Strongyloides stercoralis.

Strongyloides stercoralis, a nematode not well known to many Canadian physicians, infects 35% of some tropical populations. Larvae can be isolated from the stools in 25% of cases and from duodenal aspirates in 95%. Treatment is with thiabendazole given twice daily in a dose of 25 mg/kg up to a maximum of 1.5 g/d. Frenquently an individual with a previously asymptomatic infection presents with hyperinfection and death rapidly ensues, but usually classical symptoms are present. Such a case is described. Immunosuppression is frequently associated with the hyperinfective state.     

Strongyloides stercoralis infection in the ferret

The ferret (Mustela putorius furo) was evaluated as an animal model for infection with human strains of Strongyloides stercoralis. Results indicate that such infections can be easily and reproducibly accomplished.     

Strongyloides stercoralis genotypes in humans in Cambodia

Little is known about the genetic variability of the soil-transmitted nematode, Strongyloides stercoralis, in humans. We sequenced portions of the small subunit rDNA (SSU), including the hyper variable regions (HVR) I and IV from S. stercoralis larvae derived from individuals living in a rural setting in Cambodia. We identified three polymorphic positions, including a previously reported one within the HVR I. HVR IV was invariable. Six different SSU alleles existed in our sample. Although different genotypes of S. stercoralis were found in the same individuals, no heterozygous larvae were found. This indicates that there is no or very little interbreeding between the different genotypes. Further studies are needed to examine if this is because sexual reproduction, which is facultative, is rare in our study area's S. stercoralis population or because what is considered to be S. stercoralis today is actually a complex of closely related species or subspecies.     

Frequency of Strongyloides stercoralis infection in alcoholics

Several studies have shown that chronic alcoholics have increased susceptibility to infections due to higher exposure to infectious agents as well as breakdown in their immune defenses. As Strongyloides stercoralis infection is usually more relevant in immunocompromised patients, the aim of this study was to evaluate the frequency of S. stercoralis infection in alcoholics. Thus, coproparasitological examination was carried out in 145 subjects, from which 45 were chronic alcoholics (mean age of 45.7 +/- 11.0 years), 10 were nonalcoholic cirrhotic patients (mean age of 50.2 +/- 13.1 years), and 90 were asymptomatic nonalcoholic subjects (mean age of 46.7 +/- 10.1 years), which served as controls. From the alcoholics, 9 had hepatic cirrhosis, 9 had chronic pancreatitis and 27 had neither cirrhosis nor pancreatitis. For the diagnosis of strongyloidiasis, the Baermann-Moraes and Lutz methods were used in three fecal samples from each subject. Samples were collected at alternated days, and three slides of each sample were analyzed for each method, thus totalizing 2,610 slides examined. The frequency of strongloidiasis in the total alcoholic group (33.3%) and in the subgroups of alcoholics, i.e., patients with hepatic cirrhosis (44.4%), with chronic pancreatitis (33.3%), and those with no cirrhosis or pancreatitis (29.6%) was statistically higher than that found in the control group (5.5%). None of the individuals with nonalcoholic hepatic cirrhosis had S. stercoralis infection. Our results showed that the chronic alcoholism itself is an important factor that predisposes to strongyloidiasis.     

Transmammary transmission of Strongyloides stercoralis in dogs

Vertical transmission of larvae is a major pathway in the life cycle of several species of Strongyloides, but evidence for it occurring in humans or dogs with Strongyloides stercoralis is absent. In an effort to determine if vertical transmission could occur with S. stercoralis, each of 3 female dogs was infected with filariform larvae at a different stage of the reproductive cycle, i.e., preconception, gestation, or postpartum. Results showed that none of 6 pups born to a female infected before conception or any of 6 pups born to another female infected during gestation harbored any stage of S. stercoralis when necropsied at parturition. Conversely, all 5 pups that nursed from the female infected immediately postpartum became infected with adult S. stercoralis in their small intestines (range, 56-129 adult worms). Significantly, live filariform larvae of S. stercoralis were observed on 2 different occasions from milk samples taken from the lactating female. Because arrested development of larvae is not known in S. stercoralis, there is no reservoir of larvae in the parenteral tissues of females to queue for passage to the pups and, thus, it is not surprising that only timely infections, perhaps very late in gestation and during lactation, can be successful. These data support previous work in dogs with S. stercoralis, which concluded that vertical transmission through prenatal pathways does not occur, but they are the first from the dog to indicate that vertical transmission of this parasite through transmammary routes is possible. Whether transmammary transmission of S. stercoralis occurs in humans remains unknown but given its immense pathological potential, it should not be overlooked.     

Strongyloides stercoralis and the immune response

The immune system is a highly evolved network of cells and molecules that can distinguish between invading pathogens and the body's own cells. But helminths, in their complex forms, are capable of down-regulating host immunity, protecting them from being eliminated and also minimizing severe pathology in the host. This review focuses on Strongyloides stercoralis and the immune responses in immunocompetent and/or immunocompromised individuals. It also highlights the implications for diagnosis/treatment and draws attention to an emerging public health disease. The solution to reducing the prevalence of strongyloidiasis remains on the effectiveness of pre-emptive measures in endemic communities, increased awareness, prompt early diagnosis as well as timely treatment.     

Towards effective control of Strongyloides stercoralis

A widespread intestinal parasite of humans, Strongyloides stercoralis has long been considered very difficult to control in endemic communities. This situation is now changing. In this article, David Conway, John Lindo, Ralph Robinson and Don Bundy review recent advances in diagnosis, chemotherapy and epidemiology of S. stercoralis infection, and highlight new options for control.     

Amphids in Strongyloides stercoralis and other parasitic nematodes

In this review, Francis Ashton and Gerhard Schad examine the ultrastructure of the amphids of several animal parasitic nematodes. These structures are the main chemosensory organs of these worms and probably play an important role in host-finding behavior and the control of development. Reconstructions made from serial micrographs of the neurons in the amphids of the threadworm Strongyloides stercoralis are shown. These stereo images permit three-dimensional visualization of these complex sense organs. The association between each amphidial neuron and its cell body has not been made previously for a parasitic nematode; however, this has been done for the free-living nematode Caenorhabditis elegans, which served as a model for these studies. Recognition of the cell bodies will provide a point of departure for laser microbeam ablation studies to determine individual neuronal function.     

A case of Strongyloides stercoralis infection.

Strongyloidiasis has been recognized as one of the life-threatening parasitic infections in the immunocompromised patients. We report an intestinal infection case of Strongyloides stercoralis in a 61-year-old man. Rhabditiform larvae were detected in the stool examination and developed to filariform larvae having a notched tail through the Harada-Mori filter paper culture. The patient received five courses of albendazole therapy but not cured of strongyloidiasis.     

Seroprevalence of Strongyloides stercoralis infection in a South Indian adult population

BackgroundThe prevalence of Strongyloides stercoralis infection is estimated to be 30–100 million worldwide, although this an underestimate. Most cases remain undiagnosed due to the asymptomatic nature of the infection. We wanted to estimate the seroprevalence of S. stercoralis infection in a South Indian adult population.MethodsTo this end, we performed community-based screening of 2351 individuals (aged 18–65) in Kanchipuram District of Tamil Nadu between 2013 and 2020. Serological testing for S. stercoralis was performed using the NIE ELISA.ResultsOur data shows a seroprevalence of 33% (768/2351) for S. stercoralis infection which had a higher prevalence among males 36% (386/1069) than among females 29.8% (382/1282). Adults aged ≥55 (aOR = 1.65, 95% CI: 1.25–2.18) showed higher adjusted odds of association compared with other age groups. Eosinophil levels (39%) (aOR = 1.43, 95% CI: 1.19–1.74) and hemoglobin levels (24%) (aOR = 1.25, 95% CI: 1.11–1.53) were significantly associated with S. stercoralis infection. In contrast, low BMI (aOR = 1.15, 95% CI: 0.82–1.61) or the presence of diabetes mellitus (OR = 1.18, 95% CI: 0.83–1.69) was not associated with S. stercoralis seropositivity.ConclusionsOur study provides evidence for a very high baseline prevalence of S. stercoralis infection in South Indian communities and this information could provide realistic and concrete planning of control measures.     

Strongyloides stercoralis infection and re-infection in a cohort of children in Cambodia

Information on Strongyloides stercoralis re-infection after ivermectin treatment is scarce in S. stercoralis endemic countries. In semi-rural Cambodia, we determined S. stercoralis infection and re-infection rates among schoolchildren, two years after ivermectin treatment (2 × 100 μg/kg PO, 24 h apart). The study was conducted among 484 children from four primary schools in semi-rural villages in Kandal province from 2009 to 2011, using Koga agar plate culture and the Baermann method on two stool samples per child. Complete data were available for 302 participants. We observed infections in 24.2% and 22.5% of the children at baseline and at follow-up, respectively. At baseline, 73 children were treated for S. stercoralis infection. At follow-up, one-third of those treated for S. stercoralis infection had been reinfected, while 19.6% of the 229 healthy children (at baseline) had been newly infected with S. stercoralis. Possession of shoes and defecation in toilet were negatively associated with S. stercoralis infection at follow-up. Infection and re-infection rates of S. stercoralis among schoolchildren are considerably high. However, 68.5% of infected children remained free of infection for at least two years. A large-scale cohort study is required to understand age-specific infection and re-infection dynamics in endemic countries.     

Residual trophoblastic tissue as a source of highly atypical cells in the postpartum cervicovaginal smear

A cervicovaginal smear containing atypical cells, which were interpreted as dysplastic cells, was obtained from a women one-year postpartum. These cells were seen singly, in small groups and in clusters embedded in an amorphous pink matrix. They had amphophilic cytoplasm and increased nuclear/cytoplasmic ratios, as well as hyperchromatic nuclei with variably prominent nucleoli, features that are characteristic of trophoblastic cells. No evidence of dysplasia was seen on subsequent colposcopic examination or cervical biopsy. Endocervical curettage yielded fragments of exfoliated endometrium and residual trophoblastic tissue associated with a placental implantation site. Although involution of the placental site is generally complete by six to seven weeks postpartum, maternal-fetal tissue may in fact continue to be exfoliated for several months or longer after delivery. If seen on a cervicovaginal smear, these cells can be highly atypical and may be mistaken as dysplastic or malignant. The cytologic features that characterize trophoblasts and their persistence in postpartum cervicovaginal smears are discussed.     

Community control of Strongyloides stercoralis by thiabendazole.

Mass treatment of a community in Costa Rica with thiabendazole in 1965 reduced the prevalence of S. sterocoralis from 19.2% to 0.3%, and the rates remained low 2 years thereafter. Re-examination of the treated population 7 years after initial treatment showed S. stercoralis prevalence still at a 0.5% level.     

Strongyloides stercoralis and Trypanosoma cruzi coinfections in a highly endemic area in Argentina

BackgroundStrongyloidiasis and Chagas disease are endemic in northern Argentina. In this study we evaluate the association between S. stercoralis and T. cruzi infections in villages with diverse prevalence levels for these parasites. Further understanding in the relationship between these Neglected Tropical Diseases of South America is relevant for the design of integrated control measures as well as exploring potential biologic interactions.MethodologyCommunity based cross-sectional studies were carried in different villages of the Chaco and Yungas regions in Argentina. Individuals were diagnosed by serology for S. stercoralis and T. cruzi. The association between S. stercoralis and T. cruzi, and between anemia and the two parasites was evaluated using two approaches: marginal (Ma) and multilevel regression (Mu).ResultsA total of 706 individuals from six villages of northern Argentina were included. A total of 37% were positive for S. stercoralis, 14% were positive for T. cruzi and 5% were positive for both. No association was found between infection with S. stercoralis and T. cruzi in any of the models, but we found a negative correlation between the prevalence of these species in the different villages (r = -0.91). Adults (> 15 years) presented association with S. stercoralis (Ma OR = 2.72; Mu OR = 2.84) and T. cruzi (Ma OR = 5.12; Mu OR = 5.48). Also, 12% and 2% of the variance of infection with S. stercoralis and T. cruzi, respectively, could be explained by differences among villages. On the other hand, anemia was associated with infection with S. stercoralis (Ma OR = 1.73; Mu OR = 1.78) and was more prevalent in adults (Ma OR = 2.59; Mu OR = 2.69).ConclusionWe found that coinfection between S. stercoralis and T. cruzi is not more frequent than chance in endemic areas. However, the high prevalence for both parasites, raises the need for an integrated strategy for the control of STH and Chagas disease.     

Evaluation of Strongyloides stercoralis infection in patients with HTLV-1

Introduction: Individuals infected with the human T-lymphotropic virus type 1 (HTLV-1) may present severe and disseminated forms of Strongyloides stercoralis infection with low therapeutic response.Objective: To investigate the S. stercoralis infection and the seroprevalence of IgG anti-S. stercoralis antibodies in individuals infected with HTLV-1 attending the Reference Center for HTLV-1 (CHTLV) in Salvador, Bahia, Brazil.Materials and methods: We conducted a cross-sectional study in 178 HTLV-1-infected individuals treated at the HTLV specialized center between January, 2014, and December, 2018. The parasitological diagnosis of S. stercoralis was performed using the Hoffman, Pons and Janer, agar plate culture, and Baermann-Morais methods. The IgG anti-S. stercoralis detection was performed using an in house enzyme-linked immunosorbent assay (ELISA). The HTLV-1 infection was diagnosed using a commercial ELISA and confirmed by Western blot.Results: The frequency of S. stercoralis infection was 3.4% (6/178). Individuals infected with S. stercoralis from rural areas (50.0%; 3/6) also showed S. stercoralis hyperinfection (>3,000 larvae/ gram of feces). The frequency of circulating anti-S. stercoralis IgG antibodies was 20.8% (37/178). Conclusions: HTLV-1-infected people living in precarious sanitary conditions are more prone to develop severe forms of S. stercoralis infection. Considering the high susceptibility and unfavorable outcome of the infection in these individuals, the serological diagnosis for S. stercoralis should be considered when providing treatment.