2020-10-23 10:39:10
Like all influenza viruses (also called influenza), those responsible for influenza in pigs are constantly evolving. Pigs can be infected by porcine influenza viruses but also by human or avian influenza viruses. It can therefore become an intermediate host for the transmission of avian influenza viruses to humans, but also serve as a “crucible”, where, thanks to co-infections, new so-called reassortant viruses can emerge (reassortant viruses have genes from influenza viruses of different origins). Thus, a large number of different strains have been isolated over the years through surveillance carried out on pig farms. Overall, viruses of three subtypes (H1N1, H3N2 and H1N2) circulate in the pig population, but numerous genetic lineages (or genotypes) are distinguished within each of these subtypes, depending on the origin of each of the viral genes.
Monitoring the health of pigs to anticipate pandemics in humans
Porcine influenza viruses type A (or swIAV for swine influenza A virus) have zoonotic potential, and can therefore be transmitted to humans. In 2009, the H1N1pdm09 virus, which caused a pandemic in humans, came from a reassortment of several swIAVs. Its emergence has served as a reminder of the need to monitor and study influenza viruses in pigs, both from an animal health and human health perspective. This virus then spread in numerous pig populations around the world from 2009. Thanks to co-infections with other swIAVs, the H1N1pdm09 virus was at the origin of the emergence of new reassortant viruses, including some have also spread in certain pig populations. Among them, a few have been responsible for cases of human infections.
ANSES, reference laboratory for swine flu
The Agency’s Ploufragan-Plouzané-Niort laboratory has been a national reference laboratory for swine influenza (LNR IP) since August 2009. This NRL is hosted by the Swine Virology Immunology Unit (VIP). As such, the VIP Unit develops, validates and controls diagnostic tools allowing the detection and identification of influenza A virus subtypes and lineages in pigs. It runs the network of veterinary laboratories approved for the molecular diagnosis of these infections. In particular, it verifies that their suitability is maintained by organizing inter-laboratory tests. It provides reference reagents (which make it possible to detect viruses or antibodies directed once morest these viruses) and offers technical support to more precisely characterize the viruses identified.
Active surveillance of virus strains present in France
Although it has a significant economic and health impact on the pig industry, and can affect humans, swine flu is not a regulated disease and there are few formalized and lasting surveillance systems. Knowledge of viruses circulating in a territory varies depending on the country, and is often scattered or incomplete. In France, the Virology Immunology Porcine (VIP/LNR IP) and Epidemiology Health Well-Being (EPISABE) units of the Ploufragan-Plouzané-Niort laboratory have contributed very actively to the surveillance of porcine influenza viruses since 2005. This This has been amplified since 2011, with the establishment of the national surveillance network “Résavip”. The surveillance carried out by this network makes it possible to describe the genetic diversity and geographical distribution of swine influenza viruses.
In addition, ANSES develops or contributes to specific surveillance programs, in certain farms, or even certain regions, depending on particular epidemiological contexts. Occasional surveys are also carried out on wild boars. Prospective work also concerns influenza viruses types B, C and D, which are much less pathogenic or less frequent in pigs than influenza viruses type A.
An activity that is available internationally
The Agency is represented within the OFFLU international network, a joint OIE-FAO network for animal influenza viruses, which allows discussions on viruses circulating beyond European borders. More particularly, the VIP Unit is an active member of the “Swine Influenza Virus Technical Group” of this network. The results exchanged make it possible to inform the World Health Organization (WHO) of the emergence of swine influenza viruses which might present pandemic risks. The objective is to select strains for the development of new vaccines when necessary.
Research activities to better understand the virus, its transmission factors and its effects on pigs
The Agency is carrying out several research projects on swine flu:
Monitor the genetic and antigenic evolution of porcine influenza viruses
The viruses identified in France as part of epidemiological surveillance are the subject of in-depth studies at the level of their genes and their antigens (antigens being viral molecules recognized by the immune system of the infected animal). These studies aim to improve knowledge on the evolution of swIAV in France, their diversity and the contexts of emergence of new virus lineages. The in-depth analysis of the genetic sequences of viruses aims to identify molecular determinants of virulence as well as characteristics which might contribute to facilitating the transmission of porcine viruses to other animal species, and in particular to humans. These properties are studied via bioinformatics analyses, in cell culture, and when necessary in animals.
This knowledge helps to support the expertise, and makes it possible to inform the French authorities of any new emergence of risk, both for animal health and human health.
Study the dynamics of porcine influenza viruses and their pathogenicity
Influenza infection in pigs generally causes mild clinical manifestations and only affects a portion of pigs on the same farm. However, the infection can take a more severe and almost general turn, depending on the virulence of the strain involved and breeding practices. Concomitant infections with other pathogens affecting the respiratory system may lead to complications. Other unfavorable conditions, still poorly defined, might also influence the severity of the disease.
In addition, while influenza infection is usually responsible for a one-off (episodic) flu syndrome, a recurrent form of the disease has become more common on farms in recent years. These repeated influenza episodes lead to destabilization of infected farms and might promote co-infections with several strains of influenza viruses, and therefore viral reassortments. Research work is carried out on farms (observational epidemiological studies) and in silico (epidemiological modeling), in order to better understand the determinants of virus persistence within pig farms
Studying the role of influenza viruses in respiratory syndromes in pigs
The Agency studies the dynamics of strains in breeding and the factors associated with the different severities and epidemiological forms of the disease. Experimental and modeling work focuses on the characteristics of the transmission of swine influenza viruses from one animal to another. The modalities of transmission by air are also studied, taking into account the different ventilation conditions in farms. swIAV infections are sometimes associated with infections by other pathogens, bacteria or viruses. This double infection can cause complications for the animal’s health. Experimental studies are carried out on pigs with a high health status (pigs free from specified pathogenic organisms, EOPS), in order to study the mechanisms underlying the synergy or, on the contrary, the interference between these pathogens of the pig’s respiratory system. Together, the results of epidemiological surveys, experimental research and modeling work make it possible to better understand the disease and to propose prevention and control measures to veterinarians and breeders.
The research work carried out on porcine influenza viruses at the Agency is shared within the Research Group on Influenza Viruses, created by the CNRS on 1is January 2020 and called RésaFLU. Its mission is to promote an interdisciplinary network, which brings together French teams working on influenza viruses responsible for influenza in humans and animals. Its scientific areas focus on understanding the mechanisms of emergence of new influenza viruses, identifying the determining factors in the pathophysiology of influenza virus infections, or developing new preventive and therapeutic strategies.
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