NEWCASTLE DISEASE

Three categories of viral pathogenicity result in different clinical forms of the disease.

  • Velogenic-viscerotropic virus (vvND) infection results in acute onset, highly lethal disease.
  • Mesogenic virus causes acute, moderately lethal disease with nervous and respiratory signs.
  • Lentogenic virus is responsible for mild respiratory infection.

Velogenic and mesogenic forms are exotic to the USA, Canada, the UK and other European countries but are widespread in Asia, Africa, and Latin America. The lentogenic form is encountered in most poultry-producing areas including the USA. Severe losses from mortality, depressed egg production and lowered feed conversion efficiency occur as a result ofexposure to vvND.

The lentogenic form is responsible for erosive losses in broilers including lowered gain and feed conversion efficiency and elevated mortality andcondemnation. The severity and financial impact depends on climatic and management stress and intercurrent exposure to pathogenic E. coli andother viral respiratory disease and immunosuppressive agents.

Velogenic Viscerotropic Newcastle Disease
This form is characterized by acute onset with up to 100% flock morbidity and rapidly ascending high mortality (20% in 2 days, 50% in 3 days, 80% in 5 days) accompanied by respiratory and nervous signs. In susceptible commercial egg production flocks and breeders, peracute cessation of production occurs with the presence of shell-less eggs due to premature oviposition. Exposure of immunized flocks results in variable decline in production.
Mesogenic
Variable to high morbidity is evident in an exposed flock which will show moderate mortality characterized by nervous and respiratory signs. An acute drop in egg production occurs in susceptible mature flocks with the presence of shell-less eggs.
Lentogenic
Acute onset with moderate to high morbidity. Mild to inapparent respiratory signs are noted but negligible mortality occurs in uncomplicated cases. Lentogenic ND may be responsible for asymptomatic drops in egg production in incompletely immunized commercial layer or breeder flocks.

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NEWCASTLE DISEASE

Etiology

Antigenically related strains of Avian paramyxovirus, type 1.

Occurrence and Economic Significance

Three categories of viral pathogenicity result in different clinical forms of the disease.

  • Velogenic-viscerotropic virus (vvND) infection results in acute onset, highly lethal disease.
  • Mesogenic virus causes acute, moderately lethal disease with nervous and respiratory signs.
  • Lentogenic virus is responsible for mild respiratory infection.

Velogenic and mesogenic forms are exotic to the USA, Canada, the UK and other European countries but are widespread in Asia, Africa, and Latin America. The lentogenic form is encountered in most poultry-producing areas including the USA. Severe losses from mortality, depressed egg production and lowered feed conversion efficiency occur as a result ofexposure to vvND.

The lentogenic form is responsible for erosive losses in broilers including lowered gain and feed conversion efficiency and elevated mortality andcondemnation. The severity and financial impact depends on climatic and management stress and intercurrent exposure to pathogenic E. coli andother viral respiratory disease and immunosuppressive agents.

The cost and consequences (respiratory stress) of vaccination are significant, especially during winter and following immunosuppression.

Disruption of trade and the cost of eradication of vvND in non-endemic countries imposes a significant burden on producers and the public sector after outbreaks.

Transmission

ND virus is highly contagious. Infection occurs either by the inhalation of virus in aerosol form or ingestion of contaminated feed or litter.

  • Wind dispersal may occur over distances of 5 km.
  • Direct and indirect contact with contaminated material (fomites) is associated with deficiencies in biosecurity.
  • Companion birds, backyard flocks and gamefowl serve as reservoirs.

Clinical Signs

Velogenic Viscerotropic Newcastle Disease

This form is characterized by acute onset with up to 100% flock morbidity and rapidly ascending high mortality (20% in 2 days, 50% in 3 days, 80% in 5 days) accompanied by respiratory and nervous signs. In susceptible commercial egg production flocks and breeders, peracute cessation of production occurs with the presence of shell-less eggs due to premature oviposition. Exposure of immunized flocks results in variable decline in production.

Mesogenic

Variable to high morbidity is evident in an exposed flock which will show moderate mortality characterized by nervous and respiratory signs. An acute drop in egg production occurs in susceptible mature flocks with the presence of shell-less eggs.

Lentogenic

Acute onset with moderate to high morbidity. Mild to inapparent respiratory signs are noted but negligible mortality occurs in uncomplicated cases. Lentogenic ND may be responsible for asymptomatic drops in egg production in incompletely immunized commercial layer or breeder flocks.

Pathology

Velogenic

Prominent hemorrhages occur throughout the digestive tract especially in the mucosa of the proventriculus and gut-associated lymphoid tissue.

Severe tracheitis and pulmonary congestion are evident in acute cases. These changes are not specific to vvND and may be observed with highly pathogenic strains of avian influenza and vvIBD.

Lentogenic

Mild conjunctivitis and tracheitis are observed. Recovered flocks show septicemia and airsacculitis due to secondary infection with E. coli.

Diagnosis

Isolation. The virus can be detected applying PCR technology to obtain a provisional diagnosis within a working day. Identification and characterization of the virus by a suitably equipped laboratory is the usual confirmatory procedure. Retrospective serology (ELISA, hemagglutination inhibition and serumvirus neutralization) demonstrates the presence of antibodies which indicates exposure to ND virus and the titer (level) can differentiate between field infection and previous vaccination.

Prevention

Vaccination. Conventional programs:

  • Lentogenic infection of broilers can be prevented by day old administration of aerosol or eye drop vaccine using Hitchner B1 with subsequent boosters in drinking water or by the aerosol route.
  • Administration of a preparation comprising live virus with complementary antibody by the in ovo route at 18-days of incubation is protective in countries where the vaccine is available.
  • Recombinant pox and HVT-vector vaccines expressing the fusion (F) protein of NDV are available for either in ovo or subcutaneous vaccination.
  • Lentogenic infection of breeders can be prevented by 10 day administration of Hitchner B1, by the aerosol or eye drop route.
  • Subsequent vaccinations include 24 day, and 8 week Hitchner B1 or LaSota in non-chlorinated drinking water, followed by multivalent oil inactivated emulsion at 18-20 weeks. An optional 45 week multivalent oil inactivated emulsion may be administered to boost maternal antibody transfer, depending on antibody titer of the flock, risk of exposure, and other factors relating to the operation.
  • In areas with a defective cold-chain the V-strain live thermostable mutant ND can be distributed to subsistence and backyard flocks.

A variety of vaccination programs can be followed depending on the risk of infection, virulence of agent, management system, and economic factors.

In countries with endemic vvND, rigorous programs are implemented, incorporating day-old subcutaneous emulsion vaccine together with attenuated live vaccine by the eye-drop route. Hitchner or LaSota vaccine is administered to broilers by the aerosol route at 10 day intervals thereafter.

Breeders may be immunized with mesogenic-strain vaccines in some countries. This expedient is only justified if birds have previously received one or more live attenuated lentogenic vaccines

Fowl Cholera

Fowl cholera is a contagious, bacterial disease that affects domestic and wild birds worldwide. It usually occurs as a septicemia of sudden onset with high morbidity and mortality, but chronic and asymptomatic infections also occur.

ASPERGILLOSIS

The disease is world-wide in distribution but cases are more frequently diagnosed in tropical countries especially during warm and humid weather.

Severe outbreaks associated with hatchery contamination may result in up to 15% chick mortality during the first two weeks. Decreased growth rate and ascites complex are noted in affected survivors.

Fowl cholera is the reason for great economic loss of poultry in bangladessh

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