EUROPEAN SWINE VIRUS AS A POSSIBLE SOURCE FOR THE NEXT INFLUENZA PANDEMIC

According to phylogenetic data, about 100 years ago an avian influenza virus passed the species barrier (possibly first) to pigs and (possib ly from there) to humans. In 1979 an avian influenza A virus (as a who le, without reassortment) again entered the pig population in northern Europe, forming a stable lineage. Here it is shown that the early Nor th European swine viruses exhibit higher than normal evolutionary rate s and are highly variable with respect to plaque morphology and neutra lizability by monoclonal antibodies. Our results are consistent with t he idea that, in order to pass the species barrier, an influenza A vir us needs a mutator mutation to provide an additional number of variant s, from which the new host might select the best fitting ones. A mutat or mutation could be of advantage under such stress conditions and mig ht enable a virus to pass the species barrier as a whole even twice, a s it seems to have happened about 100 years ago. This stressful situat ion should be over for the recent swine lineage, since the viruses see m to be adapted already to the new host in that the most recent isolat es - at least in northern Germany - are genetically stable and seem to have lost the putative mutator mutation again. (C) 1995 Academic Pres s, Inc.