Effect Measure

An interesting piece on an infection trial of novel H1N1 in pigs appeared on ProMed over a week ago, but with dealing with swine flu up close and personal and all, I am only just getting to comment on it. This was a study done in the EU (VLA-Weybridge, Mammalian Influenza Group) to see how easy it was to infect pigs with the human-adapted swine flu, what kinds of symptoms and pathology it produced, and how transmissible it was. The answer seems to be easy, mild and very, in that order.

11 pigs were inoculated intranasally and when they began to shed virus a naive pair of pigs placed in contact with them. As each pair was infected and began to shed virus, a new pair was placed in contact with them to test transmissibility. This means a chain of five transmission cycles was tested. Direct infection was readily accomplished. nasal and ocular discharge, fever, cough, lethargy and loss of appetite. Fever developed on days 5 through 9 post contact, but were shedding virus via nasal discharge anywhere from day 1 to day 9 (peak shedding, 3 – 5 days). During the course of observation the directly infected pigs did not die of the disease, but were sacrificed at intervals and examined post mortem. There was little lung pathology initially, but by day 7, acute bronchopneumonia had developed in the 2 pigs that had not yet been sacrificed.

The contact pigs had similar profiles to the directly infected ones. There was no apparent difficulty in propagating infection over 4 additional contact cycles. This was human virus, originally of swine origin, had lost none of its transmissibility. The ProMed commentator interprets the preliminary results to mean the human strain behaves in pigs like a mild swine influenza virus. In a sense this is not a surprising finding, since Canadian scientists had already reported a case of a swine herd being infected via a human handler early in this outbreak. But it once again points up the importance of more thorough surveillance of pigs for influenza virus, not just this one, but any they may harbor. Nor is it just pigs. We really have remarkably little data on which animal species are actual or potential reservoirs for influenza virus.

If giant anteaters, mammals as unlike humans as I can imagine, can get human seasonal influenza, I’d say all bets are off as to the possibilities.


  1. #1 Tom DVM
    June 8, 2009

    They should continue-repeat this experiment with small shoreline mammals, rats and mice…and with dog-H3N8 in pigs.

  2. #2 Lowlander
    June 8, 2009

    Nobody wants to pay for it. Thats the problem. In Europe, after the H5N1 crisis a sero-surveillance system was installed to test activelly domestically kept birds and a semi-active system to test large dye-offs of wild birds.
    However, 2 years past the scare the systems (which were never perfect) are clearly being scalled down.
    And as I understand it the states have the additional problem that livestock keepers are not required by law to notify authorities of what they keep and where. Therefore it is very complicated to keep good databases of livestock populations.