View source for Streptobacillus moniliformis

* Causes '''[[Causes::rat-bite fever]]'''

== Background ==
=== Microbiology ===
* Pleomorphic, [[Has motility::non-motile]], non-sporulating, non-encapsulated filamentous [[Stain::Gram-negative]] [[Has cell shape::bacillus]]
** Often long, but can even be coccoid
** Lateral bulbar swellings
* Anaerobic, requires 8-10% CO<s>2</s> to grow in culture, and requires an enriched medium
** Blood cultures often negative because it is inhibited by SPS in blood culture bottles
* Nonhemolytic cotton-like colonies on blood agar
* Forms small flocculent puffballs in liquid media
* Can form a penicillin-resistant, cell-wall-deficient L-phase variant
** &quot;Fried egg&quot; appearance on plate

=== Epidemiology ===
* Transmitted by the bite or scratch (or sometimes merely handling) of a rat, mouse, guinea pigs, or squirrel, or of an animal that eats these (e.g. dog, cat, pig, ferret, weasel, or python)
** Oral flora of these animals
* Can have occupational exposures in a labs or pet stores, household exposure due to rat infestation, or exposure from pet rats
** 50% of cases are in children
** Occurs in about 10% of rat bites, though only 200 cases reported in the US
* Can also be acquired by ingestion of turkey, or milk or water contaminated with rat feces
** Milk outbreak in Haverhill, MA, gives it its name of Haverhill fever

=== Pathophysiology ===
* Likely gains access through a broken skin (or mucosal) barrier
* Relapses may be related to spontaneously changing to and from the L variant
* Autopsy shows erythrophagocytosis, hepatosplenomegaly, interstitial pneumonia, and lymph node sinus hyperplasia

== Clinical Manifestations ==
* Incubation period 10 days (range 1 to 22 days)
* Fever, chills, headache, nausea/vomiting, severe migratory arthralgias and myalgias
** Wound has often healed by presentation
* Significant leukocytosis
* Can have false-positive non-treponemal syphilis serology
* After 2 to 4 days, develops a nonpruritic rash that can be maculopapular, morbilliform, petechial, vesicular, or pustular, on extremities
** May become purpuric and confluent
** Involves palms and soles
* Arthralgias progress to arthritis
* Fever resolves within days, and the other symptoms within about 2 weeks
* However, can develop a relapsing-remitting course over months, and arthritis can persist for years

=== Haverhill fever ===
* When acquired from oral ingestion, can present with pharyngitis and severe vomiting, then progress to the usual

=== Rare sequelae ===
* Endocarditis, myocarditis, pericarditis, sepsis, systemic vasculitis, meningitis, pneumonia, hepatitis, septic arthritis, amnionitis, and anemia
* Abscesses in any organ, including brain, liver, spleen, kidney, epidural space, bone, skin, muscle, and genital tract
* Diarrhea and weight loss in children
* Mortality as high as 13% if untreated

== Diagnosis ==
* Often on the differential with leptospirosis, and can mimic RMSF, secondary syphilis, gonococcal infection, Lyme disease, brucellosis, septic arthritis, and other
* On microscopy, the bacilli stain with Giemsa, acridine orange, or Gram stain
* Must be cultured with specific enriched media
* ELISA exists for antibodies, and PCR exists

== Treatment ==
* Penicillin G 12m units total daily dose IV, step down to oral after a week if well
* Alternative: tetracycline 500 mg po q6h, streptomycin 7.5 mg/kg IM q12h
* Duration 10 to 14 days

== Prevention ==
* Rat bites should be cleansed thoroughly
* Tetanus prophylaxis if appropriate
* Can do 3 days of prophylactic penicillin 2 g daily divided

== Further Reading ==
* Rat Bite Fever and ''Streptobacillus moniliformis''. ''Clin Microbiol Rev''. 2007;20(1):13-22. doi: [https://doi.org/10.1128/CMR.00016-06 10.1128/CMR.00016-06]


{{DISPLAYTITLE:''Streptobacillus moniliformis''}}
[[Category:Gram-negative bacilli]]
[[Category:Fever syndromes]]