Rat-bite Fevers

Synonyms: streptobacillary fever, streptobacillosis, Haverhill fever, epidemic arthritic erythema, spirillary fever, sodoku

Rat-bite fever is a rare zoonosis caused by infection with either Actinobacillus muris (Streptobacillus moniliformis) 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 in Europe.¹

• Transmitted usually by bite (A. muris 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.
• Children and those with reduced sensitivity to bites (e.g. 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 pestis), murine typhus, Rocky Mountain spotted fever, rickettsial pox (rickettsia), leptospirosis, salmonellosis, lymphocytic choriomeningitis, haemorrhagic fevers (arenaviruses), hantavirus haemorrhagic pulmonary syndrome, Venezuelan equine encephalitis (alphavirus), Powassan encephalitis (flavivirus), trench fever (bartonella), melioidosis, tularaemia, trichinosis, taeniasis, eosinophilic meningitis.

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

Actinobacillus muris 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 arthriticum 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: blood cultures, 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 (A. muris) or tetracycline (S. minus) 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 rate) if untreated.⁴

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

1. Medline Plus; Rat Bite Fever
2. Wilkins EG, Millar JG, Cockcroft PM, et al; Rat-bite fever in a gerbil breeder. J Infect. 1988 Mar;16(2):177-80. [abstract]
3. Graves MH, Janda JM; Rat-bite fever (Streptobacillus moniliformis): a potential emerging disease. Int J Infect Dis. 2001;5(3):151-5. [abstract]
4. Elliott SP; Rat bite fever and Streptobacillus moniliformis. Clin Microbiol Rev. 2007 Jan;20(1):13-22. [abstract]

• Health Protection Agency; Rat-bite fever.