Fluctuations of larval excretion in Strongyloides stercoralis infection

Strongyloides infection screening in transplant candidates: What is the best strategy?

BACKGROUND

The potential that Strongyloides stercoralis infection has to cause major morbidity and high mortality when the disseminated form occurs in transplant patients is of particular concern.

METHODS

In this study, the objective was to observe S. stercoralis infection in patients who are candidates for transplantation by using parasitological, serological, and molecular techniques and to propose an algorithm for the detection of that infection in transplant candidates.

RESULTS

By parasitological techniques, 10% of fecal samples were positive. Anti-Strongyloides antibodies immunoglobulin G were detected in 19.3% and 20.7% of patients by immunofluorescence assay and enzyme-linked immunosorbent assay, respectively. S. stercoralis DNA was observed in 17.3% of samples by conventional polymerase chain reaction and 32.7% of samples by quantitative polymerase chain reaction (qPCR).

CONCLUSION

The set of results allows us to reinforce that a positive result by parasitological techniques and/or qPCR indicates that the specific treatment should be applied. However, the improvement of diagnostic techniques may suggest changes in the screening for strongyloidiasis in these patients.

Multiple Stool Sampling and Specific Parasitological Technique are Crucial to Diagnose Strongyloidiasis in Alcoholic Patients

PURPOSE

Chronic alcoholism is a well-known risk factor for strongyloidiasis, in these patients the disease is potentially more severe, probably due to the breakdown of local protective barriers and immunosuppression caused by alcohol, which can lead to autoinfection and dissemination. The aim of this study was to evaluate multiple stool sampling and a specific parasitological assay agar plate culture (APC) for the diagnosis of Strongyloides stercoralis in alcoholics.

METHODS

APC was compared to sedimentation technique (HPJ; Hoffman, Pons and Janer), as parasitological methods to detect S. stercoralis infection in alcoholic individuals. Three stool samples from 60 alcoholic and 60 non-alcoholic individuals were analyzed.

RESULTS

S. stercoralis larvae were observed in 11 (18.3%) alcoholic individuals and 1 (1.7%) nonalcoholic individual (P = 0.0042). In view of the combined results, sensitivity for the APC method was 63.6% (CI 31.6-87.6%) with the first sample reaching 100% (CI 67.8-100%) after analyzing three fecal samples. The HPJ sensitivity was 36.4% (CI 12.4-68.4) in the first sample, reaching 72.7% (CI 39.3-92.7) after three samples analyzed.

CONCLUSION

The present results suggest that in alcoholic patients, it is important to repeat stool sampling with specific techniques, especially using the APC method, to avoid misdiagnosis in cases that could evolve to disseminated strongyloidiasis.

A Rare Case of Strongyloides stercoralis Hyperinfection in a Diabetic Patient from Romania—Case Report and Review of the Literature

Severe cases of strongyloidiasis are most often associated with multiple causes of immune suppression, such as corticoid treatment and HTLV (human T-lymphotropic virus) coinfection. Diabetes is not traditionally considered a risk factor for the development of severe strongyloidiasis. We report a rare case of autochthonous severe strongyloidiasis in Romania, a European country with a temperate climate. A 71-year-old patient with no prior travel history was admitted with multiple gastrointestinal complaints and recent weight loss. CT (computed tomography) scans indicated duodenal wall thickening, and duodenal endoscopy evidenced mucosal inflammation, ulcerations and partial duodenal obstruction at D4. Microscopic examination of stool samples and biopsy specimens from the gastric and duodenal mucosa revealed an increased larval burden characteristic of Strongyloides stercoralis hyperinfection. Sequential treatment with albendazole and ivermectin achieved parasitological cure and complete recovery. The novelty of our case stems from the scarcity of severe strongyloidiasis cases reported in Europe and especially in Romania, the absence of other risk factors in our patient aside from diabetes, the involvement of the gastric mucosa and the rare presentation as partial duodenal obstruction. This case highlights the importance of considering strongyloidiasis as a differential diagnosis, even in temperate climates where cases are sporadic, in cases in which immune suppression is not evident and in the absence of eosinophilia. The case is presented in the context of the first literature review examining the relationship between severe strongyloidiasis and diabetes, emphasizing diabetes as a possible risk factor for severe strongyloidiasis.

The diagnosis of human and companion animal Strongyloides stercoralis infection: Challenges and solutions. A scoping review

Strongyloidiasis is the infection caused by soil-transmitted nematodes of Strongyloides species, infecting humans and some animals. Strongyloides stercoralis is the species with most clinical and epidemiological relevance in humans and dogs, due to its high prevalence and its capacity of inducing a life-threatening hyperinfection. Diagnosis of strongyloidiasis is challenging, due to the absence of a single reference standard test with high sensitivity and specificity, which also hampers the estimation of the accuracy of other diagnostic tests. In this chapter, we review the deployment and performance of the parasitological, immunological, molecular tests for the diagnosis of strongyloidiasis in humans and in dogs. Further, we comment the available evidence from genotyping studies that have addressed the zoonotic potential of S. stercoralis. Finally, we discuss the use of different diagnostic methods in relation to the purpose (i.e., screening, individual diagnosis, inclusion in a clinical trial) and the setting (endemic/non-endemic areas) and report the accuracy figures reported by systematic reviews on either parasitological, serological or molecular techniques published in literature.

Time of incubation of agar-plate culture for the diagnosis of Strongyloides stercoralis infection

PURPOSE

Agar-plate culture (APC) remains the most sensitive parasitological technique for S. stercoralis diagnosis. Although it was first described three decades ago, the time of incubation of the plates is neither a commonly described feature nor usually standardized. The aim of the study was to analyze the required time to detect S. stercoralis larvae in APC.

METHODS

A prospective laboratory-based study including all patients with at least one positive APC was performed. The plates were incubated at room temperature for 7 days. Clinical, analytical and parasitological features including results of the direct visualization of the stool (DV) after formalin-ether concentration and time-to-detection (TTD) of the larvae in APC were recorded.

RESULTS

A total of 141 samples from 75 patients had a positive APC. In 49 of them (65.3%) three or more stool samples were processed for direct visualization (DV) and APC. Of these 49 patients, 8 (16.3%) were also diagnosed with DV and 41 (83.7%) were diagnosed only with APC. In 38 samples from 23 (30.7%) patients, the TTD was below 2 days, while in 27 samples from 13 (17.3%) patients, the larvae were detected on the 6th and 7th day.

CONCLUSION

Direct visualization failed to detect S. stercoralis in most of the patients that were diagnosed with APC. Incubation periods below 2 and 5 days would miss an important percentage of infections. At least 7 days of incubation of the APC are required to detect presumably low-burden chronic infections in non-endemic countries.

Diagnosis of human strongyloidiasis: Application in clinical practice

This review considers the advantages and disadvantages of parasitological techniques, methods of detecting antibodies and antigens, as well as molecular biology techniques in the diagnosis of human strongyloidiasis. In addition, it elucidates the potential of different techniques for rapid and effective detection of clinical cases, thus enabling early treatment and preventing fatal consequences of this helminthiasis.

Endemic parasitic infections in donors and recipients of stem cell and solid organ transplants: focus on strongyloidiasis and Chagas disease

PURPOSE OF REVIEW

The aim of the article is to review recent recommendations on the management of Strongyloidiasis and Chagas disease (ChD) in the context of stem-cell or solid-organ transplantation.

RECENT FINDINGS

An update on laboratory screening, detection of acute disease or reactivation and recommended preventive or therapeutic options in the transplant recipients and donors is presented. Recent epidemiological data showing new estimates on the worldwide burden of both diseases and changes in the classical distribution around the globe should increase awareness and will impact the evaluation and management of transplant recipients and donors in endemic and nonendemic regions.

SUMMARY

Strongyloidiasis and ChD are potentially life threatening if unnoticed in the context of stem-cell or solid-organ transplantation and should be considered in endemic and nonendemic areas. Effective strategies for detection, monitoring, prevention and management are available for both diseases.

Improved agar plate culture conditions for diagnosis of Strongyloides stercoralis

Strongyloides stercoralis infection causes gastrointestinal symptoms and can lead to severe disease in immunocompromised hosts. Live larvae are passed in feces, encouraging the common use of diagnosis by cultivation methods including agar plate culture (APC), the gold-standard technique. Nevertheless, APC has limitations, especially since there can be considerable day-to-day fluctuations in numbers of larvae produced. Herein, we collected stool samples from heavily infected subjects with strongyloidiasis in Khon Kaen Province, Thailand, to evaluate modifications (temperature, pH, nutrition source and salinity) to APC conditions to maximize the number of S. stercoralis worms counted. Best results were obtained using a modified APC with the following conditions: pH 6.0, 0.5% of NaCl, addition of yeast extract for nutrition and incubation at 29-30 °C. This modified APC was more sensitive for detection of S. stercoralis than was standard APC or the formalin-ethyl acetate concentration technique. In brief, this finding suggests that a modification of standard APC conditions increases the counts of S. stercoralis.

Prevalence and risk factors of Strongyloides stercoralis infection among Orang Asli schoolchildren: new insights into the epidemiology, transmission and diagnosis of strongyloidiasis in Malaysia

This cross-sectional study aimed to determine the prevalence and risk factors of S. stercoralis infection among 1142 Orang Asli primary schoolchildren in six different states of Peninsular Malaysia. Fecal samples were examined using direct smear, formalin-ether sedimentation (FES), agar plate culture (APC) and PCR techniques. Overall, 15.8% of the children were found to be infected with S. stercoralis. The prevalence was 0.2, 1.3, 15.2 and 13.7% by direct smear, FES, APC and PCR, respectively. Multivariate analysis showed that an age of >10 years, being male, belonging to a Proto-Malay tribe, belonging to the Senoi tribe, indiscriminate defecation, using an unimproved water source for drinking water and not wearing shoes when outside were the significant risk factors of infection among these children. In conclusion, we provide new evidence on the occurrence of S. stercoralis in Malaysia to show that there is a relatively high prevalence of infection among Orang Asli schoolchildren. Therefore, the use of specific methods for detecting S. stercoralis should be considered when screening these children for intestinal parasites. Moreover, prevention and control measures specific to S. stercoralis should be integrated into the intestinal parasitic infections control programme in Malaysia.

Molecular and Immnune Diagnosis: Further Testing for Human Strongyloidiasis

INTRODUCTION

Detection of Strongyloides stercoralis larvae is particularly challenging because only a small number of larvae are released into the feces, regardless of infection stage.

OBJECTIVE

Our objective was to apply conventional polymerase chain reaction (PCR) to the detection of S. stercoralis DNA in feces samples to evaluate its performance in samples of patients with strongyloidiasis and compare results with those of immunodiagnosis.

METHODS

Stool, serum, and saliva samples were collected from each individual (n = 48) at the clinic hospital of the State University of Londrina, Brazil, for parasitological, immunological, and molecular tests. Stool samples were processed via parasitological methods. Serum samples were used for immunoglobulin G (IgG) detection and saliva samples for IgA detection by ELISA.

RESULTS

For amplification by conventional PCR, two different primers were used: species specific (101 bp) and genus specific (392 bp). The results showed that 34 (97.1%) of the 35 copro-positive individuals for S. stercoralis were positive for serum IgG and 19 (54.3%) were positive for salivary IgA. Regarding molecular analysis, both primers (species and genus specific) demonstrated positivity in 100% of the samples, which was confirmed by sequencing the positive samples.

CONCLUSION

Complementary examinations of the parasitological method demonstrated excellent results in the context of the diagnosis of strongyloidiasis, especially in asymptomatic patients with irregular larval release in the feces.

Disseminated Strongyloidiasis: Breaking Brain Barriers

Strongyloides stercoralis (SS) is one of the most overlooked helminthic infections despite being highly endemic in tropical and subtropical areas. In immunocompromised patients, especially those on long-term steroids, infection can often escalate to fatal dissemination into major organs. We present a compendium of two immunocompromised patients, who were on high-dose steroids and presented with worsening neurological status. Cerebrospinal fluid analysis was notable for larvae of SS as diagnosed by direct visualization. A syndrome of SS hyperinfection with dissemination was made after stool, and sputum samples also revealed SS larvae. SS is an elusive disease and should be considered early on, especially in endemic regions like India. Early diagnosis and prompt initiation of antihelminthic therapy is indispensable for favorable outcomes.

IgG reactivity with 40-35 kDa soluble and membrane antigen of Strongyloides venezuelensis in immunocompromised patients

Immunocompromised patients constitute a risk group for the development of severe clinical forms of human strongyloidiasis. The diagnosis of this infection is primarily performed by parasitological techniques, but with low sensitivity. Serological techniques appear as an alternative, especially with heterologous antigens use. The aim of this study was to perform the Western blot technique by using S. venezuelensis infective third stage larva (iL3) soluble (TS) and membrane (TM) saline antigens to reveal immunoreactive bands in immunocompromised patients with strongyloidiasis. Serum samples from 117 parasitologically well-characterized patients were divided into four groups: S. stercoralis positive and immunocompetent (S + IC); S. stercoralis positive and immunocompromised (S + IP); negative and immunocompetent (S-IC); negative and immunocompromised (S-IP). A 40-35 kDa band was recognized by 100% of patients in the S + IC group in both antigenic fractions, and by 62.5% and 50% in the S + IP group using the TS and TM fractions, respectively. A 29 kDa band was recognized by 86.3% and 72.7% (for TS and TM, respectively) of patients in the S + IC group, and only by 12.5% of patients in the S + IP group on the TM antigen. Regardless of the patients' immunological condition, the 40-35 kDa band from S. venezuelensis was detected more frequently and can be used as an important marker to the immunodiagnosis of human strongyloidiasis.

Screening of Strongyloides infection using an ELISA test in transplant candidates

OBJECTIVES

Hyperinfection or disseminated strongyloidiasis has been frequently reported after transplants and is related to high mortality. This study aimed to screen for strongyloidiasis using serological diagnoses in transplant candidates.

METHODS

An ELISA test was performed with filariform larvae of Strongyloides venezuelensis as a source of antigen.

RESULTS

In the serum from transplant candidates, anti-Strongyloides IgG antibodies were detected in 35/150 (23.3%) samples by soluble fractions in phosphate buffered saline (PBS), 31/150 (20.7%) samples by soluble fractions in Tris-HCl, 27/150 (18.0%) samples by membrane fractions in PBS and 22/150 (14.7%) samples by membrane fractions in Tris-HCl.

CONCLUSIONS

The present results suggest the ELISA test, ideally using soluble fractions of filariform larvae S. venezuelensis in PBS, as an additional strategy for the diagnosis of strongyloidiasis in transplant candidates.

Hypermetabolic Diffuse Proximal Small Bowel Wall Thickening on Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography? Consider Strongyloidiasis among the Differentials

Strongyloidiasis is an emerging tropical/subtropical parasitic infection commonly encountered in immunocompromised patients and often accompanied by life-threatening gram-negative bacteremia. We presented an interesting image of a critically ill 66-year-old lady, an asthmatic on high dose steroids, presenting with unexplained fever and vomiting where fluorodeoxyglucose positron emission tomography/computed tomography and endoscopic biopsy revealed this often neglected pathogenic nematode.

Molecular diagnosis of Strongyloides stercoralis among transplant candidates

Strongyloidiasis can occur without any symptoms or as a potentially fatal hyperinfection or disseminated infection, principally in immunosuppressed patients. Our study aimed to evaluate the application of conventional polymerase chain reaction (cPCR) and real-time PCR (qPCR). Polymerase chain reaction (PCR) and real-time PCR (qPCR) targeting the 18S rRNA gene for detection of Strongyloides stercoralis infection among transplant candidates were applied in stool samples obtained from 150 transplant candidates, preliminarily analyzed by parasitological methods. S. stercoralis larvae were visualized in 15/150 (10.0%) transplant candidates by parasitological methods. DNA from S. stercoralis was amplified in 26/150 (17.3%) and 49/150 (32.7%) stool samples of transplant candidates, using cPCR and qPCR, respectively. The results suggest that molecular methods, especially qPCR, should be used as an additional tool for diagnostic of S. stercoralis infection among transplant candidates.

Immune complex detection in saliva samples: an innovative proposal for the diagnosis of human strongyloidiasis

Human strongyloidiasis is caused by helminth Strongyloides stercoralis. It has a worldwide distribution, often neglected and cause of severe morbidity. The parasitological diagnosis is hindered by the low and irregular amount of larvae in feces. The goal of the present study was to detect IgG and IgG immune complex using conventional serum samples and saliva as alternative samples. We collected samples from 60 individuals, namely: group I composed of 30 healthy individuals; and group II composed of 30 individuals eliminating S. stercoralis larvae in feces. We calculated the area under the curve, general index of diagnostic accuracy, Kappa index and determined the correlations between different diagnostic tests. The detection of IgG levels was performed by an immunoenzymatic assay with alkaline extract of S. venezuelensis larvae as antigen. Positivity of anti-S. stercoralis IgG in serum samples from group I was 3·3%, and from group II 93·3%. The detection of immune complex indicated that group I exhibited 3·3% and group II 56·7%. In the saliva samples, IgG detection was 26·7% for group I and 43·3% for group II. Immune complex was detected in 20% of group I, and 30% of group II. IgG immune complex in conventional serum samples and saliva as alternative samples can be considered biomarkers for the diagnosis of active strongyloidiasis.

Influence of parasite load on the diagnosis and occurrence of eosinophilia in alcoholic patients infected with Strongyloides stercoralis

Alcoholic patients are more susceptible to Strongyloides stercoralis infection. The chronic use of alcohol raises the levels of endogenous corticosteroids, which regulates the development of larvae and stimulates the differentiation of rhabditiform into infective filariform larvae, thus inducing internal autoinfection. Therefore, early diagnosis is important to prevent severe strongyloidiasis. The aim of this study was to evaluate the efficacy of parasitological methods, according to the parasite load and the number of stool samples, for diagnosis of S. stercoralis infection, as well the peripheral blood eosinophil count in alcoholic patients. A total of 330 patients were included in this study. The diagnosis was established using three parasitological methods: agar plate culture, Baermann-Moraes method and spontaneous sedimentation. Peripheral eosinophilia was considered when the level was >600 eosinophils/mm3. The agar plate culture (APC) had the highest sensitivity (97.3%). However, the analysis of multiple samples increased the sensitivity of all parasitological methods. The sensitivities of the methods were influenced by the parasite load. When the larval number was above 10, the sensitivity of APC was 100%, while in spontaneous sedimentation the sensitivity reached 100% when the larval number was above 50. In the present study, 15.4% of alcoholic patients infected with S. stercoralis (12/78) had increased peripheral blood eosinophil count (above 600 eosinophils/mm3). For an efficient parasitological diagnosis of S. stercoralis infection in alcoholic patients, repeated examination by two parasitological methods must be recommended, including agar plate culture due to its higher sensitivity. Moreover, S. stercoralis infection was associated with eosinophilia, mostly in patients excreting up to 10 larvae/g faeces.

Strongyloides stercoralis is associated with significant morbidity in rural Cambodia, including stunting in children

Background

Strongyloides stercoralis is a soil-transmitted nematode that can replicate within its host, leading to long-lasting and potentially fatal infections. It is ubiquitous and highly prevalent in Cambodia. The extent of morbidity associated with S. stercoralis infection is difficult to assess due to the broad spectrum of symptoms and, thus, remains uncertain.

Methodology/Principal findings

Clinical signs were compared among S. stercoralis infected vs. non-infected participants in a cross-sectional survey conducted in 2012 in eight villages of Northern Cambodia, and before and after treatment with a single oral dose of ivermectin (200μg/kg BW) among participants harboring S. stercoralis. Growth retardation among schoolchildren and adolescents was assessed using height-for-age and thinness using body mass index-for-age. S. stercoralis prevalence was 31.1% among 2,744 participants. Urticaria (55% vs. 47%, OR: 1.4, 95% CI: 1.1–1.6) and itching (52% vs. 48%, OR: 1.2, 95% CI: 1.0–1.4) were more frequently reported by infected participants. Gastrointestinal, dermatological, and respiratory symptoms were less prevalent in 103 mono-infected participants after treatment. Urticaria (66% vs. 11%, OR: 0.03, 95% CI: 0.01–0.1) and abdominal pain (81 vs. 27%, OR: 0.07, 95% CI: 0.02–0.2) mostly resolved by treatment. S. stercoralis infection was associated with stunting, with 2.5-fold higher odds in case of heavy infection.

Conclusions/Significance

The morbidity associated with S. stercoralis confirmed the importance of gastrointestinal and dermatological symptoms unrelated to parasite load, and long-term chronic effects when associated with malnutrition. The combination of high prevalence and morbidity calls for the integration of S. stercoralis into ongoing STH control measures in Cambodia.

Strongyloides stercoralis is an intestinal parasite that infects humans by penetrating intact skin. It thrives particularly in tropical countries with poor sanitation. Because it can replicate within its host, it causes long-lasting infections and is potentially fatal in patients with a disseminated infection. S. stercoralis is largely neglected due to the difficulty in detecting it with standard field diagnostic techniques but has recently been found to be very common in Cambodia, with prevalence rates exceeding 40%. It is difficult to identify symptoms associated with infection in endemic areas because co-infections with other helminths or protozoan parasites, which cause similar health problems, are common. We compared clinical signs in infected vs. non-infected participants living in eight villages in Northern Cambodia, and before and after treatment with ivermectin, the drug of choice against S. stercoralis, among 103 patients infected with S. stercoralis only. We also assessed the association between infection and growth retardation among children and adolescents. Of the participants, 31.1% were infected with S. stercoralis. Infected participants were more likely to report itching and urticaria. After treatment, fewer participants reported urticaria, abdominal pain, vomiting and, to a lesser extent, nausea, diarrhea, cough, and tiredness. S. stercoralis infection was associated with growth retardation as expressed by stunting.

Estimating occurrence of Strongyloides stercoralis in the Caribbean island countries: Implications for monitoring and control

BACKGROUND

Few data are available for the prevalence of Strongyloides stercoralis in the Caribbean region. This frequently under diagnosed soil-transmitted helminth (STH) can result in long-term low intensity chronic infections that are asymptomatic or can cause varied intestinal disturbances. With autoinfections, infections lasting over 60 years can occur and hyperinfections lead to high morbidity and mortality.

METHODOLOGY/PRINCIPAL FINDINGS

Historical literature was searched to determine the prevalence of S. stercoralis in the Caribbean island countries with some additional countries and islands included for comparative data. A previously published model was used to calculate prevalence taking in to account the sensitivity of the diagnostic methods used. Data for 17 islands/Caribbean countries were found and sufficient data were located to calculate prevalence for 14 locations. Prevalence ranges from <1% to 20.3% and while it has decreased in many islands it has not decreased at the same rate as other STHs in the last 40 years within the Caribbean region.

CONCLUSIONS/SIGNIFICANCE

S. stercoralis continues to be an important STH within the Caribbean. Potential reasons for the current prevalence include: long lasting infections, populations not targeted with mass drug administration (MDA) programs being infected, low efficacy of commonly used drugs in MDA programs, and under-diagnosis resulting in infections not being treated.

Improved Detection of Strongyloides stercoralis in Modified Agar Plate Cultures

AbstractA modification of Koga agar plate culture was performed, consisting of a 2 × 2-cm cellophane paper centered on the agar plate to prevent bacterial contamination of the agar and daily dish examinations (days 2-5). Between January 2000 and July 2005, we examined 1,708 infection-suspected patients, of which 147 (8.6%) harbored S. stercoralis. Single modified agar plate cultures exhibited superior sensitivity (93.2%), compared with different three-sample screening methods (sensitivity-Baermann: 76.6%, formalin-ethyl acetate: 22%, and direct smear: 15.3%). Agar plate cultures stand out as helpful alternatives for improved detection and therapy monitoring in poor countries and endemic areas. Combined with Baermann methods, they provide increased probability for S. stercoralis detection.

DIAGNOSIS OF Strongyloides stercoralis INFECTION IN IMMUNOCOMPROMISED PATIENTS BY SEROLOGICAL AND MOLECULAR METHODS

Strongyloidiasis is a potentially serious infection in immunocompromised patients. Thus, the availability of sensitive and specific diagnostic methods is desirable, especially in the context of immunosuppressed patients in whom the diagnosis and treatment of strongyloidiasis is of utmost importance. In this study, serological and molecular tools were used to diagnose Strongyloides stercoralis infections in immunosuppressed patients. Serum and stool samples were obtained from 52 patients. Stool samples were first analyzed by Lutz, Rugai, and Agar plate culture methods, and then by a quantitative real time polymerase chain reaction (qPCR). Serum samples were evaluated by an enzyme-linked immunosorbent assay (ELISA) using a soluble (AS) or a membrane fractions antigen (AM) obtained from alkaline solutions of the filariform larvae of Strongyloides venezuelensis. Of the 52 immunosuppressed patients, three (5.8%) were positive for S. stercoralis by parasitological methods, compared to two patients (3.8%) and one patient (1.9%) who were detected by ELISA using the AS and the AM antigens, respectively. S. stercoralis DNA was amplified in seven (13.5%) stool samples by qPCR. These results suggest the utility of qPCR as an alternative diagnostic tool for the diagnosis of S. stercoralis infection in immunocompromised patients, considering the possible severity of this helminthiasis in this group of patients.

Occurrence of and risk factors for Strongyloides stercoralis infection in South-East Asia

The soil-transmitted nematode, Strongyloides stercoralis is one of the most-neglected of all neglected tropical diseases. It is globally distributed, favouring the humid, wet climates of the tropics and subtropics. Inadequate sanitary conditions promote the spread of S. stercoralis infection. In South-East Asia, many countries provide the ideal ecological and economic setting for high S. stercoralis infection rates. Yet, in most of these countries, little is known about the actual prevalence and distribution of S. stercoralis. One reason for this lack of knowledge pertains to the time- and resource-intensive diagnostic methods used to detect S. stercoralis infection. The Koga Agar culture method and the Baermann method are considered to be the best coprological diagnostic methods for field settings today. Both detect the parasite with high sensitivity. This sensitivity can be increased further by examining stool samples for several consecutive days, thereby increasing the chances of detecting low-intensity chronic infections. Diagnostic challenges, however, lead to the omission of S. stercoralis in studies of soil-transmitted helminths and few studies focus on S. stercoralis, specifically. These factors lead to an underreporting of the nematode's prevalence, not only in South-East Asia but worldwide. We have reviewed the scientific literature of the last 25 years and estimated country-wide prevalence rates for South-East Asia. We aim to summarise what is known today about the prevalence of S. stercoralis in South-East Asia, as well as to ascertain the risk factors and diagnostic methods most commonly applied.

Strongyloidiasis: A Disease of Socioeconomic Disadvantage

Strongyloidiasis is a disease caused by soil transmitted helminths of the Strongyloides genus. Currently, it is predominately described as a neglected tropical disease. However, this description is misleading as it focuses on the geographical location of the disease and not the primary consideration, which is the socioeconomic conditions and poor infrastructure found within endemic regions. This classification may result in misdiagnosis and mistreatment by physicians, but more importantly, it influences how the disease is fundamentally viewed. Strongyloidiasis must be first and foremost considered as a disease of disadvantage, to ensure the correct strategies and control measures are used to prevent infection. Changing how strongyloidiasis is perceived from a geographic and clinical issue to an environmental health issue represents the first step in identifying appropriate long term control measures. This includes emphasis on environmental health controls, such as better infrastructure, sanitation and living conditions. This review explores the global prevalence of strongyloidiasis in relation to its presence in subtropical, tropical and temperate climate zones with mild and cold winters, but also explores the corresponding socioeconomic conditions of these regions. The evidence shows that strongyloidiasis is primarily determined by the socioeconomic status of the communities rather than geographic or climatic conditions. It demonstrates that strongyloidiasis should no longer be referred to as a "tropical" disease but rather a disease of disadvantage. This philosophical shift will promote the development of correct control strategies for preventing this disease of disadvantage.

Molecular testing for clinical diagnosis and epidemiological investigations of intestinal parasitic infections

Over the past few decades, nucleic acid-based methods have been developed for the diagnosis of intestinal parasitic infections. Advantages of nucleic acid-based methods are numerous; typically, these include increased sensitivity and specificity and simpler standardization of diagnostic procedures. DNA samples can also be stored and used for genetic characterization and molecular typing, providing a valuable tool for surveys and surveillance studies. A variety of technologies have been applied, and some specific and general pitfalls and limitations have been identified. This review provides an overview of the multitude of methods that have been reported for the detection of intestinal parasites and offers some guidance in applying these methods in the clinical laboratory and in epidemiological studies.

A Fatal Strongyloides Stercoralis Hyperinfection Syndrome in a Patient With Chronic kidney Disease: A Case Report and Literature Review

Strongyloides stercoralis hyperinfection syndrome is a rare but fatal disease, which occurs commonly in immunocompromised patients. Strongyloidiasis among patients with chronic kidney disease is rarely reported.A 55-year-old Chinese male presented to hospital with diarrhea and abdominal pain. He developed acute respiratory failure and progressed to diffuse alveolar hemorrhage owing to disseminated strongyloidiasis immediately. The bronchoalveolar lavage revealed filariform larvae of Strongyloides stercoralis.This patient was diagnosed with Strongyloides hyperinfection syndrome. Although albendazole, mechanical ventilator support, fluid resuscitation, vasopressor support, extracorporeal membrane oxygenation, hydrocortisone, and broadspectrum antimicrobials were actively used, the patient eventually died.Similar cases in patients with chronic kidney disease in the literature are also reviewed. Through literature review, we recommend that strongyloidiasis should be routinely investigated in patients with chronic kidney disease who will undergo immunosuppressive therapy.

Association between Strongyloides stercoralis infection and cortisol secretion in alcoholic patients

A higher prevalence of Strongyloides stercoralis infections has been reported in alcoholic patients compared to nonalcoholic patients living in the same area. Excessive alcohol consumption increases the levels of endogenous corticosteroids that subsequently enhance the fecundity of S. stercoralis parthenogenetic females. These corticosteroids also enhance the transformation of rhabditiform larvae into infective filariform larvae by mimicking the effect of the ecdysteroid hormones produced by the parasite, thus leading to autoinfection. In addition, alterations in the intestinal barrier and host immune response contribute to the development of hyperinfection and severe strongyloidiasis in alcoholic patients. The aim of this study was to evaluate the frequency of S. stercoralis infections in alcoholic patients and to determine the association between S. stercoralis infection and endogenous cortisol levels. The frequency of infection was evaluated in 332 alcoholic and 92 nonalcoholic patients. The parasitological diagnosis was carried out by agar plate culture, the modified Baermann-Moraes method and spontaneous sedimentation. The immunological diagnosis was performed using an ELISA with anti-S. stercoralis IgG. The cortisol levels were measured in serum samples by ELISA. The frequency of S. stercoralis infection in alcoholic patients was 23.5% (78/332), while in nonalcoholic patients, it was 5.4% (5/92) (p<0.05). The cortisol levels were higher in alcoholic than in nonalcoholic patients (p<0.05). However, among the alcoholic patients, the cortisol levels did not differ between S. stercoralis-infected and uninfected patients (p>0.05). As demonstrated in this work, 81.3% (26/32) of patients with a high parasite load, considered as more than 11 larvae per gram of feces, presented serum cortisol levels above the normal reference value (24 mg/dL). High endogenous cortisol levels in alcoholic patients were not associated to susceptibility to S. stercoralis infection, however once infected, this may lead to a high parasite load.

Strongyloides stercoralis Infection in Alcoholic Patients

The course of Strongyloides stercoralis infection is usually asymptomatic with a low discharge of rhabditoid larva in feces. However, the deleterious effects of alcohol consumption seem to enhance the susceptibility to infection, as shown by a fivefold higher strongyloidiasis frequency in alcoholics than in nonalcoholics. Moreover, the association between S. stercoralis infection and alcoholism presents a risk for hyperinfection and severe strongyloidiasis. There are several possible mechanisms for the disruption of the host-parasite equilibrium in ethanol-addicted patients with chronic strongyloidiasis. One explanation is that chronic ethanol intake stimulates the hypothalamic-pituitary-adrenal (HPA) axis to produce excessive levels of endogenous cortisol, which in turn can lead to a deficiency in type 2 T helper cells (Th2) protective response, and also to mimic the parasite hormone ecdysone, which promotes the transformation of rhabditiform larvae to filariform larvae, leading to autoinfection. Therefore, when untreated, alcoholic patients are continuously infected by this autoinfection mechanism. Thus, the early diagnosis of strongyloidiasis and treatment can prevent serious forms of hyperinfection in ethanol abusers.

Membrane fractions from Strongyloides venezuelensis in the immunodiagnosis of human strongyloidiasis

Strongyloides venezuelensis is a parasitic nematode of rodents frequently used to obtain heterologous antigens for the immunological diagnosis of human strongyloidiasis. The aim of this study was to evaluate membrane fractions from S. venezuelensis for human strongyloidiasis immunodiagnosis. Soluble and membrane fractions were obtained in phosphate saline (SS and SM) and Tris-HCl (TS and TM) from filariform larvae of S. venezuelensis. Ninety-two serum samples (n = 92) were obtained from 20 strongyloidiasis patients (Group I), 32 from patients with other parasitic diseases (Group II), and 40 from healthy individuals (Group III), and were analyzed by enzyme-linked immunosorbent assay (ELISA). Soluble fractions (SS and TS) showed 90.0% sensitivity and 88.9% specificity, whereas the membrane fractions (SM and TM) showed 95.0% sensitivity and 94.4% specificity. The present results suggest the possible use of membrane fractions of S. venezuelensis as an alternative antigen for human strongyloidiasis immunodiagnosis.

Effect of dilution of stool soluble component on growth and development of Strongyloides stercoralis

Dispersion or dilution of stool by water from heavy rainfall may affect Strongyloides stercoralis free-living development producing infective filariform larvae (FL). This study examined effect of water dilution of stool on survival of S. stercoralis free-living development. One g of stool was prepared in water so that its soluble component was diluted sequentially from 1:2 to 1:480. Three dishes were used to compare FL production in three culture conditions: stool suspension, stool sediment deposited in soil, and isolated rhabditiform larvae (RhL) deposited in soil. The fourth dish was for developmental observation of RhL into free-living stages. Numerous FL were generated from undiluted or 1:2 diluted stool and stool sediment placed on soil. However, starting from dilution 1:5, FL production continuously decreased in both stool suspensions and stool sediments placed on soil. RhL isolated from stool dilutions placed on soil gave rise to few FL. Worm mating were seen at 24-30 hours in dilutions 1:20-1:120 only. Highest numbers of FL from indirect free-living cycle were 1/3 of those from control. FL production decreased as stool dilution increased, and reached zero production at 1:160 dilution. Rainfall may disperse or dilute stool so that nutritional supplement for S. stercoralis free-living development is insufficient.

Novel approaches to the diagnosis of Strongyloides stercoralis infection

Strongyloides stercoralis differs from the other soil-transmitted helminths because it puts infected subjects at risk of a fatal syndrome (in cases of immunosuppression for medical conditions, immunosuppressant therapies, or both). Chronic strongyloidiasis is often a non-severe condition, or is sometimes even asymptomatic, but diagnosis and effective therapy are essential in order to eradicate the infection and the life-long risk involved. Therefore, diagnostic methods need to be highly sensitive. Stool microscopy and the Kato-Katz technique are commonly used in prevalence studies, but they are inadequate for S. stercoralis detection. This is probably the main reason why the global prevalence has long been underestimated. Concentration methods, the Baermann technique and Koga agar plate culture have better, but still unsatisfactory, sensitivity. Serological tests have demonstrated higher sensitivity; although some authors have concerns about their specificity, it is possible to define cut-off values over which infection is almost certain. In particular, the luciferase immunoprecipitation system technique combined with a recombinant antigen (NIE) demonstrated a specificity of almost 100%. ELISA coproantigen detection has also shown promising results, but still needs full evaluation. Molecular diagnostic methods are currently available in a few referral centres as in-house techniques. In this review, on the basis of the performance of the different diagnostic methods, we outline diagnostic strategies that could be proposed for different purposes, such as: prevalence studies in endemic areas; individual diagnosis and screening; and monitoring of cure in clinical care and clinical trials.

Coinfection of Strongyloides stercoralis and Aspergillus found in bronchoalveolar lavage fluid from a patient with stubborn pulmonary symptoms

We report a case involving coinfection with Strongyloides stercoralis (S. stercoralis) and Aspergillus found in the bronchoalveolar lavage fluid (BALF) of an elderly male patient who had a medical history of autoimmune pancreatitis (AIP) and who was treated with prednisone therapy 6 months previously. The patient presented with stubborn pulmonary symptoms and signs because of Aspergillus invasion and mechanical destruction caused by larval migration. We found S. stercoralis and Aspergillus in his BALF that provided diagnostic proof.

Tracking year-to-year changes in intestinal nematode communities of rufous mouse lemurs (Microcebus rufus)

While it is known that intestinal parasite communities vary in their composition over time, there is a lack of studies addressing how variation in component communities (between-hosts) manifests in infracommunities (within-host) during the host lifespan. In this study, we investigate the changes in the intestinal parasite infracommunities in wild-living rufous mouse lemurs (Microcebus rufus) from Ranomafana National Park in southeastern Madagascar from 2010 to 2012. We used high-throughput barcoding of the 18S rRNA gene to interrogate parasite community structure. Our results show that in these nematode communities, there were two frequently occurring putative species and four rarer putative species. All putative species were randomly distributed over host individuals and they did not occur in clear temporal patterns. For the individuals caught in at least two different years, there was high turnover of putative species and high variation in fecal egg counts. Our study shows that while there was remarkable variation in infracommunities over time, the component community was relatively stable. Nevertheless, the patterns of prevalence varied substantially between years in each component community.

Strongyloidiasis with emphasis on human infections and its different clinical forms

Strongyloidiasis (caused by Strongyloides stercoralis, and to a lesser extent by Strongyloides fuelleborni) is one of the most neglected tropical diseases with endemic areas and affecting more than 100 million people worldwide. Chronic infections in endemic areas can be maintained for decades through the autoinfective cycle with the L3 filariform larvae. In these endemic areas, misdiagnosis, inadequate treatment and the facilitation of the hyperinfection syndrome by immunosuppression are frequent and contribute to a high mortality rate. Despite the serious health impact of strongyloidiasis, it is a neglected disease and very little is known about this parasite and the disease when compared to other helminth infections. Control of the disease is difficult because of the many gaps in our knowledge of strongyloidiasis. We examine the recent literature on different aspects of strongyloidiasis with emphasis in those aspects that need further research.

Development of a rapid serological assay for the diagnosis of strongyloidiasis using a novel diffraction-based biosensor technology

BACKGROUND

Strongyloidiasis is a persistent human parasitic infection caused by the intestinal nematode, Strongyloides stercoralis. The parasite has a world-wide distribution, particularly in tropical and subtropical regions with poor sanitary conditions. Since individuals with strongyloidiasis are typically asymptomatic, the infection can persist for decades without detection. Problems arise when individuals with unrecognized S. stercoralis infection are immunosuppressed, which can lead to hyper-infection syndrome and disseminated disease with an associated high mortality if untreated. Therefore a rapid, sensitive and easy to use method of diagnosing Strongyloides infection may improve the clinical management of this disease.

METHODOLOGY/PRINCIPAL FINDINGS

An immunological assay for diagnosing strongyloidiasis was developed on a novel diffraction-based optical bionsensor technology. The test employs a 31-kDa recombinant antigen called NIE derived from Strongyloides stercoralis L3-stage larvae. Assay performance was tested using retrospectively collected sera from patients with parasitologically confirmed strongyloidiasis and control sera from healthy individuals or those with other parasitoses including schistosomiasis, trichinosis, echinococcosis or amebiasis who were seronegative using the NIE ELISA assay. If we consider the control group as the true negative group, the assay readily differentiated S. stercoralis-infected patients from controls detecting 96.3% of the positive cases, and with no cross reactivity observed in the control group These results were in excellent agreement (κ = 0.98) with results obtained by an NIE-based enzyme-linked immunosorbent assay (ELISA). A further 44 sera from patients with suspected S. stercoralis infection were analyzed and showed 91% agreement with the NIE ELISA.

CONCLUSIONS/SIGNIFICANCE

In summary, this test provides high sensitivity detection of serum IgG against the NIE Strongyloides antigen. The assay is easy to perform and provides results in less than 30 minutes, making this platform amenable to rapid near-patient screening with minimal technical expertise.

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.

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.

Usefulness of Strongyloides stercoralis serology in the management of patients with eosinophilia

Strongyloides stercoralis infection is being increasingly diagnosed out of endemic areas. The aim of this study is to evaluate the usefulness of S. stercoralis serology for the management of probable strongyloidiasis in patients presenting with eosinophilia. Overall, 147 patients were included, 89 (60.5%) patients had a positive S. stercoralis serology. Strongyloides stercoralis larvae were detected only in 15 (10.2%) patients. Twenty-eight patients had human immunodeficiency virus infection. Eighty patients received ivermectin 200 mcg/Kg/day for 2 days, and follow-up 6 months after treatment could be performed in 32 patients: 26 (81.3%) patients reached the response to treatment criteria (negative serology 6 months after treatment or when by enzyme-linked immunosorbent assay the optical density ratio of post-treatment to pre-treatment decreased to 0.6), and 11 (34.4%) patients fulfilled the cure criteria (negative serology 6 months after treatment). Strongyloides stercoralis serology is a useful diagnostic tool both in the diagnosis of probable strongyloidiasis and follow-up after treatment.

Strongyloides stercoralislarvae excretion patterns before and after treatment

The variability of larval excretion impedes the parasitological diagnosis ofStrongyloides stercoralisin infected individuals. We assessed the number of larvae excreted per gram (LPG) stool in 219 samples from 38 infected individuals over 7 consecutive days before and in 470 samples from 44 persons for 21 consecutive days after ivermectin treatment (200 μg kg−1BW). The diagnostic sensitivity of a single stool sample was about 75% for individuals with low-intensity infections (⩽1 LPG) and increased to 95% for those with high-intensity infections (⩾10 LPG). Doubling the number of samples examined per person increased sensitivity to more than 95%, even for low-intensity infections. There was no indication of a cyclic excretion of larvae. After treatment, all individuals stopped excreting larvae within 3 days. Larvae were not detected during any of the following 18 days (total 388 Baermann and 388 Koga Agar tests). Two stool samples, collected on consecutive days, are recommended in settings where low or heterogeneous infection intensities are likely. In this way, taking into account the possible biological variability in excretion, the efficacy of ivermectin treatment can be assessed as soon as 4 days after treatment.

Detrimental effect of water submersion of stools on development of Strongyloides stercoralis

Strongyloidiasis is prevalent in Thailand, yet its prevalence in the south is lower than in other parts of the country. This might be due to the long rainy season in the south resulting in stool submersion in water inhibiting worm development. In this study, the effect of water submersion of fecal samples on development of Strongyloides stercoralis was investigated. Ten ml of a 1 ∶ 5 fecal suspension were placed in 15-ml tubes, 35-mm dishes, and 90-mm dishes producing the depths of 80 mm, 11 mm and 2 mm-suspensions, respectively. The worm development was followed at 1/6, 4, 6, 8, 10, 12, 14, 16, 24, and 36 h, by determining the number of filariform larva (FL) generated from agar-plate cultures (APC). Fecal suspensions kept in tubes and 35-mm dishes showed a decline in FL yield relative to incubation time and reached zero production 14 h after incubation. In contrast, the number of FL generated from the suspension kept in 90-mm dishes remained stable up to 36 h. Cumulatively, all tubes and 35-mm dishes became negative in APC after 14 h while 90-mm dishes remained APC-positive up to 36 h. Adding more water or stool suspension to dishes resulted in a decreased number of FL. Mechanical aeration of the suspensions in tubes restored an almost normal FL yield. It appears that the atmospheric air plays a significant role in growth and development of S. stercoralis in the environment and may be one of factors which contribute to a lower prevalence of human strongyloidiasis in the south of Thailand.

Parasitological and molecular diagnosis in experimental Strongyloides venezuelensis infection

Strongyloides venezuelensis is a parasitic nematode of rats which is frequently used as a model to study human and animal strongyloidiasis. The aim of this study was to evaluate the correlation between parasitological and molecular diagnosis in Strongyloides venezuelensis infection. PCR assays were used to detect S. venezuelensis DNA in fecal samples obtained from experimentally infected Rattus norvegicus. The results showed a higher sensitivity of the PCR assay in detecting the infection compared to parasitological methods.

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.

The laboratory diagnosis and follow up of strongyloidiasis: a systematic review

BACKGROUND

Strongyloidiasis is frequently under diagnosed since many infections remain asymptomatic and conventional diagnostic tests based on parasitological examination are not sufficiently sensitive. Serology is useful but is still only available in reference laboratories. The need for improved diagnostic tests in terms of sensitivity and specificity is clear, particularly in immunocompromised patients or candidates to immunosuppressive treatments. This review aims to evaluate both conventional and novel techniques for the diagnosis of strongyloidiasis as well as available cure markers for this parasitic infection.

METHODOLOGY/PRINCIPAL FINDINGS

The search strategy was based on the data-base sources MEDLINE, Cochrane Library Register for systematic review, EmBase, Global Health and LILACS and was limited in the search string to articles published from 1960 to August 2012 and to English, Spanish, French, Portuguese and German languages. Case reports, case series and animal studies were excluded. 2003 potentially relevant citations were selected for retrieval, of which 1649 were selected for review of the abstract. 143 were eligible for final inclusion.

CONCLUSIONS

Sensitivity of microscopic-based techniques is not good enough, particularly in chronic infections. Furthermore, techniques such as Baermann or agar plate culture are cumbersome and time-consuming and several specimens should be collected on different days to improve the detection rate. Serology is a useful tool but it might overestimate the prevalence of disease due to cross-reactivity with other nematode infections and its difficulty distinguishing recent from past (and cured) infections. To evaluate treatment efficacy is still a major concern because direct parasitological methods might overestimate it and the serology has not yet been well evaluated; even if there is a decline in antibody titres after treatment, it is slow and it needs to be done at 6 to 12 months after treatment which can cause a substantial loss to follow-up in a clinical trial.