In fact, using CE from adults, metacercarie and eggs, and ESA from adults, some authors have stated that the specificity in the detection of circulating antibodies to O. viverrini is limited by the cross-reactive nature of the antigens. This is particularly important in developing countries where people are infected with liver and intestinal flukes, with other helminths, and with protozoa. In the course of C. sinensis infections, the serological diagnosis by ELISA yielded high sensitivity but low specificity in high risk groups with a history of raw fish consumption. It follows that this diagnostic test is not suitable for epidemiological surveys in developing countries where people are frequently exposed to other parasitic infections. Attempts to obtain more specific O. viverrini antigens have been done by the partial purification of fractions from adult and egg crude extracts as well as from ESA. For O. felineus human infections, information regarding the specificity of serological tests for diagnostic purposes is scarce. “ESA” is a working definition, with an unclear distinction between products actively exported through secretory pathways and those that may be diffused or that may leak from the parasite soma. ESA consists of a number of compounds, including glycans, lipids and enzymes, some of which are shared with other helminths. According to Glupov et al. and Kotelkin et al., ESA components of molecular weight of 105, 74, and 70 Kd may have a potential use for a more specific immunodiagnosis. Recently, a cathepsin B-like cysteine protease belonging to family C1 present in the O. viverrini ESA, has been variability mdd crhr1 gene antidepressant response mdd cloned, expressed, and used in an ELISA to detect specific IgG in sera from persons from an endemic area. This ELISA yielded sensitivity and a specificity of 67% and 81%, respectively. In the present work, the validated ELISA, that used complete ESA, reaches 100% sensibility and 90.31% specificity. The difference in specificity between our ELISA and that developed by Sripa et al. could be due to the two target populations characterized by a high prevalence for liver and intestinal flukes in Thailand and by the absence of trematode infections in most of the Italian territory. In the developed ELISA, more than 95% of the differences between OD values of serum duplicates are less than two standard deviations; it follows that the ability to reproduce ELISA is high. Furthermore, the interassay variability test, based on data from four sera in eight working sessions, was only 10% for the positive sera and did not exceed 20% for the negative sera, indicating a good reproducibility of the ELISA. The validated ELISA shows an excellent performance in terms of sensitivity, repeatability, and reproducibility, and an acceptable specificity. Therefore, we conclude that the method is suitable for detecting anti-O. felineus antibodies in human sera, mainly for diagnostic purposes in association with epidemiological and clinical data. We are also indebted to G. Marucci for his technical support to infect laboratory animals and to S. 
M. Caccio` for the revision of the manuscript. The mammalian DNA methylation is methylated predominantly at the C5 position of cytosine bases within CpG disnuclotides and is catalyzed by a family of DNA methyltransferases. This epigenetic modification has been implicated in various biological progresses, including X chromosome inactivation, gene regulation, transcriptional silencing, and genomic imprinting. In tumor cells, the normal pattern of DNA methylation is often altered, resulting in global hypomethylation of the genome in conjunction with hypermethylation at CpG islands within the promoters of critical genes such as tumor suppressors. Concurrently, accumulating evidence has suggested that DNA methylation may be reversible in mammalian cells.