High prevalence and intensity of fish nematodes with zoonotic potential in the Brazilian Amazon, including a brief reflection on the absence of human infections

Abstract

This study aimed to characterize the prevalence, mean abundance, and mean intensity of potential fish-borne zoonotic nematode larvae infecting the predator fish Hoplias aff. malabaricus from the Tapajós River, in the municipality of Santarém, in the Brazilian Amazon. After capture, the specimens of H. aff. malabaricus were analyzed for infection by Contracaecum sp. and Eustrongylides sp. third-stage larvae, and the prevalence, mean abundance, and mean intensity were calculated. A literature search was carried out to clarify the relationship between these indicators and eventual human cases of infection in the Amazon region. Third-stage larvae of nematodes of the Contracaecum and Eustrongylides genera were found in the specimens of H. aff. malabaricus sampled from the Tapajós River. The prevalence of Contracaecum larvae was 100%, while its mean abundance and mean intensity were both 54.8 larvae/fish. The prevalence of Eustrongylides larvae was 62.9%, and its mean abundance and mean intensity were 1.8 and 2.8 larvae/fish, respectively. Despite the high prevalence and intensity values, there are no cases of human infection by these nematode larvae in the Brazilian Amazon reported. The absence of human infections by these nematode larvae in the Brazilian Amazon despite the high prevalence/intensity of Contracaecum and Eustrongylides larvae and the high consumption of fish in the region, is most probably due to the fact that the local populations do not eat raw or undercooked fish. However, it is noteworthy that the absence of zoonotic cases in the region is based only on the examination of the available published papers. A better knowledge of the situation would require surveying hospitals and clinics, and data from the region’s medical treatment facilities. However, the authors consider that cases of human infection, if any, are extremely rare, mainly due to the eating habits of the local population. KEY WORDS: Amazon basin; freshwater fish; public health; parasitic infection; zoonosis.

Assessments and Identification of Selected Fish-Borne Zoonotic Parasites in Nile Tilapia and African Catfish Species in Lakes of Haramaya District, Ethiopia

“…On average, seven L3 of Contracaecum were collected per fish and they were found freely in the body cavities, mesenteries, and muscle of fish. The results of the present study showed that the average number of larvae of Contracaecum parasite is similar to that of reported by Tesfaye et al [37] but higher than reported by Abdullah et al [18], Mitiku [35], and Lima et al [56] and lower than Corrêa et al's [76] report. Also, the average of five EMC of Clinostomum was recorded from Clinostomum infected fish, which is lower than reported by Bera et al [80], McAllister and Robison [81], and Aghlmandi et al [82], but higher than reported by Mitiku [35] and Mahdy et al [24].…”

“…Prevalence of Contracaecum in C. gariepinus in Lake Haramaya is almost similar with Mitiku [35] and Tesfaye et al [37], but lower than Amare et al [38], Lima et al [56], and Corrêa et al [76] and higher than Abdullah et al [18,77]. Prevalence of Contracaecum in O. niloticus in Lake Haramaya is also similar with Amare et al [38] but lower than Tesfaye et al [37], Reshid et al [39], Gebawo [40], and Necho and Awake [74] and higher than reported by Mitiku [35], Hailekiros et al [57], and Muluken [59].…”

“…Hence, prevalence of parasite in the body cavity were found 51.5%, 33.3%, and 27.0% in C. gariepinus from Lake Haramaya, Lake Tinike, and Lake Adele, respectively, and 17.3% and 12.9% in O. niloticus in Lake Haramaya and Lake Tinike, respectively. However, the result of total overall prevalence of parasite in the body cavity was 29.7%, which is higher than the previous reports of Muluken [59], Bekele and Hussien [63], and McAllister and Robison [81], but lower than Abdullah et al [18], Mahdy et al [24], Salem et al [31], Tesfaye et al [37], Mahdy et al [52], Lima et al [56], Marshet [58], Corrêa et al [76], and Bera et al [80]. The overall prevalence of parasite in the muscle of fish were 32.4%, 19.6%, and 16.4% in C. gariepinus from Lake Haramaya, Lake Tinike, and Lake Adele, respectively, and 16.0% and 8.1% in O. niloticus from Lake Haramaya and Lake Tinike, respectively.…”

“…Prevalence of Contracaecum in O. niloticus in this Lake is lower than reported by Mitiku [35], Amare et al [38], Reshid et al [39], Gebawo [40], Moa and Anwar [41], Hailekiros et al [57], Bekele and Hussien [63], and Necho and Awake [74] and higher than reported by Muluken [59]. However, prevalence of Contracaecum in C. gariepinus in Lake Adele is similar with Bekele and Hussien [63], but lower than Tesfaye et al [37] and Corrêa et al [76] and higher than reported by Marshet [78] and Fasil et al [36]. However, this study was disagree with the report of Hiko et al [43] which stated that all the C. gariepinus fish obtained from Lake Adele were negative both for the cestodes and nematodes.…”