Rat Bite Fever - From Detection to Cure

Introduction:

Rat-bite fever, alternatively named Streptobacillus, spirillary fever, bogger, and epidemic arthritic erythema, presents as a zoonotic ailment characterized by episodes of acute fever followed by migrating joint pain. The transmission occurs from rodents to humans, commonly through rodent urine or mucosal secretions. This infrequent disorder is caused by two types of bacteria: Spirillum minus and Streptobacillus moniliformis. Both of these organisms are typically found in the oral flora of rodents. While the majority of cases are reported in Japan, occurrences have been documented in regions including the United States, Europe, Australia, and Africa. Transmission is often associated with rat bites, but some cases result from mere exposure to infected rodents' urine, nasal, fecal, or ocular secretions. Moreover, rat-bite fever can spread through the consumption of contaminated food or water, or even via household pets like dogs and cats that have had contact with rodents. If left untreated, the mortality rate for rat-bite fever can reach as high as ten percent.

What Is the Causative Agent for RBF?

1. In North America, the primary instigator of RBF is Streptobacillus moniliformis. These bacteria possess the subsequent microbiological traits:

• Fastidious growth pattern.

• Gram-negative, pleomorphic, non-sporulating, and lacking capsule rod shape.

• Generally, facultative anaerobes, with the exception of isolates from guinea pigs, which are obligate anaerobes.

• Lack of motility.

• Frequently arrange themselves in chains and intricate filaments with swollen portions resembling bulbs or Monilia.

2. On the other hand, RBF infections in Asia are more frequently induced by Spirillum minus, which exhibits the subsequent characteristics:

• Short, stout, motile spirochetes.

• Possessing flagellar tufts at both ends.

How Is RBF Transmitted?

Streptobacillus moniliformis and Spirillum minus, symbiotic microorganisms within the normal respiratory flora of rodents, have roles deeply ingrained. These bacteria take residence in oral, nasal, and conjunctival secretions, as well as in animal urine. The transfer of either organism to humans occurs through breaches in the skin barrier, via bites, scratches, or through close contact with infected rodents, even in the absence of apparent bites or scratches. Additionally, infection can arise from the consumption of edibles or beverages contaminated with these bacterial strains. When infection is a consequence of ingestion, it earns the name Haverhill fever, originating from a significant bacterial outbreak in Haverhill, Massachusetts, in 1926. This outbreak was traced back to the consumption of unpasteurized dairy products tainted with these bacteria. In cases where early identification and appropriate intervention are lacking, RBF can pave the way for grave infections and loss of life.

What Are the Symptoms of RBF?

• Initial signs of S. moniliformis infection encompass fever, chills, myalgia, headache, and vomiting.

• Following around two to four days from the onset of fever, a maculopapular rash might emerge on the extremities, followed by polyarthritis affecting roughly 50 percent of cases.

• The typical incubation period for S. moniliformis spans three to ten days.

• Haverhill fever exhibits distinct symptoms, including heightened nausea, vomiting, and pharyngitis.

• Symptoms linked to Spirillum minus infection surface seven to 21 days after exposure, particularly in travelers to Asia.

• Post-healing of a rat bite, Spirillum minus infection showcases fever, ulceration, lymphangitis, lymphadenopathy, and a unique purple or red plaque rash.

• Untreated RBF can result in complications such as abscesses, septic arthritis, pneumonia, hepatitis, nephritis, meningitis, and cardiac issues.

• Among these complications, those tied to endocarditis carry the utmost risk of mortality.

How Is RBF Diagnosed?

Diagnosing this condition necessitates a strong clinical suspicion. Culture is employed to identify Streptobacillus moniliformis, although its cultivation poses considerable challenges. The specimen must undergo inoculation in culture media free from sodium polyanethol sulphonate, an anticoagulant present in standard culture media, as it suppresses organism growth. For this purpose, anaerobic culture bottles are preferable since they lack Sodium Polyanethol Sulphonate. In contrast, culturing Spirillosis is unfeasible. Identification exclusively relies on dark ground microscopy or Giemsa staining techniques.

How Is RBF Treated?

Treating RBF involves considering the susceptibility of S. moniliformis to various antibiotics. Options include Penicillins, Cephalosporins, Carbapenems, Aztreonam, Clindamycin, Erythromycin, Nitrofurantoin, Bacitracin, Doxycycline, Tetracycline, Teicoplanin, and Vancomycin.

Intravenous Penicillin G is typically administered for seven days or more, followed by oral Penicillin for RBF treatment. Improvement usually occurs swiftly upon starting antibiotics, and without proper treatment, the mortality rate is approximately ten percent. For patients allergic to Penicillin, alternative options are Doxycycline or Streptomycin.

Specific Antibiotic Regimens:

• Initially, consider administering intravenous Penicillin G at a dosage of 200,000 units every four hours or one gram of Ceftriaxone intravenously daily.

• As the patient's condition improves, switch to Penicillin V 500 mg taken four times daily, Ampicillin 500 mg taken four times daily, or Amoxicillin 500 mg taken three times daily.

• The prescribed course of antibiotics typically spans two weeks.

• For patients allergic to Penicillin, an alternative option is Doxycycline 100 mg, taken twice daily, available in both intravenous and oral forms.

How Is RBF Prevented?

To prevent RBF, avoid contact with rodents, and ensure thorough hand and face washing after any contact. Clean scratches and apply antiseptics. The effect of prophylactic chemoprophylaxis following rodent bites or scratches is uncertain. Individuals exposed to rodents, such as animal handlers, laboratory workers, and sanitation, and sewer workers, should take precautions. Do not touch wild rodents, alive or deceased.

What Are the Complications of RBF?

In instances where RBF infections go untreated or are inadequately managed, complications can encompass abscesses in soft tissues and solid organs, septic arthritis, pneumonia, hepatitis, nephritis, meningitis, and inflammation of the heart's lining, muscles, or sac.

• Among these, complications tied to endocarditis carry the most elevated mortality risk. It might require combined treatment involving intravenous Penicillin G and Streptomycin or Gentamicin.

• Fulminant sepsis.

• Pneumonitis.

• Liver abscess.

• Adrenal gland failure.

• Meningitis.

What Are the Differential Diagnosis of RBF?

• Meningococcemia.

• Disseminated gonorrhea.

• Lyme disease.

• Ehrlichiosis.

• Rickettsial infections.

• Brucellosis.

Conclusion:

Rat-bite fever (RBF) requires prompt identification and tailored management. Its diverse clinical presentation, caused by Streptobacillus moniliformis and Spirillum minus, demands vigilant suspicion, especially with rodent exposure. The multifaceted nature of this infectious disease underscores the significance of early diagnosis and appropriate treatment. The symptoms, often nonspecific at onset, can swiftly escalate, emphasizing the need for a high index of suspicion, especially in cases where rodents are involved. Treatment, based on limited research, emphasizes personalized antibiotics and considers complications and allergies. While endocarditis-related issues are rare, interdisciplinary healthcare is vital.