Introduction
Avian influenza (AI) is a highly contagious viral disease of domestic and wild birds with a worldwide distribution (Vincent et al.,2011; Ansari et al. , 2016; Mohammed et al., 2017). The disease is caused by single stranded 8-segmented negative sensed riboxynucleic acid (-ssRNA) viruses belonging to the genusInfluenza A viruses in the family Orthomyxoviridae (Capua and Alexander, 2004; OIE, 2015). The natural reservoirs of influenza A viruses are avian species within the orders Anseriformes(waterfowl: ducks, swans, geese) and Charadriformes (gulls, terns and shorebirds) (Webster et al., 1992; Olsen et al.,2006). Influenza A viruses infect different species of mammals, including humans, pigs, marine mammals, and a wide range of birds, including both domestic and wild species (Abad et al., 2013). Generally, AI virus has been reported to be transmitted by the fecal-oral route without causing clinical signs in wild birds (Yu et al., 2008).
Avian influenza virus (AIV) are divided into two groups: highly pathogenic avian influenza virus (HPAI) with 100 % mortality rate and low pathogenic avian influenza virus (LPAI), often detected in wild birds (Rebel et al., 2011). All highly virulent strains of AIV isolated from disease outbreaks have been either of the H5 or H7 subtype, though other subtypes have been detected with virulent characteristics (Wood et al., 1996).
The clinical signs of AI include hemorrhages distributed all over the body, oedema, cutaneous ischemia and cyanosis of comb and wattles, respiratory and neurological signs (Feldmann et al., 2000; Zanella et al., 2001; Bowes et al., 2004; Spackman et al., 2016; Pantin-Jackwood et al., 2017). However, the absence of clinical signs is common in LPAIV infection in chickens and ducks (Swayne et al., 2013). There are no pathognomonic lesions for avian influenza in birds (Stallknecht and Brown, 2007). Severity and distribution of lesions are dependent on the pathogenicity of the virus and host factors (e.g. species, age, immunity) (Stallknecht and Brown, 2007).
In Nigeria, the first outbreak of HPAI virus H5N1 strain was detected in a commercial poultry farm in Kaduna State, North Central Nigeria in 2006 (Joannis et al., 2006; De Benedictis et al., 2007). This involved different poultry species, mostly chickens of different ages, reared and bred on the same premises with some numbers of ducks, geese, turkeys and ostriches (Akanbi et al., 2016). Also, outbreak of HPAI subtype H5N8 has been reported in Jos, Plateau State in 9-week-old pullets and 4-week-old broilers (Ameji et al., 2019).
Influenza A viruses that reside naturally in wild bird species comprise all known subtypes and these provide viral genes for influenza viruses that infect both domestic poultry and mammalian species, including humans (Nguyen et al., 2005). Migratory birds and movement of poultry and/or poultry products have been proposed as two major mechanisms of geographic spread of avian influenza (Kilpatrick et al., 2006). Therefore, the aim of this study was to detect AIV antibody and antigen in some wild birds in Zaria and its environs, Nigeria.