ABSTRACT
Marek's disease virus (MDV) is an immunosuppressive pathogen that can cause low production efficiency and high mortality rates in chickens. There is no current information on the MDV serotypes and pathotypes circulating in vaccinated commercial farms in Colombia where the birds are vaccinated in the incubator with Gallid herpesvirus (GaHV-2) and Meleagrid herpesvirus 1 (MeHV-1). Based on that, the main focus of this study was to understand the MDV's infection dynamics for the three known serotypes and to detect wild-virus pathogenic strains in 4-layer poultry farms in Antioquia. Samples of blood, feathers and spleens were collected from three randomly chosen animals according to age category: 1, 15, 30, 60, 90, and 120 days. Quantitative real-time PCR (qPCR) that differentiates between the three serotypes of MDV was used to assess viral loads over time, and phylogenetic analysis of the Meq oncogene was done to compare the strains of MDV with those of known pathogenicity. Meleagrid herpesvirus 1 (MeHV-1) was detected in all blood and feather follicle samples with an average number of genome copies (per 10,000 cells) of 31.44 in blood as expected as a result of vaccination. GaHV-2 was also detected in almost 100% of the blood and feather follicle samples throughout all defined age categories, with an average of 10.65 genome copies in blood samples. Gallid herpesvirus 3 (GaHV-3) was detected in 72% of blood and 84.61% of feather samples, with less than 1 copy per 10,000 cells. Based on the number of 132 bp repeats of the BamHI-H and BamHI-D regions in pooled feather samples, there were 70% (8/25) of attenuated MDV and 30% (17/25) of virulent MDV strains circulating in the farms. Virus isolation was performed successfully from every farm. In conclusion, different strains of MDV are circulating for up to 120 days in layers in Antioquia-Colombia and could be of major impact in poultry health. Keywords: Marek's disease virus (MDV); Antioquia-Colombia; qPCR; PCR; Meq gene phylogeny.
