A Porcine Epidemic Diarrhea Virus Outbreak in One Geographic Region of the United States: Descriptive Epidemiology and Investigation of the Possibility of Airborne Virus Spread

Abstract

This study describes a spring 2013 outbreak of porcine epidemic diarrhea virus (PEDv), using data from 222 swine sites in 14 counties area in 4 contiguous states in the United States. During the outbreak, the premises-level incidence of PEDv was 40.5 percent (90/222 sites). One of the three companies from which data were collected had a lower incidence (19.5 percent) than the other two companies (41.1 and 47.2 percent). Sow sites had the highest incidence of PEDv during the outbreak (80.0 percent). Spatial analysis showed that PEDv was clustered rather than randomly distributed, which suggested that sites near a positive site had increased risk of acquiring PEDv infection. Meteorological data were used to investigate the hypothesis that PEDv was spread by air. If airborne dissemination played a role in this outbreak, we would expect the direction of disease spread to correlate with the predominant wind direction. Two methods were used to determine the direction of disease spread—linear direction mean analysis in ArcGIS and the direction test in ClusterSeer. The former method indicated PEDv spread was south to slightly southwest, and the latter indicated spread was to the southeast. The predominant wind direction during the month of the outbreak was toward the south, with some southeast and southwest winds; the strongest wind gusts were toward the southwest. These findings support the hypothesis that PEDv was spread by air. The results, however, should be interpreted cautiously because we did not have information on direct and indirect contacts between sites, such as movement of trucks, feed, pigs or people. These types of contacts should be evaluated before pathogen spread is attributed to airborne mechanisms. Although this study did not provide a definitive assessment of airborne spread of PEDv, we believe the findings justify additional research to investigate this potential mechanism of transmission.

Porcine epidemic diarrhea virus: current insights

“…Airborne viable PEDV virus has been detected in air samples from an isolation room with infected pigs and PEDV RNA was detected by real-time polymerase chain reaction (RT-PCR) in air up to 10 miles downwind from an infected site. 92 The findings that the direction of disease spread correlated qualitatively with wind direction reported by Beam et al 93 provide support to the hypothesis of airborne PEDV spread. However, this study did not provide a definitive assessment of airborne spread of the virus; more studies should be conducted to assess the possibility of airborne transmission.…”

Role of animal movement and indirect contact among farms in transmission of porcine epidemic diarrhea virus

“…Samples were also collected during the day, when UV radiation and temperature would be expected to reduce survival. However, infectiousness of airborne PEDv has been shown experimentally (Alonso et al, 2014) and the possibility of this mechanism has been supported in epidemiological investigations (Alvarez et al, 2016;Beam et al, 2015). Thus, we believe that it is a reasonable assumption that the likelihood of infectious virus to be found in air would be proportional to the total concentration of virus (inactivated or otherwise) found in the air samples.…”

“…In addition to direct contact among farms via animal movements, indirect contact may occur between farms due to windborne propagation of aerosols and dissemination of fomites by personnel, contaminated vehicles, and feed (Alonso et al, 2014;Alvarez et al, 2016;Beam et al, 2015;Dee et al, 2014;Kim et al, 2017;Lowe et al, 2014;O'Dea et al, 2015;Pasick et al, 2014). Although the potential importance of such mechanisms in creating transmission opportunities between swine premises has been shown in experimental studies and outbreak investigations (Alonso et al, 2014;Bowman et al, 2015;Lowe et al, 2014;Pasick et al, 2014), indirect contact is less often accounted for in epidemiological models (Arruda et al, 2016;Martinez-Lopez et al, 2011;Thakur et al, 2015;Yadav et al, 2016).…”

From the field to the lab — An European view on the global spread of PEDV

“…This, plus the scale of diarrhoea per piglet plus the number of piglets per sow (with a dissemination rate close to 100%) and the scale of some pig production units, where thousands of piglets are produced per week created an almost unimaginable amount of virus under some circumstances, where even a high dilution of starting material still suffices to transmit virus effectively -including to older pigs which are more resistant. Even the possibility of airborne spread to close-by farms has to be considered as a route of virus transmission under those circumstances (Alonso et al, 2014(Alonso et al, , 2015Beam et al, 2015;Dastjerdi et al, 2015). Other routes of transmission between close by farms include contaminated trucks (Lowe et al, 2014), equipment, or people and it has been determined that the risk is associated with proximity to an infected farm, which in turn correlates with the time the virus maintains its viability (Sasaki et al, 2016).…”