Rat Bite Fever: Symptoms, Types, Causes and Treatment

Rat bite fever (RBF) is a rare but potentially serious zoonotic illness, meaning it is transmitted from animals to humans. Most commonly associated with contact with rats—whether as pets, in the wild, or in laboratory settings—this disease is underrecognized and often misdiagnosed because its symptoms can mimic those of other illnesses. As rats become increasingly common household pets, understanding the key aspects of rat bite fever is crucial for both the general public and healthcare professionals. This article explores the symptoms, types, causes, and treatment of rat bite fever, drawing from the latest scientific literature and case studies.

Symptoms of Rat Bite Fever

Recognizing the symptoms of rat bite fever is essential for early diagnosis and effective treatment. The disease often starts with general symptoms but can quickly escalate if not addressed.

Symptom	Description	Frequency/Notes	Source(s)
Fever	Sudden high temperature	Most common and early symptom	1 2 3 4 5 7 15
Rash	Petechial, maculopapular, or pustular	Frequently on hands and feet	2 3 4 5 7 8 9
Arthralgia	Joint pain, often migratory	Polyarthralgia in majority of cases	1 2 3 4 5 7 15
Myalgia	Muscle pain	Sometimes accompanies fever	7 15
Extra-articular Features	Vomiting, lymphadenopathy, malaise	Variable; includes headache, swelling, anemia	2 4 7 8 9

Table 1: Key Symptoms

Overview of Symptom Onset

The initial symptoms of rat bite fever usually appear after an incubation period ranging from a few days up to three weeks, with a median onset of about one week post-exposure. Fever is typically the first symptom, often accompanied by chills and muscle aches. The fever may be relapsing, appearing in cycles with periods of feeling almost normal in between spikes of temperature 7 8 9 11.

Characteristic Rash

A distinctive rash develops in a majority of cases. It can be petechial (small red or purple spots), maculopapular (flat and raised discolored spots), or pustular (blister-like lesions). The rash commonly appears on the hands and feet but can spread to other areas. Occasionally, these skin lesions are hemorrhagic or purpuric, particularly on the extremities 4 5 7 8 9.

Joint and Muscle Involvement

Polyarthralgia—pain in multiple joints—is another hallmark, often affecting both small and large joints. Migratory joint pain and, less commonly, true arthritis with joint swelling and effusion (fluid build-up) can occur. Myalgia (muscle aches) and general malaise often accompany these symptoms 1 2 3 4 7 15.

Other Systemic Manifestations

• Lymphadenopathy: Swelling of lymph nodes near the bite or exposure site, sometimes with local inflammation.
• Headache and Malaise: General feeling of being unwell is common.
• Gastrointestinal Symptoms: Vomiting and, less commonly, abdominal pain.
• Rare Complications: Severe cases can lead to endocarditis (heart valve infection), pneumonia, septicemia, nephritis (kidney inflammation), or anemia 7 8 13.

Types of Rat Bite Fever

Not all rat bite fevers are the same. There are two main types, each associated with a different bacterium, geographic region, and clinical presentation.

Type	Causative Agent	Geographic Prevalence	Key Features	Source(s)
Streptobacillary	Streptobacillus moniliformis	Americas, Europe, Australasia	Sudden fever, migratory polyarthritis, rash, rapid onset	1 2 3 4 6 7 13 15
Spirillary (Sodoku)	Spirillum minus	Asia (notably Japan)	Longer incubation, ulcer at bite site, lymphadenopathy, relapsing fever	6 7 8 9 11
Haverhill Fever	S. moniliformis (oral ingestion)	Worldwide, rare	GI symptoms, often from contaminated food or water	6

Table 2: Rat Bite Fever Types

Streptobacillary Rat Bite Fever

This is the most common form in the Americas, Europe, and Australasia. Caused by Streptobacillus moniliformis, infection typically follows a rat bite or, less frequently, exposure to rat secretions. Symptoms begin suddenly within 3–10 days (but can be up to 21 days) 1 7 15. Key features include:

• High fever with chills
• Migratory joint pain and swelling (polyarthritis)
• Petechial or pustular rash, especially on hands and feet
• Myalgia
• Rarely, severe complications like endocarditis or pneumonia 2 4 7 13

A rare but rising variant is caused by Streptobacillus notomytis, with clinical features similar to S. moniliformis infection 3 10.

Spirillary Rat Bite Fever (Sodoku)

Predominant in Asia, especially Japan, and caused by Spirillum minus, this type has a longer incubation period—often up to three weeks. The main distinguishing features are:

• Recurring high fever
• Ulceration and inflammation at the original bite site
• Painful regional lymphadenopathy (swollen glands)
• Papular (raised) rash
• Arthralgia without joint effusions 7 8 9 11

Haverhill Fever

A variant of streptobacillary RBF, Haverhill fever arises from ingestion of food or water contaminated with rat excreta. Gastrointestinal symptoms (nausea, vomiting, abdominal pain) are more prominent, alongside rash and arthralgia 6.

Causes of Rat Bite Fever

Understanding how rat bite fever develops is key to its prevention and management. The disease is primarily bacterial and zoonotic, involving direct or indirect contact with rodents.

Cause	Transmission Mode	Host(s) Involved	Source(s)
Streptobacillus moniliformis	Bite, scratch, exposure to saliva/urine; ingestion	Rats (Rattus norvegicus), mice, other rodents	1 3 4 6 7 10 14 15
Spirillum minus	Bite; less commonly via contaminated wounds	Rats (various species)	6 7 8 9
S. notomytis	Bite/contact; rare, emerging	Rats (Rattus rattus, R. tanezumi)	3 10
Environmental	Ingestion of contaminated food/water	Food, water, surfaces	6 14

Table 3: Causes and Transmission

Bacterial Pathogens

• Streptobacillus moniliformis: The main causative organism in most Western countries. It is a fastidious, gram-negative rod that colonizes the nasopharynx and oral cavity of rats and some other rodents 1 3 4 7 10.
• Spirillum minus: A spirochete prevalent in Asia, especially Japan. It is less easily cultured, making laboratory confirmation more difficult 6 7 8 9.
• Streptobacillus notomytis: A newly recognized cause, mainly in Asia and Africa, with similar symptoms to S. moniliformis 3 10.

Modes of Transmission

• Rat Bite or Scratch: The most common route. Even minor bites, scratches, or nibbles can transmit the bacteria.
• Contact with Rat Secretions: Handling rats or cleaning their cages, especially if there are open wounds, can also be a risk.
• Environmental Exposure: Ingestion of food or water contaminated with rat urine or feces (Haverhill fever) 6 14.
• Other Animals: Rarely, animals that prey on or have contact with rats (e.g., cats, ferrets, weasels) can transmit the bacteria to humans 11.

Host and Environmental Factors

• Rats as Reservoirs: Both wild and pet rats can carry the bacteria asymptomatically. High rat densities, poor housing conditions, and increased contact (such as children with pet rats) raise the risk 1 7 10 15.
• Susceptible Populations: Laboratory animal workers, pet owners, people living in rodent-infested areas, and children are at increased risk 7 14 15.

Pathogenesis

The bacteria enter the bloodstream through the wound or mucosal surfaces, leading to a systemic infection. The pathogens can seed distant sites such as joints, skin, and, rarely, internal organs, causing widespread symptoms 7 8 9.

Treatment of Rat Bite Fever

Prompt and effective treatment of rat bite fever is crucial to prevent serious complications and mortality. Fortunately, the disease responds well to antibiotics if diagnosed early.

Treatment	Typical Regimen/Approach	Effectiveness/Notes	Source(s)
Antibiotics	Penicillin (preferred), ampicillin, doxycycline, ceftriaxone	Highly effective, rapid improvement	2 3 12 13 15
Alternative Antibiotics	Amoxicillin-clavulanic acid, minocycline	Used in penicillin allergy or as second-line	13 15
Supportive Care	Pain relief, hydration, wound care	Adjunctive, not curative	1 7 15
Surgery	Drainage of abscess, joint surgery	Rarely needed, for complications	2
Prevention	Wound cleaning, rat control, protective equipment	Reduces incidence	1 4 14 15

Table 4: Treatment and Prevention

Antibiotic Therapy

Penicillin is the first-line treatment, with typical courses lasting 7–14 days. Alternatives include ceftriaxone, doxycycline, or ampicillin in case of allergy or intolerance. Oral amoxicillin-clavulanic acid can also be effective, especially for mild cases or after initial intravenous therapy 2 3 13 15.

• Rapid Response: Most patients show dramatic improvement within days of starting antibiotics.
• Delayed Treatment Risks: Without timely therapy, mortality rates can reach up to 10–13% due to complications like septicemia, endocarditis, or organ failure 1 10 15.

Supportive and Adjunctive Care

• Pain Management: Analgesics for joint and muscle pain.
• Hydration: Especially important if there are gastrointestinal symptoms.
• Wound Management: Immediate cleaning and disinfection of bites; early wound care can prevent infection 1 4 14.

Surgical Intervention

Rarely, if the infection localizes as an abscess or causes septic arthritis, surgical drainage may be required. In a review of cases, about 30% required surgical intervention, but all recovered with combined medical and surgical therapy 2.

Prevention Strategies

• Rodent Control: Reducing exposure to rats through environmental hygiene and pest management is the most effective strategy 14 15.
• Personal Protection: Using gloves and protective equipment when handling rodents or cleaning cages.
• Prompt Wound Care: Immediate cleaning of all rat bites or scratches with soap and water, followed by medical assessment 1 4 15.
• Public Awareness: Education of at-risk individuals, including pet owners and laboratory workers.

Conclusion

Rat bite fever is an important but often overlooked zoonosis with potentially serious consequences if left untreated. Prompt recognition and antibiotic therapy are crucial for a favorable outcome.

Main Points Covered:

• Symptoms: Sudden fever, distinctive rash, polyarthralgia, and systemic features are common.
• Types: Caused by different bacteria (Streptobacillus moniliformis, S. notomytis, Spirillum minus), with regional and clinical differences.
• Causes: Transmission mainly through rat bites, but also via scratches, contact with rat secretions, or contaminated food.
• Treatment: Penicillin is highly effective; early intervention prevents complications. Alternative antibiotics, supportive care, and, rarely, surgery may be needed.
• Prevention: Environmental control, public education, and proper wound care can significantly reduce the risk.

Increasing contact with pet and laboratory rats underscores the need for awareness among clinicians and the public alike. Early diagnosis and treatment remain the keys to successful management of rat bite fever.