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Capnocytophaga Canimorsus: Sometimes the Bark is Way Worse than the Bite

dog-licking-lipsCases of serious dog bite infections have been capturing headlines:"Woman Who Contracted Bacterial Infection Caused by Dog's Saliva Dies" (September, 2012), "Texas Mom Loses Legs, Fingers, after Contracting Rare Infection from Minor dog Bite" (January, 2013), and most recently,"Dog Bite Infection Costs Canadian her Arm, Legs" (July, 2013). In all of these cases, the bacteria that caused a life-threatening blood infection, or septicemia, were Capnocytophaga canimorsus. 

What is Capnocytophaga canimorsus?

Capnocytophaga canimorsus is a type of bacteria that is common in dogs’ and cats’ mouths.  Recent estimates using PCR techniques to amplify bacterial DNA are that Capnocytophaga canimorsus is in the mouths of 74% of dogs and 57% of cats.  Although the bacteria are common in household pets’ mouths, overwhelming infections with Capnocytophaga canimorsus or “dog bite septicemia” are rare.  Just over two hundred Capnocytophaga canimorsus cases have been documented since Capnocytophaga canimorsus was first identified in 1976, although this may underestimate the frequency of the infection since it is difficult to grow in cultures and it is not a reportable disease.

How is Capnocytophaga canimorsus transmitted and who is most at risk?

Capnocytophaga canimorsus infections are transmitted primarily through contact with a dog’s saliva, generally through a bite wound, although infections have also been caused by a pet merely licking an open wound or burn.  Capnocytophaga canimorsus infections are more commonly associated with dog bites than cat bites, perhaps because the greater tissue damage associated with dog bites facilitates the growth of Capnocytophaga canimorsus bacteria.  In two rare cases, Capnocytophaga canimorsus infections occurred when veterinarians were struck in the eye by a tooth that fractured while they were performing dental extractions.  While anyone in contact with cats’ and dogs’ saliva is at risk for Capnocytophaga canimorsus infection, at even greater risk are people who have had splenectomies, are alcoholics, have liver disease, or are heavy smokers.  These factors cause increased serum iron content which may facilitate the growth of Capnocytophaga canimorsus bacteria.  Individuals who are immunocompromised are less able to fight infections in general and likely also more susceptible to Capnocytophaga canimorsus infections.  Although a majority of Capnocytophaga canimorsus infections are in people with a predisposing condition, 40% of reported infections occurred in healthy individuals with no identifiable predisposing condition. 

What are the signs of Capnocytophaga canimorsus infection?

Initially, people exposed to Capnocytophaga canimorsus may not even show signs of local infection.  Symptoms of systemic infection generally occur 3-5 days after exposure to the bacteria.  The most common initial signs of a systemic Capnocytophaga canimorsus infection are fever, muscle aches, vomiting, diarrhea, and reduced energy and weakness.  Additional more serious signs occur as the disease progresses and results in a greater than 30% mortality rate.  Patients fortunate enough to survive the infection suffer severe medical consequences from their near-death experience--amputated limbs, kidney disease, or heart disease. 

How is Capnocytophaga canimorsus infection diagnosed?

Capnocytophaga canimorsus infection is diagnosed by culturing the bacteria from the blood of an infected person.  Since the bacteria grow slowly on culture plates, cultures may be discarded before bacteria growth occurs.  When growth does occur, it can be difficult to correctly identify as Capnocytophaga canimorsus.  Since Capnocytophaga canimorsus infections can be effectively treated with antibiotics in early stages, it is crucial that patients presenting with signs of illness discuss possible exposure to dog (or cat) saliva with their doctors.

How can Capnocytophaga canimorsus infection be prevented?

Capnocytophaga canimorsus infection can be prevented by avoiding exposure to dog or cat saliva.  During Westgate Pet Clinic’s puppy and kitten classes, clients are taught that their pets should never be allowed to nip, bite, or scratch them, even in play.  Additionally, pets should not be allowed to lick at wounds or burns.  Any bite, scratch, or open wound in contact with a pet’s saliva should be immediately cleaned, flushed, and disinfected.  Individuals with health conditions that might make them more susceptible to Capnocytophaga canimorsus infections should contact their health care provider to determine if a course of antibiotics is indicated.  Otherwise healthy individuals experiencing progressive signs of illness in the days following exposure to dog or cat saliva should contact their doctor and relate this important part of their health history.  Capnocytophaga canimorsus bacteria are susceptible to common antibiotics and prompt antibiotic treatment can help prevent a serious and potentially deadly systemic infection. 

This article is dedicated to Steve Bishop, beloved uncle and brother of two Westgate Pet Clinic clients, who died from a Capnocytophaga canimorsus infection in 2012.

References available upon request.


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