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Cat scratch fever, also referred to as cat scratch disease (CSD), is a zoonotic infection that occurs when someone comes into contact with Bartonella henselae bacteria. Zoonotic diseases are types of infections or diseases that are spread from animals to humans or from humans to animals. In the case of CSD, cats are the main culprits behind the majority of infections in humans.
Roughly 12,000 people will be diagnosed with cat scratch fever every year, and 500 people will be hospitalized because of the infection. Read on to find out more about cat scratch fever and how the infection affects humans.
What Are the Symptoms of Cat Scratch Fever?
Cats can be considered carriers of the bacteria that causes CSD because they do not always fall ill when they have contracted it and they can infect others. Since they rarely show symptoms, it is hard to tell if a cat is infected or not.
When a person becomes infected, they may experience symptoms such as:
- Fever, especially one that is above 100.9 degrees Fahrenheit and that has lasted for several weeks or has defied diagnosis
- A bump or blister (typically red or brown), where the scratch or bite occurred, appearing three to 14 days after the injury
- One or more enlarged or swollen lymph nodes, usually on the same side as the cat scratch or bite (most people have only a single enlarged lymph node, and the swelling may last for several months)
- Muscle aches and pains
- A general feeling of discomfort or illness (malaise)
- Abdominal pain
- Loss of appetite
- Inflammation of the eyes and pink eye
Rare but Serious Complications of CSD
In some cases, rare but serious complications can occur in people with CSD, such as:
- Liver inflammation
- Inflammation of the brain that leads to headaches, a stiff neck, and sensitivity to light
- Bone inflammation
- Arthropathy, which is a disease of the joints that acts similar to arthritis
- Life-threatening inflammation of the inner lining of the heart’s chambers and valves
- Enlarged spleen (splenomegaly)
These conditions likely require in-hospital treatment as soon as possible.
What Is the Cause of Cat Scratch Fever?
Cats are responsible for cat scratch fever, although in rare cases humans can contract the bacteria that causes the disease directly from infected fleas. Fleas are typically responsible for giving the infection to cats. Other mammals that can carry the bacteria include guinea pigs, rabbits, and, in some cases, dogs.
When a cat or another infected animal bites or scratches hard enough to break the skin, the bacteria can be transmitted into the bloodstream. It can also be transmitted if an infected animal licks an open wound.
Are All Cats Infected With the Bacteria That Causes Cat Scratch Fever?
According to one study published in Advances in Dermatology and Allergology, as many as 90% of cats are thought to have the bacterial infection that causes CSD. However, the Centers for Disease Control and Prevention (CDC) suggests that only 40% of cats will contract the bacteria in their lifetime.
The CDC also states that kittens under 1 year of age are the most likely to have the disease. Although the reason for the disparities in numbers isn't clear, it could be because of where each study took place and the cat population used.
How Is Cat Scratch Fever Diagnosed?
To diagnose CSD, your doctor will conduct a physical exam and collect a record of your symptoms, health history, and possible exposure to cats that may have the disease. They will also likely perform blood tests to look for antibodies, which are special proteins made by the body to help fight off a bacterial infection.
These tests, although good to confirm a diagnosis if positive, are not always effective in the initial stages of infection. That is because it can take several weeks for the body to make enough of the antibodies to determine if you have been infected with CSD. Because of this, these tests can typically tell if someone has been infected in the past, but not if they have an active infection.
A PCR (polymerase chain reaction) test can be used to determine if there is any evidence of the bacteria in a person’s blood. Because of this, the PCR test may be used to diagnose an active infection of the disease.
When to Call a Doctor
Although the majority of CSD infections clear up on their own, you should see a doctor if you experience redness around the wound that is starting to expand, you have a fever a few days after being scratched or bitten by a cat, or you notice swelling or pain in your lymph nodes.
How Is Cat Scratch Fever Treated?
Treating CSD will depend on the severity of the infection. As mentioned above, many cases resolve on their own. For those that do require treatment, the antibiotic medication azithromycin (Zithromax) is typically used for a period of five days. Antibiotics are medications designed to kill off harmful bacteria in the body.
Other antibiotics that can be used include:
- Rifampicin (Rifampin)
- Ciprofloxacin (Cipro)
- Trimethoprim-sulfamethoxazole (Bactrim, Septra)
Rifampicin and Antibiotic Resistance in CSD
Research has shown that rifampicin is becoming less effective because of antibiotic resistance, which is the term used to describe a bacteria or germ’s ability to defeat the antibiotics designed to kill it. Because of this, some medical experts believe that rifampicin should be used in combination with other antibiotics such as azithromycin or gentamicin (Garamycin).
What Is the Prognosis for People With Cat Scratch Fever?
The majority of people with CSD completely recover from the infection with the right treatment, or even on their own without any form of treatment.
Roughly 5% to 10% of people with the disease will suffer serious complications; however, less than 1.3% of CSD cases are lethal. Once a person contracts the bacteria, they are immune to it for the rest of their life, so there is no risk of coming into contact with it again.
Cat scratch disease, or cat scratch fever, is a zoonotic bacterial illness that can affect anyone who comes into contact with it. The disease is primarily spread by infected cats; however, other domesticated animals can also contract and spread the disease, such as guinea pigs, rabbits, and dogs.
In most cases, having CSD will not seriously affect your health, and many people recover from the mild symptoms without needing treatment. For those who do develop more serious health repercussions, getting the proper treatment with antibiotics is typically associated with a full recovery.
A Word From Verywell
You may be worried about getting cat scratch fever, especially if you’re a cat owner. However, not all cats will have the bacterial infection, and thus, not all cats can spread it to you. Most cats show no symptoms, so it can be hard to determine if yours has been infected.
If you think your cat may have the disease, you can take them to the vet to have them checked out. To prevent your cat from giving you the bacterial infection, keep their claws trimmed and wash any cat scratches or bites right away with soap and water. Also, since fleas are the biggest culprit of spreading the infection to your cat, you can control fleas by keeping your cat indoors and checking for fleas regularly.
Frequently Asked Questions
- Is cat scratch fever serious?
Most cases of cat scratch fever are mild and require little or no treatment. However, serious health effects can occur that lead to hospitalization and the need for immediate treatment. If you experience any serious signs of CSD such as a high and unrelenting fever or pain in your lymph nodes, call your doctor because you may need treatment.
- Does cat scratch fever ever go away?
The symptoms of cat scratch fever do go away either on their own or with treatment. The body will also develop lifelong immunity to the disease after contracting it.
- Who usually suffers from serious complications of CSD?
Children between the ages of 5 and 14 are the most likely to develop rare complications of CSD. People of any age who have weakened immune systems also have a higher risk of a serious case of CSD and the symptoms that go along with it.