Parainfluenza virus. – Credit CDC PHIL
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History has shown that pigs can be an efficient reservoir host and `mixing vessel’ for influenza viruses. The 2009 pandemic H1N1 virus had kicked around swine herds for a decade or longer before it finally acquired the ability to jump to man.
But influenzas are not the only viruses that pigs can harbor, nor are they the only ones with zoonotic potential.
We’ve a new study appearing in the Journal of General Virology that describes a novel paramyxovirus – which researchers at Hong Kong University have dubbed porcine parainfluenza virus 1 (PPIV-1) – detected in 12 of 386 pig carcasses collected from a slaughterhouse in Sheung Shu (located in the New Territories of Hong Kong) between 2008 and 2012.
Identification and characterization of a novel paramyxovirus, porcine parainfluenza 1 virus, from deceased pigs
Susanna K. P. Lau, Patrick C. Y. Woo, Ying Wu, Annette Y. P. Wong, Beatrice H. L. Wong, Candy C. Y. Lau, Rachel Y. Y. Fan, Jian-Piao Cai, Hoi-Wah Tsoi, Kwok-Hung Chan and Kwok-Yung Yuen1
Abstract
We describe the discovery and characterization of a novel paramyxovirus, porcine parainfluenza 1 virus (PPIV-1), from swine. The virus was detected in 12 (3.1%) of 386 nasopharyngeal and 2 (0.7%) of 303 rectal swab samples from 386 deceased pigs by RT-PCR, with viral load up to 106 copies/ml. Complete genome sequencing and phylogenetic analysis showed that PPIV-1 represented a novel paramyxovirus within Respirovirus, being most closely related to human parainfluenza virus 1 (HPIV-1) and Sendai virus (SeV).
In contrast to HPIV-1, PPIV-1 possesses mRNA editing function in phosphoprotein gene. Moreover, PPIV-1 is unique among respiroviruses in having 2 G residues instead of 3-5 G residues following the A6-run at editing site. Nevertheless, PPIV-1, HPIV-1 and SeV shared common genomic features and may belong to a separate group under Respirovirus. The presence of PPIV-1 in mainly respiratory samples suggested possible association with respiratory disease, similar to HPIV-1 and SeV.
The South China Morning Post has an interview with microbiologist Yuen Kwok-yung, lead researcher on the project, who warns this virus could one day mutate and jump to humans.
The article quotes Yuen as saying:
“The new virus is closely related to some human influenza viruses. We should watch for possible cross-species transmission from pigs to humans, just as in the case of [human] swine influenza H1N1 and the Nipah virus."
Although this article refers to this virus as a `swine flu’ and `a new strain of influenza’, in fact, this virus is not a true influenza virus (family Orthomyxoviridae), but is a parainfluenza virus, of the family Paramyxoviridae.
The journal states that this novel porcine virus is most closely related to human parainfluenza virus 1 (HPIV-1) – which is the most common cause of croup in young children - and the Sendai virus (SeV), which primarily affects mice, but can also infect hamsters, guinea pigs, rats, and (rarely) pigs.
This table on the human parainfluenza viruses from the CDC.
HPIV Seasons
In the United States, human parainfluenza viruses (HPIVs) commonly cause respiratory tract illnesses.
There are four types of HPIVs and two subtypes that circulate at different times of the year.
- HPIV-1 infections often cause croup in children. There are usually more cases in the fall of odd-numbered years.
- HPIV-2 infections can also cause croup. HPIV-2 infections occur more commonly in the fall. It is less frequently detected than HPIV-1 and HPIV-3.
- HPIV-3 infections usually occur in spring and early summer months each year. However, HPIV-3 infections can occur throughout the year, particularly when HPIV-1 and HPIV-2 are not in season.
- HPIV-4 (subtypes 4a and 4b) seasonal patterns are not as well characterized.
According to the Hong Kong Post interview, researchers believe this novel paramyxovirus has been circulating in pigs for some time. Dr. Yeun is calling for enhanced surveillance of pigs and other animals in Hong Kong.
While the future of this virus is unknown, we’ve seen other paramyxoviruses jump from swine to humans, with dramatic results. Perhaps the best example being Nipah, which emerged in the late 1990s.
In 1999, hundreds of abattoir workers in Malaysia and Singapore were infected from pigs carrying the virus (see MMWR Update: Outbreak of Nipah Virus -- Malaysia and Singapore, 1999) killing more than 100.
And once infected, they discovered that humans can transmit the virus on to others, albeit not terribly efficiently (see EID Journal Person-to-Person Transmission of Nipah Virus in a Bangladeshi Community).
Note: Nipah (and its Australian cousin Hendra, discovered in 1994) are sufficiently different from other members of the Paramyxoviridae family to have led to the creation of a new genus; Henipavirus.
Nipah was eventually traced to bats, and swine were determined to have been an intermediate host.
While Hong Kong actively does surveillance for new or emerging viruses in swine, the same cannot be said for most places around the globe. A topic Helen Branswell addressed in her terrific piece in SciAm from late 2010 called Flu Factories.
Flu Factories
The next pandemic virus may be circulating on U.S. pig farms, but health officials are struggling to see past the front gate
By Helen Branswell | December 27, 2010 |
For more on the human strains of parainfluenza, you may wish to visit the CDC’s website.
Human Parainfluenza Viruses (HPIVs)
