Avian Influenza - Endemic to Pandemic

**55**

clades [4].

**Chapter 4**

Pandemic

*and Kashif Saleemi*

and patterns of infection [3].

**1. Introduction**

phenomena [4].

HPAI outbreaks [1].

**2. Influenza A virus**

Prologue: Avian Influenza - An

*Muhammad Abubakar, Abdullah Iqbal, Shumaila Manzoor* 

Avian influenza also called as bird flu is an acute, contagious disease caused by Influenza A virus. Birds of order *Anseriformes* and *Charadriiformes are reservoir hosts of* influenza A viruses [1]. These viruses have the ability to infect many mammal species such as horses, pigs, cats, dogs, and humans. Influenza A viruses are negative-sense single-stranded RNA viruses with enveloped structure [2]. Influenza A viruses have shown high antigenic variability due to antigenic drift and shift phenomena. These mutation methods result in the emergence of new variants. These new variants can have different host ranges, mortality rates, morbidity rates,

Influenza A viruses are further divided into highly pathogenic avian influenza (HPAI) or low pathogenic avian influenza (LPAI). Up till now, only some H5 and H7 subtypes have been confirmed as HPAI viruses. However, it is reported that some LPAI H5 and H7 subtypes can mutate to HPAI due to antigenic shift and drift

Some influenza A viruses have a zoonotic potential and can cause a pandemic hazard to human population. Outbreaks of HPAI in poultry have affected the poultry industry worldwide [5]. In 2002, due to HPAI outbreaks, Chile suffered a loss of almost \$31 million USD. In 2003, the HPAI outbreak resulted in the loss of more than \$3387 million USD in Indonesia and \$55 million USD in Vietnam. Similarly, in 2012, Mexico suffered an economic loss of approximately \$475 million USD due to

Influenza A viruses belong to family *Orthomyxoviridae*. Influenza A viruses are single-stranded negative-sense RNA viruses having genome with 8 segmentation that encode for 10 viral proteins: hemagglutinin (HA), neuraminidase (NA), matrix proteins (M1 and M2), nucleocapsid protein (NP), nonstructural proteins (NS1 and

Influenza viruses are further classified into subtypes on the basis of their hemagglutinin (HA) and neuraminidase (NA) genes [7]. A total of 18 HA and 11 NA types has been identified up till now. On the basis of phylogenetic analysis and sequence homology of the HA gene, these viruses are clustered into virus

NS2), and polymerase proteins (PB1, PB2, and PA) [6].

Overview from Endemic to
