Paired sera should be obtained wherever possible:
(a) acute sample - as early as possible in the illness, and
(b) convalescent sample 2 - 3 weeks after onset.
3.5 mL SST Serum (Preferred) 4 mL Plain Serum Reference Intervals
Studies indicate that approximately 90% of suspected cases of CSD result in serum IgG titres of >1:64 by IFA, and/or IgM titres of >1:20 during the acute phase. Background titres in healthy people are rare.
Tests performed every 1 - 2 weeks.
Diagnostic Use and Interpretation
The causative organism of Cat Scratch Disease (CSD) is a Gram-negative bacterium Bartonella henselae, formerly known as Rochalimaea henselae. B.henselae bacteremia occurs in flea infected, well-appearing kittens usually less than one year old, and less commonly older cats. The organism is transmitted among cats by the cat flea; it is transmitted to humans by a cat scratch, bite or other intimate contact.
· Cats act only as a vector for the disease. They are not ill with their B.henselae bacteraemia.
· CSD can also be transmitted by splinters, thorns, beef bone fragments, dog and monkey scratches.
Epidemiology of CSD
Worldwide, especially in temperate climates.
· 90% of patients with CSD have a history of exposure to cats and 75% have a cat scratch or bite.
· In USA: ~22,000 cases/year
· 2,000 hospitalisations
· 60 million cats for ~ 250 million people, ~ 1/3 of households have a cat.
· Most patients are < 20 years (80% are children), males > females.
Etiology & Pathogenesis
· 17-100% of cats tested have B.henselae bacteraemia. 17% of a sample of domestic cats in Auckland had B.henselae bacteraemia.
· Bacteraemia may last for >22 months.
· B.henselae has also been recovered from the cat flea, Ctenocephalides felis.
· C.felis feed repeatedly, are often not specific with regard to host, biting cats, humans, as well as dogs. Their life span may be more than a year in warmer regions. Direct transmission from fleas to people could be either by regurgitation (e.g. Y.pestis) or inoculation of flea faeces during scratching (e.g. R.quintana in trench fever). It is not known how important flea transmission is as a route of acquisition of this organism in human infection.
· For CSD: Cases more likely to have a kitten < 12 months (odds ratio, 15) to have been scratched or bitten by a kitten (OR, 27) and to have at least one kitten with fleas (OR, 29). The scratch or bite is often not recalled by the patient.
· For neuropsychological decline or dementia in HIV infected patients: IgM to B.henselae associated with decline/dementia (OR, 7), cat ownership associated with IgM antibodies (OR, 6) and with decline/dementia (OR, 2).
CSD occurs as both typical and atypical disease.
Typical CSD in an immunocompetent host is manifested by a characteristic and highly predictable clinical course. In nearly all cases patients give a history of a scratch, bite or contact with a cat or kitten. Typically a round, red-brown, nontender papule develops in the scratch line after 3-10 days. It may vary in size from one to several millimetres (mm) and may persist for a few days to as long as 2-3 weeks. In the following 1-2 weeks one or more regional lymph nodes that drain the area gradually enlarge.
CSD lymph nodes tend to be large with an average diameter of 4-6cm at the time of maximum size, but can be as large as 10-13cm. After 1-2 weeks of enlarging, they remain the same size for 2-3 weeks and then resolve over an additional period of 2-3 weeks. The usual course of the disease is 2-3 months. Some cases are more severe and more protracted, and may last up to 6-7 months.
Most patients with typical CSD remain afebrile and are not ill appearing. Some patients experience anorexia, malaise, headache arthralgia, and abdominal, neck, back and or extremity pain. CSD lymphadenopathy is unilateral and isolated to a region group of lymph nodes in immunocompetent patients.
Typical CSD is a self-limited disease in immunocompetent hosts and will usually resolve spontaneously in 1-3 months.
Parinaud's Oculoglandular Syndrome (POGS) is a fairly common presentation of atypical CSD. It consists of unilateral conjuctivitis with adjacent preauricilar lymphadenopathey. The palpebral conjuntivae of the involved eye displays a characteristic granulomatous lesion that measures 2-3mm - >1cm. Infection of the eye is contracted by inoculation of the organism indirectly into the eye. It is a predictable self-limited infection with a good outcome.
Hepatosplenic CSD occurs in immunocompetent patients who present with fever of unknown origin. These patients have daily high fevers lasting up to a month for some patients. Diagnosis is made by the presence of lytic lesions in the liver and/or spleen and positive B.henselae titres. Fever usually resolves within a day or two with intravenous aminoglycoside.
CSD Encepalopathy and Neuroretinitis. CSD encephalopathy (CSDE) was first reported in1952. Convulsions occur in about one half of cases and may last from a few minutes to 3-4 hours, requiring intubation and intensive care. Another neurologic form of atypical CSD is a distinctive type of neuroretinitis, called Leber's stellate neuroretinits. It presents with painless unilateral, rarely bilateral, loss of vision with central scotomata, optic disc swelling, macular star formation and complete recovery of vision within 1-3 months.
The primary immune response to Bartonella is an IgM class antibody which appears early in the infection and is highly diagnostic when present. The IgG antibody response follows the initial IgM response closely, maximising at 8-12 weeks and becoming non-reactive six months after lymphadenopathy onset. In the majority of cases, by the time patients are symptomatic, serology will be reactive. In a small percentage of cases, IgM can persist for over 12 months. Since the IgG response is broadly cross reactive between species, these results must be interpreted with caution.
Recently there has been a resurgence of interest in another species of the genus bartonella, B.quintana. This organism is the causative agent of classical Trench Fever. B.quintana has been implicated in acute endocarditis and baciliary angiomatosis in HIV patients. B.quintana serological diagnosis is similar to B.henselae. There is extensive IgG cross reactivity between these two species while the IgM response is more species specific.
Communicable Disease Report; Cat Scratch Disease: A Review. Hawaii Department of Health. Judy M. Vincent, M.D., Denise M. Demers, M.D. and James W. Bass, M.D. Department of pediatrics, Tripler Army Medical Center.
For further information contact the laboratory (contact via Lablink: 22000 or (09) 307-8995 or 0800 522 7587) ,or:
the Virology team email@example.com