Mexican Swine Flu Being Complicated By Canadian H3N2 Virus?

The following report is of great interest, and the people that come here should take the time to read the whole post and understand it as best you can considering how complex the flu viruses are.

From Reuters AlertNet 5/6/2009:

Second strain of flu may complicate picture-study

WASHINGTON, May 6 (Reuters) – A second strain of influenza, one of the seasonal strains, may have mutated and may be complicating the picture in Mexico, Canadian researchers reported on Wednesday. They have found a strain of the H3N2 virus that appears to have made a shift and could have complicated the flu picture in Mexico, epicenter of an outbreak of a new strain of the H1N1 swine flu virus. One was seen in a traveler returning from Mexico, the team at the British Columbia Centre for Disease Control reported to Pro-MED, an online forum for infectious disease experts. And it may have been involved in an unusually late outbreak of flu in long-term care facilities this year. The new H1N1 virus has killed at least 42 people in Mexico and two in the United States, has spread globally and brought the world to the brink of a pandemic. It appears to act like seasonal flu but doctors have been confused because it has also killed some young and apparently healthy adults — not the usual pattern for influenza, which picks off the elderly, chronically ill and very young.

“In British Columbia, these H3 mutations arose sometime in early March 2009 and we observe at least one returning traveler to have likely acquired illness due to this virus in Mexico,” they wrote. “We thus also wonder to what extent the profile of influenza-like illness initially reported from mid-March in Mexico may in part be attributed to this H3N2 variant in addition to emergence of the novel A/H1N1 virus.”

What you are not reading in this news report is that H3N2 is an Influenza A virus that can infect birds, pigs, and humans.  The seasonal strain that they have found is from H3N2.

Influenza A virus subtype H3N2

Influenza A virus subtype H3N2 (also H3N2) is a subtype of viruses that cause influenza (flu). H3N2 viruses can infect birds and mammals. In birds, humans, and pigs, the virus has mutated into many strains. H3N2 is increasingly abundant in seasonal influenza, which kills an estimated 36,000 people in the United States each year.

The Hong Kong Flu was a category 2 flu pandemic caused by a strain of H3N2 descended from H2N2 by antigenic shift, in which genes from multiple subtypes reassorted to form a new virus. This pandemic of 1968 and 1969 killed an estimated one million people worldwide.[5][6][7] The pandemic infected an estimated 500,000 Hong Kong residents, 15% of the population, with a low death rate.[8] In the United States, approximately 33,800 people died.[9]

Both the H2N2 and H3N2 pandemic flu strains contained genes from avian influenza viruses. The new subtypes arose in pigs coinfected with avian and human viruses and were soon transferred to humans. Swine were considered the original “intermediate host” for influenza, because they supported reassortment of divergent subtypes. However, other hosts appear capable of similar coinfection (e.g., many poultry species), and direct transmission of avian viruses to humans is possible. H1N1 may have been transmitted directly from birds to humans (Belshe 2005).[10]

Since the amount of information about swine flu, avian flu and human flu viruses is so complex, I have decided to discontinue the swine flu series and just try to impart the basics in day to day posts about the current pandemic.  My belief is that to do it any other way would definitely make heads explode, as I have had a massive headache for 3 weeks now due to the research.

There are three main types of influenza viruses; A, B, and C.

Influenza A:

Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. Influenzavirus A includes only one species: Influenza A virus which causes influenza in birds and some mammals. Strains of all subtypes of influenza A virus have been isolated from wild birds, although disease is uncommon. Some isolates of influenza A virus cause severe disease both in domestic poultry and, rarely, in humans.[1] Occasionally viruses are transmitted from wild aquatic birds to domestic poultry and this may cause an outbreak or give rise to human influenza pandemics.[2] [3]

Influenza A viruses are negative sense, single-stranded, segmented RNA viruses. There are several subtypes, labeled according to an H number (for the type of hemagglutinin) and an N number (for the type of neuraminidase). There are 16 different H antigens (H1 to H16) and nine different N antigens (N1 to N9). The newest H type (H16) was isolated from black-headed gulls caught in Sweden and the Netherlands in 1999 and reported in the literature in 2005. [4]

Each virus subtype has mutated into a variety of strains with differing pathogenic profiles; some pathogenic to one species but not others, some pathogenic to multiple species.

This genus has one species, influenza A virus. Wild aquatic birds are the natural hosts for a large variety of influenza A. Occasionally, viruses are transmitted to other species and may then cause devastating outbreaks in domestic poultry or give rise to human influenza pandemics.[33] The type A viruses are the most virulent human pathogens among the three influenza types and cause the most severe disease. The influenza A virus can be subdivided into different serotypes based on the antibody response to these viruses.[34] The serotypes that have been confirmed in humans, ordered by the number of known human pandemic deaths, are:

In 2009, a recombinant influenza virus derived in part from H1N1 was first detected in Mexico and the United States (see 2009 H1N1 flu outbreak).

Influenza B:

Influenzavirus B is a genus in the virus family Orthomyxoviridae. The only species in this genus is called “Influenza B virus”.

Influenza B viruses are only known to infect humans and seals,[1] giving them influenza. This limited host range is apparently responsible for the lack of Influenzavirus B caused influenza pandemics in contrast with those caused by the morphologically similar Influenzavirus A as both mutate by both genetic drift and reassortment.[2][3][4]

Further diminishing the impact of this virus “in man, influenza B viruses evolve slower than A viruses and faster than C viruses“.[5] Influenzavirus B mutates at a rate 2-3 times lower than type A.[6] However, influenza B mutates enough that lasting immunity is not possible.

Influenza C:

Influenzavirus C is a genus in the virus family Orthomyxoviridae, which includes those viruses which cause influenza. The only species in this genus is called “Influenza C virus”.

Influenza C viruses are known to infect humans and pigs[1], giving them influenza. Flu due to the type C species is rare compared to types A or B, but can be severe and can cause local epidemics.

Types A and B have 8 RNA segments and encode 11 proteins. Subtype C has 7 RNA segments and encodes 9 proteins.

Avian influenza

There are many subtypes of avian influenza viruses, but only some strains of four subtypes have been highly pathogenic in humans. These are types H5N1, H7N3, H7N7 and H9N2.[8]

For a complete table of avian flu viruses with all the different combinations, country of origin, and fowl type, go here.

Here is the report that is one of the most disturbing to me and bears watching.

Influenza A virus subtype H5N3

H5N3 is a subtype of the species Influenza A virus (sometimes called bird flu virus).

H5N3 was identified in Quebec in August 2005 [1] and in Sweden in October 2005. [2]


H5N3 virus was identified at a La Garnache farm in France in late January. 90 birds were found dead between 29 January 2009 and 31 January 2009. The remaining stock of 4932 birds was destroyed on 1 February 2009. [3]

The original Wiki page that was written about wild canadian birds with long range migratory patterns who are infected with 3 different forms of avian influenza, including H5N3, has been scrubbed since the reports of the infected pigs in Canada surfaced on 5/3/2009.  The swine in Canada have been quarantined, and there is no further word as to their status.

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