# Epidemiology and Risk Modelling of Influenza A Virus Within and Between Pig Herds in Northern Lao PDR

## TL;DR

This study explores how influenza A virus spreads among pigs in northern Laos and identifies risk factors for transmission between farms.

## Contribution

The study combines field data with modeling to identify risk factors for IAV transmission in Laos, focusing on pig producer types and movement patterns.

## Key findings

- IAV seroprevalence was higher in exotic pig breeds compared to local breeds.
- Stochastic models suggest that IAV transmission between farms is unlikely without high local transmission rates and infected commercial farms.
- Transmission risks are linked to pig movement and farm types, especially in smallholder networks.

## Abstract

Animal‐origin influenza A virus (IAV) is a perennial candidate for causing the next pandemic. With high risk for interspecies IAV transmission but limited resources for surveillance, particularly in rural areas of low‐ and middle‐income countries (LMICs) such as Laos, there is a need to develop targeted, risk‐based strategies for early detection of novel IAVs that may emerge in pigs. We conducted (1) a cross‐sectional survey to characterise pig producer types, management practices and pig movement patterns; (2) sampling among pigs in slaughterhouses to quantify IAV seroprevalence and infection; and (3) within‐ and between‐herd disease modelling exploring the relative importance of farm type for the IAV epidemiology. Overall, 31.3% (100/319) of sera and 1.4% (7/515) of nasal swab samples from pigs tested positive for IAV antibodies (ELISA) and viral RNA (PCR detection of IAV M‐gene), respectively. Most pigs sampled were exotic breeds and supplied by commercial farms. Using hierarchical Bayesian logistic regression models, seropositivity was significantly higher among exotic breeds compared with local breeds and higher among pigs originating from provinces outside of our study area. Stochastic, individual‐based models of within‐ and between‐herd transmission were developed and calibrated for five pig producer types using the cross‐sectional data from 202 study participants. The modelling results suggested sustained IAV transmission between farms was unlikely unless the probability of local transmission, independent of pig movement, was relatively high, and the initial infection was seeded in areas with higher densities of smallholders. Between‐herd IAV transmission was only sustained in scenarios where persistently infected commercial farms were present to continuously seed infection among the pig smallholder network. Together, these factors underscore risks associated with livestock intensification in commercial and smallholder productions. A larger study is warranted to fully characterise the interprovincial pig movement and evaluate IAV transmission within Laos to inform the national surveillance strategy.