Paragonimiasis

An immunochromatographic test using whole blood for rapid diagnosis of human paragonimiasis and its diagnostic usefulness

Paragonimiasis is a harmful food-borne zoonosis caused by lung flukes of the genus Paragonimus. The disease is found on most continents, several million people are at risk of infection, and it is a re-emerging disease in developing countries. The gold standard for diagnosis of pulmonary paragonimiasis requires the finding of eggs in sputa and/or fecal samples. In ectopic paragonimiasis cases, eggs are typically not seen, and supportive information is required such as a history of eating freshwater crabs or crayfishes, radiographic findings and immunological tests. Here, we developed a proof of concept based on lateral flow assay, an immunochromatographic test kit, named the paragonimiasis whole-blood test kit, for detection of specific IgG antibody in simulated whole-blood samples (WBSs) using worm excretory-secretory antigens to diagnose human paragonimiasis. The laboratory diagnostic values of this kit were compared with the detected IgG in serum samples. In simulated WBSs, the diagnostic sensitivity and specificity were 97.8 % and 96.1 %, respectively, while for serum samples, these values were 100.0 % and 94.8 %, respectively. The comparative IgG antibody detections whether a result was positive or negative between simulated WBSs and serum samples did not differ significantly with a concordance of 97.8 % in laboratory conditions using a circumscribed set of samples. The tool is fast and easy to use. The next step involves observing and evaluating native whole blood samples and using specific recombinant antigens need to be evaluated for support diagnosis of paragonimiasis caused by P. heterotremus, P. westermani and P. miyazakii at the bedside or at local and remote hospitals with limited facilities. It will also be valuable for epidemiological surveys in Asia where paragonimiasis is endemic.

Epidemiology and Geographical Distribution of Human Trematode Infections

Digenetic trematodes infecting humans are more than 109 species that belong to 49 genera all over the world. According to their habitat in the definitive hosts, they are classified as 6 blood flukes (Schistosoma japonicum. S. mekongi, S. malayensis, S. mansoni, S. intercalatum, and S. haematobium), 15 liver flukes (Fasciola hepatica, F. gigantica, Clonorchis sinensis, Opisthorchis viverrini, O. felineus, Dicrocoelium dendriticum, D. hospes, Metorchis bilis, M. conjunctus, M. orientalis, Amphimerus sp., A. noverca, A. pseudofelineus, Pseudamphistomum truncatum, and P. aethiopicum), nine lung flukes (Paragonimus westermani, P. heterotremus, P. skrjabini, P. skrjabini miyazakii, P. kellicotti, P. mexicanus, P. africanus, P. uterobilateralis, and P. gondwanensis), 30 heterophyid intestinal flukes (Metagonimus yokogawai, M. takahashii, M. miyatai, M. suifunensis, M. katsuradai, M. pusillus, M. minutus, Heterophyes heterophyes, H. nocens, H. dispar, Haplorchis taichui, H. pumilio, H. yokogawai, H. vanissinus, Centrocestus formosanus, C. armatus, C. cuspidatus, C. kurokawai, Procerovum calderoni, P. varium, Pygidiopsis genata, P. summa, Stictodora fuscata, S. lari, Stellantchasmus falcatus, Heterophyopsis continua, Acanthotrema felis, Apophallus donicus, Ascocotyle longa, and Cryptocotyle lingua), 24 echinostome intestinal flukes (Echinostoma revolutum, E. cinetorchis, E. mekongi, E. paraensei, E. ilocanum, E. lindoense, E. macrorchis, E. angustitestis, E. aegyptica, Isthmiophora hortensis, I. melis, Echinochasmus japonicus, E. perfoliatus, E. lilliputanus, E. caninus, E. jiufoensis, E. fujianensis, Artyfechinostomum malayanum, A. sufrartyfex, A. oraoni, Acanthoparyphium tyosenense, Echinoparymphium recurvatum, Himasthla muehlensi, and Hypoderaeum conoideum), 23 miscellaneous intestinal flukes (Brachylaima cribbi, Caprimolgorchis molenkampi, Phaneropsolus bonnei, P. spinicirrus, Cotylurus japonicus, Fasciolopsis buski, Gastrodiscoides hominis, Fischoederius elongatus, Watsonius watsoni, Gymnophalloides seoi, Gynaecotyla squatarolae, Microphallus brevicaeca, Isoparorchis hypselobagri, Nanophyetus salmincola, N. schikobalowi, Neodiplostomum seoulense, Fibricola cratera, Plagiorchis muris, P. vespertilionis, P. harinasutai, P. javensis, P. philippinensis, and Prohemistomum vivax), one throat fluke (Clinostomum complanatum), and one pancreatic fluke (Eurytrema pancreaticum). The mode of transmission to humans includes contact with cercariae contaminated in water (schistosomes) or ingestion of raw or improperly cooked food, including fish (liver flukes, heterophyid flukes, echinostomes, and throat flukes), snails (echinostomes, brachylaimids, and gymnophallid flukes), amphibia, reptiles (neodiplostomes), aquatic vegetables (fasciolids and amphistomes), and insect larvae or adults (lecithodendriids, plagiorchiids, and pancreatic flukes). Praziquantel has been proven to be highly effective against almost all kinds of trematode infections except Fasciola spp. Epidemiological surveys and detection of human infections are required for a better understanding of the prevalence, intensity of infection, and geographical distribution of each trematode species.

Diagnosis of Human Trematode Infections

Digenetic trematodes form a major group of human parasites, affecting a large number of humans, especially in endemic foci. Over 100 species have been reported infecting humans, including blood, lung, liver and intestinal parasites. Traditionally, trematode infections have been diagnosed by parasitological methods based on the detection and the identification of eggs in different clinical samples. However, this is complicated due to the morphological similarity between eggs of different trematode species and other factors such as lack of sensitivity or ectopic locations of the parasites. Moreover, the problem is currently aggravated by migratory flows, international travel, international trade of foods and changes in alimentary habits. Although efforts have been made for the development of immunological and molecular techniques, the detection of eggs through parasitological techniques remains as the gold standard for the diagnosis of trematodiases. In the present chapter, we review the current status of knowledge on diagnostic techniques used when examining feces, urine, and sputum and also analyze the most relevant characteristics used to identify eggs with a quick key for the identification of eggs.

General overview of the current status of human foodborne trematodiasis

Foodborne trematodes (FBT) of public health significance include liver flukes (Clonorchis sinensis, Opisthorchis viverrini, O. felineus, Fasciola hepatica and F. gigantica), lung flukes (Paragonimus westermani and several other Paragonimus spp.) and intestinal flukes, which include heterophyids (Metagonimus yokogawai, Heterophyes nocens and Haplorchis taichui), echinostomes (Echinostoma revolutum, Isthmiophora hortensis, Echinochasmus japonicus and Artyfechinostomum malayanum) and miscellaneous species, including Fasciolopsis buski and Gymnophalloides seoi. These trematode infections are distributed worldwide but occur most commonly in Asia. The global burden of FBT diseases has been estimated at about 80 million, however, this seems to be a considerable underestimate. Their life cycle involves a molluscan first intermediate host, and a second intermediate host, including freshwater fish, crustaceans, aquatic vegetables and freshwater or brackish water gastropods and bivalves. The mode of human infection is the consumption of the second intermediate host under raw or improperly cooked conditions. The major pathogenesis of C. sinensis and Opisthorchis spp. infection includes inflammation of the bile duct which leads to cholangitis and cholecystitis, and in a substantial number of patients, serious complications, such as liver cirrhosis and cholangiocarcinoma, may develop. In lung fluke infections, cough, bloody sputum and bronchiectasis are the most common clinical manifestations. However, lung flukes often migrate to extrapulmonary sites, including the brain, spinal cord, skin, subcutaneous tissues and abdominal organs. Intestinal flukes can induce inflammation in the intestinal mucosa, and they may at times undergo extraintestinal migration, in particular, in immunocompromised patients. In order to control FBT infections, eating foods after proper cooking is strongly recommended.

Diagnosis of Human Trematode Infections

Digenetic trematodes form a major group of human parasites, affecting a large number of humans, especially in endemic foci. Over 100 species have been reported infecting humans, including blood, lung, liver, and intestinal parasites. Traditionally, trematode infections have been diagnosed by parasitological methods based on the detection and the identification of eggs in different clinical samples. However, this is complicated due to the morphological similarity between eggs of different trematode species and other factors such as lack of sensitivity or ectopic locations of the parasites. Moreover, the problem is currently aggravated by migratory flows, international travel, international trade of foods, and changes in alimentary habits. Although efforts have been made for the development of immunological and molecular techniques, the detection of eggs through parasitological techniques remains as the gold standard for the diagnosis of trematodiases. In this chapter, we review the current status of knowledge on diagnostic techniques used when examining feces, urine, and sputum and also analyze the most relevant characteristics used to identify eggs with a quick key for the identification of eggs.

Is Opisthorchis viverrini Emerging in Cambodia?

Opisthorchis viverrini infection is widely prevalent in Southeast Asia. In Cambodia information on this helminth infection is scare. Recent reports suggest that O. viverrini is an emerging public health problem. We aimed to synthesize all information in relation to the infection, epidemiology, and morbidity of O. viverrini in Cambodia; from published as well as thus far unpublished sources. First reports on O. viverrini date back to 1995. In 2006 an O. viverrini initiative was launched by the national helminth control program. Since then O. viverrini has been reported in all - except two - provinces. Villages with high prevalences (>20%) were found in provinces from Preah Vihear to Takeo. The infection has a highly focal distribution. In many villages no infections were detected. O. viverrini infection was also reported in cats, dogs and intermediate hosts. No report on morbidity associated with O. viverrini was found. The current evidence suggests that O. viverrini infection remains underreported in Cambodia. It is likely that the transmission will further increase in the future with potentially serious consequences for human health.

Epidemiology of Trematode Infections: An Update

Digenetic trematodes infecting humans are more than 91 species which belong to 46 genera all over the world. According to their habitat in definitive hosts, they are classified as blood flukes (Schistosoma japonicum. S. mekongi, S. mansoni, S. haematobium, and S. intercalatum), liver flukes (Clonorchis sinensis, Opisthorchis viverrini, O. felineus, Metorchis conjunctus, M. bilis, M. orientalis, Fasciola hepatica, F. gigantica, Dicrocoelium dendriticum, and D. hospes), lung flukes (Paragonimus westermani, P. heterotremus, P. skrjabini, P. miyazakii, P. kellicoti, P. mexicanus, P. africanus, and P. uterobilateralis), throat fluke (Clinostomum complanatum), pancreatic fluke (Eurytrema pancreaticum), and intestinal flukes (Metagonimus yokogawai, M. miyatai, M. takahashii, Heterophyes nocens, H. heterophyes, Haplorchis taichui, H. pumilio, H. yokogawai, Centrocestus formosanus, Echinostoma revolutum, E. ilocanum, Isthmiophora hortensis, Echinochasmus japonicus, E. lilliputanus, Artyfechinostomum malayanum, A. sufrartyfex, A. oraoni, Fasciolopsis buski, Gymnophalloides seoi, Neodiplostomum seoulense, Caprimolgorchis molenkampi, Phaneropsolus bonnei, and Plagiorchis muris). The mode of transmission to humans includes contact with cercariae contaminated in water (schistosomes) and ingestion of raw or improperly cooked fish (liver and throat flukes, heterophyids, and echinostomes), snails (echinostomes and gymnophallids), amphibia, reptiles (neodiplostomes), aquatic vegetables (amphistomes), or insect larvae or adults (plagiorchiids, lecithodendriids, and pancreatic fluke). Praziquantel has been proved to be highly effective against most species of trematode infections except fascioliasis. Epidemiological surveys and detection of human infections are required for better understanding of the geographical distribution and endemicity of each trematode species.

Infection with Paragonimus westermani of boar-hunting dogs in Western Japan maintained via artificial feeding with wild boar meat by hunters

Infection of boar-hunting dogs with Paragonimus westermani was investigated in Western Japan. Blood and rectal feces were collected from 441 dogs in the three districts (205 in Kinki, 131 in Chugoku and 105 in Shikoku District). In a screening ELISA for serum antibody against P. westermani antigen, 195 dogs (44.2%) showed positive reaction. In the 195 dogs, 8 dogs were found excreting P. westermani eggs after molecular analysis of fecal eggs, and additional 7 were identified serologically for the parasite infection because of their stronger reactivity against P. westermani antigen than against antigens of other species of Paragonimus. A spatial analysis showed that all of the P. westermani infections were found in Kinki and Chugoku Districts. In this area, dogs’ experience of being fed with raw boar meat showed high odds ratio (3.35) to the sero-positivity in the screening ELISA, and the frequency of such experiences was significantly higher in sero-positive dogs. While clear relationship was not obtained between predation of boars by dogs during hunting and their sero-positivity. Therefore, it is suggested that human activity of feeding with wild boar meat is the risk factor for P. westermani infection in boar-hunting dogs. Considering that hunting dogs could play as a major definitive host and maintain the present distribution of P. westermani in Western Japan, control measures for the infection in hunting dogs, such as prohibition of raw meat feeding and regular deworming, should be undertaken.

A singleplex real-time fluorescence resonance energy transfer PCR with melting curve analysis for the differential detection of Paragonimus heterotremus, Echinostoma malayanum and Fasciola gigantica eggs in faeces

BACKGROUND

Because the eggs of Paragonimus, Echinostoma and Fasciola are very similar in size and shape, it is difficult to distinguish and accurately identify species by the morphology of their eggs, which is a standard diagnostic method.

METHODS

In this study, a novel assay combining a real-time fluorescence resonance energy transfer PCR and melting curve analysis using one set of primers and fluorophore-labelled hybridization probes specific for the 28S rDNA region was developed for the molecular detection of Paragonimus heterotremus, Echinostoma malayanum and Fasciola gigantica eggs.

RESULTS

This assay could detect and distinguish P. heterotremus, E. malayanum and F. gigantica DNA with the distinct melting temperature (Tm) values of 57.99±0.08, 62.12±0.15 and 74.10±0.18, respectively. The assay can also be used to detect and distinguish DNA from P. bangkokensis, P. harinasutai, P. machorchis, E. revolutum, Hypodereum conoideum and F. hepatica, which have different Tm values. The sensitivity of this assay enabled the detection of one egg of P. heterotremus, E. malayanum or F. gigantica per 100 mg of faeces. In addition, the specificity testing showed no fluorescence signal for other parasites.

CONCLUSIONS

Due to the sensitivity and specificity of our assay in detecting P. heterotremus, E. malayanum and F. gigantica, our method could be used to accurately diagnose these three medically important parasitic groups and has potential implications for molecular epidemiological investigations of human and/or animal infections.

Molecular identification of the trematode Paragonimus in faecal samples from the wild cat Prionailurus bengalensis in the Da Krong Nature Reserve, Vietnam

Conventional identification of Paragonimus species and their natural definitive hosts is based on the morphological features of adult parasites isolated from the lungs of wild mammalian hosts. However, wild animals are protected by strict regulations and sampling is not always possible. Recently, molecular techniques have been developed to identify the internal transcribed spacer (ITS) sequences of Paragonimus eggs in faeces/sputum of human patients. Also, mammalian hosts can be identified using the D-loop sequence of mitochondrial DNA in faecal samples. In this study, we used molecular techniques on faeces from wild animals collected in Da Krong Nature Reserve, Quang Tri province, central Vietnam, where Paragonimus metacercariae are highly prevalent in mountain crabs, to identify Paragonimus species and their natural definitive hosts. The results indicated that wild cats, Prionailurus bengalensis, were infected with at least three different Paragonimus species, P. westermani, P. skrjabini and P. heterotremus. Because all of these species can infect humans in Asian countries, human paragonimiasis should be considered in this area.

Zoonotic enteric parasites transmitted from dogs in Egypt with special concern to Toxocara canis infection

AIM

This work aimed to study the role played by dogs in transmitting zoonotic enteric parasites to humans in Egypt and to analyze the risk factors associated with the occurrence of such infection in dogs. Serodiagnosis of anti-Toxocara immunoglobulin G (IgG) antibodies among human beings as well as analyzing risk factors predispose to Toxocara canis infection in human beings are another objectives of this study.

MATERIALS AND METHODS

From June to December 2013, a total of 130 fecal samples from 4 dog populations (Military, nomadic and domiciled dogs from rural and high standard districts) and 150 stool samples of 6 occupational groups were examined for the presence of enteric parasitic infection. Moreover, 150 serum samples were collected from humans from whom stool samples were collected and examined for the presence of anti-T. canis antibodies.

RESULTS

Enteric parasites were detected in 30% of fecal samples from 4 dog populations in Egypt. High infectivity had been reported in nomadic dogs (63.33%) (Crude odds ratios [COR]=67.36, 95% confidence interval [CI]=8.09-560.8, p<0.000), followed by domiciled dogs from rural areas (40%) (COR=26, 95% CI=3.14-215.54, p=0.003), domiciled dogs from high standard areas (23.33%) (COR=11.87, 95% CI=1.37-102.69, p=0.025) and military dogs (2.5%). Twelve species of enteric parasites were identified, Ancylostomatidae (6.15%), T. canis and Cryptosporidium spp. (5.38%, each), Heterophyes spp. (3.85%), Toxocara leonina and Blastocystis spp. (3.07%), Taenidae eggs (2.31%), Hymenolepis diminuta (1.54%) and Entamoeba canis, Cyclospora cayetanensis, and Paragonimus spp. (0.77%, each). Univariate logestic regression revealed significant association of age (COR=4.73, 95% CI=2.13-10.53, p<0.000), gender (COR=2.63, 95% CI=1.22-5.68, p<0.014), housing system (COR=5.10, 95% CI=2.04-12.75), p<0.000) with enteric parasitic infection in dogs. However, breeds (COR=6.91, 95% CI=0.88-54.52, p=0.067) and type of feeding (COR ranged from 3.5 to 7.62, p>0.05) did not seem to have a significant association among the examined dogs. Enteric parasitic infection was reported in 31/150 human stools (20.67%). Students were the most affected groups (37.14%), followed by nomadic people (24%), house wives (20%), house guarders and military workers (12%, each), and employees (10%). The identified parasites were Cryptosporidium spp. (9.33%), Ascaris lumbercoides (3.33%), Heterophyes spp. and Ancylostoma spp. (2.66%, each) and Paragonimus spp. and Hymenolepis nana (1.33%, each). Toxocara IgG antibodies were detected in 36/150 (24%) serum samples investigated. Toxocara IgG antibodies were more prevalent in males (26.66%) than females (20%). Seroprevalence was highest (17/35, 48.57%) in 7-15 years old (COR=6.93, 95% CI=1.75-27.43, p=0.006). Seroprevalence values for T. canis antibodies were higher in those; raising dogs (29.85%), eating raw vegetables (25.21%) and not washing hands before meals (25.45%). T. canis antibodies were detected in 25% of those contacted with soil compared to 30% of those did not. Students were mostly affected (34.29%), followed by nomadic people (32%), house guarders (28%), housewives (20%), military workers (13%), and employees (10%).

CONCLUSION

Detection of enteric parasites in dogs and humans in Egypt substantiates the role posed by dogs in transmitting zoonotic parasites to humans and knock an alarm for common sources of infection for humans and dogs. Common sources may be infected fish or contaminated vegetables that are consumed by dogs or humans or even infected rodents that may contaminate their feed. This pilot study necessitate the need for similar studies and tracing such infection in fish, vegetables, rodent that may be responsible for infecting humans and dogs in order to understand the epidemiology of zoonotic parasitic infection transmitted from dogs to humans.

Evaluation of the MGL method to detect Paragonimus eggs and its improvement

Dog feces containing 500 Paragonimus westermani eggs per gram were examined by the Medical General Laboratory (MGL), the simple sedimentation (SS), and the Army Medical School III (AMS III) methods. The number of eggs per gram of feces (EPG) obtained by the MGL method was 17.2 and was significantly lower than those obtained by the SS method (324.0) and the AMS III method (505.6). When isolated P. westermani eggs were processed by the MGL method and four layers (ether, ether-fecal, formalin layers, and sediment) of the final centrifugation product were separately examined, almost 100% of eggs were found at the ether-fecal layer. Similarly, when fecal samples containing P. westermani, Paragonimus skrjabini miyazakii, Paragonimus ohirai, or Paragonimus harinasutai eggs were processed by the MGL method, more than 95% of the eggs were found in the supernatant layers. The formalin-ethyl acetate (FEA) method showed a similar tendency as the MGL method and over 90% of eggs remained in the supernatant layers. Contrary to Paragonimus eggs, 63 and 96% of Clonorchis and Metagonimus eggs were found in the sediment in the MGL method, respectively. When surfactant (Tween 80) was added to fecal solution, most of Paragonimus eggs spun down in the sediment in the MGL and FEA methods, suggesting that Paragonimus eggs have hydrophobic components on their surface. It is suggested that surfactant addition to the fecal solution should be considered when the MGL method is used for detection of Paragonimus eggs.

Application of a real-time fluorescence resonance energy transfer polymerase chain reaction assay with melting curve analysis for the detection of Paragonimus heterotremus eggs in the feces of experimentally infected cats

Paragonimus heterotremus is a medically important lung fluke that causes human and animal paragonimiasis in Southeast Asia, including Thailand. In the current study, a real-time fluorescence resonance energy transfer polymerase chain reaction (real-time FRET PCR) with melting curve analysis was developed and evaluated to detect P. heterotremus eggs in the feces of experimentally infected cats. The detection limit of this method for the P. heterotremus DNA sequence was 3 × 102 copies of the positive control plasmid and 10−3 ng of P. heterotremus genomic DNA. The assay system could detect 10 eggs of P. heterotremus per gram of cat feces. No fluorescence signal was observed when DNA purified from 16 other organisms or genomic DNA from cats and human beings were tested. Real-time FRET PCR yielded positive results for all fecal samples from 17 P. heterotremus–infected cats and showed a negative relationship ( r = −0.852, P < 0.001) between the number of parasite eggs in feces and the number of PCR cycles. The assay could detect genomic DNA from P. heterotremus, P. westermani, P. macrorchis, P. siamensis, P. harinasutai, and P. bangkokensis and can differentiate P. heterotremus from the other 5 species. The 6 Paragonimus species examined were divided into 4 groups by melting peak analysis. This assay can be useful for the detection of, and epidemiological studies on, P. heterotremus infection in endemic areas.

Discovery of Paragonimus skrjabini in Vietnam and its phylogenetic status in the Paragonimus skrjabini complex

Two members of the Paragonimus skrjabini complex, P. skrjabini and P. miyazakii, are now considered as two sub-species, P. skrjabini skrjabini and P. skrjabini miyazakii. They are well known as important pathogens for human paragonimiasis in China and Japan. Recently, members of this species complex have been reported from India. Here we report the first discovery of P. skrjabini from freshwater crab hosts in Thanh Hoa province, Vietnam. For morphological and molecular phylogenetic studies, adult worms were obtained by experimental infection in cats and dogs. Molecular analyses of metacercariae and adults revealed that the P. skrjabini population from Thanh Hoa, Vietnam was almost completely identical with that from Yunnan province, China. Those populations from Thanh Hoa, Vietnam and Yunnan, China and those from Manipur, India were significantly different from P. skrjabini populations reported from other localities of China in cytochrome oxidase subunit 1 (CO1) gene sequences, indicating considerable genetic variation within the P. skrjabini complex. Moreover, low bootstrap values in the CO1 tree suggested that more variant genotypes belonging to P. skrjabini complex may be found in other Asian countries in between Vietnam and India, such as Myanmar, Laos and Thailand. Since P. skrjabini is known as a pathogen for humans, paragonimiasis cases caused by P. skrjabini might be found in Vietnam and other Asian countries.

In memory of Patrick Manson, founding father of tropical medicine and the discovery of vector-borne infections

Patrick Manson, a clinician-scientist serving in China (1866–1889), discovered that many tropical infectious diseases require a vector peculiar to warm climate for person to person transmission. He demonstrated the nocturnal periodicity of microfilariae in the blood of patients with elephantiasis. These microfilariae undergo metamorphosis when ingested by the mosquito acting as the vector for the completion of their life cycle. Furthermore, he demonstrated the linkage between the lung fluke and endemic haemoptysis by finding operculated eggs in patients' sputa. He predicted that the miracidium from hatched eggs uses crustaceans, such as fresh-water snails found at tropical conditions, as the intermediate hosts in the life cycle of many trematodes. His vector hypothesis leads to vector control which is now the cornerstone for the World Health Organization's programme for the elimination/control of lymphatic filariasis, dracunculiasis and malaria. Before leaving China, he established the Alice Memorial Hospital, the Hong Kong College of Medicine for Chinese (the forerunner of the University of Hong Kong), and the Hong Kong Medical Society for medical service and education. He also incepted the Hong Kong Dairy Farm for supplying hygienic milk affordable by pregnant women, children and patients.

Presence of three distinct genotypes within the Paragonimus westermani complex in northeastern India

The name Paragonimus westermani (Kerbert, 1878) is commonly applied to members of a species complex that includes the well-known Asian lung fluke of medical and veterinary importance. Unambiguous molecular and morphological evidence showing the presence of a member of the complex in India has recently been published. In the present study we report the occurrence of 2 more members of the P. westermani complex in northeastern (NE) India. Surveys of the freshwater crabs Maydelliatelphusa lugubris in NE India revealed 2 morphologically distinct types of lung fluke metacercariae. Phylogenetic analyses, using DNA sequences from ITS2, 28S and cox1 gene regions indicate that these lung metacercariae belong to P. westermani complex. Type 1 metacercariae have a more basal position within the complex whereas type 2 metacercariae are closely related to the relatively derived forms of P. westermani from NE Asia (Japan, Korea, China) and Vietnam. A third type of metacercaria (type 3), detected in another crab host, Sartoriana spinigera in Assam, was phylogenetically close to P. siamensis, also a member of the P. westermani group. Molecular evidence has demonstrated the existence of 3 genotypes of lung flukes within the Paragonimus westermani complex in NE India. Two of these were previously unknown.

Molecular identification of a case of Paragonimus pseudoheterotremus infection in Thailand

Paragonimiasis is an important food-borne parasitic zoonosis caused by infection with lung flukes of the genus Paragonimus. In Southeast Asia, Paragonimus heterotremus is the only proven causative pathogen. Recently, a new Paragonimus species, P. pseudoheterotremus, was found in Thailand. This species is genetically similar to P. heterotremus and is considered as a sister species. However, infectivity or pathogenicity of P. pseudoheterotremus to humans remains unclear. We report the first confirmed human pulmonary paragonimiasis case caused by P. pseudoheterotremus infection. After polymerase chain reaction/sequencing of the DNA extracted from Paragonimus eggs in the sputum of the patient, partial internal transcribed spacer 2 and cytochrome c oxidase subunit 1 sequences were approximately identical (98-100%) with those of P. pseudoheterotremus. For P. heterotremus, the partial internal transcribed spacer 2 sequence was approximately identical (99-100%), but the partial mitochondrial cytochrome c oxidase subunit 1 sequence showed a similarity of 90-95%.

Current status of food-borne trematode infections

Food-borne trematodiases constitute an important group of the most neglected tropical diseases, not only in terms of research funding, but also in the public media. The Trematoda class contains a great number of species that infect humans and are recognized as the causative agents of disease. The biological cycle, geographical distribution, and epidemiology of most of these trematode species have been well characterized. Traditionally, these infections were limited, for the most part, in populations living in low-income countries, particularly in Southeast Asia, and were associated with poverty. However, the geographical limits and the population at risk are currently expanding and changing in relation to factors such as growing international markets, improved transportation systems, and demographic changes. The diagnosis of these diseases is based on parasitological techniques and only a limited number of drugs are currently available for treatment, most of which are unspecific. Therefore, in-depth studies are urgently needed in order to clarify the current epidemiology of these helminth infections and to identify new and specific targets for both effective diagnosis and treatment. In this review, we describe the biology, medical and epidemiological features, and current treatment and diagnostic tools of the main groups of flukes and the corresponding diseases.

Food-borne trematodiases

An estimated 750 million people are at risk of infections with food-borne trematodes, which comprise liver flukes (Clonorchis sinensis, Fasciola gigantica, Fasciola hepatica, Opisthorchis felineus, and Opisthorchis viverrini), lung flukes (Paragonimus spp.), and intestinal flukes (e.g., Echinostoma spp., Fasciolopsis buski, and the heterophyids). Food-borne trematodiases pose a significant public health and economic problem, yet these diseases are often neglected. In this review, we summarize the taxonomy, morphology, and life cycle of food-borne trematodes. Estimates of the at-risk population and number of infections, geographic distribution, history, and ecological features of the major food-borne trematodes are reviewed. We summarize clinical manifestations, patterns of infection, and current means of diagnosis, treatment, and other control options. The changing epidemiological pattern and the rapid growth of aquaculture and food distribution networks are highlighted, as these developments might be associated with an elevated risk of transmission of food-borne trematodiases. Current research needs are emphasized.

Update on eosinophilic meningoencephalitis and its clinical relevance

Eosinophilic meningoencephalitis is caused by a variety of helminthic infections. These worm-specific infections are named after the causative worm genera, the most common being angiostrongyliasis, gnathostomiasis, toxocariasis, cysticercosis, schistosomiasis, baylisascariasis, and paragonimiasis. Worm parasites enter an organism through ingestion of contaminated water or an intermediate host and can eventually affect the central nervous system (CNS). These infections are potentially serious events leading to sequelae or death, and diagnosis depends on currently limited molecular methods. Identification of parasites in fluids and tissues is rarely possible, while images and clinical examinations do not lead to a definitive diagnosis. Treatment usually requires the concomitant administration of corticoids and anthelminthic drugs, yet new compounds and their extensive and detailed clinical evaluation are much needed. Eosinophilia in fluids may be detected in other infectious and noninfectious conditions, such as neoplastic disease, drug use, and prosthesis reactions. Thus, distinctive identification of eosinophils in fluids is a necessary component in the etiologic diagnosis of CNS infections.