‘Cat scratch disease’ (CSD) is also known as ‘cat scratch fever’, or ‘subacute regional lymphadenitis’, if you prefer. It is a disease of humans, caused by a bacteria called Bartonella henselae which can be transmitted to people following a cat scratch or bite. This bacteria very rarely causes disease in cats themselves, but it can cause problems in humans if they become infected.

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How can you catch it?

Bartonella henselae is carried by fleas, so cats with flea infestations are much more likely to pass on CSD to a human. The fleas produce faeces (you might recognise this as flea dirt) which sits on the cat’s skin. Flea infestations make cats itch, so when they scratch or bite themselves, the bacteria in the flea dirt is transmitted onto the cat’s claws or teeth. If the cat then goes onto scratch or bite a person, the bacteria are passed into their broken skin, hence giving them CSD. Children are statistically more likely to catch CSD, probably because they are more likely to play with…. and annoy…. cats! It cannot be spread from person to person. 

What happens if I catch it?

The severity of the disease depends on how well your own immune system is functioning.

A healthy human

If a healthy person is infected with Bartonella henselae, they will develop CSD. Within 3 – 12 days of being scratched or bitten, small, red lumps will develop at the site of injury. These lumps are often fluid filled, like blisters, that will crust over and scab. By about 2 weeks after the injury, the infection will have spread from the bite / scratch site to the closest lymph node (often in the armpit or neck area), resulting in swelling, pain and tenderness here. Other symptoms are usually mild, including a slight fever, headaches, muscle and joint aches, and a general feeling of malaise. Usually, your body’s own immune system will rid the infection without any trouble and you may never know you even had CSD. 

If your symptoms are more severe (e.g. a very large lymph node, multiple swollen lymph nodes, or a persistent fever), your doctor may give you antibiotics, but they usually aren’t necessary as most people will clear the infection on their own with time. 

People whose immune systems are compromised or weakened

However, if you are immunocompromised (e.g. are undergoing chemotherapy, have had your spleen removed, are taking immunosuppressive drugs, or are HIV positive), the disease can be much more serious, even life-threatening if not treated. It can spread to other parts of the body (i.e. beyond the lymph node), such as the brain, eye, blood vessels, heart, liver, spleen or bone, with associated symptoms. The affected lymph node may also swell dramatically with the formation of an abscess.  

Serious symptoms include:

  • Confusion
  • Seizures
  • Severe headaches and vomiting
  • Bone pain
  • Abdominal pain
  • Sudden loss of sight

It is important to note that while these symptoms are characteristic of CSD, they can also be indicative of other medical conditions. Therefore, it is essential to seek advice from your doctor for a proper diagnosis and treatment. Informing your doctor of a recent cat bite / scratch can help guide their diagnostic plan, and the disease can be confirmed with a blood test or sample of the affected lymph node. If you are immunocompromised or get a severe form of the disease, antibiotics are likely to be prescribed to help your body rid the infection, along with medication like paracetamol to help with the pain and fever.  

Is cat scratch disease dangerous?

As outlined, the seriousness of CSD will depend on the person’s individual immune status. It can range from self-limiting and mild in healthy people, to serious and life-threatening in immunocompromised people. It’s important to remember that serious disease is very rare, and typically occurs only in vulnerable people. It also relies on the cat who has bitten / scratched being infected with Bartonella henselae. Not all are, but unfortunately it is impossible to know preemptively. 

Prevention and management

Preventing CSD primarily involves taking precautions to minimise the risk of exposure to the bacteria, and the chances of getting scratched or bitten in the first place. 

  1. Preventative parasite control in your cat: 

Using regular anti-parasiticides to prevent fleas is a good starting point, as it is the fleas which carry the bacteria. Your vet can advise which product is best for your cat. 

  1. Avoiding rough play: 

It sounds obvious, but discouraging rough play with cats, particularly with kittens or unfamiliar animals, will reduce the likelihood of scratches or bites. It is particularly important to educate young children about this; not only will they be at risk of catching CSD, but it may not make for a very happy cat either!

Conclusion 

While most individuals may experience only mild, self-limiting symptoms with CSD, awareness of the potential risks in immunocompromised people is important. Remembering to tell your doctor about a recent cat bite or scratch if you experience any of the more serious symptoms is highly relevant and may speed up the diagnosis, enabling treatment to start early and improve the prognosis. Taking preventative measures is important for safeguarding human health, especially if you are an immunocompromised cat owner.

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