H5N1 in blood might open way for new test -experts
HONG KONG, May 10: Scientists in Thailand have detected live H5N1 bird flu virus in the blood of a boy who died in December, a discovery that might lead to a safer way to diagnose the disease in humans.
At present, respiratory secretions are collected to test for the H5N1 virus. But that practice, which is physically irritating, can result in the patient coughing violently and spraying the virus, infecting doctors and nurses conducting the procedure.
During SARS in Hong Kong in 2003, scores of healthcare workers ended up infected when they carried out intubation on patients.
Intubation is the procedure of passing a breathing tube through the mouth or nose and down the throat. The tube is then used to pass oxygen into the lungs and help a person breathe.
Parvapan Bhattarakosol, a member of the Thai team and a microbiologist from Chulalongkorn University, said a huge amount of live H5N1 virus in the blood plasma of the five-year-old boy was detected more than 12 days after the sample was collected.
This is unusual. According to other microbiologists, respiratory viruses generally are not present in the blood stream after such a long time because they are confined to the respiratory tract and do not replicate well in the blood.
Bhattarakosol also called for the scientific community to study if blood samples can be a reliable means for diagnosis.
''If we can find virus in blood, so maybe blood is another type of sample that we can take and use for diagnosis, instead of using only respiratory secretions,'' she told Reuters.
''It is easily done and better than taking respiratory secretions, which can be dangerous because it is the secretions that are very infectious.'' ''There must be another study to see if blood is a suitable sample. If there are other cases of human H5N1, we should draw blood samples and try to detect the virus in blood and then we can see if blood is suitable as a diagnostic test.''
The finding, to be published in the June issue of the Centers for Disease Control and Prevention's Emerging Infectious Diseases Journal, might explain why H5N1 victims suffer from systemic infections, when the virus spreads throughout the body and victims die from multi-organ failure.
''When viruses get into blood, there is a risk of all organs in the body being affected,'' Bhattarakosol said.
There are implications for blood donation and people working with blood samples too. Although 207 people have reportedly been infected since late 2003, and 115 of them have died, scientists say many mild cases of H5N1 infection might have gone undetected.
In Hong Kong, where the virus made its first known jump to humans and killed six people in 1997, later tests showed some hospital workers and others who had not fallen sick during the period carrying H5N1 antibodies -- which means they were infected.
''We should keep this (that H5N1 can live in blood) in mind when donating blood or blood transfusions,'' Bhattarakosol said.
But Julian Tang, a microbiologist at the Chinese University in Hong Kong, said the finding gave reasons to be optimistic.
In systemic infections, such as those caused by chickenpox or measles, viruses might last longer than a week in the blood stream, allowing for the production of T and B memory lymphocytes in the patient's immune system, which tend to produce lifelong immunity.
''If avian H5N1 influenza produces a detectable blood viraemia for several days, then the response to an H5N1 vaccine may be more long-lasting and protective, than the reponse to other non-H5N1 influenza vaccines, as there will be a more intense antigenic stimulation to produce specific T and B memory lymphocytes,'' Tang said.
Lymphocytes, the blood cells that make antibodies, have memory cells and this function allows them to remember a past encounter with the H5N1 strain, and produce antibodies to neutralise the virus in future encounters, experts say.
''Those who survive avian H5N1 influenza may be more effectively protected for a longer period against the same strains of H5N1 (i.e.
naturally acquired immunity), should they be re-exposed to the same strain in the near future.''