Introduction

Paramyxovirus 1 or Newcastle Disease is a highly contagious viral disease affecting poultry of all ages. Affected species include chickens, turkeys, pigeons and ducks. The condition is rarely diagnosed in ducks but is a possible cause of production drops/fertility problems. Other species can be infected including mammals occasionally (e.g. conjunctivitis in man).

The virus involved is Paramyxovirus PMV-1, which is of variable pathogenicity. Signs are typically of disease of the nervous, respiratory or reproductive systems. Morbidity is usually high and mortality varies 0-100%. Higher mortality is seen in velogenic disease in unvaccinated stock.

Four manifestations have been identified:

• ND - Velogenic Viscerotropic (VVND) - sometimes called 'asiatic' or exotic. It is highly virulent for chickens, less for turkeys and relatively apathogenic in psittacines.
• ND - Neurotropic Velogenic - Acute and fatal in chickens of any age causing neurological and some respiratory signs. Intestinal lesions are absent.
• ND - Mesogenic - Mortality and nervous signs in adult. These viruses have sometimes been used as vaccines in previously immunised birds.
• ND - Lentogenic - Mild disease, sometimes subclinical. Can affect any age. Strains can be developed as vaccines.

Transmission is via aerosols, birds, fomites, visitors and imported psittacines (often asymptomatic). It is not usually vertical (but chicks may become infected in hatcheries from contaminated shells).

The virus survives for long periods at ambient temperature, especially in faeces and can persist in houses (in faeces, dust etc). for up to 12 months. However it is quite sensitive to disinfectants, fumigants and sunlight. It is inactivated by temperatures of 56°C for 3 hours or 60°C for 30 min, acid pH, formalin and phenol, and is ether sensitive.

Signs

Signs are highly variable and will depend on the nature of the infecting virus (see above), the infective dose and the degree of immunity from previous exposure or vaccination.

• Sudden Death
• Depression.
• Inappetance.
• Coughing.
• Dyspnoea.
• Diarrhoea.
• Nervous signs.
• Paralysis.
• Twisted neck.
• Severe drop in egg production.
• Moult.

Post-mortem lesions

• Airsacculitis.
• Tracheitis.
• Necrotic plaques in proventriculus, intestine, caecal tonsil.
• Haemorrhage in proventriculus.
• Intestinal lesions primarily occur in the viscerotropic form.

Diagnosis

A presumptive diagnosis may be made on signs, post-mortem lesions, rising titre in serology. It is confirmed by isolation in CE, HA+, HI with ND serum or DID (less cross reactions), IFA. Cross-reactions have mainly been with PMV-3. Pathogenicity evaluated by Mean Death Time in embryos, intracerebral or IV pathogenicity in chicks. Samples - tracheal or cloacal.

Differentiate from Infectious bronchitis, laryngotracheitis, infectious coryza, avian influenza, EDS-76, haemorrhagic disease, encephalomyelitis, encephalomalacia, intoxications, middle ear infection/skull osteitis, pneumovirus infection.

Treatment

None, antibiotics to control secondary bacteria.

Prevention

Figure 28. Severe haemorrhagic and necrotic lesions in proventriculus and Peyers patches in the intestines of a broiler chicken suffering from one of the severe forms of Newcastle disease (viscerotropic velogenic).

Quarantine, biosecurity, all-in/all-out production, vaccination. It is common to monitor response to vaccination, especially in breeding birds by the use of routine serological monitoring. HI has been used extensively; Elisa is now also used. These tests do not directly evaluate mucosal immunity, however.

Vaccination programmes should use vaccines of high potency, which are adequately stored and take into account the local conditions. A typical programme may involve Hitchner B1 vaccine at day old followed by LaSota-type vaccine at 14 days. The LaSota-type vaccine may even repeated at 35-40 days of age if risk is high. Use of spray application is recommended but it needs to be applied with care to achieve good protection with minimal reaction.

Inactivated vaccines have largely replaced the use of live vaccines in lay but they do not prevent local infections.

To prevent or reduce vaccinal reactions in young chicks it is important that day old have uniform titres of maternal immunity. Vaccinal reactions may present as conjunctivitis, snicking, and occasionally gasping due to a plug of pus in the lower trachea. In some countries it has been customary to provide antibiotics prophylactically during periods of anticipated vaccinal reaction. Use of Mycoplasma gallisepticum free stock under good management reduces the risk of vaccinal reactions.