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H5N1 Bird Flu Infection in Mink Expands Host Range

Recombinomics Commentary
March 28, 2006

Swedish veterinarians have found a mink with an aggressive form of the H5 bird flu virus and had the mammal put down, the National Veterinary Institute said on Monday.

The animal was found in the Blekinge region of south Sweden, an area where several bird flu cases have been found. What is initially described as an aggressive form of H5 bird flu is often later confirmed as the highly pathogenic H5N1 virus.

The mink probably got the disease from eating wild birds which were already infected, the Institute said in a statement.

The above comments provide additional evidence that the Qinghai version of H5N1 is causing widespread infections and death in carnivores that eat H5N1 infected birds.  The H5N1 in the mink is in addition to recent reports of H5N1 in a stone marten, dogs, and cats who have eaten H5N1 infected birds.

Linkage of H5N1 infections to carnivores after eating infected birds has been noted previously in southeast Asia and confirmed.  The largest number of cases was recorded at a zoo in Thailand in 2004.  Bengal tigers were fed uncooked H5N1 infected chickens, and although the number of tiger infections initially was small, the H5N1 spread tiger to tiger and eventually 147 tigers died or were euthanized.  H5N1 was isolated from the tigers, and sequencing identified PB2 E627K.  This change had been previously reported in H5N1 from some patients in outbreaks in 1997 and 2004 as well as in H7N7 from a fatal infection of a veterinarian in the Netherlands in 2003.

In the lab PB2 E627K was associated with increased virulence in mice and had been isolated from mouse brain.  In the tigers from the Thai zoo, the H5N1 was also neurotropic and also causes hind leg paralysis in lab infected ferrets.

E627K is found in all human H1, H2, H3 serotypes and is associated with the ability of the polymerase to efficiently function at lower temperatures (33 C) compared to E627 (41 C).  Prior to last year, E627K had not been found in any bird H5N1 isolates.  However, at Qinghai Lake, all 16 bird isolates has E627K and all Qinghai H5N1 strain isolates reported since last year have had E627K.

The presence of E627K in all Qinghai isolates may increase the likelihood of mammalian infections from eating H5N1 infected birds.  Therefore, the number of mammalian species infected with H5N1 may be significantly higher than those reported above.  Transmission of H5N1 to other mammalian species increases the likelihood of recombination and acquisition of mammalian polymorphisms, which can lead to an expanded host range.

The fixing of E627K in H5N1 in long range migratory birds may have significant impact on H5N1 expansion of both geographical and host ranges.

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