AEROSOL VACCINATION OF PIGS AGAINST MYCOPLASMA-BYOPNEUMONIAE INFECTION

Aerosol vaccination is used effectively to immunize poultry against Ne wcastle disease, but to the authors' knowledge, this vaccination proce dure is not well studied in other species. The efficacy of IM and aero sol vaccination of pigs against Mycoplasma hyopneumoniae infection was evaluated. Twenty-one pigs from a Mycoplasma-free herd were randomly allotted by litter and body weight into 3 groups. One group was given aerosolized phosphate-buffered saline solution (PBSS) by inhalation. T he second group (AERO) was given aerosolized M hyopneumoniae vaccine b y inhalation. The third group (IM) was given the same vaccine by IM in jection. Vaccination by IM administration was repeated once, and aeros ol vaccination was repeated twice at 2-week intervals. Two weeks after the last vaccination, all pigs were intratracheally challenge-exposed with 3 ml of broth culture containing 10(7) color-changing units (CCU ) of a low-passage strain of virulent M hyopneumoniae. Pigs were obser ved daily for coughing. Four weeks after challenge exposure, all pigs were necropsied. Percentage of lung affected by gross pneumonia was me asured, bronchioalveolar lavage fluid (BALF) cells were counted, and q uantitative culture for mycoplasmas was performed on lung sections. Ad ditionally, M hyopneumoniae-specific antibodies were measured in preva ccination, postvaccination, and postchallenge-exposure serum and BALF by use of indirect ELISA. Mean prevalence of persistent coughing in pi gs of the AERO group (4.6 d/pig) was not different from that in pigs o f the PBSS group (3.7 d/pig). Prevalence of coughing in IM vaccinated pigs (1.0 d/ pig) was lower (P < 0.05) than that in pigs of the PBSS g roup. Mean gross lung lesion scores and BALF cell counts were not diff erent between the AERO (15% pneumonia, 5,233 cells/mu l) and PBSS (11% pneumonia, 3,022 cell/mu l) groups, but were lower (P < 0.05) in the IM group (1.5% pneumonia, 400 cells/mu l) than in the PBSS group. Mean lung mycoplasmal counts were not significantly (P < 0.05) different a mong the PBSS (10(5.6) CCU/g), AERO (10(5.3) CCU/g), and IM (10(3.3) C CU/g) groups. Postvaccination M hyopneumoniae-specific IgG or IgA was not detectable in BALF after either vaccination procedure. Postvaccina tion M hyopneumoniae-specific serum IgG concentration was not differen t among the 3 groups. Postchallenge exposure M hyopneumbniae-specific IgG and IgA were detectable in BALF of all pigs, but were not differen t among the 3 treatment groups. Postchallenge exposure-specific serum IgG concentration was not different between the PBSS (mean OD, 0.739) and AERO (mean OD, 0.672) groups, but was higher (P < 0.05) in the IM group (mean OD, 1.185) than in the PBSS group. Aerosol vaccination fai led to induce local and systemic antibody responses detectable by ELIS A, and failed to protect pigs against mycoplasmal pneumonia. Intramusc ular vaccination failed to induce local and systemic antibody response s detectable by ELISA, but substantially reduced the clinical signs an d lesions caused by challenge exposure to virulent M hyopneumoniae.