Friday, October 12, 2012

Influenza (98): human-animal interface, WHO

Published Date: 2012-10-11

Date: Mon 1 Oct 2012

Source: WHO, Programmes and Projects [edited]

A. Human infection with avian influenza A(H5N1) virus and associated animal health events:


From 2003 through 1 Oct 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 [10 Sep 2012], no new laboratory-confirmed human cases with influenza A(H5N1) virus infection have been reported to WHO. Public health risk assessment for avian influenza A(H5N1) viruses: The public health risk for the virus remains unchanged.

B. Human infection with other non-human influenza viruses


A(H3N2) variant virus infection


The United States of America (USA) reported few additional human cases of influenza A(H3N2)v, and no additional deaths. 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 [1-4] indicate that adults may have some pre-existing immunity to this virus but children do not. Seasonal vaccines do not provide cross protection against A (H3N2)v infection. WHO has identified several candidate vaccine viruses specific for A(H3N2)v that could be used to produce an (H3N2)v vaccine if needed [5].

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 autumn. Close monitoring of the situation is warranted as schools have started again and changing weather conditions may favor influenza transmission.

A(H1N1) variant virus infections


As a result of enhanced surveillance around the agricultural fairs, a case of human infection with H1N1 variant influenza virus was detected and reported from the USA [6]. The case occurred in August 2012 in a previously healthy woman. She was not hospitalized and recovered from her illness. The person had direct contact with swine at a State Fair. No further cases were identified. This is the 2nd case of infection with this H1N1v virus in the USA; the previous case occurred in 2011.

Canada also reported a case of human infection with influenza A(H1N1)v in an adult male with underlying risk factors. He developed symptoms at the end of August [2012] and was hospitalized with pneumonia in September. He had occupational exposure to swine. No additional cases have been reported.

The influenza A(H1N1)v viruses isolated from patients in the USA and Canada have an haemagglutinin similar to human seasonal influenza viruses circulating very recently in people, which might suggest some existing population immunity except in young children. Current seasonal vaccines would provide cross protection against these viruses. Available data indicates that the virus would be susceptible to antivirals (neuraminidase inhibitors; oseltamivir and zanamivir).

Overall public health risk assessment for influenza A(H1N1)v viruses:

Further human cases and small clusters of human infection with these viruses may be expected as they are circulating in swine populations. No human-to-human transmission with this virus has been reported. It is expected that the human populations are largely protected by existing immunity except for young children and by the seasonal influenza vaccine.

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.

All human infections with non-human influenza viruses as such are reportable to WHO under IHR (2005). More information on influenza at the human-animal interface is available from WHO (; additional information on influenza in animals is available from OIE ( and FAO (, and OFFLU (



1. CDC. Antibodies cross-reactive to influenza A(H3N2) variant virus and impact of 2010-11 seasonal influenza vaccine on cross-reactive antibodies -- United States. MMWR 2012; 61(14): 237-41; [available at].

2. Skowronski, et al. Cross-reactive antibody to swine influenza A(H3N2)subtype virus in children and adults before and after immunisation with 2010/11 trivalent inactivated influenza vaccine in Canada, August to November 2010. Euro Surveillance 2012; 17(4); available at

3. Waalen et al. Age-dependent prevalence of antibodies cross-reactive to the influenza A(H3N2) variant virus in sera collected in Norway in 2011; Euro Surveillance 2012; 17(19); available at

4. Danuta Skowronski, et al. Cross-reactive and vaccine-induced antibody to emerging swine influenza A(H3N2)v, JID 2012; available at

5. WHO. Candidate vaccine viruses for variant influenza A(H3N2); available at

6. CDC. H1N2 variant virus detected in Minnesota; available at

Relevant links


- WHO table: cumulative number of confirmed human cases of avian influenza A/(H5N1) reported to WHO:

- WHO table: H5N1 avian influenza: timeline of major events

- WHO archive: avian influenza situation updates:

- World Organisation of Animal Health (OIE) webpage: web portal on avian influenza:

- Food and Agriculture Organization of the UN (FAO) webpage: avian influenza:

- Updated unified nomenclature system for the highly pathogenic H5N1 avian influenza viruses:


communicated by:

ProMED-mail rapporteur Marianne Hopp

[This document includes an epidemiological curve of avian influenza H5N1 cases in humans by country and month of onset, and a useful map of avian influenza H5N1 cases in humans for 2012. Readers are recommended to view these illustrations, which can be accessed, via the source URL above. - Mod.CP]

[all editing is mine]

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