Francisella tularensis infection

edited November, 2016

The Francisella tularensis infection in cats guidelines were published in J Feline Med Surg 2013; 15: 585-587; this update has been compiled by Maria Grazia Pennisi.

 

 

Synopsis

 

This bacterial species was discovered in ground squirrels in Tulare County, California, in 1911. Tularaemia is a potentially fatal zoonosis. Various clinical syndromes occur, but most patients either present with a localized infection of the skin and draining lymph nodes (the ulceroglandular form) or with a systemic infection (typhoidal tularaemia). Oropharyngeal and pneumonic forms are rare. The risk of acquiring the infection from cats is low, but exists for owners of outdoor cats, veterinarians and technicians (Liles and Burger, 1993). Regular external parasiticidal treatment to prevent tick infestations is recommended for outdoor cats. When handling animals with suppurative or draining skin or lymph node lesions in endemic areas, gloves and goggles should be worn. Gloves should also be worn when examining the oral mucosa. Handling of diagnostic samples by laboratory staff requires adherence to the appropriate biosafety procedures (Greene, 2012).

 

 

Agent properties

 

Francisella tularensis (formerly Pasteurella tularensis) is a small, gram-negative, non-spore-forming, vector borne zoonotic bacterium (Greene, 2012). Two biovars have been described as causing disease in the cat: type A or F. tularensis tularensis present in North America (virulent, associated with a tick/rabbit cycle), and type B or F. tularensis holarctica (used in the past for a human live attenuated vaccine) with a broader distribution. The latter has a more complex life cycle involving lagomorphs and ticks or mosquitoes, as well as contaminated water. F. tularensis has a wide host range involving more than 100 mammals, birds, fish, reptiles and amphibians. Cats are more susceptible than dogs, but rodents (included pet hamsters) and lagomorphs are considered the most susceptible mammalian hosts, that may suffer from an often fatal disease (Rhyan et al., 1990).

 

 

Epidemiology and vectors

 

Tularaemia is a rural, potentially fatal zoonosis sporadically occurring throughout temperate zones of the Northern hemisphere: North America, Eurasia, parts of the Middle East and the north coast of Africa (Goetherth et al., 2004; Foley and Nieto, 2010).  F. tularensis infection may be acquired through many species of blood-sucking arthropods, included fleas; flies and mosquitos are mechanical vectors, only ticks (Dermacentor, Amblyomma, Haemaphysalis and Ixodes) are also long-term reservoir and pass the infection to a new generation transovarially (Foley and Nieto, 2010). Cats may also be infected by their rodent or lagomorph prey carrying the bacteria.

 

Infected domestic cats may transmit tularaemia to humans by bites and scratches but also by direct contact with infected body fluids or tissues with the skin. Persons can also become infected by ingestion of contaminated food or water, by contact with lagomorphs, or by inhalation during farming activities (Foley and Nieto, 2010).

 

In the USA, the human incidence is about 120 cases per year and the infection has been reported in all the states, with the exception of Hawaii (Anonymous, 2013). In the USA, 12-24% of client-owned cats have antibodies directed against F. tularensis (Magnarelli et al., 2007). Moreover, investigation on 106 isolates detected a high percentage of feline-associated strains from regions where the bacterium is endemic (Larson et al., 2014).

 

In Scandinavian countries, the human disease has been studied – feline cases have never been reported. A study of an outbreak in Sweden showed that human cases were linked to mosquito bites as the main risk factor, but contact with cats was also thought to be important. In that outbreak, pneumonia was related with farm work (Eliasson et al., 2002). Tularaemia has been reported from Norway after a cat bite (Yaqub et al., 2004). Based on the number of reported cases, the risk of tularaemia is small, even in endemic areas. The risk for free-roaming cats is related to tick exposure and to hunting rodents or lagomorphs.

 

 

Clinical signs

 

In humans

 

Tularaemia is a potentially fatal zoonosis. Various syndromes occur, but most patients either present with a localized infection of the skin and draining lymph nodes (the ulceroglandular form) or with a systemic infection (typhoidal tularaemia). The oropharyngeal and the pneumonic forms are more rare.

The ulceroglandular form usually occurs following a tick or fly bite or after handing of an infected animal. A skin ulcer appears at the site where the organism entered the body (Fig. 1). The ulcer is accompanied by swelling of regional lymph glands, usually in the armpit or groin.

Fig. 1. Ulceroglandular form of tularemia: a skin ulcer at the site where the organism entered the body - accompanied by swelling of regional lymph nodes. From the Centers fro Disease Control and Prevention (http://www.cdc.gov/tularemia/signssymptoms/index.html)

Fig. 1. A skin ulcer at the site where the organism entered the body – accompanied by swelling of regional lymph nodes (The Centers for Disease Control and Prevention)

 

In cats

 

Most cases were reported retrospectively, when cats were suspected of having transmitted tularaemia to humans, because clinical signs are often uncharacteristic. Severity is variable, ranging from a mild chronic localized infection (the ulceroglandular form) to a fatal acute disease (systemic). Kittens develop a more severe systemic disease (typhoidal) associated with fever, depression, enlargement of lymph nodes, liver and spleen, jaundice (Baldwin et al., 1991; Woods et al., 1998). The localized form is represented by chronically draining subcutaneous abscesses (Valentine et al., 2004). Some cats show oral and/or lingual ulcerations (Greene, 2012). Laboratory abnormalities may include leukocytosis or panleukopenia, thrombocytopenia, increased serum aminotransferase and alkaline phosphatase activities, hyperbilirubinaemia. Hyperplastic lymph nodes are found upon cytological examination (Greene, 2012).

 

Lesions and signs can be therefore similar to those of plague, and the two bacteria have also similar epidemiological characteristics (Rhyan et al., 1990). Tularaemia should be included in the differential diagnosis of fever of unknown origin in cats in tick-endemic areas, as well as of chronic subcutaneous infections or affected draining tracts.

 

Lesions and signs can be therefore similar to those of plague, and the two bacteria have also similar epidemiological characteristics (Rhyan et al., 1990). Tularaemia should be included in the differential diagnosis of fever of unknown origin in cats in tick-endemic areas, as well as of chronic subcutaneous infections or affected draining tracts.

 

 

Diagnosis

 

Specific antibodies can be detected by  microagglutination (MA) tests as well as indirect fluorescent antibody test (IFAT); however, antibodies appear about three weeks after infection, and negative results are obtained at the onset of clinical signs (Feldmann, 2003). A fourfold rise of antibody titre or a positive titre of 160 is considered suggestive of acute infection (Greene, 2012). In seropositive cats, bacterial DNA could not be evidenced by PCR in all cases, which suggests residual antibody from prior subclinical or undiagnosed infections (Magnarelli et al., 2007).

 

Definitive diagnosis requires bacterial culture, which appeared to be more sensitive than immunohistochemistry in one case report (Valentine et al., 2004). Culture requires special media, but above all biosafety measures when handling infected tissues.

 

 

Treatment

 

We have limited information on treatment of tularaemia in cats. Gentamycin is the treatment of choice in humans. Tetracycline (doxycycline) and fluoroquinolone for about 2 weeks are considered good second choices (Greene, 2012).

 

 

Recommendations to avoid zoonotic transmission from cats

 

The risk of acquiring the infection from cats is low, but certainly not negligible for owners of outdoor cats, veterinarians and technicians (Liles and Burger, 1993).

 

Regular external parasiticidal treatment to prevent tick infestations are recommended for outdoor cats. When handling animals with suppurative or draining skin or lymph node lesions in endemic areas, gloves and goggles should be worn, also when examining the oral mucosa. Handling diagnostic samples by laboratory staff should follow biosafety procedures (Greene, 2012).

 

 

 

References

 

Anonymous (2013): Tularaemia. Centers for disease control and prevention. http://www.cdc.gov/tularaemia/statistics/

Baldwin CJ, Panciera RJ, Morton RJ, Cowell AK, Waurzyniak BJ (1991): Acute tularaemia in three domestic cats. J Am Vet Med Assoc 199, 1602-1605.

Eliasson H, Lindbäck J, Pekka Nuorti J, Arneborn M, Giesecke J, Tegnell A (2002): The 2000 tularaemia outbreak: a case-control study of risk factors in disease-endemic and emergent areas, Sweden. Emerging Inf Dis 8, 956-960.

Feldmann KA (2003): Tularaemia. J Am Vet Med Assoc 222, 725-730.

Foley JE, Nieto NC (2010): Tularaemia. Vet Microbiol 140, 332-338.

Goetherth HK, Shani I, Telford SR III (2004): Genotypic diversity of Francisella tularensis infecting Dermacentor variabilis ticks on Martha’s Vineyard, Massachussets. J Clin Microbiol 42, 4968-4973.

Greene CE (2012): Francisella and Coxiella infections. In: Greene CE (ed). Infectious diseases of the dog and cat. IV ed. St. Louis, Missuri, Elsevier, pp. 476-482.

Larson MA, Fey PD, Hinrichs SH, Iwen PC (2014): Francisella tularensis bacteria associated with feline tularemia in the United States. Emerging Inf Dis 20, 2068-2071.

Liles WC, Burger RJ (1993): Tularaemia from domestic cats. West J Medicine 158, 619-622.

Magnarelli L, Levy S, Koski R (2007):  Detection of antibodies to Francisella tularensis in cats. Res Vet Sci 82, 22-26.

Rhyan JC, Gahagan T, Fales WH (1990): Tularaemia in a cat. J Vet Diagn Invest 2, 239-241.

Valentine BA, De Bey BM, Sonn RJ, Stauffer LR, Pielstick LG (2004): Localized cutaneous infection with Francisella tularensis resembling ulceroglandular tularaemia in a cat. J Vet Diagn Invest 16, 83-85.

Woods JP, Crystal MA, Morton RJ, Panciera RJ (1998): Tularaemia in two cats. J Am Vet Med Assoc 212, 81-83.

Yaqub S, Biørnholt JV, Enger AE (2004): Tularaemia from a cat bite. Tidsskr Nor Laegeforen 124, 3197-3198.

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