GUIDELINE for Capnocytophaga canimorsus infection

The Capnocytophaga canimorsus infection guidelines were first published in the J Feline Med Surg 2013; 15: 588-590 by Albert Lloret et al. This update was compiled by Etienne Thiry with valuable input from Damien Thiry, Liège University, Belgium.

Key points

• Capnocytophaga canimorsus, cynodegmi, C. canis, C. stomatis and C. felis are part of the oral microbiota of dogs and cats.
• C. canimorsus is more pathogenic and causes more severe infections in humans.
• Disease after a cat bite, scratch or close contact is less frequently seen than after dog contacts.
• Serious disease has been reported especially, but not solely, in immunocompromised and alcoholic individuals. Other comorbidities such as smoking, splenectomy, diabetes mellitus are associated with zoonotic Capnocytophaga infection.
• Disease in cats is not well documented; two cases of respiratory infection have been associated with presence of the bacteria.
• Diagnosis is based on culture in specific media, but these are slow growing bacteria so PCR and sequencing may aid in more rapid diagnosis and species identification.
• Based on incidence surveys, the zoonotic potential is low; the risk may be higher for immunocompromised and alcoholic people, where dog and cat ownership must be discussed.

Agent properties

The genus Capnocytophaga belongs to the Flavobacteriaceae family and contains several species (https://lpsn.dsmz.de/search?word=capnocytophaga). C. canimorsus is a fastidious, slow growing, capnophilic bacterium (capnophiles are microorganisms which thrive in the presence of high concentrations of carbon dioxide); it is facultative anaerobic, gram-negative, and rod-shaped, displaying gliding mobility, and belongs to the normal microbiota of the oral cavity of dogs and cats (Blanche et al., 1998; Dolieslager et al., 2011). C. cynodegmi, C. canis, C. felis, C. stomatis are also present in the oral microbiota (Beauruelle et al., 2022). All can cause wound infections in humans after a bite, C. canimorsus being associated with more severe infections (Brenner et al., 1989). C. canimorsus comprises 9 different serotypes, 3 of them causing 90% of the human infections and are observed in 10% of dogs’ oral microbiota (Renzi et al., 2015 ; Renzi et al., 2018; Spentzouri et al., 2024).

Epidemiology and pathogenesis

C. canimorsus was first cultured in 1976 from the blood and spinal fluid of a dog-bite patient, hence its name (canis = dog and morsus = bite). Infections occur worldwide. Many dogs and cats carry C. canimorsus in their oral cavities. In dogs, a range of prevalences between 3% to 74% was observed in USA, UK, Japan, France, The Netherlands and Switzerland (Butler, 2015). In cats, a range of prevalences between 1% and 57% was observed in France, UK, Japan and The Netherlands (Butler, 2015). The bacteria are also found in sheep, cattle, horses, guinea pigs and rabbits (Butler, 2015). Cat bites and scratches or contact with cats have been reported in less than 10% of the cases (Lion et al., 1996). In a ten year retrospective French study, 12% of the human cases (out of 44) were reported after a contact with a cat (Beauruelle et al., 2022). In general, cat bites cause less tissue damage than dog bites, which might create less favourable conditions for bacterial growth (Gaastra and Lipman, 2010). Capnocytophaga infection is quite uncommon after dog and cat bites. In surveys from Denmark and The Netherlands, a yearly incidence of sepsis due to C. canimorsus was calculated to be 0.5 and 0.63 per million population, respectively (Pers et al., 1996; Van Dam and Jansz, 2010).

Clinical signs

Disease in humans

Most cases occur in immunocompromised people after a dog bite. The range of clinical features varies from an infected local wound to sepsis, meningitis, nephritis, osteomyelitis, endocarditis, peritonitis, pneumonia, purulent arthritis, abscesses and disseminated intravascular coagulation (Lion et al., 1996; Janda et al., 2006; Gaastra and Lipman, 2010). The severe course of infection is mainly found in chronic alcohol users, asplenic and immunocompromised people (Lion et al., 1996; Janda et al., 2006), but has also been reported in healthy persons (Hantson et al., 1991). The case/fatality rate is around 26% (Buttler, 2015). Most cases have been related to contact with dogs but infection after cat bites or scratches has also been described (Mahrer and Raik, 1992; Valtonen et al., 1995; McLean et al., 2004).

Disease in cats

Capnocytophaga infections after bite trauma in cats have not been reported, and only two cases of a possible pathogenic role of the bacterium have been documented. In one instance, Capnocytophaga spp. were isolated from a case of chronic sinusitis and rhinitis, and – based on DNA sequencing – a strain closely related to C. canimorsus and C. epidegmi was identified from the nasal discharge. Since no other causes for chronic nasal discharge were found, the role of Capnocytophaga spp. was considered likely (Frey et al., 2003). Another case report describes the isolation of C. cytodegmi from bronchoalveolar lavage samples of a cat with lower respiratory tract infection and pulmonary carcinoma. Clinical signs and bacterial colonization resolved after treatment with a fluoroquinolone (Forman et al., 2005).

Diagnosis

In humans, diagnosis of a C. canimorsus infection is usually based on bacterial culture of blood or other body fluids; isolation directly from bite wounds is rare. The bacterium grows slowly on special media (chocolate agar or heart infusion agar with 5% rabbit blood, incubated at 37°C in a 5% CO₂  atmosphere; Lion et al., 1996). PCR methods can distinguish between C. canimorsus and C cytodegmi (Suzuki et al., 2010). Maldi-Tof is also reported as a good diagnostic tool to identify the bacterium (Magnette et al., 2016).

Treatment and prevention

In humans, beta-lactams, with or without beta-lactamase inhibitors, remain the first choice antibiotic. As several reports showed the presence of beta-lactamases, susceptibility testing is encouraged (Spentzouri et al., 2024). Immediate cleaning and disinfection of bite wounds and scratches is important, as well as antibiotic prophylaxis depending on the wound and the immune status of the patient (Oehler et al., 2009; Gaastra and Lipman, 2010).

Zoonotic risk

The risk of disease after a cat bite in immunocompetent persons is low, if minimal prophylactic measures are taken. Immunocompromised cat owners, however, are at risk of developing a serious infection and should be informed to contact a health professional following receiving a bite. Rough playing with cats, with the inevitable bites and scratches should be discouraged.

Acknowledgement

ABCD Europe gratefully acknowledges the support of Boehringer Ingelheim (the founding sponsor of the ABCD), Virbac and MSD Animal Health.

References

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Brenner DJ, Hollis DG, Fanning GR, Weaver RE (1989): Capnocytophaga canimorsus sp. nov. (formerly CDC group DF-2), a cause of septicaemia following dog bite, and C. cynodegmi sp. nov., a cause of localized wound infection following dog bite. Journal of Clinical Microbiology 27, 231-235.

Butler T (2015): Capnocytophaga canimorsus: an emerging cause of sepsis, meningitis, and post-splenectomy infection after dog bites. European Journal of Clinical Microbiology and infectious Diseases 34, 1271–1280.

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Forman MA, Johnson LR, Jang S, Foley J ( 2005): Lower respiratory tract infection due to Capnocytophaga cynodegmi in a cat with pulmonary carcinoma. Journal of Feline Medicine and Surgery 7, 227-231.

Frey E, Pressler B, Guy J, Pitulle C, Breidtschwerdt E (2003): Capnocytophaga sp. isolated from a cat with chronic sinusitis and rhinitis. Journal of Clinical Microbiology 41, 5321-5324.

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Hantson P, Gautier PE, Vekemans MC, Fievez P, Evrard P, Wauters G, Mahieu P (1991): Fatal Capnocytophaga canimorsus infection in a previously healthy woman. Annals of Emergency Medicine 20, 93-94.

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McLean CR, Hargrove R, Behn E (2004): The first fatal case of Capnocytophaga canimorsus sepsis caused by a cat scratch. Journal of the Royal Naval Medical Service 90, 13-15.

Oehler RL, Velez AP, Mizrachi M, Lamarche J, Gompf S (2009): Bite-related and septic syndromes caused by cats and dogs. Lancet Infectious Diseases 9, 439-447.

Pers C, Gahrn-Hansen B, Frederiksen W (1996): Capnocytophaga canimorsus septicemia in Denmark, 1982-1995: review of 39 cases. Clinical Infectious Diseases 23, 71-75.

Renzi F, Dol M, Raymackers A, Manfredi P, Cornelis GR  (2015): Only a Subset of C. canimorsus Strains Is Dangerous for Humans. Emerging Microbes and Infections  4, e48.

Renzi F, Hess E, Dol M, Koudad D, Carlier E, Ohlén M, Moore E, Cornelis GR  (2018): Capsular Serovars of Virulent Capnocytophaga Canimorsus Are Shared by the Closely Related Species C. canis and C. cynodegmi. Emerging Microbes and Infections 7, 124.

Spentzouri D, Baliou S, Ioannou P (2024): Infective Endocarditis by Capnocytophaga Species—A Narrative Review. Medicina 60, 382.

Suzuki M, Kimura M, Imaoka K, Yamada A (2010): Prevalence of Capnocytophaga canimorsus and Capnocytophaga cynodegmi in dogs and cats determined by using a newly established species-specific PCR. Veterinary Microbiology 144, 172-176.

Valtonen M, Lauhio A, Carlson P, Multanen J, Sivonen A, Vaara M, et al (1995): Capnocytophaga canimorsus septicemia: fifth report of a cat associated infection and five other cases. European Journal of Clinical Microbiology and infectious Diseases 14, 520-523.

Van Dam AP, Jansz A (2010): Capnocytophaga canimorsus infections in The Netherlands: a nationwide survey. Clinical Microbiology and Infection 17, 312-315.