CLINICAL-EVALUATION OF THE SERODIAGNOSTIC VALUE OF ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR RHODOCOCCUS-EQUI INFECTION IN FEATS

An enzyme-linked immunosorbent assay (ELISA) for detection of serum Ig G antibodies against Tween 20-extracted antigen of strain ATCC 6939 wa s applied in Hidaka, Japan to a total of 752 sick foals showing a vari ety of signs of infectious disease, An optical density (OD) value of m ore than 0.3 was tentatively fixed to be positive on the basis of read ings made of healthy horse sera in previous studies, During a 2 year s tudy, 138 of the 752 sick foals showed an OD value of 0.3 or higher an d were designated as 'suspected of R. equi infection', Age distributio n during the initial medical examination of the 138 seropositive foals was significant in that most (64%) foals were age 31-60 days, with a sharp decrease in subjects beyond that age, Of the 138 foals suspected of having R. equi infection, 34 foals (25%) showed OD values of over 0.9 at the initial medical examination, in addition to high blood leuc ocyte counts and serum fibrinogen and alpha-globulin values, The infec tious foals had been treated with antibiotics just before and after se rodiagnosis and 126 foals (91%) recovered from the disease, However, n o clinical improvement was observed in 12 foals (9%). At necropsy, the se foals revealed suppurative pneumonia and lymphadenitis of gut assoc iated lymph nodes accompanied by abdominal abscesses, All isolates fro m the pulmonary and abdominal abscesses revealed R. equi. These result s suggest that OD readings in the high range are associated with sever e disseminated infection with R. equi.