A comparison of Kato-Katz technique to three other methods for diagnosis of Amphimerus spp. liver fluke infection and the prevalence of infection in Chachi Amerindians of Ecuador

Abstract

BackgroundRecently, a high prevalence of infection by the liver fluke Amphimerus spp. has been documented in the Chachi Amerindians of Ecuador. For diagnosis, no studies exist that compare the sensitivity of different coproparasitological detection techniques. The present study compares the Kato-Katz technique with three other coproparasitological methods for detecting eggs of Amphimerus in stools, as well as determines the prevalence of infection in Chachi residents in a Tropical rain forest area in the northwest coast of Ecuador.Methodology/ResultsA total of 105 samples, utilizing the Kato-Katz technique (KK), the spontaneous sedimentation technique in tube (SSTT), the formalin-ether concentration technique (FEC), and direct smear microscopy (DM), were examined. Combining the four methods (fixed “gold” standard), 38 samples were positive with a prevalence of infection of 36.2%. The sensitivities of individual methods were 71%, 58%, 50% and 3% for KK, SSTT, FEC, and DM respectively. Our results indicated that KK alone had the best performance, detecting 27 (71%) of the 38 positive samples. The combination of KK and SSTT detected amphimeriasis in 36 (95%) samples, and KK and FEC in 31 (82%) samples.ConclusionsDM showed the lowest sensitivity, which raises concern for its value, because it is the standard technique for stool examination for detection of parasites in both public and private laboratories in Ecuador. SSTT alone detected eggs in 22 samples (58%) and would be recommended for field studies because of its simplicity. Performing two techniques on a single sample enhances the detection of Amphimerus infection. Its sensitivity is relative to a fixed “gold” standard, determined as the combined results of the four techniques performed. This study confirms the high prevalence of human infection by Amphimerus in the indigenous Chachi group where the first human cases were described.

Liver fluke infections by Amphimerus sp. (Digenea: Opisthorchiidae) in definitive and fish intermediate hosts in Manabí province, Ecuador

“…The high prevalence of small trematode eggs in the human population of the three communities reported here may still be an underestimate considering the low sensitivity of small trematode egg detection using the formalin-ether concentration technique and one-time fecal sample examination, as we have shown recently [15]. The Kato-Katz coprological technique, immunological, or LAMP-based methods of diagnosis should be encouraged to characterize the true prevalence of human-fluke infections in current endemic areas, discover new foci of human infections, and to complete the knowledge of other components of the Amphimerus sp.…”

“…The Cayapas River area belongs to the Chocó region, from the tropical and subtropical moist broadleaf forest biome [28]; roughly, it has a mean annual temperature of~23-26˚C and a mean annual precipitation of~2000 mm [44]. A mean prevalence of 23.9% (71/297) of small trematode eggs was reported in humans among three villages in 2011, whereas a prevalence of 36.2% (38/105) was reported recently (2018) in a more remote village, not included in the previous study [15]; access to these villages depends mainly on boats. These rural populations are composed of indigenous native Ecuadorians of the 'Chachi' ethnicity who catch freshwater fish, and prepare and eat smoked fish dishes [13].…”

“…Flasks were transported to the Centro de Biomedicina at the Universidad Central del Ecuador. For coproparasitological diagnosis, we used the formalin-ether concentration method (Ritchie's technique), as recently described [15]. In brief, stools were processed in a cycle of homogenization and dilution with 10% formalin, decantation, and centrifugation (2500 rpm for 5 minutes) after the addition of ethyl ether (~3 ml); sediments were examined for the presence of small trematode eggs [10,15].…”

“…For coproparasitological diagnosis, we used the formalin-ether concentration method (Ritchie's technique), as recently described [15]. In brief, stools were processed in a cycle of homogenization and dilution with 10% formalin, decantation, and centrifugation (2500 rpm for 5 minutes) after the addition of ethyl ether (~3 ml); sediments were examined for the presence of small trematode eggs [10,15]. Positive and negative individuals were divided by gender, age group, and community; univariate associations between these variables and small trematode egg infection status (positive/negative) were addressed using chi-square tests with a criterion of statistical significance of p = 0.05.…”

“…Parasitological diagnosis of opisthorchiid trematodes affecting biliary ducts is usually achieved by examining stools via different techniques such as direct smear, simple sedimentation in tube, Kato-Katz, or formalin-ether concentration [5,15,16]. When present, pyriform operculated eggs can be identified through simple microscopy; however, these characteristics are also shared by eggs from the intestinal flukes of the family Heterophyidae (e.g., Haplorchis spp.…”