PEDV survivability and disinfection researched

PEDV survivability and disinfection researched

Research continues to find the best ways to battle herd infections of porcine epidemic diarrhea virus.

Disinfection continues to be an important topic and area of interest for the swine industry. For many years, the focus of our biosecurity and disinfection protocols was porcine reproductive and respiratory syndrome.

Although PRRS continues to be the most important swine disease in the United States, the recent emergence of porcine epidemic diarrhea has lead the swine industry to broaden the primary targets of biosecurity measures to other pathogens, not just PRRS.

The 2013 introduction of PED into the United States resulted in a gap of knowledge in trying to understand the survivability of this pathogen in the environment and what disinfectants would work against this emerging virus.

PED virus is an enveloped, single-stranded RNA virus under the Coronaviridae family which also includes transmissible gastroenteritis virus. Traditionally enveloped viruses, like PEDV, tend to be less durable in the environment as compared to non-enveloped virus like porcine circovirus type 2. Many studies have been done in the past few years working to confirm this susceptibility as cleaning and disinfection play a critical role in biosecurity which is of utmost importance in disease control and elimination. Research and clinical experience have highlighted two characteristics of PEDV infections that re-emphasize the importance of proper cleaning and disinfection.

1. Animals infected with PEDV, especially piglets, will shed extremely large amounts of virus in their feces.

2. The infectious dose for PEDV, especially in piglets, is extremely low meaning it takes very few virus particles to infect a piglet.

Several studies have shown that samples can be diluted several fold so as to become polymerase chain reaction-negative, yet can still contain enough virus to infect piglets. Thomas et al., (2015) showed that 5-day old piglets had a minimum infectious dose around 1,000 fold less than that required by 21-day old pigs. Niederwerder, et al., (2016) have shown that in 4-week old pigs, shedding occurs primarily during the first two weeks with peak shedding occurring at days 5-6. Shedding can occur for a long time and was still detected via PCR for four weeks post-infection.

PEDV pathogen survival
The PEDV can survive for variable periods outside the pig depending on the temperature and relative humidity. Because PEDV is shed primarily in feces, there has been a great emphasis to better understand its survivability in manure pits and lagoons. Tun et al., (2016) recently reported that PEDV could survive up to nine months in infected lagoons after the initial farm outbreak. They evaluated the amount of viral load (amount of genetic material) present at different levels of two lagoon waters. The viral load averaged 1.1 × 105 copies per milliliter independent of lagoon temperature (0-52 F) and pH (range 6.8 to 8.4). Viral load in the top layer of the lagoons was low and mostly non-infective based on pig bioassay, suggesting that environmental factors, such as UV and sunlight, could diminish the replicability and infectivity of the virus. Interestingly the researchers reported evidence of viral replication observed through increased viral load in the later weeks after samplings while there was no new influx of infected manure into the lagoon. The cause for this increase is unknown.

In a 2014 National Pork Board Research update, Steven Tousignant for Swine Vet Center in Minnesota, reported sampling 30 manure pits from barns in southern Minnesota and northern Iowa. He found that on average, pits had a PCR cycle threshold value of about 30, indicating a relatively high amount of viral genetic material present and through swine bioassay, manure from two barns was still infective four months after having PEDV-positive pigs.

Based on swine bioassay testing, Verma et al. (2014), have shown PEDV survives in fresh feces for seven days at both 104 F and 122 F and for three days at 140 F. In slurry, virus was infectious for ≥28 days at -4 F, 39 F and 77F. In drinking and recycled water, PEDV survived for one and two weeks, respectively.

The survival of PEDV on metal surfaces alone based on time and temperature are reported in Tables 1 and 2, along with several disinfection protocols.

PEDV disinfection
These high-shedding volumes and low required infectious dose re-emphasize the critical role of proper cleaning and definition in mitigating PEDV spread. The following is a summary of some of the relevant published research in regards to PEDV survival and disinfection. Additional studies are under way so this information continues to grow. For a general review on disinfectants please review “Four steps to effective cleaning and disinfecting.”

When looking at the effectiveness of disinfection, it is important to remember that currently the best way to confirm infectivity for PEDV is the swine bioassay. PCR technology is a highly sensitive and great technology, but unfortunately it detects genetic material (DNA or RNA) and does not distinguish infectious from non-infectious material. In other words, disinfectants can actually kill/inactivate PEDV, yet the genetic material may still be left behind and detected by PCR technology. For example, Radke et al. (2016), showed that after power washing, disinfecting and 10 days of downtime, 75% of their environmental swabs still tested positive for PEDV by PCR yet weaned pigs placed on site after this time period did not show any clinical signs of PEDV. For PEDV infectivity, swine bioassays are also preferred over cell culture assays which are less sensitive and may be affected by feces and disinfectant present in a sample that may destroy the cells in the cell culture.

For disinfectants Tables 1 and 2 summarize the reported results from research regarding the effectiveness of different times and temperatures on infectivity of PEDV. Refer to the reference section for complete details on these research protocols.

It is also good to note that a 2014 OIE (World Health Organization for Animal Health) summary reports PEDV is susceptible to Formalin (1%), anhydrous sodium carbonate (4%), lipid solvents, iodophores in phosphoric acid (1%) and sodium hydroxide (2%).

Summary
This article emphasizes the current data available regarding the survivability of PEDV in manure as well as the effectiveness of different disinfection protocols. It is critical to remember that this particular virus is being shed in extraordinary quantities and that the infectious dose is extremely small, thus cleaning and disinfection practices must be done correctly and thoroughly to prevent disease spread. In absence of disinfectants, high temperatures (≥160 F for at least 10 minutes) or longer periods of time (≥7 days at room temperature) may be used to inactivate contaminated aluminum trailer surfaces.

References
Bowman AS, Nolting JM, Nelson SW, Bliss N, Stull JW, Wang Q, Premanadan C. Effect of disinfection on the molecular detection of porcine epidemic diarrhea virus. Vet Microbiol. 2015:179 (3-4);213-218.

Holtkamp DJ, Gerardy KL, Thomas PR, Karriker LA, Ramirez A, Zhang J, and Wang C. Update on PEDV inactivation on swine trailers. Proc. ISU James D. McKean Swine Disease Conference. 2015:31-33.

Niederwerder MC, Nietfeld JC, Bai J, Peddireddi L, Breazeale B, Anderson J, Kerrigan MA, An B, Oberst RD, Crawford K, Lager KM, Madson DM, Rowland RRR, Anderson GA, and Hesse RA. Tissue localization, shedding, virus carriage, antibody response, and aerosol transmission of porcine epidemic diarrhea virus following inoculation of 4-week-old feeder pigs. J Vet Diagn Invest. 2016:1-8.

OIE. Infection with Porcine epidemic diarrhea virus. OIE Technical Factsheet. 2014:1-4.

Radke S, Pitkin A, Nelson E, and Neuberger D. Evaluation of disinfectants to neutralize porcine epidemic diarrhea virus. Proc Am Assoc Swine Vet. 2016:117-118.

Thomas JT, Chen Q, Gauger PC, Giménez-Lirola LG, Sinha A, Harmon KM, et al. Effect of Porcine Epidemic Diarrhea Virus Infectious Doses on Infection Outcomes in Naïve Conventional Neonatal and Weaned Pigs. PLoS ONE 2015:10(10);e0139266.

Thomas P, Karriker LA, Ramirez A, Zhang J, Ellingson JS, And Holtkamp DL. Methods for inactivating PEDV in hog trailers. Proc. ISU James D. McKean Swine Disease Conference. 2014:43-50.

Tun HM, Cai Z, and Khafipour E. Monitoring Survivability and Infectivity of Porcine Epidemic Diarrhea Virus (PEDV) in the Infected On-Farm Earthen Manure Storages. Frontiers Microbiol. 2016:7:265.

Verma H, Erber J, Goede DP, Morrison RB, Goyal SM. Survival of Porcine Epidemic Diarrhea virus in environmental samples. Proc Allen D. Leman Swine Conference. 2014:20.

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