A surgical case of inflammatory pseudotumor by hepatic anisakiasis

Anisakiasis is a parasitic infection caused by the ingestion of raw or undercooked seafood infected with Anisakis larvae. It generally affects the gastrointestinal tract, particularly the stomach, but very rare cases have been reported in which infection of the liver leads to the formation of inflammatory pseudotumors. We herein report an extremely rare case of an inflammatory pseudotumor induced by hepatic anisakiasis that was laparoscopically resected for the purpose of both diagnosis and treatment. A 51-year-old woman underwent a routine medical checkup by ultrasound examination, which incidentally detected a 15-mm mass on the surface of S6 of the liver. Because a malignant tumor could not be ruled out on several preoperative imaging studies, laparoscopic partial resection of the liver was performed. Histopathological examination revealed Anisakis larva in the inflammatory pseudotumor, suggesting hepatic anisakiasis. This report describes an extremely rare case of an inflammatory pseudotumor induced by hepatic anisakiasis. Because the preoperative diagnosis could not be obtained by several imaging modalities, laparoscopic liver resection with a sufficient margin might be suitable for diagnosis and treatment of this disease.

Population genetics study of Strongyloides fuelleborni and phylogenetic considerations on primate-infecting species of Strongyloides based on their mitochondrial genome sequences

Strongyloides is a genus of parasitic nematodes of vertebrates comprising approximately 50 documented species, each with various host ranges. Among these, three species (S. stercoralis, S. fuelleborni, and S. cebus) are known to infect primate hosts. S. fuelleborni typically infects non-human primates in the Old World. To complement the existing information on the global genetic structure of this species, we conducted a genotyping study of S. fuelleborni samples collected from rhesus macaques in Myanmar, Japanese macaques in Japan, and some zoo-kept primates. This study identified a novel haplotype group in isolates from the Myanmar rhesus macaques. Subsequently, we obtained the complete or nearly complete mitochondrial genome sequences of S. fuelleborni, S. cebus (Strongyloides of New World monkeys), and S. vituli (Strongyloides of cattle). Phylogenetic analysis based on concatenated mitochondrial protein sequences of various Strongyloides species indicated a close relationship between S. fuelleborni, S. vituli and S. papillosus (Strongyloides in sheep and cattle). S. cebus is quite distantly related to both S. fuelleborni and S. stercoralis, which led to the hypothesis that the three primate Strongyloides species evolved independently as parasites of primates.

Diagnostic value of recombinant nanoluciferase fused Toxoplasma gondii antigens in Luciferase-linked Antibody Capture Assay (LACA) for Toxoplasma infection in pigs

Toxoplasmosis is a widespread protozoan zoonosis. Since ingesting undercooked meat harboring Toxoplasma gondii cyst is considered one of the major transmission routes to humans, the screening of T. gondii in meat-producing animals can reduce the risk of food-borne toxoplasmosis in humans. Among serological diagnostic methods, Luciferase-linked Antibody Capture Assay (LACA) has been found to be a promising platform with high sensitivity and specificity. In this study, we aimed to evaluate recombinant nanoluciferase fused-T. gondii antigens (rNluc-GRA6, rNluc-GRA7, rNluc-GRA8 and rNluc-BAG1) for their potential use in LACA for pigs. As a result, the sensitivity of GRA6-, GRA7-, GRA8- and BAG1-LACA were 70.0%, 80.0%, 80.0% and 30.0% with specificity 87.0%, 81.5%, 74.1% and 50.0%, respectively. The cocktail LACA using a mixture of rNluc-GRA6, rNluc-GRA7 and rNluc-GRA8 indicated higher sensitivity (90.0%) and a similar specificity (96.3%) in comparison with the commercial ELISA kit. Compared to the Dye-Test as a reference test, cocktail LACA showed strong agreement (kappa value=0.811) when we assessed pig sera collected at the slaughterhouse. In addition, we also successfully established the rapid LACA format for the detection of Toxoplasma infection in pigs (called Rapid-LACA) in which the test could be performed within 30 min. In Rapid-LACA, the protein A pre-coated/blocked plates could be preserved at −30°C, 4°C or room temperature conditions for at least two months without compromising on the quality of assay.

Ancylostoma ceylanicum infections in humans in Vietnam

Ancylostoma ceylanicum is recognized as the only zoonotic hookworm species that is able to mature into adult stage in the human intestine. While human infections caused by this hookworm species have been reported from neighboring countries and this hookworm is prevalent in dogs in Vietnam, human infection has never been reported in Vietnam. The present study, therefore, aimed to identify human infections with A. ceylanicum in Vietnam. A total of 526 fecal samples from the residents in Long An Province were collected and the presence of hookworm eggs was detected by the Kato-Katz method. The results indicated that the overall prevalence of human hookworm infection was 85/526 (16.2%). After filter paper culture, 3rd stage larvae were successfully obtained from 48 egg-positive samples. The larvae were identified for their species using semi-nested PCR-RLFP on the cox1 gene. As a result, two hookworm species were confirmed; single species infections with Necator americanus or A. ceylanicum, and mixed infections with both species were found in 47.9%, 31.3%, and 20.8% of the samples, respectively.

First demonstration of Strongyloides parasite from an imported pet meerkat - Possibly a novel species in the stercoralis/procyonis group

Strongyloides is a genus of parasitic nematodes of vertebrates that contains over 50 species, each with a variable host range. A recent molecular phylogenetic analysis on this genus showed that Strongyloides spp. from various carnivore hosts form a strongly supported clade together with Strongyloides stercoralis, a major pathogen of humans and dogs (named the "stercoralis/procyonis group"). In the present study, we obtained DNA sequencing data of Strongyloides sp. isolated from an imported meerkat (Suricata suricatta). Based on the phylogenetic analysis, we considered this a new member of the stercoralis/procyonis group. This study represents the first isolation and molecular characterization of a Strongyloides species from hosts belonging to the family Herpestidae (mongooses and meerkat). However, whether the meerkat serves as a natural host of this Strongyloides species remains to be investigated.

Seroprevalence of toxoplasmosis among reproductive-aged women in Myanmar and evaluation of luciferase immunoprecipitation system assay

BACKGROUNDS

Primary infection with Toxoplasma gondii during pregnancy can pose serious health problems for the fetus. However, the epidemiological status of toxoplasmosis among reproductive-aged population in Myanmar is largely unknown. Although luciferase immunoprecipitation system (LIPS) assays for serodiagnosis of toxoplasmosis was developed mostly using mouse infection model, had not been tested by using field-derived human samples.

METHODS

A total of 251 serum samples were collected from reproductive-aged women, residing in Shwegyin township, Bago region, Myanmar and analyzed with a commercial ELISA kit, as well as in-house LIPS assays.

RESULTS

The overall seroprevalence for Toxoplasma gondii infection by the commercial ELISA was 11.5%. No clear risk factor was identified except for being in the younger age group (15-30 years old). Overall, LIPS assays showed low sensitivity when the commercial ELSA was used as a reference test.

CONCLUSION

We identified the epidemiological situation of toxoplasmosis in some rural communities in Myanmar. The data obtained here will serve as a primary information for the effort to reduce toxoplasmosis in this region. Although looked promising in the previous experiments with mouse infection model, we found that the reported LIPS procedures need further improvements to increase the sensitivities.

Strongyloides stercoralis colitis in a patient positive for human T-cell leukaemia virus with rheumatoid arthritis during an anti-rheumatic therapy: a case report

An elderly woman with rheumatoid arthritis (RA) presented with a chief complaint of abdominal pain and diarrhoea while undergoing treatment with low-dose corticosteroids and abatacept. Endoscopic and histopathological findings revealed manifestations of ulcerative colitis (UC). An intermediate dose of corticosteroids and 5-aminosalicylic acid were administered. Abatacept was discontinued; the anti-TNF biologic, golimumab, was administered for treatment of both RA and UC. However, colitis worsened in response to this therapeutic regimen. Colonoscopy revealed severe mucosal lesions; larvae were detected in samples taken from multiple shallow mucosal ulcers. The patient was diagnosed with Strongyloides stercoralis colitis based on the results of an anti-parasite antibody test and examination of the larval DNA. Furthermore, serology revealed a positive test for antibodies against human T-cell leukaemia virus type 1 (HTLV-1). Immunosuppressive treatment was terminated; ivermectin was administered, which resulted in improvements in colitis symptoms within a few weeks. There are several published reports describing S. stercoralis colitis as a lethal mimic of UC. Corticosteroid and anti-TNF therapies have been reported as among the major risk factors associated with strongyloidiasis in patients with HTLV-1 infection. Therefore, HTLV-1 and Strongyloides infections may be considered in cases of new-onset gastrointestinal symptoms during immunosuppressive therapy, particularly in HTLV-1-endemic regions.

Phylogenetic relationships of Strongyloides species in carnivore hosts

Strongyloides stercoralis is a parasitic nematode and a major pathogen responsible for human strongyloidiasis. The presence of this species in the dog population has led to an interest in studying the phylogenetic relationships among Strongyloides spp. in carnivore hosts. In the present study, Strongyloides spp. from various carnivore hosts (raccoon, Japanese badger, Siberian weasel, raccoon dog, masked palm civet, and domestic cat) were sought. Except for civets, Strongyloides spp. were identified in all host species. Based on 18S rDNA sequences, nine OTUs (operational taxonomy units) were identified. Molecular phylogenetic analyses using 18S28S rDNA and mitochondrial cox1 (cytochrome c oxidase subunit 1) sequences clustered them into two groups. The first group (named the stercoralis/procyonis group) was comprised of six OTUs and occurred in cats, raccoon dogs, raccoons (S. procyonis), Siberian weasels, and Japanese badgers and included S. stercoralis from humans and dogs. The second group (named the planiceps group) was made up of Strongyloides spp. from raccoon dogs (two OTUs) and one OTU from Siberian weasels. Subsequent analysis using almost the full-length nucleotide sequences of protein-coding genes in their mitochondrial genomes placed Strongyloides spp. of cats in a sister taxon position to S. stercoralis, whereas S. procyonis from raccoons was more distantly related to them. The presence of Strongyloides spp. from various carnivore hosts, which are close relatives of S. stercoralis, suggests this group of Strongyloides (the stercoralis/procyonis group) essentially evolved as parasites of carnivores, although more data on Strongyloides spp. from primate hosts are needed.

A novel luciferase-linked antibody capture assay (LACA) for the diagnosis of Toxoplasma gondii infection in chickens

Toxoplasma gondii is an obligate intracellular protozoan parasite that causes the most common parasitic zoonosis worldwide in multiples species of mammals and birds. Although free-range chickens may play a role as an important reservoir for T. gondii, there is no reliable and commercially available diagnostic test for this disease in chickens. In this study, we aimed to develop a novel Luciferase-linked Antibody Capture Assay (LACA) for the serodiagnosis of Toxoplasma infection in chickens. Recombinant nanoluciferase fused-T. gondii dense granule antigen 8 (rNluc-GRA8) was produced and applied to LACA assay as a diagnostic antigen. GRA8-LACA was tested with the sera from uninfected and experimentally infected chickens with T. gondii and other parasitic pathogens and showed unexpectedly high sensitivity (90.5%) and specificity (95.4%). Interestingly, E. coli lysate expressing rNluc-GRA8 could be applied in GRA8-LACA with 85.7% sensitivity and an increased specificity (96.9%) that gave better diagnostic performance compared to conventional ELISA. We applied our diagnostic system to examine 267 free-range chicken sera collected from 12 farms and 100 closed-house broiler chicken sera from local poultry abattoirs. The overall seroprevalence of toxoplasmosis in free-range chickens was 10.9% (95% CI: 10.6%-11.1%), while no positive case was found in broiler chickens. GRA8-LACA could be a useful diagnostic technique for T. gondii infection in chickens. The detection of T. gondii seropositive chickens in this study warns a potential risk of Toxoplasma transmission by the consumption of raw or undercooked chicken meat.

A doublecortin-domain protein of Toxoplasma and its orthologues bind to and modify the structure and organization of tubulin polymers

BACKGROUND

TgDCX is a doublecortin-domain protein associated with the conoid fibers, a set of strongly curved non-tubular tubulin-polymers in Toxoplasma. TgDCX deletion impairs conoid structure and parasite invasion. TgDCX contains two tubulin-binding domains: a partial P25α and the DCX/doublecortin domain. Orthologues are found in apicomplexans and their free-living relatives Chromera and Vitrella.

RESULTS

We report that isolated TgDCX-containing conoid fibers retain their pronounced curvature, but loss of TgDCX destabilizes the fibers. We crystallized and determined the 3D-structure of the DCX-domain, which is similar to those of human doublecortin and well-conserved among TgDCX orthologues. However, the orthologues vary widely in targeting to the conoid in Toxoplasma and in modulating microtubule organization in Xenopus cells. Several orthologues bind to microtubules in Xenopus cells, but only TgDCX generates short, strongly curved microtubule arcs. EM analysis shows microtubules decorated with TgDCX bundled into rafts, often bordered on one edge by a "C"-shaped incomplete tube. A Chromera orthologue closely mimics TgDCX targeting in Toxoplasma and binds to microtubules in Xenopus cells, but does not generate arcs or "C"-shaped tubes, and fails to rescue the defects of the TgDCX-knockout parasite.

CONCLUSIONS

These observations suggest that species-specific features of TgDCX enable it to generate strongly curved tubulin-polymers to support efficient host-cell invasion.

Prevalence and associated risk factors of Strongyloides stercoralis infection in Lower Myanmar

Background

Strongyloidiasis is prevalent in Southeast Asian regions along with other soil-transmitted helminthiases, but only limited present-day data was available for Myanmar.

Methods

A prevalence survey for Strongyloides stercoralis infection was conducted among villagers in rural areas of three townships located in the Lower Myanmar during 2014–2016 by agar plate culture method in combination with specific identification by molecular assays. Risk factors associated with S. stercoralis infection were assessed by analyzing questionnaires obtained from study participants.

Results

Strongyloides stercoralis was identified in 40 out of 703 participants (5.7% overall prevalence). The highest prevalence (14.4%) was observed in Htantabin, while other two communities (Thabaung and Thanlyin) had much lower prevalence (2.2 and 2.5%, respectively). Infection was relatively rare (1.2%) in younger generations under 20 years compared to older generations (9.5%). Even in Htantabin, none of the female residents under age 40 (n = 33) had infection. In adult Htantabin residents, those who answered that they do not wear shoes regularly had an elevated risk of infection (odds ratio = 2.50, 95% confidence interval = 1.03–6.08).

Conclusions

This study showed that there is still an on-going transmission of strongyloidiasis in Lower Myanmar. It is highly desirable that the soil should be free of fecal contamination by improving the management of fecal waste. Meanwhile, health education to promote shoe-wearing would be beneficial to reduce the risk of transmission, especially for those who have frequent and intense contact with soil.

Evaluation of LIPS (luciferase immunoprecipitation system) for serodiagnosis of Toxoplasmosis

Development of reliable, quantitative technologies for serodiagnosis of Toxoplasma gondii infection remains desirable. The luciferase immunoprecipitation system (LIPS) is a relatively simple, highly sensitive, and rapid quantitative immunoassay. The major advantages of this assay over ELISA are a wider dynamic range, shorter overall assay time, and less sample volume. In this study, we aimed to use this method for the serodiagnosis of toxoplasmosis. Recombinant Toxoplasma antigens (dense granule antigens GRA6, GRA7, and GRA8 and bradyzoite antigen BAG1) fused with nanoluciferase (Nluc, a small luciferase enzyme) were expressed in Escherichia coli, purified, and tested in LIPS assays with sera from experimental mice infected with T. gondii and a WHO standard anti-Toxoplasma human immunoglobulin (TOXM). In the experimentally infected mice, LIPS assays detected antibodies against Nluc-GRA6, Nluc-GRA7, and Nluc-GRA8 as early as day 14, whereas antibodies against Nluc-BAG1 remained undetected until day 21 and then showed significant elevation on day 60. In TOXM sera, LIPS assays with each Nluc recombinant protein produced reliable standard curves with a coefficient of determination (R²) of 0.980-0.989 for GRA6, 0.986-0.990 for GRA7, 0.998-0.999 for GRA8, and 0.942-0.987 for BAG1. The detection limits were estimated to be 3.9, 2, 1, and 1 IU/ml for rGRA6, rGRA7, rGRA8, and rBAG1, respectively. The LIPS assay for toxoplasmosis could detect antibodies against T. gondii in the mouse and human sera with a reasonably high sensitivity. We consider the LIPS assay to be a promising alternative tool for screening, diagnosing, and monitoring toxoplasmosis. In particular, detection of antibodies against BAG1 may be useful for a longitudinal seroprevalence study in suspected high-risk areas on the basis of its elevated serum concentration in the chronic phase.

Wuchereria bancrofti infection at four primary schools and surrounding communities with no previous blood surveys in northern Uganda: the prevalence after mass drug administrations and a report on suspected non-filarial endemic elephantiasis

BACKGROUND

A prevalence study of Wuchereria bancrofti infection was carried out in 2014 at 4 study sites in northern Uganda using antigen and microfilaria tests. Each study site consists of a primary school and surrounding communities. These sites are inside the filariasis endemic area and have been covered by mass drug administration under the national elimination programme. However, no prevalence study had been conducted there before the present study. Without information on past and present endemicity levels, our study was meant to be an independent third-party investigation to know the latest filariasis situation.

RESULTS

A total of 982 people including 570 schoolchildren (7-19 years) and 412 community people (7-25 years) were examined, all of them for filarial antigen and 695 for microfilariae. The study revealed that all subjects were negative by both methods.

CONCLUSIONS

It was considered that annual mass drug administrations together with anti-malarial activities such as indoor residual spraying had contributed to the reduction of the filarial infection. However, based on the past data obtained near our study sites, we cannot exclude the possibility that filarial prevalence rates in our study sites were very low or even zero originally. During the study, we encountered several patients with lower leg edema and pachydermic (elephant skin-like), mossy skin lesion of the foot. Judging from clinical features and bare-footed life-style of people in the area, non-filarial elephantiasis, possibly podoconiosis, was suspected. This elephantiasis has been reported in areas where filariasis is not endemic.

Stability and function of a putative microtubule-organizing center in the human parasite Toxoplasma gondii

KinesinA and APR1 maintain the stability of the apical polar ring, a putative organizing center for the 22 cortical microtubules of Toxoplasma. Parasites lacking these two proteins are defective in invasion, motility, secretion, and growth but can still make 22 cortical microtubules, suggesting that ring stability is not tightly coupled to templating.

The organization of the microtubule cytoskeleton is dictated by microtubule nucleators or organizing centers. Toxoplasma gondii, an important human parasite, has an array of 22 regularly spaced cortical microtubules stemming from a hypothesized organizing center, the apical polar ring. Here we examine the functions of the apical polar ring by characterizing two of its components, KinesinA and APR1, and show that its putative role in templating can be separated from its mechanical stability. Parasites that lack both KinesinA and APR1 (ΔkinesinAΔapr1) are capable of generating 22 cortical microtubules. However, the apical polar ring is fragmented in live ΔkinesinAΔapr1 parasites and is undetectable by electron microscopy after detergent extraction. Disintegration of the apical polar ring results in the detachment of groups of microtubules from the apical end of the parasite. These structural defects are linked to a diminished ability of the parasite to move and invade host cells, as well as decreased secretion of effectors important for these processes. Together the findings demonstrate the importance of the structural integrity of the apical polar ring and the microtubule array in the Toxoplasma lytic cycle, which is responsible for massive tissue destruction in acute toxoplasmosis.

Loss of a doublecortin (DCX)-domain protein causes structural defects in a tubulin-based organelle of Toxoplasma gondii and impairs host-cell invasion

The ∼6000 species in phylum Apicomplexa are single-celled obligate intracellular parasites. Their defining characteristic is the apical complex-membranous and cytoskeletal elements at the apical end of the cell that participate in host-cell invasion. The apical complex of Toxoplasma gondii and some other apicomplexans includes a cone-shaped assembly, the conoid, which in T. gondii comprises 14 spirally arranged fibers that are nontubular polymers of tubulin. The tubulin dimers of the conoid fibers make canonical microtubules elsewhere in the same cell, suggesting that nontubulin protein dictates their special arrangement in the conoid fibers. One candidate for this role is TgDCX, which has a doublecortin (DCX) domain and a TPPP/P25-α domain, both of which are known modulators of tubulin polymer structure. Loss of TgDCX radically disrupts the structure of the conoid, severely impairs host-cell invasion, and slows growth. Both the conoid structural defects and the impaired invasion of TgDCX-null parasites are corrected by reintroduction of a TgDCX coding sequence. The nontubular polymeric form of tubulin found in the conoid is not found in the host cell, suggesting that TgDCX may be an attractive target for new parasite-specific chemotherapeutic agents.

Genome-Wide Analyses of Individual Strongyloides stercoralis (Nematoda: Rhabditoidea) Provide Insights into Population Structure and Reproductive Life Cycles

The helminth Strongyloides stercoralis, which is transmitted through soil, infects 30–100 million people worldwide. S. stercoralis reproduces sexually outside the host as well as asexually within the host, which causes a life-long infection. To understand the population structure and transmission patterns of this parasite, we re-sequenced the genomes of 33 individual S. stercoralis nematodes collected in Myanmar (prevalent region) and Japan (non-prevalent region). We utilised a method combining whole genome amplification and next-generation sequencing techniques to detect 298,202 variant positions (0.6% of the genome) compared with the reference genome. Phylogenetic analyses of SNP data revealed an unambiguous geographical separation and sub-populations that correlated with the host geographical origin, particularly for the Myanmar samples. The relatively higher heterozygosity in the genomes of the Japanese samples can possibly be explained by the independent evolution of two haplotypes of diploid genomes through asexual reproduction during the auto-infection cycle, suggesting that analysing heterozygosity is useful and necessary to infer infection history and geographical prevalence.

Strongyloides stercoralis, one of the most neglected helminths causes strongyloidiasis mainly in tropical and subtropical regions worldwide. The parasite’s complex lifecycle includes sexual and asexual reproduction outside and inside the host, respectively. The parasite can also asexually complete a life cycle within the host's body, which is called autoinfection causing life-long infection. In order to investigate the population structure and transmission patterns of this parasite we sequenced individual nematodes isolated from human faeces in Japan and Myanmar, where the parasite is present at low and high frequencies, respectively. Whole genome sequencing of small parasites is generally difficult because the amount of DNA is limiting. However, we overcame this problem by combining whole genome amplification with next-generation sequencing. Sequence comparisons revealed 0.6% of the genome is variable among samples, and the variants showed clear separation by the location of their origin. We found that heterozygosity within the genomes was higher in Japan, which is likely explained by the predominance of asexual reproduction through auto-infection, suggesting that analyses of heterozygosity are required to better understand the history of a population.

The genomic basis of parasitism in the Strongyloides clade of nematodes

Soil-transmitted nematodes, including the Strongyloides genus, cause one of the most prevalent neglected tropical diseases. Here we compare the genomes of four Strongyloides species, including the human pathogen Strongyloides stercoralis, and their close relatives that are facultatively parasitic (Parastrongyloides trichosuri) and free-living (Rhabditophanes sp. KR3021). A significant paralogous expansion of key gene families--families encoding astacin-like and SCP/TAPS proteins--is associated with the evolution of parasitism in this clade. Exploiting the unique Strongyloides life cycle, we compare the transcriptomes of the parasitic and free-living stages and find that these same gene families are upregulated in the parasitic stages, underscoring their role in nematode parasitism.

Paragonimiasis in Japan: a twelve-year retrospective case review (2001-2012)

OBJECTIVE

Paragonimiasis, or lung fluke infection, is a food-borne parasitic disease caused by infection with trematodes belonging to the genus Paragonimus. Although paragonimiasis was once considered successfully controlled in the 1970s, new cases began to emerge in the late 1980s. To apprehend the current-day situation of the re-emergent cases of paragonimiasis in Japan, we conducted a retrospective review of 443 patients who were referred to our laboratory and diagnosed as having paragonimiasis during 2001-2012.

METHODS

Patients were diagnosed as having paragonimiasis based primarily on immunodiagnostic methods in addition to clinical, laboratory, and radiographic findings. Patient data were extracted from consultation sheets from attending physicians and were analyzed.

RESULTS

Majority of the patients were residents of Kyushu Island. However, a substantial number of cases were also from other parts of Japan. Immigrants (mostly from China, Thailand, and Korea) accounted for a quarter of the cases. Native Japanese contracted paragonimiasis by consuming wild boar meat or freshwater crabs, whereas immigrants contracted the infection almost exclusively by consumption of freshwater crabs. Eosinophilia and elevated serum IgE levels were found in around 80% of the patients. Parasite egg detection was documented only in 11.7% of the cases, showing the reliance on serological tests for diagnosing paragonimiasis in current clinical practice.

CONCLUSION

Paragonimiasis remains a public health issue in Japan, and the situation should be closely monitored.

Cutaneous paragonimiasis due to triploid Paragonimus westermani presenting as a non-migratory subcutaneous nodule: a case report

INTRODUCTION

Paragonimiasis is a food-borne infection caused by Paragonimus parasites. The lungs and pleura are the primary sites for the infection; however, ectopic infection can occur in other organs such as skin, liver and brain. It is difficult to make a diagnosis of ectopic paragonimiasis due to an ignorance of, and unfamiliarity with the disease. We report the case of a patient with subcutaneous paragonimiasis diagnosed by histopathological analysis and serological testing.

CASE PRESENTATION

A 39-year-old Chinese immigrant woman presented with a subcutaneous nodule in her left lower back. The nodule was initially suspected of lipoma and she was followed up on without any treatment. However, it gradually indurated and the nodule was resected surgically. A magnetic resonance imaging scan revealed a polycystic lesion with inhomogeneous low or high intensity on T1- or T2-weighted images, respectively. The rim of the lesion was enhanced after contrast enhancement, but the inside did not show high-signal intensity. A histological analysis of the surgically resected specimen revealed variable-sized tubulo-cystic structures. The cyst wall showed a granulomatous change with scant eosinophilic infiltration. A number of parasite ova were observed in the necrotic tissue inside the cysts, and a parasite body with a presumed oral sucker and reproductive organ was also detected, suggesting a trematode infection. A subsequent serological examination showed a positive reaction of her serum to the Paragonimus westermani antigen. No abnormal findings were found on her chest computed tomography scan. The diagnosis of subcutaneous paragonimiasis caused by Paragonimus westermani was made.

CONCLUSIONS

We report a case presenting only as a non-migratory subcutaneous nodule without any pleuropulmonary lesion, which was initially suspected of lipoma but denied by magnetic resonance imaging scan results. The case was subsequently diagnosed as subcutaneous paragonimiasis from the results of histopathological analysis and serological testing.

Efficient de novo assembly of highly heterozygous genomes from whole-genome shotgun short reads

Although many de novo genome assembly projects have recently been conducted using high-throughput sequencers, assembling highly heterozygous diploid genomes is a substantial challenge due to the increased complexity of the de Bruijn graph structure predominantly used. To address the increasing demand for sequencing of nonmodel and/or wild-type samples, in most cases inbred lines or fosmid-based hierarchical sequencing methods are used to overcome such problems. However, these methods are costly and time consuming, forfeiting the advantages of massive parallel sequencing. Here, we describe a novel de novo assembler, Platanus, that can effectively manage high-throughput data from heterozygous samples. Platanus assembles DNA fragments (reads) into contigs by constructing de Bruijn graphs with automatically optimized k-mer sizes followed by the scaffolding of contigs based on paired-end information. The complicated graph structures that result from the heterozygosity are simplified during not only the contig assembly step but also the scaffolding step. We evaluated the assembly results on eukaryotic samples with various levels of heterozygosity. Compared with other assemblers, Platanus yields assembly results that have a larger scaffold NG50 length without any accompanying loss of accuracy in both simulated and real data. In addition, Platanus recorded the largest scaffold NG50 values for two of the three low-heterozygosity species used in the de novo assembly contest, Assemblathon 2. Platanus therefore provides a novel and efficient approach for the assembly of gigabase-sized highly heterozygous genomes and is an attractive alternative to the existing assemblers designed for genomes of lower heterozygosity.

Identification of a bacteria-like ferrochelatase in Strongyloides venezuelensis, an animal parasitic nematode

Heme is an essential molecule for vast majority of organisms serving as a prosthetic group for various hemoproteins. Although most organisms synthesize heme from 5-aminolevulinic acid through a conserved heme biosynthetic pathway composed of seven consecutive enzymatic reactions, nematodes are known to be natural heme auxotrophs. The completely sequenced Caenorhabditis elegans genome, for example, lacks all seven genes for heme biosynthesis. However, genome/transcriptome sequencing of Strongyloides venezuelensis, an important model nematode species for studying human strongyloidiasis, indicated the presence of a gene for ferrochelatase (FeCH), which catalyzes the terminal step of heme biosynthesis, whereas the other six heme biosynthesis genes are apparently missing. Phylogenetic analyses indicated that nematode FeCH genes, including that of S. venezuelensis (SvFeCH) have a fundamentally different evolutionally origin from the FeCH genes of non-nematode metazoa. Although all non-nematode metazoan FeCH genes appear to be inherited vertically from an ancestral opisthokont, nematode FeCH may have been acquired from an alpha-proteobacterium, horizontally. The identified SvFeCH sequence was found to function as FeCH as expected based on both in vitro chelatase assays using recombinant SvFeCH and in vivo complementation experiments using an FeCH-deficient strain of Escherichia coli. Messenger RNA expression levels during the S. venezuelensis lifecycle were examined by real-time RT-PCR. SvFeCH mRNA was expressed at all the stages examined with a marked reduction at the infective third-stage larvae. Our study demonstrates the presence of a bacteria-like FeCH gene in the S. venezuelensis genome. It appeared that S. venezuelensis and some other animal parasitic nematodes reacquired the once-lost FeCH gene. Although the underlying evolutionary pressures that necessitated this reacquisition remain to be investigated, it is interesting that the presence of FeCH genes in the absence of other heme biosynthesis genes has been reported only for animal pathogens, and this finding may be related to nutritional availability in animal hosts.

Transcriptomic analysis of four developmental stages of Strongyloides venezuelensis

Strongyloides venezuelensis is one of some 50 species of genus Strongyloides, obligate gastrointestinal parasites of vertebrates, responsible for strongyloidiasis in humans and other domestic/companion animals. Although S. venezuelensis has been widely used as a model species for studying human/animal strongyloidiasis, the sequence information for this species has been quite limited. To create a more comprehensive catalogue of expressed genes for identification of genes potentially involved in animal parasitism, we conducted a de novo sequencing analysis of the transcriptomes from four developmental stages of S. venezuelensis, using a Roche 454 GS FLX Titanium pyrosequencing platform. A total of 14,573 contigs were produced after de novo assemblies of over 2 million sequencing reads and formed a dataset "Vene454". BLAST homology search of Vene454 against proteome and transcriptome data from other animal-parasitic and non-animal-parasitic nematode species revealed several interesting genes, which may be potentially related to animal parasitism, including nicotinamide phosphoribosyltransferase and ferrochelatase. The Vene454 dataset analysis also enabled us to identify transcripts that are specifically enriched in each developmental stage. This work represents the first large-scale transcriptome analysis of S. venezuelensis and the first study to examine the transcriptome of the lung L3 developmental stage of any Strongyloides species. The results not only will serve as valuable resources for future functional genomics analyses to understand the molecular aspects of animal parasitism, but also will provide essential information for ongoing whole genome sequencing efforts in this species.

A novel C-type lectin identified by EST analysis in tissue migratory larvae of Ascaris suum

C-type lectins (CTLs) are a group of proteins which bind to carbohydrate epitopes in the presence of Ca(2+), which have been described in a wide range of species. In this study, a cDNA sequence coding a putative CTL has been identified from the cDNA library constructed from the pig round worm Ascaris suum lung L3 (LL3) larvae, which was designated as A. suum C-type lectin-1 (As-CTL-1). The 510 nucleotide open reading frame of As-CTL-1 cDNA encoded the predicted 169 amino acid protein including a putative signal peptide of 23 residues and C-type lectin/C-type lectin-like domain (CLECT) at residue 26 to 167. As-CTL-1 was most similar to Toxocara canis C-type lectin-1 and 4 (Tc-CTL-1 and 4), and highly homologous to namatode CTLs and mammalian CTLs as well, such as human C-type lectin domain family 4 member G (CLECG4). In addition, As-CTL-1 was strongly expressed in tissue migrating LL3 and the L4 larvae, which were developmental larvae stages within the mammalian host. These results suggest that A. suum larvae might utilize As-CTL-1 to avoid pathogen recognition mechanisms in mammalian hosts due to it is similarity to host immune cell receptors.

Transcripts analysis of infective larvae of an intestinal nematode, Strongyloides venezuelensis

Free-living infective larvae of Strongyloides nematodes fulfill a number of requirements for the successful infection. They need to endure a long wait in harsh environmental conditions, like temperature, salinity, and pH, which might change drastically from time to time. Infective larvae also have to deal with pathogens and potentially hazardous free-living microbes in the environment. In addition, infective larvae must recognize the adequate host properly, and start skin penetration as quickly as possible. All these tasks are essentially important for the survival of Strongyloides nematodes, however, our knowledge is extremely limited in any one of these aspects. In order to understand how Strongyloides infective larvae meet these requirements, we examined transcripts of infective larvae by randomly sequencing cDNA clones constructed from S. venezuelensis infective larvae. After assembling successfully sequenced clones, we obtained 162 unique singletons and contigs, of which 84 had been significantly annotated. Annotated genes included those for respiratory enzymes, heat-shock proteins, neuromuscular proteins, proteases, and immunodominant antigens. Genes for lipase, small heat-shock protein, globin-like protein and cytochrome c oxidase were most abundantly transcribed, though genes of unknown functions were also abundantly transcribed. There were no hits found against NCBI or NEMABASE4 for 37 (22.3%) EST out of the total 162 EST. Although most of the transcripts were not infective larva-specific, the expression of respiration related proteins was most actively transcribed in the infective larva stage. The expression of astacin-like metalloprotease, small heat-shock protein, S. stercoralis L3Nie antigen homologue, and one unannotated and 2 novel genes was highly specific for the infective larva stage.

Molecular complexity of sexual development and gene regulation in Plasmodium falciparum

The malaria parasite, Plasmodium falciparum, has a complex life cycle which alternates between the vertebrate host and the invertebrate vector. Various morphological changes as well as stage-specific transcripts and gene expression profiles that accompany parasite's asexual and sexual life cycle suggest that gene regulation is crucial for the parasite's continual adaptations to survive the changing environments as well as for pathogenesis. Development of sexual stages is crucial for malaria transmission and relatively little is known about the role of specific gene products during asexual to sexual differentiation and further development. Therefore, in order to have a full understanding of the biology of the malaria parasite, gene regulation on a genome-wide global level must be understood, an area remaining to be elucidated in P. falciparum. Parasite features, such as A-T bias, difficulties in cloning, labor-intensive culture and purification of specific stages of the parasite, all contribute to the difficulties to investigate many aspects of parasite biology. However, despite these challenges, limited studies have revealed a number of parallelisms with eukaryotic transcription. For example, the parasite's genes are organised in a similar fashion, contain promoter elements and upstream activation sequences, as shown by structural searches and functional assays, and some of the basal machinery and general transcription factors have been found in Plasmodium. The completion of the full genome sequence of P. falciparum and other species of Plasmodium has resulted in the search for specific transcription factors through genome mining. Although genome mining may identify some of the factors, search for these factors solely by primary sequence homology would result in a non-comprehensive list for transcription factors present in the genome. Here, we present further discussion on putative transcription factors like activities detected in the asexual and sexual stages of P. falciparum.

Effects of dipyridamole on Plasmodium falciparum-infected erythrocytes

This study assessed the antimalarial activity of dipyridamole, a well-known vasodilator and inhibitor of platelet aggregation. Dipyridamole was effective against all of the erythrocytic stages such as rings, trophozoites and schizonts, and induced ultrastructural changes during the transition from trophozoite to schizont in vitro. Merozoites were also inhibited from invading dipyridamole-treated erythrocytes. It seems that dipyridamole binds to the erythrocyte membrane blocking the receptors for the merozoite. The 50% inhibitory concentration (IC(50)) of dipyridamole against Plasmodium falciparum infection was 30 nM. The IC(50) of chloroquine decreased from 97.0 nM to 13.7 nM when combined with dipyridamole (0.1 nM). Therefore, we suggest that dipyridamole has antiplasmodial activity due to its ability to arrest parasite development and by inhibiting merozoite invasion of the erythrocytes. Chloroquine activity against P. falciparum is also enhanced by the addition of dipyridamole. Treatment with a combination of chloroquine and dipyridamole may lead to a more effective treatment for chloroquine-resistant strains of P. falciparum.

Association of a determinant on mouse chromosome 18 with experimental severe Plasmodium berghei malaria

Experimental severe malaria (ESM; also known as experimental cerebral malaria) is an acute lethal syndrome caused by infection with Plasmodium berghei ANKA and associated with coma and other neurological manifestations in mice. Various inbred strains of mice exhibit differences in susceptibility to the development of ESM. For example, C57BL/6 mice are highly susceptible and DBA/2 mice are relatively resistant. We report here the results of a genomewide scan for host genomic regions that control resistance to ESM in DBA/2 mice using an F(2) intercross population of susceptible and resistant strains. A region of mid-chromosome 18 was found to be a major determinant of resistance to ESM.

Surface charge of Plasmodium falciparum merozoites as revealed by atomic force microscopy with surface potential spectroscopy

Electric charges on the surface of Plasmodium falciparum merozoites and erythrocytes were investigated by atomic force microscopy with surface potential spectroscopy. The apical end of merozoites was positively charged, while the entire erythrocyte surface was negatively charged. Transmission electron microscopy also demonstrated that negatively charged nanogold particles attached to the apical end of merozoites, and cationized ferritin particles attached to the entire surface of the erythrocyte. This indicates that the surface charge at the apical end of the merozoite may play an important role in invasion of the erythrocyte.

Invasive forms of Toxoplasma gondii, Leishmania amazonensis and Trypanosoma cruzi have a positive charge at their contact site with host cells

We examined the surface charges of invasive forms of Toxoplasma gondii, Leishmania amazonensis, and Trypanosoma cruzi by atomic force microscopy and surface potential spectroscopy. We found that the specific part of the protozoan which makes initial contact with the host cell is positively charged. This indicates that the positive charge at the site of contact facilitates binding of the invasive protozoan to negatively charged host cells.

CR1 density polymorphism on erythrocytes of falciparum malaria patients in Thailand

Complement receptor type 1 (CR1) on erythrocytes shows an inherited numerical polymorphism which correlates with a HindIII-RFLP (restriction fragment length polymorphism) of the CR1 gene in various populations. To investigate the relationship between CR1 density polymorphism and disease severity, we typed 185 Thai patients with acute falciparum malaria (55 severe and 130 uncomplicated) for their genotypes of this polymorphism. The level of expression of erythrocyte CR1 from 42 randomly selected patients was measured by enzyme-linked immunosorbent assay (ELISA). We observed a significantly higher frequency of homozygotes of the CR1 low density allele (LL) among the severe group as compared to the uncomplicated group (P = 0.005). CR1 expression on erythrocytes from patients with the LL genotype was significantly lower than homozygotes with the high density allele (HH) (P < 0.0001) and heterozygotes (HL) (P = 0.013). The results suggest that a genetically-determined low CR1 density on erythrocytes may be a risk factor for developing a more severe form of malaria in Thai subjects.