Cat scratch disease at a glance
What is cat scratch disease?
Also known as cat scratch fever, subacute regional lymphadenitis or Teeny’s disease, cat scratch disease (CSD) is a self-limiting, zoonotic infection (transmitted from animals to humans). As the name would suggest, cat scratch disease is most often associated with cat scratches (although cat bites and licks can often lead to CSD too). More than 90% of those infected have a history of contact with a cat.
The disease is caused by a recently discovered gram-negative bacterium called Bartonella henselae and is found worldwide, however, it is more common in warm and humid climates as fleas are more prevalent under these conditions. 80% of those affected are children (under 17 years). Most cases come from kittens, although adult cats can also pass on the disease.
How do cats become infected?
Fleas pass Bartonella from one cat to another via flea feces which contains the bacterium. As the flea feeds on the cat, it deposits feces onto the cat’s skin, which is then transferred to the mouth and claws as the cat grooms himself. It is not possible to pass on the disease from human to human.
One study showed approximately 80% of cats had positive antibodies to the bacteria and approximately 50% of cats carry the Bartonella henselae but are asymptomatic.
How do people become infected with cat scratch disease?
Cats are the main reservoir of CSD although puncture wounds and scratches from dogs, thorns, splinters and even fish bones have been implicated in a few cases too. Although the bacterium is relatively common in cats, it is quite rare to catch CSD, which indicates that it’s somewhat difficult to catch. Humans become infected when the bacteria is introduced via a wound (bite, scratch, puncture).
It has been speculated that tick bites may also transmit the bacteria to humans, however, there is no evidence that the bacteria can be spread from fleas to humans.
What are the symptoms in cats?
Generally, cats don’t display symptoms but when present they generally include:
- Swollen lymph nodes
- Muscle soreness
- Uveitis (inflammation of the uvea in the eye)
What are the symptoms of cat scratch disease in humans?
Typical CSD occurs in immunocompetent people. In between 25 and 60% of cases, a small red-brown erythematous papule (tiny skin nodule) develops after a bite or scratch has occurred. At this time it may be mistaken for an insect bite. This blister or bump is called an inoculation lesion (a wound at the site where the bacteria enter the body).
Lymphadenopathy (swollen lymph nodes, especially those in the armpits, head, and neck) appear approximately 1-3 weeks after the scratch in between 85-90% of patients.
Other common symptoms may include:
- Loss of appetite (anorexia)
Bacillary angiomatosis is a “syndrome” that is most often seen in immunocompromised people such as those with AIDS, undergoing chemotherapy or organ recipients. Serious skin lesions develop, patients may develop a prolonged high fever, sweats, chills, poor appetite, myalgia (muscle pain), vomiting, weight loss, bone lesions and occasionally seizures.
A small number of immunocompromised people develop other atypical manifestations affecting different organs including:
- Hepatosplenic CSD – Liver and spleen involvement. Symptoms include fever and abdominal pain.
- Neuroretinitis (inflammation of the neural retina and optic nerve) can occur in approximately 2% of cases. Typical symptoms include ocular pain, partial vision loss and photopsia (perceived flashes of light).
- Encephalitis – Inflammation of the brain, occurring in 1-7% of cases. Symptoms may include a headache, lethargy, fever, confusion, and seizures.
- Parinaud’s oculoglandular syndrome occurs in between 17-20% of CSD cases, conjunctivitis with swollen lymph nodes near the inoculation site. Symptoms of which include the feeling of a foreign body in the eye, red-meaty appearance to the eye, ocular discharge and tearing. Transmission can occur if the eyelid or conjunctiva are scratched by an infective cat, or if a person rubs their eyes after recent contact with a cat.
Between 12-29% of veterinarians have shown positive skin tests and 5% of healthy people in other jobs, which indicates that while they have had the infection, symptoms have been mild it not apparent at all.
Diagnosis of cat scratch disease
Diagnosis may be based on a history of patient contact with a cat.
The bacteria can be somewhat tricky to culture in cats and people as it may only circulate in the blood intermittently. Tests may include a blood culture, indirect fluorescent assay (IFA) or a polymerase chain reaction (PCR).
A biopsy of the affected lymph node will be taken for evaluation in some cases.
Some people (such as those who are immunocompromised) may choose to test their cat also.
Treatment for cat scratch disease
In most cases, the disease is self-limiting and will resolve itself in time. Thoroughly clean the site of infection with antiseptic.
It can take several months for lymph nodes to go down.
Reduce the pain of swollen lymph nodes with warm, damp compresses.
Pain relief if necessary, your doctor will be able to advise on the best medicaiton.
Occasionally your doctor will aspirate pus from the lymph node to reduce pressure and pain.
In severe cases or patients who are immunocompromised, antibiotics will be prescribed. Azithromycin (Zithromax), rifampin, ciprofloxacin, doxycycline, and gentamicin are usually the antibiotics of choice.
How can I reduce my risk of getting cat scratch disease from my cat?
- Avoid bites and scratches (especially in children) by teaching them to be gentle with cats, and avoid roughhousing.
- Disinfect the wound immediately if a cat bites or scratches you.
- Consult your doctor if the wound becomes infected, or you develop any of the symptoms described (such as swollen lymph nodes, flu-like symptoms etc).
- Don’t let cats lick your eyes, wounds or chapped skin on your body.
- Proper flea control is especially important as fleas are responsible for transmitting the bacteria to cats. The majority of the flea’s life cycle is spent off the cat, therefore it is important to treat the environment too.