76. Newcastle disease (aetiology, epidemiology, pathogenesis, clinical signs).

Question 1

History, Occurrence?

Answer 1

Newcastle disease

• Paramyxoviridae, Paramyxovirinae, Avulavirus genus, Newcastle disease virus (NDV)

History, occurrence

• 1800s italyʹ first description
• 1927, Doyle ʹ differentiation from Avian influenza
• Genotypes: III SEA, IV Europe, II USA
• World-wide occurrence
• Velogenic NDV is endemic in areas of Mexico, Central & S. America, widely spread in Asia, the Middle East & Africa, & in double crested wild cormorants in the US & Canada
• Lentogenic strains of NDV are worldwide in their distribution
• Widespread mesogenic pathotypes with a special adaptation to pigeons (i.e. pigeon paramyxovirus)
• do not appear to infect other poultry readily
• Velogenic, mesogenic, lentogenic and apathogenic strains of the virus
• (highest virulence is velogenic cause severe disease)
• Mesogenic, lentogenic & apathogenic strains used as vaccines (isolate the virus to make vaccine) ʹ
• presence of these viruses is not notifiable
• Velogenic strain (not the ND virus) = notifiable disease !!

Question 2

Causative agent?

Answer 2

Causative agent:

• Avian paramyxovirus 1 ʹ Newcastle disease virus
• Several genotype, geno-group, variant
• Pathotypes/virulence variants: RNA dependent polymerase Æ many mutants
• Velogenic (viscerotropic & neuro/pneumotropic) ʹ E, C, A (embryo, chick,͙͍Ϳ
• Pneumotrop (neurotrop) ʹ neural & resp symptoms stronger
• viscerotrop ʹ higher mortality, haemorrhages etc.
• Mesogenic (H strain) ʹ E, C
• Lentogenic (LaSota, B1) ʹ E
• Apathogenic (NDV/6 etc.) ʹ E
• Determine virulence
• A) Chicken embryo survival index (10-11-day-old embryo)
• B) Intracerebral pathogenicity index (ICPS) (days old chick)
• C) IV pathogenicity index (IVPI) (6-week old chicken)
• D) Nucleotide-sequence analysis
• Resistance
• o 56oC/3h; 60oC/30 min; < pH 2; lipid solvents
• Long survival in faeces, excretes, secrets, raw meat
• Broad host spectrum - euryxen
• Poultry (chicken > turkey)
• Wild birds, pet birds, ostrich
• Waterfowl, raptors less frequently

Question 3

Epizootiology?

Answer 3

Epizootiology

• Source of infection
• Resp secretions/discharges & faeces of infected birds
• All parts of the carcass
• Virus is shed during the incubation period, during clinical stages & for a limited period during convalescence
• Wild birds & waterfowl may act as reservoir hosts for lentogenic pathotypes of ND
• Subsequently, these viruses could become virulent following mutation upon establishment in domestic poultry
• Some psittacine birds have been demonstrated to shed ND virus intermittently for over 1 year (&
• been associated with introduction into poultry)
• Transmission
• Direct contact with secretions of infected birds; principally via ingestion (faecal/oral route) &
• inhalation
• Fomites: feed, water, implements, premises, human clothing, boots, sacks, egg
• trays/crates etc.
• Survival of agent is prolonged by presence of faeces; as in soiled egg shells
• Hatching chicken may be infected through egg for some NDV strains;
• transmission of highly virulent isolates is uncommon
• No clear evidence of role of flies in mechanical transmission
• Velogenic viscerotropic: high morbidity & mortality
• In immunised flocks velogenic strains cause sporadic cases & subclinical infections
• Sporadic in chicken with yolk immunity
• Rarely high morbidity & mortality with neurotropic strains
• Mesogenic strains may cause resp & CNS disease in young birds

Question 4

Pathogenesis?

Answer 4

Pathogenesis

• Aerogen/PO entry , resp mucosa ,viraemia ʹ generalisation (lung, intestine, CNS);
• intestinal mucosa ʹ long term shedding
• BV damages ,oedema, conjunctions, haemorrhages , Immunosuppression (2dary infections!)
• CNS: neuron death, inflammation, oedema
• Oviduct damage , egg production problems, lethal for embryo

Question 5

Clinical signs?

Answer 5

Clinical signs:

• 3-6 days incubation
• Vary widely
• Pathotype
• Host species and age and health condition
• Co-infections
• Environmental stress
• Morbidity & mortality depend on;
• virulence of the virus strain
• degree of vaccinal immunity
• environmental conditions
• condition of the flock

Question 6

Lentogenic strain, mesogenic strain velogenic strain?

Answer 6

Lentogenic strain

• (LaSota, B1) ʹ E
• Least virulent

Mesogenic strain

• (H strain) ʹ E, C

Velogenic strain

• (viscerotropic & neuro/pneumotropic) ʹ E,
• C, A
• Most virulent
• Subclinical disease:
• mild resp disease ʹ
• cough, gasping,
• sneezing rales
• Co-infections
• severe signs
• Negligible mortality
• Can cause acute resp
• disease/CNS signs
• Mortality rate <10%
• Co-infections
• severe signs
• Severe disease in C with mortality: resp and
• CNS signs
• First: lethargy, inappetence, ruffled
• feathers, edema, conjunctiva injection
• Later: green/white watery diarrhoea,
• dyspnoea, inflammation of head/neck with
• cyanotic discoloration
• Later: CNS ʹ tremors, tonic/clonic spasms,
• wing/leg paresis/paralysis, torticollis,
• circling behaviour
• Drop in egg production: watery albumin and
• misshaped with abnormally
• colored/rough/thin shells
• Often cause sudden death without signs
• If survive, may develop CNS and stop egg
• production
• Morbid/mortality can reach 100% in
• unvaccinated