Healthy Living

What Causes Cat Scratch Fever?

What Causes Cat Scratch Fever?

What is cat scratch fever?

Cat scratch fever is also known as "cat scratch disease", which is a type of bacterial infection. The disease got its name because humans contract the infection from cats that are infected with the bacterium called Bartonella henselae, which is one of the most common bacteria found all over the world.

In case if you are bitten, scratched, or licked by a cat that is already infected with this bacterium, you may contract cat scratch disease.


Cat scratch fever is caused by Bartonella henselae. This bacterium can be passed from an infected cat to humans when the cat bites or scratches the skin’s outer layer. Another mode of transmission is when an infected cat licks a person’s open wound. For this reason, when you have open wounds, it is very important not to allow cats or any animal to lick on them.

Now, the question is, how do cats contract B. henselae in the first place? Cats contract the disease through contact with flea feces that contain the bacteria. Cats may unknowingly consume the feces of infected fleas on their skin while grooming themselves and get infected with the bacteria.

In the United States, the disease is usually seen during winter and fall. Moreover, cat scratch fever often affects children who are 15 years old and below. You can get cat scratch disease from any type of cat. Both feral and domestic cats can carry the infection. Most of the time, kittens are more likely to carry the bacteria. The bacterium is also often found in stray cats than pet cats. It is also possible for cat fleas infected with the bacteria to bite humans and cause cat scratch fever.

Cats are also known to get infected while fighting with other cats that are already infected with B. henselae. About 40 percent of kittens and cats are known to carry this bacterium, which is either present in their mouths or in their claws. Even though cats have this bacterium in them, they usually show no symptoms of the infection. However, in severe cases, they would find it difficult to breathe, have infections in their eyes, mouth, or urinary tract.

Children are more likely to develop cat scratch fever than adults. Moreover, people who have an impaired immune system due to certain medical conditions or treatment are more prone to contract the disease. 


Cat Symptoms

Cats are known to be carriers of Bartonella henselae, but most of the time, they do not get sick from this bacterium. Hence, it would be difficult to confirm whether they are carriers of the infection or not. As previously mentioned, cats are said to contract the bacteria from infected fleas. However, there has been no evidence that says whether humans can also directly contract the bacterium from infected fleas.

According to a report from the CDC, about 40-50 percent of cats are said to carry this bacterium at a certain point in their lives. This type of infection is also common among kittens. If you have a pet cat at home, then a veterinarian would be the best person to help identify if your cat is carrying the bacterium or not. Treatment in cats is not usually recommended in such cases. 

Human Symptoms

The symptoms of cat scratch disease in humans may include:

Lesser known symptoms of the disease:


If the doctor suspects cat scratch fever, then a physical examination would be first performed to check if there is a presence of an enlarged spleen, which is anatomically located just above the stomach and under the ribcage. 

It is quite difficult to diagnose cat scratch fever just by checking a patient's symptoms alone. The doctor would be able to confirm if it is cat scratch fever by conducting an indirect fluorescent antibody blood test, which is also called as IFA. This blood test is used to check if Bartonella henselae is present in the body or not. In this test, the antibodies are labeled with the help of a dye, which would then get itself attached to the existing antibodies of Bartonella.


Most of the time, cat scratch fever is not much of a serious problem, and would not require any kind of treatment. In certain instances, the doctor may prescribe certain antibiotics if the disease tends to become severe and also in cases of individuals who suffer from an impaired immune system due to medical conditions such as HIV/AIDS, lupus, or arthritis.


The following conditions are possible complications of cat scratch fever:

  • Osteomyelitis: This complication is a bacterial or fungal infection of the bones, which may lead to bone damage. In a few cases, the bone damage becomes aggravated that the doctor may suggest an amputation of that portion of the body due to the spread of the infection.
  • Neuroretinitis: This complication is an inflammation of the optic nerve and the retina of the eye that can lead to a blurry vision. The inflammation occurs when the bacterium responsible for cat scratch fever tends to travel to the region of the eye, thereby impairing the vision of the individual. However, this condition is said to be only temporary. The vision of the individual would return back to normal once the infection is treated. In certain cases, vision problems may go away on their own. 
  • Parinaud Oculoglandular Syndrome: This syndrome is known to be an infection of the eye that often leads to symptoms that are quite similar to a pink eye infection or conjunctivitis. Cat scratch fever is also known to be one of the most common causes that can lead to this particular syndrome. This condition responds well to antibiotic treatment. In a few rare cases, surgery may be required to remove infected tissues of the eye. 
  • Encephalopathy: This complication is a disease of the brain, which is said to occur when the causative bacteria of cat scratch fever spread the infection in the regions of the brain. In a few of cases, encephalopathy can also lead to a permanent damage to the brain or even death in certain individuals.


Below are some preventive measures to avoid contracting the bacterium from infected cats:

  • Make sure to instantly wash any bites or scratches from a cat using mild soap and water.
  • Once you are done playing with a cat, ensure to wash your hands with soap and water as well. This preventive measure is quite important if you have small children in the house and if you are living with a family member who has a compromised immune system.
  • Individuals who have a weak immune system but plan on having a cat should adopt cats that are at least one year old since younger cats are more likely to carry the infection. 
  • Avoid rough playing with cats to prevent being bitten or scratched. 
  • Do not allow cats or any animals to lick on your open wounds as it can lead to infections of any kind.
  • Do not try to touch or pet stray cats since they are more prone to carrying the bacterium.

Other Preventive Measures

  • It is important to control fleas since they are the main culprit behind the spread of infection to cats.
  • Make sure to keep the nails of your cat trimmed.
  • Once approved by the veterinarian, you can also apply an anti-flea product, which can be in the form of oral or topical medication at least once a month. In the meanwhile, beware of using over-the-counter flea products, which may not be safe for your pet cat.
  • Before the application of any anti-flea product, ensure to first consult a veterinarian. You can also check for any presence of fleas on the cat by using a comb as well as inspect for any flea dirt that usually sticks to their hair.
  • It is also important to control fleas at home by making sure that your home is frequently vacuumed.
  • When required, you can contact a pest control agency to get the work done once in six months.
  • It is important to monitor your cat's health and report any changes in their health to the vet. Schedule routine appointments with the vet for check-ups.
  • Make sure to keep your pet cat indoors as much as possible to limit their contact with fleas. Staying indoors would also prevent your cat from fighting with other stray cats that are potentially infected with B. henselae.