Capnocytophaga canimorsus

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

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 can evade the immune system through a variety of virulence factors, including the production of cell-killing toxins (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.

People with impaired immunity are at higher risk for infection with this bacterium.

Those especially at risk include the following:

• People who drink alcohol excessively (> two drinks daily)
• People who have no spleen or have impaired spleen function
• People with liver disease
• People with uncontrolled diabetes
• Newborns
• People with inherited or acquired immune deficiency. Examples include advanced HIV infection, certain cancers, chemotherapy, or treatments for autoimmune or rheumatological disorders.

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

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.

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

Symptoms and signs include:

• fever;
• shivering, feeling unusually cold, or shaking chills;
• confusion;
• joint pain, muscle pain;
• headache;
• stomach pain, vomiting, and diarrhea; and
• blisters and/or pus by the bite site.

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:

• pale or grayish skin;
• rapid pulse;
• low blood pressure;
• rash that appears purple and lace-like or marbled;
• change in color of digits, limbs, nose, or ears (from blue to black) as gangrene sets in;
• respiratory failure (inability to breathe without medical support);
• kidney failure (inability to make urine, inability to eliminate waste from the blood); and
• heart attack or heart failure may occur due to very low blood pressure or oxygen levels, as well as toxin damage.

There is usually a team of specialists enlisted to care for a patient with Capnocytophaga infection, depending on the progression of the disease. This may include the following:

• Emergency medicine specialist
• Pediatrician
• Hospitalist
• Surgeon
• Infectious disease specialist
• Pulmonary and critical care specialist
• Kidney specialist

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.

Depending on the severity and progression of the 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 the cleaning of toxins from the blood via dialysis or other methods.
• Gangrene may require the cutting away of dead tissue (debridement) or amputation to control life-threatening 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 in the illness. The prognosis for recovery also depends greatly on how impaired the immune function is. Antibiotics cannot sterilize all infections in the body. Some of the recoveries require 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.

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

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

As the 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 the mother and fetus at a mildly 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.

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 with 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. A medical evaluation can determine whether you need a vaccine. A doctor may prescribe antibiotics to prevent the above infections.