Cat scratch disease: symptoms, treatment and how long it lasts

Cat scratch disease is a bacterial infection caused by Bartonella henselae. The UK Health Security Agency (UKHSA) lists it among the most common human infections caused by Bartonella bacteria and says it is usually transmitted by cat fleas. Other Bartonella species cause trench fever and Carrion's disease, which are different illnesses.

Patient.info explains that most cats are infected with the bacterium at some point in their lives, usually as kittens under a year old, and it rarely causes them any problems. Cats catch it from fleas that have picked it up from another cat, or directly from an infected cat during fighting.

People get it when a cat scratches or bites hard enough to break the skin, or licks an open wound. Patient.info says most people who develop it can remember a scratch, bite or lick in the previous week to two months, but occasionally the person does not remember any contact with a cat and may have caught it from an infected cat flea.

Patient.info says Bartonella henselae can be spread from cats to humans through cat scratches, cat bites, or a cat licking a human wound, but that it cannot spread from human to human.

UKHSA says cat scratch disease is usually transmitted by cat fleas. Patient.info says cats catch it from fleas that have picked it up from another cat, or directly from an infected cat if they have been fighting, and that it rarely causes the cats any problems.

Patient.info describes a typical sequence. Small red marks appear where the skin has been in contact with the cat, then become fluid-filled like little blisters and finally crust over. They can sometimes be yellow and pus-filled and are often mistaken for insect bites. They appear between 3 and 12 days after the scratch, bite or lick.

The next symptom is swelling of the gland (lymph node) nearest the place where the spots developed, usually starting about two weeks after the scratch. Patient.info says the most common nodes to swell are in the armpit and in the head and neck. They can get very large, bigger than a tennis ball, and be painful, hot, red and tender. In 2 or 3 people out of every 10, the node can fester and discharge pus.

• About half of people only get swollen lymph nodes.

• Others feel generally unwell with aching, tiredness and exhaustion, going off food and headache.

• About 1 in 10 get a slight temperature, painful joints and muscle pain.

• Rare features include sudden loss of sight, tummy pain, bone pain, confusion, seizures, and severe headache with vomiting.

Patient.info says treatment is not always needed because the body is usually good at clearing the bacterium by itself, and some people recover without even knowing they had it. Simple painkillers such as paracetamol can be used for pain and fever.

Antibiotics such as azithromycin and doxycycline can be used. Patient.info says they may shorten the illness but are not absolutely necessary for most people, and it is not known whether they prevent severe complications. Antibiotics are more likely to be recommended for people with more severe symptoms such as lots of swollen nodes, for people with complications such as eye or organ infection, and for people with a weakened immune system as a precaution.

Most people make a complete recovery in 2 to 5 months, according to Patient.info, and the affected lymph gland should be checked again to make sure it has returned to normal.

Patient.info says cat scratch disease is quite rare and that anyone can get it, but it particularly affects children aged 5 to 9, possibly because they play with kittens in a way that encourages scratching.

People whose immune systems are not working properly, such as people with HIV or AIDS or those having immune-suppressing treatment such as chemotherapy, may get more severe symptoms. Patient.info says it can be very serious and even life-threatening if not treated, and that such people are more likely to develop a red or purple rash caused by growths of blood vessels which can bleed when knocked. UKHSA adds that Bartonella species, especially B. henselae and B. quintana, are causes of culture-negative endocarditis.

Doctors are likely to suspect cat scratch disease from the symptoms and examination. Patient.info stresses telling your doctor if you have a cat or kitten, especially if it has recently scratched you or your child. Blood tests looking for antibodies to B. henselae are used to confirm the diagnosis, and may be repeated if the first result is not clear.

UKHSA says testing should be considered when there is a compatible illness (fever, fatigue, swollen glands, skin lesions or culture-negative endocarditis) and a potential exposure such as cat contact. Its Rare and Imported Pathogens Laboratory provides PCR testing and serological testing for Bartonella henselae, and UKHSA notes that antibodies can take time to rise, so an initial negative result should be interpreted with caution and a follow-up sample may be sent two weeks later.

Because many causes of swollen glands exist, including some cancers, other tests are sometimes needed, such as a lymph node biopsy, ultrasound, CT or MRI scan. Patient.info says that if the diagnosis is clear from typical symptoms and a positive antibody test, other tests may not be needed.

Complications can occur if the infection gets into the eye or spreads to other parts of the body. Patient.info lists Parinaud's oculoglandular syndrome (infection in the eye spreading to the gland in front of the ear), neuroretinitis (damage to the optic nerve), and, rarely, osteomyelitis (bone infection). Rare, potentially life-threatening complications include bacillary angiomatosis, hepatitis and splenitis, infective endocarditis, and encephalitis or meningitis.

These are uncommon, and most people have a mild illness and recover completely. Any new eye symptoms, severe headache, confusion or marked tiredness after a cat scratch deserve prompt medical attention.

Patient.info advises washing cat bites and scratches well with soap and clean running water, not letting cats or kittens lick open wounds, using good flea control for cats, avoiding rough play that encourages scratching, and washing hands thoroughly after contact with cats.

See a doctor if symptoms are severe or persistent, or if you have a weakened immune system, according to Patient.info. For a bite that has broken the skin, the NHS says to get help from NHS 111 if the bite is hot or swollen, you have a high temperature or feel hot, cold or shivery, fluid is leaking from it, it smells unpleasant, or you were bitten on the hands, feet, face or head.

On the NHS, the first step is usually a GP assessment, with blood tests looking for antibodies to the bacterium and further tests if the diagnosis is unclear. UKHSA says its Rare and Imported Pathogens Laboratory provides PCR testing for Bartonella species and serological testing for Bartonella henselae.

Private doctors can also arrange blood tests. Because most cases settle without antibiotics, the key points are knowing what to expect and what would change the plan, whichever route you take.