Assessing the Contamination of Food and the Environment With Taenia and Echinococcus Eggs and Their Zoonotic Transmission

Abstract

Purpose of Review Cystic and alveolar echinococcosis, caused by Echinococcus granulosus sensu lato and E. multilocularis, respectively, and Taenia solium cysticercosis are serious but neglected zoonotic diseases, caused by extra-intestinal cestode (tapeworm) infections. Humans are dead-end hosts for Echinococcus spp and acquire the infections by uptake of parasite eggs, either with contaminated food or via exposure by hand-mouth contact to eggs derived from the contaminated environment, including skin or coat of definitive hosts. Data related with the production of eggs of these parasites, their survival in the environment and the methodology for detection in food and environmental samples are summarized.Recent Findings The detection of taeniid DNA, more specifically from E. multilocularis, in food and soil has recently been described in some European countries. These findings have been directly connected with an increase in prevalence of human infections in countries like Poland. Summary The isolation and molecular identification of taeniid eggs is technically challenging and little standardized. The detection of taeniid DNA per se does not imply viability of eggs, and this must be considered when interpreting molecular results for transmission risk. Finally, easy, affordable, and sensitive methods replacing animal experiments should be developed to assess the viability of taeniid eggs isolated from environmental and food/water sources.

Public health risks associated with food‐borne parasites

“…The sensitivity of PCR amplification is high and claimed to detect theoretically one single egg. This is convincing, as taeniid eggs contain between 18 and 56 cells (Alvarez Rojas et al., ) and it has been estimated that a single taeniid egg (based on Taenia hydatigena ) contains around 7,000 mitochondrial targets, while the detection limit of PCRs targeting the mitochondrial DNA was estimated at 33 copies (Trachsel et al., ). A critical point that needs to be addressed is the fact that the detection of DNA from Echinococcus spp.…”

“…The scientific literature provides several reports on microscopy‐based findings of taeniid eggs on vegetables, mainly in Asia and Africa, with contamination rates ranging between 0.9 and 18.3% (Alvarez Rojas et al., ). Studies performed in Norway (Robertson and Gjerde, ), France (Hohweyer et al., ), and Italy (Caradonna et al., ) did not detect taeniid eggs.…”

“…In Europe, the association of human cystic and alveolar echinococcosis, with contaminated food has to be considered based on the few preliminary data concerning food contamination with taeniid eggs and or parasite DNA. Standardised methods and more studies are needed to document the risk of food being contaminated with viable Echinococcus eggs (Alvarez Rojas et al., ). Expert knowledge elicitation indicates wide uncertainty for both CE (4–40% of cases) and AE (12–79% of cases) (Hald et al., ), and discussions on risk factors based on systematic review and meta‐analysis indicate the need for more primary studies.…”

Potential risk factors associated with human cystic echinococcosis: a semi-structured questionnaire from a large population-based ultrasound cross-sectional study in Eastern Europe and Turkey

“…Multiple potential habits/sources may result in human ingestion of infective parasite eggs. However, so far very few experimental data are available on the actual contamination of different materials by E. granulosus eggs [12], and the analyses of questionnaires investigating potential risk factors gave contrasting results [14]. Our questionnaire-based study, carried out in the context of the largest research-based cross-sectional survey on human CE [19], applying stringent case definition, may help better framing the general characteristics of risk factors for human infection.…”

“…“Ingestion of contaminated food and water”, together with “direct contact/playing with dogs” are classically mentioned as the sources of human infection and are biologically plausible potential risk factors. However, actual data on contamination of and relative attribution from such sources are extremely scant and uncertain [7, 11, 12]. Further, Chaabane-Banaoues et al [13] found that degree of environmental contamination by E. granulosus -positive dog faeces did not necessarily correlate with human prevalence of CE, highlighting that multiple ecological factors, likely varying from area to area, and involving human behaviour and hygiene habits, are at the basis of human transmission.…”