New flu virus strain found in Cambodian pigs poses pandemic risk

Previously unknown strains of influenza A virus have been found circulating unnoticed in Cambodian pig populations according to research led by scientists at the Duke-NUS Medical School in Singapore.

The findings published in the journal PNAS suggests “undetermined risk” of pandemic among both humans and pigs. The authors call for systematic surveillance for early detection and warnings about new viral strains to prevent new pandemics before they emerge.

They believe the viruses have been in the pig population for 15 years.

Among the several strains uncovered are viruses passed by humans to pigs and strains with genes showing they originated as far away as North America.

Pigs are common intermediary between the spread of influenza viruses between animals and human. They provide a suitable environment for the development of new strains as genetic material is shuffled between avian, swine and human hosts.

The US CDC estimates that 284,000 died during the 2009 swine flu pandemic.

“The long-term evolution of different lineages has led to the establishment of genetically distinct viruses that have been continuously circulating in pig populations undetected for decades,” says senior author, Associate Professor Yvonne Su. “Our study revealed the hidden and complex genomic landscape of swine flu virus evolution in Southeast Asia, marking the region as a hotspot for virus diversity and risk of new virus emergence.”

Swine influenza surveillance in 18 Cambodian pig slaughterhouses was conducted by the Duke-NUS scientists between March 2020 and July 2022. 4,089 nasal swabs from pigs in four provinces revealed that 72 animals – about 2% of those swapped – tested positive for influenza A.

The scientists found 9 different influenza A strains, 7 of which had not been detected for 2–15 years.

Map of cambodia divided into districts
Geographical area of swine influenza surveillance study conducted in Cambodia, 2020 to 2022. Striped lines indicate the location by district (D1 to D9) of sampled pig slaughterhouses. Credit: Proceedings of the National Academy of Sciences (2023).

“While swine influenza viruses typically cause mild symptoms in pigs, they pose a pandemic threat to humans, as the human population may lack immunity or have inadequate protection against new strains of swine influenza viruses,” says co-author Professor Gavin Smith. “Therefore, systematic surveillance is crucial in early detection and warning of new subtypes or strains.”

The Duke-NUS researchers are currently developing a platform to identify major swine flu genetic subtypes.

“Routine and sustained surveillance is indispensable in identifying new viruses so that their transmission risk can be assessed,” says Professor Patrick Tan. “It is therefore critical that more efficient and continuous surveillance methods are integrated with automated analytical tools to rapidly provide information on changes in human and animal pathogens.

“Such a system as the team at Duke-NUS is developing would improve animal health through selection of effective vaccines, and aid in human health by monitoring viruses with the potential for transmission.”

Sign up to our weekly newsletter

Please login to favourite this article.