TULAREMIA

TULAREMIA


Tularemia is a bacterial infection, commonly known as rabbit fever or deer tick fever. The disease is endemic to certain areas of the United States and is highly infectious. It has been identified as a possible agent of biological warfare in aerosol form. As few as 10 organisms can cause disease.



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ETIOLOGY: BACTERIAL


Tularemia is caused by Francisella tularensis, a small, gram-negative coccobacillus. The bacterium has a capsule that allows it to survive for several months in water, mud, and decomposing materials, including carcasses.



HOSTS


F. tularensis has been found in over 200 species of vertebrates and invertebrates. The most important hosts in North America are wild rabbits, hares, rodents, pheasants, quail, ticks, and deer flies. Humans are not a natural host. Every state in the United States except Hawaii has reported tularemia. Most cases occur in rural areas in south-central and western states.



TRANSMISSION


Transmission occurs through direct contact with an infected animal, from insect or arthropod bites, or by ingestion of the organism in contaminated food or water. Hunters may come in contact with F. tularensis when skinning or dressing infected rabbits or other wild animals.


Ticks have become the most important vector for transmission of tularemia to humans and domestic animals. They also act as a reservoir to carry F. tularensis from one geographic area or group of animals to another. Exposure to infected rabbits is the second most common source of tularemia. Horse flies, biting flies, sucking lice, and mosquitoes are other vectors, but not as important as ticks (Figure 48).


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FIGURE 48 Tularemia.


F. tularensis can also be aerosolized by riding on particles of dust or mist and can be inhaled. This happens most often during gardening, landscaping, construction, or any activity that disturbs soil. Another less common mode of transmission is handling infected animals or tissues in a laboratory. Person-to-person transmission does not occur.



TULAREMIA IN ANIMALS


Tularemia is more common in wild animals than domestic ones, and is more often fatal in wild animals. Domestic animals are usually considered accidental hosts for F. tularensis. Some species are more susceptible than others to developing clinical disease. The incubation period is 1 to 10 days.



WILD RABBITS, HARES, AND RODENTS


Wild rabbits, hares, and rodents are very susceptible to F. tularensis infection and are often found dead, having exhibited no observable clinical signs. When clinical signs are present, they include depression, anorexia, incoordination, roughened hair coat, and huddling. Pet rabbits and rodents rarely develop tularemia if they are kept indoors.



SHEEP


Tularemia in sheep can be fatal. It shows up as a seasonal disease that coincides with tick season. The clinical signs include fever, diarrhea, weight loss, dyspnea, polyuria (excessive urination), rigid movements, and isolation from the rest of the flock. Mortality is greatest in lambs, and ewes may abort.



CATS


Cats vary in their susceptibility to F. tularensis infection. Some infections are inapparent; others result in septicemia and death. Clinical signs include fever, depression, jaundice, anorexia, weight loss, pneumonia, abscesses, mouth ulcers, splenomegaly (abnormally enlarged spleen), and hepatomegaly (abnormally enlarged liver).

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Oct 1, 2016 | Posted by in EXOTIC, WILD, ZOO | Comments Off on TULAREMIA

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