Cat Scratch Disease – What is Bartonella hensalae

Picture of a calico cat

Bartonellosis in cats, which goes by the name of ‘cat scratch fever’ or ‘cat scratch disease,’ is caused by a bacteria called Bartonella hensalae. This is a zoonotic disease, so it can be transmitted from animals to humans, which is why it is paramount to prevent or treat it as soon as possible.

In this post, we will look at the symptoms of CSD in cats, how it is diagnosed, and how it is treated, but we’ll also look at the same in humans that become infected with Bartonella, too.

Causes and Symptoms of CSD

This bacterium can be transmitted by an infected cat to a completely healthy one. Therefore, direct contact is the primary cause of the infection. The disease is also carried by fleas, which excrete it through their feces.

So, what that means is that even if your feline companion doesn’t come in contact with a cat that has a Bartonella infection, she can still get fleas from the outdoors, for example, and develop the disease.

Most cats don’t show any symptoms at all, which makes this zoonosis even more dangerous to humans as they might not even realize when they become infected. There are cats that present some clinical signs, and they consist of fever, swollen glands, and muscle aches.

The infection can be transmitted to other cats or humans through the animal’s saliva. Therefore, if you get bitten or scratched by a cat, you should keep in mind that you could develop Bartonellosis.

It’s important to note that CSD is more common in strays and kittens, as they are more susceptible to become bacteria carriers due to flea infestations. This bacteria can be found more predominantly in warmer regions, which make it more possible for fleas to thrive.

To date, it is estimated that approximately 40% of all cats can carry this bacteria at one point in their lives, especially when they are young. Fortunately, the infection is rarely fatal, in both cats and humans.

How Do People Become Infected?

Since the bacteria can be transmitted through saliva, a cat bite is the most likely way of transmission. However, some cats can carry the germ under their nails, particularly after having fought with another outdoor cat, for instance. Therefore, even if your cat scratches you on a superficial level of the skin, you could still become infected.

The people that have the highest risk of becoming infected are those that have weakened immune systems, such as seniors and children younger than the age of 6.

While most people can be asymptomatic and the infection could resolve on its own, it can be quite problematic in certain categories of individuals who have a depressed immune system, such as those who have AIDS, those that have received a transplant, or those that have cancer or diabetes.

Even though the infection can be mild in most humans, the CDC estimates that approximately 12,000 individuals become infected with CSD in the United States alone over the course of a year. Out of these, around 500 end up being hospitalized. Many of those that are infected are children, as they’re more likely to play with strays or kittens that might bite or scratch them as part of their play behavior.

Symptoms in Humans

After sustaining an injury such as a bite or a scratch, people can be asymptomatic for a period of one to two weeks. In some cases, it might take as many as eight weeks for the symptoms to become apparent.

Here are some of the typical clinical signs that infected people might show:

  • Red and round bumps or papulae at the site of the bite or scratch
  • Swelling of the lymph nodes
  • Swelling and the appearance of an infection at the bite site
  • Chills and fever
  • Lack of appetite
  • General malaise
  • Muscle pain

Around 11-12% of the patients develop more severe symptoms, which consist of conjunctivitis, a variety of neurologic manifestations (seizures, encephalopathy, paraplegia, and others), and very rarely, liver disease (hepatosplenic granulomatous disease).

Patients that have a history of heart disease can also develop endocarditis. Since one of the symptoms that we have mentioned is the inflammation of lymph nodes, we’d also like to note that it can take between 2 and 5 months for the lymphadenopathy to subside. Usually, it does so spontaneously and without any apparent reason.

Picture of 2 kittens

How Can the Infection Be Treated?

It’s very likely that cats won’t show any symptoms at all or that the infection will resolve on its own without you even noticing anything. If you’re lucky enough not to be bitten or scratched by your feline companion or by a stray when they are still infectious, you might not develop the disease, either.

Even in humans, the infection is generally benign, and it typically disappears on its own over the course of a couple of months. The bumps or blisters can remain on the patient’s skin for up to three weeks, while the swollen lymph nodes take a while to recover, as we have previously mentioned.

However, since some of the symptoms associated with this disease are fever, muscle aches, and general malaise, go see your doctor as soon as you can. Some of the individuals that have more serious symptoms or those that are known to have a weakened immune system can receive treatment with antibiotics.

How to Prevent CSD

If you know that you have an immunocompromised individual living in your home or if you have a weakened immune system yourself, you should get your cat tested before adopting her and bringing her home.

Indoor cats have a considerably lower risk of being Bartonella carriers, because they usually come in contact with no other animals that could infect them, neither are they exposed to flea feces if you practice good flea control.

If you have been bitten or scratched by a cat, you should disinfect the wound as soon as possible. Also, if you notice any symptoms such as fever or swollen glands in your cat, call your veterinarian, and schedule an appointment.

Keeping your home flea-free and making sure that your cat has trimmed nails are two other pieces of advice that we can give you. If you haven’t gotten your cat tested yet, avoid engaging in rough play with your feline companion, and more importantly, avoid playing with strays.

To date, there is no vaccine against this infection in both humans and cats.



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