A coronavirus was isolated from feces of a diarrheic foal and serially propagated in human rectal adenocarcinoma (HRT-18) cells. Antigenic and genomic characterizations of the virus (isolate NC99) were based on serological comparison with other avian and mammalian coronaviruses and sequence analysis of the nucleocapsid (N) protein gene. Indirect fluorescent-antibody assay procedures and virus neutralization assays demonstrated a close antigenic relationship with bovine coronavirus (BCV) and porcine hemagglutinating encephalomyelitis virus (mammalian group 2 coronaviruses). Using previously described BCV primers, the N protein gene of isolate NC99 was amplified by a reverse transcriptase PCR (RT-PCR) procedure. The RT-PCR product was cloned into pUC19 and sequenced; the complete N protein of NC99 (446 amino acids) was then compared with published N protein sequences of other avian and mammalian coronaviruses. A high degree of identity (89.0 to 90.1%) was observed between the N protein sequence of NC99 and published sequences of BCV (Mebus and F15 strains) and human coronavirus (strain OC43); only limited identity (<25%) was observed with group 1 and group 3 coronaviruses. Based on these findings, the virus has been tentatively identified as equine coronavirus (ECV). ECV NC99 was determined to have close antigenic and/or genetic relationships with mammalian group 2 coronaviruses, thus identifying it as a member of this coronavirus antigenic group.

Recently, a technique was described for amplification of Rhodococcus equi-specific chromosomal and vapA DNA from blood and tracheal wash fluids. It was hypothesized that this technique would be more sensitive than standard culture techniques or serology for diagnosis of R. equi pneumonia in foals. Tracheal wash fluid, nasal swabs, whole blood samples, and serum samples from 56 foals with pneumonia were analyzed. Final clinical diagnosis was determined by the attending clinician on the basis of final interpretation of all available information about each foal, including clinical presentation, diagnostic test results, response to therapy, and outcome. Clinical diagnosis was used as a final reference standard for calculation of sensitivity, specificity, and predictive values for PCR, serology using an agar gel immunodiffusion test, and tracheal wash fluid culture. PCR of tracheal wash fluid using primers that recognized the vapA virulence plasmid of R. equi had a diagnostic sensitivity of 100% and specificity of 90.6%. Sensitivity and specificity were 57.1 and 93.8%, respectively, for standard microbiologic culture of tracheal wash fluid and 62.5 and 75.9%, respectively, for serology. PCR of tracheal wash fluid is more sensitive and specific for diagnosis of R. equi pneumonia than are other available diagnostic tests.Rhodococcus equi is a gram-positive, pleomorphic coccobacillus that causes pneumonia and enteritis in foals less than 6 months of age and has been associated with a variety of suppurative processes in immune-suppressed humans (19). The organism is worldwide in distribution and commonly isolated from soil and environmental samples (2,4,23). Strains of R. equi isolated from sick foals uniformly contain an 85-to 90-kb plasmid that carries the gene responsible for expression of a 15-to 17-kDa antigen of undetermined function (vapA) (24,25). Environmental strains of R. equi not associated with equine disease do not contain this plasmid.The onset of clinical signs of R. equi pneumonia in foals is often insidious, and the infection is not recognized until severe abscessation has occurred and prognosis is poor. Culture of the organism from tracheal wash (TW) fluid is currently considered the "gold standard" for diagnosis (7). However, it can be difficult to reliably grow R. equi from a single TW sample, possibly because of prior antibiotic administration (12,14) or the presence of multiple pathogenic bacterial species (5, 21). Hillidge reported that only 7 of 11 foals (62%) with positive R. equi cultures at necropsy, and 57 of 89 foals (64%) with radiographic evidence of lung abscessation, yielded R. equi on culture of TW (10). Other studies reported a 100% positive result on cultures of TW fluid from foals later confirmed to have R. equi pneumonia at necropsy (14,17).Recently, a technique was described for amplification of R. equi-specific chromosomal and vapA DNA from blood and TW fluids (20). It was hypothesized that this technique would be more sensitive than standard culture techniques or serology for dia...

Compared with adult horses given 5 mg of enrofloxacin/kg IV, foals have higher AUC0-infinity, longer t1/2beta, and lower clearance. Concentration of ciprofloxacin was negligible. Using a target Cmax to minimum inhibitory concentration ratio of 1:8 to 1:10, computer modeling suggests that 2.5 to 10 mg of enrofloxacin/kg administered every 24 hours would be effective in foals, depending on minimum inhibitory concentration of the pathogen.

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