aviculture au maroc

 

study of poultry projects

 

 

 

 

 

 

 


Bird flu

 

Definition of avian flu:  

 

Avian influenza, or chicken flu, is an infection caused by a virus of the family of Orthomyxoviridae which includes several genera (or types) including Influenza virus A. This is divided into subtypes among which the subtypes H5 and H7.
This infection can affect almost all species of birds, wild and domestic. It can be highly contagious, especially in chickens and turkeys, and is likely to cause high mortality in these species.



Seasonal flu

The low pathogenic strains of this virus can mutate genetically by spreading from one farm to another, in particular if the health barriers between farms are insufficient.

From a certain virulence, these strains cause a disease called avian influenza, one of the most pathogenic of which is that caused by the H5N1 virus, capable of infecting other animal species such as pigs or other mammals. We speak of an avian flu epizootic when the disease brutally affects a large number of animals at the same time in a given region.

Risks linked to the H5N1 virus

Of the 15 avian influenza virus subtypes, H5N1 is the most worrisome for several reasons. It mutates quickly and has a proven propensity to acquire genes from viruses infecting other species.
Birds that survive this infection shed the virus for at least 10 days, orally and in faeces, which facilitates its spread to live poultry markets and by migratory birds.

Man can himself be contaminated in conditions of extreme promiscuity with sick animals, which has been observed in Asia. However, the H5N1 virus is not transmissible from human to human. A human pandemic would only occur if the virus mutated to become contagious to humans.

Influenza pandemic

A pandemic is defined as a sharp increase in space and time in influenza cases with or without virological confirmation, accompanied by a number of serious cases and high mortality. It follows the detection of a virus of new antigenic composition, against which the immunity of the population is weak or zero. (Hannon, Euro surveillance 1998). This weak or nonexistent population immunity is due to a brutal antigenic variation, the "antigenic break".

Avian flu is distinguished from seasonal flu, an acute, contagious respiratory infection of viral origin that affects humans. Seasonal flu most often evolves in an epidemic mode and can affect in France, in winter, 5 to 15% of the population. Influenza is responsible for a non-negligible mortality in people at risk who have not been vaccinated.

There are indeed two main modes of variation of influenza viruses, one progressive, the slip, the other brutal, the break:

The slip is due to the accumulation of point mutations in genes that cause minor modifications to the virus. This accumulation results in an antigenic difference which results in less recognition of the new virus by the immune systems which have encountered the original virus in the past. It is responsible for seasonal and winter epidemics and requires the change of vaccine strains.

The break, a major brutal antigenic variation of the surface antigenic proteins (hemagglutinin and sometimes neuraminidase) of influenza A virus, gives rise to a new virus.

Pre-existing immunity does not protect. The break is the result of exchanges between animal and human strains, which are rare. It is at the origin of pandemics, but, after a pandemic, the virus circulates in the human species, and settles down to induce epidemics. The break is consecutive either to a reassortment event between two parental viruses of different origin, either to the complete transmission of an animal virus subtype unknown in humans or then to the re-emergence in humans of a Formerly human subtype.