Abstract
ABSTRACT Marek’s disease virus (MDV) has been shown to be evolving to higher virulence. One of the genetic sites involved in virulence which enables such characterization is the 339-amino acid Meq protein encoding gene (meq). The reemergence of clinical Marek’s disease (MD) in vaccinated flocks can be associated to changes in meq. Our studies have shown the presence of very virulent MDV strains in the Brazilian industrial and free-range poultry. We present an overview of MD increasing severity and indicate the necessity of using phylogenetic tools for best accompanying MDV evolution.
Highlights
During the last fifty years, the increased intensification of poultry has provided high numbers of chickens concentrated in industrial farms and specific geographical areas
Several very virulent strains of Marek’s disease virus (MDV) have been described since the 1980s, with the pathogenicity determined by the capacity of oncogenesis in Herpesvirus of turkeys (HVT) vaccinated chickens (Eidson et al, 1981)
Lesions were mostly observed in the liver, spleen and gonads, as localized or diffuse tumors, the meq oncogene was detected in five out of the 30 chickens, with substitutions in positions 77(E/K), 80(Y/D), 88(T/A), 112(F/S), 139(A/T) and 176(R/P), with deducted amino acid sequences showing five strains with identity (≥ 98%) with the very virulent MDV (vvMDV) strains ATE (Hungary), C12/130 (UK) and Chinese LMS, YA, WS03 and GX070060 (Hassanin et al, 2013)
Summary
During the last fifty years, the increased intensification of poultry has provided high numbers of chickens concentrated in industrial farms and specific geographical areas. An additional preoccupation has come to light in Brazil, with the description of MD in peafowl (Pavo cristatus) at a Zoological Park, characterized by visceral lymphomatosis and the detection of a virulent MDV (serotype 1) strain, through PCR and partial sequencing of the Meq protein encoding gene (Blume et al, 2016).
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