An adult double-crested cormorant tested positive for a highly pathogenic strain of Newcastle disease virus (NDV), referred to as virulent Newcastle disease virus (vNDV) or exotic Newcastle disease (END). Additional supporting gross findings of splenic necrosis and subcutaneous edema were found on necropsy. 

NDV, also referred to as avian orthoavulavirus 1 (AOAV-1) and historically known as avian paramyxovirus serotype 1 (APMV-1), is a pleomorphic, enveloped, negative-sense ssRNA virus in the family Paramyxoviridae.⁴ The species comprises class I and class II viruses, and genetically diverse class II strains cause virulent disease in poultry. While NDV is zoonotic, it only causes conjunctivitis in humans.^2,4 Virulence spans three pathotypes: the highly pathogenic, velogenic/virulent; the intermediate, mesogenic; and the low-virulence/asymptomatic, lentogenic. Velogenic viruses cause acute, contagious disease in many kinds of poultry, wild and caged birds, characterized by severe lesions in the respiratory, gastrointestinal, reproductive, immune and central nervous systems.² Unlike other viruses in which pathogenicity is based on genotyping, with NDV, virulence is determined by the fusion (F) protein cleavage site.¹

NDV is shed primarily through respiratory secretions and feces of infected birds. Indirect spread also occurs through fomites such as contaminated equipment, clothing, footwear and vehicles. Wild birds can move virus over long distances through migration while introducing it to domestic poultry through shared environments, feed and water.² NDV exists worldwide and remains endemic in many regions. Outbreaks in poultry recur even where vaccination is practiced. Genetic divergence between genotype I/II vaccine strains and circulating virulent field genotypes can alter key F and hemagglutinin-neuraminidase neutralizing epitopes, weakening cross-protection. This means that vaccinated chickens may avoid severe mortality yet still support viral replication, transmission and occasional disease outbreaks.² Additionally, wild and feral birds can contribute to circulation of paraymyxoviruses. Double-breasted cormorants can serve as reservoirs of NDV, and pigeons can serve as a reservoir of pigeon paramyxovirus serotype 1 (PPMV‑1).²

Because clinical signs in poultry – respiratory distress, diarrhea, anorexia, decreases in egg quality and amount, neurologic abnormalities (tremors, torticollis, circling, or complete rigidity), and sudden death – are nonspecific and similar to highly pathogenic avian influenza (HPAI), laboratory confirmation is required. Virulent NDV is reportable and designated as Tier 1 Select Agent by the USDA, which means that virulence assessment requires initial NDV PCR detection at an approved National Animal Health Laboratory Network (NAHLN) laboratory, followed by testing of the fusion-gene cleavage-site region at the USDA National Vetereinary Services Laboratory (NVSL) in Ames, Iowa.^3,4 In this case, a choanal swab PCR result of “detected,” suggestive of virulent NDV, was performed at the AHDC, a NAHLN lab. The choanal swab and brain tissue were then forwarded to NVSL for confirmation by detection of the fusion (F) protein cleavage site gene in brain tissue.

Prevention depends on strict biosecurity combined with an effective vaccination program. Laying hens can be vaccinated with multiple priming doses with live attenuated vaccines, followed by an inactivated vaccine to promote sustained immunity. Available vaccines reduce morbidity and mortality but cannot reliably prevent infection or transmission. Unfortunately, there is no effective treatment for NDV.

References

1. Bhande, P., et al. (2023). Improvement of a real-time reverse transcription–polymerase chain reaction assay for the sensitive detection of the F gene of avian orthoavulavirus-1 (AOAV-1). Veterinary Sciences, 10(3), 223.
2. Brown, V. R., & Bevins, S. N. (2017). A review of virulent Newcastle disease viruses in the United States and the role of wild birds in viral persistence and spread. Veterinary Research, 48, Article 68.
3. Hu, Z., et al. (2022). Current situation and future direction of Newcastle disease vaccines. Veterinary Research, 53(1), 99.
4. Morris, E. R., et al. (2025). Optimization and validation of universal real-time RT-PCR assay to detect virulent Newcastle disease viruses. Viruses, 17(5), 670.
5. Song, H. S., et al. (2026). High-sensitivity multiplex real-time RT-PCR for universal detection and virulence typing of Newcastle disease virus in poultry field samples. Poultry Science, 105(6), 106790.
6. USDA. (2025, July 30). Virulent Newcastle Disease [Governmental]. U.S. DEPARTMENT OF AGRICULTURE: Animal and Plant Health Inspection Service.