Pathogenecity of Porcine Epidemic Diarrhea Virus Field Isolates in 4-Week-Old Piglets
The study aimed to assess the pathogenesis of porcine epidemic diarrhea virus(PEDV)field isolates in 4-week-old piglets.Sixty PEDV antigen and antibody negative weaned pigs were randomly assigned into four groups at age of 4 weeks,15 piglets each group.Piglets in Groups 1,2 and 3 were orally inoculated with 2.0 mL of field isolates PEDV-FJ06,PEDV-0016 and PEDV-TT,respectively.Piglets in Group 4 were used as a negative control(NC)and orally inoculated with 2.0 mL PBS.Diarrhea was observed in infected piglets beginning at day 1 post inoculation(DPC 1)in Groups 1 and 3,at DPC 2 in Group 2.The morbidity was observed in Groups of PEDV-FJ06(90％),PEDV-0016(80％),PEDV-TT(100％)andNC(0％).PEDV fecal shedding occurred in virus inoculated piglets at DPC 1 and peaked from DPC 2 till DPC 7.Some piglets shed viruses throughout the study.Average daily weight gain(ADWG)in virus inoculated groups was significantly lower(P＜0.001)than NC group at DPCs 3 and 7.Five piglets in each group were randomly selected for necropsy at PDCs 7,14 and 21.Gross pathology of virus inoculated pigs included dilation of intestinal bowels,thinning of intestinal walls and mesenteric congestion.Microscopic lesions were atrophic enteritis in small intestines.PEDV specific antigen was detected in villous enterocytes of duodenums,jejunums,and ileums in virus inoculated pigs using immunohistochemistry(IHC),of which 100％positive IHC was observed in ileums at DPC 7.The results from the present study indicated that field isolates PEDV-FJ06,PEDV-0016 and PEDV-TT were all highly pathogenic to 4-week-old piglets and viruses rapidly proliferated in small intestinal epithelial cells,causing damages to intestinal villi,diarrhea and low ADWG.Fecal shedding of PEDV were observed throughout the study,thus increasing the risk of viral transmission.
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