A swine production system had 3 sections located a few kilometers apart. Sections A and C contained several thousand sows and nursery and finishing pigs. Section B, located between the other 2 sections, was the smallest and had 6 finishing sites and 2 sow sites. The entire system was infected with porcine reproductive and respiratory syndrome virus, Mycoplasma hyopneumoniae, and Actinobacillus pleuropneumoniae. Section B was depopulated, cleaned, disinfected, and repopulated with negative gilts. Despite extreme measures, recontamination occurred for each pathogen, with aerosol considered the most plausible contamination source.
Transmission suspectée d’agents pathogènes porcins par aérosol : un cas de terrainUn système de production porcine comportait 3 sections situées à quelques kilomètres l’une de l’autre. Les sections A et C contenaient plusieurs milliers de truies et de porcs en maternité et en finition. La section B, située entre les 2 autres sections, était la plus petite et comptait 6 sites de finition et 2 sites de truies. L’ensemble du système était infecté par le virus du syndrome reproducteur et respiratoire porcin, Mycoplasma hyopneumoniae et Actinobacillus pleuropneumoniae. La section B a été dépeuplée, nettoyée, désinfectée et repeuplée de cochettes négatives. Malgré des mesures extrêmes, une recontamination s’est produite pour chaque agent pathogène, les aérosols étant considérés comme la source de contamination la plus plausible.(Traduit par Dr Serge Messier).

The aim of this study was to determine the optimal vaccination strategies for the control of porcine respiratory disease complex (PRDC) caused by Mycoplasma hyopneumoniae, porcine reproductive and respiratory syndrome virus (PRRSV), and porcine circovirus type 2 (PCV2) in case of early mycoplasmal infection.
A total of 120 pigs were randomly divided into 6 groups (20 pigs per group). Four separate vaccine regimen groups were selected. Pigs from the four vaccinated groups were challenged with M. hyopneumoniae at 28 days old followed by a challenge of PRRSV or PCV2 at 49 days old.
Regardless of PRRSV or PCV2 vaccination, pigs vaccinated with one of the M. hyopneumoniae vaccines at 7 days old had a significantly better growth performance over the whole length of the study compared to pigs vaccinated with a second M. hyopneumoniae vaccine at 21 days old. Vaccination of pigs with M. hyopneumoniae at 7 days and PRRSV at either 7, 14 or 21 days old resulted in significantly reduced PRRSV viremia and lung lesions compared to vaccination of pigs with M. hyopneumoniae and PRRSV at 21 days old.
The efficacy of the PRRSV MLV vaccine is influenced by the different timing of M. hyopneumoniae vaccination whereas the efficacy of the PCV2 vaccine is not. This experiment study demonstrated that early vaccination with a M. hyopneumoniae vaccine should be the highest priority in order to control M. hyopneumoniae and PRRSV infection in cases of early M. hyopneumoniae infection.

When conducting their investigations to diagnose infectious diseases in swine, practitioners are often forced to use reduced numbers of animals in their samples in order to minimize costs for farmers. A cross-sectional study was conducted approximating such field conditions to show the limits of interpretation with reduced sample sizes in case of Enzootic Pneumonia. Compared with other respiratory pathogens, Mycoplasma hyopneumoniae, the etiologic agent of Enzootic Pneumonia spreads very slowly, mainly when animals are in direct contact. Furthermore, the interpretation of serological results is difficult because several weeks must usually pass for serological reactions to become apparent. Serological testing is normally used to confirm a clinical diagnosis by detecting an increase in antibodies against the etiologic agent. Samples are collected at the beginning of disease and four to six weeks later. An increasing number of serological positive animals in a herd is usually interpreted as spread of infection. The ,,true\" prevalence we observed in our investigation was used to make a statistical analysis describing the probability of detecting an increasing prevalence from 0.07 to 0.33 with a reduced sample size. We showed that the probability of detecting an increase of two seropositive animals was 44% if 5 samples per group were analysed. When only 3 samples were analysed per group, this probability decreases to 21%. Compromise must be found between epidemiological necessary and financially acceptable sample size; this could be a minimum of 10 samples per age group.