Rat Bite Fevers

Synonyms: Streptobacillary fever; Streptobacillosis; Haverhill fever; Epidemic arthritic erythema; Spirillary fever; Sodoku

• Rat-bite fever is commonly used to describe a rare infection with either Streptobacillus moniliformis (Actinobacillus muris) or Spirillum minus. Most reported cases of rat-bite fever occur in Japan, but the disease has also been seen in Australia, Africa, North and South America, and Europe.¹
• Transmitted usually by bite (S.moniliformis can be isolated in the pharyngeal flora of 50% of wild and laboratory rats), but also through abrasions, or perhaps even contact with infected secretions.
• In the case of Haverhill fever it was thought transmission occurred via infected milk.
• Children, and those less sensitive to bites as in diabetic or leprous neuropathy, are particularly vulnerable.
• The organisms can also be isolated in other rodents and their predators, but the significance of this seems to be limited to a case report in a gerbil breeder.²

• Increasing overcrowding is exposing both humans and domestic animals to zoonotic diseases previously not considered in differential diagnoses.³
• Rodents can also transmit other illnesses via bites, or indirect contact (infected urine/faeces, or via fleas, lice, and mosquitoes): rabies; plague (yersinia); murine-typhus, Rocky Mountain Spotted fever, rickettsialpox (rickettsia); leptospirosis; salmonella; lymphocytic choriomeningitis, haemorrhagic fevers (arenaviruses); hantavirus haemorrhagic pulmonary syndrome; Venuzualan equine encephalitis (alphavirus); powassan encephalitis (flavivirus); trench fever (bartonella); meilioidosis; tularaemia; and via parasitisms: trichinosis; taeniasis; eosinophilic meningitis.

The disease should be considered whenever there is fever, rash, and a history of exposure to rat-bite.

Streptobacillus moniliformis infection

• This (although rare) is the form more likely to be seen in the USA.
• Incubation period is usually <10 days when evidence of the bite may have disappeared.
• Initially sudden high fever with rigors, vomiting, severe headache, myalgia, muscle tenderness.
• Followed within 1-8 days by a diffuse rash in 75% of cases (erythema athriticum epidemicum).
• Discrete erythematous macules are seen symmetrically over joints and on lateral and extensor surfaces, usually most apparent on palms and soles with petechiae.
• Asymmetrical migratory polyarthralgia (large joints) or arthritis occurs in around 50% of cases.

Spirillum minus infection

• Disease predominant in Africa, Asia and Japan where it is known as 'Sodoku'.
• Incubation period is usually longer (1-3 weeks).
• Fever, myalgia and arthralgia as above, but joint effusions are rare.
• The healed bite often breaks down, and there is marked local lymphadenopathy.
• A characteristic rash often spreads from the wound, consisting of red/purple plaques.
• S.minus may be isolated from the wound.

• Full blood count: leucocytosis
• Culture of organisms from blood, joint fluid or pus
• Serology antibody tests: high or rising titre of agglutinins, complement-fixing or fluorescent antibodies, may be detected between 2 and 3 weeks

• Penicillin (initially IV/IM in severe cases) for 7-10 days
• Erythromycin (Streptobacillus) or tetracycline (Spirillum) are alternatives³

• Parotitis
• Tenosynovitis
• Bronchitis, pneumonia
• Metastatic abscesses, septicaemia
• Endocarditis, myocarditis, pericarditis
• Meningitis, encephalitis
• Renal involvement
• Splenitis
• Anaemia

• If treated, prognosis is excellent and symptoms usually subside in a few days.
• Fever and arthritis may last for several months (with a 10-13% mortality) if untreated.

• Avoiding contact with rats or rat-contaminated dwellings.
• Taking antibiotics after a rat bite may also help prevent the illness.