A ProMED Mail Post:
Published Date: 2013-05-04 15:29:56
PRO/AH/EDR> Avian influenza (51): H5N1/H1N1 hybrids, transmissibility
Date: Thu 2 May 2013
Source: CIDRAP News [abridged and edited]
http://www.cidrap.umn.edu/cidrap/content/influenza/avianflu/news/may0213h5n1.htmlChinese
scientists report that lab-generated hybrid viruses combining genes
from avian H5N1 and pandemic 2009 H1N1 (pH1N1) influenza viruses can
achieve airborne spread between guinea pigs, a finding that seems likely
to renew the debate about the risks of creating novel viruses that
might be able to spark a human pandemic. Writing in Science, the
researchers say that 5 of 127 hybrids they generated by shuffling genes
[that is, genome subunits] from the 2 subtypes showed "highly efficient"
transmission in guinea pigs. None of the guinea pigs died, but some
mice that were infected with the reassortant strains did succumb.
Guinea
pigs are not regarded as the best experimental model for human flu, a
distinction that belongs to ferrets [that is, the most susceptible
mammal]. The Chinese team did not test any of the hybrid viruses in
ferrets, because a voluntary moratorium on "gain of function" research
on H5N1 virus -- studies involving the creation of potentially dangerous
new strains -- intervened in January 2012 and lasted a year. The
moratorium was prompted by the controversy that erupted in late 2011
over 2 earlier studies in which researchers generated novel H5N1 strains
that spread among ferrets via respiratory droplets. One of the studies
involved an H5N1-H1N1 reassortant, while the other involved an H5N1
virus in which specific mutations were induced. The US National Science
Advisory Board for Biosecurity (NSABB) sought to prevent publication of
full details of the 2 studies but eventually reversed itself, and the
studies were published in May and June of 2012. In a statement to
reporters, the editors of Science said the new Chinese study "provides
evidence that H5N1 viruses spread by air between mammals can be
generated by reassortment. Reassortment, as it occurs in nature,
however, is much slower."
In another study on H5N1
transmissibility, also published today [2 May 2013] in Science, another
team of Chinese researchers examined how hemagglutinin (HA) from H5N1
attaches to human cell receptors. They identified a mutation, Q226L,
that enables a mutant form of H5N1 HA to bind to both avian and human
receptors.
In the reassortant study, the team focused on H5N1 and
pH1N1 because both viruses can infect pigs, suggesting the possibility
that reassortants could arise naturally. The researchers, led by Ying
Zhang of the Harbin Veterinary Research Institute, conducted their
experiments in enhanced animal biosafety level 3 (ABSL-3) conditions at
that institute. They say all the experiments were done before the
moratorium began. The scientists used an H5N1 virus isolated from a duck
in China in 2001 and the 1st pH1N1 strain that was identified in China
during the 2009 pandemic. Using reverse genetics, they generated 127
reassortants that combined the H5N1 virus's HA gene with all possible
combinations of the other 7 genes from the pH1N1 isolate. The
reassortants were easily generated, and all grew efficiently in chicken
eggs, the report says. The authors used genetically modified mice to
test the virulence of the hybrid viruses. They found that 54 of the
reassortants had about the same virulence as the original H5N1 duck
virus, killing some of the mice; 38 viruses were less pathogenic than
the H5N1 strain; and 35 viruses were more virulent, killing all the
mice.
The researchers say guinea pigs are comparable with ferrets
as models of human flu transmission. Although guinea pigs have both
avian and mammalian types of airway receptors, flu viruses that bind
only to avian receptors (alpha2,3-linked sialic acids) don't spread by
respiratory droplets in the animals, they report. The team used the
original H5N1 and pH1N1 viruses and 19 of their reassortants to test for
airborne transmission in guinea pigs. For each strain, 3 guinea pigs
were dosed with the virus, and 3 other guinea pigs were placed in cages
near them but not close enough for direct contact. The scientists found
"highly efficient" airborne transmission of the pH1N1 virus in 5 of the
19 reassortants. The results indicated that the PA (acidic polymerase)
and NS (nonstructural protein) genes of the pH1N1 virus can make H5N1
highly transmissible by respiratory droplets in guinea pigs and that the
NA (neuraminidase) and M (matrix) genes from the pH1N1 also promote
such transmission of H5N1. "These transmission studies indicate that
many of the H5N1 hybrid viruses bearing one or more of the PA, NA, M, or
NS genes of 2009/H1N1 were transmissible in guinea pigs," the report
states.
The scientists say they previously showed that a mutant
strain of a duck H5N1 isolate, with changes at HA positions 226 and 228,
bound exclusively to human receptors (alpha2,6-linked sialic acids).
They found that this mutant, which contains the same combination of
mutations as reported in the ferret-transmissible H5N1 virus reported by
Ron Fouchier, PhD and colleagues in 2012, did not transmit in guinea
pigs. "Our studies provide evidence that H5N1 viruses that are capable
of respiratory droplet transmission between mammals can be generated by
reassortment between mammalian 2009/H1N1 and avian H5N1 viruses," the
report concludes. "Since the internal genes of these reassortants can
already replicate efficiently in mammalian hosts, we predict that
similar reassortants could infect humans and subsequently acquire
mutations that improve binding efficacy for alpha2,6-linked sialic
acids," it states.
The Science statement says that studies in a
more human-like animal model, such as ferrets, were halted by the
research moratorium, "but these are the potential next steps if the
influenza research community decides it is important to quantify the
degree of threat from avian influenza viruses."
[These experiments are described in the following publications:
Zhang
Y, Zhang Q, Kong H, et al. H5N1 hybrid viruses bearing 2009/H1N1 virus
genes transmit in guinea pigs by respiratory droplet. Science 2013 May 2
(Early online publication) [abstract
http://www.sciencemag.org/content/early/2013/05/01/science.1229455]
Zhang
W, Shi R, Lu X, et al. An airborne transmissible avian influenza H5
hemagglutinin seen at the atomic level. Science 2013 May 2 (Early online
publication) [abstract
http://www.sciencemag.org/content/early/2013/05/01/science.1236787]
The reactions
-------------
The
report drew varied reactions from other experts consulted by CIDRAP
News, with one hailing it as a useful contribution and others
questioning whether the findings were worth the risks involved in the
experiments.
Andrew Pekosz, PhD, a virologist at Johns Hopkins
Bloomberg School of Public Health in Baltimore, said the study provides
new information about the kinds of genetic combinations that can lead to
flu transmission, which is useful for flu surveillance. "The more we
understand how wide-ranging those combinations of genetic changes are
that can lead to this kind of transmission, the better off we'll be," he
said. "That knowledge helps inform us what we should be looking for
regarding viruses that are potential human pathogens." He commented that
the study doesn't provide "any kind of lightning-strike or light-bulb
observations, but it helps tell us what to be looking for in terms of
viruses acquiring transmissibility."
Pekosz said he thinks the
findings justify any risks involved in the experiments: "As far as I
could tell from reading this and being familiar with the group and how
they do their research, everything falls under the guidelines that apply
to labs in the US regarding biocontainment, respiratory protection, and
monitoring. ... I think the safety concerns are well taken care of." He
also commented that it's difficult to make "direct leaps" from the
guinea pig findings to what would happen in the human population, but
the results suggest the possibility that the reassortants could spread
in humans. He noted that guinea pigs are not as widely used as ferrets
in flu transmission experiments because they've only been rediscovered
in that regard in the past decade or so. "I think another important
thing about this paper is this is a directed or systematic creation of
reassortant viruses, which makes it hard to say if these would occur in
natural infection," Pekosz said. "You're not allowing for the natural
competition that would take place in an infected animal."
David
Relman, MD, a microbiologist and infectious disease expert at Stanford
University, expressed concern over the biosecurity implications of the
study. "It clearly has biosecurity concerns," he said in an interview.
"I would have liked to see these experiments discussed by a wider
community of scientists and nonscientists before they were undertaken.
... I would have some grave questions about doing these without having a
clearer idea of how exactly the results would lead to tangible
real-time benefits. Having a BSL-3 lab and not working during the
moratorium does not address the issue," he said.
Simon
Wain-Hobson, PhD, a veteran HIV researcher and an opponent of
gain-of-function experiments, was more sharply critical of the study. He
is a professor at the Pasteur Institute in Paris and chairs the board
of the Foundation for Vaccine Research, a privately funded group that
recently asked President Obama's Commission for the Study of Bioethical
Issues to review the ethics of experiments designed to increase the
transmissibility of H5N1 viruses. In a written statement, Wain-Hobson
said this study, along with the earlier ones by Fouchier and Yoshihiro
Kawaoka, DVM, PhD, show that many different starting points and
different experimental protocols can lead to a flu virus capable of
airborne transmission. He said it's impossible to predict the pathway
that might lead to a pandemic flu virus in nature. "Which evolutionary
trajectory will nature take?" he said. "We don't know because there are
simply too many. So what is the use [of the findings] for surveillance?
What we learn [from the H5N1 transmissibility studies in general] is
that, qualitatively, flu can exploit a huge fraction of sequence space
and can adapt to almost anything given time," Wain-Hobson said. "But
this we knew, not only from flu work, but also from RNA virology in
general. ... The benefits are general knowledge which we basically knew,
while the risks are increased by this work."
Wain-Hobson said
the authors did "a super piece of work" from the science standpoint and
undoubtedly meant well. But he labeled the study "very dangerous work
disguised as big science. Given this, one wonders why it is published in
Science."
[byline: Robert Roos]
--
communicated by:
ProMED-mail
<promed@promedmail.org>
[These
experiments provide evidence that H5N1 viruses that are capable of
respiratory droplet transmission between mammals can be generated by
reassortment between mammalian 2009/H1N1 and avian H5N1 viruses. The
authors conclude since the internal genes of these reassortants
facilitate efficient replication in mammalian hosts, it is likely that
similar reassortants could promote infection of humans and subsequently
acquire mutations that improve binding efficacy to the alpha2,6-linked
sialic acids receptors.
These are remarkable experiments in
molecular genetics that provide better understanding of the determinants
of host range of influenza viruses. Whether such experiments should
have been carried out at all, even under BSL-3 conditions, is another
matter. - Mod.CP]
http://www.promedmail.org/direct.php?id=20130504.1691399
