A triad of research trials shows porcine reproductive and respiratory syndrome (PRRS) virus can be spread by contaminated hands of personnel following contact with infected pigs, needles, coveralls, boots and mosquitoes.

University of Minnesota researchers found no evidence of aerosol transmission of PRRS virus to pigs housed in facilities located within 1-30 yds. from buildings that housed infected animals.

In the first experiment, 10 pigs were infected with PRRS virus to test for transmission by people and needles. Five people spent one hour with the infected pigs, contacting secretions and bodily fluids excreted from the infected animals. Then, each person spent 30 min. with three naive pigs in one of five other rooms, again contacting all pigs. Before moving to the second room, the people either:

  • Did not change coveralls and boots or wash hands;

  • Changed coveralls and boots and washed hands;

  • Changed coveralls and boots, showered and waited for 12 hours of downtime;

  • Changed coveralls and boots, showered and waited for no downtime; or

  • In the fifth room, needles were used to vaccinate the infected and naive pigs for Mycoplasma pneumonia.



The researchers found that PRRS virus was transmitted by the coveralls, boots and needles in two of the four replicates of the study. PRRS virus was detected on the coveralls, boots and hands of personnel upon leaving the infected room. PRRS virus was not transmitted when people changed coveralls and boots and either washed their hands or showered.

In the second study, the researchers used a mechanically ventilated, partially slotted finishing barn to test for aerosol transmission of PRRS.

One hundred and forty pigs were infected with PRRS and commingled with 60 direct-contact control pigs. A pen of 10 control pigs was separated in the barn by an empty 8-ft.-wide pen. Two stock trailers, with 10 naive sentinel pigs each, were set up either 1 yd. or 30 yd. directly in line with the barn's exhaust fans. Contact of the pigs with the exhaust was confirmed in the trailer located 1 yd. from the infected barn on a daily basis.

The pigs were held in the trailers for 72 hours and then moved to two other barns (30 and 80 yd. from the infected facility) on the site and tested for 30 days.

PRRS virus was transmitted to the direct-contact, control pigs commingled with the infected pigs. The pigs separated by the empty pen space also became infected. However, the pigs held in the trailers did not become infected.

In the third experiment, the researchers examined if mosquitoes could transmit PRRS to naive pigs.

First, during an experimental PRRS virus infection on the research site, the researchers collected blood-fed mosquitoes from the barn and tested them for PRRS virus. They found the same PRRS virus strain in both the pigs and mosquitoes.

Second, an experimental study was conducted using 12, 6-week-old pigs (three pigs in four replicates). In each replicate, a donor pig infected with PRRS virus, a recipient pig naive to PRRS and a control pig were housed in separate rooms. The control pig received the same treatment, without mosquitoes, as the recipient pig.

Mosquitoes were collected and tested to show they were PRRS-virus-negative.

The mosquitoes were allowed to bite the infected (donor) pig for 30 to 60 seconds. Then, the mosquitoes were removed and allowed to bite the naive (recipient) pig.

In two of the four replicates, the recipient, naive pigs became infected with PRRS virus and homogenates from pooled mosquito tissues were PRRS-virus-positive.

The researchers plan more studies on the cause of area spread of PRRS virus, including more work on mosquitoes, house flies and transport vehicles.

Researchers: Scott Dee, Satoshi Otake, Kurt Rossow, Roger Moon, Tom Molitor and Carlos Pijoan, University of Minnesota. Phone Dee at (612) 625-4786 or e-mail deexx004@umn.edu.

Zinc's Impact on E. coli Scours

Zinc oxide has a big impact on E. coli scours, says Mike Tokach, extension swine specialist, Kansas State University.

At low levels, zinc is an essential nutrient. At high levels, zinc is a growth promotant. “Most people would use about 3,000 ppm. in the diets until the pigs were about 15 lb.,” he says. “We then recommend 2,000 ppm. from 15 lb. to 25 lb. Then we pull it out of the diets.” Some people leave it in a little longer at a low level.

“Our data suggests you don't get any benefit in growth performance past 25 lb.,” states Tokach, even though pigs aren't past the danger of breaking with F18 E. coli scours.

“Zinc oxide doesn't cure E. coli,” he declares, “But if you've got normal E. coli problems and you pull it out, the E. coli will be a lot worse.”

In a research report, Tokach and collaborators point out there are several suppositions as to why zinc oxide can reduce diarrhea problems in both pigs and people. In one study, the addition of zinc at 2,500 ppm prevented postweaning diarrhea without affecting the number of E. coli excreted in the feces.

Similar experiments showed that a high prevalence of diarrhea occurred when pigs did not receive high concentrations of zinc oxide when challenged.

Other experiments also indicated that zinc apparently does not reduce the number of E. coli present, but interferes with the ability of the E. coli to produce a toxic environment in the gut.

Researchers: Lisa Tokach, DVM, Abilene Animal Hospital, Abilene, KS; Steve Dritz, DVM, and Mike Tokach, both of Kansas State University. Phone Tokach at (785) 532-2032 or e-mail mtokach@oz.oznet.ksu.edu.

E. coli Concerns Turn to Flooring

Missouri has seen substantial growth in swine enteric disease problems in early weaned pigs, particularly in young pigs moved to wean-to-finish (W-F) facilities.

“In many cases, highly toxigenic strains of E. coli have been isolated. The problem has been significant in some systems, so much so that the University of Missouri is collaborating with Stress Physiologist Jeff Carroll from the Animal Physiology Research Unit of the USDA's Agricultural Research Service (both are located in Columbia, MO) on a two-year project to study pathogenic E. coli,” reports Tom Fangman, University of Missouri swine extension veterinarian.

Treating E. coli with antibiotics has not been very successful, he says. Sometimes, pigs appear better off left untreated.

Fangman says newer floor designs may have played a role in the resurgence of enteric pathogens. Plastic-coated wire floors used in conventional nurseries reduce scours problems because pigs walk most of the defecation through the slots and the floors clean up well.

Slotted floors in newer W-F barns provide a solid, warm surface for younger weaned pigs. But they also promote growth of bacterial organisms because some manure remains on the slats and often they are not properly cleaned.

One possible solution is to use a hand-held sprayer to sanitize the slats. Use a wooden divider to confine pigs out of the way to spray the slats with a disinfectant, suggests Fangman.

Researchers: Tom Fangman, DVM, University of Missouri, and Jeff Carroll, USDA's Agricultural Research Service. Phone Fangman at (573) 882-7848 or e-mail FangmanT@missouri.edu.