A novel protocol to isolate, detect and differentiate taeniid eggs in leafy greens and berries using real-time PCR with melting curve analysis

Performance evaluation of protocols for Taenia saginata and Ascaris suum egg recovery from the house fly's gastrointestinal tract and exoskeleton

BACKGROUND

The synanthropic house fly (Musca domestica) can potentially contribute to the mechanical spread of eggs of Taenia and Ascaris spp. in the environment and between hosts. However, the absence of validated protocols to recover eggs hampers an in-depth analysis of the house fly's role in parasite egg transmission.

METHODS

The gastrointestinal tract and exoskeleton of euthanized house flies were spiked with Taenia saginata eggs. The performance of several recovery protocols, in terms of both the recovery rate and ease-of-use, was (microscopically) evaluated and compared. These protocols employed steps such as washing, maceration, filtration, flotation and both passive and centrifugal sedimentation. The final validated protocols were subsequently evaluated for the recovery of Ascaris suum eggs.

RESULTS

The final protocol validated for the recovery of T. saginata eggs from the house fly's gastrointestinal tract involved homogenization in phosphate-buffered saline and centrifugation at 2000 g for 2 min, yielding a recovery rate of 79.7%. This protocol required 6.5 min to perform (which included 1.5 min of hands-on time) and removed large debris particles that could hinder the differentiation of eggs from debris. Similarly, the final protocol validated for the recovery of T. saginata eggs from the fly's exoskeleton involved washing by vortexing for 2 min in Tween 80 (0.05%), 15 min of passive sedimentation and centrifugation at 2000 g for 2 min, yielding a recovery rate of 77.4%. This protocol required 20.5 min to perform (which included 3.5 min of hands-on time) and successfully removed debris. The same protocols yielded recovery rates of 74.2% and 91.5% for the recovery of A. suum eggs from the fly's gastrointestinal tract and exoskeleton, respectively.

CONCLUSIONS

Effective, simple and easy-to-use protocols were developed and validated for the recovery of T. saginata and A. suum eggs from the house fly's gastrointestinal tract and exoskeleton. These protocols can be applied to investigate the importance of flies as parasite egg transmitters in laboratory and field settings.

Taenia martis in a white-headed lemur (Eulemur albifrons) from a zoological park in North Rhine-Westphalia, Germany

We present the case of Taenia martis metacestode infection in a white-headed lemur (Eulemur albifrons) from a zoological park. A post-mortem examination was conducted on the unexpectedly perished animal and focal granulomatous pneumonia with metacestodic tissue was discovered. Identification of T. martis was conducted through amplification and sequencing of a 12S rRNA gene fragment. We discuss the possible sources of infection and underline the importance of this infection in public health and conservation.

Verification and Use of the US-FDA BAM 19b Method for Detection of Cyclospora cayetanensis in a Survey of Fresh Produce by CFIA Laboratory

To facilitate the harmonized surveillance and investigation of cyclosporiasis outbreaks in the US and Canada, we adapted and verified the US-FDA’s BAM 19b method and employed it in a national produce survey. Performance was verified by spiking 200, 10, 5 or 0 C. cayetanensis oocysts onto berries (50 ± 5 g, n = 85) and 200, 10 or 0 oocysts onto green onions (25 ± 3 g, n = 24) and leafy greens (25 ± 1 g, n = 120) and testing these samples by the BAM method on Bio-Rad CFX96. Method robustness was assessed by aging (0 or 7 days) and freezing the produce and washes prior to testing, then implementing the method for the surveillance testing of 1759 imported leafy green, herb and berry samples. Diagnostic sensitivity was 100/44% and 93/30% for berries and leafy greens spiked with 200/10 oocysts, respectively. The diagnostic and analytical specificity were 100% for all matrices and related parasites tested. The proportion positive was unaffected (p = 0.22) by age or condition of produce (7d, fresh, frozen) or wash concentrate (3d, fresh, frozen); however, the Cq values were higher (p = 0.009) for raspberries aged 7d (37.46 ± 0.29) compared to fresh (35.36 ± 0.29). C. cayetanensis was detected in berries (two), herbs (two) and leafy greens (one), representing 0.28% of the tested survey samples. These results independently verified the reported performance characteristics and robustness of the BAM method for the detection of C. cayetanensis in a variety of matrices, including under adverse sample conditions, using a unique detection platform and demonstrating its routine diagnostic use in our Canadian Food Inspection Agency (CFIA) laboratory.

Diagnostic tools for the detection of taeniid eggs in different environmental matrices: A systematic review

The cestode family Taeniidae consists of the genera Echinococcus and Taenia, both of which include zoonotic tapeworms of serious public health importance. Various environmental matrices have been identified from which parasite transmission to animals and humans can occur, and many techniques for detecting taeniid eggs in different environments have been developed. However, the majority lack appropriate validation, and standardized egg isolation procedures are absent. This hampers interstudy comparisons and poses a challenge for future researchers when deciding which technique to implement for assessing taeniid egg contamination in a particular matrix. Therefore, the aim of this systematic review was to present an overview of the detection methods for taeniid eggs in the environment, to discuss and compare them, and to provide recommendations for future studies. In total, 1814 publications were retrieved from scientific databases, and, ultimately, data were systematically reviewed from 90 papers. The results provide an overview of numerous diagnostic tests for taeniid egg detection in (or on) water, food, soil, insects, objects, and air. These tools could be categorized as either conventional (light microscopy), molecular, or immunodetection tools. The relatively cheap microscopy techniques often lack sensitivity and are unable to identify a taeniid egg at the genus level. Nevertheless, several records ascribed a genus, or even species, to taeniid eggs that had been detected by light microscopy. Molecular and immunodetection tools offer better specificity, but still rely on the preceding egg recovery steps that also affect overall sensitivity. Finally, the majority of the methods lacked any attempt at performance evaluation and standardization, especially at the earlier stages of the analysis (e.g., sampling strategy, storage conditions, egg recovery), and viability was rarely addressed. As such, our review highlights the need for standardized, validated detection tools, that not only assess the extent of environmental contamination, but also the egg genus or species, and address viability.

•

The cestode family Taeniidae contains species of serious public health importance.

•

Parasite transmission may occur from several environmental matrices.

•

Many methods for environmental detection of taeniid eggs have been developed.

•

These often lack standardization, performance evaluation, and viability assessment.

Detection of Cyclospora cayetanensis, Echinococcus multilocularis, Toxocara spp. and microsporidia in fresh produce using molecular methods: - A review

The current trend for a healthy lifestyle corresponds with a healthy diet, which is associated with regular and frequent consumption of raw fruit and vegetables. However, consumption of ready-to-eat (RTE) food without heat treatment or sufficient washing may pose a risk to consumers. Among the well-known protozoan parasites associated with RTE food and water are Cryptosporidium spp., Giardia duodenalis and Toxoplasma gondii. These belong among prioritized parasitic pathogens, as they are associated with numerous disease outbreaks in humans all around the world. Nevertheless, other parasitic agents such as Cyclospora cayetanensis, Toxocara cati, Toxocara canis, Echinococcus multilocularis and zoonotic microsporidia should not be neglected. Although these selected parasites belong to phylogenetically diverse groups, they have common characteristics associated with fresh produce and each of them poses a health risk to humans. Ensuring healthy food is produced requires the standartization of laboratory methods for the detection of parasitic agents. This article reviews the molecular methods currently used in laboratories for detection of Cyclospora cayetanensis, Toxocara cati, Toxocara canis, Echinococcus multilocularis and zoonotic microsporidia in fresh produce.

An integrated approach to control Cystic Echinococcosis in southern Italy

Cystic echinococcosis (CE) is a severe zoonosis, caused by the larval stage of the tapeworm Echinococcus granulosus. This helminth infection is of increasing public health and socio-economic concern due to the considerable morbidity rates that cause economic losses both in the public health sector and in the livestock industry. Control programmes against E. granulosus are considered long-term actions which require an integrated approach and high expenditure of time and financial resources. Since 2010, an integrated approach to control CE has been implemented in a highly endemic area of continental southern Italy (Campania region). Innovative procedures and tools have been developed and exploited during the control programme based on the following strategies: i) active and passive surveillance in livestock (using geospatial tools for georeferencing), ii) diagnosis in dogs (using the FLOTAC techniques and molecular analysis), iii) targeted treatment of farm dogs (using purpose-built confinement cages), iv) early diagnosis in livestock (by ultrasonography), v) surveillance in humans (through hospital discharge records analysis), vi) monitoring the food chain (analysing raw vegetables), vii) outreach activities to the general public (through dissemination material, e.g. brochures, gadgets, videos, virtual reality). Over eight years, the integrated approach and the new strategies developed have resulted in a noteworthy reduction of the parasite infection rates in livestock (e.g. up to 30 % in sheep). The results obtained so far highlight that using a one health multidisciplinary and multi-institution effort is of pivotal importance in preparing CE control programmes at regional level and could be extended to other endemic Mediterranean areas.

Zoonotic Taenia infections with focus on cysticercosis due to Taenia solium in swine and humans

Zoonotic taeniasis caused by the adult stage of Taenia solium, Taenia saginata or Taenia asiatica are considered neglected tropical diseases by the World Health Organization. The life cycle of these 3 metazoan species is very similar and includes an intermediate host: pigs in the case of T. solium and T. asiatica, and cattle in the case of T. saginata. By eating meat (pork/T. solium, T. asiatica; beef/T. saginata) containing live cysticerci, humans develop taeniasis, which is practically asymptomatic but is the main risk factor for intermediate hosts to become infected. T. saginata causes bovine cysticercosis, while T. solium and T. asiatica cause swine cysticercosis, of veterinary and economic importance. T. solium cysticerci cause neurological disease in humans: neurocysticercosis. Cysticerci develop after ingesting microscopic eggs released from a human tapeworm carrier. Here we describe the life stages of the parasites, diagnosis, pathogenesis, symptomatology of neurocysticercosis, and prevention and control measures. Highlighting the need to validate diagnostic tools, treatments and vaccination in endemic areas, with the challenge of addressing the most vulnerable populations that lack resources. If people understand the transmission route, avoid eating uncooked or insufficiently cooked meat and have adequate hygienic habits, the life cycle of the 3 zoonotic Taenia species may be interrupted. In addition, we describe the growing field of immune response and immunomodulation elicited by the parasites, which may provide essential tools for diagnosis, treatment, control of taeniasis/cysticercosis, as well as for identification of parasite-derived immunomodulators that could aid in the treatment of emerging inflammatory diseases worldwide.

A Sensitive, One-Way Sequential Sieving Method to Isolate Helminths' Eggs and Protozoal Oocysts from Lettuce for Genetic Identification

Different helminths and protozoa are transmitted to humans by oral uptake of environmentally resistant parasite stages after hand-to-mouth contact or by contaminated food and water. The aim of this study was to develop and validate a method for the simultaneous detection of parasite stages from fresh produce (lettuce) by a one-way isolation test kit followed by genetic identification (PCR, sequencing). Three sentinel zoonotic agents (eggs of Toxocara canis, Echinococcus multilocularis and oocysts of Toxoplasma gondii) were used to investigate the practicability and sensitivity of the method. The detection limits (100% positive results) in the recovery experiments were four Toxocara eggs, two E. multilocularis eggs and 18 T. gondii oocysts (in 4/5 replicates). In a field study, helminth DNA was detected in 14 of 157 lettuce samples including Hydatigera taeniaeformis (Syn. Taenia taeniaeformis) (four samples), T. polyacantha (three), T. martis (one), E. multilocularis (two) and Toxocara cati (four). Toxoplasma gondii was detected in six of 100 samples. In vivo testing in mice resulted in metacestode growth in all animals injected with 40–60 E. multilocularis eggs, while infection rates were 20–40% with 2–20 eggs. The developed diagnostic strategy is highly sensitive for the isolation and genetic characterisation of a broad range of parasite stages from lettuce, whereas the sensitivity of the viability tests needs further improvement.

Reinventing the Wheel of Echinococcus granulosus sensu lato Transmission to Humans

Control of cystic echinococcosis (CE) relies on interrupting Echinococcus granulosus sensu lato transmission through interventions in dogs and livestock. However, primary prevention measures aimed at avoiding ingestion of Echinococcus eggs may help reduce the burden of human CE. CE is generally considered, to variable extents, to be foodborne, but there is little evidence on the actual contamination of matrices and sociocultural factors involved in parasite transmission. An overall appraisal of published literature suggests that environmental contamination, possibly through hand-to-mouth transmission, may be of primary importance. While in most endemic areas sufficient epidemiological information is available to start CE control programs, identifying the main sources of infection to humans would allow optimization of site-specific interventions while avoiding irrelevant health education messages.