Novel avian influenza A virus has potential for both virulence and transmissibility in humans

September 10, 2013

A new study has found that a novel avian-origin H7N9 influenza A virus, which has recently emerged in humans, attaches moderately or abundantly to the epithelium of both the upper and lower respiratory tracts. This pattern has not been observed before for avian influenza A viruses. The report, published in the October issue of The American Journal of Pathology, suggests that the emerging H7N9 virus has the potential to cause a pandemic, since it may transmit efficiently in humans and cause severe pneumonia.

The first report of infections of humans with the influenza A virus of the subtype H7N9 surfaced in March 2013. Three patients from eastern China developed severe pneumonia and acute and died as a result. By May 30, 2013, the H7N9 infection was confirmed in 132 patients from China and Taiwan, 37 of whom died, according to the World Health Organization. Infected poultry were thought to be the source of the virus.

In the current study, investigators focused on the virus' pattern of attachment in order to assess its potential transmissibility and virulence. "Abundant virus attachment to the human correlates with efficient transmissibility among humans," explains Thijs Kuiken, DVM, PhD, of the Department of Viroscience at Erasmus University Medical Centre in Rotterdam, The Netherlands. "Virus attachment to Clara cells in the bronchioles and pneumocytes and macrophages in the alveoli correlates with high virulence."

Using virus histochemical analysis, the investigators looked at the pattern of attachment of two genetically engineered emerging H7 viruses (containing the hemagglutinin (HA) of either influenza virus A/Shanghai/1/13 or A/Anhui/1/13) to fixed human respiratory tract tissues and compared the findings to attachment patterns seen with human with high transmissibility but low virulence (seasonal H3N2 and pandemic H1N1) and highly pathogenic (HPAI) viruses with low transmissibility and high virulence (H5N1 and H7N7).

They found that like other avian influenza viruses, the H7N9 viruses attached more strongly to lower parts of the human respiratory tract than to upper parts. However, compared to other avian influenza viruses, the attachment to epithelial cells by H7N9 in the bronchioles and alveoli of the lung was more abundant and the viruses attached to a broader range of cell types. "These characteristics fit with increased virulence of these emerging avian H7 viruses compared to that of human influenza viruses," says Dr. Kuiken.

A third notable finding was a more concentrated attachment of H7N9 viruses in ciliated cells of the nasal concha, trachea, and bronchi, suggesting the potential for efficient transmission among humans. "However, the fact that the emerging H7N9 virus has caused infection mainly in individual human cases suggests that it has not acquired all the necessary properties for efficient transmission among humans," notes Dr. Kuiken.

"Our results indicate that based just on the pattern of virus attachment the H7N9 currently emerging in China has the potential both to cause severe pulmonary disease and to be efficiently transmitted among humans," says Dr. Kuiken. He emphasizes that attachment is only the first step in the replication cycle of in its host cell, and that other steps, as well as the host response, need to be taken into account to fully understand the potential of these emerging H7 viruses to cause an influenza pandemic.

Explore further: Study puts troubling traits of H7N9 avian flu virus on display

More information: "Novel avian-origin influenza A (H7N9) virus attaches to epithelium in both upper and lower respiratory tract of humans," by Debby van Riel, Lonneke M.E. Leijten, Miranda de Graaf, Jurre Y. Siegers, Kirsty R. Short, Monique I.J. Spronken, Eefje J.A. Schrauwen, Ron M.A. Fouchier, Albert D.M.E. Osterhaus, and Thijs Kuiken. (DOI: 10.1016/j.ajpath.2013.06.011). It appears in The American Journal of Pathology, Volume 183, Issue 4 (October 2013)

Related Stories

Study puts troubling traits of H7N9 avian flu virus on display

July 10, 2013
The emerging H7N9 avian influenza virus responsible for at least 37 deaths in China has qualities that could potentially spark a global outbreak of flu, according to a new study published today (July 10, 2013) in the journal ...

Evidence of host adaptation of avian-origin influenza A virus

May 15, 2013
The connection between human avian-origin influenza A (H7N9) virus infection and environmental sources of the virus were determined based on clinical data, epidemiology, and virological characteristics of the three early ...

Source identification of H7N9 influenza virus causing human infections

April 25, 2013
In March 2013, a novel H7N9 influenza virus was identified in China as the etiological agent of a flu-like disease in humans, resulting in some deaths. A group of scientists, led by Professor Chen Hualan (National Avian Influenza ...

Scientists find another flu virus in Chinese chickens

August 21, 2013
Scientists studying the H7N9 bird flu virus that has killed more than 40 people since March said Wednesday they had discovered another H7-type virus lurking in chickens in China.

H7N9 influenza: History of similar viruses gives cause for concern, researchers report

July 9, 2013
The H7N9 avian flu strain that emerged in China earlier this year has subsided for now, but it would be a mistake to be reassured by this apparent lull in infections. The virus has several highly unusual traits that paint ...

Bird flu in live poultry markets are the source of viruses causing human infections

May 13, 2013
On 31 March 2013, the Chinese National Health and Family Planning Commission announced human cases of novel H7N9 influenza virus infections. A group of scientists, led by Professor Chen Hualan of the Harbin Veterinary Research ...

Recommended for you

Two lung diseases killed 3.6 million in 2015: study

August 17, 2017
The two most common chronic lung diseases claimed 3.6 million lives worldwide in 2015, according to a tally published Thursday in The Lancet Respiratory Medicine.

New test differentiates between Lyme disease, similar illness

August 16, 2017
Lyme disease is the most commonly reported vector-borne illness in the United States. But it can be confused with similar conditions, including Southern Tick-Associated Rash Illness. A team of researchers led by Colorado ...

Addressing superbug resistance with phage therapy

August 16, 2017
International research involving a Monash biologist shows that bacteriophage therapy – a process whereby bacterial viruses attack and destroy specific strains of bacteria - can be used successfully to treat systemic, multidrug ...

Can previous exposure to west Nile alter the course of Zika?

August 15, 2017
West Nile virus is no stranger to the U.S.-Mexico border; thousands of people in the region have contracted the mosquito-borne virus in the past. But could this previous exposure affect how intensely Zika sickens someone ...

Compounds in desert creosote bush could treat giardia and 'brain-eating' amoeba infections

August 15, 2017
Researchers at Skaggs School of Pharmacy and Pharmaceutical Sciences at University of California San Diego and the University of Colorado Anschutz Medical Campus have found that compounds produced by the creosote bush, a ...

New malaria analysis method reveals disease severity in minutes

August 11, 2017
Left untreated, malaria can progress from being mild to severe—and potentially fatal—in 24 hours. So researchers at the University of British Columbia developed a method to quickly and sensitively assess the progression ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.