Streptobacillus moniliformis

Background

Pleomorphic, non-motile, non-sporulating, non-encapsulated filamentous Gram-negative bacillus
- Often long, but can even be coccoid
- Lateral bulbar swellings
Anaerobic, requires 8-10% CO2 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
- "Fried egg" appearance on plate

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

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

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

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

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

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

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