How Cats Become Infected
Most companion cats are infected with Bartonella. There are five or more different types of Bartonella bacteria that are known to infect cats, the most common of which is Bartonella henselae. It used to be thought that cats became infected with Bartonella through the saliva of inflected fleas after they fed. More recently, the consensus is that cats usually get Bartonella infection from the feces of infected Ctenocephalides felis fleas and possibly other external parasites, while dogs are thought to become infected from the saliva of infected ticks. Ticks and fleas, which are considered “vectors” or carriers of this disease, become infected by feeding on animals that have Bartonella organisms in their bloodstream. When the vectors eliminate, their feces contains live Bartonella bacteria. Flea feces, also known as flea dirt, can be gathered under a cat’s claws while the cat scratches, and in its mouth from licking and grooming.
How the Disease is Transmitted
Many cats carry these bacteria without ever showing any noticeable symptoms of being sick. However, when cats are very young, elderly or have a suppressed or weakened immune system (such as cats with FIV or FeLV), or if they are in especially stressful, overcrowded environments or situations, they can become clinically ill from this disease. Bartonella have a propensity to infect red blood cells, which are called erythrocytes, and certain cells of the skin. The bacteria are covered by small finger-like structures called pili, which help them stick to and then enter their target cells. Once the bacteria are inside, they disrupt the cells’ normal functions.
Potential Danger to Humans
Feline bartonellosis is not exactly a contagious or zoonotic disease. However, because the Bartonella bacteria can be transferred from cats to people in flea feces as a result of cat scratches and bites, it should be treated as a transmissible illness. In most cases, people are resistant to developing infections from exposure to Bartonella henselae. However, those that have compromised immune systems definitely have an increased chance of developing so-called “cat scratch fever.” People who get cat scratch fever typically develop a raised red sore at the site of the scratch, lick or bite 3 to 10 days after exposure. The sore may progress to a red streak extending outward. Lymph nodes in the person’s neck, groin, armpits and/or elsewhere become tender and enlarged, which can persist for many months.