Pandemic H1N1 in Quebec Swine Lack Human Link

An isolated case of the pandemic strain of (H1N1) influenza has been
confirmed in a Quebec hog herd that has since "completely recovered."

The provincial agriculture, food and fisheries ministry (MAPAQ) said
in a release Tuesday [28 Jul 2009] that the strain had been dentified Friday [24 Jul 2009] at the labs of the National Centre for Foreign Animal Disease in Winnipeg. MAPAQ emphasized Tuesday that no other case has been reported on any other hog farm in Quebec and no people have caught the virus from the herd, saying "there is no human case related to this situation." A MAPAQ spokesman said Tuesday that it's not known how the hogs caught the virus.

The above comments add to a growing body of evidence supporting widespread pandemic H1N1 in swine. The sequences of pandemic H1N1 leave little doubt that the strain has a swine origin. The human PB1 is from 1993 H3N2 and has been in swine since 1993. Similarly, the avian PB2 and PA have been in swine for more than a decade. Thus, all eight gene segments have been in swine for some time.

However, the pandemic H1N1 in humans was not closely related to swine H1N1 which had been isolated prior to the outbreak. However, this match failure was largely linked to a poor surveillance system, and possibly also due to the hoarding of matching sequences.

The first closely related sequences were identified in an Alberta herd. Media reports suggested the swine had been infected by a worker who had developed symptoms during or after a trip to Mexico. However, that worker tested negative, so there was no linkage between H1N1 from the worker and the infection in swine.

Sequences were subsequently released, and although the sequences were closely related to human sequence, there was considerable heterogeneity in the swine sequences which was not consistent with a recent infection from a common source. Thus, the heterogeneity and difference with humans flu sequences strongly suggested the swine were not recently infected by a human source.

The outbreak in Alberta was followed by two outbreaks outside of Buenos Aires. These outbreaks were also said to be kinked to infected workers, but the latest OIE report indicates the Buenos Aires swine sequences are closely related to than Alberta sequences (greater than 99.99%), further supporting swine to swine transmission and not human to swine transmission.

The outbreak in Quebec supports swine to swine transmission because no human link has been identified.

None of the four swine outbreaks involved swine deaths, and none have been linked to a specific human isolate or even been shown to be homogeneous, as would be expected in a recent introduction from a common source.

Thus, the evidence is increasing that H1N1 has been spreading swine to swine and is much more widespread than reported in the four outbreaks in Canada and Argentina.

Full sequences from the two outbreaks near Buenos Aires, as well as the outbreak in Quebec would be useful, as would a more robust surveillance system of swine worldwide.