Rabbit Fever

Fall is upon us, and many people are getting ready for fall and winter hunting.  Now is a good time to review some of the zoonotic diseases to remember when dressing game in the field.  One such disease is tularemia. 

Tularemia is commonly called “rabbit fever” because small mammals such as rabbits and hares are the natural reservoir of the bacteria Francisella tularensis.  This is a Gram-negative coccobacillus.  It is a stable bacteria that can survive in the environment for weeks to months.      

The disease occurs worldwide.  It has been listed as a potential biological weapon by the Centers for Disease Control and Prevention (CDC).  Many mammals are susceptible to the disease, including wild rodents, rabbits, livestock (especially sheep), fish, birds, dogs, cats, and humans.  Cattle seem to be resistant to the disease.  Most human cases are reported from Arkansas, Oklahoma, and Missouri

The bacteria can be found in body fluids of infected animals.  These fluids can contaminate the environment, including vegetation, water, and soil.  Mammals can become infected by ingesting the bacteria from eating vegetation or drinking contaminated water.  Infection can also occur from tick or fly bites, direct contact with the bacteria to broken skin or on mucous membranes, or from inhaling the bacteria in dust.  Ticks commonly associated with tularemia include Amblyomma americanum (Lone Star tick in the southern US), Dermacentor andersoni (Rocky Mountain wood tick), D. variabilis (American dog tick throughout the US).  Some biting flies and mosquitos can transmit the bacteria as well.

Humans can be exposed to the bacteria from animal bites, handling infected tissues, ingesting infected meat that has not been cooked properly, ingesting contaminated water, inhaling contaminated dust, or from tick bites. 

The incubation period of tularemia can range from 1 to 10 days, with most developing signs in 3-5 days.  The clinical syndrome presented is related to the mode of transmission.  The six forms are ulceroglandular, oculoglandular, pneumonic, oropharyngeal, gastrointestinal, and typhoidal.

Common clinical signs in animals include fever, depression, lack of appetite, vomiting and diarrhea, and weakness.  Often, a sudden die-off of rabbits is noted during an outbreak. 

Humans can exhibit flu-like symptoms, cough, skin rash, pneumonia, or swollen lymph nodes that can rupture and drain pus.  Some cases can progress to fatal septicemia or pneumonia.  

Tularemia is a rare disease of humans and often presents with symptoms that are confused with other infections.  It is important to inform your physician of any history of exposure to ticks or wild animals or possibly contaminated environments.  If caught early, treatment with antibiotics is usually successful. 

With multiple routes of exposure, prevention is multi-faceted.  Common safety practices will reduce the chance of contracting tularemia, as well as many other zoonotic diseases.

• Prevention of tick bites is very important.
• Regular use of insect repellents containing DEET is effective.
• Use proper respiratory PPE when mowing or landscaping to prevent inhalation of aerosols.
• Wear gloves when cleaning game, and properly cook meat before consuming. Freezing meat does not kill the bacteria. 
• Do not drink untreated water.