Review of the concentration procedures used to determine the parasitological water quality in Latin America (2000–2022)

In parasitological studies of human and animal health, knowledge of environmental sanitation is essential for a comprehensive view of the parasitic epidemiology (FAO/OIE/WHO 2009). In Latin America, the availability of water and sanitation services is limited, making access to safe drinking water difficult (Jouravlev et al. 2021). Ruiz-Taborda et al. (2018) found that the region shows a synergistic relationship between parasitic infections and socio-environmentally vulnerable living conditions. In this regard, water sources become contaminated with intestinal parasites when infected humans or animals discharge the different infecting forms with excreta (cysts, oocysts, eggs, larvae) in water bodies due to inadequate sanitary infrastructure, which spreads the different infective stages of parasites throughout the environment (Chalmers et al. 2020).

Cryptosporidium spp. and Giardia spp. are the most frequently identified waterborne parasite species around the world (Efstratiou et al. 2017; Bourli et al. 2023). Giardia spp. cysts and Cryptosporidium spp. oocysts have been reported together in epidemiological outbreaks caused by consumption of treated water mainly due to their resistance to chlorine (Efstratiou et al. 2017; Silva & Sabogal-Paz 2021). In Latin America, soil-transmitted nematodes are present throughout the region and are deemed to increase the probability of water contamination (surface water, groundwater) due to their biological cycle and the lack of adequate sanitary infrastructure (Saboyá et al. 2013; Mahapatra et al. 2022). In this regard, studies on parasitological water quality have found protozoa and geohelminths together (Cacciabue et al. 2014; de Freitas et al. 2015; Martínez & Caicedo 2016; Silva et al. 2017; Traviezo et al. 2017).

The design of the study and the methodologies to be applied in parasitological analyses of environmental samples are important considerations to obtain acceptable results and know the real state of the environmental health (Falcone 2021). However, the methods used for parasitological diagnosis in water present discrepancies, which have an impact on the selection of the diagnostic method and evaluation of its efficacy. It should be highlighted that the waterborne and foodborne disease surveillance systems in this region focus on the detection of bacteria as indicators of contamination, and there are few controls for the identification of parasite species (Gilardi et al. 2018; Chalmers et al. 2020).

In this context, the aim of this study was to review the available information on parasitological analyses carried out on water samples in Latin America in the period from 2000 to 2022. This review will optimize the possibilities of concentrating parasitic forms in water samples from the region and provide scientific knowledge to support public health and food safety policy management processes.

The methodologies used in Latin America for the diagnosis of parasitic species in water samples were manually recovered from specific bibliographies. Data were systematically collected from three databases: Google Scholar, PubMed, and SciELO Argentina. The search was performed using the following combination of keywords in Spanish, Portuguese, and English: ‘parásitos’ or ‘parasitas’ or ‘parasites’ + ‘agua’ or ‘water’ + ‘Argentina, Bolivia, Brazil, Chile, Colombia, Costa Rica, Cuba, Dominican Republic, Ecuador, El Salvador, Guatemala, Haiti, Honduras, Mexico, Nicaragua, Panama, Paraguay, Peru, Uruguay or Venezuela’. The bibliographic study comprised the period from 2000 to 2022, and the data were organized and analyzed in MS Excel data sheets between September and November 2022.

Inclusion was based on whether they were original articles and short communications published in journals with ISSN. If more than one report of the same study was published, only one was included in its native language. Experimental and field studies were included in the analysis, but not bibliographic reviews, theses, repositories, and conferences. Only articles identifying species were included, and these were named in general terms, i.e. only at the genus level.

Of the total number of countries, 11 had matched with the specified keywords (55% = 11/20). In the comprehensive literature reviewed, 87 articles corresponding to the specified keywords were located from three academic search engines (Basualdo et al. 2000; Quintero-Betancourt & Botero de Ledesma 2000; Abramovich et al. 2001; Franco et al. 2001; Franco & Cantusio Neto 2002; Luna et al. 2002; Lura et al. 2002; Cinco et al. 2003; Dowd et al. 2003; Kato et al. 2003; Lopez et al. 2003; Cifuentes et al. 2004; Hachich et al. 2004; Alarcón et al. 2005; Chaidez et al. 2005; Costamagna et al. 2005; Ryu et al. 2005; de Moura et al. 2006; Guzmán-Quintero et al. 2007; Campos-Pinilla et al. 2008; Cermeño et al. 2008; Balthazard-Accou et al. 2009; Bracho et al. 2009; Gamboa et al. 2009; Machado et al. 2009; Mota et al. 2009; Betancourt et al. 2010; Mora et al. 2010; Neto et al. 2010; Razzolini et al. 2010; Araújo et al. 2011; Brasseur et al. 2011; Olivas-Enriquez et al. 2011; Razzolini et al. 2011; Xavier et al. 2011; Betancourt & Mena 2012; Poma et al. 2012; Rodríguez et al. 2012; Damiani et al. 2013; Guillen et al. 2013; Guzmán et al. 2013; Olivas Enríquez et al. 2013; Osaki et al. 2013; Sato et al. 2013; Cacciabue et al. 2014; da Silva Barbosa et al. 2014; de Paiva Barçante et al. 2014; Gallego Jaramillo et al. 2014; Verant et al. 2014; Balderrama-Carmona et al. 2015; Campos-Almeida et al. 2015; de Freitas et al. 2015; Juárez et al. 2015; Rodriguez-Alvarez et al. 2015; Tiyo et al. 2015; Lora-Suarez et al. 2016; Martínez & Caicedo, 2016; Rey et al. 2016; Santos et al. 2016; Triviño-Valencia et al. 2016; Vielma et al. 2016; Balthazard-Accou et al. 2017; Grothen et al. 2017; Hernandez-Cortazar et al. 2017; Palacios 2017; Silva et al. 2017; Toledo et al. 2017; Traviezo et al. 2017; Bautista et al. 2018; de Araújo et al. 2018; Sánchez et al. 2018; Arocha et al. 2019; Bataiero et al. 2019; Delgado Vargas et al. 2019; Hernández et al. 2019; Borja-Serrano et al. 2020; Breternitz et al. 2020; González-Ramírez et al. 2020; Norberg et al. 2020; Prato-Moreno et al. 2020; Campo-Portacio et al. 2021; de Almeida Mendonça et al. 2021; González-Fernández et al. 2021; Morales et al. 2022; Morales-Mora et al. 2022; Scherer et al. 2022). Of these, 72.4% (63 articles) were exclusively identified in one search engine, 24.1% (21 articles) were retrieved in two search engines, and 3.5% (3 articles) were located in all three search engines. Specifically, 16.1% (14 articles) were located on PubMed, while a substantial 56.3% (49 articles) were located through Google Scholar. In addition, 2.3% (2 articles) were found in PubMed and SciELO, 20.7% (18 articles) in PubMed and Google Scholar, 1.2% (1 article) in Google Scholar and SciELO, and 3.5% (3 articles) were concurrently present in PubMed, Google Scholar, and SciELO.

Keywords in English were the most frequent combination, 60.9% (53/87), followed by keywords in Spanish, 35.6% (31/87), and to a lesser extent in Portuguese, 3.4% (3/87). Brazil was the country that published the majority of the articles with a percentage of 28.7% (25/87), followed by Venezuela and Mexico, with 14.9% (13/87) and 12.6% (11/87), respectively, (Table 1). Argentina was in the fourth place with 10.3% (9/87), and similar percentages were found in Colombia with 9.2% (8/87) and Costa Rica with 8% (7/87). The rest of the countries showed percentages that varied between 1 and 5.5% (Supplementary Table 1).

The studies are diverse in terms of their aims, their designs, and the techniques implemented. The articles focus on the search for species and could be experimental or for the evaluation of pathogens in general. In this sense, the articles surveyed vary in the type and volume of the water sample studied (DW: drinking water; SW: surface water; GW: groundwater), as well as in the concentration technique implemented. However, taking into account of these limitations, it is possible to reach common considerations in their analysis.

Most of the studies were conducted in surface water (SW: 75.9% = 66/87), being the type of sample in over half of the articles surveyed (68.2% = 45/66). In particular, these studies were realized in places where there was possible fecal contamination, such as rivers adjacent to agricultural activities. The second most analyzed type of sample was drinking water, which was found in a similar percentage as in the articles analyzing drinking and surface water samples (DW: 19.5% = 15/87 and DW-SW: 17.2% = 15/87, respectively). Groundwater was found in very low percentages when analyzed separately, or with samples of surface water and/or drinking water (GW: 10.3% = 9/87, SW-GW: 3.4% = 3/87, and DW-SW-GW: 4.6% = 4/87, respectively). The low frequency of parasitological studies of groundwater compared to drinking water confirms the need for further environmental studies to determine the source of parasitological infection that would explain the high prevalence observed in populations living in rural areas compared to urban areas in Latin America (Pincay et al. 2022).

Parasitological concentration is an enrichment technique to concentrate oocysts, cysts, eggs, and larvae of parasites in the smallest sample volume and to determine their presence and identification (Falcone 2021). Most of the articles utilized methodologies with physical separation by some type of filtration or centrifugation (89.6% = 78/87) without subsequent parasitological concentration (76.9% = 60/78). Of the total number of articles that applied a parasitological enrichment technique (32.2% = 28/87), 67.9% (19/28) used flotation with saturated sucrose solution. Among the physical methods of separation, the majority, 63.2% (55/87), used filtration with separation by membranes with a pore diameter of ≥0.22 μm, while 4.6% (4/87) used the ultrafiltration methodology, a method adopted also to recover viruses (Poma et al. 2012; Cacciabue et al. 2014; Juárez et al. 2015; González-Fernández et al. 2021). Organic and inorganic flocculation methods were used to a lesser extent (10.3% = 9/87), which could be related to the infrastructure needed and the cost to implement these methodologies in the region. Moreover, these methodologies recovered a lower number and type of species compared to those that used some method of filtration.

The methodologies frequently used for parasite diagnosis varied from study to study. The methodology identified as being of general use was optical microscopy (OM). Specific methodologies were also identified such as DAPI (4′,6-diamidino-2-phenylindole) staining and immunofluorescence base microscopy (IMF), ELISA, and the different variations of the polymerase chain reaction (PCR) molecular technique. Moreover, the techniques OM, IMF, ELISA, and PCR were recognized in some studies to be the only methods of diagnosis (29.89% = 26/87, 28.74% = 25/87, 2.30% = 2/87, and 10.34% = 9/87, respectively). The use of species-specific diagnostic methodologies was also reported in 65.5% (57/87), and the number of species found varied from one to five. On the other hand, 31 out of 87 papers used OM as the diagnostic methodology, finding between 1 and 14 different species. Only two articles that employed the general and specific methodologies for parasitological diagnosis identified between eight and 12 different species.

Of the total number of articles evaluated, 26 different species of parasites, 14 species of protozoa (+Blastocystis spp.), 7 species of nematodes, and 5 species of flatworms were identified. Of the articles surveyed, protozoan species alone were found in 83.9% (73/87), while both protozoa and nematodes were reported in the remaining 16.1% (14/87). The species that were usually concentrated were the protozoa Cryptosporidium spp. (70.1% = 61/87) and Giardia spp. (67.8% = 59/87). Other parasites reported were Blastocystis spp. (18.4% = 16/87), Toxoplasma gondii (9.2% = 8/87), Cyclospora sp. (8% = 7/87), Balantidium coli (5.7% = 5/87), and Trichomonas sp. (2.3% = 2/87). Among the commensal species Entamoeba spp. (18.4% = 16/87) and Endolimax nana (13.8% = 12/87) were the most frequent. In the helminths, Enterobius spp. and Trichuris sp. were occasionally reported (8% = 7/87 and 6.9% = 6/87, respectively), as well as geohelminths Ascaris spp. (6.9% = 6/87), Trichostrongylus sp. (5.7% = 5/87), and species of the family Ancylostomidae (4.6% = 4/87). Among the flatworms, Fasciola hepatica was identified (2.3% = 2/87), and the most frequent cestode species was Hymenolepis spp. (5.7% = 5/87) (Tables 2 and 3).

The study of the articles reviewed shows that the ultrafiltration method (UFM) with a pore diameter of less than 1 μm recovered the greatest number of different species (20.1% = 18/87). The UFM was first evaluated in samples of drinking water; SW, and groundwater (Oshima 2001; Morales-Morales et al. 2003). Oshima (2001) utilized a first step of blocking the filter with fetal bovine serum for 24 h and subsequently, several authors complemented UFM with a second step of concentration by centrifugation (Hill et al. 2009; Rhodes et al. 2011; Liu et al. 2012; Kahler et al. 2015; Kimble et al. 2015; Rangel-Martínez et al. 2015). Rajal et al. (2007) introduced modifications to the UFM methodology to determine the viral quality of aquatic environments. Among the adaptations, the authors eliminated the filter-blocking step before UFM and observed a decrease in the sample processing time with a similar percentage of recovery.

Poma et al. (2012) and Cacciabue et al. (2014) adopted the UFM to study smaller volumes of water samples. In fact, the sample volume was adjusted from 100 to 20 L to evaluate the virological and parasitological quality of SW. Also, Poma et al. (2012) performed a second step of concentration by passing the sample through a gauze, followed by the treatment with Sheather's flotation solution and Charles Barthelemy's method. This allowed them to concentrate several parasites, such Balantidium coli, Blastocystis spp., Giardia spp., Cyclospora sp., Trichomonas sp., Dientamoeba sp., Enteromonas hominis, Endolimax nana, Enterobius spp., Ascaris spp., Hymenolepis spp., Necator americanus, Strongyloides spp., Trichuris sp., Dipylidium caninum, Trichostrongylus sp., and Fasciola hepatica, including those less than 6 μm in size, such as Microsporidium and Cryptosporidium spp.

It is important to highlight that intestinal parasites are found in low concentrations in the environment, and the smaller sample volume may affect the availability of microorganisms or DNA for molecular methodologies (Juárez & Rajal 2013). In this regard, Juárez et al. (2015) evaluated the quality of samples of groundwater for human consumption and increased the sample volume to 60 L. They also carried out a secondary concentration process involving spontaneous sedimentation, which allowed them to concentrate parasites of smaller sizes, such as Chilomastix mesnili and Giardia spp. These adaptations could explain the differences observed in the number and type of parasite species concentrated with this method in the mentioned articles. In addition, differences between the number of protozoan (+Blastocystis spp.) and nematode species could be due to intrinsic morphological characteristics related to the adaptation of resistant forms of protozoa, oocysts, and cysts to adverse environmental conditions (Hassan et al. 2021; Unzaga & Zonta 2023).

The present review highlights the techniques available for parasite concentration from three types of water samples (DS, WS, and GW) in Latin America. The UFM method recovered the highest number and the type of parasite species. The descriptive study of the review shows that the procedure of using UFM with a parasitological method of flotation and sedimentation would allow an efficient concentration of the parasite species present in the water sample. However, the differences in the types and volumes of samples, protocols, and study designs expose the need for further study under controlled conditions that allow comparison of the techniques implemented to strengthen the analysis and arrive at an effective and efficient technique for the study of parasites in water. On the other hand, diagnosis of any type of sample should be performed in a complementary manner using microscopy and PCR-based methodologies.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.