Domain : Bacteria
Kingdom : Bacteria
Phylum : Fusobacteria
Class : Fusobacteria
Order : Fusobacteriales
Family : Fusobacteriaceae
Genus : Streptobacillus
Species : Streptobacillus moniliformis
Classification
Gram
negative, pleomorphic or filamentous rod
Family
Fusobacterium
Affected
species
Mice
develop clinical disease; rats are asymptomatic nasopharyngeal carriers of this
organism. Gerbils and guinea pigs have been infected as well. This is a zoonotic
infection, and the two synonyms listed above are names of the disease in
humans.
Frequency
Common
in wild and pet rats, rare in laboratory rats, laboratory mice, and wild mice.
Transmission
S.
moniliformis is usually transmitted through rat saliva, via a bite. It may also
be transmitted through ocular or nasal secretions.
Clinical
Signs and Lesions
Generally
none in carrier rats; rarely, opportunistic pulmonary infections or abscesses
are seen. In mice, susceptibility varies by strain, with C57BL/6 and outbred
Swiss mice very susceptible, DBA/2 mice intermediate in susceptibility, and
BALB/c and C3H/He mice resistant. Affected mice may present with sudden death
due to septicemia, or a more prolonged septicemic course. Typical clinical
signs include cervical lymphadenitis, diarrhea, conjunctivitis, cyanosis, haemoglobinuria,
and weight loss. If animals survive the acute stages of disease, suppurative
polyarthritis, osteomyelitis, and abscesses may be seen. On
necropsy,
the liver and spleen may contain widespread foci of necrosis and inflammation.
Petechiae and ecchymoses may be seen on serosal surfaces. Renal involvement is
secondary to septicemia, and usually consists of interstitial nephritis with
bacterial colonies often noted.
Humans
have a variety of clinical presentations, including fever, rash, polyarthritis,
and endocarditis. S. Moniliformis infection in humans may be fatal. Wild or pet
rat bites should be reported to a physician and treated immediately.
Diagnosis
S.
moniliformis may be cultured on blood agar from the nasopharynx of carrier rats
or infected mice. Serology and PCR are also available.
Interference
with Research
Although
otherwise healthy, carrier rats are not suitable for use in research, due to
the zoonotic potential of this organism. Affected mice are generally clinically
ill and unfit for research purposes.
Prevention
and Treatment
Since
S. moniliformis infection is transmitted through direct contact with infected
animals, their exclusion from the animal facility is a key point. Wild, feral,
and pet rats should all be excluded from laboratory rodent areas. Incoming
animals from non-commercial sources should be quarantined and tested for the
presence of this organism. Staff working with laboratory rodents should not
keep pet rats or work with wild or feral rats.
Although
vertical transmission has been reported in mice (accompanied by fetal demise),
hysterectomy or embryo transfer appears to be effective for elimination of S.
moniliformis from carrier animals. The organism does not form spores, and is
thought to have no significant environmental persistence, so normal
environmental decontamination procedures should serve to remove S. moniliformis
from the environment.
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