By MEGAN TREMELLING, DVM, LVS
This summer, a Wisconsin woman died of an infection caused by a bacterium called Capnocytophaga canimorsus, and a Wisconsin man suffered serious illness requiring multiple amputations from the same organism. The infections are believed to be derived from contact with family pet dogs. This is scary stuff for those of us who share our lives with dogs, but there is no need to panic about Capnocytophaga.
Capnocytophaga species are found in the mouths of healthy dogs, cats, and humans. Normally it does no harm, but under certain circumstances, it can cause disease. Studies estimate that up to 74 percent of dogs and up to 57 percent of cats have Capnocytophaga living in their oral cavities. In short, if you have a dog, odds are very good that it carries Capnocytophaga.
In spite of how common Capnocytophaga is, however, serious infections are exceedingly rare. Nobody knows exactly how many cases occur, but the Centers for Disease Control and Prevention (CDC) received only 12 case reports in 2017, and only about 200 cases have been reported worldwide since this type of bacteria was first identified in 1976.
Capnocytophaga infections can be transmitted by bites from dogs or cats, or through close contact with an animal, especially contact with its saliva. Since humans also frequently carry Capnocytophaga, it is possible to develop an infection without any animal exposure.
Most of the time, Capnocytophaga is not your main concern after a dog or cat bite. Other bacteria, such as Pasteurella, Streptococcus, and Staphylococcus, cause many more infections. Rabies is uncommon in the United States but is so deadly that any possibility must be taken very seriously. Lastly, deep puncture wounds of any origin can result in tetanus.
When Capnocytophaga does cause problems, they can vary widely. Local cellulitis (tissue swelling, redness, and pain) is the most common finding associated with bite wounds contaminated by Capnocytophaga. In more serious cases, the bacteria can spread to other parts of the body such as the heart, brain, or joints. When the infection affects the whole body in a condition called sepsis, there can be long-term effects from infection, including gangrene that necessitates amputations; heart attacks; or kidney failure. About 3 in 10 people who develop sepsis due to Capnocytophaga will die.
Most people who are exposed to dog saliva don’t get Capnocytophaga infections because their immune systems protect them. However, there are factors that can affect your immune system’s ability to keep you safe. One of the most serious risk factors is having had your spleen removed as a result of an injury or illness. Other risk factors include alcohol abuse, old age, or immune compromise due to disease such as cancer, diabetes, or HIV, or taking certain medications such as chemotherapy or glucocorticoids. Some people do get sick with no known risk factors.
Capnocytophaga infections are hard to test for. The bacteria are very difficult to grow in a lab. Fortunately, new technologies such as PCR amplification and gene sequencing are becoming increasingly useful for identifying challenging organisms like Capnocytophaga. The good news is that Capnocytophaga can be treated with common antibiotics, and so far antibiotic resistance isn’t a big problem. However, treatment must be started quickly, without waiting for a lab to confirm the infection.
There are ways to reduce your risk of a Capnocytophaga infection. Don’t let your pets lick faces, wounds, or irritated skin, and wash with soap and water after handling your animals. Minor bite wounds should be washed thoroughly with soap and water. See a health care provider if the wound is deep or serious; if it becomes red, painful, warm, or swollen; or if you feel feverish or weak. You should also see a doctor if the dog was acting strangely or is not known to be vaccinated against rabies. Most people who are going to become ill with Capnocytophaga will do so within 3 to 5 days after exposure, but it can take as little as a day. If you have any risk factors such as immune compromise, you should see your doctor right away for any bite wound that breaks skin, even if you don’t feel sick.