EXPERIMENTAL DUAL INFECTION OF CESAREAN-DERIVED, COLOSTRUM-DEPRIVED PIGS WITH MYCOPLASMA-HYOPNEUMONIAE AND PSEUDORABIES VIRUS

To determine whether pseudorabies virus (PRV) infection increases the severity of pneumonia by Mycoplasma hyopneumoniae, 18, 10-week-old Ces arean-derived, colostrum-deprived pigs were randomly assigned to 3 gro ups of 6 pigs each. Pigs in groups A and C were inoculated intranasall y with M. hyopneumoniae at 10-week-old. At 11-week-old, pigs in groups B and C were inoculated intranasally with PRV. All pigs were initiall y seronegative for M. hyopneumoniae and PRV. Three pigs of each group were euthanized at 12-week-old, and remaining pigs at 14-week-old. At necropsy, gross lesions in the lung were observed in the pigs of group s A and C. On postinoculation-week (PIW) 2 with M. hyopneumoniae (at 1 2-week-old), lung lesions were recognized in one of the 3 pigs in grou p A and all the pigs in group C. The mean percentage of the lung lesio ns were 0.1% in group A and 9.8% in group C. M. hyopneumoniae was isol ated from broncho-alveolar ravage fluids (BALF) of pigs in group A wit h titer of 10(2) to 10(9) CCU/0.2 ml and in group C with titer of 10(5 ) to 10(6) CCU/0.2 ml. On PIW 4 (at 14-week-old), lung lesions were ob served in all the pigs in groups k and C, and the mean percentage of t he lung lesions were 8.3% in group A and 17.2% in group C. M. hyopneum oniae was isolated from BALF in group A with titer of 10(4) to 10(7) C CU/0.2 ml and in group C with titer of 10(6) to 10(7) CCU/0.2 ml. PRVs were isolated from nasal swab and tissue samples in groups B and C. A fter inoculation, antibody against M. hyopneumoniae was detected in gr oups A and C, and against PRV in groups B and C. Under the present exp erimental conditions, PRV infection appear to have effect on the sever ity of experimentally induced acute mycoplasmal pneumonia in young pig s.