Determination of organ tropism of Newcastle disease virus (strain I-2) by virus isolation and reverse transcription-polymerase chain reaction.

The vaccines I-2 and V4 are avirulent strains of Newcastle disease virus. Organ tropism of strain V4 has been determined and the virus has a predilection for the digestive tract. Tropism of strain I-2 has not yet been determined. The objective of this study was to determine the distribution of strain I-2 in various body organs and fluids following vaccination in comparison with V4. Four-week-old chickens were vaccinated by eye drop separately with these two avirulent strains. Virus isolation and the reverse transcription-polymerase chain reaction technique were employed to detect I-2 and V4 viruses in various tissues and body fluids for 7 days following vaccination. Tissues from the respiratory tract showed earlier positive signals than tissues from other organs for chickens vaccinated with strain I-2. Conversely, tissues from mainly digestive tract produced earlier positive signals than from respiratory tract and other organs from chickens vaccinated with strain V4. In early infection, strain I-2 had preferential predilection for the respiratory tract and strain V4 for the digestive tract. Later after vaccination, other organs showed positive results from chickens vaccinated with both I-2 and V4 strains. The differences in organ tropism observed in this study suggest that I-2 may perform better than V4 as a live vaccine strain.