Measuring airborne microorganisms and dust from livestock houses

Airborne transmission has been suspected to be responsible for epidemics of highly infectious disease in livestock production. In such transmission, the pathogenic microorganisms may associate with dust particles. However, the extent to which airborne transmission plays a role in the spread of diseases between farms, and the relationship between microorganisms and dust remain unclear. In order to better understand airborne transmission and to set up effective control techniques, this study investigated the performance of multi-stage air scrubbers on the reduction of emissions of microorganisms and dust from pig houses, and to evaluate the effectiveness and efficiency of different sampling devices for collecting microorganisms and dust. In winter, multi-stage scrubbers reduced emissions of airborne total bacteria by between 46% and 85%, PM 10 by between 61% and 93%, PM 2.5 by between 47% and 90%, and ammonia by between 70% and 100%. The EU reference dust sampler with an impaction pre-separator, which was designed for sampling dust in ambient air, could not be used to sample PM 2.5 in livestock houses where dust concentrations were high, because overloading occurred. A sampler with a cyclone pre-separator was more tolerant of dust loads in livestock houses and was validated as a reference equivalent sampler. The method for evaluating the efficiency of bioaerosol samplers for airborne microorganisms was appropriate. It calculated the physical and biological sampling efficiencies separately, by excluding the viability losses in the non-sampling processes. The Andersen six-stage impactor, the All Glass Impinger (AGI-30) and the MD-8 had higher physical efficiencies than the OMNI-3000. The Andersen impactor and the AGI-30 had high (100%) biological efficiencies on sampling all five aerosolized microbial species (Enterococcus faecalis, Escherichia coli, Campylobacter jejuni, Mycoplasma synoviae and Gumboro vaccine virus). C. jejuni and Gumboro vaccine virus were inactivated by the OMNI-3000 during sampling, whereas E. coli and C. jejuni were inactivated by MD8. As a result, these two bioaerosol samplers had lower biological efficiencies. Although recipient broilers became infected, no culturable airborne Campylobacter were detected by the Andersen impactor, the AGI-30 and the OMNI-3000 in an airborne transmission of Campylobacter in broilers. From this study we concluded that installing multi-stage scrubbers at the air exhausts makes it possible to appreciably reduce aerial pollutant emissions from livestock production systems. As PM samplers with cyclone pre-separators are less vulnerable to high dust loadings, it is recommended that they are used to sample dust in livestock production systems. The efficiency of the bioaerosol samplers varies according to the microbial species sampled. Suitable samplers can be selected on the basis of their efficiencies and detection limits. Low aerial concentrations of specific microbial species are difficult to detect with current bioaerosol samplers. Knowledge gaps still exist throughout the process of long-distance airborne transmission of microorganisms, from suspension and transportation to deposition and infection.