In late April, the world was alerted to an influenza virus believed to
have originated in swine that had crossed the species barrier and was
infecting hundreds of people in Mexico, resulting in numerous deaths.
In late April, the world was alerted to an influenza virus believed to have originated in swine that had crossed the species barrier and was infecting hundreds of people in Mexico, resulting in numerous deaths. As cases were discovered in the U.S. and several other countries in the Northern Hemisphere (including Canada), the World Health Organization (WHO) sounded the alarm that the “swine flu” virus, influenza A subtype H1N1, could become a worldwide flu pandemic.
Fear over a possible pandemic has been haunting the poultry industry for the past six years, as an avian-adapted influenza A subtype H5N1 (commonly referred to as “bird flu”) began to infect poultry and other bird species in Asia and Africa. This avian H5N1 is highly virulent and is lethal to birds. Although very close contact with infected birds is required for humans to acquire the virus and such transmission is inefficient, H5N1 is lethal to 60 per cent of humans that become infected, according to the WHO. Human to human transmission of the virus has not been confirmed, although suspected in one case.
In contrast, the H1N1 influenza strain originating in Mexico has been lethal to less than one per cent of its human hosts, but it is transferred among humans quite readily. Since the WHO and the Centers for Disease Control (CDC) in the U.S. made public their suspicions that a late-season influenza infecting Mexicans was cause for concern, the world became obsessed with pandemic talk. Media reports were all-consuming for several weeks and the pork industry suffered a major public relations challenge. Culling of healthy pigs began in several countries and trade restrictions on pork from countries with human cases were quickly put into place by China.
After several weeks, one could ponder whether or not this “swine flu” pandemic was over-hyped.
However, experts say we should still be concerned. They believe the world is overdue for a pandemic, but what makes the H1N1 virus in question so worrisome to them is that it is a “hybrid” of avian, swine, and human H1N1 subtypes, containing genetic material from subtypes known to infect each species. This is what makes it so readily transferable between swine and humans, as an Albertan hog farmer discovered in early May when more than 200 pigs on his farm were infected by a worker who had recently returned from a trip to Mexico.
The genetic savvy of influenza viruses is really what is at the core of the issue. Although human to human transmission of H5N1 is extremely rare, what if it mixes with H1N1 in a host animal and advantageous genes are transferred – making H5N1 able to more readily infect humans, or if H1N1 acquires the pathogenicity of H5N1?
The same week the WHO reported that the number of new H1N1 cases was beginning to show signs of decline, it reported two human infections of H5N1, one resulting in death. In an Associated Press article, WHO Director-General Chan was quoted as saying “We have no idea how H5N1 will behave under the pressure of a pandemic.”
The case of human to swine transfer in Alberta and the continued presence of H5N1 in Asia and Africa demonstrate that the North American poultry industry must remain vigilant with respect to biosecurity.
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