Diptera (Insecta: Pterygota) larvae as predators of Strongyloides stercoralis causing false negative stool cultures.

A stool sample of a five-year-old boy with suspected STH infection arrived at the Laboratory of the Instituto de Investigaciones de Enfermedades Tropicales (IIET), National University of Salta in Oran, province of Salta, Argentina in 2017. Three Harada Mori were prepared, of which only one showed the presence of S. stercoralis. In the other two, the presence of an unknown larva was observed, which was later identified as an insect larva of the Diptera order. PCR analysis of the liquid medium of Harada Mori and Diptera larvae revealed presence of S. stercoralis DNA. These results, added to the predatory characteristics of the dipteran larvae, indicate that the S. stercoralis larvae were prey for these organisms, resulting in a negative diagnosis for S. stercoralis in the Harada Mori.

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

BACKGROUND: Strongyloidiasis 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. METHODOLOGY: Community 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). RESULTS: A 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). CONCLUSION: We 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.

Scope and limitations of a multiplex conventional PCR for the diagnosis of S. stercoralis and hookworms.

OBJECTIVES: Describe the diagnostic characteristics of a conventional multiplex PCR for the diagnosis of S. stercoralis, N. americanus and Ancylostomas spp. METHODS: Fecal samples were collected from a cross-sectional study in Orán department, Salta province, Argentina. The stool samples were analyzed using concentration-sedimentation, Harada Mori, McMaster, and Baermann techniques. DNA was extracted from 50 mg fecal sample using the FastPrep® Spin Kit for Soil. Three pairs of primers were used for the amplification of three products of 101, 330, and 577 base pairs (bp) for S. stercoralis, N. americanus and Ancylostoma spp, respectively. The sensitivity and analytical specificity of multiplex PCR were evaluated, as well as the sensitivity and diagnostic specificity, using a composite standard and Bayesian approach. RESULTS AND CONCLUSIONS: Multiplex PCR did not present cross-reaction with other intestinal parasites, and the detection limit for multiplex PCR was between 2 and 20 pg of genomic DNA. In addition it presented a diagnostic sensitivity of 97.4% for S. stercoralis and 90.3% for hookworms with a specificity of 100% and 87.6%, respectively. PCR identified a higher proportion (p <0.01) of coinfections (15.3%) than microscopic techniques (3.5%). Also, multiplex PCR showed that there was a positive association between S. stercoralis and hookworms (odds ratio = 2.12). However, this association was due to N. americanus (odds ratio= 3.22), since no association was observed between S. stercoralis and Ancylostoma spp. Neither was an association observed between the two species of hookworms.

Seroprevalence of the Strongyloides stercoralis Infection in Humans from Yungas Rainforest and Gran Chaco Region from Argentina and Bolivia.

The threadworm, Strongyloides stercoralis, is endemic in tropical and subtropical areas. Data on the prevalence and distribution of infection with this parasite species is scarce in many critical regions. We conducted a seroprevalence study of S. stercoralis infection in 13 locations in the Gran Chaco and Yungas regions of Argentina and Bolivia during the period 2010-2016. A total of 2803 human serum samples were analyzed by ELISA-NIE which has a sensitivity of 75% and specificity of 95%. Results showed that 551 (19.6%) of those samples were positive. The adjusted prevalence was 20.9%, (95% confidence interval (CI) 19.4%-22.4%). The distribution of cases was similar between females and males with an increase of prevalence with age. The prevalence in the different locations ranged from 7.75% in Pampa del Indio to 44.55% in Santa Victoria Este in the triple border between Argentina, Bolivia, and Paraguay in the Chaco region. Our results show that S. stercoralis is highly prevalent in the Chaco and Yungas regions, which should prompt prospective surveys to confirm our findings and the design and deployment of control measures.

Serologic Monitoring of Public Health Interventions against Strongyloides stercoralis.

Northwestern Argentina is endemic for soil-transmitted helminths, and annual deworming programs are carried out in prioritized areas. High prevalence of Strongyloides stercoralis was reported in this area; therefore, control programs including ivermectin are being evaluated. The NIE-enzyme linked immunosorbent assay (ELISA) was used for this purpose. In this community trial, two groups of patients, classified according to housing and living conditions were evaluated. Simultaneous with baseline survey, Group 1 was moved to new households with access to improved water and sanitation facilities (W and S), where deworming (MDA, massive drug administration) took place within 1 month; whereas Group 2 received MDA but remained living with unimproved W and S. The mean time interval between baseline and the follow-up was 331 days for Group 1 and 508 for Group 2. Anti-NIE levels were measured for each individual before and after interventions and follow-up optical density (OD) ratios were calculated to quantify the variation. A significant decrease of the anti-NIE levels between baseline and follow-up was observed in both groups. Nonetheless, the number of patients that achieved the cure criteria (OD ratio < 0.6) was higher in Group 1 than Group 2 with values of 72.7% (24/33) and 45.0% (18/40), respectively (P = 0.0197). Our results support the conclusion that a combined intervention including deworming and improvements in life conditions is more effective, in terms of the proportion of subjects cured than deworming alone. Furthermore, we found that NIE-ELISA is a useful test for assessing the response to treatment and to evaluate the outcome of control intervention programs.

Effect of Poor Access to Water and Sanitation As Risk Factors for Soil-Transmitted Helminth Infection: Selectiveness by the Infective Route.

BACKGROUND: Soil-transmitted helminth (STH) infections are a public health problem in resource-limited settings worldwide. Chronic STH infection impairs optimum learning and productivity, contributing to the perpetuation of the poverty-disease cycle. Regular massive drug administration (MDA) is the cardinal recommendation for its control; along with water, sanitation and hygiene (WASH) interventions. The impact of joint WASH interventions on STH infections has been reported; studies on the independent effect of WASH components are needed to contribute with the improvement of current recommendations for the control of STH. The aim of this study is to assess the association of lacking access to water and sanitation with STH infections, taking into account the differences in route of infection among species and the availability of adequate water and sanitation at home. METHODS AND FINDINGS: Cross-sectional study, conducted in Salta province, Argentina. During a deworming program that enrolled 6957 individuals; 771 were randomly selected for stool/serum sampling for parasitological and serological diagnosis of STH. Bivariate stratified analysis was performed to explore significant correlations between risk factors and STH infections grouped by mechanism of entry as skin-penetrators (hookworms and Strongyloides stercoralis) vs. orally-ingested (Ascaris lumbricoides and Trichuris trichiura). After controlling for potential confounders, unimproved sanitation was significantly associated with increased odds of infection of skin-penetrators (adjusted odds ratio [aOR] = 3.9; 95% CI: 2.6-5.9). Unimproved drinking water was significantly associated with increased odds of infection of orally-ingested (aOR = 2.2; 95% CI: 1.3-3.7). CONCLUSIONS: Lack of safe water and proper sanitation pose a risk of STH infections that is distinct according to the route of entry to the human host used by each of the STH species. Interventions aimed to improve water and sanitation access should be highlighted in the recommendations for the control of STH.