Newcastle disease

A virus of the family Paramyxoviridae

Strains of the virus are present in most countries. The severe form of the disease occurred in Australia in the 1930s (VIC) and in 1998 (NSW), 1999 (NSW) and 2002 (VIC & NSW). An avirulent strain of NDV, designated 'V4' was isolated in QLD in 1966 and later was used as the seed of ND vaccine.

The incubation period is usually 5-6 days but may vary from 2-15 days.

In poultry

ND is usually seen in domestic poultry as a rapidly fatal, high-mortality condition characterised by gastrointestinal, respiratory or nervous signs. In other avian species, the disease produced by virulent ND viruses ranges clinically from inapparent to a rapidly fatal condition.

The severity of the symptoms depends on the strain of the virus and the age and health of the bird.

The ND virus produces 4 broad clinical syndromes.

Viscerotropic velogenic ND

• This clinical syndrome appears suddenly and spreads rapidly.
• Symptoms are marked depression, loss of appetite, sharp drop in egg production, increased respiration, swollen heads, blue combs, and, often, a profuse green diarrhoea that leads to dehydration and collapse
• Birds may die within 2 days. Birds that survive the initial phase often develop nervous signs such as twisted necks and muscle twitching. Up to 90% of birds may die.

Neurotropic velogenic ND

• Severe respiratory and nervous signs predominate, including coughing and gasping, head tremors, wing and leg paralysis and twisted necks.
• Depression, loss of appetite and a drop in egg production also occur. Between 10-20% of adults and a larger proportion of younger birds may die.

Mesogenic ND

• Signs are mainly respiratory, with coughing but no gasping.
• Other signs include depression, loss of weight and decrease in egg quality and production for up to 3 weeks.
• Nervous signs may develop late in the course of the disease.
• Death rates are about 10%.

Lentogenic ND

• Symptoms are mild or absent, and include mild respiratory signs, impaired appetite and a drop in egg production.
• No nervous signs occur and deaths are usually negligible.

In humans

A mild form of disease can affect people, causing headaches, flu-like symptoms and conjunctivitis.

ND spreads easily by contact with infected or diseased birds. The virus is excreted in manure and is expired into the air. Other sources of infection are contaminated equipment, carcasses, water, food and clothing.

The emergence of Australian-origin ND viruses by mutation from lentogenic strains caused a rethink of the control of the disease in Australia. The National Newcastle Disease Management Plan 2002/03–2003/04 was developed and the National Newcastle Disease Steering Committee formed in 2002. A vaccination program was introduced to protect commercial flocks against ND viruses. From 1 April 2005, vaccination of chickens in commercial flocks in Queensland has been compulsory under the Stock Regulation 1988. There have been no outbreaks of ND since compulsory vaccination. Currently the National Newcastle Disease Management Plan 2013-2016 is in place. The Plan includes vaccination (according to the nationally agreed Newcastle disease vaccination program – Standard operating procedures (SOPs) of commercial domestic chickens in all states and territories). In jurisdictions considered to be of low risk for an outbreak of ND (QLD, SA, WA and TAS), vaccination of short-lived birds (i.e. birds of relatively low risk) may be reduced as per the revised SOPs. However, in flocks that opt for reduced vaccination, surveillance protocols as detailed in the plan must be implemented under the Biosecurity Act 2014 in Queensland.

Exotic strains of virulent ND virus detected in Australia will be eradicated by immediate movement restriction of the flock and the elimination of the virus by stamping out the infected flocks, vaccination of at-risk flocks, and cleaning/disinfection of all affected premises.