The short end of the stick

INRA researchers have demonstrated that when a surface protein from an avian influenza virus strain found in wild ducks becomes shortened, the virus is more prone to infect chickens. The shortening also determines the virus’ virulence in chickens. This discovery will help to better anticipate and manage risks in poultry production.

Influenza A virus (H1N1) 2009. © M.C. Prevost, M. Desdouits and P.E. Ceccaldi, S. Van des Werf and N. Naffakh, J.M. Panaud, Institut Pasteur
Updated on 01/21/2015
Published on 01/14/2015

A single virus family is responsible for both human flus and animal flus: influenza A virus. The family is divided into many subtypes on the basis of the combination of two membrane proteins, haemagglutinin (with 16 variations, from H1 to H16) and neuraminidase (N1 to N9).  Seasonal influenza in humans is caused by types H1, H2, or H3 in combination with N1 or N2. Subtypes H1 through H15 are found in birds, but only three – H5, H7, H9 – are pathogenic.

Primarily found in wild and domestic birds, these flus are carried in their digestive tracts and circulate constantly. “Chickens are permanent carriers of several, very mild influenza viruses” says Jean-Luc Guerin, INRA veterinarian and avian virologist. Together with his team, Guerin studies point mutations in the viruses. “Low-pathogenic avian influenza viruses are studied very little, despite the fact they act as precursors to highly pathogenic strains.  These viruses, like all RNA viruses, have a very high genetic variability. They are very creative; they are constantly recombining to generate very complex communities able to evolve rapidly” says Guerin. With the use of high-throughput genetic sequencing, Guerin’s Unit for Pathogen–Host Interactions investigates virus biodiversity in duck and turkey flocks, on the lookout for low-abundance mutants.

In 2012, the team identified a short genomic sequence within a virus that provided a critical trait conferring an adaptation to turkeys and a high level of virulence. The researchers infected a turkey flock and a duck flock with a low-pathogenic strain (H6N6) and found that, after eight days, the turkeys had mostly become infected by a “mutant” virus while only traces of the virus could be found in the ducks. The mutation, which modified the length of the neuraminidase, made the virus pathogenic to turkeys. “The speed the virus adapted from one species to another is remarkable. The shortened protein allowed the virus to spread from the turkey’s intestine to its respiratory system and become pathogenic” says Guerin. “These genetic discoveries help us to identify avian viruses with greater accuracy. By analysing the original genomic sequence of a virus from one species, soon we will be able to know what other species the virus will be adapted to and how virulent it will be.”