Modelling a potential zoonotic spillover event of H5N1 influenza
Listed in
This article is not in any list yet, why not save it to one of your lists.Abstract
Background
Highly Pathogenic Avian Influenza (HPAI) is a prominent candidate for a future human pandemic arising from a zoonotic spillover event. Its best-known strain is H5N1, with South- or South-East Asia a likely location for an initial outbreak. Such an outbreak would be initiated through a primary event of bird-to-human infection, followed by sustained human-to-human transmission. Early interventions would require the extraction, integration and interpretation of epidemiological information from the limited and noisy case data available at outbreak onset.
Methods
We studied the implications of a potential zoonotic spillover of H5N1 influenza into humans. Our simulations used BharatSim , an agent-based model framework designed primarily for the population of India, but which can be tuned easily for others. We considered a synthetic population representing farm-workers (primary contacts) in a farm with infected birds. These primary contacts transfer infections to secondary (household) contacts, from where the infection spreads further. We simulate outbreak scenarios in such a setting, accounting for the network structure of human contacts and the stochasticity of the infection process. We further simulated multiple interventions, including bird-culling, quarantines, and vaccinations.
Findings
We show how limited, noisy data for primary and secondary infections can be used to estimate epidemiological transmission parameters, such as the basic reproductive ratio R 0 , in realistic settings. We describe the impact of early interventions (bird-culling, quarantines, and vaccination), taken together or separately, in slowing or terminating the outbreak.
Interpretation
An individual-based model allows for the most granular description of the bird-human spillover and subsequent human-to-human transmission for the case of H5N1. Such models can be contextualised to individual communities across varied geographies, given representative contact networks. We show how such models allow for the systematic real-time exploration of policy measures that could constrain disease-spread, as well as guide a better understanding of disease epidemiology.
Research in context
Evidence before this study
To identify similar modelling studies, we searched PubMed using the search terms “(“HPAI” OR “H5N1” OR “avian influenza”) AND (“zoonosis” OR “zoonotic”) AND (“modeling” OR “modelling”)”. Only a few mathematical modelling studies assessed the risk of human infection from novel avian influenzas. None of these studies examined potential sustained human-to-human transmission. We identified studies that simulated pathogen transmission within realistic poultry production and distribution networks, but they did not use these simulations to estimate disease parameters. The available evidence suggesting the potential of zoonotic spillover of avian influenza supports the inclusion of such parameters into transmission models.
Added value of this study
South- and South-East Asia have in recent years recorded a number of significant outbreaks of avian influenza in birds, accompanied by spillover events into non-poultry species. Within the past three months, India has recorded 34 epicentres of infection across 8 states, raising concerns about the possibility of a pandemic driven by an adaptation of the virus to infectious spread between humans. Our agent-based simulation framework can be used to tune policy measures for a potential outbreak of H5N1 influenza, as well as to calibrate both epidemiological parameters and the impact of interventions.
Implications of all the available evidence
Apart from providing realistic models for the consecutive events of a bird-human spillover infection followed by human-human transmission for the case of H5N1 influenza, our models can describe the impact of a variety of policy measures aimed at stemming a potential HPAI-initiated pandemic in humans. These include bird culling, quarantines and vaccination drives. We show that that timing of such measures is crucial if they are at all to be effective: culling of infected birds and quarantining of primary contacts should happen well before the force of infection peaks.
