Most dogs with parvo virus infection may appear asymptomatic (showing no canine parvo symptoms), but when stressed (e.g. boarding, running, pining, and grief etc.), the stress itself may trigger clinical features of the disease. (dog-health-handbook.com)
Q: In the last three weeks we have had six dogs diagnosed with parvo... We're vaccinating everyone, but a couple of these pups already had three shots before they got sick. (aspcapro.org)