What is the clinical evidence from this study?

Study design: Other. Population: Foot-and-mouth disease. Intervention: 30-day storage, routine genome detection assays every two weeks, and RT-PCR testing of semen vs. Scenarios without routine serum testing or shorter storage. Primary outcome: Annual likelihood of releasing at least one frozen semen batch containing viable FMD virus (1.5 x 10^-10).

November 7, 2023PLoS ONE1 citationsOpen Access

Laboratory testing and on-site storage are successful at mitigating the risk of release of foot-and-mouth disease virus via production of bull semen in the USA

AMAnne Meyer JWJay Weiker RMRory Meyer

Key Result

A combination of 30-day storage, routine genome detection assays every two weeks, and RT-PCR testing of semen reduced the median annual risk of releasing FMD-contaminated bull semen to 1.5 x 10^-10.

Structured PICO

Population

Simulated population of bulls from five of the largest commercial bull studs in the US to assess the risk of foot-and-mouth disease virus release via frozen semen.

Intervention

Mitigation measures including 30-day storage, routine genome detection assays every two weeks, and RT-PCR testing of semen

Comparator

Alternative scenarios with different or no testing/storage mitigation measures

Outcome

Annual likelihood of releasing at least one frozen semen batch containing viable FMD virus (risk of release)

A combination of 30-day storage, routine genome detection, and RT-PCR testing of semen effectively mitigates the risk of releasing FMD virus from US bull studs.

Main Result

Effect estimate: 1.5 x 10^-10

Limitations

The compartmental model was deterministic and did not account for variability and uncertainty in input parameter values or state transitions.
The multinomial process used to estimate risk assumed independence between semen batches, which is unlikely to hold in practice.
The effective contact rate estimate did not include indirect transmission pathways and may be biased.
There is a lack of published data on the incidence of FMD outbreaks in high-biosecurity facilities such as bull studs.

Abstract

Thousands of frozen bovine semen doses are produced daily in the US for domestic use. An incursion of foot-and-mouth disease (FMD) in the country would pose strong challenges to the movements of animals and animal products between premises. Secure supply plans require an estimation of the risk associated with target commodities and the effectiveness of mitigation measures. This study presents the results of a quantitative assessment of the risk of release of FMD virus from five of the largest commercial bull studs in the US via contaminated frozen processed semen. The methodology from a previous study was adapted to better fit the US production system and includes more recent data. Two models were combined, a deterministic compartmental model of FMD transmission and a stochastic risk assessment model. The compartmental model simulated an FMD outbreak within a collection facility, following the introduction of a latent-infected bull. The risk of release was defined as the annual likelihood of releasing at least one frozen semen batch, defined as the total amount of semen collected from a single bull on a given collection day, containing viable FMD virus. A scenario tree was built using nine steps leading from the collection to the release of a contaminated batch from a given facility. The first step, the annual probability of an FMD outbreak in a given facility, was modeled using an empirical distribution fitted to incidence data predicted by five models published between 2012 and 2022. An extra step was added to the previously published risk pathway, to account for routine serological or virological surveillance within facilities. The results showed that the mitigation measures included in the assessment were effective at reducing the risk of release. The median annual risk of release from the five facilities was estimated at less than 2 in 10 billion (1.5 x 10-10) in the scenario including a 30-day storage, routine genome detection assays performed every two weeks and RT-PCR testing of the semen. In this scenario, there was a 95% chance that the risk of release would be lower than 0.00041. This work provides strong support to the industry for improving their response plans to an incursion of FMD virus in the US.

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