The past year has seen a bumper crop of new avian strains of influenza and the persistent presence of older ones.
A new strain, at least as far as human infections, has just been identified by Chinese authorities and other Health Monitoring agencies, and the understanding is that the novel strain is a recombination of two other strains which already have distinct advantages compared to others that could allow it to easily spread.
The first case materialized on November 30th. An elderly woman came in with symptoms of respiratory distress and fever in Nanchang city in China. She died in early December. Since China is already monitoring two new strains, one of them being one that has killed nearly 50% of known infected people, it was a matter of routine that they would test the woman to see what infected her.
The tests showed a novel strain was responsible for her infection and death, an avian strain of the H10N8 type that was given the name JX346.
Although this is the first time that H10N8 has been found in humans, the strain had actually been detected in fowl for the first time in 2007 in Guangdong province.
But the examined strain from the first case of human infection was found to be a recombinant strain that had 6 genes from a different strain, H9N2.
From the case history, the researchers in the case found that her infection stemmed from her frequenting an open wet market in Nanchang, and that judging from her story, the incubation period was estimated to be about four days which is about the norm with avian strain infections.
When the researchers went to the wet market however, they found no evidence of fowl that carried the strain.
The fact that H10N8 is a recombinant mix of several strains of avian influenza means that in this particular case, the virus has acquired the ability to replicate more easily in humans.
The genetic change, or shift, that has occurred in H10N8 is one that resides in the PB2 gene, which is the gene that allows the virus to better 'attach' itself to human and mammals.
Since that first case, another one has surfaced this week, in the same locality as the first one.
The genes from the H9N2 are also the ones that combined with the H5N1 virus that has killed 380 people since 2003 and the H7N9 strain, which has been monitored since last spring when it first surfaced, and which has a very high mortality in known infected cases.
So far, none of the people who have come in contact with the infected patients have shown signs of infection, leading researchers to believe that for now, the virus is not being easily transmitted from human to human. But scientists worldwide are very concerned of the potential for an epidemic from the new strain and are urging renewed vigilance in tracking new cases.
The reason for the concern stems from the fact that the genetic recombination of the genes in H10N8 means that it has a better ability to attach itself to tissue in the respiratory tract. The novel virus is able to bind avian-like alpha2,3-linked sialic acid receptors, which are dominant in human lung tissue. This was a pattern also observed in H5N1, where the damage to the lungs was a marker for the virus' ability to bind to human lung tissue. H5N1 also has genetic elements that originate from a recombination with H10N8 viral strains.
The additional mutation in the Glutamic Acid and Lysine in the PB2 protein means that the adaptation of the virus has increased its ability to infect mammals in particular.
In fact, the first case, the woman who died in early December, although in frail health, did have a majority of the infective viral presence in her trachea, showing that it was a primary cause of the elderly woman's death.
What is also worrisome in H10N8 is that it does not affect poultry like other avian strains, which usually sicken or kill the affected chickens. For that reason, it can easily spread without detection, and be free to further recombine and shift and mutate, potentially into a more dangerous strain.
Source: MNT/CIDRAP/ 1.6.14
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