EPIDEMIOLOGISTS have developed an improved method for estimating the time window for the introduction of avian influenza on poultry farms.
It uses mortality data in the period before suspicions that avian influenza might be present on farm to estimate the infectious period.
Previous models have tended to overestimate the number of animals that can be infected by one animal over a certain period of time.
The work was conducted by Wageningen Bioveterinary Research (WBVR) in collaboration with researchers from Utrecht University.
“Estimating the time window for the introduction of the highly pathogenic avian influenza virus (HPAI) on poultry farms is especially important to help trace the source of infection (back tracing),” says epidemiologist Armin Elbers, the project leader for this study.
“It also helps officials to compile a list of farms (and to monitor them clinically and diagnostically) that have had contact with the infected farm during the infectious period.
“This may limit the further spread of the infection (forward tracing).”
This study aimed to develop an effective approach for estimating farm-specific time windows for virus introduction and to evaluate this approach by applying it to 11 outbreaks of HPAI subtype H5N8 on commercial poultry farms in the Netherlands between 2014 and 2016.
Two approaches were developed and evaluated. Thomas Hagenaars, senior mathematical modeller within the project team, said: “When using existing field data, we were able to conclude that one of the two models is generally more useful when data on disease-induced mortality is scarce. This approach was successfully applied to 8 out of 11 HPAI H5N8 outbreaks”.
The method is part of the EpiTools toolbox, designed to help control notifiable animal diseases.
In addition to the module for estimating the time window of introduction of a virus on a livestock farm, the EpiTools toolbox contains four modules that help officials monitor the development of the epidemic, and which enable them to intervene with more robust measures if the epidemic continues unabated:
- A risk map showing the locations of higher risk and lower risk farms in different colours;
- The most critical transmission parameters such as the reproduction number (infection rate) for the current epidemic;
- The expected magnitude and duration of the current outbreak
- The effect of various scenarios, including interventions.
The EpiTools toolbox has been developed for outbreaks of avian influenza, foot and mouth disease and classical swine fever.
Results of this study were published in the journal Scientific Reports of the Nature Publishing Group. More details can be found on the Wageningen website.