Outbreak of tularemia in muskrats and beavers from Quebec

A beaver and two muskrats were submitted for analysis to the Quebec regional centre. These animals were found dead in May 2022 near Sainte-Anne-de-Sorel, Quebec. Several beaver and muskrat carcasses had been observed in this region in recent weeks.

The animals submitted for analysis showed multifocal pulmonary hemorrhages (Figure 1).

Figure 1. Multifocal pulmonary hemorrhages on macroscopic examination of a beaver with tularemia.

In addition, the beaver had an enlarged spleen speckled with white spots. Histologic examination of the organs revealed an acute multifocal necrotizing hepatitis and splenitis, occasionally associated with the presence of small Gram-negative bacteria (Figure 2).

Figure 2. Acute necrotizing hepatitis, characterized by a coagulated appearance of hepatocytes (asterisk), in a muskrat with tularemia.

The presence of Fransicella tularensis was confirmed by molecular analysis (PCR) in the liver of the three individuals. The bacterial strain associated with these mortalities was identified as type B (ssp. holarctica) by the National Microbiology Laboratory.

To our knowledge, these are the first cases of tularemia diagnosed in wild animals in this region of the province. In Quebec, tularemia is usually observed in snowshoe hares. The presence of this disease in a beaver and in muskrats is therefore unusual for the province. It should be mentioned that F. tularensis holarctica (type B), which is mainly described in aquatic rodents, is less virulent for humans than F. tularensis tularensis (also called F. t. neartica or type A), which mainly circulates in the snowshoe hares.

Tularemia, a zoonosis that can lead to death, can be transmitted to humans following contact with an infected animal or through contaminated material or environment. A person can contract the disease by being bitten or licked by an infected animal, by handling an infected animal, dead or alive, by inhaling air or dust contaminated by the bacteria (risk during opening an infected carcass) or by ingesting contaminated water or food. Tularemia can also be transmitted by tick bites. The disease is not transmitted from person to person. Symptoms of tularemia in people include fever, headache, muscle pain, dry cough and pneumonia. Antibiotic treatment usually manages to control the infection.

CWHC – Quebec

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