Brazil is halting chicken exports to the European Union and Argentina after a virulent poultry disease was found on a commercial farm, disrupting shipments from the world’s largest exporter. 

A chicken farm in Rio Grande do Sul state has been shut after the presence of the Newcastle virus was confirmed on Wednesday, according to the country’s agriculture ministry. The birds at the site are set to be destroyed as part of measures to stop the illness from spreading. 

The South American nation is also suspending exports of chicken, eggs and other poultry-based products from the southern state, which borders Uruguay, to other countries including China, India, South Africa and Mexico, according to a notice issued by the ministry.

Newcastle disease, which is highly transmissible among birds but doesn’t affect humans, typically prompts major importing countries to raise bans on imports of chicken from infected regions. That would deal a blow to the likes of BRF SA, Brazil’s largest chicken producer, which has been recovering from a a poultry industry downturn. 

Shares of BRF closed down 7.9% on Thursday, the biggest loss since November. Marfrig Global Foods SA, which controls BRF, fell 9.1%, the most since late 2022. JBS SA fell 2.5%.

Brazil’s Agriculture Minister Carlos Favaro said one chicken tested positive for Newcastle disease, which attacks the respiratory, nervous and digestive systems. The collapse of a roof in a coop after a storm may have exposed the chicken to the virus, which can be found in infected wild bird feces, he told reporters on Thursday.

“This seems to be an isolated case,” Favaro said. “There’s no sign of sick animals in the area, let alone in the region.” 

Newcastle disease was last found in backyard birds in Brazil in 2006. There have been no previous reports of the illness in commercial flocks in the country, according to data from the World Organisation for Animal Health.