Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2002
Publication Date: 8/1/2003
Citation: Henzler, D.J., Kradel, D.C., Davison, S., Ziegler, A.F., Singletary, D., Debok, P., Castro, A.E., Lu, H., Eckroade, R., Swayne, D.E. 2003. Epidemiology, Production Losses, And Control Measures Associated With An Outbreak Of AI Subtype H7N2 In Pennsylvania (1996-1998). Avian Diseases 47:1022-1036, 2003.
Interpretive Summary: An outbreak of H7N2 mildly pathogenic (MP) avian influenza (AI) occurred in Pennsylvania between December of 1996 and April of 1998. The AI virus infected 2,623,116 commercial poultry in 47 flocks on 24 farms. The AI virus originated from the live bird market system of the northeastern US. Farms with infected egg laying chickens experience 1.6-29.1% decrease in egg production and death rate in birds increased to 1.5-18.3 times normal daily mortality rate. Quarantine of infected flocks, strict biosecurity and controlled marketing of products resulted in elimination of the disease.
Technical Abstract: An outbreak of H7N2 mildly pathogenic (MP) avian influenza (AI) occurred in a two county area in Pennsylvania from December of 1996 through April of 1998 and resulted in infection of 2,623,116 commercial birds on 24 premises encompassing 47 flocks. Twenty of the 24 infected premises were egg-laying chickens (includes 1 suspect premise) and 1 premises each of turkeys, pullets, quail and a mixed backyard dealer flock. Despite close proximity of infected flocks to commercial broiler flocks, no broiler flocks were known to be infected, although experimentally, when market age broilers were placed in an influenza infected premise they did serologically convert and developed oviduct lesions. The outbreak was believed to have originated from two separate introductions into commercial layer flocks from premises and by individuals dealing in sales of live fowl in the metropolitan New York and New Jersey live bird markets. Source flocks for these markets are primarily in the northeast and mid-Atlantic areas including Pennsylvania. Mixed fowl sold include: ducks, geese, guinea hens, quail, chukar partridges and a variety of chickens grown on perhaps hundreds of small farms. Infections with the H7N2 AI virus were associated with variable morbidity and temporary decreases in egg production ranging from 1.6% to 29.1% in egg-laying chickens. Egg production losses averaged 4.0 weeks duration among all flocks. Mortality ranged from 1.5 to 18.3 times normal with a mean of 4.3 times normal. Duration of mortality ranged from 2 to 13 weeks in flocks not depopulated. Mortality losses averaged 3.9 weeks duration among all flocks. Lesions observed were primarily oviducts filled with a mucous and white gelatinous exudates and atypical "egg yolk peritonitis". Quarantine of premises and complete depopulation were the early measures employed to attempt to control this outbreak. Epidemiological studies suggested that depopulation furthered the spread of influenza to nearby flocks. Thereafter, later control measures included quarantine, strict biosecurity and controlled marketing of products.