Philipp J Vet Anim Sci 2015, 41(1): 49-57 1 Department of Veterinary Paraclinical Sciences, School of Veterinary Medicine, Isabela State University, San Fabian, Echague, Isabela, Philippines (email: kmgnicolas@gmail.com); 2 Department of Veterinary Paraclinical Sciences; 3 Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of the Philippines Los Baños, Laguna, Philippines. 49 COMPARATIVE EVALUATION OF REVERSE TRANSCRIPTASE-POLYMERASE CHAIN REACTION AND IMMUNOHISTOCHEMISTRY FOR THE DIAGNOSIS OF PORCINE EPIDEMIC DIARRHEA IN LUZON, PHILIPPINES Karina Marie G. Nicolas 1* , Helen A. Molina 2 and Amadeo A. Alcantara 3 ABSTRACT Reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC) were used to demonstrate the presence of porcine epidemic diarrhea virus (PEDV) antigen in the intestinal cells of suckling pigs in Luzon. The PEDV antigen was detected in 11 (13.75%) and 32 (40%) out of 80 intestinal samples using RT-PCR and IHC, respectively. RT-PCR generated a 412-bp cDNA probe which amplifed the viral RNA encoding the membrane protein of PEDV from the intestinal segments of the jejunum. Immunohistochemistry revealed positive cells in the jejunum as indicated by the brown staining in the cytoplasm of infected cells. Comparative evaluation of the two tests revealed a fair agreement. Histopathological changes observed include vacuolation of enterocytes, villous atrophy as exemplifed by 2:1 villous:crypt height ratio and exfoliation of enterocytes which are associated with the clinical signs of PED such as watery diarrhea, dehydration and acidosis. RT-PCR may be used as a screening test for PEDV antigen detection using jejunal tissue with feces because of the shorter duration of processing and testing. IHC, on the other hand, can be performed as confrmatory test using formalin-fxed jejunal samples. Keywords: histopathology, immunohistochemistry, porcine epidemic diarrhea, RT-PCR, swine INTRODUCTION Porcine epidemic diarrhea (PED) is a viral enteric disease of swine caused by a single stranded, positive sense, enveloped RNA virus with approximately 28 kb viral genome called Porcine Epidemic Diarrhea Virus (PEDV). PEDV is categorized under the genus Alpha coronavirus, family Coronaviridae, order Nidovirales (Pan et al., 2012). Transmission occurs via feco-oral route after the introduction of infected animals or contaminated materials (Carvajal et al., 1995). The disease is characterized by vomiting, watery diarrhea and dehydration in all ages of swine and manifests as sporadic outbreaks (Song et al., 2012) causing signifcant economic losses in the swine industry. PED has been reported to cause a 100% morbidity and mortality rate in less than 5 days old neonatal piglets and 10% mortality in infected piglets older than 10 days old (Kim and Chae, 2002). Methods for detection of PED infection are necessary prerequisite for assessing the current epidemic situation in herds and for subsequent immunoprophylactic measures (Roda’k et al., 2005). Many diagnostic methods have been used for the detection of ORIGINAL ARTICLE