types of diseases are called zoonoses.  The official definition of a zoonosis from the Oxford Dictionary is “a disease which can be transmitted to humans from animals.”

Civilization has dealt with epidemics caused by zoonoses for thousands of years.  The black plague, which is responsible for killing almost a third of the world’s inhabitants was passed along by fleas carried by rats.  Rabid animals were documented and described by the ancient Greeks and Mesopotamians as early as 2300 BC (Fu 1997).  These diseases molded history and society and continue to haunt us today. 

 In addition to these devastating and world-changing diseases, we continue to fight several other lesser-known zoonoses such as tularemia, histoplasmosis, Lyme disease, toxoplasmosis, and Baylisascariasis.  Since most of these (including rabies) can be found in the East Tennessee area, I think it is important to be aware of the symptoms and how each is transferred.

Rabies is a virus carried by some mammals. (primarily bats in this area).  It is transferred by contact with the saliva of a sick animal.  Symptoms appear approximately three weeks to several months later as flu-like symptoms and progress to paralysis, confusion, paranoia, delirium, and death.  Because the virus paralyzes the throat muscles, the sick person or animal can no longer swallow and a foam can be seen around their mouth.

Rabies has no cure, but pets and anyone potentially exposed can and should get a vaccine to protect them.  Very few rabies deaths occur in the U.S. but Africa and Asia still have thousands who die each year.

Tularemia is a bacterial infection most closely associated with flying squirrels in our area.  It is transferred most often by the inhalation of the dust from dried feces.  Symptoms typically appear 3-5 days after exposure and consist of high fever, chills, fatigue, and headache.

Mortality from tularemia is extremely rare as current antibiotics are very effective.  The death rate has dropped from 15% to 2% in the past few decades.

Histoplasmosis is caused by a common fungal spore closely associated with the guano from birds and bats.  The spores can be inhaled, where they embed themselves in the lungs and begin growing.  The symptoms of histoplasmosis appear 3-17 days after exposure and closely mirror flu symptoms (headache, fever, dry cough, and nausea).  It is commonly diagnosed as the flu or a cold in most people, however can be fatal in immune-compromised and older individuals 

Lyme disease is caused by a spirochete carried by the deer tick and carried by mice and deer.  A rash typically appears 7-14 days after an infected tick bite causing a progression of fever, fatigue, muscle and joint pain and potentially cardiac problems if left untreated.

Mortality from Lyme disease is extremely low, however symptoms can plague an individual for the remainder of their lives as there is no known cure.

Baylisascariasis is also called raccoon roundworm because it is found in the intestines of raccoons.  It is transferred by the ingestion of the feces from a raccoon.  Two to four weeks after the accidental ingestion an individual will begin experiencing symptoms of lethargy, slurred speech, loss of coordination, and, if untreated, potentially seizures, coma, and death.  Sadly, most affected individuals are persons under 2 years of age.

Balisascariasis can be treated with a few drugs when caught early.  Unfortunately after 3 days, there will be irreparable damage.

Zoonoses can be controlled and virtually eliminated by taking necessary precautions and limiting one’s contact with wild animals and their droppings.  If you suspect you’ve had a squirrel or raccoon in your attic or crawlspace, you’ll want to limit exposure to that area.  

Thankfully the immediate risk can be eliminated by removing the animal and properly decontaminating its living area.  The best advice is to keep an eye on the outside of your house and keep the animal from ever making entry into your space.   

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