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.