Antibiotic prophylaxis of lower respiratory tract contamination in horses confined with head elevation for 24 or 48 hours

Objective To evaluate the administration of procaine penicillin prior to or during confinement with head elevation as a means of reducing the associated accumulation of inflammatory lower respiratory tract secretions and increased numbers of bacteria within the lower respiratory tract of confined horses. Design and Procedure Two experiments were conducted to evaluate the efficacy of different dose rates and dosing frequencies. In experiment A a single low dose (15,000 IU/kg) of procaine penicillin was administered to four horses immediately prior to confinement with head elevation for 48 hours. The systemic leucocyte response, gross and cytologic characteristics of transtracheal aspirate and bacterial numbers in lower respiratory tract samples were compared with corresponding samples from two horses confined with heads elevated but not given penicillin. The efficacy of higher dose rates (20,000 IU/kg and 40,000 IU/kg) given before and during confinement with heads elevated for 24 hours was evaluated in experiment B. Results Treatment with procaine penicillin had no effect on the systemic leucocyte response or on the accumulation of inflammatory lower respiratory tract secretions at any of the dosing schedules evaluated. The number of bacteria isolated from trans-tracheal samples was reduced at 12 hours for treated horses in experiment A and at 24 hours for experiment B. β-haemolytic Streptococcus spp were not isolated from treated horses in either experiment. Bacterial species isolated from treated horses were predominantly Pasteurella and/or Actinobacillus spp, however, members of the family Enterobacteriaceaé and a Staphylococcus sp were isolated from treated horses. One treated horse in experiment A developed clinically apparent pulmonary disease. Conclusions The prophylactic administration of penicillin before or during confinement did not reliably reduce bacterial numbers or prevent the accumulation of purulent lower respiratory tract secretions in horses confined with their heads elevated. Numbers of β-haemolytic Streptococcus spp were reduced following treatment, suggesting that the repeated administration of procaine penicillin may have some merit as part of a strategy to prevent transport-associated respiratory disease. However, methods directed at minimising the duration of confinement with head elevation, augmentation of the clearance of accumulated secretions and prompt identification of animals in which airway inflammation has extended to the pulmonary parenchyma remain the best ways of minimising transport-associated respiratory disease.     

Effect of transportation on lower respiratory tract contamination and peripheral blood neutrophil function

Objective To evaluate the effect of transportation on lower respiratory tract contamination and peripheral blood neutrophil function in horses and to compare results from transported horses with those obtained in earlier experiments from horses confined with heads elevated. Design A prospective study. Procedure Six horses were transported by road for 12 h. Clinical and haematological examination, transtracheal aspiration and cell function studies were conducted before and after transportation. Results obtained after transportation were compared to pre-transportation values. Results After transportation, peripheral blood leucocyte and neutrophil numbers were increased and rectal temperatures were elevated. Transtracheal aspirates showed an accumulation of purulent respiratory tract secretions with increased numbers of bacteria, particularly β-haemolytic Streptococcus spp and members of the Pasteurellaceae family. Three horses also had increased numbers of bacteria from the Enterobacteriaceae family relative to corresponding samples from earlier studies. Phagocytosis by peripheral blood neutrophils was significantly reduced, while the oxidative burst activity of peripheral blood leucocytes was either unchanged or enhanced. Clinical Implications Bacterial contamination of the lower respiratory tract occurs as a routine consequence of transportation of horses and is likely to be an important determinant in the development of transport-associated respiratory disease. Inflammatory airway secretions and increased numbers of bacteria were rapidly cleared, without clinical evidence of significant pulmonary disease and without additional treatment, in normal horses that were allowed to lower their heads after transportation. Peripheral blood neutrophilia and a reduction in neutrophil phagocytic function were evident for at least 36 h after transportation, suggesting that horses may require a number of days to recover from the stress of transportation. As the potential role of bacteria from the Enterobacteriaceae family in the development of transport-associated respiratory disease has not been elucidated, horses which develop clinical disease following transportation should undergo thorough bacteriological investigation to ensure appropriate treatment.     

Growth and metabolic characterization of Macrorhabdus ornithogaster.

Macrorhabdus ornithogaster (M. ornithogaster) is an anamorphic ascomycetous yeast found only in the stomach of birds. Infection is often benign but has also been associated with disease in some species of birds under some circumstances. In vitro efforts to grow M. ornithogaster have been largely unsuccessful. In this report, multiple liquid and solid media of varying pH, sugar concentration, and fetal bovine serum (FBS) concentrations, incubated at various temperatures in room air or microaerophilic conditions, were examined for their ability to support the growth of M. ornithogaster, obtained from a budgerigar (Melopsittacus undulatus). Optimum growth conditions were found to be Basal Medium Eagle's, pH 3 to 4, containing 20% FBS, and 5% glucose or sucrose under microaerophilic conditions at 42 degrees C. Using these conditions, M. ornithogaster was repeatedly passaged without loss of viability. Polyclonal isolates of M. ornithogaster consistently assimilated glucose, sucrose, and trehalose. M. ornithogaster did not grow with prolonged exposure to atmospheric oxygen, but growth in microaerophilic conditions was moderately enhanced by preincubation with atmospheric oxygen for 24 hours. An isolate of M. ornithogaster was found to be infective to day-old chickens, reduce their rate of weight gain, and induce a mild to moderate heterophilic inflammation of the isthmus. M. ornithogaster was reisolated from the chicks 7 days after infection, fulfilling Koch's postulates. A 761-bp sequence of 18S rDNA from this isolate was compared to the originally reported M. ornithogaster sequence and was found to be 97% identical.