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TULARAEMIA ("RABBIT FEVER")

Note for Pet Owners:

This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Tularaemia is a zoonosis and so precautions including the wearing of gloves and masks   should be taken when handling suspected infected animals or materials from such animals

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Description
Tularaemia is a bacterial infection which causes acute illness in many species including birds and mammals - including humans.. The disease occurs in the Northern Hemisphere.

Also known as Rabbit Fever

Cause
The cause of Tularaemia is a small gram-negative rod-shaped bacterium called Francisella tularensis which occurs in two variants - A and B. Type A only occurs in the USA and  is very virulent for rabbits, Type B occurs throughout the Northern Hemisphere and  is not virulent for rabbits and rarely causes disease in its main hosts eg rodents . The organism can survive for long periods of time in carcases, mud or water but it is susceptible to heat and disinfectants.

Ectoparasites (ticks and mosquitoes) provide a reservoir of infection and act as vectors for the disease, transmitting it to rabbits, rodents and other hosts. Cats and dogs become infected through tick bites or when they hunt or eat infected rabbits, hares or rodents.

In the USA the majority of human cases are thought to be contracted from tick bites or contact with the infected tissue of wild animals, especially rabbits. Some cases (1.6%) are associated with cat bites or scratches and only a few cases are associated with dogs.

The disease can be transmitted by :

  • Aerosol spread
  • Inoculation - bites, scratches, wounds, open skin sores
  • Through the conjunctiva of the eye

Exposure to very few organisms is necessary to cause disease , and in humans less than 100 organisms are needed and humans are most often infected through one of the following routes :

  • Direct contact with blood, body secretions or tissues of an infected animal
  • Bite from an infected  parasite (eg fleas, lice or ticks)

 

Breed Occurrence
There is no breed predisposition, but dogs and cats that hunt rabbits are at greater risk

Humans most often contract the disease from :

  • Rabbits
  • Muskrats
  • Others

Human workers most at risk to contract the disease include :

  • Abattoir workers
  • Agricultural workers
  • Forestry workers
  • Hunters
  • Veterinarians

Signs

Various signs have been described in this disease,  including the following :

In cats :

  • Some cats are unaffected
  • Kittens are more susceptible than adults
  • Anorexia
  • Depression
  • Multiple abscesses in organs eg liver and spleen
  • Hepatomegaly - occasionally jaundice
  • Splenomegaly
  • Oral ulcers
  • Respiratory signs eg pneumonia
  • Panleukopenia
  • Weight loss
  • Death

In dogs :

In humans the signs of tularemia depend upon the route of infection :

  • The incubation period is 2-10 days
  • Fever
  • A local reaction (skin ulcer) occurs at the site of inoculation (eg scratch or bite)
  • Enlargement of local and regional lymph nodes (lymphadenopathy)
  • Splenomegaly
  • Spread via the bloodstream to multiple organs.
  • In one form of the disease an atypical pneumonia occurs - mortality may be over 30%

Diagnosis
Diagnosis can be made by several methods :

  • Finding antibodies in blood samples - ELISA and FA tests
  • Isolation of the bacterium F.tularensis from fluids or tissue samples

Because so few organisms (<100) are necessary to cause disease in humans safety precautions (eg use of a biohazard cabinet) should be taken to ensure that staff are not contaminated during sampling, testing or post-mortem examination.

Treatment
Antibiotics that are reported to be effective against F.tularensis include :

  • Aminoglycosides -  used to treat human cases of tularemia (eg gentamicin and streptomycin). 
  • Chloramphenicol 
  • Fluorquinolones
  • Tetracycline

No vaccine is available.

Routine ectoparasite treatment for ticks may be important to minimise transmission to domestic animals living in endemic areas. Direct contact with rabbits and rodents should be avoided in endemic areas.

Prognosis
Poor if untreated and once the disease has become disseminated throughout the body. Mortality can be high in certain forms of the disease - eg pneumonic form in humans.

 

Updated October 2013