May 01, 2003


 Critical thinking

Veterinarian questions some biosecurity measures

Posted April 15, 2003

Just because something is the gold standard doesn't mean you can't question it. According to Dr. Scott Dee, an associate professor at the University of Minnesota's Swine Disease Eradication Center, this is true for some biosecurity measures. At the AASV annual meeting, Dr. Dee shared his doubts about two biosecurity measures—personnel downtime and birdproofing facilities.

"These protocols are based on very old papers which probably couldn't be reproduced today," Dr. Dee said to convention-goers.

Today, veterinarians are being forced to follow downtime policies of 48 and even 72 hours. The 48-hour rule, however, is based on three somewhat old publications that assessed the ability of people to harbor foot-and-mouth disease and Mycoplasma hyopneumoniae, Dr. Dee said.

A 1985 study in the Veterinary Record reported the recovery of foot-and-mouth disease from the nares of personnel exposed to infected animals at 28 hours after exposure, but not 48 hours. Two other studies in the early 1970s, one in the Journal of Hygiene and the other in the Veterinary Record, could not recover M hyopneumoniae from the breath or hair of exposed personnel, but could recover the organism from clothing over a 24- to 48-hour postinfection period. These studies are the basis of the 48-hour rule. Others have taken it one step further and are following a 72-hour rule, just to be safe.

"These are very difficult, costly procedures. Twenty-four, 48, 72—that's a lot of time down. We all know what pressure that puts on our schedules," Dr. Dee said. "I think that overall, there is mounting evidence that some of it is very unnecessary."

Recent work by Dr. Sandy Amass, an assistant professor of veterinary clinical sciences at Purdue University, and Dr. Laura Batista, a swine researcher at the University of Minnesota, is providing evidence to refute these early studies. Their studies indicate shorter recovery times of FMD virus from people and the inability of personnel to spread M hyopneumoniae from infected to naïve herds, despite multiple attempts over extended periods of time.

In addition, recent work by University of Minnesota researcher Dr. Satoshi Otake demonstrates that personnel who follow basic sanitation protocols do not harbor or transmit porcine respiratory and reproductive syndrome. And other work by Purdue researcher Dr. Roberta Alvarez showed that sanitation-abiding personnel did not harbor or transmit transmissible gastroenteritis virus.

"The human body has very limited means of harboring these agents and bringing them onto the farm," Dr. Dee said. "If you do some basic sanitation, you can remove the risk of taking the pathogen into a herd."

Standard operating protocols for sanitizing exposed personnel are quite effective, he said; swine veterinarians should think about reducing the length of downtime to 12 hours.

Dr. Dee also has doubts about the benefits of birdproofing facilities. A single paper, he says, describing an experiment where starlings transmitted TGE virus up to 32 hours after feeding on a suspension of TGE virus, has been the foundation for keeping birds out of swine facilities. This American Journal of Veterinary Research paper, however, was published in 1965. Starlings and sparrows are not biological vectors of PRRSV. And while one paper has suggested that Mallard ducks can transmit PRRSV, Dr. Dee says that his research group, as well as two others, couldn't replicate its results. Even after Dr. Dee provided Mallard ducks with close contact with infected pigs for a 21-day period, the ducks did not contract the virus.

"I'll argue that there is more evidence of transmission of pathogens by insects than there truly is of birds," Dr. Dee said. Several studies have shown that PRRSV, TGE virus, Streptococcus suis, pseudorabies virus, African swine fever virus, and classical swine fever virus have been recovered from insects, mainly houseflies, and can be transmitted to pigs. And recent work by Dr. Otake has shown that PRRSV can be detected in the gastrointestinal tract of houseflies.

The bottom line, Dr. Dee argues, is that practitioners owe it to their clients to constantly challenge and reevaluate biosecurity protocols. "We always have to challenge ourselves, challenge the work that is out there, and think out of the box," he said.