Feature: Microbial filters provide a new line of defence against PRRS

Friday, May 30, 2008

Danbred is the first in Ontario to install the filters in its barn and a Quebec study indicates that they are 95 per cent successful in cutting down on aerosol transmission of the disease

by KATE PROCTER

For decades, pork producers have introduced increasing levels of biosecurity to keep costly diseases out of their herds. Yet Porcine Reproductive and Respiratory Syndrome virus (PRRS) still manages to elude the best efforts at keeping it out.

This has led breeding stock company Danbred North America to tackle one of the toughest areas of transmission – aerosol. Danbred is the first in Ontario to install Canadian-designed filters at their boar stud, hoping to keep their PRRS-negative boars safe from the virus.

"We installed antimicrobial filters to filter all the air because there is so much PRRS in Ontario," says Danbred operational manager Dave Riach. "PRRS is expensive and, after going through it, I have a lot more empathy. As an industry, we have to help each other out so that we don't get it," he adds. 

Danbred decided to purchase Novek O2 Antimicrobial Air filters, which are designed and manufactured in Canada by Noveko Inc. The filters provide three layers of protection. The first takes out large particles, including insects; the next has three layers of antimicrobial filtering material; and the third includes seven layers of antimicrobial filtration. 

Riach explains that they went with this filter instead of Hepa, another type that has been installed in all of the Danbred studs in the United States. While the Novek filters cost about $10 - $15 more, they have a longer lifespan and can be cleaned, so will prove less expensive in the long run. A 24-by-24-inch filter costs about $200 and is expected to have a lifespan of four to five years. The Novek filters also restrict airflow less than Hepa filters.

The Danbred stud completely redid all the ventilation, which needed updating, says Riach, and installed the filters during February, when the barn was empty due to a PRRS outbreak in January. All the air entering the barn during prime PRRS season – September through May or June – will be filtered. The filters slightly restrict airflow, so the air will not be filtered during the summer. 

"The barns have to be pretty tightly sealed," says Riach. His staff caulked around every door, window and plywood joint and runs the barn at negative air pressure. All the air that enters the barn comes in through the attic. 

They also improved other areas of biosecurity in the stud. Employees shower before going in and coming out, and access is restricted only to necessary service people and veterinarians. They have also increased their tool inventory, so that fewer tools have to be brought into the barn, and all supplies that do come in sit for three days and are misted with disinfectant before entering the barn.

Riach says the fans still run in the same manner as they did before the filters were installed and there is no additional operating cost. They did add some circulating fans inside the barn and, overall, there is better air quality and movement, he notes. 

The filter was recently evaluated in a study developed by the Centre de developpement du porc du Québec (CDPQ) and Dr. Laura Batista from the Faculté de medicine veterinaire de l'Université de Montréal (FMV). The FMV estimates that PRRS annually costs Canadian pork industry up to $150 million. The losses in a farrow-to-finish operation with endemic infection vary between $6.25 and $15.25 per pig.

The objective of the study was to evaluate the ability of this filter, which is embedded with viricide, bactericide and fungicide, to reduce or avoid aerosol PRRSV transmission under experimental conditions. The full report of this research can be obtained online at www.cdpqinc.qc.ca and www.agrireseau.qc.ca/porc. 

The study concluded that, regardless of the sow barn size, over 10 years, the cost would be $1.76 per weaned piglet. Two thirds of this cost is due to replacing the filters, with initial installation and purchase accounting for the remaining third.

The researchers found that the filters had a 95 per cent success rate, reducing aerosol transmission of PRRSV in 19 of 20 replicates. In the study, the nozzle of the aerosolizer was directed straight at the filter and a very large quantity of virus was used.

In field conditions, researchers expect that a combination of the air filtration that they studied, together with other preventative measures, may provide a high level of biosecurity against PRRS. BP