Evidence of mixed persistent infections in calves born to cows challenged with a pool of bovine viral diarrhea virus isolates

Abstract

RESUMO.-[Evidências de infecção persistente mista em bezerros nascidos de vacas inoculadas com um pool de isolados do vírus da diarréia viral bovina.]Vacas prenhes infectadas com isolados não-citopáticos (NCP) do vírus da diarréia viral bovina (BVDV) entre os dias 40 e 120 de gestação frequentemente produzem bezerros imunotolerantes, persistentemente infectados (PI). Este artigo relata a caracterização de bezerros PI produzidos experimentalmente, pela inoculação de vacas prenhes com um pool de isolados brasileiros de BVDV-1 (n=2) e BVDV-2 (n=2) entre os dias 60 e 90 de gestação. Dois bezerros nasceram positivos para vírus, negativos para anticorpos, mas morreram aos dias 7 e 15 pós-nascimento, respectivamente. Pregnant cows infected with noncytopathic (NCP) isolates of bovine viral diarrhea virus (BVDV) between days 40 and 120 days of gestation frequently deliver immunotolerant, persistently infected (PI) calves. We herein report the characterization of PI calves produced experimentally through inoculation of pregnant cows with a pool of Brazilian BVDV-1 (n=2) and BVDV-2 isolates (n=2) between days 60 and 90 of gestation. Two calves were born virus positive, lacked BVDV antibodies, but died 7 and 15 days after birth, respectively. Six other calves were born healthy, seronegative to BVDV, harbored and shed virus in secretions for up to 210 days. Analysis of the antigenic profile of viruses infecting these calves at birth and 30 days later with a panel of monoclonal antibodies indicated two patterns of infection. Whereas three calves apparently harbored only one isolate (either a BVDV-1 or BVDV-2), co-infection by two antigenically distinct challenge viruses was demonstrated in three PI calves. Moreover, testing the viruses obtained from the blood of PI calves by an RT-PCR able to differentiate between BVDV-1 and BVDV-2 confirmed the presence/persistence of two co-infecting viruses of different genotypes (BVDV-1 and BVDV-2) in these animals. These findings indicate that persistent infection of fetuses/calves -a well characterized consequence of fetal infection by BVDV -may be established concomitantly by more than one isolate, upon experimental inoculation. In this sense, mixed persistent infections with antigenically distinct isolates may help in understanding the immunological and molecular basis of BVDV immunotolerance and persistence. ou BVDV-2), enquanto outros três bezerros apresentavam co-infecção com mais de um vírus. Além disso, testandose o sangue dos animais PI com um PCR capaz de diferenciar entre BVDV-1 e BVDV-2 observou-se a presença concomitante de vírus dos dois genótipos (BVDV-1 e BVDV-2) nestes três animais. Esses resultados indicam que infecção persistente -uma consequência bem conhecida da infecção fetal pelo BVDV -pode ser estabelecida concomitantemente por mais de um vírus, após infecção experimental. Nesse sentido, infecções persistentes mistas com isolados antigenicamente distintos podem ser úteis para o estudo das bases imunológicas e moleculares da imunotolerância e infecção persistente p...

Pathomorphological Aspects of Relevant Gastrointestinal Diseases in Newborn and Growing Calves

“…Embryos infected between the 60 th and 90 th gestational days are born as immunotolerant and persistently infected (PI) calves (35). Congenital malformations have been observed in newborn calves including cerebral hypoplasia, microcephaly, hydrocephaly, osteochondrosis, stunted growth, ocular neuritis, retinal degeneration, hypoplasia of the thymus, hypotrichosis, alopecia, osteosclerosis, microphthalmia and cataract (36). The virus induces degenerative and necrobiotic processes in the myocardium and lungs of intrauterinely infected calves.…”