Avian Influenza

Avian influenza (AI) is caused by viruses that can infect poultry (primarily 

chickens and turkeys) and some wild bird species (such as wild ducks 

and swans). AI viruses are classified by a combination of two groups of 

proteins: hemagglutinin or “H” proteins, of which there are 16 (H1–H16), 

and neuraminidase or “N” proteins, of which there are 9 (N1–N9). They 

are further classified by their ability to produce disease, or pathogenicity, 

in domestic chickens. Highly pathogenic avian influenza (HPAI) strains 

are extremely infectious, often fatal to domestic poultry, and spread 

rapidly. Low pathogenic avian influenza (LPAI) strains occur naturally in 

wild migratory waterfowl and shorebirds without causing illness. However, 

because LPAI H5 and H7 viruses can change to HPAI in poultry, infection of 

commercial poultry with H5 and H7 viruses is reportable to State, Federal, 

and international animal health authorities.

Newcastle Disease 

Newcastle disease (ND) in commercial poultry is reportable to both 

domestic and international animal health authorities. A finding of this 

disease negatively impacts international trade in poultry and poultry 

products. The two most devastating outbreaks in the United States 

occurred in southern California. The 1971–1974 outbreak was caused by 

imported, infected exotic pet birds and cost over $56 million in Federal 

funds to eradicate. The 2002–2003 outbreak began in illegally imported 

backyard game fowl and spread to commercial poultry. It cost over $180 

million in Federal funds to eradicate. Although the disease has been 

eradicated from the U.S. poultry population, it is found periodically in 

illegally imported birds and migratory waterfowl. These sources of ND 

are an ongoing threat to the U.S. poultry industry.

Avian Surveillance

Animal and Plant Health Inspection Service

NATIONAL ANIMAL HEALTH LABORATORY NETWORK
Surveillance Efforts

The National Animal Health Laboratory Network (NAHLN) can handle both 

nationwide surveillance testing and large-volume testing during disease 

outbreaks. Screening tests conducted at the NAHLN labs determine 

whether the AI or ND viruses are present in the sample. AI samples are also 

tested for the H5 and H7 subtypes. Regardless of subtype, all presumptive 

positive AI and ND samples from commercial poultry, the live-bird marketing 

system, and backyard flocks are sent to USDA’s National Veterinary Services 

Laboratories (NVSL) for confirmation and additional testing. H5 and H7 

presumptive positive samples from wild birds are also sent to NVSL.

DOMESTIC POULTRY

USDA conducts routine surveillance for AI in commercial poultry, the 

live-bird marketing system, and backyard flocks. State and Federal staff 

collect samples, NAHLN and National Poultry Improvement Plan-authorized 

laboratories test the samples, and NVSL carries out all confirmatory testing. 

At this time, there is no nationwide surveillance program for ND taking 

place, but personnel at approved NAHLN labs are trained on ND-specific 

testing methods and ready to respond when needed. 

WILD BIRDS

For several years, AI surveillance also took place in wild birds due to 

concerns about the potential for highly pathogenic H5N1 AI entering 

the United States. This testing was a joint effort between USDA, the 

U.S. Department of the Interior, and State wildlife management agencies. 

Wild migratory species, including primarily ducks, geese, and shorebirds, 

were tested. USDA and State wildlife agencies collected the samples, 

which were tested by 35 NAHLN laboratories and the National Wildlife 

Health Center. NVSL conducted all confirmatory testing. This surveillance 

effort ended in 2011, but USDA continues to test for AI in wild bird 

mortality events.

National Animal Health Laboratory Network 

NAHLN, a State and Federal partnership to safeguard animal health

Phone: (515) 337-7731

Email: NAHLN@aphis.usda.gov

Web site: www.aphis.usda.gov/nahln

USDA is an equal opportunity provider and employer.

This publication supersedes APHIS 91-95-009, “Avian Influenza (AI),” which was published in October 2011. 

Issued September 2014 • APHIS 91-95-014