HPAI update #6: Increasing avian influenza outbreaks in America

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The highly pathogenic avian influenza (HPAI) H5N8 virus originated in Asia and spread rapidly along wild bird migratory pathways during the end of 2014. However, in the Pacific flyway, this HPAI H5N8 avian influenza virus (AIV) mixed with North American AIV creating new mixed-origin highly pathogenic H5N2 and H5N1 viruses, so far detected in United States (US) and Canada.

The US Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) has established the presence of HPAI in 77 poultry outbreaks (12 backyard and 65 commercial), distributed in 44 counties in 13 states since the end of 2014. However, over 75% of these events in the US occurred in April, 2015. Detection of HPAI H5N8 and H5N1 have been also notified by USDA APHIS, but mainly limited to wild or captive birds, while HPAI H5N2 represent over 95% of AI outbreaks in US poultry since December 2014.

In Canada, HPAI H5N2 affected 13 poultry premises in the British Columbia, but as of March 9, 2015, the Canadian Food Inspection Agency (CFIA) removed the AI Primary Control Zone. However, on 8 April 2015 CFIA reported to the World Organization for Animal Health (OIE) the re-occurrence of HPAI H5N2 in a turkey farm in Southern Ontario, a different province. Since the initial report, two more outbreaks have been reported in Ontario: a broiler breeder farm and a turkey farm in Oxford County, Ontario.

Clear evidence that the AI situation is under control is the lack of new AI outbreaks for the remainder of the 21-day period after completion of the required cleaning and disinfection procedures of infected premises. However, during the last three weeks, the US and Canada experienced new AI outbreaks, in some cases in new territories. This can be considered as a current worsening of the disease situation.

Elsewhere, Mexico reported HPAI H7N3 to the OIE on 9 April, 2017, affecting two backyard poultry flocks in the States of Oaxaca and Puebla, without any identifiable epidemiological link between them. Another notification to the OIE by Mexico, also on 9 April 2015, closed the former HPAI H7N3 event which started in Guanajuato on 3 January 2013 and resolved on 11 September 2014.

All over the world the source of the AIV outbreaks or origin of infection in some cases have been wild bird contact. AI virus can also spread by movements of live poultry, contaminated equipment and poultry meat. Direct or indirect contact with poultry manure is of particular risk, because one gram of faeces from an infected bird is enough to infect thousands of poultry. In the case of poultry meat, a chain of events is required, among them, undercooked scraps from infected chickens in contact with poultry.  It is also important to consider that the AI virus could remain viable for some time in water; therefore, the poultry water intake from natural lakes or ponds could enhance the probability of AIV introduction into poultry premises.

HPAI H5N2 seems more adapted to persist in the environment according to the high proportion of outbreaks occurred in poultry with regard to other circulating strains either in US or in Canada. In fact, among AIV recently observed in North America, the HPAI H5N2 virus is the only detected in the Pacific, Mississippi and Central Flyways, so it must confer them higher risks to travel in wild birds and to reach new locations.  Considering, next waterfowl migration season is approaching, opportunities to enhance poultry biosecurity must be taken where is needed. Another important action is to report sick or dead birds immediately to veterinary services, in order to avoid AIV persistence on the environment and likely secondary transmission in case of infection.

By Pastor Alfonso, CENSA, and Victor Gongora (Belize Poultry Association) member of the Avian Diseases Working Group, 25/4/2015

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