Strongyloides stercoralis

A silent threat behind bars: Serosurvey and associated risk factors for strongyloidiasis in female inmates and correctional officers

Strongyloidiasis has been a neglected parasitic infection caused by Strongyloides genus parasites. Despite assessment of S. stercoralis exposure in different vulnerable populations, seroprevalence in inmates worldwide remains to be fully established. Due to poor sanitation and lack of personal hygienic practices, incarcerated individuals have been considered prone to spread infectious illnesses. Accordingly, the present study has assessed exposure and associated risk factors for strongyloidiasis in women inmates and correctional officers at the Women's State Penitentiary of Parana, part of the third largest incarceration complex in Brazil at the time. Blood samplings were performed in 2020 and 2021from a total of 503 women inmates and 92 correctional officers. Participants voluntarily responded to an epidemiological questionnaire to assess associated risk factors to strongyloidiasis. Serological analysis was performed by ELISA for anti-S. stercoralis IgG detection. Statistical analysis was performed using R software, adopting a 5% level of significance. The data were submitted to univariate analysis by chi-square or Fisher´s Exact test for assessing the association among seropositivity and the variables. The variables with p-value < 0.2 in the univariate analysis were considered fit to be included in the logistic regression. In overall, 356/503 (70.8%; 95% CI: 66.7-74.6) inmates were seropositive for anti-S. stercoralis antibodies, with no statistically associated risk factor to seropositivity. A total of 57/92 (62.0%; 95% CI: 51.8-71.2) correctional officers were seropositive, and logistic regression revealed that individuals older than 50 years were more likely seropositive. In conclusion, the high endemicity observed herein has indicated a history of previous exposure to S. stercoralis and warned for a systematic strongyloidiasis screening for inmates, to prevent long term morbidity and disseminated infection during incarceration.

Strongyloides stercoralis infection in solid organ transplant recipients

PURPOSE OF REVIEW

Strongyloides stercoralis infection remains of concern due to its high associated morbidity among solid organ transplant recipients (SOTR) and the risk of donor-derived infection (DDI). We review key aspects of epidemiology to inform screening for and treatment of chronic infection among organ transplant candidates to reduce the risk of infectious complications in the posttransplant setting.

RECENT FINDINGS

In this work, we offer guidance regarding the optimal management of Strongyloides hyperinfection syndrome and disseminated infection and offer recommendations regarding posttreatment surveillance and the potential need for repeat treatment during subsequent periods of augmented immunosuppression. This review also provides updated recommendations for screening of deceased and living donors as recently proposed by the Organ Procurement and Transplantation Network's Ad Hoc Disease Transmission Advisory Committee.

SUMMARY

Risk reduction of Strongyloides infection in the SOTR population can be further enhanced by optimized treatment of infection, posttreatment surveillance during at-risk periods and recent proposed policy shifts to universal donor screening.

Strongyloides stercoralis in two dogs from a household in temperate Australia

Strongyloides stercoralis is parasite affecting both humans and dogs and is most prevalent in tropical and subtropical areas of Australia. This case report describes two dogs from a household in Sydney, New South Wales, one with chronic gastrointestinal signs and the other who was asymptomatic who were subsequently diagnosed with S. stercoralis. Diagnosis can be challenging in humans and dogs due to intermittent shedding and low worm burdens and in this case the symptomatic dog had Strongyloides spp. rhabitiform larvae detected on a direct faecal smear and PCR, the asymptomatic dog on PCR only. Obtained sequences from the symptomatic dog confirmed the presence of the S. stercoralis clade affecting both dogs and humans. Infection does not respond to commonly used deworming drugs for dogs. Treatment in both cases was undertaken using off-label doses of ivermectin and follow-up PCR testing was negative. This case report should increase practitioner awareness of this parasite as present and transmissible in temperate areas of Australia.

A case of disseminated strongyloidiasis diagnosed by worms in the urinary sediment

Strongyloidiasis is a chronic infection caused by the intestinal nematode parasite Strongyloides stercoralis and is characterized by a diverse spectrum of nonspecific clinical manifestations. This report describe a case of disseminated strongyloidiasis with urination difficulty, generalized weakness, and chronic alcoholism diagnosed through the presence of worms in the urinary sediment. A 53-year-old man was hospitalized for severe abdominal distension and urinary difficulties that started 7-10 days prior. The patient also presented with generalized weakness that had persisted for 3 years, passed loose stools without diarrhea, and complained of dyspnea. In the emergency room, approximately 7 L of urine was collected, in which several free-living female adult and rhabditiform larvae of S. stercoralis, identified through their morphological characteristics and size measurements, were detected via microscopic examination. Rhabditiform larvae of S. stercoralis were also found in the patient's stool. During hospitalization, the patient received treatment for strongyloidiasis, chronic alcoholism, peripheral neurosis, neurogenic bladder, and megaloblastic anemia, and was subsequently discharged with improved generalized conditions. Overall, this report presents a rare case of disseminated strongyloidiasis in which worms were detected in the urinary sediment of a patient with urination difficulties and generalized weakness combined with chronic alcoholism, neurogenic bladder, and megaloblastic anemia.

A Rare Case of an Eosinophilic Pleural Effusion and Loculated Ascites Associated with Strongyloides stercoralis Hyperinfection Syndrome in California

Introduction. Strongyloides stercoralis causes a helminthic infection that occurs via penetration of the skin with migration to the bloodstream, tracheobronchial tree, and gastrointestinal system. Pulmonary manifestations are rare and are typically seen in immunosuppressed patients who have Strongyloides stercoralis hyperinfection syndrome. Eosinophilic pleural effusions are rare in strongyloidiasis and only cited in a few case reports. Case Presentation. A 45-year-old male with a past medical history of diabetes mellitus, alcoholic cirrhosis, and end-stage renal disease presented to the emergency department with abdominal pain and dyspnea. Imaging studies demonstrated large bilateral pleural effusions, and he subsequently underwent an ultrasound-guided thoracentesis on the right hemithorax, yielding an exudative eosinophilic pleural effusion. An extensive hematology, gastroenterology, and infectious work-up was pursued. Strongyloides immunoglobulin G was positive, and he was successfully treated with ivermectin. Discussion. Eosinophilic pleural effusions related to strongyloidiasis are exceedingly rare. Clinicians should consider Strongyloides stercoralis infection as a part of the differential diagnosis when evaluating immunosuppressed patients with eosinophilic pleural effusions. Loculated abdominal fluid may also be a rare manifestation of Strongyloides stercoralis hyperinfection syndrome.

Carbon dioxide shapes parasite-host interactions in a human-infective nematode

Skin-penetrating nematodes infect nearly one billion people worldwide. The developmentally arrested infective larvae (iL3s) seek out hosts, invade hosts via skin penetration, and resume development inside the host in a process called activation. Activated infective larvae (iL3as) traverse the host body, ending up as parasitic adults in the small intestine. Skin-penetrating nematodes respond to many chemosensory cues, but how chemosensation contributes to host seeking, intra-host development, and intra-host navigation - three crucial steps of the parasite-host interaction - remains poorly understood. Here, we investigate the role of carbon dioxide (CO2) in promoting parasite-host interactions in the human-infective threadworm Strongyloides stercoralis. We show that S. stercoralis exhibits life-stage-specific preferences for CO2: iL3s are repelled, non-infective larvae and adults are neutral, and iL3as are attracted. CO2 repulsion in iL3s may prime them for host seeking by stimulating dispersal from host feces, while CO2 attraction in iL3as may direct worms toward high-CO2 areas of the body such as the lungs and intestine. We also identify sensory neurons that detect CO2; these neurons are depolarized by CO2 in iL3s and iL3as. In addition, we demonstrate that the receptor guanylate cyclase Ss-GCY-9 is expressed specifically in CO2-sensing neurons and is required for CO2-evoked behavior. Ss-GCY-9 also promotes activation, indicating that a single receptor can mediate both behavioral and physiological responses to CO2. Our results illuminate chemosensory mechanisms that shape the interaction between parasitic nematodes and their human hosts and may aid in the design of novel anthelmintics that target the CO2-sensing pathway.

Introduction to Strongyloides stercoralis Anatomy

Strongyloides stercoralis, commonly known as the human threadworm, is a skin-penetrating gastrointestinal parasitic nematode that infects hundreds of millions of people worldwide. Like other Strongyloides species, S. stercoralis is capable of cycling through a single free-living generation. Although S. stercoralis and the free-living nematode Caenorhabditis elegans are evolutionarily distant, the free-living adults of S. stercoralis are similar enough in size and morphology to C. elegans adults that techniques for generating transgenics and knockouts in C. elegans have been successfully adapted for use in S. stercoralis. High-quality genomic and transcriptomic data are also available for S. stercoralis. Thus, one can use a burgeoning array of functional genomic tools in S. stercoralis to probe questions about parasitic nematode development, physiology, and behavior. Knowledge gained from S. stercoralis will inform studies of other parasitic nematodes such as hookworms that are not yet amenable to genetic manipulation. This review describes the basic anatomy of S. stercoralis.

Pulmonary strongyloidiasis and hyperinfection in a Patient with idiopathic inflammatory myopathy：A case report

Pulmonary strongyloidiasis is a rare infection in patients with autoimmune diseases, and immunosuppression can lead to the development of hyperinfection syndrome with a high mortality rate. We present a case of a 78-year-old male with previous idiopathic inflammatory myopathy (IIM) with interstitial lung disease. He developed hyperinfection syndrome and respiratory failure, and diagnostic metagenomic next-generation sequencing (mNGS) of bronchoalveolar lavage fluid (BALF) confirmed the presence of Strongyloides stercoralis. After treatment with ivermectin, the patient's symptoms improved. Therefore, adequate screening and prophylactic treatment are needed for people at risk of immunosuppression, which can reduce the occurrence of the devastating S. stercoralis hyperinfection syndrome. It also highlights mNGS as a highly accurate test for the detection of difficult to atypical pathogens.

Invade or die: behaviours and biochemical mechanisms that drive skin penetration in Strongyloides and other skin-penetrating nematodes

Skin-penetrating nematodes, including the human threadworm Strongyloides stercoralis and hookworms in the genera Necator and Ancylostoma, are gastrointestinal parasites that are a major cause of neglected tropical disease in low-resource settings worldwide. These parasites infect hosts as soil-dwelling infective larvae that navigate towards hosts using host-emitted sensory cues such as odorants and body heat. Upon host contact, they invade the host by penetrating through the skin. The process of skin penetration is critical for successful parasitism but remains poorly understood and understudied. Here, we review current knowledge of skin-penetration behaviour and its underlying mechanisms in the human parasite S. stercoralis, the closely related rat parasite Strongyloides ratti, and other skin-penetrating nematodes such as hookworms. We also highlight important directions for future investigations into this underexplored process and discuss how recent advances in molecular genetic and genomic tools for Strongyloides species will enable mechanistic investigations of skin penetration and other essential parasitic behaviours in future studies. This article is part of the Theo Murphy meeting issue 'Strongyloides: omics to worm-free populations'.

Antiparasitic activity of ivermectin: Four decades of research into a "wonder drug"

Parasitic diseases still pose a serious threat to human and animal health, particularly for millions of people and their livelihoods in low-income countries. Therefore, research into the development of effective antiparasitic drugs remains a priority. Ivermectin, a sixteen-membered macrocyclic lactone, exhibits a broad spectrum of antiparasitic activities, which, combined with its low toxicity, has allowed the drug to be widely used in the treatment of parasitic diseases affecting humans and animals. In addition to its licensed use against river blindness and strongyloidiasis in humans, and against roundworm and arthropod infestations in animals, ivermectin is also used "off-label" to treat many other worm-related parasitic diseases, particularly in domestic animals. In addition, several experimental studies indicate that ivermectin displays also potent activity against viruses, bacteria, protozoans, trematodes, and insects. This review article summarizes the last 40 years of research on the antiparasitic effects of ivermectin, and the use of the drug in the treatment of parasitic diseases in humans and animals.

Frequency of strongyloidiasis and associated factors: Analysis of 13 years of laboratory results in a tertiary referral hospital in Honduras, 2010-2022

INTRODUCTION

The frequency of detected strongyloidiasis is affected by the selected laboratory method in the studied population. Considering that Honduras has few community-based studies, the analysis of the laboratory record data can provide information helping to understand this parasitosis.

OBJECTIVE

To estimate the frequency and to identify the factors associated with strongyloidiasis, analyzing the laboratory records of the Servicio de Parasitología at Hospital Escuela in Tegucigalpa (Honduras) between 2010 and 2022.

MATERIALS AND METHODS

We carried out a descriptive, cross-sectional, analytical study. The laboratory diagnosis consisted of stool samples' examination by direct smear and modified Baermann technique. We estimated frequencies and percentages. The statistical association was calculated with prevalence ratios and a 95% confidence interval. Software R, version 4.2.0, and epiR package, version 2.0.46, were used to perform the analysis.

RESULTS

The frequency of strongyloidiasis was 0.29% (112/38,085). It was higher with the modified Baermann technique (0.87%; 40/4,575) among male patients (0.44%; 70/15,758). Regarding the age, strongyloidiasis was higher in the 20-40 years old group (0.41%; 28/6,886) with direct smear and 41-61 years old (1.14%; 14/1,232) group with the modified Baermann technique. Among the factors associated with strongyloidiasis were age between 20 and 61 years old (PR=2.26, CI 95%=1.53-3.31), male patients (PR=2.34, CI 95%=1.60‑3.44), mucus (PR=1.86, CI 95%=1.22-2.83) and Charcot-Leyden crystals in stool (PR=8.47, CI 95%=5.14-13.96); watery stool (PR=2.39, CI 95%=1.55-3.68), and other helminthiases (PR=6.73, CI 95%=3.98-11.38). Associated factors to cases detected with the modified Baermann technique were outpatient consultation (PR=4.21, CI 95%=1.91-9.28) and formed stools (PR=3.99, CI 95%=1.94-8.19).

CONCLUSIONS

The modified Baermann technique increased the detection of strongyloidiasis almost four times. Most cases were distributed among male adults. The cases diagnosed exclusively with the modified Baermann technique have differences from those with observed larvae in the direct smear. It is necessary to develop community-based population studies.

Strongyloides stercoralis infection reduces Fusicatenibacter and Anaerostipes in the gut and increases bacterial amino-acid metabolism in early-stage chronic kidney disease

Understanding gut bacterial composition and proteome changes in patients with early-stage chronic kidney disease (CKD) could lead to better methods of controlling the disease progression. Here, we investigated the gut microbiome and microbial functions in patients with S. stercoralis infection (strongyloidiasis) and early-stage CKD. Thirty-five patients with early stages (1-3) of CKD were placed in two groups matched for population characteristics and biochemical parameters, 12 patients with strongyloidiasis in one group and 23 uninfected patients in the other. From every individual, a sample of their feces was obtained and processed for 16S rRNA sequencing and metaproteomic analysis using tandem liquid chromatography-mass spectrometry (LC-MS/MS). Strongyloides stercoralis infection per se did not significantly alter gut microbial diversity. However, certain genera (Bacteroides, Faecalibacterium, Fusicatenibacter, Sarcina, and Anaerostipes) were significantly more abundant in infection-free CKD patients than in infected individuals. The genera Peptoclostridium and Catenibacterium were enriched in infected patients. Among the significantly altered genera, Fusicatenibacter and Anaerostipes were the most correlated with renal parameters. The relative abundance of members of the genus Fusicatenibacter was moderately positively correlated with estimated glomerular filtration rate (eGFR) (r = 0.335, p = 0.049) and negatively with serum creatinine (r = -0.35, p = 0.039). Anaerostipes, on the other hand, showed a near-significant positive correlation with eGFR (r = 0.296, p = 0.084). Individuals with S. stercoralis infection had higher levels of bacterial proteins involved in amino-acid metabolism. Analysis using STITCH predicted that bacterial amino-acid metabolism may also be involved in the production of colon-derived uremic toxin (indole), a toxic substance known to promote CKD. Strongyloides stercoralis infection is, therefore, associated with reduced abundance of Fusicatenibacter and Anaerostipes (two genera possibly beneficial for kidney function) and with increased bacterial amino-acid metabolism in the early-stages of CKD, potentially producing uremic toxin. This study provides useful information for prevention of progression of CKD beyond the early stages.

Fatal Disseminated Strongyloidiasis in an Immunosuppressed Patient During COVID-19 Pandemic

INTRODUCTION

This report presents a fatal case of disseminated strongyloidiasis in a patient with myasthenia gravis and diabetes mellitus who had received corticosteroid therapy.

CASE REPORT

The patient was a 67-year-old woman living in a rural area endemic for Strongyloides stercoralis in northern Iran. Disseminated strongyloidiasis was diagnosed in the advanced stage of the disease, with enormous numbers of larvae demonstrated in direct smears prepared from stool samples and stomach biopsy. Despite treatment with ivermectin and antibiotics, the patient succumbed to the severity of the infection.

CONCLUSION

Clinicians working in endemic areas should be mindful of the possibility of gastric involvement in strongyloidiasis, even if symptoms are nonspecific. We recommend that high-risk individuals be screened for S. stercoralis prior to immunosuppressive therapy in endemic regions to raise awareness and prevent similar cases.

Assessment of gastrointestinal nematode anthelmintic resistance and acaricidal efficacy of fluazuron-flumethrin on sheep and goat ticks in the North West province of South Africa

Background and Aim

Anthelmintic resistance (AR) and acaricide resistance (ACR) pose great economic threat to communal livestock raised by rural communities, limiting sustainable production. This study was conducted to assess the occurrence of AR and ACR against nematodes and ticks that infest small ruminants (sheep and goats) from small-scale farming communities in the North West Province of South Africa, as well as document the associated risk factors.

Materials and Methods

The study was conducted on small-scale farming locations in two districts of the North West Province, namely, Dr. Ruth Segomotsi Mompati district and Dr. Kenneth Kaunda district, from November 2019 to March 2020. A questionnaire survey based specifically on antiparasitic treatment and related management practices was administered to 86 small-scale farmers. A fecal egg count reduction test (FECRT) was used to determine in vivo AR in small ruminants against benzimidazole (BZD), levamisole, and macrocyclic lactone on nine ruminant farms. Then, deoxyribonucleic acid was extracted from L3 larvae and resistant nematodes were identified using a polymerase chain reaction, targeting the internal transcribed spacer 2 gene. An egg hatch assay (EHA) and a larval mortality assay (LMA) were used to determine in vitro AR against thiabendazole (TBZ and BZD) in the same farms. Acaricide resistance against fluazuron-flumethrin (Drastic Deadline eXtreme) pour-on was assessed using an adult immersion test (AIT) on Rhipicephalus evertsi.

Results

Questionnaire results indicated that most farmers (89%) relied solely on anthelmintics. Farmers used visual appraisal to estimate the dosage, which is the primary cause of resistance. The FECRT revealed AR in all the farms. Egg hatch assay results revealed AR development against TBZ in all districts, with >95% of the eggs hatching at variable doses. Larval mortality assay results revealed the development of resistance against BZD, with 50% of L3 larvae surviving at different doses in all farms. Adult immersion test results indicated that fluazuron-flumethrin (>99%) exhibited high acaricidal efficacy against R. evertsi by inhibiting tick oviposition.

Conclusion

This investigation found that sheep and goats in the studied areas are developing AR to gastrointestinal parasites. The findings of in vivo tests showed resistance with fecal egg count reduction percentage of <95% or lower confidence limit of <90%. The results of EHA and LMA revealed no evidence of inhibition of egg development and larval mortality, indicating the development of resistance. Acaricide resistance was not detected against fluazuron-flumethrin, which is commonly used in the study areas. Thus, developing management methods for these economically significant livestock nematodes, including teaching small-scale farmers how to properly administer anthelmintics and acaricides to their livestock, is urgently needed.

Overlapping Infection by Strongyloides spp. and Cytomegalovirus in the Immunocompromised Host: A Comprehensive Review of the Literature

Strongyloides and cytomegalovirus co-infections are rarely reported, even though they are distinguished by high morbidity and mortality, especially in immunocompromised hosts. We narratively reviewed the literature on reported cases of Strongyloides and CMV co-infections in immunosuppressed patients. Most cases occurred in males with a median age of 47 (IQR, 37-59). Strongyloides/CMV co-infections occurred among immunocompromised hosts, especially in solid organ transplants and hematological or rheumatological diseases. Most of the patients underwent a course of steroid treatment before the diagnosis of co-infections. Other common immunomodulatory agents were tacrolimus and mycophenolate. The first clinical manifestations of co-infections were mainly gastrointestinal, followed by respiratory symptoms. CMV was, in most patients, co-infected with an isolated reactivation, although Strongyloides manifested especially as hyperinfection syndrome. Ganciclovir and ivermectin are the mainstays of CMV and Strongyloides treatment. However, the treatment mortality reported in this narrative review is around 52.4%. Interestingly secondary bacterial infections are common in CMV/Strongyloides-infected patients.

Efficacy of Oral Ivermectin as Empirical Prophylaxis for Strongyloidiasis in Patients Treated with High-Dose Corticosteroids: A Retrospective Cohort Study

People living in areas endemic for strongyloidiasis are at risk of latent Strongyloides stercoralis infection. Corticosteroid therapy is a well-established risk factor for life-threatening hyperinfection syndrome and disseminated disease owing to suppression of the immune system. There are limited data available on the efficacy and cost of providing oral ivermectin prophylaxis to all patients receiving high-dose corticosteroids for strongyloidiasis in endemic areas. We thus conducted this retrospective cohort study at Khon Kaen University's Srinagarind Hospital from 2015 to 2019. Inclusion criteria were as follows: age ≥ 18 years, having received ≥ 0.5 mg/kg/day of prednisolone or equivalent for at least 14 days, and hospitalization during the study period. A total of 250 patients were included in the study: 125 in the empirical prophylaxis group (prescribed ivermectin even if fecal examination results were negative or nonexistent) and the remaining patients in the definite therapy group (prescribed ivermectin only if S. stercoralis was detected by fecal examination). The prevalence of strongyloidiasis at enrollment estimated by fecal examination was 5.5%. Ivermectin was given to 125 patients (100%) in the prophylaxis group compared with 12 (9.6%) in the definite therapy group (P value < 0.001). During the 12-month follow-up period, S. stercoralis was detected in three patients, two in the prophylaxis group and one in the definite therapy group (P value = 1.000). No cases of hyperinfection syndrome or disseminated disease were found. The empirical prophylaxis strategy had a significantly higher cost than the definite therapy strategy (563 versus 254, P value < 0.001) and did not demonstrate superior efficacy in strongyloidiasis prevention.

Coinfection with Strongyloides and SARS-CoV-2: A Systematic Review

BACKGROUND

Treatments for COVID-19, including steroids, might exacerbate Strongyloides disease in patients with coinfection. We aimed to systematically review clinical and laboratory features of SARS-CoV-2 and Strongyloides coinfection, investigate possible interventions, assess outcomes, and identify research gaps requiring further attention.

METHODS

We searched two electronic databases, LitCOVID and WHO, up to August 2022, including SARS-CoV-2 and Strongyloides coinfection studies. We adapted the World Health Organization-Uppsala Monitoring Centre (WHO-UMC) system for standardized case causality assessment to evaluate if using corticosteroids or other immunosuppressive drugs in COVID-19 patients determined acute manifestations of strongyloidiasis.

RESULTS

We included 16 studies reporting 25 cases of Strongyloides and SARS-CoV-2 coinfection: 4 with hyperinfection syndrome; 2 with disseminated strongyloidiasis; 3 with cutaneous reactivation of strongyloidiasis; 3 with isolated digestive symptoms; and 2 with solely eosinophilia, without clinical manifestations. Eleven patients were asymptomatic regarding strongyloidiasis. Eosinopenia or normal eosinophil count was reported in 58.3% of patients with Strongyloides reactivation. Steroids were given to 18/21 (85.7%) cases. A total of 4 patients (19.1%) received tocilizumab and/or Anakirna in addition to steroids. Moreover, 2 patients (9.5%) did not receive any COVID-19 treatment. The causal relationship between Strongyloides reactivation and COVID-19 treatments was considered certain (4% of cases), probable (20% of patients), and possible (20% of patients). For 8% of cases, it was considered unlikely that COVID-19 treatment was associated with strongyloidiasis reactivations; the relationship between the Strongyloides infection and administration of COVID-19 treatment was unassessable/unclassifiable in 48% of cases. Of 13 assessable cases, 11 (84.6%) were considered to be causally associated with Strongyloides, ranging from certain to possible.

CONCLUSIONS

Further research is needed to assess the frequency and risk of Strongyloides reactivation in SARS-CoV-2 infection. Our limited data using causality assessment supports recommendations that clinicians should screen and treat for Strongyloides infection in patients with coinfection who receive immunosuppressive COVID-19 therapies. In addition, the male gender and older age (over 50 years) may be predisposing factors for Strongyloides reactivation. Standardized guidelines should be developed for reporting future research.

Strongyloides and COVID-19: Challenges and Opportunities for Future Research

Strongyloides stercoralis is a soil transmitted helminth endemic to tropical and subtropical areas that can persist for decades in immunocompetent human hosts as a chronic asymptomatic infection. The use of corticosteroids, a mainstay of treatment for patients hospitalized with severe coronavirus disease (COVID-19), can trigger a life-threatening Strongyloides hyperinfection syndrome and disseminated disease. We identified 22 previously published cases of strongyloidiasis occurring in individuals with COVID-19, with one death reported among the seven patients who had Strongyloides hyperinfection syndrome. A total of seventeen patients had previously received corticosteroids, and of the five with no prior corticosteroid use, one presented with hyperinfection syndrome. We identify the key challenges in the diagnosis and treatment of Strongyloides within the context of COVID-19, including our imprecise knowledge of the global distribution of Strongyloides, the overlapping symptoms and signs of COVID-19 and Strongyloides hyperinfection syndrome, the limited utility of eosinophilia as a clinical marker for strongyloidiasis in this setting, the lack of validated algorithms to screen for Strongyloides prior to corticosteroid use, and the paucity of treatment options for critically ill patients with COVID-19 who cannot take oral ivermectin. Future research should focus on improved diagnostic methods and population prevalence estimates, optimizing the approaches for Strongyloides screening in persons with COVID-19 (including clinical trial participants and strategies for resource-limited settings) and better defining the role of pre-emptive treatment.

Evaluation of the Immunomodulatory Effect of the Recombinant 14-3-3 and Major Antigen Proteins of Strongyloides stercoralis against an Infection by S. venezuelensis

Strongyloidiasis, caused by Strongyloides stercoralis, is a neglected parasitic disease that represents a serious public health problem. In immunocompromised patients, this parasitosis can result in hyperinfection or disseminated disease with high levels of mortality. In previous studies, the mRNAs encoding for the 14-3-3 and major antigen proteins were found to be expressed at high levels in S. stercoralis L3 larvae, suggesting potential key roles in parasite-host interactions. We have produced them as recombinant proteins (rSs14-3-3 and rSsMA) in a bacterial protein expression system. The serum levels of anti-rSs14-3-3 and anti-rSsMA IgGs are increased upon infection with S. venezuelensis, validating the use of the mouse model since the native 14-3-3 and MA proteins induce an immune response. Each recombinant protein was formulated in the adjuvant adaptation (ADAD) vaccination system and injected twice, subcutaneously, in CD1 mice that were experimentally infected with 3000 S. venezuelensis L3 to evaluate their protective and immunomodulatory activity. Our results, including the number of parthenogenetic females, number of eggs in stool samples and the analysis of the splenic and intestinal indexes, show that the vaccines did not protect against infection. The immunization with rSs14-3-3 induced changes in the cytokine profile in mice, producing higher expression of IL-10, TGF-β, IL-13 and TNF-α in the spleen, suggesting a Th2/Treg-type response with an increase in TNF-α levels, confirming its role as an immunomodulator.

Using newly optimized genetic tools to probe Strongyloides sensory behaviors

The oft-neglected human-parasitic threadworm, Strongyloides stercoralis, infects roughly eight percent of the global population, placing disproportionate medical and economic burden upon marginalized communities. While current chemotherapies treat strongyloidiasis, disease recrudescence and the looming threat of anthelminthic resistance necessitate novel strategies for nematode control. Throughout its life cycle, S. stercoralis relies upon sensory cues to aid in environmental navigation and coordinate developmental progression. Odorants, tastants, gases, and temperature have been shown to shape parasite behaviors that drive host seeking and infectivity; however, many of these sensory behaviors remain poorly understood, and their underlying molecular and neural mechanisms are largely uncharacterized. Disruption of sensory circuits essential to parasitism presents a promising strategy for future interventions. In this review, we describe our current understanding of sensory behaviors - namely olfactory, gustatory, gas sensing, and thermosensory behaviors - in Strongyloides spp. We also highlight the ever-growing cache of genetic tools optimized for use in Strongyloides that have facilitated these findings, including transgenesis, CRISPR/Cas9-mediated mutagenesis, RNAi, chemogenetic neuronal silencing, and the use of fluorescent biosensors to measure neuronal activity. Bolstered by these tools, we are poised to enter an era of rapid discovery in Strongyloides sensory neurobiology, which has the potential to shape pioneering advances in the prevention and treatment of strongyloidiasis.