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Each month the World Health Organization releases a Monthly Risk Assessment Summary on influenza at the human-animal interface.
That is, influenza viruses that currently reside primarily in non-human hosts, but pose a threat of jumping to humans.
With the Northern Hemisphere flu season soon upon us, conditions for the spread of influenza viruses grow more favorable. So today, some excerpts from the latest assessment from the WHO.
Influenza at the human-animal interface
Summary and assessment as of 10 September 2012
Human infection with avian influenza A(H5N1) virus and associated animal health events
From 2003 through 10 September 2012, 608 laboratory-confirmed human cases with avian influenza A(H5N1) virus infection have been officially reported to WHO from 15 countries, of which 359 died.
Since January 2012, 30 human cases of influenza A(H5N1) virus infection have been reported to WHO.
Since the last update, no new laboratory-confirmed human cases with influenza A(H5N1)virus infection
were reported to WHO.
The epidemiologic curve of recent human cases (Figure 1) follows the same pattern seen in previous
years, with larger numbers of cases in the winter months, decreasing towards summer in the northern
hemisphere. This curve follows the seasonal curve of outbreaks in birds.
An increase in the number of H5N1 poultry outbreaks would be expected to occur over the coming
months, with the arrival of winter, and there are indications that the normal seasonal increase in
outbreaks in poultry in endemic countries is beginning. Human infections can be expected any time the virus is circulating in poultry.
Human infection with other non-human influenza viruses
A(H3N2) variant virus infectionThe United States of America (USA) continues to report an increase in the number of human cases of
A(H3N2)v virus infection. The recent increase in cases is likely due to an increased exposure associated with numerous state and local agricultural fairs and events, and improvements in testing protocols, including improved diagnostic protocols and testing of the contacts of patients.
Up to 7 September, 16 human cases have been hospitalized as a result of their illness and one H3N2v-associated death has been reported. The large majority of cases have been associated with swine exposure though instances of likely human-to-human transmission have been identified.
No sustained human-to-human transmission has been reported. Limited serological studies indicate that adults may have some pre-existing immunity to this virus but children do not. Seasonal vaccines do not provide cross-protection to influenza A(H3N2)v in adults or children. WHO has identified several candidate vaccine viruses specific for A(H3N2)v that could be used to produce an (H3N2)v vaccine if needed.
Overall public health risk assessment for influenza A(H3N2)v viruses : Further human cases and small
clusters may be expected as this virus is circulating in the swine population in the USA and people may
continue to be exposed, especially through the fall. Close monitoring of the situation is warranted as
schools have started again and changing weather conditions may favor influenza transmission.
A(H1N2) variant virus infection
As a result of enhanced surveillance around the animal fairs, 3 human cases of infection with H1N2
variant influenza virus were detected and reported from the USA. The cases occurred in a previously
healthy adult, a child with asthma and an elderly person with diabetes. All 3 had prolonged contact with swine at the State fair in Minnesota, USA. All recovered from their illness. The viruses isolated have an hemagglutinin similar to human seasonal influenza viruses circulated in people as recently as 2007, which might suggest some existing population immunity except in young children. Available data
indicates that the virus would be susceptible to the antivirals (neuraminidase inhibitors; oseltamivir and
zanamivir). Investigation around these cases is ongoing.
Overall public health risk assessment for influenza A(H1N2)v viruses : Further human cases and small
clusters of human infection with the virus may be expected as this virus is circulating in the swine
population in the USA.
A(H7N3) influenza virus infection
Two cases of human infection with avian influenza A(H7N3) virus were reported from Mexico. The two
cases presented with conjunctivitis without fever or respiratory symptoms and fully recovered. Both
cases were exposed while working on a farm where poultry was infected with H7N3. No further
epidemiologically linked human cases have been reported. Sporadic human cases of influenza A(H7N3) virus infection linked with outbreaks in poultry have been reported previously in Canada, Italy and the UK, with H7N2 in US and the UK, and with H7N7 in the UK and the Netherlands. Most H7 infections in humans have been mild with the exception of one fatal case in the Netherlands, in a veterinarian who had close contact with infected birds.
Overall public health risk assessment for influenza H7N3 viruses: Further human cases and small
clusters may be expected as long as the virus is circulating in poultry. Countries experiencing outbreaks of influenza virus infection in animals should implement appropriate biosafety measures to protect people working with or living nearby infected and potentially infected animals. Collaboration with animal health partners is necessary to optimally control this disease and decrease risks to public health.
Because influenza viruses evolve constantly and change characteristics and behavior unpredictably, WHO continues to stress the importance of global monitoring of variant influenza viruses and recommends to all Member States to strengthen routine surveillance activities.
Not mentioned in this report is The Return Of H1N1v in Missouri and in Ontario, as both reports came after its release date.
As I discussed a month ago in An Increasingly Complex Flu Field, the past few years have seen an expansion of the number of zoonotic influenza threats, particularly from avian and swine hosts.
And there are other flu threats out there, that have yet to infect man, but are worthy of our attention. One of those was detected in more than a hundred dead seals last year along the New England coastline (see mBio: A Mammalian Adapted H3N8 In Seals).
For now, there are no signs that we are on the verge of another pandemic.
But the fact remains these viruses continue to change and evolve, and the threat they may pose tomorrow, next month, or next year could differ from threat they pose today.
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