Evaluation of Inactivated Avian Influenza H7 Vaccines for Protection of Chickens against an HPAI Virus H7N3 Isolated from Chickens in Mexico in 2012

Current inactivated H7 vaccines were found in USDA ARS studies to be effective against the H7N3 subtype of the highly pathogenic avian influenza (HPAI) virus that caused the outbreaks of bird flu in Mexico in 2012 and a similar low-pathogenic virus of the same subtype.
calendar icon 4 February 2013
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At the International Poultry Scientific Forum 2012 in Atlanta, Dr Darrell Kapczynski reminded the audience about a recent outbreak of highly pathogenic avian influenza (HPAI) H7N3 in Jalisco, Mexico, beginning in June 2012. To date, more than 22 million birds have died or been slaughtered there in an effort to stop the spread of disease.

In response to the outbreak, he and his colleagues at the USDA ARS South Eastern Poultry Research Lab in Athens, Georgia - with support from SENASICA, Mexico's National Health Service, Food Safety and Food Quality in Cuajimalpa - conducted vaccine efficacy trials to determine if US- and Mexican-origin inactivated H7 vaccine would protect birds from clinical disease and shedding of virus.

In the first set of experiments, four phylogenetically-related US low pathogenic avian influenza (LPAI) isolates - either H7N2 or H7N3 - were formulated into inactivated emulsion vaccines and injected into seven-week-old specific pathogen-free (SPF) birds. These isolates contained between 92 and 97 amino acid similarity to the haemagglutinin gene of the challenge virus (A/chicken/Jalisco/CPA1/2012 H7N3).

The APHIS-approved H7 vaccine antigens were included into this experiment for testing.

Birds were challenged at 10 weeks of age with 106 EID50 per bird delivered via the intranasal route.

Results demonstrate that three of the four H7 vaccine isolates tested provided 100 per cent protection, whereas the fourth isolate provided 90 per cent protection.

In the second experiment, a Mexican-lineage LPAI H7N3 isolate from wild birds, with 98 per cent sequence similarity to the HPAI virus, was formulated into an inactivated vaccine and applied to two-week-old birds. Birds were challenged as previously described and demonstrated 100 per cent protection from challenge.

Dr Kapczynski and co-authors observed that all the vaccines tested reduced virus shedding compared to sham-vaccinated birds.

Taken together, they concluded, the results indicate that both US and Mexican vaccine isolates can provide protection to poultry against this recent HPAI H7N3 virus. Most of the H7 vaccines protected agianst a lethal challenge and the US master seed isolates were fully protective, Dr Kapczynski added.

In answer to a question about the reported recurrence of HPAI in Jalisco, he indicated that the latest outbreaks have been initially attributed to the second vaccination being missed in the affected flocks.

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February 2013

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