# Modeling of H5N1 influenza virus kinetics during dairy cattle infection suggests the timing of infectiousness

## TL;DR

This study estimates how long dairy cattle infected with H5N1 influenza remain infectious, which is crucial for managing outbreaks and protecting public health.

## Contribution

The study provides the first estimates of the duration of infectiousness in dairy cattle infected with H5N1 clade 2.3.4.4b.

## Key findings

- Minimum Ct values in infected cattle are reached within 1–2 days, with a mean of 15.7.
- A Ct threshold of 21.8 indicates little-to-no infectious viral load.
- The median duration of infectiousness is estimated at 7.8 days.

## Abstract

Since early-2024 unprecedented outbreaks of highly pathogenic avian influenza H5N1 clade 2.3.4.4b have been ongoing in dairy cattle in the United States with significant consequences for the dairy industry and public health. Estimation of key epidemiological parameters is required to support outbreak response, including predicting the likely effectiveness of interventions and testing strategies. Here, we pool limited publicly available data from four studies of naturally and experimentally infected dairy cattle. We quantify Ct value trajectories of infected dairy cattle and the relationship between Ct value and the log-titer of infectious virus, a proxy for infectiousness. We estimate that following infection minimum Ct values are rapidly reached within 1–2 days with a population mean Ct value of 15.7 (12.9, 18.4). We identify a threshold Ct value of 21.8 (19.9, 24.6), with values of Ct value above this threshold representing little-to-no infectious viral load. Finally, assuming a direct relationship between Ct value and infectiousness, we estimate the distribution of the duration of infectiousness for dairy cattle (i.e., the duration their Ct value remains below the critical threshold) with a population median of 7.8 (4.1, 13.9) days. Our estimates will be critical inputs to the development of outbreak management guidelines and modeling analyses informing response strategies.

Ongoing outbreaks of H5N1 influenza in U.S. dairy cattle represent a serious threat to the dairy industry and public health. This study analyzes publicly available data to quantify the viral kinetics of infected cattle, estimating the timing and duration of infectiousness (~8 days), providing key parameters for effective outbreak control.