Recently, along with the development of biochemical and molecular immunological techniques, the diagnosis methods have been improved in which preparing natural parasite antigens, and genetically engineered recombinant antigens have been applied by using agglutination test, complement fixation methods to detect the human’s serum antibodies for parasite identification of paragonimus infections. To improve the detection rate, some scholars have used phage peptide library technology to further improve the diagnostic effect on Paragonimus westermani in humans. In this paper, we summarized recent studies on diagnosis, pathogenesis and treatment of Paragonimus flukes in China.
The ovum of Paragonimus westermani is oval in shape and golden yellow in color and its operculum is big, conspicuous and inclined usually. Its ootheca is near papery and the other side is incrassate. There is an egg cell in the center of ovum surrounded by several yolk cells.
The imago looks like a half peanut, the reverse side of which is upheaval and the abdomen sucker is planar, while the size of oral sucker is similar to ventral sucker. Every adult has two intestinal tubes, arranging along the two sides of polypide. The ovary and uterus are tied behind the ventral sucker, meanwhile the testicular is divided into two and tied in polytide after a third position [
The life cycle of Paragonimus westermani includes ovum, miracidium sporocyst, redia, cercaria, metacercariae and adults. When the ovum passed into water, it would grow and mature under appropriate environment for almost three weeks, then the miracidium would be hatched from ovum. The worm would invade into the first intermediate host, then, the miracidium would live through the phase of sporocyst and redia, and finally develop into cercaria, which then escape from the snails and intrude into the body of second intermediate host, such as freshwater crab or crayfish in which it grow into a mature metacercariae. People would often be infected if they ate the raw freshwater crab or crayfish containing living metacercariae which would take off the capsule with the help of decomposing of digestive enzyme in small intestine, then enter into pulmonary across the diazoma. It would mature and form cyst in the pulmonary finally called paragonimiasis. The immunopathological effect caused by the migration and the parasitism of paragonimiasis was the primary mechanism of pathopoiesis [
Patients at acute stage would appear some symptoms such as chilly, remittent fever, bellyache, diarrhoea, feeblity, night sweat and anorexia during a week of infection. Then it would appear pectoralgia, cough, asthma in two or three weeks. On the other hand, the chronic typical symptoms were cough and hemoptysis [
Previous morphological methods on parasitic detection with the electron microscope are used for identifications of eggs and adults of Paragonimus westermani, even though the specificity is high, and the sensitivity is relatively low. Cultivation of the adult worms is also effective upon time, temperature, humidity and other restrictions. In addition, the shape characteristics of worms are similar to accurate identification [
Antigens of lung fluke tested include circulating antigen (CAg) and circulating immune complexes (CIC). It is very helpful to clinically diagnose patients in endemic areas using CAg-dot-ELISA and CAb-ELISA methods. Some parasitologists had used CAg-dot-ELISA to detect 70 cases of patients with Paragonimus trematodes that has een confirmed that 29 cases were positive with sensitivity of 41.5% comparing with Clonorchis trematodes. Using CAb-ELISA to detect 70 cases of Paragonimus trematodes, 67 patients appeared positive with the sensitivity as 95.7% comparing with clonorchiasis diseases. CAg-dot-ELISA method was also used for the early diagnosis of Paragonimus infections because of CAg appearing earlier, at that time, a low level of antibodies had not yet been detected [
Using intradermal test with 1: 0.1 ml antigen to detect adults’ paragonimiasis, the positive rate is up to 95%. The method is simple, but the specificity is not high, and there exists a higher cross-reactivity among schistosomiasis and chlonochiasis which would be used for epidemiological screenings [
Currently, rapid detection methods for paragonimiasis include using P-IgG4-DIGFA for indication, the sensitivity and specificity were 95.2% and 100% respectively. Gold filtration assay for rapid detection of specific IgG4 of lung flukes is not only simple, fast, but also high sensitivity and specificity which is suitable for clinical laboratory and field investigation applications [
Paragonimiasis and paragonimus infections could be identified by SDS-PAGE, spectrometry detection and immuno-gold labeling that showed the main components of the parasite surface membrane and secretions [
Genetic screening and expression of recombinant antigens of Paragonimus westermani were screened by ELISA and cell cultures. Performed with Paragonimus westerman, the cDNA library was screened five times and the positive clones were amplified by PCR using in vivo phage of recombinant plasmids of DNA sequence determination. BLAST method (accounting sequence database search program) was used to detect DNA sequence homology that may act as a Paragonimus westermani’s gene fragment of positive clones [
Ribosomal DNA gene and a second section (ITS2) sequences of mitochondrial cytochrome C oxidase subunit (COI) partly on Paragonimus westermani had been studied and colonizated. COI gene belongs to the mitochondrial genome, its evolutionary rate was faster than the nuclear genome, and with maternal inheritance, it was basically not affected by genetic recombination, genetic differences within species. ITS2 gene evolution rate is relatively slow and conservative, reflecting the level of variation in parasites suitable for Paragonimus genetic differences between species, especially for close genetic relationship and is the ideal targets for detection and identification of parasites. In 1970s, Japanese researchers found that Paragonimus had two types of genotyping such as triploid (2n = 22 3n = 33) which was very similar to the metacercariae, worms and eggs. Diploid type worms have sperms, the reproductive mating lines, known as Paragonmus westermani. Triploid type worms have no sperms, but pathogenic impacts are significantly stronger than diploid of Paragonimus [
Excluding diagnosis on lung flukes and identification of patients experienced more than parasites with electron microscopy and optical microscopy, identifications of antigen-antibody agglutination test and other immunological methods were used and developed. Due to limitations of parasites’ antigens, a large-scale preparation of recombinant antigens and improving its purity would enter a new field conducted in-depth research. Positive clones have been obtained with immunological method for Paragonimus cDNA library by PCR amplification which addressed the questions of quantity and improved the specificity and accuracy of detections. At the genetic levels, specific primers and probes designed by PCR or real-time PCR methods for identification of similar paragonimus species are made as possible.
Dingli Xu,Jing Li,Qi Liao,Tuergong Jiang,Jiang Cai,Yuelong Lv,Jiakuan Lv,Baile Shen,Zexian Xu,Yanting Zhang,Jianfa Liu, (2015) Recent Research Progress on Study of Paragonimus westermani in China. Open Access Library Journal,02,1-4. doi: 10.4236/oalib.1101511