RESUMO
In searching for the cause of experimental variations in respiratory research data, serology revealed the prevalence of antibodies against parainfluenza virus type 3 (PIV 3) in guinea pigs. The aim of the present study was to explore the transmission rate, course, and kinetics of enzootic PIV 3 infection in guinea pig breeding units. In the first part of the study, blood samples to be analyzed for PIV 3 antibodies were collected from guinea pigs of a PIV 3-positive breeding colony at different times after birth. In the same breeding unit, 6 of 12 2-week-old guinea pigs were relocated and separately housed. The PIV 3 serum antibody titers of the two groups were compared at various times from birth to 13 weeks after birth. In the second part of the study, the spread of infectious virus and virus persistence were explored by housing seronegative sentinel animals together with 2- to 3-week-old guinea pigs from three different PIV 3-positive breeding units. The guinea pigs remaining in the breeding colony as well as those removed and housed separately showed declining serum antibody titers for about 1 month after birth, thereafter the titers were stable until about 8 weeks after birth. Five weeks later, the mean antibody titer of the guinea pigs remaining in the breeding colony had increased to a markedly higher level than that of the relocated, separately housed guinea pigs. Seroconversion was demonstrated in 7 of the 14 sentinels housed with the 2- to 3-week-old guinea pigs from PIV 3-positive breeding units. Sentinels housed together with PIV 3-positive guinea pigs 24 weeks after the start of the experiment did not seroconvert. We conclude that young guinea pigs born to PIV 3-positive mothers were protected by maternal immunity against infection with PIV 3 during their first 14 days of life. The guinea pig offspring became infected during the period from about 2 weeks until 8 weeks after birth, as demonstrated by seroconversion of sentinel animals and an increasing mean antibody titer seen beyond 8 weeks of age. The study did not reveal any indication of virus persistence or prolonged carrier status.