Discussion
This study has confirmed the presence of AIV H5 antibody and antigen in some wild birds in Zaria and its environs. The overall prevalence (6.62 %) recorded for AIV H5 antibody is higher than 4.5 % reported in Kogi State (Ameji et al., 2017) and 0.8 % in Uganda (Kirunda et al.,2014); but lower than 6.8 % in Egypt (Ahmed et al., 2017). The species distribution showed that Laughing doves (10 %), Speckled pigeons (13.64 %) and mallards (19.05 %) were positive for AIV H5 antibody. Although wild aquatic birds, particularly waterfowls, have been reported to be the natural hosts for influenza A viruses (Olsen et al., 2006), these species of birds are not strictly aquatic birds, yet had antibodies against AIV. This implies that non-aquatic birds could play roles in the spread of AIV. Thus, avian influenza represents one of the greatest concerns to the poultry industry and public health (Capua and Marangon, 2006).
The detection of AIV antibody in mallards (19.05 %) in this study, is higher than 2.7 % reported by Kirunda et al. (2014) in Uganda. The AIV seroprevalence in mallards is suggestive of previous exposure to the virus, resulting from possible interaction with other infected birds.
The AIV seroprevalences in Laughing doves (10 %) and Speckled pigeons (13.64 %) recorded in this study were higher than zero prevalence recorded by Adamu et al. (2017) in both Laughing doves and Speckled pigeons in Kano Metropolis, Nigeria. Also, Musa et al. (2017) reported AIV seroprevalence of 0.0 % among Laughing doves and Speckled pigeons following studies in three States (Bauchi, Gombe and Kaduna States) of Nigeria. Furthermore, Ameji et al. (2017) reported AIV seroprevalence of 0.0 % for Laughing doves in Kogi State, Nigeria. This suggests that the Laughing doves and Speckled pigeons in this study might have been previously exposed to AIV through possible interaction with other species of wild birds that were infected with the virus.
Senegalese parrot, geese and cattle egrets were seronegative for AIV H5 in this study. Musa et al. (2017) reported similar observation but 23.5 % AIV seroprevalence in Cattle egrets in Nigeria. This higher AIV seroprevalence reported by Musa et al. (2017) in Cattle egrets might be due to the higher number of Cattle egrets sampled, and these birds have been reported to frequently visit poultry premises to feed on maggots and insects (Fagbohun et al., 2000). The absence of AIV antibody recorded for Senegalese parrot, geese and Cattle egrets in this study indicates possible recovery or no previous exposure to the virus.
However, AIV antigen was detected in Senegalese parrot (20.0 %), with an overall detection of 3.85 % in this study with no detection (0.0 %) in other species of birds studied. This is contrary to the findings of Adamu et al . (2017) who reported 8.0 % detection of AIV H5 antigen using ELISA in Speckled pigeon despite 0.0 % for AIV antibody in Kano Metropolis, Nigeria and an overall detection of 1.96 %. The higher AIV antigens detection prevalence observed in this study might be due to the increased sensitivity of the detection test (RT-PCR) utilized as opposed to ELISA. Hence, the use of PCR allows for rapid identification of AI in clinical specimens, faster decision making at the early stages of an outbreak and implementation of effective control measures. Senegalese parrots were negative for AIV H5 antibody but positive for AIV H5 antigens using RT-PCR. This therefore, suggests a possible active infection resulting from interaction in the bush and wetland with other species of wild birds that were likely infected with the virus (Adamu et al., 2017) and the higher sensitivity of RT-PCR. The absence of AIV H5 antigen in seropositive birds is suggestive of possible virus clearance.