Interstitial pneumonia associated with equid gammaherpesvirus 5 infection in 2 neonatal foals, and a retrospective study in Hokkaido, Japan.

Overview

• This study reports the association of equid gammaherpesvirus 5 (EqGHV5) infection with interstitial pneumonia in two neonatal foals and reviews additional cases in Hokkaido, Japan, to explore the potential role of EqGHV5 in causing this lung disease.

Background and Study Purpose

• Interstitial pneumonia in foals under one month old is a serious lung condition characterized by inflammation affecting the interstitial tissue of the lungs.
• Various infectious agents, including bacteria and viruses, have been linked to this disease, but establishing a direct causal relationship can be challenging.
• Recent suggestions have implicated equid gammaherpesvirus 5 (EqGHV5), a type of equine herpesvirus, as a possible cause of interstitial pneumonia in foals, but direct histological proof demonstrating this link has been limited.
• The study aimed to investigate cases of neonatal foals with interstitial pneumonia to detect the presence of EqGHV5 and analyze histological evidence supporting viral infection.

Case Examination and Findings

• Two neonatal foals aged 12 and 24 days, both suffering from acute respiratory distress and showing poor responses to treatment, were examined postmortem.
• Histological examination revealed:
  • Interstitial pneumonia characterized by diffuse alveolar damage.
  • Presence of intranuclear inclusion bodies within alveolar macrophages, which are indicative of viral infections.
• Molecular and visual detection techniques were used:
  • PCR (polymerase chain reaction) testing identified the presence of EqGHV5 DNA in lung tissues.
  • In situ hybridization (ISH) localized EqGHV5 within alveolar macrophages, confirming the virus in the affected cells.
• Importantly, no other bacterial or viral pathogens were detected in these two cases, strengthening the association between EqGHV5 and the observed pneumonia.

Retrospective Study in Hokkaido

• To further investigate, researchers analyzed 23 additional foals aged 2 to 89 days, previously diagnosed with interstitial pneumonia in Hokkaido between 2015 and 2020.
• These retrospective cases were tested for EqGHV5 using PCR and ISH methodologies.
• EqGHV5 was not detected in any of the 23 cases from this retrospective cohort.
• This suggests that while EqGHV5 can be found in some cases of neonatal interstitial pneumonia, it may not be a common or universal cause in all affected foals within this region or timeframe.

Conclusions and Implications

• The combination of histologic lesions, viral inclusion bodies in alveolar macrophages, and detection of EqGHV5 via PCR and ISH in the two neonatal foal cases provides strong evidence supporting a potential causal role for EqGHV5 in foal interstitial pneumonia.
• However, the absence of EqGHV5 in the broader retrospective study highlights the need for further investigation to clarify:
  • The prevalence and significance of EqGHV5 infection in neonatal foal interstitial pneumonia.
  • The conditions under which EqGHV5 contributes to disease versus when other pathogens might be involved.
  • The pathogenesis of EqGHV5-associated pneumonia, including viral tropism and host immune response.
• This study underscores the importance of combining histopathology with molecular diagnostic techniques to accurately identify causative agents in infectious diseases of equine neonates.
• Future research could lead to improved diagnostics, preventive strategies, and targeted therapies for viral causes of interstitial pneumonia in foals.