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Summary

Seventy-three aerobic bacterial isolates were cultured from 64 eyes of 63 horses with infectious keratitis. Forty-two (58%) of the organisms isolated initially were gram-positive (g+, 10 genera) and 31 (42%) were gram-negative (g-, 5 genera). After local antimicrobial treatment, repeat cultures from samples obtained from 15 eyes of hospitalized horses yielded 21 secondary bacterial isolates. Staphylococci spp and Streptococci spp were the most common g(+) isolates and accounted for 79% of g(+) organisms isolated initially. Antibiograms revealed ticarcillin to be the most efficacious antibiotic tested on g(+) organisms, with 28 of 30 (93%) being susceptible. Of commercially available topical ophthalmic antibiotics tested on g(+) organisms, erythromycin was the most efficacious, with 32 of 35 (91%) isolates being susceptible. Pseudomonas spp, Escherichia coli, and Acinetobacter spp accounted for 68% of g(-) organisms isolated initially. Gentamicin, tobramycin, polymyxin B, and neomycin were highly effective in vitro against initial g(-) isolates. Chloramphenicol was ineffective against g(+) and g(-) organisms isolated initially. A significantly (P < 0.05) higher frequency of g(-) organisms was noticed on repeat cultures after intensive topical antimicrobial treatments as compared to organisms isolated at initial examination. Pseudomonas organisms isolated from second cultures were resistant to gentamicin, but susceptible to ciprofloxacin. Overall, secondary g(-) isolates were more susceptible to ciprofloxacin, neomycin, tobramycin, or amikacin than to gentamicin. Fungi were isolated in 24 of 63 (38%) horses in the study. Twenty-five filamentous fungi and 2 yeasts were identified from 24 eyes. Aspergillus spp was the predominant fungi; it was detected in 17 of 22 (77%) eyes in which filamentous fungi were identified.

Free access
in Journal of the American Veterinary Medical Association

Summary

The ability of monovalent and bivalent equine herpesvirus (EHV) vaccines to stimulate cellular and antibody responses to EHV-1 and EHV-4 was compared in healthy horses. Comparison of data from lymphocyte blastogenesis tests in which live viruses were used as antigens and that were conducted prior to vaccination and after 2 vaccinations revealed that horses given modified-live EHV-1 had significant increases in proliferative responses to EHV-1 (P = 0.03) and EHV- 4 (P = 0.04). Responses to EHV-1 and EHV-4 in horses given the inactivated-virus bivalent vaccine were less; however, significant differences were not noticed when postvaccinal lymphocyte blastogenesis tests were compared between the groups of vaccinees.

Interleukin-2 activity was not detected in leukocyte cultures from either group of vaccinees following stimulation with live EHV-1 or EHV-4; however, interferon activity was found in similar cultures from both groups of vaccinees. For EHV-4, interferon activity in cultures from both groups of vaccinees was significantly (P < 0.05) greater than that in leukocyte cultures from unvaccinated controls.

Both vaccines induced significant (P < 0.05) increases in serum antibodies that neutralized EHV-1 infectivity. The ELISA for EHV-1 and EHV-4 antibodies revealed that both vaccines induced significant (P < 0.05) increases (compared with preinoculation values) in antibodies reactive with these 2 types of EHV. Total serum antibody responses, as measured by ELISA, to EHV-1 and EHV-4 were significantly (P < 0.05) higher in horses that received the bivalent inactivated-virus vaccine, compared with that in horses that received monovalent vaccine. Evaluation of these data revealed that vaccination with modified-live EHV-1 can stimulate cellular and antibody responses that cross-react with EHV-4.

Free access
in Journal of the American Veterinary Medical Association

Summary

A study was designed to determine if inactivated bovine respiratory syncytial virus (brsv) vaccines induce the same types of antibody and cellular responses as does a modified-live brsv vaccine. Ninety mixed-breed, 5- to 6-month-old beef calves were randomly assigned to 1 of 6 groups with 15 animals/group. Calves in 5 of the groups were inoculated on days 0 and 14 with 1 of 4 inactivated virus vaccines or with a modified-live virus vaccine. The remaining 15 calves were maintained as unvaccinated controls. Immune responses were measured on days 0 and 24, by means of elisa, virus neutralization assay, blocking elisa for the brsv fusion (F) protein, immunoblotting, and lymphocyte blastogenesis assay. All vaccines induced production of antibodies that recognized the F protein; however, the ratio of neutralizing antibody titer to change in brsv-specific IgG antibody concentration (as determined by use of elisa) was lower for calves that received an inactivated virus vaccine than for calves that received the modified-live virus vaccine. All of the vaccines induced lymphocyte proliferative responses to brsv. Results suggest that commercially employed inactivation processes can alter functionally important epitopes on brsv envelope glycoproteins, leading to production of predominantly nonneutralizing antibodies in immunized cattle.

Free access
in Journal of the American Veterinary Medical Association

Summary

Undifferentiated distal respiratory tract disease (nasal discharge, cough, pneumonia) in foals (1 to 8 months old) is a burdensome economic problem on breeding farms; yet, the infective agents associated with these episodes have not been well described. Possible causes of these episodes of illness were investigated by culturing specimens of proximal and distal airways of clinically diseased foals (n = 101), prior to any treatment, for aerobic and anaerobic bacteria and viruses (rhinoviruses, equine arteritis virus, equine herpesvirus subtype 1 [ehv-1], influenza virus, and adenovirus). Pairs of sera (n = 47) were examined for antibodies to influenza A virus, equine subtypes 1 and 2, ehv-1, and adenovirus antigens, and sera obtained from foals during acute infection were examined for antibodies (by agar gel immunodiffusion [agid]) to equi factor antigens of Rhodococcus equi. Viruses were not isolated from the proximal (swab) or distal (bronchial lavage) airway specimens in foals, and only 2 of 47 randomly selected foals seroconverted to ehv-1. Serotiters to the other viruses were low and frequently decreasing between samples, which was compatible with maternally derived antibody. Streptococcus zooepidemicus was the predominant isolate from bronchial lavage specimens (88/101 cases), accompanied by α-hemolytic streptococci (8 cases), Bordetella bronchiseptica (13 cases), Staphylococcus epidermidis (9 cases), and other organisms in lesser frequency. Only Str zooepidemicus was recovered significantly (P < 0.05) more often in cases than in controls. The agid test was found useful to detect foals with presumed exposure to R equi, but positive tests results did not correspond well with bacterial culture results; positive agid results were recorded in 34% of culturenegative foals. However, foals from which R equi was isolated were distinctive from the other foals on the basis of fever (> 39 C), lack of nasal discharge, blood neutrophilia, and decreased percentage of neutrophils in bronchial lavage fluid samples. Isolation of Str zooepidemicus was significantly (P < 0.01) associated with increasing neutrophil percentage in bronchial lavage fluid. In conclusion, the pathogenic roles of Str zooepidemicus and R equi were established in this group of foals with distal respiratory tract infections by use of clinical, endoscopic, hematologic, and cytologic methods. There was no evidence of a viral cause for these infections, indicating that manifestations of distal respiratory tract infection are attributable to bacterial infection causing inflammation of the airways. Further studies are warranted to pursue more-sensitive methods for detection of viral antigen or antibody in undifferentiated distal respiratory tract disease episodes in foals.

Free access
in American Journal of Veterinary Research

Summary

Despite the high incidence of distal respiratory tract infection of undetermined cause on farms, to our knowledge, the microbiologic effects of conventional antimicrobial treatment for this condition have not been studied. We evaluated the possible pathogenic role of bacterial isolates from the distal airways of foals with clinical respiratory tract disease, by correlating changes in their numbers (increase or decrease) with clinical, endoscopic, and pulmonary cytologic signs of disease resolution during treatment with antimicrobial drugs. We also determined qualitative changes in in vitro antimicrobial susceptibility of bacterial isolates after 7 days of treatment and relapse rate of foals. Significant (P < 0.05) decrease in the numbers of an isolate in the airways was considered strong evidence of a pathogenic role in this disease syndrome. Foals with endoscopically confirmed distal respiratory tract infection (drti; n = 65) were selected at random for treatment (n = 56) or nontreatment (n = 9), and bronchial lavage specimens were cultured and evaluated cytologically before and after 7 days of treatment with trimethoprim-sulfamethoxazole (tms) and a β-lactam drug (penicillin, ampicillin, or sulbactam-ampicillin), the standard treatment in all foals. The effect of treatment was to abruptly reduce the clinical (nasal discharge, cough, adventitious lung sounds) and cytologic signs of airway infection. Severity of disease in nontreated foals, however, did not change or did worsen over time. Reduction in the frequency and numbers of Streptococcus zooepidemicus isolated during treatment supported a causal role for this organism in the clinical syndrome observed. On the other hand, the frequency of non-Str zooepidemicus isolates (eg, Staphylococcus epidermidis, Streptomyces spp, α-hemolytic streptococci) actually increased during treatment, compatible with a commensal or competitive role for these organisms. Significantly (P < 0.001) more pretreatment isolates were susceptible in vitro to either tms or β-lactam drugs than to β-lactam drugs alone; more posttreatment isolates were susceptible to either tms or β-lactam than to either drug alone. These data indicate that there may be some benefit to combined use of tms plus β-lactam drugs in foals with drti. Mean ± sem relapse rate was 31 ± 6% (range 0 to 57%); risk factors (clinical signs of disease, laboratory variables) for relapse could not be identified. In conclusion, treatment resulted in significant (P < 0.001) reduction in airway inflammation in foals with clinical drti. The high reinfection rate indicates that a predisposing factor, possibly age-related immunodeficiency, may predispose foals to illness and persists after treatment.

Free access
in American Journal of Veterinary Research
in Journal of the American Veterinary Medical Association

Summary

One indication for referral of horses to veterinary hospitals is for diagnosis of the microbiologic cause of pneumonia, particularly when the initial treatment fails. Although endoscopic methods have long been available for microbiologic sample collection, accuracy of these methods under these conditions have not been studied in detail. We compared the bacteria isolated from samples obtained by bronchoalveolar lavage (bal) with those obtained by protected catheter brush (pcb) from foals with unilateral pneumonia induced by inoculation with Klebsiella pneumoniae. As part of previously described clinical trials, foals were administered antimicrobial therapy im (n = 15) or vehicle im (n = 7), and collection of distal airway secretion samples was conducted during the treatment period. Sensitivity and specificity of the sample collection methods were assessed by comparison of the isolates from bal or pcb samples with isolates from tissue of the inoculated lung lobe, which was the most severely affected lung region. Sensitivity and specificity of bal for recovery of K pneumoniae (challenge strain) and Streptococcus zooepidemicus (common secondary pathogen) was 90 and 69%, respectively, compared with 76 and 85%, respectively, for the pcb method. Sensitivity was significantly (P = 0.03) higher for bal (100%) than for pcb (69%) for recovery of K pneumoniae (P = 0.03) from lungs. However, difference in the sensitivity of these methods for recovery of S zooepidemicus was not significant. In conclusion, bal was a more reliable method for recovery of bacteria from the lungs in chronically infected foals that received antimicrobial treatment.

Free access
in American Journal of Veterinary Research

Summary

Random fragments of dna were obtained from a cosmid library of Salmonella agona genomic dna. From this library, 2 fragments were chosen and pooled to probe isolates of S typhimurium obtained during an episode of salmonellosis in a veterinary medical teaching hospital. Chromosomal dna from the Salmonella isolates was digested with restriction endonucleases, and was probed with the random fragments of chromosomal dna. This procedure resulted in a fingerprint pattern for each isolate. We found that the method permitted discrimination between isolates involved in the disease episode and S typhimurium obtained prior to the episode. We conclude that random fragments of chromosomal dna are useful for fingerprinting isolates of S typhimurium. Analysis of plasmid dna obtained from the isolates was not as useful. Some isolates found to be identical by restriction site analysis, had plasmids of different molecular weight. These results indicate that plasmid analysis may not be as useful a fingerprinting tool as previously reported.

Free access
in American Journal of Veterinary Research

Summary

To evaluate the clinical, laboratory, and histologic effects of 2 methods of treatment for infectious arthritis in horses, Staphylococcus aureus (3.4 to 3.9 × 103 colony-forming units) was inoculated into the tarsocrural joints of 8 horses on day 0. Each horse was treated with phenylbutazone (2 g, po, q 24 h) and gentamicin sulfate (2.2 mg/kg of body weight, iv, q 8 h) for 14 days. On day 2, general anesthesia was induced, and each horse had 1 tarsocrural joint treated by arthrotomy, with removal of accessible fibrin and lavage with 3 L of sterile balanced electrolyte solution. An indwelling plastic drain was placed in the standing horse to provide a means for lavage with 3 L of balanced electrolyte solution twice daily for 72 hours. The contralateral tarsocrural joint was treated via arthroscopic debridement, synovectomy, and lavage with 3 L of balanced electrolyte solution. Arthrotomy and arthroscopic portals were allowed to heal by second intention. Lameness and thermographic examinations, analysis and bacteriologic culture of synovia, cbc, and wbc differential count were performed prior to inoculation and on days 1, 3, 6, 8, and 13. On day 14, each horse was euthanatized, and the joints were measured, opened, and photographed. Synovium and articular cartilage were obtained for semiquantitative histologic (H&E stain) and histochemical (safranin O fast green stain) evaluation. Lameness and joint circumference were significantly (P < 0.05) greater in limbs treated by arthroscopy, synovectomy, and lavage. Arthrotomy with lavage eliminated the S aureus infection significantly (P < 0.05) earlier than arthroscopy, synovectomy, and lavage; however, both treatments eliminated the infection in all but a single joint. Contamination with other organisms (Streptococcus spp and Enterobacter spp) developed significantly (P < 0.05) more often in joints treated by arthrotomy. These results suggested that arthrotomy with lavage was more effective in eliminating joint infection by providing better drainage than arthroscopy, synovectomy, and lavage; however, arthrotomy had a higher risk of ascending bacterial contamination of the joint.

Free access
in American Journal of Veterinary Research