Investigation of H7N2 Avian Influenza Outbreaks in Two Broiler Breeder Flocks in Pennsylvania, 2001–02

Abstract

An avian influenza (AI) outbreak occurred in meat-type chickens in central Pennsylvania from December 2001 to January 2002. Two broiler breeder flocks were initially infected almost simultaneously in early December. Avian influenza virus (AIV), H7N2 subtype, was isolated from the two premises in our laboratory. The H7N2 isolates were characterized as a low pathogenic strain at the National Veterinary Services Laboratories based on molecular sequencing of the virus hemagglutinin cleavage site and virus challenge studies in specific-pathogen-free leghorn chickens. However, clinical observations and pathologic findings indicated that this H7N2 virus appeared to be significantly pathogenic in meat-type chickens under field conditions. Follow-up investigation indicated that this H7N2 virus spread rapidly within each flock. Within 7 days of the recognized start of the outbreak, over 90% seroconversion was observed in the birds by the hemagglutination inhibition test. A diagnosis of AI was made within 24 hr of bird submission during this outbreak using a combination of virus detection by a same-day dot-enzyme-linked immunosorbent assay and virus isolation in embryonating chicken eggs. Follow-up investigation revealed that heavy virus shedding (90%-100% of birds shedding AIV) occurred between 4 and 7 days after disease onset, and a few birds (15%) continued to shed virus at 13 days post-disease onset, as detected by virus isolation on tracheal and cloacal swabs. AIV was not detected in or on eggs laid by the breeders during the testing phase of the outbreak. The two flocks were depopulated at 14 days after disease onset, and AIV was not detected on the two premises 23 days after depopulation.

Geostatistical visualisation and spatial statistics for evaluation of the dispersion of epidemic highly pathogenic avian influenza subtype H5N1

“…Whilst outbreaks of influenza in domestic poultry continue to be blamed on contact with free-range and wild birds, based on the circumstantial evidence of co-location of wild birds and domestic poultry in time and space [7], illegal movements of poultry and other avian species have been documented as contributing to H5N1 spread in several instances [20,24]. Live bird markets have also been the presumed source of avian influenza outbreaks in domestic poultry, notably in the United States [6,10,16,18,22] and in Asia [24].…”

“…Traditional husbandry practices in China and Southeast Asia, which favour commingling of multiple avian and mammalian species -as well as the popularity of live bird markets -may have contributed to the maintenance of the H5N1 virus strain [24]. In other regions of the world, HPAI outbreaks in commercial poultry have been traced to live bird markets [6,10,16].…”

The challenge of avian influenza to the veterinary community

“…Swayne & Beck (2004) cited P. Dunn as reporting failure to isolate AI virus from the albumen of 9930 eggs tested during the monitoring of three layer flocks in Pennsylvania infected with H7N2 LPAI during 1996 to 1998. Equally, Lu et al (2004) failed to demonstrate the presence of LPAI H7N2 virus in egg shell swabs, albumen or yolk of eggs laid by hens with respiratory signs and egg production problems despite the virus being present in tracheal and cloacal swabs. In contrast Ziegler et al (1999) reported the isolation of virus from the oviduct in hens infected with H7N2 LPAI during the 1996 to 1998 Pennsylvania outbreak.…”

Flock-Based Surveillance for Low Pathogenic Avian Influenza Virus in Commercial Breeders and Layers, Southwest Nigeria

“…Most LPAI viruses (LPAIVs) produce mild to moderate disease in commercial rearing settings, especially when complicated by secondary pathogens, immunosuppression, and stress factors in the environment. Drops in egg production have also been observed in chicken breeders and layers infected with these viruses (Lu et al, 2004;Pillai et al, 2009). Furthermore, outbreaks of HPAI that resulted from circulating LPAI H5, H7 and H9 viruses have been reported in poultry worldwide (Iqbal et al, 2009;Snoeck et al, 2011).…”