Bird flu or avian influenza, has recently generated significant international media attention due to widespread activity in many regions. Although many people worry about the threat of avian influenza to humans, the greater threat is the economic impact associated with outbreaks in poultry. Authorities often react severely at the first sign of disease activity to mitigate financial losses. Fortunately, the risk of human infection from avian influenza is low for individuals not in contact with live or recently deceased poultry.
Avian Influenza Infection in Birds
Avian influenza viruses are an extremely diverse group of viruses that primarily affect birds. Disease activity occurs worldwide, and nearly every region since the start of 2017 has reported outbreaks to the World Organization for Animal Health. As of Jan. 26, outbreaks have occurred in Africa, Asia, Europe, the Middle East, and North America.
Avian influenza viruses are divided into two general categories: low pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (HPAI). LPAI, such as H7N9, causes only mild or asymptomatic infection in birds; whereas, HPAI, such as H5N1 and H5N8, spreads rapidly and causes high mortality in bird flocks. Since HPAI viruses can cause large numbers of infected birds to die, authorities often cull tens of thousands of susceptible birds merely to prevent the spread of disease. Such severe infections and significant reactions by authorities can dramatically reduce the availability of poultry for sale - causing extreme economic distress, depending on the extent of the outbreak. Even in the event of LPAI activity, consumption of poultry products often declines due to serious concerns regarding food safety.
Avian Influenza Infection in Humans
Some avian influenza viruses have developed the ability to infect humans; however, the risk of bird flu transmission from birds to humans is relatively low. The risk is higher for individuals with frequent, close contact with wild birds and/or live or recently dead poultry. Human-to-human transmission through close, prolonged personal contact has been reported; however, the risk of sustained transmission among humans remains low.
According to the US CDC, most human infections of avian influenza worldwide are caused by H7N9 and H5N1. These infections are generally characterized by rapidly progressing severe pneumonia, with nonspecific symptoms including fever, cough, and shortness of breath. Complications can include acute respiratory distress, septic shock, and multi-organ failure requiring intensive care and mechanical ventilation. However, contact tracing from clinical cases has identified a small number of mild or asymptomatic cases in otherwise healthy children and young adults.
Avian Influenza H5N1
Human infections of avian influenza H5N1 were first detected in 1997 in Hong Kong. Since then, the WHO has reported more than 850 cases, including 452 deaths, as of Jan. 16. Indonesia reported the highest number of cases per year between 2005-2008; however, since 2009, most human infections have occurred in Egypt. According to the European Centre for Disease Control and Prevention (ECDC), most human cases in Egypt are reported from central Egypt, especially along the Nile River and in the Nile Delta. These are areas where outbreaks in poultry have also occurred.
Avian Influenza H7N9
Human infections of avian influenza H7N9 were first detected in March 2013 in China. It was also the first time a LPAI virus had been associated with severe disease in humans. Since then, more than 1,000 cases have been reported in China or in individuals returning from a recent trip to mainland China. Most cases have occurred in individuals who reported exposure to infected poultry or contaminated environments, such as live poultry markets.
In late January 2017, the US CDC issued a Watch Level 1 travel advisory for China, Hong Kong, and Macau due to a large increase in human cases of avian influenza H7N9 in mainland China since late 2016. This advisory is the lowest of three advisory levels notifying travelers of a baseline or slightly elevated risk at a destination, and emphasizes the need for travelers to practice usual health precautions - predominantly avoiding live poultry markets, ensuring eggs and poultry are fully cooked before eating, and maintaining hand hygiene. Based on prior seasonal patterns, health officials expect that sporadic cases will continue to be reported in mainland China at an elevated rate through March. It is important to note that the risk of infection for individuals not in contact with live or recently deceased poultry remains low.
Avian influenza viruses are an extremely diverse group of viruses that primarily affect birds. Outbreaks in poultry can have a significant impact on the local, regional, and national economies. In order to mitigate revenue losses, authorities often react severely at the first sign of an outbreak. Some avian influenza viruses, such as H5N1 and H7N9, have developed the ability to infect humans. However, the risk of human infections remains low for individuals not in contact with live or recently deceased poultry.