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Health Experts Call Novel H7N9 Bird Flu ‘Unusually Dangerous’ As It Spreads Beyond China

April 25, 2013
Image Credit: Photos.com

Lawrence LeBlond for redOrbit.com – Your Universe Online

A novel strain of the bird flu (H7N9) that has now infected more than 100 people in China and has taken the lives of at least 22 is being called “one of the most lethal” strains known, according to the World Health Organization (WHO). And as of Wednesday April 24, the strain has moved beyond the constraints of the Far East nation.

Taiwanese officials reported that a 53-year-old citizen who had made regular trips to the Chinese city of Suzhou for work had fallen ill on April 12, three days after returning to Taiwan. He was tested on Wednesday and the results confirmed that it is H7N9 bird flu. The patient, who is described as severely ill, is being treated in isolation; 139 people who had contact with him — including 110 healthcare workers — are also being monitored for symptoms.

Currently, there is no evidence that supports the virus is being transmitted between humans, but if symptoms begin showing up in those who were in close contact with the patient, it may indicate that the strain has leapfrogged from bird-to-human to human-to-human transmissions.

The WHO at a news conference in Beijing on Wednesday described the novel bird flu as “unusually dangerous.”

Dr. Keiji Fukuda, an assistant director general with the WHO, said the virus is “definitely one of the most lethal influenza viruses we´ve seen,” as cited by the New York Times.

The US Centers for Disease Control and Prevention (CDC) had received samples of the virus from China and shared them with five laboratories to study the virus and develop a vaccine. While the new strain has yet to make the switch to humans infecting humans, the CDC said a vaccine will be important if it does make that leap, hopefully keeping a global pandemic from breaking out. Researchers are worried that this strain may be much better at making that jump than others have in the past.

According to WHO data, the H5N1 bird flu virus of 2003 infected 622 people, of which 371 (60 percent) have died. Because of the high death rate, the virus caused global fears that a lethal pandemic was in the making, and as a result, millions of birds were slaughtered.

GENETIC EVIDENCE

As for the new strain, studies of the Chinese samples have provided some new evidence on the origins of the novel H7N9 strain.

Led by Professor Chen Hualan of the National Avian Influenza Reference Laboratory, a group of scientists analyzed influenza virus samples collected from live poultry markets in Shanghai and Anhui and found that the viruses circulating among birds were in fact responsible for the human infections.

The team collected a total of 970 samples taken from drinking water, feces, contaminated soil and cloacal and tracheal swabs from birds. Of the samples collected, 20 tested positive for the presence of H7N9 influenza, and all originated from live poultry in Shanghai. Of the 20 positive samples, 10 were isolated from chickens, three from pigeons, and seven came from environmental samples.

The researchers sequenced the genomes of three H7N9 isolates, from the chicken, pigeon and environmental samples, and deposited them into the GISAID database. Through further genetic analysis of the isolates, the team found high homology across all eight gene segments. Phylogenetic analysis revealed that six internal genes in the isolates were derived from avian H9N2 viruses.

According to the database, HA genes in the isolates were most similar to the duck H7N3 virus and NA genes from H4N9 or H11N9 viruses isolated from ducks and duck farms located in the Dongtin Lake region. The researchers believe the novel H7N9 virus is the product of reassortment, with internal genes from one donor, and HA and NA genes from several donors.

Furthermore, through analysis of human isolates, the team found that a lysine residue found in the PB2 protein likely contributes to the replication and transmission of avian influenza viruses in mammalian hosts. They believe that the acquisition of the lysine in H7N9 viruses during the replication in human hosts is a significant contributor to the virulence and lethality seen in humans.

Hualan and her colleagues suggest that strong measures be taken to prevent a possible pandemic. Measures should include close surveillance of avian and human hosts, animal movement control, live poultry market shutdowns and culling of poultry in affected areas. The team also noted that it is highly important to continue evaluations of the H7N9 viruses and to develop effective vaccines and antiviral drugs.

The emergence of this completely new strain of flu virus is “very, very unsettling,” John Oxford, a flu virologist at Queen Mary University of London (QMUL), said in an interview with Reuters. “This virus seems to have been quietly spreading in chickens without anyone knowing about it.”

Flu experts warn that until a source of infection can be completed confirmed and effectively controlled, new cases will likely continue to emerge in the coming weeks, if not longer.

Nancy Cox, a flu expert with the CDC, said that available evidence points to live bird markets as being the most likely pathway for the transmissions of bird-to-humans seen. While it is still early in the game, “we can now understand that the likely source of infection is poultry–that the virus originates from poultry,” said Cox, as cited by Science Insider.

Anne Kelso, director of the WHO Collaborating Centre for Reference and Research on Influenza (VIDRL) in Melbourne, Australia, said that immediately following closures of live poultry markets on April 6, there was “a decline in the number of new cases.” She added that the quick decision to close down markets was “appropriate” and is “a very encouraging outcome so far.”

But she maintained that continued vigilance is necessary. “It’s going to be very important to watch over the next days, weeks, even months, what happens as a result of a shutdown of the live markets. It’s possible other routes of infection will be found that we don’t know about yet,” Science Insider reported her as saying.

As for the Taiwanese patient, he told health officials that he had not been exposed to birds and had not eaten any undercooked poultry or eggs. This case and similar ones have puzzled scientists, leading some to suspect that either another animal, other than birds, is harboring the virus and spreading it to humans. However, no other animals have been confirmed to carry H7N9.


Source: Lawrence LeBlond for redOrbit.com - Your Universe Online



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