What is cat scratch disease and how is it detected?

Cat scratch disease is a pathology of an infectious nature, caused by bacteria of the genus Bartonella. According to the MSD Manual portal, 99% of patients with this disease report having been in recent contact with cats. It is a mild disorder that usually remits spontaneously in most cases.

As data of interest, it is essential to emphasize that in countries like the US up to 50% of domestic felines have antibodies to this bacterium. This means that they have the disease – even though they are asymptomatic – or that they have had it at some point. If you want to know everything about cat scratch disease, read on.

What is cat scratch disease?

According to medical studies, cat scratch disease is defined as an infectious process characterized by self-limited regional lymphadenopathy, that is, an inflammation of the lymph nodes. The main etiological agent is bacteria Bartonella henselae and the transmission vector the domestic cat.

The English portal ContagionLive estimates that this disease causes hospitalization in 0.6 of every 100,000 children – the most prone group – approximately. Therefore, we are facing a pathology of fairly low clinical relevance. In 2013 it was estimated that there were a total of 4 cases per 100,000 people in the United States.

The bacteria Bartonella henselae It is the cause of cat scratch disease.

How can a cat get infected?

Information brochures of a veterinary nature indicate that there are a total of 22 species of the genus Bartonella, of which 3 can infect cats. In Europe, the prevalence of antibodies -sign of having passed the infection- in felines varies from 8% to 53%. Fortunately, most parasitized cats do not have any symptoms.

Bartonella henselae, the most common etiological agent, it is transmitted mainly through the feces of cat fleas, since it is believed that the microorganism survives in the stools of this invertebrate for up to 9 days. These feces end up on the inside of the cat's claw and the feline transmits the bacteria to the human through scratching.

To know more: Infections due to Campylobacter: What you should know

Symptoms in humans

The US National Library of Medicine shows us the major clinical signs of cat scratch disease in humans. Among them, we find the following:

  • Appearance of a blister at the site of injury. This is usually the first clinical sign.
  • Fatigue.
  • Fever. It does not occur in all cases.
  • Headache.
  • Swelling of the lymph nodes (lymphadenopathy). This event occurs near the cat's bite or scratch.
  • General discomfort.

Possible complications

Unfortunately, other complications are possible for the patient as well. Although these only manifest 5% to 14% of the time, it is necessary to mention them:

  • Parinaud ocuglandular syndrome: redness of the ocular conjunctiva, foreign body sensation and continuous tearing. It happens when the bacteria enter the body through the eyelid and occurs in 6% of those infected.
  • Neurological manifestations: encephalopathy, seizures, myelitis, paraplegia, cerebral arthritis and other events. It occurs in 2% of patients.
  • Hepatosplenic granulomatous disease: appearance of granulomas – circumscribed lesions – in the liver. They occur in less than 1% of patients.


The diagnosis is usually clear: if two weeks after having been in contact with a cat that scratched you, you have swollen lymph nodes, it is very likely that you are infected with Bartonella. In addition, between 3-10 days after the accident with the feline, the previously described blister usually appears in the wound area.

The confirmation of the disease is usually done by antibody tests or amplification of the DNA of the bacteria in a patient sample, that is, a PCR. If cancer is suspected and not infection, The specialist may choose to perform a tissue biopsy from the swollen nodes.

Treatment of cat scratch disease

As indicated in the journal Anales de Pediatría, almost all cases of cat scratch disease resolve on their own and no specific treatment is required. On the other hand, if the infection were to spread throughout the patient's body, it would be necessary to resort to the use of antibiotics, such as rifampicin and gentamicin.

In cases that are not serious, you can also choose certain treatments. For example, if the patient has a swollen lymph node, and it is filled with pus, the doctor may choose to drain to relieve symptoms. Even so, the lymphadenopathy disappears after 2 to 4 months without any treatment.

Most of the time, cat scratch disease resolves without the need for treatment. In few cases, there are complications.

When to visit a doctor?

Lymphadenopathy is always a reason to visit the doctor. If your child or yourself has an inflammation or discomfort in the lymph nodes, it is essential to go to a specialist promptly, as it is always better to be safe than sorry.

In 2/3 of cases, lymphadenopathy is caused by viral and bacterial infections, So it will be the healthcare professional who decides whether the patient requires treatment or not.

These lymphatic inflammations can also be due to autoimmune diseases, cancerous processes and other events, although these are less common.

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What to remember about cat scratch disease?

As you have just seen, cat scratch disease is a fairly rare pathology that also tends to resolve itself over time. It is especially common in children, They are usually the people who have the least care when handling domestic animals.

In any case, it never hurts to take certain precautions. The best prevention will always be to respect domestic felines and learn to read their bodily signals, as a cat that does not feel threatened has no reason to scratch a human being.