Abstract
Bovine vaccinia (BV) is a zoonosis caused by Vaccinia virus (VACV), which affects dairy cattle and humans. Previous studies have detected the presence of viable virus particles in bovine milk samples naturally and experimentally contaminated with VACV. However, it is not known whether milk contaminated with VACV could be a route of viral transmission. However, anti-Orthopoxvirus antibodies were detected in humans from BV endemic areas, whom had no contact with affected cows, which suggest that other VACV transmission routes are possible, such as consumption of contaminated milk and dairy products. Therefore, it is important to study the possibility of VACV transmission by contaminated milk. This study aimed to examine VACV transmission, pathogenesis and shedding in mice orally inoculated with experimentally contaminated milk. Thirty mice were orally inoculated with milk containing 107 PFU/ml of VACV, and ten mice were orally inoculated with uncontaminated milk. Clinical examinations were performed for 30 consecutive days, and fecal samples and oral swabs (OSs) were collected every other day. Mice were euthanized on predetermined days, and tissue and blood samples were collected. Nested-PCR, plaque reduction neutralization test (PRNT), viral isolation, histopathology, and immunohistochemistry (IHC) methods were performed on the collected samples. No clinical changes were observed in the animals. Viral DNA was detected in feces, blood, OSs and tissues, at least in one of the times tested. The lungs displayed moderate to severe interstitial lymphohistiocytic infiltrates, and only the heart, tonsils, tongue, and stomach did not show immunostaining at the IHC analysis. Neutralizing antibodies were detected at the 20th and 30th days post infection in 50% of infected mice. The results revealed that VACV contaminated milk could be a route of viral transmission in mice experimentally infected, showing systemic distribution and shedding through feces and oral mucosa, albeit without exhibiting any clinical signs.
Highlights
Vaccinia virus (VACV), an Orthopoxvirus, is the causative agent of bovine vaccinia (BV), which is an occupational zoonosis that affects lactating cows, their calves, and milkers
The strain used to infect the milk was Vaccinia virus Guarani P2 (VACV-GP2), which was isolated from teat lesions of a cow during a BV outbreak that occurred in the municipality of Guarani, Minas Gerais (MG) State, Brazil, in 2001; the strain was serologically and molecularly characterized as VACV [14]
No clinical signs were observed in the mice during the 30-day monitoring period, following the inoculation with VACV-GP2–contaminated milk
Summary
Vaccinia virus (VACV), an Orthopoxvirus, is the causative agent of bovine vaccinia (BV), which is an occupational zoonosis that affects lactating cows, their calves, and milkers. Cases of the disease have been frequently reported in several regions of Brazil since the end of the 1990s. Lesions begin with the formation of vesicles and papules that progress to ulcers and crusts with subsequent healing. A sudden decrease in milk production, mastitis, milkers’ absenteeism from work, medical expenses, and diseased calves are noted as the main losses caused by BV. The natural reservoirs of VACV have not yet been established. Virus detection in sentinel and wild rodents suggests that they are the main reservoirs [1,2,3], as reported for Cowpox virus (CPXV) in Europe [4]
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