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H5N1 Outbreak Explosion in Turkey Raises Pandemic Concerns
Recombinomics Commentary
January 5, 2006
The explosion of H5N1 bird flu infections in people and birds in Turkey is cause for concern. The number of suspected cases may have topped 30 with 3 new admissions from Agri and 2 from Ercis. The bird outbreaks have expanded to the south and west in Turkey.
The human cases have been alarming because of the sudden appearance of cases, the size of the clusters, and the severity of the disease. The bird cases have also suddenly appeared and significantly extended a geographic reach over significant portions of Turkey.
The simultaneous appearance of the human sequences suggests the H5N1 has change and become more efficient at infecting humans. The widespread nature of the human cases suggest this change has happened and has been amplified in birds.
These types of changes could be explained by the acquisition of HA S227N. This polymorphism was identified in H5N1 Z_+ genotype isolates from two Hong King residents who had visited Fujian Province in 2003. The polymorphism led to a decreased affinity for avian receptors and an increased affinity for human receptors. Although the affinity for the avian receptors was reduced, the HA still had a significant affinity. Similarly, although the affinity for human receptors increased, the affinity was significantly lower than the affinity of human influenza sero-types.
These changes would allow the H5N1 to spread in birds, yet have a significant increase in efficiency of infecting humans. The H5N1 in the wild bird sequences also have the PB2 polymorphism, E627K, which increases virulence in mammals and favors viral replication at lower temperatures.
The increased virulence could explain the severity of the infections in humans. Many have pneumonia and are on ventilators and many are bleeding from the mouth.
Sequence data on the new isolates could address the genetic basis for the apparent increased efficiency in infecting humans. The number of infections over the next several days will address the severity and implications in the sudden appearance of advanced H5N1 symptoms.
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