Evaluation of the infectivity, length of infection, and immune response of a low-pathogenicity H7N2 avian influenza virus in specific-pathogen-free chickens

Huaguang Lu, Anthony E. Castro

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32 Citations (Scopus)

Abstract

The H7N2 subtype of avian influenza virus (AIV) field isolate (H7N2/chicken/ PA/3779-2/97), which caused the 1997-98 AIV outbreak in Pennsylvania, was evaluated for its infectivity, length of infection, and immune response in specific-pathogen-free (SPF) chickens. The composite findings of three clinical trials with various concentrations of virus indicated that this H7N2 subtype contained minimal pathogenicity for chickens. The concentration of the virus in the inoculum proved critical in the establishment of a productive infection in a chicken. Seven-day-old SPF chickens were not infected when inoculated with 100.7-2.0 mean embryo lethal dose (ELD50) of the H7N2 virus per bird. At this dose level, the immune response to this virus was not detected by the hemagglutination-inhibition (HI) test. Nonetheless, chickens at ages of 5 and 23 wk old tested were successfully infected when exposed to 104.7-5.7 ELD50 of H7N2 infectious doses per bird by various routes of administration and also by direct contact. Infected birds started shedding virus as early as 2 days postinoculation, and the period of virus shedding occurred mostly within 1 or 2 wk postinoculation (WPI). This H7N2 subtype of AIV induced a measurable immune response in all birds within 2 wk after virus exposure. Antibody titers were associated with AIV infectious doses and age of exposure of birds. Challenge of these infected birds with the same H7N2 virus at 5 and 10 WPI indicated the infective virus was recoverable from cloacal swabs at 3 days postchallenge and disappeared thereafter. In these challenged birds, the antibody levels as measured by the HI test spiked within 1-2 wk.

Original languageEnglish (US)
Pages (from-to)263-270
Number of pages8
JournalAvian Diseases
Volume48
Issue number2
DOIs
StatePublished - Jan 1 2004

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Specific Pathogen-Free Organisms
Influenza in Birds
Orthomyxoviridae
Influenza A virus
Birds
Virulence
H7N2 Subtype Influenza A Virus
Chickens
pathogenicity
immune response
chickens
viruses
pathogens
birds
Infection
infection
Viruses
Hemagglutination Inhibition Tests
Virus Shedding
hemagglutination inhibition test

All Science Journal Classification (ASJC) codes

  • Food Animals
  • Animal Science and Zoology
  • Immunology and Microbiology(all)

Cite this

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abstract = "The H7N2 subtype of avian influenza virus (AIV) field isolate (H7N2/chicken/ PA/3779-2/97), which caused the 1997-98 AIV outbreak in Pennsylvania, was evaluated for its infectivity, length of infection, and immune response in specific-pathogen-free (SPF) chickens. The composite findings of three clinical trials with various concentrations of virus indicated that this H7N2 subtype contained minimal pathogenicity for chickens. The concentration of the virus in the inoculum proved critical in the establishment of a productive infection in a chicken. Seven-day-old SPF chickens were not infected when inoculated with 100.7-2.0 mean embryo lethal dose (ELD50) of the H7N2 virus per bird. At this dose level, the immune response to this virus was not detected by the hemagglutination-inhibition (HI) test. Nonetheless, chickens at ages of 5 and 23 wk old tested were successfully infected when exposed to 104.7-5.7 ELD50 of H7N2 infectious doses per bird by various routes of administration and also by direct contact. Infected birds started shedding virus as early as 2 days postinoculation, and the period of virus shedding occurred mostly within 1 or 2 wk postinoculation (WPI). This H7N2 subtype of AIV induced a measurable immune response in all birds within 2 wk after virus exposure. Antibody titers were associated with AIV infectious doses and age of exposure of birds. Challenge of these infected birds with the same H7N2 virus at 5 and 10 WPI indicated the infective virus was recoverable from cloacal swabs at 3 days postchallenge and disappeared thereafter. In these challenged birds, the antibody levels as measured by the HI test spiked within 1-2 wk.",
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