PRO/AH/EDR> Influenza (13): Cambodia, swine, influenza A, H3, H1N1, H1N2


A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases

Date: Sun 10 Sep 2023
Source: Khmer Times [edited]

Scientists from Duke-NUS Medical School in Singapore have made a
significant discovery, identifying several previously unknown strains
of swine flu viruses that have been circulating quietly in Cambodian
pig populations for the past 15 years. This finding raises concerns
about potential pandemic risks.

Pigs play a crucial role in the emergence and spread of influenza
viruses between animals and humans. Their unique biological
characteristics make them ideal hosts for the exchange of gene
segments between avian, swine, and human hosts, ultimately leading to
the creation of new viruses. With pork production increasing worldwide
and global trade and movement, the risks of a pandemic have been

Professor Gavin Smith, director of the Emerging Infectious Diseases
Programme at Duke-NUS, emphasizes the importance of systematic
surveillance for early detection and warning of new subtypes or
strains. Swine influenza viruses typically cause mild symptoms in pigs
but pose a significant threat to humans due to the lack of immunity or
inadequate protection against new strains.

To conduct their study, the research team collected 4089 nasal swabs
from pigs in 18 slaughterhouses across different districts of 4
provinces in Cambodia between March 2020 and July 2022. Out of these
samples, 72 pigs, or approximately 2%, tested positive for influenza A

The findings, published in the journal PNAS [see citation below],
revealed the presence of 9 distinct swine influenza A virus groups,
with at least 7 having not been detected for 2 to 15 years. Among
these groups were multiple H3 lineages that had been transmitted from
humans to pigs and had been circulating unnoticed for a decade. The
H1N1 subtype, originating from human sources during the 2009 pandemic,
was also detected and found to be predominant. Two seasonal viruses
originating from Thailand were detected in pigs from Kandal, Phnom
Penh, and Takeo provinces.

In addition, the research team also isolated a new swine European H1N2
variant, which originated from birds but possessed North American
genes. Genomic analysis suggests that this variant has been
circulating in pigs in Cambodia since 2014, highlighting the need for
enhanced surveillance.

The study also examined the movement of viruses across geographical
borders. Genetic evidence indicated that European swine flu viruses
had sporadically been introduced into South Central China and
Southeast Asia in the early 2000s. Since around 2010, South Central
China has been identified as the primary source of European-like swine
flu virus transmission in the region, with the viruses subsequently
spreading across China and other Southeast Asian countries like

Further studies are required to fully understand the potential
pandemic threat posed by these new swine flu strains, including their
interaction with human viruses and their ease of transmission.

Based on the content, a meaningful quote can be generated from
Professor Gavin Smith: “Swine influenza viruses typically cause mild
symptoms in pigs, but they pose a pandemic threat to humans since the
human population may lack immunity or have inadequate protection
against new strains of swine influenza viruses. Therefore, systematic
surveillance is crucial for early detection and warning of new
subtypes or strains.”

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