Cat Scratch Disease: Has Identification of
The Causative Agent Been Solved?
Cat Scratch Disease (CSD) was first recognized more than
60 years ago. The majority of human cases, most frequently
affecting children and young adults, have a history of recent
traumatic exposure to cats, including bites and scratches.
While cats do not appear to be clinically affected, humans,
immunocompromised or immunocompetent, tend to show a variety
of clinical manifestations, including systemic and cutaneous
angiomatosis, prolonged or relapsing fever with bacteremia,
and central nervous system disorders. Typically, a papule
develops within three to five days after feline contact
at the site of the injury. Within ten to fourteen days,
the lymph nodes of the draining site proximal to the lesion
become markedly enlarged and inflamed. The patients may
also exhibit fever, malaise, weight loss, myalgia, headache,
conjunctivitis, skin eruptions and arthralgia. A substantial
proportion of the patients develop suppurative lymphadenitis,
necessitating the drainage of the lymph nodes. Rarely, although
reported in the literature, encephalitis and neuroretinitis
occurs. The disease tends to be self-limiting, but the lymphadenitis
may persist for several months. Surgical excision of the
affected lymph nodes is usually not required and treatment
with aminoglycosides and 3rd generation cephalosporins(cefotaxime)
may be helpful. In the United
States the incidence of
CSD has been estimated at 9.3 cases per 100,000 population
Various viral, bacterial and chlamydial agents have been
proposed to be the etiological agent of CSD and diagnosis
has been extremely difficult until recent years. In the
past, the diagnosis has depended upon several criteria:
a compatible clinical picture, primarily with unilateral
regional lymphadenitis; documentation of exposure through
feline contact or wounds; papule formation at the site of
injury; the exclusion of other common etiologies of lymphadenopathies;
characteristic histopathologic lesions including microabscesses
and granulomas from lymph node biopsies; and a positive
reaction to the CSD skin test. This skin test relies upon
the intradermal inoculation of diluted and autoclaved pus
derived from patients known to have the disease.
In 1983, lymph node biopsies prepared with Warthin-Stany
silver stain enabled visualization of pleomorphic organisms.
In 1988, a specific bacillus was cultured from the lymph
nodes of CSD patients. This motile, gram-negative rod was
later named Afipiafelis in honor of the Armed Forces
Institute of Pathology (AFIP), where most of the work was
performed. This is the organism currently reported to
be the etiologic agent of CSD in Veterinary Clinics
of North America, Small
Animal Practice. Unfortunately, the demonstration and
isolation of this potential causative agent from CSD lesions
has been inconsistent. Information then emerged suggesting
that Rochalimaeahenselae was a more common cause
and isolate from lymph nodes of patients. Like A. felis,R.
henselae is a Proteobacteria(alpha-2 subclass) and is
visualized with Warthin-Stany stain. However, this bacterium
belongs to the Rickettsial order and is not closely related
to A. felis. When an indirect fluorescent-antibody
(IFA) test for R. henselae was used, 88% of patients
with suspected CSD had markedly elevated serum tilers of
the respective antibody. Polymerase chain reaction (PCR)
amplification of DNA from five CSD skin test antigen preparations
had yielded sequences which were consistent with
Rochalimaeasp., not withA felis. In 1994,
Minet al. applied an immunocytochemical labeling technique
to lymph node biopsies from patients with the clinical diagnosis
of CSD to assess whether the organisms demonstrated by the
Warthin-Stany stain might be R. henselae. Their results
confirmed that the bacilli detected with stain were also
identified by antibodies to R. henselae.
Rochalimaea henselae has been renamed Bartonella
henselae, and as of last year, definitive identification
of Bartonella organisms to the species level had
been done with time-consuming molecular biologic techniques.
Therefore in 1995, the development of the diagnostic tool
called repetitive element PCR (re-PCR) allowed it to become
the most novel and rapid method now used to distinguish
between the Bartonella species by genonuc DNA fingerprinting.
While the causative agent has now been specifically identified
and diagnosed, additional aspects of CSD must now be addressed.
Although fleas or ticks on the cat have been speculated
to play a role in cat-to-cat infection and transmission,
the exact pathogenetic mechanism for cats to become infected
with B. henselae and transmit infection to people
is unknown. With further research and experimentation, a
vaccination for cats or humans may be available for preventing
further outbreaks of this disease.
- by F.ClaireGaskell, Class of 1997
- edited by Tsang Long Lin,DVM,PhD
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