1. Pathogenic agent of cat-scratch disease (CSD)
    The pathogen of cat-scratch disease is Bartonella henselae, a gram-negative polymorphic bacillus. It has been reported that     B.clarridgeiae of the same genus also causes typical or atypical CSD in humans.
2. Epidemiology of CSD
    The annual number of CSD patients in the United States was around 22,000 in 1992, and the annual incidence of CSD is 0.77~0.88 per 100,000 persons. The annual incidence of patients in the Connecticut state is estimated at 3.7/100,000 people. In Japan, since this sickness was reported for the first time by Hamaguchi et al. in 1953, CSD cases have been occasionally found. However no statistics are available on the number of CSD patients throughout Japan.
CSD occurs in all age groups, but young age group is the majority. A report on the study of 63 CSD cases in Japan shows that over 60% of all the patients are females, in particular in their teens and in their forties, and that in children under the age of 9, the disease tends to strike more frequently boys than girls.
    CSD occurs frequently from July to December or from fall through winter. The number of cats infected by the disease rises during the period of cat-flea reproduction in the summertime. Later on when the season turns cold, those cats stay more often in homes, and the number of cases increases presumably because cat owners are more liable to get scratched and injured. An important etiologic source or infection source of the disease is assumedly infected kittens below 12 months of age or kittens infested with many fleas. Fleas become vectors of B.henselae amongst these animals. Infection due to wounds apparently occurs between cats or from cats to humans, since B.henselae is excreted in the buccal cavity for some reasons in cats or the bacterium shed in the feces of fleas adheres to the teeth or to the claws during grooming, and the infected fleas are ingested in the mouth and the cats become infected by the bacillus.
    Though it is not clear at present that B.henselae infection is passed from fleas to humans, it would be possible to consider that fleas having sucked the blood of infected cats transmit the bacterium to humans. In Japan, 8.8% of domestic cats (128/1,447) are antibody-positive. A high positiveness rate is found in young cats, cats that were infested by fleas, cats kept outdoors and also those staying in warm areas in the south region of Japan. Besides 7.2% of the Japanese domestic cats (50/690) are carriers of the Bartonella bacterium. The rate is ranged from 2% to 20%, and differences are noted between regions. This rate tends to be high in cats staying in southern warm regions and urban areas. The status of infection of cats in Japan may be related to the distribution of cat fleas and to the frequency of occasions of exposure to infected cats. The distribution of B.clarridgeiae is also manifest in cats in Japan.
3. Symptoms
1)Humans
    In typical CSD, lesions similar to insect bites are formed at the site of invasion by the bacterium (usually, fingers and forearms) 3~10 days after being scratched by a cat. In some cases, papules may turn into blisters, and some of them may suppurate or develop into ulcers. Swollen localized lymph nodes (in the majority, inguinal region, axilla or cervical lymph nodes) appear one or two weeks after the formation of these lesions. Usually lymphadenitis is unilateral and is accompanied by pain, and it persists from several weeks to several months. Many subjects exhibit fever, chills, tiredness, loss of appetite, headache, etc. However these symptoms are generally benign and recover naturally.
    Atypical CSD symptoms are manifested in 5~10% of the subjects. Parinaud's syndrome (inflammation of the lymph glands in the periphery of the ears, palpebral conjunctivitis, etc.), encephalitis, osteolytic lesions, endocarditis, granulomatous hepatitis, etc. have been reported. Bacterial hemangioma occurs in case immunocompromised subjects are infected by B. henselae. Its clinical manifestation is purple or colorless vesicles or cystic skin lesions such as Kaposi's sarcoma, and in some cases cysts may spread to the parenchymal organs.
2) Cats
    Cats infected by B.henselae are bacteremic for a long duration (several months to several years) without normally exhibiting any clinical symptoms. Cases of fever, transient neurological dysfunction, somnolence, anorexia, etc. have been reported in cats experimentally infected with B. henselae.
4. Diagnosis
    When diagnosing CSD, it is necessary to check for contacts with cats (notably young cats) and to confirm the presence of wounds and swollen local lymph nodes. The indirect fluorescent antibody technique using B. henselae as antigen is employed as a serological diagnostic tool. With this technique, the subject is determined to be positive in case the antibody titer in the serum shows a 64-fold or more elevation.
    Blood and lymph node materials are used for the isolation of B. henselae. However the isolation of the bacterium from patients is extremely difficult. Blood agar culture medium is used for the isolation and cultivation is performed at 35~37oC in 5% CO2 vapor phase. In case of primary isolation culture, it is necessary to continue the observation for four weeks. The technique consisting of comparing the cleavage patterns of the PCR amplification products of citric acid synthesis enzyme genes using two restriction enzymes, Taql, Hhal and strain specific PCR are used for the identification of the bacterial strain.
5. Treatment
        Treatment by means of various antibacterials has been experimented for typical CSD, but their efficacy is not so high. Antibiotics such as erythromycin, rifampicin, gentamycin, doxycycline, ciprofloxacin, etc. are efficacious against bacterial angioma in immunocompromised patients. In cats, antibiotics such as doxycycline, lincomycin, amoxicillin, etc. can inhibit bacteremia to some extent. However they cannot eliminate completely the bacterium from the blood.
6. Prevention
        There are no other means than taking general hygienic precautions such as 1) avoiding scratches from cats (notably kittens); 2)disinfection of wounds caused by cats; 3) washing hands after exposure to cats; 4) getting rid of cat fleas, etc. There are no vaccines for cats and humans. When keeping cats in households with children, it should be recommended to have cats on which fleas have been exterminated and cats negative for B.henselae bacteremia. In addition, immune compromised persons should avoid contacts with cats and keeping cats at home.