Brief glossary and background regarding airborne PRRS virus

Airborne Infectious diseases represent a major challenge to human and animal health, mainly due to the difficulty of controlling the air quality within a facility that hosts susceptible individuals.
This challenge is even greater when the cause is an agent like PRRS virus , capable of traveling long distances carried by aerosols. Here are some of the most common terms used when referring to airborne PRRS virus.

Airborne Diseases (AD): Diseases caused by pathogens and transmitted through the air.
Airborne PRRS virus: A systemic swine virus that can be shed in many body secretions and is exhaled in air1.
Airborne Transmission (AT): AT occurs from infected to naïve individuals, when pathogens travel on dust particles or on small respiratory droplets that are stirred up into the expelled air due to coughing, sneezing or exhalation.
Airborne transmission of PRRS virus: American researchers documented for the first time2 the airborne transmission of PRRS virus in 1997. A more recent study suggests that on large sow farms with good biosecurity in swine-dense regions, approximately four-fifths of PRRSV outbreaks may be attributable to aerosol transmission3.
Aerobiology: It is the study of the processes involved in the movement of microorganisms in the atmosphere from one geographical location to another, including the aerosolized transmission of disease. It employs contemporary techniques including computational fluid dynamics to study airborne particle flow, polymerase chain reaction (PCR) methodologies to identify infectious agents and quantify airborne particle concentrations in various settings, and epidemiology to track the spread of disease5.
PRRS aerobiology: Since the late 90s to date, it has been issuing increasingly strong evidence about the role of aerosol transmission of PRRS virus. Recently, the particle concentration, size distribution, and infectivity of PRRS virus emitted by infected pigs, were found associated with a wide range of particle sizes that can deposit throughout the respiratory tract and later be swallowed. PRRS virus viability was particle size dependent with virus isolated only from particles larger than 2.1 µm, supporting the relevance of the aerosol route in the transmission PRRS4.

Air filtration: In human medicine, air filtration is part of the so called -respiratory protection against biologic agents present in bio-aerosols-. These programs include individual and collective protection, mainly in health centers and other places with some risk of airborne diseases.
PRRS virus and air filtration: After several publications on PRRS virus aerosol transmission, not always conclusive or based on partially controlled studies, in 2009 a relevant study using a production region model was published7. It involved a PRRS virus infected population of pigs (source), and two naïve populations of pigs (recipients), housed in separate buildings located 120 meters away. The two recipient barns employed identical biosecurity protocols apart from the installation of bio-aerosol filtration in one barn. Non-filtered populations became infected in 8 of 26 replicates over a one year period, while none of the 26 recipient replicates in filtered barns were infected. It was demonstrated that strict bio-security measures alone were not sufficient at preventing introduction of PRRS virus into the non-filtered populations. For the first time, the effect of bio-aerosol filtration was being studied under semi-controlled conditions5, 6. In this video the principles of air filtration are explained:


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