Efficiency of the salt flotation technique in the recovery of Ascaris lumbricoides eggs from the soil

Environmental monitoring for Ascaris egg remediation: a critical review

Ascariasis affects up to 1.2 billion people globally, with a significant burden in low-income regions. Despite high prevalence and substantial morbidity, existing monitoring and intervention strategies are insufficient due to sample extraction and quantification inaccuracies. This review underscores the need for enhanced environmental monitoring to improve Ascaris egg remediation and reduce disease incidence. We critically reviewed existing environmental monitoring practices and explored advanced technologies like lab-on-a-disk for rapid detection and quantification of Ascaris eggs. A meta-analysis and meta-regression of studies on Ascaris egg recovery revealed significant variability in recovery rates, with the best methods achieving less than 60% efficiency. Advanced imaging analyses and lab-on-a-disk technologies show promise for rapid detection and viability assessment. By identifying gaps in current methodologies, we recommend more effective environmental interventions. The review incorporated high-quality data adhering to PRISMA guidelines, ensuring comprehensive coverage of the latest methodologies. Integrating improved detection methods and environmental control strategies can significantly reduce ascariasis incidence, especially in endemic regions. Future efforts should focus on refining these technologies and validating their application in real-world settings for sustainable disease control.

Soil surveillance for monitoring soil-transmitted helminths: Method development and field testing in three countries

BACKGROUND

One-fifth of the global population is infected with soil-transmitted helminths (STH). Mass drug administration (MDA) with deworming medication is widely implemented to control morbidity associated with STH infections. However, surveillance of human infection prevalence by collecting individual stool samples is time-consuming, costly, often stigmatized, and logistically challenging. Current methods of STH detection are poorly sensitive, particularly in low-intensity and low-prevalence populations.

METHODOLOGY/PRINCIPAL FINDINGS

We aimed to develop a sensitive and specific molecular method for detecting STH DNA in large volumes of soil (20 g) by conducting laboratory and proof of concept studies across field sites in Kenya, Benin, and India. We collected human stool (n = 669) and soil (n = 478) from 322 households across the three study sites. We developed protocols for DNA extraction from 20 g of soil and qPCR to detect Ascaris lumbricoides, Trichuris trichiura, Necator americanus, and Ancylostoma duodenale. Agreement between detection of STH via qPCR, digital droplet PCR (ddPCR), and microscopy-based methods was assessed using the Cohen's Kappa statistic. Finally, we estimated associations between soil characteristics and detection of STH in soil by qPCR, as well as between STH detected in soil and STH detected in stool from matched households, adjusting for soil characteristics. The overall prevalence of STH in soil by qPCR was 31% for A. lumbricoides, 3% for T. trichiura, and 13% for any hookworm species. ddPCR and qPCR performed similarly. However, there was poor agreement between STH detected in soil by qPCR versus light microscopy. Microscopy underestimated the prevalence of A. lumbricoides and N. americanus and overestimated T. trichiura. Detection of an STH species in household soil was strongly associated with increased odds of a household member being infected with that same species.

CONCLUSIONS/SIGNIFICANCE

Soil surveillance for STH has several benefits over stool-based surveillance, including lower cost and higher success rates for sample collection. Considering that delivery of MDA occurs at the community level, environmental surveillance using molecular methods could be a cost-effective alternate strategy for monitoring STH in these populations.

Assessment of environmental contamination with soil-transmitted helminths life stages at school compounds, households and open markets in Jimma Town, Ethiopia

Background

It remains largely unknown where and how infections with soil-transmitted helminths (STHs; Ascaris, Trichuris, Necator and Ancylostoma) occur. We therefore aimed to identify possible sources of infection by assessing the environmental contamination in an STH-endemic area.

Methods

We first performed a series of laboratory experiments designed to optimize a soil straining-flotation method to detect and quantify Ascaris and Trichuris eggs in soil, and to validate the diagnostic performance of the optimized method when followed by microscopy and qPCR. In a second phase, we applied this method to assess the level of STH contamination in 399 environmental samples collected from 10 school compounds, 50 households and 9 open markets in Jimma Town (Ethiopia). Subsequently, we explored associations between the environmental contamination and both the corresponding STH epidemiology at the level of the schools and the household characteristics. Finally, we assessed the knowledge, attitude and practice (KAP) towards STHs in school children.

Principal findings

Our soil straining-flotation method has an analytical sensitivity of 50 eggs per 100 grams of soil and egg recovery rate of 36.0% (Ascaris) and 8.0% (Trichuris). The analysis of field samples with both microscopy and qPCR revealed the presence of 8 different helminth species of medical importance, including but not limited to the human STHs. There was a significant association between the environmental contamination and prevalence of any STH infections at the school level only. The KAP indicated a lack of knowledge and awareness of STHs.

Conclusions/Significance

Our optimized straining-flotation method has a moderate diagnostic performance and revealed that life stages of helminths are ubiquitous in the environment, which might be due to the poor sanitary facilities at both the schools and the households, and a poor level of KAP towards STHs. Further research is required to gain more insights into the contribution of these life stages to transmission.

The recent strategies to control the morbidity caused by intestinal worms have mainly been focusing on large scale deworming programs during which drugs are administered to at-risk populations. Although these large-scale deworming programs have been successful in reducing the disease burden, re-infection in the absence of other intervention measures is unavoidable. Although there is a consensus on how infections with intestinal worms are transmitted, it remains unclear where hot spots of infectious life stages can be found in endemic communities, which in turn impedes both the design and the validation of interventions that prevent (re-)infection. We optimized a laboratory method to detect life stages in soil samples and applied this method to examine soil contamination at school compounds, households and open markets in Jimma Town (Ethiopia). Finally, we assessed the household characteristics, and the knowledge, attitude, and practice towards intestinal worms among school children. Generally, our results indicated (i) a moderate performance of our laboratory method, (ii) the ubiquitous presence of life stages in the environment, (iii) a poor level of sanitary facilities at both the schools and the households and (iv) a poor level of knowledge, attitude and practices towards intestinal worms.

Evaluating the efficacy of a centrifugation-flotation method for extracting Ascaris ova from soil

BACKGROUND

Soil transmitted helminths (STH) continue to be associated with high burdens of disease, with an estimated 1.45 billion people infected with STH globally. The promotion and construction of latrines is considered the first barrier to prevent transmission of STH. The absence of a reliable method to extract STH ova from soil makes it challenging to examine whether the use of latrines may or may not have an effect on environmental contamination with ova. The present study evaluated the recovery rate of a method developed to extract STH ova from soil.

METHODS

The adapted centrifugation and flotation technique was applied to 15 soil types, which were seeded with Ascaris suum ova. Soil type, soil moisture content, soil texture and organic matter content were assessed for each soil sample.

RESULTS

The average ova recovery rate was 28.2%, with the recovery rate of the method decreasing with increasing soil moisture content, particle size and organic matter content. The association between recovery rate and organic matter content was statistically significant.

CONCLUSIONS

The present study identified a low recovery rate for an adapted centrifugation-flotation method, although this was similar to the recovery rate demonstrated by other methods developed for soil. Soil organic matter content was significantly associated with ova recovery rates.

Detecting and enumerating soil-transmitted helminth eggs in soil: New method development and results from field testing in Kenya and Bangladesh

Globally, about 1.5 billion people are infected with at least one species of soil-transmitted helminth (STH). Soil is a critical environmental reservoir of STH, yet there is no standard method for detecting STH eggs in soil. We developed a field method for enumerating STH eggs in soil and tested the method in Bangladesh and Kenya. The US Environmental Protection Agency (EPA) method for enumerating Ascaris eggs in biosolids was modified through a series of recovery efficiency experiments; we seeded soil samples with a known number of Ascaris suum eggs and assessed the effect of protocol modifications on egg recovery. We found the use of 1% 7X as a surfactant compared to 0.1% Tween 80 significantly improved recovery efficiency (two-sided t-test, t = 5.03, p = 0.007) while other protocol modifications—including different agitation and flotation methods—did not have a significant impact. Soil texture affected the egg recovery efficiency; sandy samples resulted in higher recovery compared to loamy samples processed using the same method (two-sided t-test, t = 2.56, p = 0.083). We documented a recovery efficiency of 73% for the final improved method using loamy soil in the lab. To field test the improved method, we processed soil samples from 100 households in Bangladesh and 100 households in Kenya from June to November 2015. The prevalence of any STH (Ascaris, Trichuris or hookworm) egg in soil was 78% in Bangladesh and 37% in Kenya. The median concentration of STH eggs in soil in positive samples was 0.59 eggs/g dry soil in Bangladesh and 0.15 eggs/g dry soil in Kenya. The prevalence of STH eggs in soil was significantly higher in Bangladesh than Kenya (chi-square, χ² = 34.39, p < 0.001) as was the concentration (Mann-Whitney, z = 7.10, p < 0.001). This new method allows for detecting STH eggs in soil in low-resource settings and could be used for standardizing soil STH detection globally.

Intestinal worm infections are common in populations living in tropical, low-income countries. People primarily become infected when they consume intestinal worm eggs from contaminated water, hands, and food. Intestinal worm eggs are transmitted from infected people and spread through the environment, particularly via soil. There is no standard laboratory method for counting intestinal worm eggs in soil, which is a major barrier to comprehensive research on the transmission of infection. We tested different laboratory protocol steps to extract soil-transmitted helminth eggs, which is one type of intestinal worm, from soil and propose a new, fast, and efficient field method. We tested the method in Kenya and Bangladesh and found that soil contamination with helminth eggs was prevalent in both study areas. We propose that environmental contamination be included in discussions about intestinal worm transmission, control, and elimination, especially in areas with low infection prevalence. The method we propose will help researchers assess soil contamination, which can be used to examine the effectiveness of intestinal worm transmission control measures.

Methods for Quantification of Soil-Transmitted Helminths in Environmental Media: Current Techniques and Recent Advances

Limiting the environmental transmission of soil-transmitted helminths (STHs), which infect 1.5 billion people worldwide, will require sensitive, reliable, and cost-effective methods to detect and quantify STHs in the environment. We review the state-of-the-art of STH quantification in soil, biosolids, water, produce, and vegetation with regard to four major methodological issues: environmental sampling; recovery of STHs from environmental matrices; quantification of recovered STHs; and viability assessment of STH ova. We conclude that methods for sampling and recovering STHs require substantial advances to provide reliable measurements for STH control. Recent innovations in the use of automated image identification and developments in molecular genetic assays offer considerable promise for improving quantification and viability assessment.

Stray animal and human defecation as sources of soil-transmitted helminth eggs in playgrounds of Peninsular Malaysia

Soil contaminated with helminth eggs and protozoan cysts is a potential source of infection and poses a threat to the public, especially to young children frequenting playgrounds. The present study determines the levels of infection of helminth eggs in soil samples from urban and suburban playgrounds in five states in Peninsular Malaysia and identifies one source of contamination via faecal screening from stray animals. Three hundred soil samples from 60 playgrounds in five states in Peninsular Malaysia were screened using the centrifugal flotation technique to identify and determine egg/cyst counts per gram (EPG) for each parasite. All playgrounds, especially those in Penang, were found to be contaminated with eggs from four nematode genera, with Toxocara eggs (95.7%) the highest, followed by Ascaris (93.3%), Ancylostoma (88.3%) and Trichuris (77.0%). In addition, faeces from animal shelters were found to contain both helminth eggs and protozoan cysts, with overall infection rates being 54% and 57% for feline and canine samples, respectively. The most frequently occurring parasite in feline samples was Toxocara cati (37%; EPG, 42.47 ± 156.08), while in dog faeces it was Ancylostoma sp. (54%; EPG, 197.16 ± 383.28). Infection levels also tended to be influenced by season, type of park/playground and the texture of soil/faeces. The occurrence of Toxocara, Ancylostoma and Trichuris eggs in soil samples highlights the risk of transmission to the human population, especially children, while the presence of Ascaris eggs suggests a human source of contamination and raises the issue of hygiene standards and public health risks at sites under investigation.

Evaluation of fecal contamination indicators (fecal coliforms, somatic phages, and helminth eggs) in ryegrass sward farming

The effect of soil supplementation with biosolids at various ratios on fecal-origin microorganism activity was evaluated in a ryegrass sward farm. Fifteen plots with 3 different soil and biosolid mixture ratios were assessed. Soil and grass were sampled over a period of 4 months (days 0, 30, 45, 60, 75, and 120) for soil and on days 75 and 120 for grass, corresponding to first and second grass harvest periods. We analyzed fecal coliforms, somatic phages, helminth eggs, and environmental factors, such as rainfall, temperature, and moisture. The fecal coliforms decreased by 2 logarithmic units (LU) in all soils containing biosolids and by 1 LU in the soil alone and in biosolid control plots alone. The concentration of somatic phages decreased to 2 to 3 LU in the soil containing biosolids and to 1 to 2 LU in the control plots. In contrast, however, there was a noticeable increase in helminth eggs on days 75 ad 120, but not in the soil control alone. Maximum concentrations (10(2) CFU/g TS; colony forming units per gram total solids) of fecal coliforms were found on the grass and in other samples, but the concentrations of phages and helminth eggs were below detection limits. Environmental factors did not significantly influence the results, and grass production increased from 35 to 50 Ton/Ha (tons per hectare) with biosolid supplementation, as compared with controls (14 Ton/Ha).

Random amplified polymorphic DNA analysis of DNA extracted from Trichuris trichiura (Linnaeus, 1771) eggs and its prospective application to paleoparasitological studies

Random amplified polymorphic DNA analysis was applied to DNAs extracted from Trichuris trichiura eggs recovered from human fecal samples. Four out of 6 primers tested displayed 18 distinct and well defined polymorphic patterns, ranging from 650 to 3200 base pairs. These results, upon retrieval and DNA sequencing of some of these bands from agarose gels, might help in establishing. T. trichiura specific genetic markers, not available yet, and an important step to design primers to be used in molecular diagnosis approaches.

[Estacionalidad de parásitos intestinales en suelos periurbanos de la ciudad de Neuquén, Patagonia, Argentina]

OBJECTIVE

To determine the presence of eggs, larva, cysts and oocysts of intestinal parasites in the soil of a suburb of Neuquén city during 1 year in order to evaluate their seasonal fluctuations in relation to climatic data and soil characteristics in the studied area.

METHODS

A total of 107 soil samples were processed for parasite isolation by sedimentation and flotation methods during the four seasons of the year. Meteorological data were registered and physical, chemical and structural characteristics of the soil were analysed.

RESULTS

About 28.9% of the soil samples were positive for at least one parasite form. Six protozoa species (cysts of Entamoeba sp., Enteromonas sp., Endolimax sp., Giardia sp., Iodamoeba sp. and coccidia oocysts) were recovered, but neither larvae nor eggs of human or animal helminths parasites were detected. The percentage of contaminated soil samples and the diversity of species showed a marked decrease in the warm and dry months of the summer. The soil was sandy, without vegetable cover, well drained, and with scarce organic matter content.

CONCLUSION

The frequencies of parasite recovery and the number of species show seasonal fluctuations related to the rainfall. The importance of soil as a risk factor for the transmission of intestinal parasites in the studied area is conditioned by its structural characteristics, which prevent retaining the humidity, and by climatic variables. The interrelation of both factors determines unfavourable conditions that could explain the low level of contamination observed in soil as well as the absence of eggs and helminth larvae.

Improved methods for recovering eggs of Toxocara canis from soil

The ingestion of soil in parks and public places containing eggs of Toxocara may constitute a significant health risk, particularly to children. To determine the most efficient method for extracting eggs from experimentally contaminated soil, two consecutive studies were undertaken. Four techniques, including washing, sieving, vacuum, and the one recommended by the World Health Organization, were evaluated. Recovery rates of over 85% were recorded with both washing and sieving methods. Using the washing technique, all combinations of the four pre-treatment solutions, distilled water, acetoacetic solution pH 5, 0.1 n sodium hydroxide and 1% Tween 20, and seven flotation fluids with different specific gravities (S.G.) ranging from 1.20 to 1.35 were assayed. The association of distilled water and saccharose solution with an S.G. of 1.27 showed the best results, with a recovery rate of 99.91%.

Induction of protective immunity in cattle against infection with Fasciola hepatica by vaccination with cathepsin L proteinases and with hemoglobin

Two cathepsin L proteinases, cathepsin L1 and cathepsin L2, secreted by liver flukes may be involved in tissue penetration, nutrition, and protection from immune attack. To ascertain the immunoprophylactic potential of these proteinases, and of another molecule, liver fluke hemoglobin (Hb), we performed vaccine trials in cattle. In the first vaccine trial various doses of cathepsin L1 were tested. The mean protection level obtained was 53.7%. In a second vaccine trial cathepsin L1 and Hb elicited 42.5 and 43.8% protection levels, respectively, while a combination of the two molecules induced a significantly higher level of protection (51.9%). Cathepsin L2 was not examined alone; however, vaccination of cattle with a combination of cathepsin L2 and Hb elicited the highest level of protection (72.4%). The animals that received cathepsin L1-Hb or cathepsin L2-Hb showed reduced liver damage as assessed by serum glutamic dehydrogenase and gamma-glutamyl transferase levels. Furthermore, a reduced viability was observed for fluke eggs recovered from all vaccine groups. This anti-embryonation effect of vaccination was particularly evident in the group that received cathepsin L2-Hb where >98% of the eggs recovered did not embryonate to miracidia. Although all vaccine preparations induced high antibody titers which were boosted following the challenge infection, there was no correlation between antibody titers and protection. The results of these trials demonstrate that cathepsin Ls and Hb could form the basis of a molecular vaccine that would not only reduce parasite burden but would also prevent transmission of liver fluke disease.