Bartonella Species (Cat-Scratch Disease)

The Pathogen And Epidemiology

Bartonella spp. are pleomorphic, gram-negative bacilli with fastidious growth requirements. The domestic cat is a major reservoir for B. henselae and the major vector for transmission to humans. B. henselae bacteremia in otherwise well-appearing cats is common and can be prolonged. Studies have demonstrated that 41% of pet and impounded cats have bacteremia with B. henselae , whereas 93% of feral cats and 75% of pet cats have been found to be seropositive. Although flea-borne (Ctenocephalides felis) transmission of B. henselae from cat to cat appears to be efficient, epidemiologic data do not support the efficient transmission from cats to humans by cat fleas.

A cat scratch can result in cat-scratch disease. The incubation time from the cat scratch until the appearance of lymphadenopathy is 5–50 days (median, 12 days). The true incidence of cat-scratch disease in the US is unknown, although the diagnosis is made in an estimated 22,000 ambulatory patients annually, with a national incidence of hospitalization of 0.77 in 100,000 to 0.86 in 100,000. ^, A slightly larger proportion of cases occurs in males than in females. The incidence is highest in children 5–9 years of age and in southern states.

Cat-scratch disease is a sporadic illness with no evidence of person-to-person transmission. Even if asymptomatic, members of households in which a case has been diagnosed are more likely to be seropositive than the general population. Multiple cases have occurred in families, presumably resulting from direct contact with the same animal. Several widespread outbreaks also have been described. A survey of 33 geographic regions throughout North America showed correlation of prevalence of antibody to B. henselae in cats with climate. Seroprevalence was highest in regions with warm, humid climates, which also have a higher incidence and severity of flea infestation of cats.

Most cases of cat-scratch disease occur in fall and winter; 71%–93% of cases are reported from August through January. ^{, ,} Seasonality may be related to feline reproductive cycles, in combination with flea activity; that is, a cohort of kittens is born in midsummer (while flea activity is high) and is weaned in early fall. Kittens are more commonly implicated as sources of infection than adult cats, possibly because kittens are more likely to scratch. A survey of cats indicated that seroconversion occurred during the first year of life, a finding suggesting that young cats are more likely than older cats to have active infection.

Humans are the only known vertebrate hosts for B. quintana and B. bacilliformis . ^, The arthropod vector for B. bacilliformis is the sandfly. The vector involved in transmission of B. quintana is the body louse, and the association of body lice with trench fever was recognized during World War I. Both these Bartonella species can produce prolonged periods of asymptomatic bacteremia, thus providing a reservoir from which the body louse and sandfly can transmit the organisms to human hosts sequentially.

Clinical Manifestations

Cat-Scratch Disease

Human infections with B. henselae can be asymptomatic or symptomatic ( Fig. 160.1 ). For symptomatic patients, regional lymphadenopathy, fever, and mild constitutional symptoms are common. Cat-scratch disease is the most common cause of chronic unilateral regional lymphadenitis in children in the US. ^, After an incubation period of 7–12 days, 1 or more erythematous papules 2–5 mm in diameter will appear at the inoculation site. This primary lesion persists for ≥1 week and then regresses spontaneously. Lymphadenitis, the hallmark of cat-scratch disease, appears at 2–4 weeks. A hypersensitivity type of reaction can cause the appearance of reactivation of the primary lesion at this time.

Lymphadenitis usually involves nodes that drain the site of inoculation; however, in as many as 20% of cases, additional lymph node groups are affected. At any site of lymphadenitis, a single lymph node is involved in approximately one half of cases, and multiple nodes are involved in the remainder. The site most commonly involved is the axilla, followed by the cervical, submandibular, and inguinal areas. The area around an affected lymph node typically is tender, warm, erythematous, and indurated. In as many as 30% of cases, the affected lymph node suppurates spontaneously. Untreated, lymphadenitis usually regresses over 4–6 weeks.

Most patients with cat-scratch disease are afebrile and lack constitutional symptoms. When present, constitutional symptoms typically are low-grade fever, malaise, anorexia, fatigue, and headache. Atypical cat-scratch disease occurs in a small proportion of cases with ocular, hepatosplenic, and neurologic manifestations. Parinaud oculoglandular syndrome is a distinctive presentation of cat-scratch disease in which the site of inoculation is the eyelid or conjunctiva, and a papular lesion and conjunctivitis develop at the inoculation site accompanied by ipsilateral preauricular lymphadenitis ( Fig. 160.1 ). Patients with systemic cat-scratch disease typically come to medical attention for prolonged fever (1–3 weeks), malaise, listlessness, myalgia, and arthralgia; some have skin eruptions, weight loss, abdominal pain (which can be severe), peripheral lymphadenopathy, hepatomegaly, and splenomegaly. In a case series in which the presentation was fever of unknown origin, abdominal pain was present in more than one-half of patients and lymphadenopathy in less than one-half. Using ultrasonography and CT imaging, multiple microabscesses or granulomas of the liver or spleen can be identified in some cases. Other less common manifestations include encephalopathy or encephalitis, aseptic meningitis, neuroretinitis, osteolytic lesions, bone marrow granulomas, granulomatous hepatitis, pneumonia, thrombocytopenic purpura, and erythema nodosum.

Bartonella is a significant cause of culture-negative endocarditis. Cases are most often reported in adults, and >95% of cases are caused by B. quintana or B. henselae .