Published Date: 2012-09-26 22:56:16
Subject: PRO/AH/EDR> Influenza (91): Canada (ON) H1N1v, human case
Archive Number: 20120926.1311060
INFLUENZA (91): CANADA (ONTARIO) H1N1V, HUMAN CASE
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Tue 25 Sep 2012
Source: The Canadian Press, via CBCNEWS Windsor [edited]
Case of Influenza A H1N1v Detected in Southwestern Ontario
Ontario has found a case of an infection with a new swine flu virus, in a man who worked with pigs. The infection was caused by an H1N1-variant virus (H1N1v), which is not the swine flu virus that has been jumping from pigs to people in the United States this summer. That virus, an H3N2-variant (H3N2)v), has caused 305 infections this year in the U.S. but has not been spotted in Canada to date. Most infections with the H3N2v influenza virus have been in people who visited pig barns at state and county fairs.
Dr. Arlene King, Ontario's chief medical officer of health, said the man is being treated in a hospital in southwestern Ontario. She did not indicate whether that is as a precaution or because he is seriously ill. "It's likely an isolated occurrence," she said. The man worked with pigs in both Canada and the United States, but it's still unclear where he may have picked up the new virus, she said.
The new virus is one that rarely spreads from animals to people, and human-to-human spread is also rare. So far, none of the man's family or friends are showing signs of illness, King said. She stressed the discovery of the infection does not trigger food safety concerns. "Proper cooking of meats, including pork, kills all bacteria and viruses." She also urged people to remember that hand washing and getting a flu shot are the best way to protect against contracting the flu.
This H1N1v virus would be a distant cousin of the H1N1 viruses that have been circulating in people for most of the last century. That family includes the virus that caused the 2009 pandemic. But viruses within a large family group such as H1N1 can be sufficiently different from one another that antibodies to one won't fully protect a person from becoming infected with another. The U.S. authorities have also seen one case of infection with an H1N1v virus there this summer, in Missouri. King could not say whether the genetic blueprints of the Ontario and Missouri viruses were closely related. Genetic sequencing of the Ontario virus is still being done, so they haven't had a chance to compare it to the one spotted in Missouri, King said.
She said they do know it contains the M gene of the pandemic H1N1 virus, which is also present in the swine flu viruses that have been causing human infections in the USA this summer. Scientists suspect it may make it easier for swine viruses to infect people, but that hasn't been proven.
[Earlier this month (September 2012), the US Centers for Disease Control and Prevention (CDC) reported an H1N1v case in Missouri in which the virus contained the matrix (M) gene from the 2009 pandemic H1N1 strain -- only the 2nd isolation of this H1N1v strain. Previously 12 H1N1v cases isolated in the USA since 2005 did not contain the 2009 H1N1 M gene. It is not known yet whether the Ontario case involved an H1N1v virus with the 2009 M gene.
Recently Nelson et al. have published an analysis of the transmission of influenza viruses from humans to swine and vice versa. [See: Global transmission of influenza viruses from humans to swine. By: Martha I. Nelson, Marie R. Gramer, Amy L. Vincent Edward C. Holmes. In: J Gen Virol October 2012 93:2195-2203
To determine the extent to which influenza viruses jump between human and swine hosts, these authors undertook a large-scale phylogenetic analysis of pandemic A/H1N1/09 (H1N1pdm09) influenza virus genome sequence data. From this, they identified at least 49 human-to-swine transmission events that occurred globally during 2009 to 2011, thereby highlighting the ability of the H1N1pdm09 virus to transmit repeatedly from humans to swine, even following adaptive evolution in humans.
Conversely, they identified at least 23 separate introductions of human seasonal (non-pandemic) H1 and H3 influenza viruses into swine globally since 1990. Overall, their results reveal the frequency with which swine are exposed to human influenza viruses, and indicate that humans make a substantial contribution to the genetic diversity of influenza viruses in swine. These findings emphasize the need to improve biosecurity measures at the human-swine interface, and may require influenza vaccination of swine workers.
The interactive HealthMap of Ontario can be accessed at: http://healthmap.org/r/1*Y3. - Mod.CP]
[How about requiring swine workers to wear masks for protection in both directions? - Mod.JW]