Strongyloides hyperinfection syndrome: an emerging global infectious disease

Update on immunologic and molecular diagnosis of human strongyloidiasis

Human strongyloidiasis is an intestinal parasitosis that may affect 100 million individuals. However, the prevalence rates of this infection may represent smaller values than the actual data, mainly due to difficulties in its diagnosis. The aim of this study was to update the immunological and molecular methods applied to the diagnosis of human strongyloidiasis. There is a great diversity of techniques used in the diagnosis of this parasitosis, such as immunofluorescence antibody test (IFAT), enzyme-linked immunosorbent assay (ELISA), immunoblotting, luciferase immunoprecipitation system (LIPS), dispstick and polymerase chain reaction (PCR), all with advantages and disadvantages, and with unique features for specific purposes. Considering the magnitude of strongyloidiasis and the importance of early diagnosis, due to the possibility of chronicity and hyperinfection, this study analyzes the different methods currently employed, and demonstrates the necessity of developing innovative methodologies, which also maintain diagnostic accuracy, particularly for regions with limited technological resources.

The expression and activity of 5-LOX in the large intestine of horses harbouring encysted cyathostomin larvae

Leukotrienes are products of the arachidonic acid metabolism and act as potent inflammatory mediators modulating the immune response and various physiological processes. This study evaluated the expression and activity of 5-lipoxygenase (5-LOX), the enzyme that catalyzes the first two steps in the biosynthesis of leukotrienes, in horses infected by larval cyathostomins. Tissue samples from dorsal and ventral colon, and from the cecum were collected from 16 horses slaughtered for human consumption. Samples were analyzed to estimate the burdens of encysted cyathostomin larvae and adult luminal stages, and then processed for the evaluation of biochemical parameters. No significant differences were found in the protein expression and enzymatic activity of 5-LOX between animals harbouring only adult parasites and negative horses. The protein expression and enzyme activity of 5-LOX were significantly higher in horses harbouring encysted larvae in comparison with horses free of encysted larvae. Although preliminary, these results indicate that 5-LOX is an important mediator in the course of horse cyathostominosis and further studies are warranted to unveil the possible role this enzyme plays in the pathogenesis of horse cyathostominosis, and its potential as a diagnostic marker.

High prevalence and spatial distribution of Strongyloides stercoralis in rural Cambodia

Background

The threadworm, Strongyloides stercoralis, endemic in tropical and temperate climates, is a neglected tropical disease. Its diagnosis requires specific methods, and accurate information on its geographic distribution and global burden are lacking. We predicted prevalence, using Bayesian geostatistical modeling, and determined risk factors in northern Cambodia.

Methods

From February to June 2010, we performed a cross-sectional study among 2,396 participants from 60 villages in Preah Vihear Province, northern Cambodia. Two stool specimens per participant were examined using Koga agar plate culture and the Baermann method for detecting S. stercoralis infection. Environmental data was linked to parasitological and questionnaire data by location. Bayesian mixed logistic models were used to explore the spatial correlation of S. stercoralis infection risk. Bayesian Kriging was employed to predict risk at non-surveyed locations.

Principal Findings

Of the 2,396 participants, 44.7% were infected with S. stercoralis. Of 1,071 strongyloidiasis cases, 339 (31.6%) were among schoolchildren and 425 (39.7%) were found in individuals under 16 years. The incidence of S. stercoralis infection statistically increased with age. Infection among male participants was significantly higher than among females (OR: 1.7; 95% CI: 1.4–2.0; P<0.001). Participants who defecated in latrines were infected significantly less than those who did not (OR: 0.6; 95% CI: 0.4–0.8; P = 0.001). Strongyloidiasis cases would be reduced by 39% if all participants defecated in latrines. Incidence of S. stercoralis infections did not show a strong tendency toward spatial clustering in this province. The risk of infection significantly decreased with increasing rainfall and soil organic carbon content, and increased in areas with rice fields.

Conclusions/Significance

Prevalence of S. stercoralis in rural Cambodia is very high and school-aged children and adults over 45 years were the most at risk for infection. Lack of access to adequate treatment for chronic uncomplicated strongyloidiasis is an urgent issue in Cambodia. We would expect to see similar prevalence rates elsewhere in Southeast Asia and other tropical resource poor countries.

Data on the prevalence and distribution of Strongyloides stercoralis (threadworm) is scarce in many resource-poor countries. We carried out a cross-sectional study during the dry season among 2,396 rural Cambodians of all ages. We used a rigorous diagnostic approach, involving two stool samples per person and two examination techniques, namely, Koga agar plate culture and the Baermann method. We predicted the spatial distribution of S. stercoralis using Bayesian Kriging analysis. Almost half of the participants (44.7%) were infected with S. stercoralis. Of the S. stercoralis cases, 39.7% involved participants under 16 years old. S. stercoralis infection prevalence was significantly higher in males than in females. Participants younger than 10 years old had a lower risk of infection than did older participants. Furthermore, our study showed that toilet use could prevent threadworm infections by 39%. Infection prevalence in the province was negatively associated with rainfall and soil organic content and positively associated with land covered by rice fields. We conclude that access to adequate treatment for S. stercoralis must be addressed in Cambodia. Infection prevalence is likely to be similar in other countries of the region and the developing world.

Conventional PCR for molecular diagnosis of human strongyloidiasis

Strongyloidiasis is frequently asymptomatic and diagnosis of latent infection is difficult due to limitations of current parasitological and serological methods. This study aimed to verify the use of conventional polymerase chain reaction (PCR) assay for molecular diagnosis of Strongyloides stercoralis infection. Fresh stool samples were obtained from 103 individuals: 33 S. stercoralis positive, 30 positive for other parasites and 40 negative for parasitological methods. These samples were examined by the Lutz, Rugai and agar plate culture methods and conventional PCR assay. Two sets of primers (S. stercoralis species-specific and genus-specific sets), located in the 18S ribosomal RNA gene, were used for PCR. Of the 33 samples positive for S. stercoralis by parasitological methods, 28 (84.8%) were also detected by PCR assay using species-specific primers and 26 (78.8%) using genus-specific primers. Among the stool samples negative by parasitological methods, seven (17.5%) were positive by PCR using species-specific primers and two (5.0%) using genus-specific primers. In conclusion, the conventional PCR assay described in this study using a species-specific primer pair provided a molecular method for S. stercoralis diagnosis in human stool samples.

Comparison of three immunoassays for detection of antibodies to Strongyloides stercoralis

Due to the limited sensitivities of stool-based microscopy and/or culture techniques for Strongyloides stercoralis, the detection of antibodies to this intestinal nematode is relied upon as a surrogate for determining exposure status or making a diagnosis of S. stercoralis infection. Here, we evaluated three immunoassays, including the recently released InBios Strongy Detect IgG enzyme-linked immunosorbent assay (ELISA) (InBios International, Inc., Seattle, WA), the SciMedx Strongyloides serology microwell ELISA (SciMedx Corporation, Denville, NJ), and the luciferase immunoprecipitation system (LIPS) assay performed at the National Institutes of Health (NIH), for their detection of IgG antibodies to S. stercoralis. A total of 101 retrospective serum samples, previously submitted for routine S. stercoralis antibody detection using the SciMedx assay, were also evaluated by the InBios and LIPS assays. The qualitative results from each assay were compared using a Venn diagram analysis, to the consensus result among the three assays, and each ELISA was also evaluated using the LIPS assay as the reference standard. By Venn diagram analysis, 65% (66/101) of the samples demonstrated perfect agreement by all three assays. Also, the numbers of samples considered positive or negative by a single method were similar. Compared to the consensus result, the overall percent agreement of the InBios, SciMedx, and LIPS assays were comparable at 87.1%, 84.2%, and 89.1%, respectively. Finally, the two ELISAs performed analogously but demonstrated only moderate agreement (kappa coefficient for the two assays, 0.53) with the LIPS assay. Collectively, while the two commercially available ELISAs perform equivalently, neither should be used independently of clinical evaluation to diagnose strongyloidiasis.

Diagnostic accuracy of Kato-Katz, FLOTAC, Baermann, and PCR methods for the detection of light-intensity hookworm and Strongyloides stercoralis infections in Tanzania

Sensitive diagnostic tools are crucial for an accurate assessment of helminth infections in low-endemicity areas. We examined stool samples from Tanzanian individuals and compared the diagnostic accuracy of a real-time polymerase chain reaction (PCR) with the FLOTAC technique and the Kato-Katz method for hookworm and the Baermann method for Strongyloides stercoralis detection. Only FLOTAC had a higher sensitivity than the Kato-Katz method for hookworm diagnosis; the sensitivities of PCR and the Kato-Katz method were equal. PCR had a very low sensitivity for S. stercoralis detection. The cycle threshold values of the PCR were negatively correlated with the logarithm of hookworm egg and S. stercoralis larvae counts. The median larvae count was significantly lower in PCR false negatives than true positives. All methods failed to detect very low-intensity infections. New diagnostic approaches are needed for monitoring of progressing helminth control programs, confirmation of elimination, or surveillance of disease recrudescence.

Development of free-living stages of Strongyloides ratti under different temperature conditions

It is well known that the Strongyloides species have two different developmental courses-direct and indirect development-and selection of these courses is affected by various environmental factors. This study examined the effect of temperature on the development of first-stage larvae (L1s) of Strongyloides ratti, to clarify how larvae adapt and survive at unsuitable temperatures. It was revealed that L1s cultured at 4 or 10 °C for 120 h could not develop because of growth arrest or delay. However, L1s could develop after transfer to culture at 25 °C for 48 h. Although larvae cultured at 25 °C take indirect development, larvae subjected to low-temperature stimulation (at 4 or 10 °C) take direct development into infective third-stage larvae (L3s), and only 1 min of low-temperature stimulation was sufficient to induce direct development. Morphological study of low-temperature-stimulated L3s revealed that those stimulated at 4 °C (L3-4) showed less development, but those stimulated at 10 °C (L3-10) developed as well as the control (no low-temperature stimulation). Furthermore, we revealed that L3-10 showed similar infectivity to the control when they were injected subcutaneously into rats as the final host, which indicated that L3-10 grew normally. We conclude that S. ratti has a survival strategy of growth arrest or delay if excreted in cold conditions. Moreover, even if they start development after transfer to suitable conditions, they memorize low-temperature stimulation, which leads them to direct development thereafter so that they can immediately infect the final host.

Seroprevalence of Schistosomiasis and Strongyloides infection in HIV-infected patients from endemic areas attending a European infectious diseases clinic

Background

Although the Centres for disease Control and Prevention (CDC) recommends empiric treatment for schistosomiasis and strongyloidiasis (prevalent but treatable parasitic infections) in some refugee groups it is unclear if these guidelines should be extended to non-refugee immigrants from endemic areas. We aimed to assess seroprevalence of, and risk factors for, positive schistosomiasis and strongyloides serology in HIV-infected patients from endemic areas attending a European Infectious Diseases clinic.

Methods

In a prospective cohort study, HIV-infected patients from helminth endemic areas underwent clinical assessment and blood draw for schistosomiasis and strongyloides serology, routine haematology and inflammatory markers (ESR and CRP). Between-group differences were analyzed by Wilcoxin Signed Rank and Fisher’s t tests as appropriate.

Results

Ninety HIV-infected patients (mean [standard deviation (SD)] age 34 [6] years, 29% male) were recruited from May 2008 to June 2009. Nine (10%) subjects tested positive for helminth infections. Seven tested positive for schistosomiasis (8%) while two tested positive for strongyloides (2%). Seropositive subjects were more likely to have higher eosinophil counts (mean [SD]) (0.3 [0.3] vs. 0.15 [0.2] x10³cells/cm, P = 0.021) with a trend towards lower CD4+ T-cell counts (mean [SD]) (280 [218] vs. 395 [217] cells/mm³, P = 0.08).

Conclusion

The high prevalence of helminth infections (10%) in asymptomatic HIV infected adults identified in this study supports routine screening of immigrants from helminth endemic areas or with exposure history.

Strongyloides stercoralis: Global Distribution and Risk Factors

BACKGROUND

The soil-transmitted threadworm, Strongyloides stercoralis, is one of the most neglected among the so-called neglected tropical diseases (NTDs). We reviewed studies of the last 20 years on S. stercoralis's global prevalence in general populations and risk groups.

METHODS/PRINCIPAL FINDINGS

A literature search was performed in PubMed for articles published between January 1989 and October 2011. Articles presenting information on infection prevalence were included. A Bayesian meta-analysis was carried out to obtain country-specific prevalence estimates and to compare disease odds ratios in different risk groups taking into account the sensitivities of the diagnostic methods applied. A total of 354 studies from 78 countries were included for the prevalence calculations, 194 (62.4%) were community-based studies, 121 (34.2%) were hospital-based studies and 39 (11.0%) were studies on refugees and immigrants. World maps with country data are provided. In numerous African, Asian and South-American resource-poor countries, information on S. stercoralis is lacking. The meta-analysis showed an association between HIV-infection/alcoholism and S. stercoralis infection (OR: 2.17 BCI: 1.18-4.01; OR: 6.69; BCI: 1.47-33.8), respectively.

CONCLUSIONS

Our findings show high infection prevalence rates in the general population in selected countries and geographical regions. S. stercoralis infection is prominent in several risk groups. Adequate information on the prevalence is still lacking from many countries. However, current information underscore that S. stercoralis must not be neglected. Further assessments in socio-economic and ecological settings are needed and integration into global helminth control is warranted.

Strongyloides stercoralis, the hidden worm. Epidemiological and clinical characteristics of 70 cases diagnosed in the North Metropolitan Area of Barcelona, Spain, 2003-2012

BACKGROUND

The nematode Strongyloides stercoralis has a very particular autoinfection life-cycle which leads to chronic infections remaining undetected for decades. However, hyperinfection can occur in patients receiving immunotherapy resulting in high mortality rates. The main objective of this study was to assess the results of a 10-year multicenter surveillance program performed in an area with dense immigration in Barcelona, Spain.

METHODS

From January 2003 to December 2012, all individuals with Strongyloides stercoralis infection attending the four centers with diagnostic capability in the North Metropolitan area of Barcelona were recorded.

RESULTS

The annual detection rate was 0.2 new diagnosed cases x10 000 inhabitants/year and 1 case x10 000 immigrants/year. Many patients were immigrants (63; 90.0%), asymptomatic (45; 64.3%) and with a high eosinophil count (63; 90.0%). Immunosuppression was present in 11 (15.7%) patients, among whom two (2.8%) cases of disseminated hyperinfection were recorded. Ivermectin was prescribed in 45 (76.3%) and albendazole in 14 (23.7%). Following treatment seven patients (11.9%) receiving albendazole presented relapse, that is, albendazole failed to clear the parasite in 50% of these drug-treated patients (p < 0.001).

CONCLUSIONS

During the study period, 90% of the cases of Strongyloides stercoralis diagnosed could be considered as imported by immigrants, most being asymptomatic and with eosinophilia. The infection is probably largely underestimated and population-based studies are needed to determine its true prevalence. Meanwhile, diagnosis must be based on active investigation of the helminth (serology and feces culture), especially in immunocompromised patients. The implementation of pre-immunosuppression protocols with the aim of identifying Strongyloides stercoralis is encouraged with empirical treatment with ivermectin being recommended in sites without diagnostic facilities.

Evaluation of real-time PCR for Strongyloides stercoralis and hookworm as diagnostic tool in asymptomatic schoolchildren in Cambodia

Diagnosis of soil-transmitted helminths such as Strongyloides stercoralis and hookworms (Ancylostoma duodenale and Necator americanus) is challenging due to irregular larval and egg output in infected individuals and insensitive conventional diagnostic procedures. Sensitive novel real-time PCR assays have been developed. Our study aimed to evaluate the real-time PCR assays as a diagnostic tool for detection of Strongyloides spp. and hookworms in a random stool sample of 218 asymptomatic schoolchildren in Cambodia. Overall prevalence of 17.4% (38/218) and 34.9% (76/218) were determined by real-time PCR for S. stercoralis and hookworms, respectively. Sensitivity and specificity of S. stercoralis specific real-time PCR as compared to the combination of Baermann/Koga Agar as gold standard were 88.9% and 92.7%, respectively. For hookworm specific real-time PCR a sensitivity of 78.9% and specificity of 78.9% were calculated. Co-infections were detectable by PCR in 12.8% (28/218) of individuals. S. stercoralis real-time PCR applied in asymptomatic cases showed a lower sensitivity compared to studies undertaken with symptomatic patients with the same molecular tool, yet it proved to be a valid supplement in the diagnosis of STH infection in Cambodia.

Strongyloidiasis and infective dermatitis alter human T lymphotropic virus-1 clonality in vivo

Human T-lymphotropic Virus-1 (HTLV-1) is a retrovirus that persists lifelong by driving clonal proliferation of infected T-cells. HTLV-1 causes a neuroinflammatory disease and adult T-cell leukemia/lymphoma. Strongyloidiasis, a gastrointestinal infection by the helminth Strongyloides stercoralis, and Infective Dermatitis associated with HTLV-1 (IDH), appear to be risk factors for the development of HTLV-1 related diseases. We used high-throughput sequencing to map and quantify the insertion sites of the provirus in order to monitor the clonality of the HTLV-1-infected T-cell population (i.e. the number of distinct clones and abundance of each clone). A newly developed biodiversity estimator called “DivE” was used to estimate the total number of clones in the blood. We found that the major determinant of proviral load in all subjects without leukemia/lymphoma was the total number of HTLV-1-infected clones. Nevertheless, the significantly higher proviral load in patients with strongyloidiasis or IDH was due to an increase in the mean clone abundance, not to an increase in the number of infected clones. These patients appear to be less capable of restricting clone abundance than those with HTLV-1 alone. In patients co-infected with Strongyloides there was an increased degree of oligoclonal expansion and a higher rate of turnover (i.e. appearance and disappearance) of HTLV-1-infected clones. In Strongyloides co-infected patients and those with IDH, proliferation of the most abundant HTLV-1⁺ T-cell clones is independent of the genomic environment of the provirus, in sharp contrast to patients with HTLV-1 infection alone. This implies that new selection forces are driving oligoclonal proliferation in Strongyloides co-infection and IDH. We conclude that strongyloidiasis and IDH increase the risk of development of HTLV-1-associated diseases by increasing the rate of infection of new clones and the abundance of existing HTLV-1⁺ clones.

HTLV-1 is a human retrovirus estimated to infect 20 million people world-wide and is causing in a small proportion of the infected individuals an inflammatory disease or a leukemia/lymphoma. HTLV-1 persists lifelong by driving clonal proliferation of infected T-cells. Strongyloidiasis, a gastrointestinal infection by an helminth (Strongyloides stercoralis) and Infective Dermatitis associated with HTLV-1 (IDH), a skin inflammation with bacterial infection, appear to increase the risk of developing HTLV-1-related diseases. It is well known that the chance of developing HTLV-1-related diseases increases with the number of cells infected by the virus (also called proviral load). It is also known that HTLV-1-infected individuals co-infected by Strongyloides or affected by IDH have a higher proviral load, but the mechanism is still unclear. Consequently, the aim of this study was to test if co-infection increases the total number and/or the abundance (or size) of HTLV-1-infected T-cell clones. We have shown that the significantly increased proviral load in HTLV-1-infected individuals with IDH or strongyloidiasis is due to an increase in the mean clone abundance (bigger clones), not to an increase in the number of infected clones. These patients appear to be less capable of restricting clone abundance than those with HTLV-1 alone.

Parasitic disease screening among HIV patients from endemic countries in a Toronto clinic

BACKGROUND

Many North American-based HIV patients originate from parasitic disease-endemic regions. Strongyloidiasis, schistosomiasis and filariasis are important due to their wide distribution and potential for severe morbidity.

OBJECTIVES

To determine the prevalence, as determined by serological screening, of strongyloidiasis, schistosomiasis and filariasis among patients in an HIV-focused, primary care practice in Toronto, Ontario. A secondary objective was to determine factors associated with positive serological screens.

METHODS

A retrospective review of electronic patient records was conducted. Results of serological screens for parasites and relevant laboratory data were collected.

RESULTS

Ninety-seven patients were identified. The patients' mean CD4(+) count was 0.45×10(9)/L, median viral load was undetectable and 68% were on highly active antiretroviral therapy (HAART). Most originated from Africa (37%) and South America (35%). Of the 97 patients, 10.4% and 8.3% had positive or equivocal screening results for strongyloidiasis, respectively, 7.4% and 4.2% had positive or equivocal screening results for schistosomiasis and 5.5% and 6.8% had positive or equivocal screens for filariasis. Persons with positive parasitic serologies were more often female (28% versus 9%, P=0.03), younger in age (36 versus 43 years of age, P<0.01), had been in Canada for a shorter duration (5 versus 12 years, P<0.0001) and had a higher viral load (10,990 copies/mL versus <50 copies/mL, P <0.001). All patients were asymptomatic. Eosinophilia was not associated with positive screening results.

CONCLUSIONS

Using symptoms and eosinophilia to identify parasitic infection was not reliable. Screening for strongyloidiasis and schistosomiasis among patients with HIV from parasite-endemic countries is simple and benign, and may prevent future complications. The clinical benefits of screening for filariasis require further elucidation, but this practice appears to be the least warranted.

BACKGROUND

Many North American-based HIV patients originate from parasitic disease-endemic regions. Strongyloidiasis, schistosomiasis and filariasis are important due to their wide distribution and potential for severe morbidity.

OBJECTIVES

To determine the prevalence, as determined by serological screening, of strongyloidiasis, schistosomiasis and filariasis among patients in an HIV-focused, primary care practice in Toronto, Ontario. A secondary objective was to determine factors associated with positive serological screens.

METHODS

A retrospective review of electronic patient records was conducted. Results of serological screens for parasites and relevant laboratory data were collected.

RESULTS

Ninety-seven patients were identified. The patients’ mean CD4⁺ count was 0.45×10⁹/L, median viral load was undetectable and 68% were on highly active antiretroviral therapy (HAART). Most originated from Africa (37%) and South America (35%). Of the 97 patients, 10.4% and 8.3% had positive or equivocal screening results for strongyloidiasis, respectively, 7.4% and 4.2% had positive or equivocal screening results for schistosomiasis and 5.5% and 6.8% had positive or equivocal screens for filariasis. Persons with positive parasitic serologies were more often female (28% versus 9%, P=0.03), younger in age (36 versus 43 years of age, P<0.01), had been in Canada for a shorter duration (5 versus 12 years, P<0.0001) and had a higher viral load (10,990 copies/mL versus <50 copies/mL, P <0.001). All patients were asymptomatic. Eosinophilia was not associated with positive screening results.

CONCLUSIONS

Using symptoms and eosinophilia to identify parasitic infection was not reliable. Screening for strongyloidiasis and schistosomiasis among patients with HIV from parasite-endemic countries is simple and benign, and may prevent future complications. The clinical benefits of screening for filariasis require further elucidation, but this practice appears to be the least warranted.

Diagnosis, treatment and risk factors of Strongyloides stercoralis in schoolchildren in Cambodia

Background

Worldwide, an estimated 30 to 100 million people are infected with Strongyloides stercoralis, a soil-transmitted helminth. Information on the parasite is scarce in most settings. In semi-rural Cambodia, we determined infection rates and risk factors; compared two diagnostic methods (Koga agar plate [KAP] culture and Baermann technique) for detecting S. stercoralis infections, using a multiple stool examination approach; and assessed efficacy of ivermectin treatment.

Methods/Principal Findings

We performed a cross-sectional study in 458 children from four primary schools in semi-rural villages in Kandal province, using three diagnostic procedures (Kato-Katz, KAP culture and Baermann technique) on three stool samples. Infected children were treated with ivermectin (100 µg/kg/day for two days) and re-examined three weeks after treatment. Hookworm, S. stercoralis, Trichuris trichiura, and small trematode eggs were most prevalent, with 24.4% of children being infected with S. stercoralis. The sensitivity of KAP culture and Baermann technique was 88.4% and 75.0%, respectively and their negative predictive values were 96.4% and 92.5%, respectively. The cumulative prevalence of S. stercoralis increased from 18.6% to 24.4%, after analyzing three stool samples, which was close to the modeled ‘true’ prevalence of 24.8%. Children who reported defecating in latrines were significantly less infected with S. stercoralis than those who did not use latrines (p<0.001). Itchy skin and diarrhea were significantly associated with S. stercoralis infection. The cure rate of ivermectin was 98.3%.

Conclusions/Significance

S. stercoralis infection is highly prevalent among semi-rural Cambodian schoolchildren. The sensitivity of KAP culture is higher than that of the Baermann technique. In the absence of a “gold standard”, analysis of multiple stool samples by different diagnostic methods is required to achieve a satisfactory level of sensitivity. Almost three-quarters of the infections could have been avoided by proper sanitation. Ivermectin is highly efficacious against S. stercoralis but prohibitive costs render the drug inaccessible to most Cambodians.

The difficulty of diagnosing Strongyloides stercoralis infections is the reason why up to date, accurate information on its geographic distribution in endemic regions and the total global burden is lacking. We conducted a cross-sectional study among 458 schoolchildren, with the purpose of comparing two methods for diagnosing S. stercoralis infection (Koga agar plate ‘KAP’ culture and Baermann technique) on three stool samples from each individual and to assess the efficacy of ivermectin three weeks after treatment. About one quarter of the schoolchildren examined were infected with S. stercoralis. The sensitivity of KAP culture and Baermann technique was 88.4% and 75.0%, respectively. The prevalence of S. stercoralis infection increased considerably (from 18.6% to 24.4%) when three stool samples were examined. Almost three-quarters of the infections could have been avoided by proper sanitation. Ivermectin was highly efficacious against S. stercoralis infection, with a cure rate of 98.3%. In the absence of a “gold standard”, it is necessary to examine multiple stool samples using different diagnostic techniques in order to reach a “true” prevalence.

E. coli Meningitis Presenting in a Patient with Disseminated Strongyloides stercoralis

Introduction. Spontaneous Escherichia coli meningitis is an infrequent condition in adults and is associated with some predisposing factors, including severe Strongyloides stercoralis (SS) infections. Case Presentation. A 43-year-old Hispanic man, with history of travelling to the jungle regions of Peru and Brazil two decades ago, and who received prednisone due to Bell's palsy for three weeks before admission, presented to the Emergency Department with diarrhea, fever, and hematochezia. A week after admission he developed drowsiness, meningeal signs, abdominal distension, and constipation. A cerebrospinal fluid culture showed extended spectrum β -lactamase producing E. coli. A colonoscopy was performed and showed pancolitis. Three days after the procedure the patient became unstable and developed peritoneal signs. He underwent a laparotomy, which ended up in a total colectomy and partial proctectomy due to toxic megacolon. Three days later the patient died in the intensive care unit due to septic shock. Autopsy was performed and microscopic examination revealed the presence of multiple Strongyloides larvae throughout the body. Conclusion. Strongyloides stercoralis infection should be excluded in adults with spontaneous E. coli meningitis, especially, if gastrointestinal symptoms and history of travelling to an endemic area are present. Even with a proper diagnosis and management, disseminated strongyloidiasis has a poor prognosis.

Pathology of CNS parasitic infections

Parasitic infections of the central nervous system (CNS) include two broad categories of infectious organisms: single-celled protozoa and multicellular metazoa. The protozoal infections include malaria, American trypanosomiasis, human African trypanosomiasis, toxoplasmosis, amebiasis, microsporidiasis, and leishmaniasis. The metazoal infections are grouped into flatworms, which include trematoda and cestoda, and roundworms or nematoda. Trematoda infections include schistosomiasis and paragonimiasis. Cestoda infections include cysticercosis, coenurosis, hydatidosis, and sparganosis. Nematoda infections include gnathostomiasis, angiostrongyliasis, toxocariasis, strongyloidiasis, filariasis, baylisascariasis, dracunculiasis, micronemiasis, and lagochilascariasis. The most common route of CNS invasion is through the blood. In some cases, the parasite invades the olfactory neuroepithelium in the nasal mucosa and penetrates the brain via the subarachnoid space or reaches the CNS through neural foramina of the skull base around the cranial nerves or vessels. The neuropathological changes vary greatly, depending on the type and size of the parasite, geographical strain variations in parasitic virulence, immune evasion by the parasite, and differences in host immune response. Congestion of the leptomeninges, cerebral edema, hemorrhage, thrombosis, vasculitis, necrosis, calcification, abscesses, meningeal and perivascular polymorphonuclear and mononuclear inflammatory infiltrate, microglial nodules, gliosis, granulomas, and fibrosis can be found affecting isolated or multiple regions of the CNS, or even diffusely spread. Some infections may be present as an expanding mass lesion. The parasites can be identified by conventional histology, immunohistochemistry, in situ hybridization, and PCR.

Hyperinfection with Strongyloides stercoralis

Strongyloidiasis is caused by Strongyloides stercoralis, which commonly produces gastrointestinal problems. If immune systems are compromised, the nematode larvae may spread and produce Strongyloides hyperinfection. Diagnosis of strongyloidiasis is based on the observation of larvae in coproparasitological studies. We present a case of a 49-year-oldman, VIH, who developed Strongyloides hyperinfection, diagnosed postmortem. Our patient reached the dissemination stage, which resulted in severe damage to the stomach and intestine, perforation of the intestinal wall, as well as sepsis due to the dissemination of bacteria. The diagnosis is difficult because of the low larvae excretion in stools. It is usually performed by the microscopic examination of fresh and fixed enriched stool samples. Serology was reported to be useful for screening and follow-up after treatment. This case reaffirms that HIV immunosuppression favours the dissemination of S stercoralis larvae. Thus, a search for intestinal parasites should be considered in similar cases.

Decreasing intestinal parasites in recent Northern California refugees

Beginning in 2005, the Centers for Disease Control and Prevention (CDC) expanded the overseas presumptive treatment of intestinal parasites with albendazole to include refugees from the Middle East. We surveyed the prevalence of helminths and protozoa in recent Middle Eastern refugees (2008-2010) in comparison with refugees from other geographical regions and from a previous survey (2001-2004) in Santa Clara County, California. Based on stool microscopy, helminth infections decreased, particularly in Middle Eastern refugees (0.1% versus 2.3% 2001-2004, P = 0.01). Among all refugees, Giardia intestinalis was the most common protozoan found. Protozoa infections also decreased somewhat in Middle Eastern refugees (7.2%, 2008-2010 versus 12.9%, 2001-2004, P = 0.08). Serology for Strongyloides stercoralis and Schistosoma spp. identified more infected individuals than stool exams. Helminth infections are increasingly rare in refugees to Northern California. Routine screening stool microscopy may be unnecessary in all refugees.

[A case of steroid-induced hyperinfective strongyloidiasis with bacterial meningitis]

Strongyloides stercoralis is a soil transmitted intestinal nematode that is endemic in the tropical and subtropical regions. In most individuals who are infected, chronic, usually asymptomatic, gastrointestinal infection persists. But, in immunocompromized hosts or in patients receiving immunosuppressive therapy, autoinfection of S. stercoralis may result in the dissemination of larvae, leading to fatal hyperinfection and increased rate of complications. We report a case of hyperinfective strongyloidiasis with bacterial meningitis in a patient receiving steroid therapy. Strongyloidiasis was diagnosed by the presence of filariform larvae of S. stercoralis in the bronchoalveolar lavage cytology and upper gastrointestinal endoscopic biopsy specimen. Her clinical symptoms had progressively aggravated and developed bacterial meningitis during treatment. She died despite aggressive antibiotic and antihelminthic therapy.

Imported strongyloidiasis: epidemiology, presentations, and treatment

Strongyloidiasis is extremely more frequent in immigrants than in travellers. Clinical presentations do not differ significantly between the two groups, and the most frequent picture is a chronic infection characterized by intermittent, mild, non-specific symptoms. Acute presentation is rare but it has been reported in travellers. Screening of asymptomatic subjects is not generally recommended, while a presumptive treatment with ivermectin might be justified for all travellers and immigrant patients presenting unexplained eosinophilia and/or compatible symptoms, even in case of negative test results. In fact, delayed diagnosis and treatment has life-threatening consequences in patients with conditions predisposing to development of hyperinfection and dissemination.

Azathioprine hypersensitivity presenting as sweet syndrome in a child with ulcerative colitis

Sweet syndrome is a cutaneous lesion characterized by tender, red inflammatory nodules or papules. We describe a pediatric case of Sweet syndrome presenting 10 days after treatment with azathioprine. As azathioprine is widely used in children with inflammatory bowel disease, clinicians should be aware of this unusual adverse reaction.

Strongyloides stercoralis infection: a health issue regarding indigenous people in Taiwan

Strongyloidiasis, caused by Strongyloides stercoralis, is endemic in tropical and subtropical regions. Whether or not the infection rate is higher among indigenous populations in Taiwan remains unclear. The aim of our study was to assess the racial demographics, diagnoses and clinical details of strongyloidiasis. A total of 41 patients (27 males and 14 females) with strongyloidiasis at a tertiary referral centre in eastern Taiwan in a 21-year period were investigated retrospectively. The majority (36/41, 88%) of these patients lived in rural townships. Common clinical symptoms were anorexia, abdominal pain, nausea, vomiting, fever, coughing and diarrhea. The laboratory abnormalities were anemia, eosinophilia, and leukocytosis. The average age of the indigenous patients was younger than that of the Hans Chinese patients. Alcoholism among the indigenous Taiwanese (all males) was significantly more frequent than in the Hans Chinese, which might be one of the reasons that the indigenous males had a higher infection rate than Hans Chinese males. The group of patients with intestinal strongyloidiasis exhibited a significant lower mortality and a higher recovery rate than those with hyperinfection syndrome. Leptospirosis should be considered as an underlying factor associated with strongyloidiasis, especially in indigenous patients. The relationship and mechanism of leptospira-induced overwhelming infection including strongyloidiasis remains to be elucidated.

Seroepidemiology ofStrongyloides stercoralisin Dhaka, Bangladesh

Human strongyloidiasis is a neglected tropical disease with global distribution and this infection is caused by the parasitic nematodeStrongyloides stercoralis. The aim of this study was to determine the prevalence of strongyloidiasis in Dhaka, Bangladesh. Sera from 1004 residents from a slum (group A) and 299 from city dwellers (group B) were tested for total IgG and IgG subclasses toStrongyloidesantigen. There was a significant difference (P < 0·001) in IgG seroprevalence between group A (22%) and group B (5%). Reactive IgG subclasses (IgG1 and IgG4) were also higher in group A (P < 0·05). The seroprevalence of strongyloidiasis in group A increased with age but was unrelated to sex. The presence of reactive IgG toStrongyloidesantigen had no correlation with either socio-economic or personal hygiene factors. However, a history of diarrhoea in a family member, in the past 6 months, but not in the respondents was associated with detection of antibodies toS. stercoralis(P < 0·01). None of the sera from either group had an HTLV-I reaction. This study demonstrates that strongyloidiasis is prevalent in Dhaka, especially among slum dwellers, but concurrent infection with HTLV-I was not found. Future epidemiological studies should identify individual risk factors and other communities at risk so that appropriate interventions can be planned.

Strongyloides, dengue fever, and tuberculosis conversions in New Zealand police deploying overseas

BACKGROUND

Members of New Zealand Police (NZP) deploy overseas in a variety of roles. There is limited published data on travel-related morbidity in police as a subgroup of travelers.

METHODS

An audit of pre- and postdeployment medical files for all NZP personnel deploying overseas during 2004 to 2010 was undertaken. Of all deployments, 58.9% were within Oceania.

RESULTS

Positive Strongyloides stercoralis serology was returned in 6.07% (95% CI: 3.80%-9.13%) at a rate of 9.00/1,000 person deployment months (pdm) (95% CI: 5.57-13.8). Dengue fever seroconversion was recorded in 4.91% (95% CI: 3.40%-6.83%) at a rate of 8.57/1,000 pdm (95% CI: 5.90-12.0). The relative risk of dengue infection was 7.47 for Timor Leste compared to all other deployment destinations. An association between seroconverting for both dengue fever and Strongyloides was found. Tuberculosis conversion was recorded in 1.76% (95% CI: 0.85%-3.21%) at a rate of 2.92/1,000 pmd (95% CI: 1.48-5.375). A single case of human immunodeficiency virus (HIV) seroconversion was recorded. There were no recorded hepatitis C seroconversions.

CONCLUSIONS

Police deploying overseas appear to have similar rates of dengue and tuberculosis conversion as other groups of travelers, and they appear to be at low risk of hepatitis C and HIV. Strongyloidiasis appears to be a significant risk; postdeployment prevalence was markedly higher than that reported in a small number of studies.

A research agenda for helminth diseases of humans: the problem of helminthiases

A disproportionate burden of helminthiases in human populations occurs in marginalised, low-income, and resource-constrained regions of the world, with over 1 billion people in developing areas of sub-Saharan Africa, Asia, and the Americas infected with one or more helminth species. The morbidity caused by such infections imposes a substantial burden of disease, contributing to a vicious circle of infection, poverty, decreased productivity, and inadequate socioeconomic development. Furthermore, helminth infection accentuates the morbidity of malaria and HIV/AIDS, and impairs vaccine efficacy. Polyparasitism is the norm in these populations, and infections tend to be persistent. Hence, there is a great need to reduce morbidity caused by helminth infections. However, major deficiencies exist in diagnostics and interventions, including vector control, drugs, and vaccines. Overcoming these deficiencies is hampered by major gaps in knowledge of helminth biology and transmission dynamics, platforms from which to help develop such tools. The Disease Reference Group on Helminths Infections (DRG4), established in 2009 by the Special Programme for Research and Training in Tropical Diseases (TDR), was given the mandate to review helminthiases research and identify research priorities and gaps. In this review, we provide an overview of the forces driving the persistence of helminthiases as a public health problem despite the many control initiatives that have been put in place; identify the main obstacles that impede progress towards their control and elimination; and discuss recent advances, opportunities, and challenges for the understanding of the biology, epidemiology, and control of these infections. The helminth infections that will be discussed include: onchocerciasis, lymphatic filariasis, soil-transmitted helminthiases, schistosomiasis, food-borne trematodiases, and taeniasis/cysticercosis.

Role of leukotrienes on protozoan and helminth infections

Leukotrienes (LTs), formed by the 5-lipoxygenase-(5-LO-) catalyzed oxidation of arachidonic acid, are lipid mediators that have potent proinflammatory activities. Pharmacologic or genetic inhibition of 5-LO biosynthesis in animals is associated with increased mortality and impaired clearance of bacteria, fungi, and parasites. LTs play a role in the control of helminth and protozoan infections by modulating the immune system and/or through direct cytotoxicity to parasites; however, LTs may also be associated with pathogenesis, such as in cerebral malaria and schistosomal granuloma. Interestingly, some proteins from the saliva of insect vectors that transmit protozoans and secreted protein from helminth could bind LTs and may consequently modulate the course of infection or pathogenesis. In addition, the decreased production of LTs in immunocompromised individuals might modulate the pathophysiology of helminth and protozoan infections. Herein, in this paper, we showed the immunomodulatory and pathogenic roles of LTs during the helminth and protozoan infections.

Co-infection of HIV and tropical infectious agents that affect the nervous system

Tropical infections refer to a group of diseases usually located in regions with a warm climate, particularly affecting developing countries, partly because of the conditions that allow them to thrive. However, due to the increased international travel, infectious agents that were previously limited to tropical regions pose an increasing threat to populations at risk for opportunistic infection (OI), especially those infected with the HIV. Tropical infections can facilitate HIV transmission and accelerate the progression of asymptomatic HIV infection to AIDS. Some have the potential to alter the epidemiology, natural history, and/or response to treatment of the other. The introduction of highly active antiretroviral therapy has provided a huge benefit for the vast majority of patients infected with the HIV, by allowing the immune system to recover, improving the clinical and radiological results and reducing the number of OI. On the other hand, some patients have developed various disorders of immune reconstitution, resulting in either hyper-immune inflammatory response to an exogenous antigen or autoimmunity. A significant proportion of these cases have been reported in immigrants from tropical countries to high-income countries, therefore awareness of these phenomena is needed since clinical presentations are often atypical and pose diagnostic challenges. This article reviews some of the key diagnostic aspects of tropical infections associated with HIV infection.

Vaccination with Strongyloides ratti heat shock protein 60 increases susceptibility to challenge infection by induction of Th1 response

The control of strongyloidiasis affecting approximately 100 million people - caused by the gastrointestinal nematode Strongyloides stercoralis - is still based on anti-helminthic treatment. In the current study we analysed the immune response to Strongyloides ratti heat shock protein 60 (srHSP60) as a possible vaccine candidate in the murine system. We show that srHSP60 is a target of both, humoral and cellular response in S. ratti-infected mice. Strikingly, vaccination with srHSP60 without adjuvant or with CFA induced a S. ratti-specific Th1 response in vivo that did not confer protection but slightly increased larval output during challenge infection. Using in vitro T cell stimulation assays we provide further evidence that srHSP60 skewed activated T cells towards a Th1 response that interfered with efficient clearance of S. ratti infection. Vaccination with alum-precipitated srHSP60, in contrast, overruled the Th1-inducing activity intrinsic to srHSP60, induced a Th2 response, and conferred partial protection against a challenge infection. As srHSP60 is actively secreted by S. ratti during all life stages, our findings strongly suggest that srHSP60 induced polarization towards a Th1 response reflects a mechanism of immune evasion by this pathogenic nematode.

Innate and adaptive immunity to the nematode Strongyloides stercoralis in a mouse model

Mice have been used to the study the mechanisms of protective innate and adaptive immunity to larval Strongyloides stercoralis. During primary infection, neutrophils and eosinophils are attracted by parasite components and kill the larvae by release of granule products. Eosinophils also function as antigen-presenting cells for the induction of a Th2 response. B cells produce both IgM and IgG that collaborate with neutrophils to kill worms in the adaptive immune response. Vaccine studies have identified a recombinant diagnostic antigen that induced high levels of immunity to infection with S. stercoralis in mice. These studies demonstrate that there are redundancies in the mechanisms used by the immune response to kill the parasite and that a vaccine with a single antigen may be suitable as a prophylactic vaccine to prevent human strongyloidiasis.

Life cycle stage-resolved proteomic analysis of the excretome/secretome from Strongyloides ratti--identification of stage-specific proteases

A wide range of biomolecules, including proteins, are excreted and secreted from helminths and contribute to the parasite's successful establishment, survival, and reproduction in an adverse habitat. Excretory and secretory proteins (ESP) are active at the interface between parasite and host and comprise potential targets for intervention. The intestinal nematode Strongyloides spp. exhibits an exceptional developmental plasticity in its life cycle characterized by parasitic and free-living generations. We investigated ESP from infective larvae, parasitic females, and free-living stages of the rat parasite Strongyloides ratti, which is genetically very similar to the human pathogen, Strongyloides stercoralis. Proteomic analysis of ESP revealed 586 proteins, with the largest number of stage-specific ESP found in infective larvae (196), followed by parasitic females (79) and free-living stages (35). One hundred and forty proteins were identified in all studied stages, including anti-oxidative enzymes, heat shock proteins, and carbohydrate-binding proteins. The stage-selective ESP of (1) infective larvae included an astacin metalloproteinase, the L3 Nie antigen, and a fatty acid retinoid-binding protein; (2) parasitic females included a prolyl oligopeptidase (prolyl serine carboxypeptidase), small heat shock proteins, and a secreted acidic protein; (3) free-living stages included a lysozyme family member, a carbohydrate-hydrolyzing enzyme, and saponin-like protein. We verified the differential expression of selected genes encoding ESP by qRT-PCR. ELISA analysis revealed the recognition of ESP by antibodies of S. ratti-infected rats. A prolyl oligopeptidase was identified as abundant parasitic female-specific ESP, and the effect of pyrrolidine-based prolyl oligopeptidase inhibitors showed concentration- and time-dependent inhibitory effects on female motility. The characterization of stage-related ESP from Strongyloides will help to further understand the interaction of this unique intestinal nematode with its host.

Epidemiological aspects of strongyloidiasis in Brazil

The objective of this review was to outline an epidemiological profile of Strongyloides stercoralis by parasitological and serological diagnosis in inhabitants, and to associate this profile with different immunosupression situations, in Brazil, over 20 years (1990-2009). The occurrence of S. stercoralis using parasitological methods was 5·5%, being 4·8% in rural and 5·0% in urban areas, characterizing the country as hyperendemic. There was a diversity of techniques used as a diagnostic tool and only 39·1% of the studies presented results based on at least 1 specific method. The occurrence increased with age, being 12·1%, for those over 60 that suggests an epidemiological condition of concern for the elderly population. Of the seroepidemiological studies in the general population the mean positivity in serum samples was 21·7% and 29·2%, using an immunofluorescence antibody test and enzyme-linked immunosorbent assay (ELISA), respectively. The occurrence of strongyloidiasis in immunosuppressed individuals was 11·8% by parasitological methods and 19·5% using immunological methods. Considering that Brazil is a tropical country and that the character of chronicity and autoinfection of the parasite that can result in severe forms of hyperinfection or dissemination makes strongyloidiasis an important medically and socially neglected problem.

[Chronic Strongyloides stercoralis infection. Larva currens as skin manifestation]

Strongyloidiasis is a nematode infection that can persist asymptomatically for years. Pathognomonic skin manifestation is the larva currens. A human immunodeficiency virus-infected patient native from an endemic area presented with pruritus, an urticarial serpiginous rash and eosinophilia. The histology was not helpful. Strongyloidiasis was confirmed on the basis of stool and serum examination. He was treated successfully with Ivermectin.

Health aspects of the pre-departure phase of migration

In the second article in a six-part PLoS Medicine series on Migration & Health, Brian Gushulak and Douglas MacPherson discuss the pre-departure phase of migration and the specific health risks and policy needs associated with this phase.

Helminths: an unrecognised disease burden prevalent among migrants in the gastroenterology clinic

OBJECTIVE

To estimate the prevalence of, and implement a diagnostic strategy for, imported helminth infection in the gastroenterology clinic.

DESIGN

A retrospective study of eosinophil count and probable tropical exposure (phase I) followed by a prospective study of parasitological investigation (phase II).

SETTING

Gastroenterology service of an inner London hospital.

PATIENTS

Adult patients newly attending general gastroenterology and inflammatory bowel disease clinics.

INTERVENTIONS

In phase I, evidence of undiagnosed helminth infection was sought by analysing patient records for associations between eosinophil count and ethnicity. In phase II, a UK guideline for investigation of eosinophilia in migrants was implemented and diagnostic yield determined.

MAIN OUTCOME MEASURES

In phase I, prevalence of eosinophilia was determined; in phase II, helminth prevalence and degree of eosinophilia before and after treatment were reported. Information on symptomatic response to treatment was recorded. Ethnicity was used as a proxy measure for tropical exposure.

RESULTS

426 new patients attended in a 12 month period. Eosinophilia was present in 27 (6.3%). 10/27 (37.0%) patients with eosinophilia were of African or Asian ethnicity whereas only 20% (85/426) of patients overall were from these ethnic groups (χ²=5.27, p=0.02). Following implementation of the protocol, 25/36 migrants with eosinophilia attended for parasitological investigations. Helminth infection was diagnosed in 10/25 (40%). Strongyloidiasis (six patients) and schistosomiasis (three patients) were the most common diagnoses. Median eosinophil count was 1.06×10⁹/l in those with helminths and 0.58×10⁹/l in those without (p=0.004). Eosinophil counts normalised in, and symptomatic improvement was reported by, most patients after treatment.

CONCLUSIONS

Eosinophilia is associated with African or Asian ethnicity in an inner city gastroenterology service. This association is probably explained by imported helminths, which are prevalent in this setting, may be a cause of gastrointestinal symptoms and is easily diagnosed and treated by standard protocols.

Migratory route of Strongyloides venezuelensis in Lewis rats: comparison of histological analyses and PCR

Strongyloides venezuelensis is a parasitic nematode that has been used as a model to study human and animal strongyloidiasis. In this study, we compared the sensitivity between traditional methodologies and PCR assay to characterize the dynamics of S. venezuelensis infection and its migration route in Lewis rats subcutaneously infected with 4000 L3. The dynamics of the infection was determined by counting the number of eggs and by detecting parasite deoxyribonucleic acid in faeces samples. Both techniques similarly detected the infection at day 6 after larvae inoculation. However, PCR performed with the genus primer showed higher sensitivity during the recovery phase. Histological analysis and PCR assay were then used to follow parasite tissue migration. S. venezuelensis migration route included the muscular fibers below the skin, the pulmonary alveoli and the small intestine vilosities. The sensitivity of these two techniques to detect parasite's presence in these tissues was statistically similar.