Echinococcoses

Echinococcus granulosus and E. multilocularis (genus Alveococcus, Abuladze, 1960, Alveococcus multilocularis) infections in man were recorded in the late 1950s and the early 1960s in the Archangelsk region, in the northern zone of Tjumen region including the Yamal peninsula, in the Novosibirsk and the Krasnoyarsk regions and in the Yakutia. Hospital and autopsy cases of E. multilocularis were up to 57% of all cases of disease in Yakutia, 58.1% in the north of the Krasnoyarsk and 64.2% in the Novosibirsk regions in 1937-1939. The highest morbidity per 100000 of population was revealed in the valleys of the Lena, Amga, and Aldan rivers. Polar and red foxes had been considered as the principal definitive hosts of E. multilocularis. Lemmus obensis, Microtus gregalis, M. oeconomus, Clethrionomus glareolus and Ondatra tibethica were recorded as additional hosts. Echinococcus granulosus was found mainly in dogs and in some cases in wolves. Larval stages of the agent were present in sheep, swine, cattle in moderate climate areas, but in the Yakutia, Chukotka, and the Archangelsk region they were found in reindeers (Shikhobalova et al. 1969).

Echinococcus multilocularis infection is transmitted to man in natural foci through the shooting of game, by eating wild berries contaminated by the excrement of wild carnivores or by drinking polluted water from natural reservoirs. The survival time of onchospheres was up to 67 days in the excrement of foxes covered with snow, in a straw stack, at the bottom of a lake in the Siberian winter. Dogs are infected with E. multilocularis by hunting for small rodents. Transmission of E. granulosus infection is due to continuous contact of man with dogs infected by eating the internal organs of reindeer, domestic animals, and garbage containing the agent cysts. Man contracts hydatid disease through close contact with infected dogs (Shikhobalova et al. 1969).

Anthropogenic factors have changed the principally natural origin of E. multilocularis infection foci and led to the possibility of formation of synathropic (settlement's) ones

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(Martinenko et al. 1984). Two hundred and seventeen cases of E. multilocularis infection were registered in the Korjak Autonomous District (Kamchatka) in 1955-1986, the morbidity rate was 6.1 in aboriginals and 0.3 in settlers and migrants (Stepchuk et al. 1990). The morbidity rates of E. multilocularis and E. granulosus were 9.5 and 15.6, respectively, in the same groups in the north of the Omsk region in 1989. But, clinical course of infection in the latter had been significantly more serious than in patients from two former groups. Migrants made 26% in the group with the severe course of disease and only 5% of moderately severe cases among 84 patients with E. multilocularis infection examined and followed up in the Clinic of the Martsinovsky Institute in 1961-1970. A 30-year-old man, a Moscow resident, died from E. multilocularis infection complicated by the hepato-renal insufficiency after 3 years of living in the Magadan region (Ozeretskovskaya 1979).

The morbidity rates of E. multilocularis and E. granulosus infections were 9.5 and 15.6, respectively, in the north of the Omsk region in 1989, at the same time sero-epidemiological survey (ELISA) gave 5.2 and 5% positive results, respectively (Klebanovski 1985), perhaps due to the quality of used diagnostic tools. In the mixed, synanthropic and natural foci of E. granulosus in the Khabarovsk region, 6.4% of the population were seropositive and contamination of soil by the parasite oncospheres was found in 6.6% of tests (Maslov, 1991). The morbidity rate (for 100000 of population) of echinococcoses in Chukotka in 1992 was 2 for the total population and 23 for aboriginals; about a half of cases were E. granulosus infection. The lung localization of cysts was found in 40% of cases, which is supposed to be the specificity of the strain (Boytsov et al. 1992; Bessonov 2001a,b). It is of interest that among 10 patients with E. granulosus cysts in the lungs (ethnically mixed group) in HLA-B5 carriers the production of IFN-gamma was significantly higher than in HLA-A2 carriers (Ozeretskovskaya et al. 1992). One presumes that the polar fox/lemming strain of E. granulosus is less virulent than the red fox/ voles, gerbils, muskrats strain spread in tajga-zone of Siberia.

Sero-epidemiological survey of the northern regions of Russia performed by the Martsinovski Institute in 1994-1996 (Report to the Ministry of Health of Russian Federation, 1996) revealed the predominance of E. granulosus infection in KPAD with its higher epidemiologically significant rate in adults (Table 6.1). In contrast, in aboriginals of the Tomsk region, the positive tests with E. multilocularis antigen were two-fold higher: 12.8 and 6.4. However, diagnostically significant rate for E. granulosus infection was almost three-fold higher than for E. granulosus (Table 6.1). In aboriginals of the Taimir peninsula, diagnostically positive tests were 2 for E. granulosus and 3.9 for E. multilocularis. In the mixed group of HMAD's population seroprevalence by E. granulosus prevailed. Perhaps that was due to the four-fold higher number of children in the examined group (Table 6.1). Seroprevalence of children (5-18-year-old) by E. granulosus was the highest in Chukotka: 15 (Table 6.1). It seems that the Tomsk region and Chukotka remain the active mixed foci of both infections. Seroprevalence in aboriginals of the Russian North by both infections was higher than of settlers.

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