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Capnocytophaga canimorsus

Capnocytophaga facts

A lick or bite from a dog can transmit Capnocytophaga bacteria to a person.
A lick or bite from a dog can transmit Capnocytophaga bacteria to a person.

What is Capnocytophaga?

Capnocytophaga is a genus of nine species of bacteria found in human and animal mouths and gums, all of which cause human infection. Capnocytophaga ochracea, gingivalis, and sputigena exist in humans and can cause pharyngeal and respiratory infections from the person's own flora. Typically, these bacteria do not cause disease except as an opportunistic infection in people with impaired immune defenses. Capnocytophaga canimorsus commonly lives in the mouths of dogs and cats without making them sick.

Capnocytophaga is a thin Gram-negative bacillus that is difficult to grow in routine laboratory cultures. It is able to evade the immune system by a variety of virulence factors, including production of cell-killing toxin (cytotoxin) and resistance to killing by complement. It also causes blockages of small blood vessels (micro-emboli) that lead to a characteristic rash, organ failure, and tissue death (necrosis) or gangrene. The spleen plays an important role in defense against this bacterium.

What are causes and risk factors of Capnocytophaga?

  • People with impaired immunity are at higher risk for infection with this bacterium. Those especially at risk include the following:

Is a Capnocytophaga infection contagious?

Capnocytophaga canimorsus is not contagious from person to person. It is contagious from animals to people (zoonosis) and spreads by lick, scratch, bite, or other close contact, usually from a dog or cat.

What is the incubation period for a Capnocytophaga infection?

Capnocytophaga canimorsus infections usually cause symptoms and signs within 3 to 8 days after a lick or bite from a cat or dog, but the incubation period may be as short as 1 day or up to 2 weeks.

What are Capnocytophaga infection symptoms and signs?

Symptoms and signs of Capnocytophaga canimorsus infections may occur suddenly and without evidence of an infected bite. Symptoms and signs include

Redness, warmth, and pain may or may not occur at the site of a bite or scratch. When infection does occur, it may occur with pain at the bite wound and blisters and draining pus may form around the wound within hours of the bite.

As the disease progresses or becomes more severe, signs of sepsis or septic shock may occur, including

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What tests diagnose Capnocytophaga infections?

Doctors diagnose Capnocytophaga canimorsus by detecting it in the blood by growing the bacterium in cultures performed in a microbiology laboratory. Blood cultures may detect most bacteria ("become positive") within 1 to 2 days of incubating the blood in the lab. However, Capnocytophaga tends to require specific nutrients and grows slowly, so diagnosis may be delayed. At this point, a Gram stain of the culture will identify a "Gram negative bacillus"; another day may be required to fully identify the species and provide information about the antibiotics that may or may not kill it.

What specialists treat Capnocytophaga infections?

There is usually a team of specialists enlisted to care for a patient with Capnocytophaga infection, depending on progression of disease. This may include an emergency medicine specialist, pediatrician, hospitalist, surgeon, infectious disease specialist, pulmonary and critical care specialist, and kidney specialist.

What are treatment options for Capnocytophaga infections?

Depending on severity and progression of disease, treatment includes intravenous antibiotics, intravenous fluids, and medications to raise low blood pressure. Respiratory failure may require non-invasive support such as positive airway pressure or insertion of a breathing tube to fully support breathing via a mechanical ventilator. Kidney failure requires cleaning of toxins from the blood via dialysis or other methods. Gangrene may require cutting away of dead tissue (debridement) or amputation to control life-threatening infection.

What are complications of a Capnocytophaga infection?

Complications include long-term disability from lung, kidney, brain or other organ damage, loss of body parts from gangrene, and death.

Can Capnocytophaga affect pregnancy or an unborn baby?

As pregnancy advances, the mother's immune system becomes mildly but progressively weaker. This prevents the mother's body from rejecting the developing fetus as a "foreign body." However, this also puts mother and fetus at mild increased risk of some infections, especially if she is diabetic.

Capnocytophaga canimorsus can cause infection of the placenta and birth sac (chorioamnionitis). This can cause premature delivery, fetal death, low birth weight, or life-threatening infection (sepsis) in the newborn.

What is the prognosis for a Capnocytophaga infection?

The prognosis of these infections often depends on how soon treatment starts. Many people underestimate the seriousness of their condition (especially if there are no signs of skin infection) and are not aware of their risk. Often people do not seek care until later into the illness. Prognosis for recovery also depends greatly on how impaired the immune function is. Antibiotics cannot sterilize all infection in the body. Some of the recovery requires the individual's immune defenses to fight the remaining bacteria.

Some infections can progress to death within days, so it is important to seek care immediately if a dog or cat bites you.

The overall mortality rate of Capnocytophaga canimorsus is approximately 30%, higher in those with septic shock and without a spleen.

Is it possible to prevent a Capnocytophaga infection?

Currently, there is no commercially available vaccine for Capnocytophaga infections.

The only way to completely avoid Capnocytophaga canimorsus infections is to completely avoid contact with pets. However, pets play a life-enriching role for many people, and this may be very difficult. Thus, it is more helpful to try to avoid frequent contact with pets during periods of impaired immune function. This may include limiting sleep with your pet or boisterous play that may lead to a scratch or bite. It is most important to avoid contact of pet saliva with intact or broken skin (especially wounds) and mucous membranes (eyes, nose, mouth). Promptly wash all skin with soap and water after being in contact with pets and items that may be soiled with pet saliva.

It is a myth that antibodies in saliva are especially therapeutic or protective against infections. Pets should never be allowed to lick wounds or a young baby's face.

It is important to talk to your doctor about how long your immune system will be impaired and what you should do.

No matter how healthy you are, you should always wash animal bites thoroughly with soap and water and seek medical attention. Aside from Capnocytophaga, animal bites may cause tetanus, rabies, and serious infections due to Staphylococcus aureus (including methicillin-resistant Staphylococcus aureus or MRSA), Streptococcus, and Pasteurella multocida. Medical evaluation can determine whether you need a vaccine. A doctor may prescribe antibiotics to prevent the above infections.

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Reviewed on 8/15/2019
References
Butler, T. "Capnocytophaga canimorsus: an emerging cause of sepsis, meningitis, and post-splenectomy infection after dog bites." Eur J Clin Microbiol Infect Dis 34.7 July 2015: 1271-80. doi: 10.1007/s10096-015-2360-7. Epub 2015 Apr 1.

Janda, J.M. Chapter 235: "Capnocytophaga." Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases, Eighth Edition. Saunders, 2015.

Low, S., and J. Greenwood. "Capnocytophaga canimorsus: infection, septicaemia, recovery and reconstruction." J. Med. Microbiol 57.7 (2008): 901-903. doi:10.1099/jmm.0.47756-0

United States. Centers for Disease Control and Prevention. "Capnocytophaga." Updated Oct. 16, 2018. Accessed Aug. 7, 2019. <https://www.cdc.gov/capnocytophaga/index.html>.

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