- TORONTO -- Live H5N1 avian flu virus can be isolated in the blood of
its human victims, a finding that will be reported by Thai researchers
in an upcoming issue of a scientific journal.
- Evidence that H5N1 can spread via the
bloodstream to parts of the body not normally attacked by influenza viruses
confirms this particular flu strain poses special challenges for both patient
treatment and infection control, experts say. It also raises theoretical
questions about the safety of the donated blood system should H5N1 trigger
- "This is the first report of a high
amount of (H5N1) virus in blood in humans," University of Ottawa virologist
Earl Brown said of the findings, outlined in a letter slated for publication
in the June issue of Emerging Infectious Diseases.
- "That's a bit surprising because
blood is poisonous to flu virus. If you take any blood ... and add it to
flu, you kill it (the virus). This showed that the virus was living in
the blood," said Dr. Brown, who was not an author of the letter.
- While some types of viruses spread well
in blood, cases of viremia - viral infection in the bloodstream - have
only rarely been reported with influenza.
- The researchers - from Chulalongkorn
University, Srinakharinwirot University and the National Institute of Animal
Health, all in Bangkok - reported on the case of a five-year-old Thai boy
who died of H5N1 infection Dec. 7.
- A blood sample drawn on the day he died
contained high levels of live virus.
- The finding helps to explain reports
that some humans with H5N1 experience what is called systemic infection,
with the flu virus spreading beyond its normal home in the respiratory
track to organs that would typically go untouched by human flu viruses.
- Other research groups have reported finding
traces of H5N1's RNA in blood. Those findings were highly suggestive that
the virus was using the bloodstream to disseminate throughout the body,
but were not strong enough evidence to rule out that spread was actually
occurring via other routes such as the lymphatic system.
- Researchers at Oxford University's clinical
research unit at the Hospital for Tropical Medicine in Ho Chi Minh City
in Vietnam, for instance, reported last year on a boy whose H5N1 infection
spread to his brain, causing encephalitis.
- The lead author of that report, virologist
Menno de Jong, said his group has found viral RNA in the blood of about
half of the H5N1 patients in which they've looked for it.
- "It was really surprising for influenza,
because the case reports of human influenza and viremia are so rare,"
he said from Ho Chi Minh City.
- "It's probably quite common in H5N1
- That poses challenges for treating patients
infected with H5N1 because if the virus is spreading through the blood,
so too must drugs that aim to combat the infection.
- Currently there are only four flu antivirals
on the market and one, zanamivir (sold as Relenza) is administered to the
respiratory tract by inhalation. The drug would need to be formulated in
an injectable form to be useful for systemic infection, Dr. de Jong said.
- It also raises concerns about infection
control for health-care workers and laboratory scientists coming in contact
with the blood of H5N1 patients - although precautions against contact
with blood are widespread as a consequence of years of experience with
blood-borne infections like HIV and hepatitis C.
- "I think for this kind of flu, infection
control measures should include all bodily secretions, basically,"
Dr. de Jong said.
- The findings also raise questions about
whether blood transfusions could be a source of infection if H5N1 were
to become a pandemic strain.
- Canadian Blood Services and the American
Red Cross have been studying the issue, but currently it is believed that
the risk is more theoretical than real, because influenza's incubation
period is so short. Once people develop symptoms they would be unlikely
to want to give blood and would probably be turned away if they showed
up to a blood-donor clinic.
- "From the blood-donor and blood-supply
point of view, the issue would be whether there's virus in the blood before
the patient becomes ill," said Dr. Jeffrey McCullough, who holds an
American Red Cross professorship in transfusion medicine at the University
- "Once you've got somebody that's
sick, of course, they wouldn't be acceptable as a blood donor," he