Excretion of pathogenic Newcastle disease virus by double‐crested cormorants (Phalacrocorax auritus) in absence of mortality or clinical signs of disease

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Abstract
Pathogenic Newcastle disease virus (NDV) caused several epidemics of Newcastle disease in double‐crested cormorants (Phalacrocorax auritus) in recent years. Eleven 16‐week‐old cormorants were infected with, or exposed to, pathogenic NDV from one of these epidemics and monitored for 70 days. No birds died, four birds had transient ataxia between 12 and 27 days post‐infection (d.p.i.), and one bird had neuronal necrosis and non‐suppurative encephalitis characteristic for Newcastle disease. The mean haemagglutina‐tion inhibiting antibody titre to NDV peaked at 1:630, 21 d.p.i., and decreased to 1:56 70 d.p.i. Duration of NDV excretion from the cloaca was 15 ± 6.2 d.p.i., with a maximum of 28 d.p.i. The absence of mortality in these birds may have been due to age‐related resistance. The excretion of NDV by cormorants in the absence of mortality or clinical signs of disease suggests that the cormorant population could maintain pathogenic NDV through serial infection of susceptible birds. The greatest risk of NDV transmission from cormorants to poultry probably is during autumn migration, through contact with infected birds, excreta or contaminated water.