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Focus on AI at 2016 Midwest Meeting

  

Mar 30, 2016

    

The 67th North Central Avian Disease Conference together with the 2016 Midwest Poultry Federation Convention held in Saint Paul, MN in mid-March provided an opportunity for veterinarians representing the egg industry and academia to review lesson learned from the 2015 epornitic.

Characterization and Epidemiology of the H5N2 AI Virus

Dr. David L. Suarez of the USDA-ARS Southeast Poultry Research Laboratory reviewed aspects of the H5N2 virus responsible for the 2015 outbreak.  This virus was classified as a Eurasian clade 2.3.4.4.  Initially the virus was introduced by migratory waterfowl and occurred predominantly in wild birds in early 2015.  The strains which were isolated in January 2015 required a high mean infectious dose for chickens and seroconversion in survivors was not pronounced suggesting that the infective viruses were poorly adapted to chickens.  Subsequently as viruses adapted to chickens in massive populations during outbreaks, the mean death time was reduced and infectivity was enhanced.

  

Dr. Suarez commented on vaccination as a last-resort control strategy. Commercial vaccines in April and May were not homologous with the field strain of H5N2.  By the time that two additional vaccines which were matched antigenically to the field virus were available, the outbreak had ceased.

Dr. Henry Wan of the College of Veterinary Medicine, Mississippi State University discussed the epidemiology of avian influenza in China.  In 1992 an H9N2 low pathogenicity avian influenza virus emerged in Southern China and became endemic in the region.  Subsequently in 1996, H5 viruses with diverse neuraminidase (N) antigens emerged followed by H7N9 in 2013 and H6 viruses in 2010.  Backyard poultry was infected by wild birds but rapid antigenic and genetic evolution occurred among all viruses including H9N2 and H5N1.  China introduced nationwide vaccination in 2004 which has suppressed clinical outbreaks in commercial flocks.  Failure to eradicate avian influenza viruses has led to infection of human contacts especially associated with live-bird markets.  There is little prospect for eradication of avian influenza in subsistence and large-scale commercial flocks in China.  Suppression of clinical infection applying vaccines coupled with the live-bird marketing system and suboptimal biosecurity will perpetuate infection and result in the evolution of new recombinant serotypes.

  

Field Experience Gained during the Outbreak of H5N2

 Dr. George Girgis of Center Fresh Group which was severely affected by the outbreak shared observations and lessons from the events of April through June 2015.  Significant points raised by Dr. Girgis included:

  • Due to extensive intra- and interstate movement of live birds, manure and poultry products, there was considerable opportunity to transmit influenza virus
  • Meaningful communication between producers, regulatory authorities and laboratories is essential to implement a control program
  • In the face of an outbreak, industry attempted to apply Operational Biosecurity without the necessary Structural Biosecurity which would have served as a barrier to introduction of infection
  • High virus loads developed as a result of delayed depopulation from very large farms
  • During the implementation of the control program, deficiencies in biosecurity contributed to dissemination of virus.  These included movement of products from infected premises, transport of material for disposal through control zones, outside composting of dead birds and unregulated movement of personnel and contractors crews from positive to negative sites
  • Early detection is essential in mounting a depopulation program.  Periodic surveillance was beneficial to early detection “buying time to be ahead of mortality”
  • Epidemiologic surveys are required to identify methods of spread of HPAI virus.  In the early stages of the infection air transmission was implicated but subsequent epidemiologic studies disfavored this mechanism with respect to infection of turkey farms in Minnesota
  • The speed of depopulation and subsequent disposal of carcasses is important in preventing spread of infection.  Using kill-carts and with available labor required 20 days to depopulate a 4- million bird complex at a rate of 200,000 hens per day.
  • It is necessary to identify an appropriate site for disposal of dead birds prior to an outbreak. Options are limited by conflicts over local and state jurisdiction, legal liability considerations and public perception.  The logistics and biosecurity associated with landfills requires prior planning. Incinerators were generally impractical due to cost, delays in assembly and rate of processing.
  • Cleaning and disinfection was initially slow due to inexperienced contract crews and the absence of predetermined cleaning and disinfection plans
  • Documentation required by USDA continuously changed in the early stages of the outbreak but with experience, problems were resolved
  • The take home message from Dr. Girgis was to be prepared and to take the initiative with regard to detection, control and disposal.  Above all effective Structural Biosecurity and efficient Operational Biosecurity are required to limit introduction of infection.

Dr. Josh Payne of Oklahoma State University reviewed disposal of carcasses during the epornitic. Federal and state authorities in cooperation with industry eventually disposed of 50 million birds.

  • Burial was employed in some states where soil conditions and the depth of the water table allowed this approach but interment is generally limited by environmental restraints.

 

  • Incineration was expensive and relatively inefficient.  In many cases, air quality permits were required, creating additional delays.

 

  • Landfills were generally the destination of birds from large farms. Permitting is frequently required and in the case of Iowa it was necessary to provide legal indemnity for operators of landfills against future claims.  Disposal using a landfill requires containers, work crews and special precautions during transportation to prevent dissemination of infection.

 

  • Composting of mortality was successful in the case of small farms holding turkeys and hens especially when carried out within houses.  Outside composting created problems relating to rodent and fly infestation, odor and cost for the carbon substrate.

Precautions by Breeder-Multipliers

Dr. Danielle Botting of Hy-Line North America considered planning by breeders in anticipation of an HPAI outbreak.  Items considered in her presentation included:-

  • Developing site-specific biosecurity programs to address risks and to specify procedures relating to personnel and movement of products.
  • Intensive surveillance for avian influenza in apparently healthy flocks (as recommended by Dr. Girgis), since early detection expedites subsequent depopulation thereby limiting the spread of virus.
  • The necessity of valid emergency response plans was stressed with reference to personnel, equipment, transport, depopulation and disposal.  Emphasis should be on containment of infected sites to prevent lateral transmission.
  • Communication is critical to an effective planning program since all stakeholders must be aware of their respective responsibilities.  Dr. Botting emphasized the need for all employees to buy-in to prevention programs based on their understanding of why their Operational biosecurity procedures are critical to successful prevention.

 

 

Secure Poultry Product Supply Programs

Dr. David Halvorson of the College of Veterinary Medicine, University of Minnesota reviewed secure egg supply and business continuity. 

  • An effective plan must be based on risks and provide guidance to safely move commercial eggs. 
  • It was noted that producers must be educated and demonstrate proficiency before receiving a permit to move low-risk product. Permits for washed, graded and packed eggs should be issued as a routine, with more consideration assigned to live and dead poultry.

 

  • Mutual cooperation among the Minnesota Board of Animal Health, USDA-APHIS Veterinary Services, and the Universities in Minnesota and Iowa, plans to allow secure movement of eggs have been harmonized provided acceptable surveillance is implemented.

January 2016 Indiana Outbreak

Dr. Duane Murphy of Farbest Farms reviewed the outbreak of avian influenza in Southern Indiana during January 2016.  The outbreak involved one farm with H7N8 HPAI and nine other farms with H7N8 LPAI.  Applying the lessons learned from the 2015 HPAI outbreak, the index flock with clinical signs was diagnosed and rapidly depleted.  Nine flocks with LPAI were identified by surveillance.  A flock of laying hens regarded as biologically contiguous was also depopulated. 

In total 397,000 birds in 41 barns were depopulated.  The benefit of prior planning is indicated by the fact that within one day, 65 commercial farms were sampled within a 10 km control zone and all ten farms were depopulated within a week.  Backyard flocks within an initial 10 km zone, subsequently extended to 20 km, were sampled without demonstrating the presence of avian influenza on two successive rotations.  The control zone was lifted on February 22nd with some farms still undergoing in-house composting of flocks. 

All the H7N8 viruses were homologous with the exception of a single gene mutation resulting in insertion of a basic amino acid at the cleavage site resulting in the isolate becoming highly pathogenic.  The LP H7N8 isolates were similar to the isolate from a scaup (Aythya spp) a diving duck, in Kentucky in November 2015. This suggests that the infection was caused by virus from a North American wild bird lineage.

(SMS 498-16 March 25th 2016)