The objective of this study was to determine in vitro activities of azithromycin (AZM), clarithromycin (CLR), and 20 other antimicrobial agents against Rhodococcus equi and other common equine bacterial pathogens. A total of 201 bacterial isolates from various equine clinical samples were examined. CLR was more active than AZM against R. equi, with MICs at which 90% of the isolates were inhibited of 0.12 and 1.0 g/ml, respectively. Other antimicrobial agents highly active against at least 90% of R. equi isolates in vitro included rifampin, gentamicin, and imipenem. Both AZM and CLR showed good activity against beta-hemolytic streptococci and Staphylococcus spp. AZM was more active than other macrolides against Pasteurella spp. and Salmonella enterica.

Among distance groups, distance ridden, speed, level of fitness, and years of experience of horses had little effect on the variables examined. Electrolyte and water supplementation and earlier arrival at the event may be beneficial for horses that are transported long distances to endurance competition.

Our findings were similar to those of previous WNV outbreaks in horses but provided additional clinical details from monitored hospitalized horses. Diagnostic testing is essential to diagnosis, treatment is supportive, and recovery rate of discharged ambulatory horses is < 100%.

Rhodococcus equi is a facultative intracellular pathogen that causes pneumonia in young foals but does not induce disease in immunocompetent adult horses. Clearance of R. equi depends mainly on gamma interferon (IFN-␥) production by T lymphocytes, whereas the predominance of interleukin 4 (IL-4) is detrimental. Young foals, like neonates of many other species, are generally deficient in the ability to produce IFN-␥. The objective of this study was to compare the cytokine profiles, as well as cell-mediated and antibody responses, of young foals to those of adult horses following intrabronchial challenge with R. equi. The lymphoproliferative responses of bronchial lymph node (BLN) cells to concanavalin A were significantly higher in foals than in adult horses. In contrast, adult horses had significantly higher lymphoproliferative responses to R. equi antigens than did foals. Infected foals had significantly lower IL-4 mRNA expression but significantly higher IFN-␥ expression and IFN-␥/IL-4 ratio in R. equi-stimulated BLN lymphocytes than did infected adults. Infection with R. equi in foals resulted in a significant increase in the percentage of T lymphocytes and CD4 ؉ T lymphocytes in bronchoalveolar lavage fluid in association with a significant decrease in the percentage of these cell populations in BLNs. Infection of foals also resulted in a marked increase in serum immunoglobulin Ga (IgGa) and IgGb levels, resulting in concentrations in serum that were significantly higher than those of adult horses. This study demonstrates that the immune response to R. equi in foals is not biased toward IL-4 and is characterized by the predominant induction of IFN-␥.

Shelter staff and veterinarians routinely make subjective dog breed identification based on appearance, but their accuracy regarding pit bull-type breeds is unknown. The purpose of this study was to measure agreement among shelter staff in assigning pit bull-type breed designations to shelter dogs and to compare breed assignments with DNA breed signatures. In this prospective cross-sectional study, four staff members at each of four different shelters recorded their suspected breed(s) for 30 dogs; there was a total of 16 breed assessors and 120 dogs. The terms American pit bull terrier, American Staffordshire terrier, Staffordshire bull terrier, pit bull, and their mixes were included in the study definition of 'pit bull-type breeds.' Using visual identification only, the median inter-observer agreements and kappa values in pair-wise comparisons of each of the staff breed assignments for pit bull-type breed vs. not pit bull-type breed ranged from 76% to 83% and from 0.44 to 0.52 (moderate agreement), respectively. Whole blood was submitted to a commercial DNA testing laboratory for breed identification. Whereas DNA breed signatures identified only 25 dogs (21%) as pit bull-type, shelter staff collectively identified 62 (52%) dogs as pit bull-type. Agreement between visual and DNA-based breed assignments varied among individuals, with sensitivity for pit bull-type identification ranging from 33% to 75% and specificity ranging from 52% to 100%. The median kappa value for inter-observer agreement with DNA results at each shelter ranged from 0.1 to 0.48 (poor to moderate). Lack of consistency among shelter staff indicated that visual identification of pit bull-type dogs was unreliable.

The objective of this retrospective study was to compare the efficacy of azithromycin-rifampin, clarithromycin-rifampin, and erythromycin-rifampin for the treatment of pneumonia caused by Rhodococcus equi in foals. Eighty-one foals with naturally acquired pneumonia caused by R equi were included in the study. Information on age, sex, breed, physical examination findings, laboratory testing, and thoracic radiography was abstracted from each medical record. Foals were divided in 3 groups based on the antimicrobial agent selected for therapy. Short-term (discharge from the hospital) and long-term (apparently healthy as a yearling) success rates, days of hospitalization, days with fever, days with tachypnea, and percentage of radiographic improvement were compared among groups. Foals treated with clarithromycin-rifampin had significantly (P ϭ .02) higher odds of overall shortterm (odds ratio [OR] ϭ 12.2) and long-term (OR ϭ 20.6) treatment success and significantly fewer days with fever than foals treated with erythromycin-rifampin. Foals treated with clarithromycin-rifampin had a significantly (P ϭ .03) higher percentage of radiographic improvement and a tendency (P ϭ .06) toward higher odds of overall short-term (OR ϭ 8.1) and long-term (OR ϭ 11.8) treatment success compared to foals treated with azithromycin-rifampin. Among foals with severe radiographic lesions, the success rates of foals treated with clarithromycin-rifampin both short-term (88%) and long-term (83%) were significantly (P ϭ .02) higher than that of foals treated with azithromycin-rifampin (0%). For each treatment group, the only reported adverse effect was diarrhea that was mild and self-limiting in most cases. The combination clarithromycin-rifampin is superior to azithromycinrifampin or erythromycin-rifampin for the treatment of pneumonia caused by R equi in foals in a referral population.Key words: Antimicrobials; Lung; Pulmonary abscesses; Respiratory tract infection; Rifampin.R hodococcus equi, a gram-positive facultative intracellular pathogen that replicates in macrophages, is one of the most important causes of pneumonia in foals between 3 weeks and 5 months of age. Other less common clinical manifestations of infection with R equi in foals include ulcerative enterocolitis, colonic or mesenteric lymphadenopathy, immune-mediated synovitis and uveitis, osteomyelitis, and septic arthritis.1 Although combined therapy with erythromycin and rifampin has dramatically improved the survival rate of foals infected with R equi at least compared to historical data, this treatment regimen is not without problems. Erythromycin has variable absorption in foals when given orally, requires multiple daily dosing, and most importantly, its administration has a high incidence of sometimes life-threatening adverse effects.2-4 The most common adverse effect of erythromycin in foals is diarrhea. 4 An idiosyncratic reaction characterized by hyperthermia and tachypnea has been reported in foals treated with erythromycin during hot weather. 4 Severe enterocolitis ...

Endotoxemia developed during endurance racing, but was significantly correlated with increased plasma lactate concentration and not with other variables indicative of endotoxemia. Plasma TxB2 and PGF1alpha concentrations and serum TNFalpha activity may be associated with performance success.

Clarithromycin offers numerous advantages over erythromycin and thus, is an attractive alternative for the treatment of Rhodococcus equi infections in foals. The disposition of clarithromycin was investigated in 6 foals after intragastric administration at a dose of 10 mg/kg body weight. Detectable serum concentrations of clarithromycin were found in 3 of 6 foals at 10 minutes and in all foals by 20 minutes post-administration. Time to peak serum concentration (Tmax) was 1.5 hours and peak serum concentration (Cmax) was 0.92+/-0.17 microg/ml. Mean serum concentrations decreased to 0.03 microg/ml at 24 h. No adverse reactions were noted during or after IG administration in any of the foals. Based on the pharmacokinetic parameters, the MIC90 of R. equi isolates, and predicted steady state concentrations, an oral dose of 7.5 mg/kg given every 12 hours would appear appropriate for the treatment of R. equi infections in foals.