Abundance of Opisthorchis felineus Metacercariae in cyprinid fish in the middle Ob River basin (Tomsk region, Russia)

Abstract

Infection with the liver fluke, Opisthorchis felineus, caused by the consumption of infected raw or undercooked cyprinid fish is common in humans and carnivores in the middle Ob River basin (Tomsk region, Russia) and can lead to diseases in humans. The goal of this study was the status of fish infection with O. felineus metacercariae in order to assess the role of fish in the infection of the human population in the middle Ob River basin. Of the 14 Cyprinidae species recorded in the middle Ob River basin, we examined 6 cyprinid species for prevalence and intensity of infection with O. felineus metacercariae. Five of these species (Leuciscus idus, Leuciscus leuciscus, Rutilus rutilus, Abramis brama, and Carassius gibelio) are of commercial value, while the common bleak is an object of amateur fishing. In addition, we conducted a survey of the fish consumption habits as part of a community-based cross-sectional study in the rural Shegarsky district, Tomsk region, Russian Federation. O. felineus metacercariae were observed in muscles of all examined species except for the Prussian carp. The ide is the main infection source in the Ob River (prevalence of infection, 100%, and intensity, 50.5 metacercariae per fish) and the common dace in the Tom River (91.1% and 12.7 metacercariae). Although the two alien species (bream and common bleak) are susceptible to infection with O. felineus metacercariae, the prevalence of infection in these fish and in the roach did not exceed 3%. The prevalence and intensity of infection in fish increased with age and size. The infection characteristics of fish in different water flows were different. The cyprinid species account on average for 69.8% of the commercial fish harvested in the Tomsk region. According to epidemiological survey, among 600 participants, 87.5% (n = 525) of respondents consumed river fish, with the most popular fish being cyprinids including Prussian carp, dace, ide and bream, followed by pike and perch. Thus, the epizootological state of the water flows in the middle Ob River basin is adverse with respect to opisthorchiasis, as indicated by high infection rates of liver fluke metacercariae in ide and common dace, which are abundant species of high commercial value. An extremely high prevalence of infection suggests a strong transmission cycle with a high rate of infection from infected humans and/or animal reservoir hosts to snails and fish. In addition to treating humans, there should be a strong focus on identifying these potential reservoir hosts to reduce subsequent infection in humans. Furthermore, since the intensity of infection in humans is determined by the presence of fish species such as ide and dace in the diet, they should be included in a dietary change campaign by eliminating the consumption of raw fish.

Keywords: Commercial stock; Cyprinid fish species; Epidemiology; Epizootology; Opisthorchiasis.

Fig. 1

Commercial fish stocks in the Tomsk region (Resource and Ecological Atlas of the Tomsk Region, 2004): 1, Aleksandrovsky district; 2, Asinovsky district; 3, Bakcharsky district; 4, Verkhneketsky district; 5. Zyryansky district; 6, Kargasoksky district; 7, Kozhevnikovsky district; 8, Kolpashevsky district; 9, Krivosheinsky district; 10, Molchanovsky district; 11, Parabelsky district; 12, Pervomaysky district; 13, Teguldetsky district; 14, Tomsky district; 15, Chainsky district; and 16, Shegarsky district, and the cities of 17, Kedroviy; 18, Seversk; 19, Strezhevoy; and 20, Tomsk. Red points indicate sampling locations. The map is based on GDM data (www.gadm.org), version 3.4, April 2018, and visualization using R (3.6.1) (http://CRAN.R-project.org/package=sp). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)`

Fig. 2

Data on the volumes of commercial fishing in the Tomsk region in 2004–2018 (according to the official data kindly provided by the Upper Ob River regional office of the Federal Agency for Fishery).

Fig. 3

Size, age, and infection characteristics of the ide in the middle Ob River basin (2016–2018). A: Size (SL, standard length; W, weight) and age characteristics. B: Dependence of the intensity of infection on the body weight. C: Dependence of the intensity of infection of the ide on the age.

Fig. 4

Common dace infection in the middle Ob River basin (2016–2018). A: Size (SL, standard length; W, weight) and age characteristics. B: Dependence of the intensity of infection on the body weight. C: Dependence of the intensity of infection on the age in the Tom River. D: Dependence of the prevalence of infection of the age in the Tom River.

Fig. 5

Size (SL, standard length; W, weight) and age characteristics of cyprinid fishes and the rate of their infection with O. felineus larvae in the middle Ob River basin (2016–2018).