Situation-based survey of avian influenza viruses in possible "bridge" species of wild and domestic birds in Nigeria

Detection of clade 2.3.4.4 highly pathogenic avian influenza H5 viruses in healthy wild birds in the Hadeji-Nguru wetland, Nigeria 2022

Background

The introduction of multiple avian influenza virus (AIV) subtypes into Nigeria has resulted in several poultry outbreaks purportedly linked to trade and wild birds. The role of wild birds in perpetuating AIV in Nigeria was, therefore, elucidated.

Methods

A cross-sectional study was conducted among wild aquatic bird species at the Hadejia-Nguru wetlands in Northeastern Nigeria between March and April 2022. A total of 452 swabs (226 cloacae and 226 oropharyngeal) were collected using a mist net to capture the birds. These samples were tested by RT-qPCR, followed by sequencing.

Results

Highly pathogenic AIV of the H5N1 subtype was identified in clinically healthy wild bird species, namely, African jacana, ruff, spur-winged goose, squared-tailed nightjar, white-faced whistling ducks, and white stork. A prevalence of 11.1% (25/226) was recorded. Phylogenetic analysis of the complete HA gene segment indicated the presence of clade 2.3.4.4b. However, these H5N1 viruses characterized from these wild birds cluster separately from the H5N1 viruses characterized in Nigerian poultry since early 2021. Specifically, the viruses form two distinct genetic groups both linked with the Eurasian H5N1 gene pool but likely resulting from two distinct introductions of the virus in the region. Whole-genome characterization of the viruses reveals the presence of mammalian adaptive marker E627K in two Afro-tropical resident aquatic ducks. This has zoonotic potential.

Conclusion

Our findings highlight the key role of surveillance in wild birds to monitor the diversity of viruses in this area, provide the foundations of epidemiological understanding, and facilitate risk assessment.

Virus-like Particle Vaccines: A Prospective Panacea Against an Avian Influenza Panzootic

Epizootics of highly pathogenic avian influenza (HPAI) have resulted in the deaths of millions of birds leading to huge financial losses to the poultry industry worldwide. The roles of migratory wild birds in the harbouring, mutation, and transmission of avian influenza viruses (AIVs), and the lack of broad-spectrum prophylactic vaccines present imminent threats of a global panzootic. To prevent this, control measures that include effective AIV surveillance programmes, treatment regimens, and universal vaccines are being developed and analysed for their effectiveness. We reviewed the epidemiology of AIVs with regards to past avian influenza (AI) outbreaks in birds. The AIV surveillance programmes in wild and domestic birds, as well as their roles in AI control were also evaluated. We discussed the limitations of the currently used AI vaccines, which necessitated the development of a universal vaccine. We evaluated the current development of AI vaccines based upon virus-like particles (VLPs), particularly those displaying the matrix-2 ectodomain (M2e) peptide. Finally, we highlighted the prospects of these VLP vaccines as universal vaccines with the potential of preventing an AI panzootic.

Seroepidemiology and assessment of risk factors for the spread of avian influenza in birds in two Nigerian states

Despite modified stamping out eradication policy adopted in Nigeria, there was resurgence in 2015 of highly pathogenic avian influenza (HPAI) H5N1 with greater infectivity. A survey of the risk of spread of HPAI in two HPAI‐infected and ‐uninfected Nigerian states were studied. A cross‐sectional study to detect avian influenza (AI) H5 antibodies was conducted using haemagglutination inhibition (HI) test and enzyme‐linked immunosorbent assay (ELISA). A total of 950 birds’ sera were tested for AI H5 antibodies. Questionnaires were also administered to evaluate risks of AI spread in two states of Nigeria in 2013. AI H5 seroprevalence of 3% and 5% were obtained in Bauchi and Gombe states, respectively. Free flying and captive wild birds had 15% and 11% seroprevalence, respectively. Ninety‐two per cent AI awareness and 90% preparedness to report outbreaks of poultry diseases were recorded. Veterinary personnel, radio and television contributed 87% to HPAI awareness. Of the 10 risk categories evaluated, Gombe state had 3 moderate and 1 high risk of AI virus spread. Bauchi state recorded 5 moderate and 1 high risk of AI virus spread. Chi‐square analysis showed associations of altitude, temperature, rainfall and presence of live bird markets (LBMs) (P < 0.05) to AI seroprevalence. Odds ratio at 95% CI (1.313–6.333) indicated LBMs presence to be three times more likely to influence AI occurrence. HPAI H5N1 resurged in many states and occurred for the first time in Gombe state in 2015. Veterinary personnel, radio and television may be reliable in changing farmers’ attitudes to adopt good biosecurity practices.

Bridge hosts, a missing link for disease ecology in multi-host systems

In ecology, the grouping of species into functional groups has played a valuable role in simplifying ecological complexity. In epidemiology, further clarifications of epidemiological functions are needed: while host roles may be defined, they are often used loosely, partly because of a lack of clarity on the relationships between a host’s function and its epidemiological role. Here we focus on the definition of bridge hosts and their epidemiological consequences. Bridge hosts provide a link through which pathogens can be transmitted from maintenance host populations or communities to receptive populations that people want to protect (i.e., target hosts). A bridge host should (1) be competent for the pathogen or able to mechanically transmit it; and (2) come into direct contact or share habitat with both maintenance and target populations. Demonstration of bridging requires an operational framework that integrates ecological and epidemiological approaches. We illustrate this framework using the example of the transmission of Avian Influenza Viruses across wild bird/poultry interfaces in Africa and discuss a range of other examples that demonstrate the usefulness of our definition for other multi-host systems. Bridge hosts can be particularly important for understanding and managing infectious disease dynamics in multi-host systems at wildlife/domestic/human interfaces, including emerging infections.