What is cat scratch fever

Cat scratch fever also called cat scratch disease, is an illness caused by Bartonella henselae bacteria (a Gram-negative organism) ¹⁾. Almost half of all cats carry the infection at some point. The infection does not make cats sick. However, the scratch or bite of an infected cat can cause symptoms in people, including:

• Swollen lymph nodes (lymphadenopathy), especially around the head, neck, and upper limbs
• Fever
• Headache
• Fatigue
• Poor appetite

Most infections usually occur after scratches from domestic or feral cats, especially kittens. Cat scratch disease occurs wherever cats and fleas are found. The most common symptoms include fever; enlarged, tender lymph nodes that develop 1–3 weeks after exposure; and a scab or pustule at the scratch site. In the United States, most cat scratch disease cases occur in the autumn and winter and illness is most common in children less than 15 years old. Mean age at presentation was 7.8 (±3.8) years, with equal sex distribution ²⁾.

Affected children typically present with lymphadenitis (swollen inflamed lymph nodes) after local cutaneous reaction at the scratch site. For people with weak immune systems, cat scratch disease may cause more serious problems. Bacillary angiomatosis caused by cat scratch disease occur primarily in immunocompromised people, such as those with advanced HIV infection. Bacillary angiomatosis may present as lesions in the skin, subcutaneous tissue, bone, or other organs. Complications such as Parinaud’s oculoglandular syndrome, erythema nodosum, and granulomas in the liver and spleen occur in approximately 10% of immunocompetent children ³⁾. Resolution of symptoms usually occurs within 2–4 weeks ⁴⁾. Lymphadenopathy is usually self-limited, not requiring antibiotic therapy.

The best way to avoid cat scratch fever is to avoid rough play with cats that could lead to scratches or bites. If you do get a scratch or bite, wash it well with soap and water. If the bite or scratch gets infected or if you have symptoms of cat scratch fever, call your doctor.

Treatment of uncomplicated cat scratch disease remains controversial. Because it is a benign and self-limiting condition, with most cases of regional lymphadenopathy resolving spontaneously in two to four months, no specific treatment is usually necessary. However, some studies suggest that certain antibiotics including azithromycin, doxycycline, erythromycin, gentamicin, rifampicin, trimethoprim + sulphamethoxazole and ciprofloxacin may significantly shorten the duration of lymphadenopathy. Antibiotics are warranted in patients with severe or persistent symptoms of catscratch disease.

In rare cases, large pus-filled lymph nodes may persist for one to three years. The pus may need to be repeatedly drained through a needle. Pain and fever can be managed by increasing fluid intake and paracetamol. Warm moist compresses to affected lymph glands may decrease swelling and tenderness.

Is cat scratch disease contagious?

Cat scratch disease is not contagious from person to person. The Bartonella henselae bacteria are spread by the scratch or bite of an infected animal, most often a kitten. They also can spread if the animal’s saliva (spit) comes in contact with a person’s eye or through broken skin. Sometimes multiple cases happen in the same family, usually through contact with the same infected animal.

Having one episode of cat scratch disease usually makes people immune for the rest of their lives.

My cat is completely healthy. How can it carry an infection?

Cats become infected with Bartonella henselae (the bacteria that cause cat scratch disease) through flea bites or less commonly, fights with other infected cats or feline blood transfusions. While some cats become ill, most simply carry the Bartonella henselae bacteria in their blood without getting sick. Some studies have found the Bartonella henselae bacteria in the blood of up to 1/3 of healthy cats, particularly kittens.

Should I get my pet treated for Bartonella, just to be safe?

Treatment is not recommended unless your pet cat becomes sick. Treating Bartonella with antibiotics can take a long time and it’s considered safer and more practical to let the pet handle the infection naturally. For cats that do become sick, the illness usually consists of fever for 2-3 days, with the cat recovering on its own. Symptoms requiring veterinary care include fever, vomiting, lethargy, red eyes, swollen lymph nodes or decreased appetite.

My daughter got scratched by the neighbor’s kitten and now my husband is worried about “cat scratch disease.” How worried should we be?

Most cat scratches do not result in cat scratch disease, and short of cleaning the wound with soap and water, there is no particular action to take. If your child develops a fever; enlarged, tender lymph nodes that develop 1–3 weeks after being scratched; or a pustule at the scratch site, please take her to your health care provider. Treatment with antibiotics is usually not necessary but may help reduce lymph node swelling.

I have a medical condition that affects my immune system. Should I give my cat away?

If you’re HIV-positive, are being treated for cancer, or have any other condition that might disrupt your immune system, you can keep your cat. Just keep the following points in mind:

• Keep the cat indoors.
• Avoid rough play with cats and situations in which scratches are likely. Declawing is not recommended.
• Promptly wash any cat scratches or bites with soap and water.
• Avoid contact with fleas.
• Treat the cat with a flea control product recommended by your veterinarian.
• It’s not necessary to test or treat a healthy cat for Bartonella henselae.
• If you are getting a cat, make sure it’s at least a year old, in good health, and free of fleas. Avoid stray cats and cats with flea infestations.

I got a tick bite. My friend said I should get tested for Lyme disease and Bartonella. Is that true?

Experts at the Centers for Disease Control and Prevention (CDC) don’t recommend it. To date, no study ⁵⁾ in the United States has shown that Bartonella can be transmitted to humans by ticks. Transmission studies with ticks have only used mice and artificial feeding systems. A single study showed that one species of tick in Europe could transmit a specific species of Bartonella to mice in a laboratory setting.

Other studies have identified Bartonella in ticks, probably from ticks feeding on animals that carry Bartonella. This doesn’t mean that the bacteria can be transmitted from the tick to a person or that the bacteria can survive in the tick for any length of time.

Unfortunately there is a great deal of misinformation regarding multiple tickborne infections (called coinfections) on the internet. The possibility of having several tickborne infections at once or having pathogens such as Bartonella that have not been shown to be tickborne, is extremely unlikely ⁶⁾.

How do you get cat scratch fever

People can get cat scratch disease from the scratches of domestic or feral cats, particularly kittens (young cats under 12 months). Cat scratch disease occurs most frequently in children under 15. Cats can harbor infected fleas that carry Bartonella henselae bacteria. These bacteria can be transmitted from a cat to a person during a scratch. Some evidence suggests that cat scratch disease may be transmitted directly to humans by the bite of infected cat fleas, although this has not been proven.

People at risk of getting catscratch fever include those:

• owning a cat younger than 12 months
• licked, bitten or scratched by an infected kitten
• petting an infected cat
• owning at least one kitten or cat with fleas.

Cat scratch disease occurs worldwide and may be present wherever cats are found. Stray cats may be more likely than pets to carry Bartonella henselae. In the United States, most cases of cat scratch disease occur in the fall and winter.

Ticks may carry some species of Bartonella henselae bacteria, but there is currently no convincing evidence that ticks can transmit Bartonella henselae infection to humans.

How long does cat scratch fever last?

Resolution of symptoms usually occurs within 2–4 weeks ⁷⁾.

Cat scratch disease prevention

• Avoid rough play with cats, particularly strays and kittens, to prevent scratches. This is especially important for immunocompromised individuals. Wash hands promptly after handling cats.
• Treat cats for fleas using fipronil and other spot-on treatments. Check with your veterinarian. Permethrin should not be used on cats.
• Use a flea collar or similar topical preventive on dogs (fipronil, methoprene, imidocloprid, or permethrin), especially if you have both cats and dogs in your household.
• Keep cats indoors and away from stray cats.
• Immunocompromised individuals should avoid owning cats less than one year of age.

Prevention and control for your pet

As fleas are involved in the transmission of Bartonella henselae among cats, the use of pesticides to reduce fleas in the environment is important. Additionally, the use of flea prevention products will stop the flea life cycle and also prevent infestation on pets. Additionally:

• Dogs should be placed on an effective oral or topical flea prevention product such as fipronil, methoprene, Imidocloprid, or permethrin to protect them from fleas and tick infestations.
• Permethrin should never be used on cats. Other oral or topical flea prevention products are safe when used as directed.
• An indoor lifestyle for cats is preferable in the prevention of Bartonella henselae transmission, as this environment will reduce the risk of flea infestation and contact time with other stray cats.
• Discourage immunocompromised individuals from playing with or owning young cats.
• To prevent scratches, some advocate declawing cats. This is controversial, however, because cats need their claws for a number of activities.
• There are currently no vaccines available for cats or dogs against Bartonella henselae.

What are the signs and symptoms of cat scratch fever?

A small red raised spot develops at the site of contact with an infected cat’s saliva. This changes into a fluid-filled blister that later forms a crusty sore. This usually heals without scarring in several days or months. It is often mistaken for an insect bite. Most are found on the hands, arms, face or neck as people often hold kittens close to their chest and face.

The nearest lymph glands then become swollen and tender, most often those on the head, neck and armpit. This is known as regional lymphadenopathy. The lymph glands may swell to 10-12 cm in the first two weeks of the disease. On questioning, patients often recall being licked, bitten or scratched by a cat in the previous one to eight weeks.

Most patients showed fever (84.3%) and 64.7% prolonged course of fever lasting more than 2 weeks. In 90% of cases, cat scratch disease manifestation is represented by subacute, localized, self-limited lymphadenitis preceded by local cutaneous reaction at the scratch site. Sites involved were cervical (45.5%), axillary (15.6%), inguinal (12.1%), epitrochlear (6.1%), submandibular (6.1%), axillary and cervical (3%), preauricular (3%), postauricular (3%), submandibular and axillary (3%), and parasternal (3%).

About 50% of patients will experience additional signs and symptoms including:

• Low-grade fever
• Enlarged, tender lymph nodes that develop 1–3 weeks after exposure
• Malaise/fatigue
• Headache
• Nausea and vomiting
• Sore throat
• Rash
• Stomach pains
• Conjunctivitis

About 10% of patients with cat scratch disease show atypical manifestations including prolonged course of fever (i.e., more than two weeks), erythema nodosum, and hepatic and splenic granulomas ⁸⁾.

Less common problems occur in about 10% of patients. These include:

• Parinaud’s oculoglandular syndrome, characterised by an inflamed lump in the eye and swollen lymph glands in front of the nearby ear
• Bacillary angiomatosis (infection of the blood vessels)
• Bacillary hepatitis and splenitis (infection of the liver and spleen)
• Erythema nodosum (red lumps on the shins)
• Sepsis (infection disseminated through the blood stream)
• Encephalopathy (brain infection)
• Bacterial endocarditis (heart valve infection)

Rarely, unusual manifestations such as eye infections, severe muscle pain, or encephalitis may occur. Encephalopathy is an uncommon complication of catscratch disease that occurs one to six weeks after the lymph glands swell up. The abrupt symptoms of fever, seizures and coma can be frightening. With hospitalization and high doses of antibiotics most patients recover completely.

Cat scratch disease diagnosis

Cat scratch disease may be diagnosed presumptively in patients with typical signs and symptoms and a compatible exposure history. Serology can confirm the diagnosis, although cross-reactivity may limit interpretation in some circumstances. In general, lymph node aspiration is not recommended except to relieve severe pain and swelling or in cases where the diagnosis is unclear.

• Bartonella henselae DNA may be detected by polymerase chain reaction (PCR) or culture of lymph node aspirates or blood, though sensitivity of these methods is not optimal for blood samples.
• Since Bartonella henselae is a fastidious, slow-growing bacterium, cultures should be held for a minimum of 21 days.
• Endocarditis due to Bartonella species can be diagnosed by serology and by PCR or culture of excised heart valve tissue.

Cat scratch fever treatment

The use of antibiotics to shorten the course of disease is debated. Most cases of cat scratch disease resolve without treatment, although some patients may develop complications from disseminated disease. Azithromycin has been shown to decrease lymph node volume more rapidly compared to no treatment. The recommended dose of azithromycin for cat scratch disease is:

• For adults and children > 45.5 kg: 500 mg on day 1, followed by 250 mg for 4 days
• For children ≤ 45.5 kg: 10 mg/kg on day 1, followed by 5 mg/kg for 4 days

A number of other antibiotics are effective against Bartonella infections, including penicillins, tetracyclines, cephalosporins, and aminoglycosides. Since aminoglycosides are bactericidal, they are typically used as first-line treatment for Bartonella infections other than cat scratch disease. Often, with serious infections, more than one antibiotic is used.