In other species, signs are very variable and the severity of illness may be quite different in species which are closely related to one another. In turkeys, clinical signs are generally less severe than in chickens, while in game birds such as pheasants (gallinaceous birds) the disease appears similar to that seen in chickens; staggering, strutting, rapid turning of the head, raising and lowering of the head, crouching, wry-neck, fluffed feathers, increased drinking and diarrhoea have been seen; some birds have been noted to “false-feed”. In ducks, if it causes illness at all, mobility problems, local incomplete paralysis, central nervous signs, gut signs, inflammation of the eyes, respiratory signs and in laying birds decreased egg production and the laying of soft-shelled eggs may be seen; it is rare for deaths to be reported with this disease in wild waterfowl, although outbreaks in domestic ducks in Hong Kong caused 35-96% mortality.

In double-crested cormorants (Phalacrocorax auritus) in the USA and Canada, outbreaks have occurred in breeding colonies in March to September; only juvenile birds, not adults, have been affected in these outbreaks. Torticollis (twisting of the head and neck), ataxia (lack of muscular coordination), tremors, paresis (incomplete paralysis) including weakness of the legs and/or wings on one or both sides, and clenched toes have been seen. It is often fatal in nestlings, and survivors may have one or less commonly both wings paralysed; birds with a paralysed wing can dive but obviously cannot fly. Fatal illness has also been reported in three other species – white pelicans, California gulls and ring-billed gulls – in association with outbreaks in double-crested cormorants in Canada (Docherty & Friend, 1994; Kuiken et al., 1999); Leighton & Heckert, 2007.

B) Wing droop and abnormal posture in this subadult

Photographed by Linda Glaser

Right) A double-crested cormorant (Phalacrocorax auritus) fleeing from observers during the Newcastle disease outbreak at the Salton Sea, California. Note only the right wing is functional. This bird is typical of juvenile birds surviving infection. The same condition was also observed in adults prior to the breeding season; these birds.

Photographed by Greg Kidd

Forms recognised in Poultry (domestic chickens)

Viscerotropic velogenic Newcastle disease VVND (Doyle's form): An acute lethal infection in all ages of chickens: Signs include acute death; listlessness; weakness; increased respiratory rate, (sometimes severe respiratory signs; oedema of the head and around the eyes, mucoid nasal discharge; prostration; green (sometimes bloodstained) diarrhoea (not seen in birds dying early in the course of the disease); muscle tremors, torticollis, opisthotonus and limb paralysis may be seen prior to death. Practically all birds in the flock may die (up to 100% mortality).

Neurotropic velogenic Newcastle disease or NVND (Beach's form): Acute lethal disease in chickens of all ages. Sudden onset respiratory signs; neurological signs develop one or two days later. Large decrease in egg production; rarely diarrhoea; deaths. All birds in the flock may be affected, with 50% of adults, and 90% of young birds dying

Mesogenic: Respiratory distress; marked decreased egg production; occasionally nervous signs; deaths in young birds. Low mortality except in young birds.

Lentigenic: In adults, mild respiratory disease may be seen or no clinical signs. Serious respiratory signs may occur in young susceptible birds, but this is not usually fatal. Mortality may occur due to complicating infections. (B32.20.w8)

Asymptomatic lentigenic: No clinical signs in chicken (infection of the intestines occurs).

Note: Acute death without clinical signs may occur with highly virulent strains.