Surveillance for avian influenza in poultry 2.0; reloaded
Prior to the emergence and spread of H5N1, surveillance for avian influenza in poultry was by and large carried out with two objectives, namely - exclude or confirm HPAI as a causative agent of episodes of sudden mortality and establish whether outbreaks of non-specific clinical disease (respiratory, enteric or reproductive) could be attributed to infection with a virus of low pathogenicity. In the case for which passive surveillance revealed the presence of a HPAI, the outbreak would be stamped out and the virus eradicated. In the case of a low pathogenicity avian influenza infection, voluntary control programmes based on disease control measures and possibly vaccination for non H5/H7 strains was implemented.
A further change in the expected outcome of surveillance efforts was led by scientific evidence which suggested that LPAI viruses of the H5 or H7 subtype could mutate and become highly pathogenic. This determined a change in legislation (except for Japan which already had this in place), making H5 and H7 viruses of low pathogenicity also notifiable, and active surveillance programmes were implemented worldwide to prove absence of H5/H7 infection, and thus enable trade and comply to national standards.
Much of this situation has remained unchanged in high income countries with efficient veterinary services and good biosecurity standards. These countries have systems in place to monitor in real time whether a novel virus is introduced and to promptly enact disease control measures, to preserve animal and human health.
In some low and middle income countries however, despite the presence of advanced poultry rearing systems, things are much more complicated and would require more attention and resourcing. Viruses with zoonotic potential such as H5N1 and H9N2 are circulating in vaccinated populations and are constantly changing from an antigenic and genetic point of view. This has tremendous implications in terms of animal health, as vaccines are not as efficacious as they were, and drifted variants are breaking through vaccine induced immunity. There are severe implications in terms of public health, since these viruses are developing genetic constellations which are completely novel and are accumulating mutations of public health relevance.
Conventional surveillance procedures are not designed to generate in-depth information as that which is required to understand the evolution of a viral population undergoing, for the first time in history, extensive immunological pressure and genetic reassortment.
International veterinary organizations such as OIE and FAO have developed networks and activities to ensure that surveillance for animal influenzas is dealt within the animal health arena. Currently, the international scientific community relies on veterinary surveillance to monitor field strains with reference to their pandemic potential and it is essential that surveillance is re-thought extensively, to make sure that as a community, we deliver on these expectations.
