Why are tapeworm carriers so difficult to find? A methodological proposal for their search and recovery

Mexico is considered as an endemic area for taeniasis/cysticercosis. Nationwide and regional studies (Larralde et al., 1992) on cysticercosis seroprevalence in swine and humans (Morales et al., 2018), along with numerous epidemiological studies on human neurocysticercosis and porcine cysticercosis, have deepened our knowledge on this parasitosis (Fleury et al., 2003; Flisser et al. 2004; Fleury et al., 2006; Flisser and Gyorkos 2007).

Taeniasis, caused by the closely related tapeworm species Taenia solium and T. saginata, only affect humans, the definitive host are responsible for disseminating parasite eggs in the environment (WHO 2015; Sciutto et al., 2000). Upon ingestion by pigs or humans, T. solium eggs hatch and release the embryo, which develops into the larval stage, causing porcine or human cysticercosis. Neurocysticercosis (NCC), the most severe form of human cysticercosis, is due to the establishment of larvae in the central nervous system (WHO 2015), a very costly disease in economic and human terms (Bhattarai et al., 2015, 2018) that can severely affect health and quality of life (Battatarai et al., 2011). In contrast, the larval stage of T. saginata only infects bovines.

Taeniasis/cysticercosis by T. solium is a public health problem in developing countries of Africa, Asia, and Latin America with high indices of economic, social, and cultural marginalization, and where poor or non-existent health services promote its transmission (WHO 2015; Sciutto et al., 2000). Taeniasis/cysticercosis by T. solium is emerging in the developed world due to human immigration in the search for better living conditions. To mention a few examples, NCC caused 124 deaths in California in the 1989–2000 period (Sorvillo et al., 2004); on the other hand, an average of 136 residents in Los Angeles County are annually hospitalized due to NCC (Croker et al., 2010).

In Mexico, the official epidemiological bulletin reported an accumulated number of 213 taeniasis cases (no species identified) and 190 cysticercosis cases in 2019 (Boletin Epidemiologico, 2010). Adult cestodes are hermaphroditic worms that lodge in the small intestine of human hosts, Tapeworms, usually 1.5–7-m long, are well-tolerated in most cases, and they often coexist with the host with no evident symptoms (Romero 2006). On rare occasions, infection-related signs include anorexia or bulimia, diffuse pain or epigastrium-focused discomfort, slow digestion, heartburn, flatulence, nausea, and weight loss (Craig & Faust, 1974). Gravid proglottids (gravid worm segments) have been reported to actively come out of the anus of individuals infected by T. saginata, causing general discomfort and anxiety. The finding of gravid segments in the underwear and bed sheets of patients infected by T. saginata was reported in the 1950s, and it was regarded as a pathognomonic sign of this species (Pawlowski and Schultz, 1972; Soberón and Parra, 1950).

The Official Norm in Mexico, NOM-021-SSA2-1994, for the surveillance, prevention, and control of the taeniasis/cysticercosis (T/C) complex, is aimed to allow medical and veterinary health professionals to monitor the epidemiological features of the T/C complex. While T. solium taeniasis (cie-10 b68) and cysticercosis (cie-10 b69) are included in the list of food-borne diseases, the former is seldom notified, since carriers do not seek medical attention because of it. Taeniasis diagnosis is challenging due to cultural factors because it requires to collect feces for 1–3 days to search for proglottids or eggs; to this end, efforts have been made to train health professionals to identify this problem (Flisser et al. 2005). Furthermore, clinical laboratories are often unavailable in rural areas, and the clinical picture of the disease is heterogeneous and usually mild, making the detection and diagnosis of adult cestode carriers difficult (Allan et al., 1996).

While several methods have been developed to detect T. solium cysticerci in infected pigs, making case location relatively simple, reliable epidemiological data on adult worm carriers is scarce. A patient with cysticercosis (either human or animal). In fact, the migration of asymptomatic carriers has promoted the transmission of neurocysticercosis as a re-emerging disease in previously disease-free areas (Del Brutto 2012; Patamia et al., 2017); this fact is increasingly important in a globalized world, with high rates migration (Schantz et al., 1992; Sorvillo et al., 2007). According to WHO, eradicating T/C or at least significantly reducing its incidence is a feasible goal in the short term, especially if intersectoral efforts are joined and act synergistically under the concept of “One Health” (OPS 2019).

This work stemmed from a deliberate search for T. solium carriers, aiming to describe some characteristics of the infection and of the patients from whom parasite specimens were recovered and identified. The proposal herein described intends to maximize the efficacy of the treatment administered to a patient suspected of taeniasis and to effectively recover the biological material for its accurate diagnosis. National health authorities could take advantage of this simple, no-cost strategy, to both improve the efficacy of treatment and achieve a closer surveillance of the disease in endemic areas.

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