The study was conducted to determine the circulation of Marek’s disease virus in local chickens in Tra Vinh province. A total
of 343 feather follicle samples were collected from 49 unvaccinated chicken flocks for Marek disease in Tra Vinh City, Cang
Long, Tra Cu, and Tieu Can districts. The samples were tested by polymerase chain reaction to detect specific meq gene of
Marek’s disease virus serotype 1 (MDV-1). Information on hygiene and vaccination programs was also collected. The results
showed that 45 out of 343 samples were positive for MDV-1, accounting for 13.12%. The prevalent MDV-1 in chickens
in Cang Long was 17.85%, followed by Tra Vinh City (15.38%). The same prevalence of MDV-1 (9.52%) was recorded
in chickens in the Tieu Can and Tra Cu districts. The differences in the prevalence of MDV-1 in chickens among surveyed
sites were not statistically significant (P>0.05). There was no significant difference in the prevalence of MDV-1 by chicken
breeds. The prevalence of MDV-1 in chickens from 3 to 6 months old was highest at 34.04%, followed by chickens from 1
to less than 3 months old (11.06%) and older 6 months of age (5.71%). The risk of MDV -1 infection in vaccinated chickens
against Avian influenza, Newcastle disease and Gumboro disease was lower than that of unvaccinated chickens (OR=0.277,
P=0.044). The combination of sanitation and disinfection decreased the risk of MDV-1 infection in chickens (OR=0.502;
P=0.031).