newcastle disease - avaava.org.af/books/newcastle1.pdf · newcastle disease • many strains of...
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Newcastle Disease
• Many strains of similar virus cause signs ranging from mild respiratory signs (pneumotropic) with low mortality to severe neurological (neurotropic) and/or visceral lesions (viscerotropic) with heavy mortality
• Affects most domestic fowl as well as many wild and pet type birds
• May cause conjunctivitis in humans
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Etiology
• Paramyxovirus type 1 = Newcastle disease.
There are 9 types of paramyxovirus.
• Single stranded RNA virus.
• The fact that this virus naturally hemagglutinates red
blood cells is used in a simple differential diagnostic
test. All paramyxoviruses will hemagglutinate
RBC's.
• Virus can survive in dust and survives well in organic
materials.
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Etiology (Cont.)
• Virus has strains that differ in pathogenicity. The
Mean Death Time (MDT) of embryos and the
Intracerebral Pathogenicity Index (ICPI) are used to
differentiate among the pathotypes.
• Enzootic strains are of low virulence and their
technical designation is paramyxovirus type 1, but
are still referred to as Newcastle disease virus.
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Etiology (Cont.)
• Lentogenic - mild - kills embryos in > 90 hours
All enzootic strains in U. S. poultry are lentogenic
• Mesogenic - moderate - kills embryos in 60-90
hours
Mesogenic strains do not occur in U.S. poultry
• Velogenic - highly virulent neurotropic or
viscerotropic - kills embryos in < 60 hours
Velogenic strains are now officially designated as Exotic
Newcastle Disease (END)
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Etiology (Cont.)
• Lentogenic & mesogenic are used as
vaccine strains.
Hitchner: B1 - B1 - milder
La Sota: B1 - La Sota - more virulent.
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Etiology (Cont.)
Exotic Newcastle Disease (END)
• ICPI of 0.7 or greater
• Synonyms: Velogenic Viscerotropic Newcastle Disease (VVND), Asiatic Newcastle Disease
• Not in the U.S. or Canada at present.
• Caused very costly outbreak in California in early 1970's which cost $54,000,000 to eradicate
• 2002 California outbreak and numerous instances in pet birds have been stamped out
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Method of Spread
• Aerosol from infected bird excretions
• Mechanical vectors
• Vaccination is done with mild viruses, but this keeps
mild forms of the disease endemic in commercial
poultry producing areas.
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Method of Spread (Cont.)
• Exotic Newcastle has brought into this country in
smuggled pet birds and game fowl
• These introductions caused the California outbreaks
• There have been many other introductions of this
virus into this country but fortunately the pet birds
have not come in contact with commercial
poultry flocks.
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Method of Spread (Cont.)
• There are about 100 quarantine stations where pet
birds are held when imported into the U.S.
• There has been no recorded incidence where pet
birds that were released from these stations caused
the dissemination of NCD.
• The greatest threat is smuggled pet birds.
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Mortality
Enzootic ND
• Lentogenic & Mesogenic -
Usually negligible but can be complicated with other infections and cause up to 30% mortality.
• Velogenic -
Variable up to 50% in adults and 90% in chicks.
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Mortality (Cont.)
Exotic ND (END)
• VVND -- up to 90-100% mortality in poultry --
much less in non-gallinaceous birds.
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Mortality (Cont.)
• Most problems in commercial poultry in U.S. are
caused by vaccinal strains acting as stressors
causing secondary infection such as E. coli
airsacculitis.
• Mortality will vary depending on severity and
virulence of secondary invaders.
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Signs
Young Chickens
Enzootic ND
• Sudden onset with depression & prostration. Respiratory signs such as gasping, coughing, rales and nasal discharge, necrotic comb.
• CNS signs closely follows respiratory signs. Twisted heads and "Stargazers". Usually less than 25% have CNS signs - opisthotonus. This occurs with either neurotropic or pneumotropic strains.
• Mortality depends on virulence of strain. May be up to 95%.
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Conjunctivitis
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Nervous Signs
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Signs (Cont.)
Adult Chickens
Enzootic ND
• Sudden onset with mild depression and anorexia. Respiratory disease may be mild and mortality is low or absent.
• CNS signs are few.
• Layers may cease to produce. Eggs that are laid are low quality and rough or soft shelled - similar to IBV.
Production may or may not return - depending on stage of lay.
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Egg Shell Malformation
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Turkey Eggs
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CNS Signs
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Signs (Cont.)
Exotic ND (END)
Young and Adult Chickens
• Marked dyspnea
• Violent diarrhea (blood stained)
• Swollen head and throats
• Conjunctivitis
• Paralysis and death in 2 to 3 days
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Signs (Cont.)
Turkeys
• Usually mild to moderate respiratory signs.
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Postmortem Lesions
ENZOOTIC NCD
• Inflammation of the trachea and air sacs
• May be no gross lesions
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Postmortem Lesions (Cont.)
Exotic ND (END)
• Severe inflammation of trachea and air sacs
• Hemorrhagic or necrotic foci in mucosa of gut and cecal tonsils
• Severe hemorrhages of mucosal surface of the proventriculus and isthmus of gizzard. Cloacal hemorrhage
• Pet bird may have mild non-specific lesions and no gross lesions. (Can have severe enteric type)
• CNS histopathological lesions are present but must be differentiated from AE and MD
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SQ Hemorrhage
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Cecal Tonsil
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Cloaca
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Proventriculus
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Differential Diagnosis
• Infectious bronchitis - respiratory
• Laryngotracheitis - respiratory
• Avian encephalomyelitis - neurological
• Vitamin E & selenium deficiency - neurological
• Mycotic encephalitis - neurological
• Avian influenza - variable pathogenicity
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Diagnosis
• History
• HI
• VN - with known ND antisera
• Immunofluorescence
• ELISA
• Paired HI test on acute and convalescent sera
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Diagnosis (Cont.)
• Isolation and identification of the virus.
Hemagglutinating virus. Tracheas are the organ of
choice for virus isolation.
• Virus neutralization with ND antiserum. In cases of
mixed viral respiratory infection, NDV will show up in
the embryos before IBV.
• Reproduce disease in susceptible chickens with
virus.
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Treatment
• None
• Broad spectrum antibiotics for secondary bacterial
involvement
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Prevention
Enzootic ND
Vaccination:
• Live Virus
B1 B1
VGGA (Glisson/ Villegas), vaccine developed at UGA, has reduced vaccinal reaction
La Sota
• Killed Virus in oil adjuvant, produced with B1 virus.
Maternal antibodies interfere with active immunity buffering the expected vaccine reaction.
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Prevention (Cont.)
Enzootic
Immature Birds - broilers, leghorn pullets, etc.
Vaccinated with live vaccines usually at 1 to 4 days
and at around 14 to 28 days.
This virus doesn’t replicate in the Harderian gland, so
lower maternal antibody is desired to prevent
vaccine blockage.
Breeders & Leghorns - give killed vaccine at
around 12-18 wks. of age after being primed with
live vaccine.
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Vaccination Cabinet
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Aerosol Vaccination
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Prevention (Cont.)
Exotic ND
• Eradicated in the U.S. by massive slaughter in early 1970's and again in 2002
• Vaccination not allowed
• Vaccinated for in foreign countries using more potent vaccines than are used in the U.S. Greater vaccine virulence causes more severe vaccine reactions.
• Requires multiple vaccination programs and success is limited.
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Conjunctivitis
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