EVALUATION OF THE EFFICACY OF A SINGLE DOSE MYCOPLASMA HYOPNEUMONIAE VACCINATION PROGRAMME IN CHALLENGED PIGS
D. Llopart, J. Clota, R. March, I. Navarra, P. Riera and C. Artigas

Abstract
The efficacy of a single dose vaccination programme using an inactivated vaccine against M. hyopneumoniae (MYPRAVAC SUIS - Laboratorios Hipra) was evaluated in pigs when challenged by an intratracheal route with 10 ml of M. hyopneumoniae virulent strain culture (106 ccu/ml) (ref. 3371.[Dr. N. Friis, Denmark]). Forty M. hyopneumoniae seronegative pigs of seven to 10 days of age were used. Four experimental groups of 10 pigs each were established. Group One was vaccinated twice (day 0 and 21) and challenged at day 70. Group Two was vaccinated once (day 0), a PBS sterile solution was injected at day 21 and they were also challenged at day 70. Group Three was not vaccinated but injected with a PBS solution (day 0 and 21) and challenged at day 70. Group Four was neither vaccinated, injected with a PBS solution at day 0 and 21 nor challenged. All pigs were slaughtered at day 98. Clinical signs of pneumonia were observed in two pigs from Group Three, 21 days post challenge. Groups One, Two and Four did not show any signs of pneumonia during the post-challenge period. Although daily weight gain during the post-challenge period was higher in the vaccinated groups (Group One: 0.61 kg; Group Two: 0.64 kg; Group Three: 0.48 kg; Group Four: 0.59 kg), no significant differences were found between groups. Blood samples showed that the percentage of positive animals was higher in Group One than Two at days 42 (80% vs 20% respectively) and 70 (90% vs 10% respectively). The administration of two doses of vaccine induced higher inhibition percentage (IP) values against M. hyopneumoniae than the administration of one dose in a competitive ELISA test. The percentage of positive animals was similar between Groups One and Two (vaccinated) but higher than Group Three at 28 days post challenge. Macroscopic pulmonary lesions scored at day 98 showed that Group One presented a significant reduction of the pulmonary lesions attributed to M. hyopneumoniae when compared with Groups Three and Four (p=0.036 and 0.011 respectively), but no significant differences were found between Groups One and Two (p=0.197). Histopathology confirmed that Group One presented a lower incidence and severity of pulmonary lesions than Groups Two and Three. The trial concluded that the administration of a single dose vaccination programme induces a humoral immune response and reduces pulmonary lesions when compared with a non-vaccinated group of pigs when challenged, though best results were obtained with the two dose vaccination programme.

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