Infectious Disease and Microbiology – Streptobacillus moniliformis

Overview

Streptobacillus moniliformis is a pleomorphic Gram-negative bacillus and an important cause of rat-bite fever, also called streptobacillosis. Infection usually follows a rat bite or scratch, although exposure to contaminated food or water can produce an outbreak-associated form historically known as Haverhill fever.

The classic illness begins with fever, headache, and malaise, followed by a maculopapular or petechial rash and prominent migratory arthralgia or polyarthritis. Untreated infection can occasionally progress to serious complications such as endocarditis, pericarditis, tenosynovitis, and metastatic abscesses.

Classification

Genus: Streptobacillus

Species: Streptobacillus moniliformis

Organism: Pleomorphic Gram-negative bacillus

Major disease: Rat-bite fever (streptobacillosis)

Food/water-associated syndrome: Haverhill fever

Microbiologic Characteristics

S. moniliformis is a:

• Pleomorphic Gram-negative bacillus

• Fastidious organism

• Nonmotile bacterium

• Rat-associated zoonotic pathogen

• Organism requiring specialized conditions for optimal laboratory recovery

Its cells may form:

Chains and filamentous structures with irregular swellings

The term:

moniliformis

refers to a:

Beaded or necklace-like appearance

High-Yield Microbiology Pattern

Pleomorphic Gram-negative bacillus

• ●

Rat exposure

• ●

Fever

• ●

Rash

• ●

Migratory polyarthralgia/polyarthritis

→ Think Streptobacillus moniliformis

Incubation Period

The usual incubation period is:

3–10 days

although it may occasionally be:

Longer

Symptoms therefore typically develop within approximately a week after rodent exposure.

Epidemiology

S. moniliformis has a:

Worldwide distribution

Human disease remains relatively:

Rare

including in:

• North America

• Europe

However, S. moniliformis is the classic cause of rat-bite fever in:

North America

Rat Reservoir

The major reservoir is:

RATS

The organism can colonize the:

Nasopharyngeal and upper respiratory flora of rodents

without causing obvious disease in the animal.

Transmission

Most patients report:

A RAT BITE

However, transmission can also occur through:

• Rat scratches

• Contact with rodent secretions

• Handling infected rodents

• Exposure to contaminated food or water

Rat-Bite Fever

The major clinical syndrome is:

RAT-BITE FEVER

also known as:

Streptobacillosis

The illness usually begins abruptly after the incubation period.

Clinical Manifestations

The classic initial manifestations include:

• Fever

• Headache

• Malaise

• Chills

• Myalgia

These systemic symptoms are typically followed by:

Rash + arthralgia/polyarthritis

Rash

A characteristic:

Maculopapular rash

may develop after the initial febrile illness.

The eruption may also become:

• Petechial

• Purpuric

• Vesicular in some patients

Lesions frequently involve the:

Extremities

and may involve:

Palms and soles

High-Yield Rash Pattern

Rat exposure

• ●

Fever

• ●

Maculopapular/petechial rash involving extremities

• ●

Arthralgia

→ Think S. moniliformis

Musculoskeletal Disease

One of the most useful clinical clues is:

MIGRATORY POLYARTHRALGIA

or:

POLYARTHRITIS

Patients may develop pain and inflammation involving multiple joints.

Tenosynovitis can also occur.

Classic Clinical Triad

FEVER

• ●

RASH

• ●

MIGRATORY POLYARTHRALGIA/POLYARTHRITIS

after:

RAT EXPOSURE

→ STREPTOBACILLUS MONILIFORMIS

Bite Wound

An important point is that the original rat-bite wound may:

Heal before systemic symptoms develop

Therefore, absence of an actively inflamed bite site does not exclude:

Streptobacillary rat-bite fever

Haverhill Fever

S. moniliformis can also produce:

HAVERHILL FEVER

This syndrome results from ingestion of:

Food or water contaminated with rat-associated organisms

rather than direct inoculation through a bite.

Haverhill Fever Pattern

Contaminated food or water

↓

S. moniliformis

↓

Fever

• ●

Rash

• ●

Arthralgia/arthritis

This can result in:

Outbreaks involving multiple people

rather than isolated cases following individual rat bites.

Rat-Bite Fever vs. Haverhill Fever

Rat-Bite Fever

Transmission: Rat bite/scratch or direct rodent exposure

Organism: S. moniliformis

Features: Fever, rash, arthralgia/polyarthritis

Haverhill Fever

Transmission: Ingestion of contaminated food or water

Organism: S. moniliformis

Features: Similar systemic illness, often with prominent pharyngitis and vomiting

Complications

Untreated streptobacillosis may occasionally result in serious invasive complications.

The source identifies:

• Endocarditis

• Pericarditis

• Tenosynovitis

• Abscesses in multiple organs

Endocarditis

One of the most serious complications is:

INFECTIVE ENDOCARDITIS

Persistent fever or bacteremia, cardiac findings, or embolic manifestations should raise concern for:

Endocardial infection

Pericarditis

Cardiac involvement may also include:

PERICARDITIS

although this is considerably less common than uncomplicated febrile disease.

Tenosynovitis

Inflammation of tendon sheaths can produce:

TENOSYNOVITIS

This fits with the strong musculoskeletal involvement characteristic of:

Streptobacillary rat-bite fever

Metastatic Abscesses

Untreated infection may disseminate hematogenously and produce:

Abscesses in internal organs

The source specifically notes possible involvement of the:

Brain

Therefore, neurologic manifestations in severe untreated disease should raise concern for:

CNS complications

Diagnosis

The source recommends:

CULTURE IN SPECIFIC MEDIA

S. moniliformis is:

Fastidious

and can be difficult to recover using routine laboratory techniques.

Laboratory Communication

When rat-bite fever is suspected, the:

Microbiology laboratory should be informed

because specialized culture conditions and specimen handling may be required.

This is particularly important because routine laboratory procedures may fail to recover the organism.

Culture

Potential specimens include:

• Blood

• Synovial fluid

• Other normally sterile specimens

Culture may require:

Specialized enriched media

because of the organism’s fastidious growth requirements.

Important Culture Pearl

Certain routine blood-culture media historically contained:

Sodium polyanethol sulfonate (SPS)

which can inhibit growth of:

S. moniliformis

This helps explain why routine blood cultures may occasionally be negative despite compatible disease.

Molecular Diagnosis

When available, molecular methods such as:

PCR

may assist with diagnosis, particularly when conventional culture is unsuccessful.

Treatment

The classic treatment is:

PENICILLIN

S. moniliformis is traditionally highly susceptible to penicillin, making β-lactam therapy a cornerstone of treatment.

Additional Treatment

The source lists:

• Doxycycline

• Azithromycin

as additional therapeutic options.

Treatment selection should account for:

Disease severity + allergy history + infection site + complications

Complicated Disease

More prolonged and intensive antimicrobial therapy may be necessary when infection is complicated by:

• Endocarditis

• CNS infection

• Deep abscess

• Septic arthritis

• Other metastatic infection

Drainable abscesses may additionally require:

Source control

Streptobacillus moniliformis vs. Spirillum minus

This is the most important examination comparison.

Both cause:

RAT-BITE FEVER

but their epidemiology and clinical patterns differ.

Streptobacillus moniliformis

→ Pleomorphic Gram-negative bacillus

→ More classically associated with North America

→ Incubation usually 3–10 days

→ Fever + rash + migratory polyarthralgia/polyarthritis

→ Bite wound often heals

→ Can cause Haverhill fever through contaminated food/water

Spirillum minus

→ Spiral Gram-negative organism

→ Classically associated with Asia, especially Japan

→ Causes sodoku

→ Incubation may extend to several weeks

→ Relapsing fever prominent

→ Bite site may become inflamed again

→ Regional lymphadenopathy is characteristic

High-Yield Comparison

Rat bite + fever + rash + migratory polyarthritis + North America

→ Streptobacillus moniliformis

Rat bite + relapsing fever + recurrent bite-site inflammation + lymphadenopathy + Asia/Japan

→ Spirillum minus

Prevention

Prevention focuses on minimizing exposure to:

Rodents and rodent secretions

Important measures include:

• Rodent control

• Protective handling of laboratory or pet rodents

• Avoiding contact with wild rats

• Prompt cleansing of rat bites and scratches

• Protecting food and drinking water from rodent contamination

• Seeking medical evaluation if fever develops after a rodent bite

High-Yield Clinical Pattern

Rat bite

• ●

3–10 day incubation

• ●

Fever and headache

• ●

Maculopapular/petechial rash

• ●

Migratory polyarthralgia or polyarthritis

→ Think STREPTOBACILLUS MONILIFORMIS

High-Yield Haverhill Pattern

No rat bite required

• ●

Rodent-contaminated food or water

• ●

Outbreak of fever + rash + arthralgia

→ Think HAVERHILL FEVER due to S. moniliformis

Exam Essentials

Genus: Streptobacillus

Species: S. moniliformis

Organism: Pleomorphic Gram-negative bacillus

Major reservoir: Rats

Distribution: Worldwide

Incubation: 3–10 days, sometimes longer

Major transmission: Rat bite or scratch

Major disease: Rat-bite fever / streptobacillosis

Food/water-associated form: Haverhill fever

Classic manifestations: Fever + rash + migratory polyarthralgia/polyarthritis

Rash: Maculopapular/petechial, often involving extremities and potentially palms/soles

Important complications: Endocarditis, pericarditis, tenosynovitis, and metastatic abscesses

Diagnosis: Specialized culture; molecular testing may assist

Culture pearl: Some routine blood-culture conditions may inhibit growth

Classic treatment: Penicillin

Additional source treatments: Doxycycline and azithromycin

Major differential: Spirillum minus

Prevention: Rodent control, wound care, and protection of food/water from rodent contamination

Memory Aid

STREPTOBACILLUS = STRAIGHT TO THE JOINTS

Rat exposure

→ S. moniliformis

→ Fever

→ Rash

→ Migratory joint pain/polyarthritis

And remember:

HAVERHILL = HAVE A DRINK

Contaminated food or water can transmit S. moniliformis without a rat bite.

Key clinical pearl: Streptobacillus moniliformis is the classic North American cause of rat-bite fever. Think of it when a patient develops fever, a maculopapular or petechial rash, and migratory polyarthralgia or polyarthritis several days after rat exposure. Unlike Spirillum minus sodoku, the bite wound may already have healed, and ingestion of rodent-contaminated food or water can produce Haverhill fever. Because the organism is fastidious, the microbiology laboratory should be alerted when infection is suspected; penicillin is the classic treatment.