Fifth Avian Influenza Epidemic in China Worse Than Before

Pam Harrison

March 03, 2017

The number of patients affected by the A(H7N9) virus in the current avian influenza A epidemic in China has increased significantly compared with past epidemics, and the influenza strain now circulating in the country appears to be highly virulent, the Centers for Disease Control and Prevention (CDC) warns.

The warning was published online March 3 in the Morbidity and Mortality Weekly Report.

"Most human infections continue to result in severe respiratory illness and have been associated with poultry exposure," lead author Danielle Juliano, PhD, from the CDC in Atlanta, Georgia, and colleagues write.

"Although the current risk to the public's health from A(H7N9) viruses is low...A(H7N9) viruses have the highest risk score and are characterized as posing moderate–high potential pandemic risk," they add.

As the CDC authors report, the fifth epidemic of avian influenza A in China, which began October 1, 2016, and is still ongoing, has already infected 460 people.

This compares with 135 infections reported during the first epidemic, 320 infections reported during the second epidemic, 226 infections reported in the third epidemic, and 119 infections reported in the fourth epidemic.

To date, the number of people who have been infected with A(H7N9) viruses totals 1258, according to reports from the World Health Organization. The first epidemic of avian influenza A in China was reported in March 2013.

"During the first four epidemics, 88% of patients developed pneumonia, 68% were admitted to an intensive care unit, and 41% died," the researchers note.

So far, no sustained human-to-human transmission appears to have taken place, they add.

Nevertheless, gene sequencing results from current viral samples show that the A(H7N9) viruses are now composed of two distinct genetic lineages: one from the Pearl River Delta and the second from the Yangtze River Delta.

Preliminary data also indicate that the avian influenza A viruses from the Yangtze River Delta lineage are "antigenically distinct" from viruses that circulated during earlier avian influenza A epidemics.

Disturbingly, they are also distinct from currently available candidate vaccine viruses, as investigators point out.

Analyses also suggest that between 7% and 9% of the viruses circulating during the current epidemic are less susceptible to the neuraminidase inhibitor class of antiviral medications, which is the class of drugs currently recommended for the treatment of avian influenza A virus infection.

The CDC authors emphasize that they are in the process of preparing a candidate vaccine they hope will prevent the further spread of avian influenza A.

In the meantime, physicians who suspect they may have a patient who has been infected with the AH7N9 virus or those who are traveling to China may consult the CDC's website for further information.

The authors have disclosed no relevant financial relationships.

Morb Mortal Wkly Rep. Published online March 3, 2017. Full text

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