The Spread and Control of Avian Influenza

Posted on 2023-03-21

Since October 2021, an unprecedented outbreak of avian flu has spread among wild birds, livestock, and has been observed infecting mammals such as foxes and minks. Avian Influenza was first distinguished from other diseases affecting birds, originally identified as fowl plague in 1878 [1]. Avian influenza is caused by the Influenza A Virus, a negative-sense RNA virus, often characterized into subtypes by variation in two surface proteins, Hemagglutinin and Neuraminidase. Influenza A is transmitted via direct and indirect contact between birds, via airborne and faecal-oral transmission routes. The most recent outbreak is caused by a variant of H5N1, also known as Highly Pathogenic Avian Influenza (HPAI). The Hemagglutinin and Neuraminidase proteins are both involved in the attachment of the virus to host cells, and the fusion of the virus and host cell membranes [2].

HPAI is a zoonotic disease, and bird-to-human infections have been observed in low numbers. Zoonosis is a process where a disease that infects non-human animals spreads to humans. The effectiveness of transmission, or transmissibility, of HPAI between humans is low at present. If HPAI gains the ability to be transmitted amongst humans, this could cause another pandemic of similar proportions to COVID-19, and modelling suggests that the economies of Low and Middle Income Countries (LMICs) would be disproportionately impacted [3]. Over the last year, there has been a sustained effort to control the spread of the virus in livestock populations, largely coordinated at a local level. Culling is the main method used to control the spread of the disease within livestock populations, with 46 million livestock birds being culled in Europe alone between the initial outbreak in October 2021 and the end of 2022 [4]. In spite of these efforts HPAI has been allowed to spread largely unchecked in wild populations, which act as a reservoir from which the disease can re-infect livestock populations. There is a rapidly growing need for cost-effective, widely available solutions to monitor the prevalence and spread of this disease. Without effective monitoring and prevention the disease will continue to circulate in livestock populations, and the likelihood of a human Influenza A pandemic increases. The response of the international scientific community and policymakers will be essential for predicting and negating the ecological, economic and potential epidemiological impacts of avian influenza.

Outbreaks of IAV in wild bird populations has been shown to have significant ecological effects, contributing to the decline of already endangered species. The most recent outbreak of H5N1 has been implicated in unusually high mortality in Cape cormorants, an endangered bird species endemic to southwestern coasts of Africa. Over 6500 carcasses of Cape cormorants were recovered over the course of January 2022 from Bird Island, Namibia, the result a mortality event believed to have begun in December 2021. Analysis of carcasses showed evidence of infection with H5N1 [5]. The source of infection in these birds has not been conclusively identified, though phylogenetic analysis has implicated contact with both livestock poultry and wild birds as potential origins. The spread of HPAI to endangered species that are already at risk of population decline is a major conservation problem. As part of normal conservation efforts, endangered bird species should be routinely monitored for HPAI infections to allow for preventative action to occur before population decline. As such, cost-effective rapid test kits need to be made widely available to conservationists to allow for close monitoring of at-risk bird species.

Mammalian infection with HPAI increases the likelihood that the virus will adapt to be sustainably transmitted between mammals. If sustainable transmission can occur in humans, this poses a substantial health risk. The current outbreak of H5N1 has showed zoonosis and led to the death of a young girl in Cambodia and the infection of another family member. As of 25 February, Cambodia has reported a total of 58 cases of human infection with H5N1 since 2003 [6]. The relatively low incidence number suggests primarily bird-to-human transmission, with no human-to-human infections being observed to date. Infection with H5N1 is not common in the human population, and so humans do not have widespread immunity to H5 Influenza A viruses, which also occurred with COVID-19. HPAI is adapted to the bird respiratory physiology, and for sustainable human-human transmission to occur, the virus would have to evolve to reproduce effectively in the mammalian upper respiratory tract, and to infect other mammals. Studies have suggested that some Avian Influenza viruses are beginning to show mammalian adaptation, and increased transmissibility in humans could lead to a pandemic [7]. To avoid the evolution of increased transmissibility in humans, the number of mammalian infections should be minimized. Human and mammalian infections often occur when the virus load in the avian population is high, leading to the virus ‘spilling over’ into other species. Ebola and COVID-19 are two diseases where spill-over events are believed to have occurred [8,9]. Within-species transmission has been observed in a farmed mammalian population of mink [10], showing that HPAI already has the potential of within-species transmission in dense mammalian populations. The risk of human-human transmission given this finding is high. To reduce the opportunities that HPAI have to adapt to mammalian physiology, the spread of the virus in farmed and wild populations should be closely monitored to reduce the incidence of mammalian infections. The current program of culling livestock is unlikely to control the disease in the longer term, leading to economic damage and unnecessary loss of avian life. Outbreaks in farmed populations should be identified early, to allow for the isolation of infected stocks and proactive vaccination of at-risk livestock. Controlling the spread in wild birds is more challenging, but should be a major target to prevent further mammalian infections, as wild birds are more likely than poultry to come into contact with mammals. Controlling the spread of HPAI in wild populations will require a sustained effort at both national and international levels to monitor transmission closely.

To prevent further damage to endangered species, and reduce the chances of HPAI adapting to humans, the spread within intensive and domestic poultry, and wild bird species must be monitored. Monitoring the disease spread could allow for effective identification of targets for preventive actions such as vaccination. Reliable rapid testing kits need to be readily available to both conservationists and domestic livestock keepers to allow for widespread reporting of infections. An increase of high-quality data will give more information for epidemiologists and policy-makers to act upon. Without the transparent reporting of monitoring, treatment and prevention research, there will be reduced opportunities for collaboration and effective responses to this outbreak. Effective monitoring requires cross-border cooperation, sufficient funding and a commitment to open science principles.

Abbexa is proud to offer an extensive range of products to support research into Avian Influenza.

Abbexa's Avian Influenza Product Range:

View the full list of our extensive range of products for research into Avian Influenza here.

References/Further reading:

[1] Alexander D, Brown I. History of highly pathogenic avian influenza. Rev sci tech Off int Epiz. 2009;28(1):19-38.

[2] Takimoto T, Taylor GL, Connaris HC, Crennell SJ, Portner A. Role of the Hemagglutinin-Neuraminidase Protein in the Mechanism of Paramyxovirus-Cell Membrane Fusion. Journal of Virology. 2002;76(24):13028-13033. doi: https://doi.org/10.1128/jvi.76.24.13028-13033.2002

[3] Burns A, Van Der Mensbrugghe D, Timmer H. Evaluating the Economic Consequences of Avian Influenza (1). https://web.worldbank.org/archive/website01003/WEB/IMAGES/EVALUATI.PDF

[4] Adlhoch C, Fusaro A, Gonzales JL, et al. Avian influenza overview March – June 2022. EFSA Journal. 2022;20(8). doi: https://doi.org/10.2903/j.efsa.2022.7415

[5] Highly pathogenic avian influenza H5N1 virus outbreak among Cape cormorants (Phalacrocorax capensis) in Namibia, 2022. Emerging Microbes & Infections. Published 2022. Accessed February 23, 2023. https://doi.org/10.1080/22221751.2023.2167610

[6] Avian flu reappears in Cambodia, UN health agency warns. UN News. Published February 27, 2023. https://news.un.org/en/story/2023/02/1133922