In contrast to the infections reviewed so far, the prevalence of diphyllobothriosis has been the highest in Estonia and is more than 10 times higher even nowadays than in the other two Baltic countries. Based on the data of Kondratjeva et al. (1963), it could have been even significantly higher in the end of the 1950s and beginning of the 1960s (3.7%) than indicated in the official publication of the National Board of Health Protection (between 0.43 and 0.3%). Since then, the prevalence has decreased significantly to 0.037% in 1995 with 548 cases. It should be pointed out that historically there have been two main foci of infection in
Estonia: the coastal regions of the Lake Peipus in the east of Estonia and on the island of Saarema (Osel). In the coastal regions of Lake Peipus the prevalence in the late 1950s and beginning of the 1960s was extremely high, constituting 53.3% of the inhabitants tested (Kondratjeva et al. 1963). In 1971, the prevalence of diphyllobotriasis in that region had decreased to between 11.2 and 2.6% in different villages thanks to the control measures (Vasiljeva, 1973). The high prevalence of D. latum in that region has been attributed to the high prevalence of plerocercoids in fish in Peipus ( Jogiste and Barotov 1993). Although the data for 1960s may not be concrete, it has been reported that nearly all the fish caught were infected. Between 1985 and 1991, the infection was found in 26.4% of burbots, 14.4% of pikes, and 3.3% of perches tested. The overall level of infection of the Peipus fish (12.5%) was much higher than in the second biggest lake of Vortsjarv (4.7%) in Estonia. Such a high prevalence in fish has been attributed to the high wastewater pressure on that lake from the city of Tartu in Estonia and the city of Pskov on the Russian side. The positive effect on the decrease of prevalence in Estonia has been associated with the freezing of fish caught from Lake Peipus since the 1980s. For the 1990s, the number of cases reported have been between 715 in 1993 and 548 in 1995.
For Latvia and Lithuania, the prevalence has been constantly significantly lower. In Latvia, the prevalence among humans has decreased from 0.002% (46 cases) in 1967 to 0.0007% (18 cases) in 1996. The cases have been registered all over the country. The number of cases has been higher in the northeastern part of the country in the regions closest to the Estonian border. A significant number of cases have been attributed to fishing in, and consumption of the fish from, Lake Peipus. The data from veterinary services indicate a low incidence of fish infected with plerocercoids in rivers and lakes of Latvia, but the geographical distribution of cases make that data dubious. Complementary studies are needed.
In Lithuania, the highest prevalence of 0.25% was recorded in 1951 (273 cases). In the 1990s, this indicator has been 0.0013% in 1995 (seven cases from 540893 people tested) and 0.0003% in 1990 and 1993 (five and two cases, respectively). In Lithuania, the foci of diphyllobothriosis have been in the region of the lagoon of Kursiu Marios and the Trakai Lake (Biziulevicius and Krotas 1961; Sangaila and Federene 1973). In 1973, it was stated that these two foci were in the state of elimination.
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