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RHODOCOCCOSIS 229Krieg, N.R. Aerobic/microaerophilic, motil, helical/vibroid gram-negative bacteria. In:Krieg, N.R., J.G. Holt, eds. Vol. 1: Bergey’s Manual of Systematic Bacteriology. Baltimore:Williams & Wilkins; 1984.McEvoy, M.B., N.D. Noah, R. Pilsworth. Outbreak of fever caused by Streptobacillusmoniliformis. Lancet 2:1361–1363, 1987.Ruys, A.C. Rat bite fevers. In: Van der Hoeden, J., ed. Zoonoses. Amsterdam:Elsevier; 1964.Savage, N. Genus Streptobacillus. In: Krieg, N.R., J.G. Holt, eds. Vol. 1: Bergey’s Manualof Systematic Bacteriology. Baltimore: Williams & Wilkins; 1984.Washburn, R.G. Streptobacillus moniliformis (Rat-bite fever). In: Mandell, G.L., R.G.Douglas, Jr., J.E. Bennett, eds. Principles and Practice of Infectious Diseases. 3rd ed. NewYork: Churchill Livingstone, Inc.; 1990.Wilkins, E.G.L., J.G.B. Millar, P.M. Cockroft, O.A. Okubadejo. Rat-bite fever in a gerbilbreeder. J Infect 16:177–180, 1988.Yamamoto, R., G.T. Clark. Streptobacillus moniliformis infection in turkeys. Vet Rec79:95–100, 1966.RHODOCOCCOSISICD-10 J15.8 other bacterial pneumoniaEtiology: Rhodococcus (Corynebacterium) equi belongs to the orderActinomycetales; it has a coccoid or bacillary shape, is gram-positive, aerobic, nonmotile,encapsulated, and nonsporogenic. Its normal habitat is the soil; it is a saprophyticbacteria that requires few nutrients and multiplies abundantly in fecal matterfrom herbivores.Most strains of R. equi belong to 4 serogroups, which in turn contain 14 serotypes.Approximately 60% of the strains in North America belong to capsular serotype 1,and 26% belong to capsular serotype 2. In Japan, capsular serotype 3 predominatesin cultures isolated from foals (Timoney et al., 1988).R. equi is an opportunistic pathogen and is harbored in the macrophages in theanimal organism, causing a granulomatous inflammation (Prescott, 1991). A 15- to17-kilodalton antigen has been identified that is probably associated with the virulenceof R. equi (Takai et al., 1991a) and could be used as a marker for it.Geographic Distribution: Worldwide. Since 1923, when the first case ofrhodococcosis was described in foals in Switzerland, the disease has been reportedon all continents. R. equi is frequently and abundantly isolated from soil where therehave been sick horses, but also from areas where there was no rhodococcosis, andeven from soil where there have been no horses or other domestic animals recently(Barton and Hughes, 1980).Occurrence in Man: Very rare. From the first human case described in 1977 upto 1983, the literature records no more than 13 human cases (Van Etta et al., 1983).