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Researchers have found that people can spread bacteria affecting plants as well as humans.

Using data from agricultural workers traveling between New Zealand farms, they built a computer model that successfully recreated a real-world kiwifruit bacterial disease outbreak.

They discovered that while crop diseases mostly spread locally, occasional long-distance trips act as sparks that trigger nationwide spread.

Data for tracking worker movements was provided by a company helping to fund the study.

This enabled the researchers to simulate how a kiwifruit disease – Psa-V – might be spread by those workers.

The simulation matched what happened during the kiwifruit disease outbreak in 2010. In the simulation, they found more than 90% of infected properties were less than 10km from an already infected property, but some movements between properties covered more than 20km, with rare trips spanning up to 1000km.

The researchers say these long journeys could help a disease suddenly appear far from an existing outbreak, making it harder to contain.

An outbreak severity also depends on where and when it starts, especially during busy farming seasons.

Mapping human movement in modelling agricultural disease outbreaks provides powerful new tools to protect crops, secure the food supply, and strengthen future biosecurity.

Ryan Higgs, Co-author of the paper & Onside Co-founder and CEO writes:

“Most people think of biosecurity as what happens at the border. This study looks at what happens next, once a disease is already here and people start moving between farms and orchards.

“The research was led by a team at Indiana University, working with Onside, a New Zealand agritech company. The Indiana team are internationally recognised for modelling how disease spreads through networks, and this study brings that approach to plant disease. We used movement data recorded through Onside’s platform, covering workers, contractors and visitors travelling between properties. That gave us around 86,600 movements across 2,281 horticulture properties in New Zealand during 2022. The team built a model on that movement network and tested it against the Psa outbreak that hit the kiwifruit industry from 2010.

“The key finding is that people moving between properties was enough to recreate how Psa spread across the country, including when the outbreak took off and the month it peaked. Most spread was local, with over 90 per cent of new infections within 10 km of an infected property. But a small number of long trips is what turned a regional outbreak into a national one.

“Timing matters too. Movement between properties rises and falls with seasonal work, and a disease that arrives in a busy month tends to cause a bigger outbreak.

That is where this data becomes useful for biosecurity. If you know how people move between properties, you can see which ones link regions together and could carry a disease a long way. Those are the places to focus surveillance, and the routes to target if movement needs to be restricted. Once it has been tested against future outbreaks, the same approach could be used to plan the response to a new disease before it arrives.”

The paper is HERE. 

Source: Science Media Centre