December 21, 2017

Purdue: Avian Flu - Public Health Readiness and Response

A coordinated effort in 2016 helped to stave off a potential pandemic and reinforced the precautions required for veterinarians who may become involved with an avian flu outbreak.
By Nicola M. Parry, BVSc, MRCVS, MSc, DACVP, ELS
Influenza is a good example of how animal and human health interconnect, according to Indiana State Public Health Veterinarian Jennifer Brown, DVM, MPH, DACVPM. Some outbreaks of avian influenza in poultry result in cooperative responses from multiple agencies at the local, state, and federal levels to implement plans to contain and stop the outbreak.

Presenting at the 2017 Purdue Veterinary Conference in West Lafayette, Indiana, Dr. Brown discussed key aspects of the public health response to the 2016 outbreak of H7N8 avian influenza virus in poultry in Dubois County, Indiana.

Human Influenza
“In a typical flu season, between 5% and 20% of the population gets the flu,” said Dr. Brown. More than 200,000 individuals are hospitalized due to complications of influenza infection, including sinus and ear infections, pneumonia, myocarditis, encephalitis, multiorgan failure, and sepsis, she added, and about 36,000 die from flu-related causes. Populations that are especially vulnerable include children younger than 5 years, adults older than 65 years, pregnant women, and patients with underlying health conditions.

Of the 4 types of influenza virus (A, B, C, and D), Dr. Brown noted that types A and B cause most infections in humans and that type A is most often associated with severe disease. “Type A influenza viruses are the scariest of the 4 types,” she said, “because they are capable of major genetic change—which is what makes them so dangerous.” Type B influenza virus typically causes less severe disease, and type C causes mild or asymptomatic disease. Type D does not cause disease in humans, she noted.

Influenza viruses are changing constantly, and they accomplish this in 2 major ways: antigenic drift and antigenic shift. All influenza viruses are capable of antigenic drift, which causes small genetic changes that continually occur and are cumulative. Because the changes are small, the population may retain some background immunity to the changed virus, Dr. Brown said. In contrast, only type A viruses undergo antigenic shift, she said, because they have a segmented genome. Although antigenic shift occurs infrequently, it leads to major abrupt genetic changes, producing a novel virus to which the population has little immunity.

The 1918 influenza pandemic involved influenza type A, sub-type H1N1, said Dr. Brown. This was the deadliest influenza pandemic in modern history. It caused illness in 20% to 40% of the world’s population and killed about 50 million people. “Almost all human influenza cases since 1918 have been a result of descendants of this virus,” Dr. Brown emphasized.

Avian Influenza
Most of the influenza A viruses can also infect birds, said Dr. Brown, and wild aquatic birds are thought to be the natural reservoir of these viruses. Avian influenza refers to the disease caused by avian influenza type A viruses. These viruses cause high morbidity and mortality in birds and are very contagious. They are categorized as highly pathogenic avian influenza (HPAI) or low-pathogenicity avian influenza (LPAI) viruses based on their effects in chickens.

Although avian influenza type A viruses typically do not infect people, rare cases of human infection have been reported. In avian influenza outbreak events, humans can be at high risk for infection with the virus for various reasons, including having direct contact with birds (dead or alive), performing necropsies, sampling birds, moving birds, and checking feeders. Symptoms of infection in these cases are similar to those associated with human influenza virus infection and can include cough, fever, sore throat, and runny nose. Conjunctivitis alone can also occur. In severe infections, illness can progress to multiorgan failure or death.

HPAI Asian H5N1 and LPAI Asian H7N9 viruses have been responsible for most cases of avian influenza in humans worldwide, said Dr. Brown. Backyard poultry can spread the virus to humans via aerosol matter, direct contact, or fomites.

Sign up to receive the latest news in veterinary medicine.

Latest Issue

Client Education

American Veterinarian