The H7N9 virus first appeared in March 2013 in China, and it has reappeared each winter and spring since then. Cases have also occurred in Taiwan, Malaysia, and Canada.
A total of four epidemics have come and gone in China, and a fifth is under way. Up to April 5, 2017, H7N9 has infected 1,364 people altogether, including 566 people affected by the current seasonal epidemic.
During the first four seasonal epidemics, 40 percent of patients with H7N9 died.
In March 2017, an outbreak of H7N9 was reported in poultry in Tennessee, but the risk to the American public from this infection is considered to be "low."
Contents of this article:
Why is bird flu dangerous for humans?
H7N9 is an avian, or bird, flu virus. The virus normally affects poultry birds, but it has mutated so that it can affect humans too.
Humans do not have immunity to these subtypes of flu virus, as they are continually evolving. This is why the infections they cause us can be severe and life-threatening.
Whenever a new type of bird flu infection is reported in a person, three key questions arise:
- Does the new virus subtype cross easily from birds to humans?
- How bad is the illness when the virus infects a person?
- Will the virus spread quickly and widely among human populations?
These questions are important, because the answers can indicate whether or not health authorities should consider preparing for an emergency.
Any flu infection causes fever and malaise, but with H7N9 the lung disease is severe and life-threatening.
Sudden changes in the virus proteins take the human immune system by surprise. This is why a new variant causes more serious illness. The human's immune system has not met it before, so there is no immunity.
During the early stage, most people have shown the following symptoms:
- cough that produces sputum
- breathing problems and wheezing
- myalgia, or muscle pain
- general malaise
These symptoms are common to other kinds of flu. Symptoms in the later stages include:
- pneumonia in both lungs
- rapid progression to acute respiratory distress syndrome (ARDS)
- multi-organ dysfunction, including impaired liver or kidney function
- septic shock which is a blood infection
- rhabdomyolysis, or muscle breakdown
- encephalopathy, a brain disease
In the critical stages, patients often have thrombocytopenia, a reduced platelet count, and lymphopenia. A person with lymphopenia will have reduced numbers of lymphocytes, or white blood cells.
How does influenza change and spread?
Flu viruses are always changing. Even the common flu virus that affects large numbers of people seasonally is slightly different every year, so that the vaccine against it must continually be adapted.
The H and N proteins in the virus change. The "H" protein, which stands for HA or hemagglutinin, and the "N" protein, which stands for NA or neuraminidase are the parts that change.
The HA protein enables the virus to enter the host cells. The NA protein enables the virus to leave, or "shed." The shedding makes it possible for the virus to spread.
Birds shed the virus in their droppings and in their mucus. If a person has contact with an infected bird, live or dead, and then they touch their eyes or mouth, for example, they may become infected.
The Centers for Disease Control and Prevention (CDC) note that the virus may travel through the air, for example, if a bird flaps its wings.
The bird may not appear to be ill, but a person can still catch the virus.
Sudden changes in the virus proteins take the human immune system by surprise. This is why a new variant causes more serious illness. The system has not met it before, so there is no immunity.
Treatment and vaccines
Existing antiviral drugs used against the common seasonal flu virus are given to people infected with the H7N9 avian flu.
This class of drugs is known as neuraminidase inhibitors. They are recommended for use as soon as possible in people suspected of infection with H7N9.
World Health Organization (WHO) guidance states that drugs should be given even before the laboratory confirms a case of H7N9.
Two neuraminidase inhibitor drugs are recommended in the treatment of infection with the H7N9 avian flu virus. They are Zanamivir (Relenza, made by GlaxoSmithKline) and Oseltamivir (Tamiflu, made by Roche).
These drugs are not effective in all people infected with H7N9, and even when they are effective - particularly when administered at the earliest opportunity - they reduce the severity of the illness rather than cure it. New drugs are being developed against influenza in general and may prove to be effective against H7N9, too.
Is there a vaccine against H7N9 flu?
There is no publicly available vaccine for H7N9, but the CDC, the WHO, and other health partners have developed three vaccines that could be adapted for the purpose, if an influenza pandemic occurred.
It is difficult to develop a vaccine for H7N9 because the virus is always changing.
People who are involved in poultry anywhere, and those who are traveling to China should be especially careful around birds.
The H7N9 outbreak has so far been confined to people working closely with poultry in China.
The CDC advise people not to touch birds, whether alive or dead, and to avoid poultry markets and places where there may be bird feces.
Meat and poultry should be fully cooked, and not pink, and eggs should be hard boiled. It is better to avoid food that contains the blood of any animal, and not to buy food from street vendors.
Hand hygiene is important. This includes frequent hand washing with soap and water or use of a hand sanitizer with at least 60 percent alcohol. People should cough or sneeze into a tissue.
If a traveler feels ill on returning home, they should see their doctor, especially if they have a cough or fever, or if they are short of breath.
They should also stay away from other people. Sustained transmission between people has not yet been reported, but sporadic transmission sometimes occurs.