Cat Scratch Disease Facts
Cat scratch disease (CSD) is a syndrome that begins usually with red, tender papules or pustules at a site where a pet cat (usually a kitten) has scratched, licked, or superficially bitten a person that later progresses to painful regional lymph nodes (which may be felt as small bumps under the skin) over one to three weeks. A significant percentage of affected patients develop a low-grade fever (about 101 F). A few investigators suggest fleas on cats may also transmit the disease under special circumstances (for example, crushed cat flea materials get into a skin break).
Although H. Parinaud described this condition in 1889, R. Debre in 1931 was the first to describe cats as vectors (carriers) of the disease and termed the condition as cat scratch disease. Most cases occur in the fall and winter months. Investigators speculate this timing may be due to the usual high number of midsummer kitten births. The bacteria responsible for the disease are Bartonella henselae; recently, two other organisms (Afipia felis and Bartonella clarridgeiae) have also been implicated in producing CSD, but investigators are still gathering data to prove this. CSD is not transmitted from person to person.
Many cases of cat scratch disease are not reported because the symptoms are often mild and the disease is self-limiting. Studies support that the disease is quite common, with a majority of cases occurring in people under 21 years of age. The studies found that many people have antibodies to Bartonella henselae, the bacteria that cause this disease. Having antibodies to a disease is called being seropositive and suggests a previous infection. Bartonellosis is termed an infectious disease produced by the bacteria of the genus Bartonella. Cat scratch disease, trench fever, and Carrión's disease are specific subsets of bartonellosis.
What Causes Cat Scratch Disease?
Bartonella henselae is a pleomorphic (multishaped), often curved-shaped Gram-negative bacterium that is responsible for the vast majority of CSD. The organisms require special laboratory conditions to be cultured so they are not routinely isolated from patient samples. These bacteria were identified in 1985 as causing CSD; the newly identified bacteria were classified first as Rochalimaea henselae but were later classified as Bartonella henselae because of genetic differences from Rochalimaea. The organisms are also found in cat fleas. The CDC estimates that about 40% of all cats carry Bartonella henselae at some point in their life. Fleas pass the bacteria to cats in a flea-cat-flea cycle, and the organisms have been detected in cat saliva and on cat claws.
What Are Risk Factors for Cat Scratch Disease?
A major risk factor for contracting cat scratch disease is any type of play or handling of a cat, especially a kitten, which can result in scratches from the cat's claws, the cat's licking a skin break, or cat bites. Handling or coming in contact with fleas on cats is also a risk factor. In addition, individuals with weakened immune status are at higher risk of getting the disease.
What Are Signs and Symptoms of Cat Scratch Disease?
The first symptoms of CSD start about three to 14 days after getting scratched, superficially bitten, or (infrequently) licked by a cat, usually a kitten. These symptoms consist of one or more papules (small raised areas on the skin with no fluid inside) or pustules (like papules but with pus inside) on the skin where the cat scratch, bite, or lick occurred. In most patients, these begin to disappear spontaneously over about one to three weeks. While the papules and pustules are receding, lymph nodes that drain the primary area of infection begin to swell (lymphoreticulosis) in about 90% of patients. The nodes most frequently involved are those in the axillary (under arms), cervical (on the neck), or inguinal (in the groin) regions. These nodes are usually painful and may suppurate (spontaneously rupture and leak pus). A low-grade fever (up to about 101 F) often develops. These are the most common symptoms of CSD. A few patients, however, develop other localized symptoms such as a reddish, painful eye with mild fever and swollen lymph nodes near the ear and neck on the affected side (termed Parinaud oculoglandular disease). Often patients with eye involvement report being licked by a pet kitten on or near the involved eye. Pictures of CSD are available on the first reference listed below. In summary, the signs and symptoms of cat scratch disease may include
- a scratch from a cat or kitten,
- papules (bumps) and/or pustules develop,
- swollen lymph nodes (some individuals may develop a fistula and drain fluid),
- rash accompanying the papules,
- poor appetite or loss of appetite,
- weight loss,
- sore throat,
- exhaustion, fatigue, or malaise,
- joint pain, and/or
- some individuals may develop an enlarged spleen.
One note of caution: A bite from a cat (usually an adult cat) can result in another rapidly progressing infection due to Pasteurella multocida bacteria (and other organisms) and should be treated within 48 hours of the bite. The symptoms of pain and swelling at the bite site develop rapidly (over eight to 24 hours) in contrast to CSD symptoms. Since about 80% of cat bites become infected, the majority of people with cat bites need to be treated with antibiotics.
When Should Someone Seek Medical Care for Cat Scratch Disease?
CSD is often treated at home without antibiotics; the disease, in most cases, is self-limiting and rarely results in any complications in healthy people. Wash any cat scratches on the skin with soap and water and take measures to remove fleas from cats. Acetaminophen (Tylenol) or ibuprofen (Motrin) may be taken for control of pain and fever; swollen lymph nodes can be treated with warm compresses. Immunosuppressed patients (for example, those with HIV or cancer) should not attempt any self-care; they should contact their physician immediately. Most physicians suggest seeing a doctor if a person develops swollen lymph nodes, headache, fever, and fatigue.
What Specialists Treat Cat Scratch Disease?
Many individuals with cat scratch disease may be treated by their pediatrician or primary-care physician. However, it is not unusual for the individual to be first treated by an emergency-medicine physician. In addition, more complicated and severe infections usually involve consultation with infectious-disease specialists, occasionally dermatologists, and/or those specialists that treat for immunosuppressed patients (for example, oncologists).
What Exams and Tests Do Physicians Use to Diagnose Cat Scratch Disease?
Most cases of CSD are diagnosed by the patient's clinical presentation and history. If the patient has a history of cat scratches (or superficial bites or a cat licking their face or cuts) and then develops papules or pustules, many physicians consider these findings enough to diagnose CSD. If the patient also develops swollen lymph nodes and fever, these findings reinforce the clinical diagnosis of CSD. Microscopic examination with special stains of biopsied tissue (lymph nodes) may show small curved Gram-negative rods, but the staining methods do not yield a definitive diagnosis of CSD. Laboratory tests are also available; indirect fluorescent antibody test, also termed indirect fluorescence assay (IFA) and rising immunoglobulin titers may provide additional evidence for infection with Bartonella henselae but are not frequently done. A polymerase chain reaction (PCR) test to detect the genetic material of the bacteria that shows good sensitivity and specificity for Bartonella can be done on the patient's tissue, but the test is not widely available.
Although laboratory tests are infrequently used, their availability is important because about 10% of patients with CSD do not recall or state an association with cats or kittens. This lack of clinical history makes the diagnosis of CSD difficult. These tests can help physicians differentiate CSD from other diseases caused by organisms similar to Bartonella (for example, Anaplasma phagocytophilum and Acinetobacter baumannii, which are both small pleomorphic Gram-negative bacilli) or from other diseases that have some similar symptoms (for example, swollen lymph nodes in lymphoma or in actinobacillosis).
What Are Cat Scratch Disease Treatments?
Treatment of CSD usually begins with symptomatic treatment of the pain and fever (if present) with acetaminophen or ibuprofen. Warm compresses to swollen lymph nodes can help reduce pain. Some doctors aspirate tender swollen lymph nodes with needles; incision and drainage of lymph nodes is not recommended because it does not speed recovery and may cause scars and fistulae (abnormal connections between the lymph node and skin) that continually drain and may develop secondary infections. Antibiotics are not used in the majority of patients. However, in patients with severe lymph node pain, azithromycin may lessen the pain but does not decrease the length of time that symptoms are present.
In contrast, most physicians advise antibiotic treatment in any immunocompromised patients. Bartonella henselae are usually resistant to several penicillin-based antibiotics like amoxicillin, but reports in the literature suggest that antibiotics such as trimethoprim-sulfamethoxazole, gentamicin, rifampin, ciprofloxacin, azithromycin, doxycycline, clarithromycin, rifampin, and others are effective. Antibiotics are suggested for immunosuppressed patients because the immune systems of these patients often are not able to limit growth of or kill bacteria (and other pathogens) as well as people with uncompromised immune systems. The antibiotics help immunocompromised patients reduce and eliminate these bacteria and thus reduce complications that may occur if the bacteria spread to other organ systems. There seems to be no consensus about which antibiotic is best; the choice of antibiotic is usually made by the treating physician with consideration of the patient's overall medical condition (for example, age, renal function, allergies).
What Are Cat Scratch Disease Complications?
The large majority of people with CSD have no complications. However, atypical presentations or complications comprise up to 10% of cases per year. These complications are most often found in immunocompromised patients and rarely in individuals with normal immune systems. Complications can be found in most organ systems and are numerous. The following is a list that exemplifies the numerous possible complications and symptoms:
Follow-up for Cat Scratch Disease
Patients diagnosed with CSD who do not require antibiotics are usually seen in follow-up by their doctors in about two to six months; however, if symptoms do not resolve or get worse, the patients should contact their doctor immediately. Patients who are immunocompromised need close (daily to weekly) follow-up even if they respond well with antibiotics; in some cases, these patients need to be hospitalized for treatment of complications. Follow-up is needed to confirm that symptoms (and complications) resolve and do not return.
What Is the Prognosis of Cat Scratch Disease?
The prognosis for both nonimmunocompromised and immunocompromised CSD patients is very good. Symptoms resolve in about two to five months in nonimmunocompromised patients, and complications are rare. Immunocompromised patients with CSD, even with complications, when appropriately treated with antibiotics, usually recover completely from both CSD and its complications, but the time to full recovery may be extended beyond five months.
How Can People Prevent Cat Scratch Disease?
Although there is no vaccine available to prevent CSD, there are several ways to reduce or eliminate exposure to Bartonella henselae organisms. Avoid any "play" that may cause a kitten or cat to become aggressive and cause it to scratch or bite. Do not allow kittens or cats to lick a person's face or any area near the eyes or near any breaks in the skin. Keep kittens and cats free of fleas. Some investigators suggest declawing pet cats. Immediately wash scratches, superficial "bites," and licks with running water and soap. Immunosuppressed people may need to take extra precautions and avoid contact with cats, especially kittens. Visually, cats and kittens carrying Bartonella henselae cannot be distinguished from those not carrying the bacteria. However, any contact with cats or kittens with fleas will increase the chance of getting CSD.
Some investigators suggest that once a person gets CSD and recovers, the person becomes immune to subsequent infections.