Hookworm-like eggs in children's faecal samples from a rural area of Rwanda

Performance of microscopy compared to conventional PCR in identification of soil-transmitted helminth infections among antenatal women in a low-prevalence setting

PURPOSE

Traditional microscopy-based methods may provide inaccurate estimates of Soil transmitted helminth (STH) infections in mild intensity of infection. Therefore, we aimed to determine the prevalence of STH infections using molecular diagnostic methods and compare the diagnostic performance of microscopy with polymerase chain reaction (PCR) in stool samples collected from pregnant women in primary care settings in Puducherry, India.

METHODOLOGY

A singleplex PCR assay was developed to detect three species of STHs, namely Ascaris lumbricoides, Necator americanus, and Ancylostoma duodenale, by targeting the internal transcribed spacer regions (ITS1 and ITS2) of 5.8S rRNA. The PCR generated 420, 662, and 515 base pairs of DNA for the respective organisms. In addition to singleplex PCR, wet and concentration microscopy techniques were used. The results were expressed as percentages with 95% confidence intervals, and the diagnostic performance of microscopy was compared with PCR in terms of sensitivity, specificity, and positive, negative predictive values and kappa statistics.

RESULTS

Among the 650 pregnant women included, 48.8% were aged 25 years or less, 59% were primigravida, and half were from rural areas. The overall prevalence of any STH infection was higher in PCR compared to microscopy (8.9% vs. 7.2%). The prevalence of Ascaris lumbricoides was higher by microscopy (5.4% vs 2.6%), while the prevalence of Necator americanus was higher by PCR (6.3%) than by microscopy (1.8%). No species of Ancylostoma duodenale was detected. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of microscopy for detecting any STH infection was 22.4%, 94.3%, 27.7%, and 92.5%, respectively. The agreement between microscopy and PCR for the identification is as follows: for any STH infection, k ​= ​0.12, Ascaris k ​= ​0.16, and Necator k ​= ​0.20, respectively.

CONCLUSION

The prevalence of any STH infection identified by PCR was higher than microscopy, and the agreement between the two methods was poor.

Trichostrongylosis: a zoonotic disease of small ruminants

In the present world a significant threat to human health is posed by zoonotic diseases. Helminth parasites of ruminants are one of the most common zoonotic organisms on the planet. Among them, trichostrongylid nematodes of ruminants, found worldwide, parasitize humans in different parts of the world with varying rates of incidence, particularly among rural and tribal communities with poor hygiene, pastoral livelihood and poor access to health services. In the Trichostrongyloidea superfamily, Haemonchus contortus, Teladorsagia circumcincta, Marshallagia marshalli, Nematodirus abnormalis and Trichostrongylus spp. are zoonotic in nature. Species of the genus Trichostrongylus are the most prevalent gastrointestinal nematode parasites of ruminants that transmit to humans. This parasite is prevalent in pastoral communities around the world and causes gastrointestinal complications with hypereosinophilia which is typically treated with anthelmintic therapy. The scientific literature from 1938 to 2022 revealed the occasional incidence of trichostrongylosis throughout the world with abdominal complications and hypereosinophilia as the predominant manifestation in humans. The primary means of transmission of Trichostrongylus to humans was found to be close contact with small ruminants and food contaminated by their faeces. Studies revealed that conventional stool examination methods such as formalin-ethyl acetate concentration or Willi's technique combined with polymerase chain reaction-based approaches are important for the accurate diagnosis of human trichostrongylosis. This review further found that interleukin 33, immunoglobulin E, immunoglobulin G1, immunoglobulin G2, immunoglobulin M, histamine, leukotriene C4, 6-keto prostaglandin F_1α, and thromboxane B₂ are vital in the fight against Trichostrongylus infection with mast cells playing a key role. This review focuses on the prevalence, pathogenicity and immunological aspects of Trichostrongylus spp. in humans.

Recent Advances and Potential Future Applications of MALDI-TOF Mass Spectrometry for Identification of Helminths

Helminth infections caused by nematodes, trematodes, and cestodes are major neglected tropical diseases and of great medical and veterinary relevance. At present, diagnosis of helminthic diseases is mainly based on microscopic observation of different parasite stages, but microscopy is associated with limited diagnostic accuracy. Against this background, recent studies described matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry as a potential, innovative tool for helminth identification and differentiation. MALDI-TOF mass spectrometry is based on the analysis of spectra profiles generated from protein extracts of a given pathogen. It requires an available spectra database containing reference spectra, also called main spectra profiles (MSPs), which are generated from well characterized specimens. At present, however, there are no commercially available databases for helminth identification using this approach. In this narrative review, we summarize recent developments and published studies between January 2019 and September 2022 that report on the use of MALDI-TOF mass spectrometry for helminths. Current challenges and future research needs are identified and briefly discussed.

A Case for Using Genomics and a Bioinformatics Pipeline to Develop Sensitive and Species-Specific PCR-Based Diagnostics for Soil-Transmitted Helminths

The balance of expense and ease of use vs. specificity and sensitivity in diagnostic assays for helminth disease is an important consideration, with expense and ease often winning out in endemic areas where funds and sophisticated equipment may be scarce. In this review, we argue that molecular diagnostics, specifically new assays that have been developed with the aid of next-generation sequence data and robust bioinformatic tools, more than make up for their expense with the benefit of a clear and precise assessment of the situation on the ground. Elimination efforts associated with the London Declaration and the World Health Organization (WHO) 2020 Roadmap have resulted in areas of low disease incidence and reduced infection burdens. An accurate assessment of infection levels is critical for determining where and when the programs can be successfully ended. Thus, more sensitive assays are needed in locations where elimination efforts are approaching a successful conclusion. Although microscopy or more general PCR targets have a role to play, they can mislead and cause study results to be confounded. Hyper-specific qPCR assays enable a more definitive assessment of the situation in the field, as well as of shifting dynamics and emerging diseases.