Vaccinia virus: Detecção e viabilidade no leite de vacas experimentalmente inoculadas

Abstract

Bovine vaccinia (VB) is an emerging zoonotic disease caused by Vaccinia virus (VACV), anOrthopoxvirus (OPV). The disease is characterized by the emergence of ulcerated lesions in theteats of dairy cows and in milkers hands and can occasionally affect calves that suck in sickcows. The DNA of VACV, as well as infectious viral particles can be detected in milk samplesof naturally infected cows. However, it is unknown the period and the pattern of viral sheddingin the milk or if the VACV detection in milk is due to a localized or systemic infection. Theobjective of this study was to detect and quantify the VACV DNA in milk, cheese, pasteurizedmilk, yogurt and milk phases after centrifugation, on milk samples collected from cowsexperimentally inoculated with VACV-GP2 strain during 33 days. Moreover, viral isolation wasattempted in milk and cheese samples. In another phase of the experiment, after the cowsreceived animmunosuppressivetreatment, the presence of viral DNA and its quantities in milksamples were determined by conventional and real time PCR, respectively. The VACV DNAcould be detected intermittently in milk of cows experimentally infected from the 1st day postinfection(dpi) until the 33thdpi, indicating that VACV is still eliminated in milk even after theresolution of the lesions, which occurred at the 22nddpi. It was possible to detect VACV DNA inmilk cream and cellular fractions, after milk centrifugation, as well as in whey frompasteurizedmilk and yogurt. Moreover, it was possible to isolate VACV viable viral particles in cheese,cheese whey and milk of cows inoculated with VACV and then subjected to treatment withimmunosuppressive drug, reinforcing the hypothesis of new viral replication in differentlocations from the initial inoculation site, after the immunosuppressive treatment. The reductionin milk production and increase in the somatic cell count (SCC) were more significant in theteats that were inoculated with VACV-GP2 when compared to teats that served as a control andtherefore were not inoculated with the virus, reinforcing the hypothesis of association betweenthe presence of virus in the teats and compromised quality of milk. The detection of both VACVDNA and infectious particles in milk samples, even after the end of the clinical stage of thedisease, strengthens the hypothesis that VACV can cause a persistent infection in cattle, as wellas draw attention to the potential risk to the Public health associated with the milk consumptionfrom cows that were affected by VB.