The prevalence and molecular epidemiology of porcine epidemic diarrhea virus in Taiwan

Porcine epidemic diarrhea (PED) is an acute and highly contagious enteric viral disease in swine. In 2013, the disease has emerged and reemerged in American and Asian countries, and caused severe economic loss in affected farms. The clinical signs of PED were observed in infected pig by vomiting, severe watery diarrhea, dehydration, and high morbidity and mortality, especially for suckling pigs. Since December 2013, the epidemic situation of diarrhea in the piglets had been remarkably deteriorating in Taiwan. During January 20, 2014 to December 30, 2015, a total of 333 diarrhea cases from 130 farms in 13 counties were submitted to the Animal Health Research Institute. The affected farm was observed severe diarrhea and vomiting in pigs of all ages. The objective of the present work was to survey the prevalence and molecular epidemiology of PED outbreaks in Taiwan.

The enteric samples were examined by reverse transcription polymerase chain reaction (RT-PCR) for differential diagnosis, including transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV), and porcine group A rotavirus (GARV).Isolation of PEDV from field specimens was conducted in Vero cells. The supernatant of cultured Vero cell was examined by electron microscopy and RT-PCR test.The S gene of isolated PEDV were sequenced and compared with that of published PEDV sequences and were aligned by MUSCLE using MEGA 5.2 software. The phylogenetic tree of PEDV S gene was constructed by maximum-likelihood method.

Among 333 specimens, 79 were positive for PEDV by RT-PCR. The prevalence of PED in farms was 40% (52/130) from 2014 to 2015. According to S gene sequences, the novel isolated PEDV Taiwan strains were clustered in group 2, together with strains PEDV/USA/2013, PEDV/ China/2012, and PEDV/Korea/2014, whereas the classical CV777 strain and historical Taiwan strain were rooted in group 1. The novel strains isolated in Taiwan were classified into 2 type strains (novel and variant novel strains) by S1 gene deletion, the variant novel strain has 205aa deletion between 23-227 positions in S1 gene. Among 52 novel PEDV outbreak farms, only 6 cases/farms were affected by the variant and novel PEDV simultaneously.

Since December 2013, the severe re-emergence of PED in Taiwan was caused by variant and novel strain. Compared with the historical PEDV, the novel PEDV strain was highly virulent and transmitted rapidly that caused high mobility and mortality in sucking pigs. The origin of the novel PEDV is still under investigation, and further studies on the virulence and antigenic characterization between variant and novel PEDV are required for developing a control strategy on PED.

Disclosure of Interest: None Declared.