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Newcastle Disease by Dr Debra Bourne MA VetMb PhD MRCVS

 

 

 

Newcastle Disease, which is distributed practically worldwide, ranks alongside Avian Influenza as one of the most feared diseases of birds; both have been called “fowl pest”.  Their reputation is partly due to the effects of the disease itself, partly because of the control measures which may be taken by governmental authorities to control the disease as a threat to poultry.  Newcastle Disease (ND) is an important disease in poultry and is also important as a disease of some wild birds, particularly the endangered double-crested cormorant (Phalacrocorax auritus) in North America.

 

Newcastle Disease is caused by Newcastle Disease Virus (NDV), the most important virus of birds within a family of viruses called the Paramyxoviridae.  There are nine serotypes of paramyxovirus, with PMV-1 (NDV, also known as Avian Paramyxovirus Type-1 or APMV-1) causing Newcastle disease.  The closely-related Pigeon PMV-1 is important in racing pigeons, and both Newcastle Disease and the Pigeon PMV-1 are Notifiable Diseases in the UK.

 

Susceptibility

 

NDV can affect hundreds of bird species and has been confirmed in more than half of the 50 orders of birds. Birds of all ages may be affected, although the severity of disease may vary with age within a given species.  NDV can also affect some mammals; in humans it causes conjunctivitis (inflammation of the tissues of the eyes).  Strains of NDV are classified according to the severity and main characteristics of the disease which they cause in domestic chickens (see Box - Forms recognised in Poultry (domestic chickens)).

 

Transmission

 

NDV is shed mainly in the droppings, but also in respiratory secretions.  This virus may be inhaled (breathed in) or ingested (eaten).  If the eggshell is contaminated, the virus can be transmitted to the developing embryo or to the chick when it hatches.  The virus may be transmitted from one group of birds to another via humans, insects, wind and objects (e.g. equipment used with infected then with healthy birds, or contaminated feed), as well as by movements of birds. In poultry, it can be spread by humans moving birds (including pet birds, poultry, game birds etc.).  Waterfowl, psittacines, some passerines and owls can carry the virus without themselves showing any signs of disease.

 

Incubation period

 

The time from infection to illness is usually two to six days but can be longer (up to 15 or even 21 days).  It depends on the host species, virus strain, dose, and any previous exposure of the host to NDV.

 

Clinical signs (illness)

Newcastle Disease can be subclinical (i.e. not cause any obvious illness), or the virus can cause variable, sometimes severe and fatal, disease.  As well as general depression, it may involve nervous signs, respiratory signs and diarrhoea.  In chickens, practically the whole flock may die over a period of just three days with severe outbreaks.

 

The descriptions of different strains of NDV are based on the disease the strains cause in poultry, specifically domestic chickens – whether the disease is severe, moderate, mild or without clinical signs; and whether, for the severe forms, the main signs are nervous signs or are more general and gut-related.

 

 

Clinical signs of Newcastle disease in double-crested cormorants (Phalicrocorax auritus) include torticollis or twisting of head and neck in these two nestlings.

Photograph by Greg Kidd