Science Page: Stability of Porcine Epidemic Diarrhea Virus on Fomite Materials at Different Temperatures

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week, we are sharing the summary of Dr. Cheeran’s team study on the stability of PEDv on fomite materials at different temperatures.

Key points:

  • Type of material and temperature have an impact on PEDV stability.
  • Infectious PEDV was not recovered from any fomite material after 2 days at room temperature (25ºC / 77ºF).
  • PEDV showed higher stability on plastic, cloth, Tyvek® coveralls, aluminum foil, Styrofoam at 4ºC (39.2ºF).
  • Virus could be detected by qRT-PCR from contaminated fomites even when infectivity was not observed.

PEDV survival on fomites Cheeran et al

Click here for our full post on the subject.

Stability of Porcine Epidemic Diarrhea Virus on Fomite Materials at Different Temperatures

Today, we are presenting a paper published by Dr. Maxim Cheeran‘s lab in Veterinary Sciences regarding the stability of PEDV on fomite materials at different temperatures.

The full article is available in open access on the journal’s website.

Porcine Epidemic Diarrhea virus and its transmission

Porcine epidemic diarrhea virus (PEDV) causes highly contagious viral enteritis in swine. In May 2013, a PEDV strain, genetically related to a Chinese strain, was introduced in the US and spread rapidly across the country causing high mortality in piglets. Over eight million pigs were killed during this outbreak, leading to an estimated loss of 1.8 billion US dollars.

Transmission of PEDV primarily occurs by the fecal-oral route, but indirect transmission can occur when an animal comes in contact with inanimate objects (fomites) contaminated with the feces of PEDV-infected animals.

Methods

200 μL of virus containing 2.1 × 106 TCID50/mL was applied on various fomite material: Styrofoam, nitrile gloves, cardboard, aluminum foil, Tyvek® coveralls, cloth, metal, rubber, and plastic. The virus-contaminated fomites were then stored at either 4◦C or at room temperature. Samples were then taken at 0,1 2, 5, 10, 15, 20 and 30 days post-contamination to test for virus stability.

PEDV survival on fomites Cheeran et al

Results

Infectious PEDV was recovered from fomite materials for up to 15 days post application at 4◦C; only 1 to 2 logs of virus were inactivated during the first 5 days post application. On the other hand, PEDV survival decreased precipitously at room temperature within 1 to 2-days post application, losing 2 to 4 log titers within 24 h as can be seen on the figure above.

Immunoplaque assay was used to identify positive fomites after 20 days of storage at 4◦C. Immunoplaque assay is much more sensitive than PCR and can detect virus as low concentration as 24 focus forming units/mL. Titers of approximately 1 × 10^3 FFU/mL were observed in eluates from Styrofoam, metal, and plastic, representing a 3-log virus inactivation after 20 days. The surviving virus on Tyvek® coverall and rubber surfaces was moderately above detection limit (24 FFU/mL).

Abstract

Indirect transmission of porcine epidemic diarrhea virus (PEDV) ensues when susceptible animals contact PEDV-contaminated fomite materials. Although the survival of PEDV under various pHs and temperatures has been studied, virus stability on different fomite surfaces under varying temperature conditions has not been explored. Hence, we evaluated the survival of PEDV on inanimate objects routinely used on swine farms such as styrofoam, rubber, plastic, coveralls, and other equipment. The titer of infectious PEDV at 4 °C decreased by only 1 to 2 log during the first 5 days, and the virus was recoverable for up to 15 days on Styrofoam, aluminum, Tyvek® coverall, cloth, and plastic. However, viral titers decreased precipitously when stored at room temperature; no virus was detectable after one day on all materials tested. A more sensitive immunoplaque assay was able to detect virus from Styrofoam, metal, and plastic at 20 days post application, representing a 3-log loss of input virus on fomite materials. Recovery of infectious PEDV from Tyvek® coverall and rubber was above detection limit at 20 days. Our findings indicate that the type of fomite material and temperatures impact PEDV stability, which is important in understanding the nuances of indirect transmission and epidemiology of PEDV.

Science page: Evaluation of biosecurity measures to prevent indirect transmission of PEDV

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

The objective of the study presented today was to evaluate the efficacy of of biosecurity procedures directed at minimizing transmission via personnel following different protocols in controlled experimental settings.

Four (4) groups were housed in different rooms:

  • INF: Pigs infected with PEDV
  • LB: Naive pigs which were exposed to personnel coming from the INF room without changing PPE at all
  • MB: Naive pigs which were exposed to personnel coming from the INF room after washing their hands and face as well as changing footwear and clothing.
  • HB: Naive pigs which were exposed to personnel coming from the INF room after showering as well as changing clothing and footwear.

Results are shown in the figure below. Naive pigs were exposed to personnel from 44h after the pigs in the INF group were infected with PEDV until 10 days post infection.

PEDV indirect transmission biosecurity measures
Viral shedding of pigs. Movements were terminated at 10 dpi. Data presented are average values of viral RNA copies (± SD) of infected (INF), low biosecurity (LB), medium biosecurity (MB) and high biosecurity (HB) groups

Key points:

  • PEDV transmission is likely to occur with contaminated fomites in low biosecurity scenarios.
  • Indirect contact transmission of PEDV can happen very rapidly. Transmission was detected 24h after personnel moved from infected to low biosecurity rooms (no change in clothes, boots or washing hands)
  • Changing PPE (personal protective equipment) and washing skin exposed areas is beneficial to decrease the risk of PEDV transmission.

 

Link to the facilities diagram explaining the experiment setup as well as the results on PEDV indirect transmission in this study.

Bioaerosol sampling for airborne virus surveillance in swine facilities

Bioaerosol sampling refers to the methods by which one is able to collect the particles of biological origin (microbial, animal, or plant) in the air. This is useful information in swine production because many economically important pathogens can be transmitted by air from one farm to the next. 73 scientific reports were included in this review published in the journal Frontiers in Veterinary Science. The information regarding the presence of viruses in the air around swine settings is limited but their findings has been compiled in the figure below. Overall, bioaerosol sampling could be a promising way to conduct non-invasive viral surveillance among swine farms.

Viruses detected in radisuses around farms
Influenza A, PRRSV, PEDV detection downwind from farms with infected source populations

Abstract

Modern swine production facilities typically house dense populations of pigs and may harbor a variety of potentially zoonotic viruses that can pass from one pig generation to another and periodically infect human caretakers. Bioaerosol sampling is a common technique that has been used to conduct microbial risk assessments in swine production, and other similar settings, for a number of years. However, much of this work seems to have been focused on the detection of non-viral microbial agents (i.e., bacteria, fungi, endotoxins, etc.), and efforts to detect viral aerosols in pig farms seem sparse. Data generated by such studies would be particularly useful for assessments of virus transmission and ecology. Here, we summarize the results of a literature review conducted to identify published articles related to bioaerosol generation and detection within swine production facilities, with a focus on airborne viruses. We identified 73 scientific reports, published between 1991 and 2017, which were included in this review. Of these, 19 (26.7%) used sampling methodology for the detection of viruses. Our findings show that bioaerosol sampling methodologies in swine production settings have predominately focused on the detection of bacteria and fungi, with no apparent standardization between different approaches. Information, specifically regarding virus aerosol burden in swine production settings, appears to be limited. However, the number of viral aerosol studies has markedly increased in the past 5 years. With the advent of new sampling technologies and improved diagnostics, viral bioaerosol sampling could be a promising way to conduct non-invasive viral surveillance among swine farms.

Link to the full article

Science Page: Analyzing swine movement patterns in relation with PEDV

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

The movement of live pigs between farms is an important mechanism for disease introduction and spread. Thus, understanding the structure of livestock contacts and studying the routes, volumes, frequency, and the risks associated with animal movement is a prerequisite for effective disease surveillance and control in animal populations.
At the same time, local area spread between neighboring farms is also implicated in the spread of viruses such as porcine epidemic diarrhea virus (PEDV) and porcine reproductive and respiratory syndrome virus (PRRSV).

Even after controlling for hog density and season of the year, we showed that the number of pigs received into neighboring farms was an important predictor of PED infection risk.

relative importance of parameters in predicting PEDV
Relative importance in predicting risk, according to the Gini index

Key Points

  • Between farm transmission research in swine has primarily come from small studies rather than large scale datasets.
  • By looking at environmental/landscape, pig movements, and spatial factors, we studied the likelihood of a farm contracting PED from it’s neighbors.
  • It was found that the number of pigs received by neighboring farms was an important predictor of PEDV infection risk.

Click here to see the full Science page report on the various parameters and their relative importance in predicting risk of PEDV infection.

Effect of different treatments on the inactivation of Porcine Epidemic Diarrhea virus (PEDv) in swine feed

Last Friday, a team of UMN swine nutritionists and veterinarians published the results of their research on the effect of thermal treatments and additives on the inactivation and survival of Porcine Epidemic Diarrhea virus (PEDv) in swine feed. They concluded that both the addition of feed additives and thermal treatments decreased PEDv load in the feed.

journal.pone.0158128.g001

Fig 1. Inactivation of PEDV in complete feed when exposed to thermal processing.
The inactivation curves determined by the Weibull model for the survival of PEDV in complete feed at 120°C, 130°C, 140°C, and 145°C.

 

Abstract: Infection with porcine epidemic diarrhea virus (PEDV) causes diarrhea, vomiting, and high mortality in suckling pigs. Contaminated feed has been suggested as a vehicle of transmission for PEDV. The objective of this study was to compare thermal and electron beam processing, and the inclusion of feed additives on the inactivation of PEDV in feed. Feed samples were spiked with PEDV and then heated to 120–145°C for up to 30 min or irradiated at 0–50 kGy. Another set of feed samples spiked with PEDV and mixed with Ultracid P (Nutriad), Activate DA (Novus International), KEM-GEST (Kemin Agrifood), Acid Booster (Agri-Nutrition), sugar or salt was incubated at room temperature (~25°C) for up to 21 days. At the end of incubation, the virus titers were determined by inoculation of Vero-81 cells and the virus inactivation kinetics were modeled using the Weibull distribution model. The Weibull kinetic parameter delta represented the time or eBeam dose required to reduce virus concentration by 1 log. For thermal processing, delta values ranged from 16.52 min at 120°C to 1.30 min at 145°C. For eBeam processing, a target dose of 50 kGy reduced PEDV concentration by 3 log. All additives tested were effective in reducing the survival of PEDV when compared with the control sample (delta = 17.23 days). Activate DA (0.81) and KEM-GEST (3.28) produced the fastest inactivation. In conclusion, heating swine feed at temperatures over 130°C or eBeam processing of feed with a dose over 50 kGy are effective processing steps to reduce PEDV survival. Additionally, the inclusion of selected additives can decrease PEDV survivability.

Link to the full article