Veterinary Parasitology- ICAR JRF/SRF 2024

• Pathotypes of Newcastle Disease Virus (Avian Paramyxovirus-1):
• Classified based on pathogenicity indices (MDT, ICPI, IVPI):
• Velogenic Strains: Highly virulent, causing severe fatal Newcastle disease ($90-100\%$ mortality; viscerotropic or neurotropic).
• Mesogenic Strains: Moderately virulent, causing acute respiratory disease, neurological signs, and egg drop (used as secondary booster vaccines).
• Lentogenic Strains: Low-virulence, causing mild subclinical respiratory infection (used as primary live vaccines, e.g., LaSota, F-strain).
• Hence, virulent disease is caused by velogenic and mesogenic strains.
• nalysis:
• ((A) and (C) only): Correct.

Correct option: (3) (A) and (C) only.

• Lymphoid Leukosis in Domestic Poultry:
• Commonly referred to as "Big liver disease" due to massive diffuse nodular enlargement of the liver (hepatomegaly) and spleen. True.
• Caused by exogenous Avian Leukosis Viruses (ALV, family Retroviridae), transmitted both vertically through the egg albumen/yolk and horizontally. True.
• Neoplastic transformation specifically targets B lymphocytes originating in the bursa of Fabricius. (In contrast, Marek's disease transforms T lymphocytes!). Statement C is False.
• The disease has a long incubation period, manifesting clinically in sexually mature adult birds ($\gt 16-24\text{ weeks}$ of age). True.
• nalysis:
• Statements (A), (B), and (D) are correct. Hence, Option 2 is correct.