Recent studies warn surveillance of bird flu strains is needed

May 3, 2013 by Lin Edwards, Medical Xpress report
Colorized transmission electron micrograph of Avian influenza A H5N1 viruses (seen in gold) grown in MDCK cells (seen in green). Credit: Cynthia Goldsmith/CDC

(Medical Xpress)—Recent scientific papers from China suggest a vigilant watch should be kept on the development of bird flu viruses, as a new strain has been identified and previously known viruses have been shown capable of mutating to forms that could spread from human to human via respiratory droplets.

The bird flu influenza virus is made up of only eight segments of RNA. One segment codes for the hemagglutinin (HA) protein, which plays an important role in helping the virus to enter host cells, while another codes for (NA), which helps in the release of the virus from infected cells. HA has 17 known sub-types and NA has 10, leading to a classification of bird as HxNy.

In a study published in the Lancet1, scientists in China looked at the genetics of a new strain of avian virus, H7N9, which has infected over 80 people and killed at least 17 in China since it was identified in March 2013. The research team compared the genome of all eight segments of the H7N9 RNA to available in global virus databases, and found that the could have evolved from four or more viruses occurring in ducks, migratory birds, and chickens. They suggest the HA segments probably originated in following the East Asian fly way, the NA segments were most likely transferred to ducks in China from birds migrating from Europe, and the remaining segments appear to have their origins in H9N2 viruses found in chickens and ducks in eastern China.

The researchers also found that the virus has already mutated into two different strains.

The H7N9 virus is currently spread only from bird to bird and from bird to humans, but no human to human transmission has so far been seen. The researchers suggest that surveillance is important in humans, , ducks, and because the virus could mutate into more virulent or infective forms.

A second study2 looked at the avian H5N1 , which is highly pathogenic in birds. The study, led by George F. Gao and Wei Zhang of the Chinese Academy of Sciences in Beijing, determined the structure of wild and mutant strains of the virus and found a cis/trans change in the conformation of the glycosidic linkage between the virus when bound to avian or human receptors. This finding explains how the virus can acquire human receptor binding properties while retaining the avian receptor binding properties.

A third study3, also on the H5N1 virus, has shown that mutations of the virus could be transmitted via respiratory droplets in guinea pig hosts. This could be an important finding, because human seasonal flu is spread in this way. Until now the H5N1 has not been transmitted easily to humans unless they were in close contact with infected birds.

The research team, from the Chinese Academy of Agricultural Sciences at Harbin, and Gansu Agricultural University at Lanzhou, used reverse genetics techniques to create 127 reassortants of the H5N1 virus from ducks and a highly transmissible human H1N1 virus. Reassortment occurs naturally when a cell is infected by two or more strains of flu virus at the same time and RNA segments from the different strains mix, potentially forming new virus strains.

All 127 reassortants had the HA gene from H5N1, which is known to bind to avian receptors (HA in H1N1 binds to human receptors). The other seven genes were present in various combinations. Ensuring all the hybrids contained the HA from H5N1 allowed the researchers to test if flu viruses that were specific to birds could also infect mammals.

To find out, the team tested the transmissibility of each reassortant in guinea pigs and their virulence in mice. The study showed that in guinea pigs (which have both avian and mammalian receptors) several genes taken from H1N1 made eight of the reassortants transmissible via respiratory droplets. None of the hybrids killed their guinea pig hosts. In the mice, 35 of the reassortants caused death. The results suggest the avian H5N1 viruses could naturally acquire the ability to be transmitted from human to human by reassortment in "current agricultural scenarios."

The symptoms of the various strains of are similar to those of seasonal flu, but the risk of complications and death is higher. If the viruses become capable of easy human to , a pandemic becomes more likely.

Explore further: Source identification of H7N9 influenza virus causing human infections

More information: 1. Origin and diversity of novel avian influenza A H7N9 viruses causing human infection: phylogenetic, structural, and coalescent analyses, The Lancet, Early Online Publication, 1 May 2013. doi:10.1016/S0140-6736(13)60938-1

2. An Airborne Transmissible Avian Influenza H5 Hemagglutinin Seen at the Atomic Level, Science DOI: 10.1126/science.1236787

3. H5N1 Hybrid Viruses Bearing 2009/H1N1 Virus Genes Transmit in Guinea Pigs by Respiratory Droplet, Science DOI: 10.1126/science.1229455

Related Stories

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 ...

Mutant version of H5N1 flu virus found to be more preferential to human infection

April 25, 2013
(Medical Xpress)—An international team of bio-researchers has found that a mutant strain of the H5N1 influenza virus (created in a lab) has a 200-fold preference for binding with receptors in human cells, over those found ...

Recommended for you

Flu infection study increases understanding of natural immunity

January 23, 2018
People with higher levels of antibodies against the stem portion of the influenza virus hemagglutinin (HA) protein have less viral shedding when they get the flu, but do not have fewer or less severe signs of illness, according ...

New long-acting approach for malaria therapy developed

January 22, 2018
A new study, published in Nature Communications, conducted by the University of Liverpool and the Johns Hopkins University School of Medicine highlights a new 'long acting' medicine for the prevention of malaria.

Virus shown to be likely cause of mystery polio-like illness

January 22, 2018
A major review by UNSW researchers has identified strong evidence that a virus called Enterovirus D68 is the cause of a mystery polio-like illness that has paralysed children in the US, Canada and Europe.

Creation of synthetic horsepox virus could lead to more effective smallpox vaccine

January 19, 2018
UAlberta researchers created a new synthetic virus that could lead to the development of a more effective vaccine against smallpox. The discovery demonstrates how techniques based on the use of synthetic DNA can be used to ...

Study ends debate over role of steroids in treating septic shock

January 19, 2018
The results from the largest ever study of septic shock could improve treatment for critically ill patients and save health systems worldwide hundreds of millions of dollars each year.

New approach could help curtail hospitalizations due to influenza infection

January 18, 2018
More than 700,000 Americans were hospitalized due to illnesses associated with the seasonal flu during the 2014-15 flu season, according to federal estimates. A radical new approach to vaccine development at UCLA may help ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

dogbert
1 / 5 (1) May 03, 2013
Recent studies warn surveillance of bird flu strains is needed


No, what is needed is a concerted effort to restrain irresponsible scientists from creating dangerous biological agents. But as long as there is no personal cost to such research, it will continue.

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.