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Efficient H7N2 Transmission To Bird Flu Patients in England
May 25, 2007
The Welsh health authorities said that in all but one of the four human cases the virus had spread from poultry. The other case may have been transmitted from person to person.
“Although the number of people involved is very small, we could be dealing with some spread of the H7 flu virus within the household setting,” said Dr. Marion Lyons, a communicable disease specialist with the Welsh health service. “We are treating this possibility very seriously.”
Officials are now following up all close contacts of the people who were ill as a precaution.
The above comments describe efficient human to human transmission of H7N2 in England. The H7N2 outbreak was confirmed yesterday, and four patients have already tested positive, including one case with human, but not poultry contact. The efficiency of H7N2 transmission to humans has been noted previously.
The most dramatic example was the H7N7 outbreak in the Netherlands in 2003. One person died and over 80 initially tested positive. These cases included contacts of cullers. However, a retrospective test of H7 antibodies in contacts indicated the number infected likely exceeded 1000. Many were asymptomatic, and the cases with symptoms generally had mild flu-like symptoms, and / or conjunctivitis.
The current patients also appear to have mild symptoms, because those hospitalized have been discharged. However, as noted above, the number infected is still not known.
This outbreak follows an H7N3 outbreak in England last year. A small number of human cases were identified, and the sequence of the H7 has been published. The sequence contained M230I, which is adjacent to the receptor binding domain, and is found in all human subtypes (H3N2, H1N1, and influenza B). The sequence encoding M230I in H7N3 poultry in England was subsequently found in H5N1 in poultry and one patient in Egypt. Other patients and poultry had M230I encoded by the sequence found in an Qinghai H5N1 infected eagle owl in northern Germany.
The co-circulation of H7 and Qinghai H5N1 is cause for concern because of the ability of H5N1 to acquire sequences that increase the efficiency of human to human transmission. The Gharbiya cluster involved three patients from the same family. H5N1 was isoaltyed from two, and both had M230I. Like all H5N1 patients in Egypt with M230I, the three cluster members died.
The efficient transmission of H7N2, which will also likely have M230I, is cause for concern.