Positive selection pressure on the B/C domains of the E2-gene of classical swine fever virus in endemic areas under C-strain vaccination

• Published in: Infection, genetics and evolution genetics and evolution, 2012-10, Vol.12 (7), p.1405-1412
• Main Authors: Pérez, Lester Josué, Díaz de Arce, Heidy, Perera, Carmen Laura, Rosell, Rosa, Frías, Maria T., Percedo, Maria I., Tarradas, Joan, Dominguez, Patricia, Núñez, Jose I., Ganges, Llilianne
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Bayes Theorem; Biological and medical sciences; Cell Line; Chronic diseases; Classical Swine Fever - epidemiology; Classical Swine Fever - prevention & control; Classical Swine Fever - virology; Classical swine fever virus; Classical swine fever virus - genetics; Classical swine fever virus - pathogenicity; clinical trials; Cuba - epidemiology; Endemic Diseases; Epidemiology. Vaccinations; evolution; Evolution, Molecular; General aspects; genes; genotype; Glycoprotein E2; hog cholera; Infectious diseases; Lung - virology; Mass Vaccination; Medical sciences; Models, Genetic; Molecular Sequence Data; Molecular Typing; Nasal Mucosa - virology; nucleotide sequences; pathogenesis; Phylogeny; Positive selective pressure; Selection, Genetic; Sus scrofa - virology; Swine; vaccination; Viral Envelope Proteins - genetics; virulence; Virulence - genetics; viruses
• ISSN: 1567-1348; 1567-7257
• DOI: 10.1016/j.meegid.2012.04.030

► We evaluate the positive selection pressure on E2 partial gene of CSF fever viruses. ► We asses a representative CSF virus for their clinical virulence. ► The analysis estimated six new sites under positive selection. ► Experimental evidence of a milder presentation of the disease is provided. ► Escape viral variants with alterations in viral pathogenicity are suggested to occur. In Cuba, classical swine fever (CSF) has become an endemic disease with several outbreaks each year, despite the implemented vaccination program. Interestingly, a trend towards a milder presentation of the disease has been observed among the animals during the last years. This study aimed to assess positive selection pressure acting on partial E2 gene of CSF viruses to gain insights into the mechanisms governing virulence and the driving forces of classical swine fever virus (CSFV) evolution in swine populations under regular vaccination. Selection pressure analysis were performed to detect positive selection acting on a particular lineage as well as among sites of the E2-B/C-domain of CSFV nucleotide sequences, reported in a previous study and in the present work, several models, available in the CODEML module of PAML 4.3, were used. In addition, a representative Cuban CSF isolate was assessed in an experimental infection trial for their clinical virulence in order to expand the knowledge regarding CSF viruses circulating in pig populations. The viral genomes sequenced in this study were grouped in a defined cluster within the genotype 1.2, as it has been reported previously for Cuban CSF viruses. The selection pressure analysis didn’t find evidence of positive selection (dN/dS of>1) along any branch. The positive selective pressure analysis estimated six new sites under positive selection on E2 partial gene analysed. Besides, the clinical manifestations of the CSF-disease were related mainly to a mild course of the illness. The high number of positively selected sites suggests that these changes could be associated to viral evasion of the host-immune response. These observations highlight a possible association between escape viral variants and the alterations observed in the virulence and pathogenesis of the virus. Therefore, while the vaccination programs have not led to a genotype change, alterations in virulence were suggested to arise.