US - Researchers at the University of Minnesota Veterinary Diagnostic Laboratory have identified a third strain of the porcine epidemic diarrhoea (PED) virus in the US.
A third strain of the PED virus (PEDV) in the US has been reported by Douglas Marthaler of the University of Minnesota Veterinary Diagnostic Laboratory and others there and with the Swine Vet Center in Saint Peter.
In a letter in the journal, 'Emerging Infectious Diseases', they explain that they sequenced the complete PEDV genome by using next generation sequencing to clarify the relationship between the US PEDV strains. Previously, the spike gene of the virus had been the main area sequenced.
This work identified a new strain of the virus, which is called 'Minnesota188' or 'S2aa-del'. This is the third variant of the virus found in the US, following the original North American PED virus strains and the North American INDEL strains, which were first detected in 2013 and identified in 2014.
In their conclusions, the Minnesota group say that so far, three naturally occurring US PEDV strains have been identified: the original PEDV, the PEDV with changes in the spike gene (INDEL), and the PEDV strain (S2aa-del) they have recently reported.
The role of genetic changes in the US PEDV strains to clinical disease has yet to be reported, they add, but the clinical presentation of diarrhoea in this case was reported to be at least as severe as in cases caused by the prototype PEDV Colorado/2013. Other factors such as concurrent infections and the rate of group exposure, which is rapid in most PEDV cases affecting neonatal piglets, may influence the clinical presentation.
Documenting PEDV variation is vital to understanding the natural evolution of the virus and possibly identifying portions of the genome associated with different clinical disease features, commented Marthaler and co-authors.
They call for animal studies to be conducted to define the effects of these mutations on clinical disease, pathogenesis and immunity the S2aa-del strain. A consistent model to properly evaluate these differences is required to control PEDV infection.
The most compelling need is to understand how exposure by sows to different PEDV strains correlates with protection of piglets from clinical disease, according to Marthaler and co-authors.
It is not yet known whether the PEDV S2aa-del strain will circulate in the North American pig population, they added.
In the introduction to their letter, the group says that PEDV was first reported in April 2013. Since then, it has continued to spread throughout the United States and has been reported in Mexico and Canada.
PEDV was first reported in Europe in the 1970s and was later reported in Asia during the 1980s, where outbreaks were more acute and severe than in Europe. In 2010, an increase of up to 100 per cent was reported in illness and deaths in piglets in China associated with PEDV infection. The original North American PEDV strains identified in 2013 caused severe illness and deaths in piglets and had a 99.5 per cent nucleotide identity with Chinese strain AH2012.
The North American PEDV variant-INDEL strain (OH851) was first reported in February 2014 by the Ohio Department of Agriculture but it was first detected in June 2013. This suggested that either the original PEDV strain mutated or that two different PEDV strains were introduced concurrently into the US.
The paper was published by D. Marthaler, L. Bruner, J. Collins and K. Rossow. 2014. Third strain of porcine epidemic diarrhea virus, United States [letter]. Emerg. Infect. Dis. 2014 Dec [Accessed 6 January 2015]. http://dx.doi.org/10.3201/eid2012.140908
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