HSPA4 and infection: Earlier works in our laboratory have shown that following experimental infection of 2-day-old Pekin ducklings with 5 × 104 PFU of Y or its rescued virus rY by intracerebral or subcutaneous routes, mortality as high as 90–100% occurred between 4 and 7 days pi (11), which is unfavorable for evaluation of immune responses against TMUV isolates.