Do Indoor Cats Harbor This Dangerous Bacteria?


Capnocytophaga is a genus of gram-negative bacteria that are commonly found in the oral flora of cats, dogs, and humans. These rod-shaped bacteria live in the mouths and gums of many mammals and can be transmitted through bites, scratches, or other close contact (CDC). Although Capnocytophaga bacteria are normal commensal organisms in animal mouths, they can occasionally cause opportunistic infections in humans.

There are over 15 different species of Capnocytophaga, but the two most common in cats and dogs are Capnocytophaga canimorsus and Capnocytophaga cynodegmi. These bacteria colonize the saliva of healthy pets and usually do not cause any illness in the animals (Lloret et al., 2013). Indoor cats can carry Capnocytophaga in their oral microflora just like outdoor cats. The presence of these bacteria in itself is not a cause for concern in pets. However, Capnocytophaga infections in humans can sometimes occur after an animal bite, scratch, or lick.

Transmission of Capnocytophaga

Capnocytophaga bacteria are commonly found in the normal oral flora of cats. Cats most often become infected or colonized with Capnocytophaga through exposure to the bacteria from other cats. This transmission can occur through activities like grooming, biting, or close contact between cats (1).

Kittens may also acquire Capnocytophaga bacteria from their mothers, either before birth or when nursing. The bacteria can spread from the mother’s mouth to the kittens (2).

Overall, Capnocytophaga transmission occurs through direct contact with saliva, respiratory secretions, urine, or feces of infected cats. Biting and scratching are common routes of infection as the bacteria can be introduced through a break in the skin. Grooming between cats allows for saliva transmission. Using the same litterboxes or food bowls can also facilitate spread. Kittens are particularly susceptible when the bacteria spreads from the mother (1).

While Capnocytophaga bacteria are normal commensals in cat mouths, overgrowth, immunocompromise, or injury can lead to infection in cats. Indoor cats can carry and transmit Capnocytophaga through typical social behaviors like grooming, playing, biting, and sharing resources (2).

Prevalence in Indoor Cats

Studies estimate that Capnocytophaga infection rates in indoor cats range from 57% to 84%. One study detected Capnocytophaga in 57% of indoor cats compared to 74% of outdoor dogs ( Another study found Capnocytophaga in 84% of indoor cats compared to 86% of dogs (

These infection rates are similar to those seen in outdoor and feral cats. One study found Capnocytophaga present in 80% of feral cats (Lloret et al., 2012). The high prevalence across indoor, outdoor, and feral cats suggests that housing environment does not significantly impact Capnocytophaga infection rates in cats.

Symptoms in Cats

Most cats infected with Capnocytophaga show no symptoms and appear healthy. The bacteria usually live harmlessly in a cat’s mouth without causing issues. However, some cats may develop mild symptoms when infected.

According to the CDC, potential symptoms in cats can include: [1]

  • Oral lesions
  • Drooling
  • Red and swollen gums
  • Loss of appetite
  • Fever
  • Lethargy

But even with these symptoms present, Capnocytophaga infection often goes undetected in cats. Routine testing is not recommended unless the cat has bitten or scratched someone. Most infected cats continue to appear healthy and exhibit normal behavior.

Risks to Humans

Capnocytophaga bacteria can potentially spread from cats to humans through bites, scratches, or close contact. According to the CDC, “Capnocytophaga bacteria (germs) can spread to people through bites, scratches, licks or other close contact with animals like dogs and cats.” Cats may carry Capnocytophaga in their mouths without showing any signs or symptoms of illness.

In humans, Capnocytophaga infections are rare but can cause severe illness in some cases. Potential diseases include sepsis, meningitis, endocarditis, and eye infections according to the CDC. Those at highest risk include people with weakened immune systems, older adults, and those who abuse alcohol. Infections require close contact with a cat and do not spread easily between humans. Prompt medical treatment is essential for serious Capnocytophaga infections.


There are several ways to help prevent the transmission of Capnocytophaga from cats to humans:

Wash hands thoroughly with soap and warm water after touching cats, cleaning litter boxes, or picking up cat waste. Alcohol-based hand sanitizers are not effective against Capnocytophaga (CDC,

Avoid kissing, nuzzling, or getting licked/bitten by cats. Bites and scratches can introduce Capnocytophaga into the body (CDC,

Clean litter boxes daily to reduce bacterial load. Use gloves and wash hands after handling litter (CDC,

Keep cats’ claws trimmed to minimize scratches. Scratches can allow entry of Capnocytophaga bacteria (Lloret et al.,

Treat cat bites promptly by thoroughly cleaning the wound. Seek medical care for redness, swelling, drainage, or fever after a cat bite (CDC,

Immunocompromised individuals may consider avoiding high-risk activities like changing litter boxes. Have someone else perform these tasks if possible (CDC,


There are a few ways to test cats for Capnocytophaga:

Bacterial culture: A sample from the cat’s mouth is taken with a swab and grown in a laboratory to look for the presence of Capnocytophaga bacteria. This is the most definitive way to diagnose the infection.

According to the CDC, routine testing of cats for Capnocytophaga is not recommended. Testing may be done if a cat has bitten someone and there is concern about transmission. Testing shortly after a bite can determine if the cat carried Capnocytophaga at the time. However, a negative test does not rule out the possibility of the cat harboring the bacteria later on (1).

PCR test: This looks for the DNA of Capnocytophaga in a mouth swab sample. It is a quicker way to detect the presence of the bacteria.

Antibody test: A blood sample can be checked for antibodies that the cat’s immune system produced against Capnocytophaga. This indicates exposure/infection but does not confirm current infection.

In general, testing is only recommended when a cat has had intensive contact with humans and there is concern about transmission of the bacteria. Routine screening of healthy cats is not necessary.


Capnocytophaga infections in cats are typically treated with antibiotics like penicillin or beta-lactams (Lloret, 2013). The specific antibiotic and dosage prescribed will depend on the severity of infection. Antibiotics are usually given for 2-3 weeks. Supportive care like fluids may also be provided if the cat is dehydrated or has other complications.

For humans infected with Capnocytophaga from cats, antibiotics are also the main treatment. Doxycycline is commonly prescribed, but other antibiotics like penicillin, cephalosporins, carbapenems, or fluoroquinolones may be used instead or in combination (WebMD, 2022). The antibiotic course is usually 2-6 weeks depending on severity. In severe cases, hospitalization and intravenous antibiotics may be needed. Wound care, surgery, and medications to maintain blood pressure may also be provided as supportive care.

It’s important for infected humans to complete the entire antibiotic course as prescribed, even as symptoms improve. Relapse is possible if antibiotics are stopped too soon. Close monitoring for complications is also necessary during and after antibiotic treatment.


The prognosis for cats infected with Capnocytophaga depends on how early the infection is detected and how quickly treatment is started. According to research, with prompt veterinary care and antibiotic treatment, most cats make a full recovery from Capnocytophaga infections ( The key is identifying the infection quickly through testing and starting antibiotics as soon as possible.

Studies show that cats treated with appropriate antibiotics like penicillin or beta-lactams have an excellent prognosis and usually recover within 1-2 weeks ( However, if an infection goes untreated, it can rapidly progress to sepsis, presenting a much graver danger. Therefore, cat owners should monitor for symptoms like oral lesions, fever, and lethargy and seek veterinary care at the first signs of illness. With quick action, most cats are expected to bounce back to full health.

Key Takeaways

Capnocytophaga is a bacteria that is commonly found in the mouths of cats and dogs. While outdoor cats have a higher risk of exposure, indoor cats can also carry Capnocytophaga.

Transmission usually occurs through bites, scratches, or close contact with saliva. In cats, the bacteria does not typically cause illness. However, Capnocytophaga can be transmitted from cats to humans, posing a rare but serious risk of infection.

In humans, Capnocytophaga can lead to sepsis, meningitis, endocarditis and other severe illnesses. People with weakened immune systems are at highest risk. Preventative measures include avoiding high-risk behaviors, proper hygiene, and monitoring cat scratches or bites for signs of infection.

While the risks are low, Capnocytophaga is one reason cat bites should never be left untreated. Understanding the risks allows owners to take proper precautions and look out for concerning symptoms in both themselves and their cats.

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