Disinfecting livestock transport vehicles is a primary step in stopping porcine reproductive and respiratory syndrome (PRRS) virus transmission.

Porcine reproductive and respiratory syndrome is commonly regarded as the most serious threat to the global swine industry. In the United States alone, losses are estimated between $560 and $760 million/year.

The PRRS virus affects pigs of all ages and causes respiratory disease, infertility, early embryonic death, late-term abortion and a high incidence of stillborn and weak newborn pigs.

Effective control of PRRS starts by limiting transmission of the virus between hog units. Livestock transport vehicles have been proven to be major vectors in the transmission of the virus, making decontamination of vehicles, especially in large establishments, vital to PRRS control.

Recent Disinfectant Tests

Under the direction of PRRS researcher Scott Dee, DVM, the Swine Disease Eradication Center at the University of Minnesota, three DuPont Animal Health Solutions' disinfectants — Virkon S, BioSentry 904 and BioPhene — were tested for effectiveness against PRRS virus in commercial livestock trailers.

The transport vehicles were represented by four, 1:150 scale models of weaned pig trailers which were initially contaminated with PRRS virus MN 30-100.

In the trials, one of the trailers was washed only (without disinfectant) to provide a positive control. Three other trailers were washed, then disinfected with one of the three DuPont disinfectants. All three products were applied with a hydrofoamer and the temperature of the water used was approximately 39° F (4°C) to reflect realistic farming conditions.

Stringent polymerase chain reaction (PCR) tests, commonly used to measure the PRRS virus at low levels, were then carried out on the four model trailers. Swabs were used to collect samples from the trailers at 0, 30, 60, 90 and 120 minutes post-treatment to confirm the presence or absence of PRRS virus.

Additionally, pigs were challenged with supernatants (clear liquid overlying material deposited by settling) from swabs collected 60 minutes after treatment. The swabs were then tested serologically for presence of PRRS virus to provide a swine bioassay.

In a separate trial, naïve sentinel pigs were housed in the scale model contaminated trailers for two hours, starting 90 minutes after treatment, and monitored serologically to assess levels of infection.

The results in Table 1 show the high level of efficacy of the DuPont disinfectants tested against the PRRS virus.

Importantly, after 90 minutes both Virkon S and BioSentry 904 provided 100% effectiveness in every test in preventing the spread of PRRS virus in livestock transport.

Testing Other Products

In earlier trials at the University of Minnesota, Dee tested the efficacy of Synergize, a disinfectant from Preserve International, also used for control of the PRRS virus in livestock trailers.

Scale-model trailers bedded with wood shavings were “contaminated” with live PRRS virus and treated with a variety of sanitation methods. Treatments included wash only (cold water), formaldehyde fumigation, Synergize disinfectant and the effectiveness of an eight-hour drying time.

Ninety minutes post-treatment, trailer interiors were monitored by PCR for PRRS virus using swabs for virus collection. Sentinel pigs placed in treated trailers were checked for infection. PRRS-naïve pigs exposed to residual wood shavings collected from trailer interiors were also tested for infection (swine bioassay). Table 2 details the results showing that when Synergize was used to disinfect trailers, zero level of infection was recorded.

When Synergize was fogged for 10 minutes into PRRS virus-infected trailers, only one swab of 11 tested positive for PRRS at 30 minutes post-treatment, and zero swabs at 60 minutes post-treatment.

When Synergize was foamed into a PRRS-infected trailer, only two of 14 swabs detected PRRS virus at 30 minutes post-treatment and zero of 14 swabs recorded PRRS virus at 60 minutes post-treatment.

In a cold weather disinfectant trial conducted by Dee, only two of 12 swabs from PRRS-contaminated trailers treated with Synergize tested positive for the presence of the virus at 39 F at 30 minutes post-treatment. At 60 minutes post-treatment, zero of 12 samples had PRRS virus.

In an extreme cold weather test (-4° F), none of the swabs collected from PRRS-treated trailers disinfected with Synergize were positive for PRRS.

Conclusions

To meet the transport needs of hog production systems, disinfectants for elimination of the PRRS virus in livestock trailers must prove efficacious in two hours or less, according to Dee.

During the tests of the disinfectants reviewed, Dee stresses there were differences between the tests, some of the methods used, and products were tested independently of each other.

“The major difference in the two sets of trials was that in the DuPont trial, we used a low-pressure foamer, and in the Synergize trials, results were mostly based on fogging,” he explains. “We've learned that fogging is not the best means of applying a disinfectant because it doesn't get to where you think it needs to go.”

There is a subset of disinfectants that through the use of low-pressure foaming are equally effective at eliminating the PRRS virus in livestock transport, notes Dee. “Those disinfectants are Virkon S, BioSentry 904 and Synergize,” he says.

Dee lists four items of importance when disinfecting livestock transport vehicles:

  • Pick the right product that has been scientifically tested and shown to be effective;

  • Consider the method of application;

  • Review product concentration; and

  • Analyze contact time needed for effective application.

Consult with your swine veterinarian to ensure proper dilution rate, application method and contact time, he adds.

Product irritation and cost are other individual issues to be decided.

Sums up Dee: “One product is not going to do everything, so each person has got to make their own decision on what is best for them.”

Table 1. Disinfectants Tested Against PRRS Virus
Virkon® S BioSentry 904 BioPhene Positive Control
PCR Testing of Swabs Positive Positive Positive Positive
0 minutes 20/20 20/20 20/20 20/20
30 minutes 20/20 20/20 20/20 20/20
60 minutes 8/20 12/20 11/20 20/20
90 minutes 0/20 0/20 0/20 20/20
120 minutes 0/20 0/20 2/20 Suspect 18/20
Swine bioassay 0/4 0/4 1/4 4/4
Trailer Infection 0/4 0/4 0/4 3/4
Table 2. Results in Trailers Sampled 90 Minutes Post-Treatment
Treatment PCR-Positive Swabs Sentinel Pigs Infected Swine Bioassay*
Wash only 20/20 2/4 2/4
Formaldehyde fumigation 20/20 2/4 2/2
Synergize 0/19 0/4 0/2
Eight-hour drying 0/20 0/4 0/2
*Sampling reflects positive PRRS virus swabs collected for each method of cleanup or exposure of pigs to the trailer environment.