OAHN Swine Project: Prevalence of PHEV in growing pig submissions to the AHL

Project Leads: Drs. Tim Blackwell and Josepha DeLay

Introduction

Porcine Haemagglutinating Encephalomyelitis Virus (PHEV) was originally associated with Vomiting and Wasting Disease in suckling pigs.   It was first reported by veterinarians at the Ontario Veterinary College in the 1950’s.  Until recently, PHEV was primarily associated with vomiting, wasting, and lethargy in suckling pigs.  The virus causes an encephalitis in affected pigs.  It is suspected that vagus nerve involvement or viral infection of the gastric mucosa causes a failure of gastric emptying resulting in the clinical signs of vomiting and wasting.  Despite the clinical signs associated with encephalitis and gastritis, the major site of viral reproduction is considered to be the respiratory track.

The first report associating (PHEV) with respiratory disease occurred in Michigan in 2015 where the virus was identified in coughing swine at agricultural fairs in Michigan.  At the time the reason for testing coughing pigs at agricultural exhibitions was to determine if swine influenza virus was present due to its importance from a public health perspective.  When flu was not discovered in the coughing pigs, further diagnostic investigations identified the presence of PHEV in coughing swine.  Because PHEV was not considered a public health concern and because all clinically affected pigs recovered, there was no opportunity to identify gross or histologic lesions in affected swine.  As a result, the relationship between PHEV and the clinical signs of respiratory disease was left undetermined.

More recently, PHEV has been identified in cases of hemorrhagic tracheitis diagnosed at animal health laboratories in North America including in Ontario and the midwestern United States.  However, PHEV is also identified in the respiratory tract of pigs without gross or histologic evidence of respiratory disease.  Therefore, the significance of finding the virus in the respiratory tract of pigs with respiratory disease was difficult to interpret.  Similarly, Astrovirus 4 has been associated with hemorrhagic tracheitis in growing pigs but is also found in pigs with no evidence of respiratory disease.  Therefore, its role in the pathogenesis of tracheitis and or respiratory disease also remains uncertain.

This OAHN funded surveillance project was designed to estimate the prevalence of PHEV positive PCR results in fresh lung tissue from pigs submitted for any reason to the Animal Health Laboratory (AHL) in Guelph over a 12-month period.  It is hoped that by establishing a baseline prevalence of PHEV in swine submissions with and without respiratory disease that this would assist in interpreting the relevance of PHEV in swine swine submissions to the  AHL.

To read the full report, please click here: https://www.oahn.ca/wp-content/uploads/2025/08/OAHN-Swine-Network-030784-Final-Report-PHEV.pdf