What is Cat Scratch Disease?
Cat Scratch Disease, also known as Cat Scratch Fever, is an illness that brings on fever and swelling of the lymph nodes, typically caused by a bacteria called Bartonella henselae. In most people, the illness resolves on its own within 2 to 4 weeks. However, in some cases, the disease can become serious and widespread, affecting people with both normal and weakened immune systems. Discovered in the 1930s and linked to cats in the 1950s, Cat Scratch Disease should be considered whenever a person has lymph nodes that are swollen for a short or long period of time.
What Causes Cat Scratch Disease?
Cat scratch disease is caused by a bacteria called B. henselae, which is a type of bacteria that prefers to live inside cells. It usually spreads to the lymph nodes, which are part of the immune system, in the area where a person has been scratched or bitten by a young cat. The disease has been known about for over 50 years, but it took a long time to identify the bacterium causing it.
A pathologist named Dr. Douglas Wear discovered a new type of bacteria in the lymph nodes of patients with cat scratch disease, which sparked many years of research to correctly identify the bacterium. At first, it was thought to be similar to chlamydia and another type of bacteria called Bartonella. But with the help of a powerful electron microscope, a particular stain called Warthin Starry stain was used to spot the bacteria in lymph node samples from patients.
In the early 1990s, during the time when AIDS was heavily studied, a related condition called bacillary angiomatosis was being investigated. This condition showed the same Warthin-Starry positive bacteria. It was eventually identified to be the same bacteria causing illness in a group of people with cat scratch disease.
Risk Factors and Frequency for Cat Scratch Disease
Cat scratch disease is a generally mild illness that tends to affect younger people, especially males below 18 years old. It’s a globally observed illness, but over half of the cases in the United States occur between September and January. The disease is carried by cats, who get the bacteria from fleabites and don’t show signs of being sick. The bacteria, B. henselae, is hard to culture but can be detected using blood tests or PCR methods. Humans can become infected through a scratch, bite, or coming into contact with infected cat saliva on broken skin. Around 56% of cats carrying the bacteria are under a year old.
- Cat scratch disease usually causes a mild illness.
- 55% of cases occur in children younger than 18 years, and of these, 60% are males.
- Over half of the infections occur between September and January in the U.S
- The disease spreads worldwide.
- Cats acquire the disease bacteria from fleabites, but show no symptoms.
- The bacteria can be detected using blood tests or PCR methods.
- Humans can get the disease from a scratch, bite, or contact with infected cat saliva on broken skin.
- Approximately 56% of cats carrying the bacteria are less than 1 year old.
Signs and Symptoms of Cat Scratch Disease
Cat scratch disease can cause lymphadenopathy, which means swelling of the lymph nodes, in 85% to 90% of child cases. Usually, this is accompanied by a high fever. However, the disease might spread and lead to a range of complications, particularly in very young, elderly, or immunocompromised individuals, like those who have received transplants or have HIV. The disease can affect the skin, lymphatic system, and various internal organs. Though less common, it can also lead to eye and neurological issues.
One of the first signs of cat scratch disease shows up on the skin as a red bump, blister, or lump known as the primary inoculation lesion. This could be on a visible part of the skin or on a mucous membrane like the conjunctiva (part of the eye) and often goes unnoticed as it heals without leaving a scar. A careful examination of skin folds and the scalp might reveal the primary lesion.
When the lymphatic system is affected, it usually results in tender, swollen lymph nodes. These could be single or multiple, measuring 1 to 5 cm in diameter and often have a red appearance. In some cases, these nodes might even burst. Enlarged nodes are generally seen close to the primary lesion site and common locations include the armpit, the inside of the elbow, the neck, above the collarbone or under the jaw. The swelling usually lasts between one and four months.
The disease can affect internal organs too, causing fever, weight loss, and abdominal pain if the liver or spleen become involved. Blood tests may show increased markers of inflammation and altered liver function. This disease might cause an unexplained fever in children.
Ocular or eye complications could happen too, including neuroretinitis, papillitis, optic neuritis, and the most common one being Parinaud Oculoglandular syndrome. This special presentation occurs only in 2% to 8% of children and involves the conjunctiva (part of the eye). The infection resolves after a few weeks, but the swollen lymph nodes may persist for a few months. The disease may also lead to retinal damage.
Neurological complications are quite serious and can present as unsteady movements, paralysis of facial muscles, and cognitive decline in older patients. Kids usually show signs like those of encephalitis or aseptic meningitis, but there could also be severe seizures.
Cat scratch disease may also lead to musculoskeletal problems including joint pain, muscle pain, and arthritis.
Testing for Cat Scratch Disease
To diagnose cat scratch disease, a doctor will usually rely on the patient’s history and physical examination findings. It’s particularly important to note whether there’s been exposure to cats, as they are typically the source of the infection. The disease is caused by ‘B. henselae,’ a bacterium that is difficult to grow in a lab.
However, to confirm the diagnosis, the doctor may also order specific blood tests such as Enzyme Immuno Assay (EIA) or Indirect Fluorescent Antibody (IFA). Despite this, negative results from these tests do not completely rule out cat scratch disease.
In some cases where the diagnosis isn’t clear, a doctor might decide to take a sample (biopsy) from the swollen lymph node. In the past, doctors avoided completely removing the infected lymph nodes due to the risk of unusual channels forming in the body, known as fistulas.
Ultrasound, an imaging technique using sound waves to create pictures of the inside of your body, can also be used to assist a needle aspiration procedure. This is a type of biopsy where a needle is used to remove a sample of tissue for examination.
Treatment Options for Cat Scratch Disease
In milder cases, treatment might not be necessary. Simple home care measures, such as applying a warm cloth to the site of infection and taking over-the-counter fever and inflammation reducers, could be all that is needed. For slightly more severe instances or those patients with a competent immune system, a 5-day course of an antibiotic named azithromycin may be suggested. Although azithromycin can help relieve the pain of severe swollen lymph nodes, it is not shown to reduce the overall duration of symptoms. The dosage of azithromycin can vary based on weight, but adults (or individuals weighing 45 kg and above) typically receive a maximum dose of 500 mg on the first day and then reduce to 250 mg daily from the second to the fifth day.
Patients with compromised immune systems should be treated to prevent the progression to severe systemic disease. For severe, widespread disease, there are different available antibiotic regimens that include rifampin, trimethoprim-sulfisoxazole, and ciprofloxacin.
What else can Cat Scratch Disease be?
When diagnosing the cause of swollen lymph nodes, doctors consider several possibilities. These could be due to viruses like CMV, HIV, and EBV. However, these viruses typically cause swelling in multiple lymph nodes all over the body. Small raised skin bumps similar to the one at the infection site can also be seen in fungal infections, leishmaniasis, and nocardiasis. In people with weakened immune systems, the cause could be any number of infectious agents. It’s also important to note that the manifestations of HIV as a condition known as bacillary angiomatosis could be mistaken for a type of skin cancer called Kaposi sarcoma.
What to expect with Cat Scratch Disease
Cat scratch disease resolves on its own in 90 to 95% of children, with treatments like pain relievers, fever reducers, and warm compresses helping to ease symptoms. However, for patients where the disease has spread throughout the body, recovery can take from several months to a year with the severity of complications varying based on which body system is affected. Individuals with a weakened immune system may experience a particularly taxing course of the disease.
