The H5N1 strain of the bird flu virus can pass through the placenta of pregnant women to the unborn fetus, and can infect organs other than the lungs in adults.
Professor Jiang Gu, Peking University, Beijing, China and colleagues studied post-mortem tissues of two adults – one man and one pregnant woman, and also tested the dead fetus of the dead woman. They investigated how H5N1 – an emerging infectious disease which causes respiratory symptoms and a high fatality rate – affects different organs in the body.
The authors say: “A pandemic outbreak of human infection with avian H5N1 currently poses a potentially serious health threat worldwide…little is known about the specific effects in organs and cells targeted by the virus.”
The researchers detected viral genetic material and antigens in the lungs, certain cells in the trachea, the T cells of the lymph node, neurons in the brain, and in cells of the placenta. Viral genetic material was also detected in the intestinal mucosa, but no H5N1 viral antigens were found there. In the fetus, both viral genetic material and antigens were found in the lungs, circulating cells of the immune system and in cells of the liver.
They conclude: “This study has shown the capacity for human vertical transmission of the H5N1 virus…[this] warrants careful investigation, since maternal infections with common human influenza virus are generally thought not to infect the fetus.”
They add: “We have shown that H5N1 virus spreads beyond the lungs…these newly obtained data are important in the clinical, pathological and epidemiological investigation of human H5N1 infection, and have implications for public-health and health care providers.”
In an accompanying Comment, Dr Wai Fu Ng, Department of Pathology, Yan Chai Hospital, Hong Kong, China and Dr Ka Fai To, Ki ka Shing Institute of Health Science, Hong Kong, China say: “Speculation about the fate of the fetus if the mother survived is interesting. With the development of antibodies in the mother and their transplacental crossing into the fetus, pathological lesions in the fetus may result.”
They conclude by analysing the techniques used by Gu and colleagues, saying: “Correlation with viral culture to confirm productive viral replication is needed and is absent from Gu’s report. Reproduction of these studies, including experimental models, is awaited.”