Characteristics of Haemophilus pleuropneumoniae Isolates and Some Epidemiological Findings on Porcine Haemophilus Pleuropneumonia in Saskatchewan

Thirty isolates of Haemophilus pleuropneumoniae from clinical and slautherhouse cases of porcine Haemophilus pleuropneumonia in Saskatchewan as well as six isolates from British Columbia and Ontario were subjected to cultural, biochemical, serological and antibiotic sensitivity tests. All strains were Gram-negative pleomorphic rods or coccobacilli which grew only in the presence of V factor and all produced porphyrin from delta-aminolaevulinic acid. Biochemically, the organism was positive for urease, O-nitrophenyl-β-D-galactopyranosidase and the fermentation of sucrose, mannitol, dextrose, lactose and xylose, but was usually negative for indole. Most strains of H. pleuropneumoniae were sensitive to chloramphenicol, furamazone, carbenicillin and ampicillin, but only about 50% were sensitive to tetracycline. Serotype 5 was more common than serotype 1 or the untyped strains among Saskatchewan isolates. In addition, serotype 3 was identified from British Columbia.

Retrospective epidemiological studies showed that Haemophilus pleuropneumonia occurred and recurred on farms in the Saskatoon and adjoining districts, serviced by the diagnostic laboratories of the Western College of Veterinary Medicine and that the disease was more common among three month old pigs during the fall-winter season.

     

Pulmonary clearance of Haemophilus pleuropneumoniae and Serratia marcescens in mice

Bacterial counts (per lung) were made from Swiss White and/or C3H mice, inoculated intranasally with either Haemophilus pleuropneumoniae or Serratia marcescens and killed at specific times. The percentages of bacterial survival and clearance at each time were determined. Serratia marcescens was cleared progressively, but not completely, from the lungs of C3H and Swiss White mice. The overall pulmonary clearance of S marcescens by Swiss White mice was significantly greater than that of C3H mice (P less than 0.01). The pulmonary clearance pattern of H pleuropneumoniae in C3H mice differed according to the dose inoculated. With a larger H pleuropneumoniae median lethal dose (0.1 LD50), the organism multiplied consistently up to 25 times by 12 hours after the inoculations were done, when clinical signs and lesions appeared in a few of the mice. The clearance rates at 24 and 48 hours after inoculations were 60.65% and 10.3%, respectively. Mice given 0.04 LD50 H pleuropneumoniae showed a 10-fold increase of H pleuropneumoniae in the first 4 hours, with clearances reaching 33%, 66%, and 99% at 8, 12, and 24 hours, respectively.     

Pulmonary Clearance of Bacillus subtilis Spores in Pigs

The pulmonary clearance rate of Bacillus subtilis was determined in ten pigs (23-39 kg) exposed simultaneously for 15 minutes to an aerosol generated by an ultrasonic nebulizer. Two pigs were killed at each interval of zero, two, four, eight and 12 hours and the concentrations of B. subtilis in lungs (all lobes), dorsal and ventral nasal turbinates, trachea, pharyngeal and bronchial lymph nodes were determined. The mean percent (± standard error) pulmonary clearance of B.subtilis was 54.2±11.7, 53.0±11.8, 77.4±5.2 and 88.1±3.7 at two, four, eight and 12 hours, respectively. The numbers of B. subtilis retained in the posterior (caudal and accessory) lobes at zero time were significantly greater than those in the anterior (cranial and middle) lobes (P<0.05). However, by 12 hours postinoculation the numbers of organisms retained in the two regions did not differ significantly (P>0.05). The mean percentage of B. subtilis retained by the turbinates, trachea, pharyngeal and bronchial lymph nodes varied between pigs at each time interval, but was usually less than that retained by the lungs.

It was concluded that deposition of B. subtilis spores took place in all parts of the respiratory tract when pigs were exposed to aerosols and that the spores were progressively cleared by the normal lung.

     

A model aerosol exposure system for induction of porcine Haemophilus pleuropneumonia.

One group of six pigs and another group of three pigs were separately exposed in a polyethylene enclosed chamber for ten minutes, respectively, to Haemophilus pleuropneumoniae serotype 1 and Bacillus subtilis aerosols generated by an ultrasonic nebulizer. Haemophilus pleuropneumoniae and B. subtilis were deposited throughout the lungs immediately following aerosol exposure. The number of H. pleuropneumoniae and B. subtilis deposited varied within and between lungs in each group. The mean numbers of both organisms deposited in the posterior (caudal and accessory) lobes were significantly greater than those in the anterior (cranial and middle) lobes (P less than 0.001). The four principals that received H. pleuropneumoniae aerosols and the two contact controls developed fatal fibrinous pneumonia which simulated that seen in natural infections. Since this exposure system consistently resulted in clinical disease it has good potential as a model for the study of pathogenesis of the disease and more specifically for the evaluation of vaccines.     

A Simple Aerosol Chamber for Experimental Reproduction of Respiratory Disease in Pigs and Other Species

The design of a simple aerosol chamber for experimental challenge of pigs and other species with respiratory pathogens is described.     

Dose response relationship of Haemophilus pleuropneumoniae aerosols in pigs.

The virulence of Haemophilus pleuropneumoniae was quantitated for ten and 12 week old pigs following aerosol exposure. The volume and concentration of culture aerosolized, the estimated numbers of organisms inhaled by the pigs and the mortality rates at 72 hours postexposure were computed and used to calculate the LD50. There was correlation between the concentration of culture aerosolized, the amount of the estimated inhaled dose and the mortality rates. The ten week old pigs were apparently more susceptible to aerosols of H. pleuropneumoniae than the 12 week old pigs. The LD50 value or a multiple of it appears to be a reasonable basis for a standardized aerosol challenge of the immunity of pigs vaccinated with experimental or commercial H. pleuropneumoniae vaccines.