Ascaris lumbricoides (Figure 5.1)
The highest prevalence of ascariosis in population in the past has been characteristic for Lithuania where in 1949, 67.3% prevalence was registered. During the 1950s, the prevalence began to decline from 55.9% in 1950 to 30.4% in 1960 due to the introduction of control measures.
For Estonia, there are data for the period from 1948 to 1951 but the numbers available for these years seem to be inadequately low (0.3-0.7%) compared with the numbers beginning from 1957 (2.58%), when the long-scale control programme was introduced. It should also
be indicated here that from the end of the 1950s to the beginning of the 1960s, there are some contradictory data available for Estonia. An independent survey of distribution of helminthosis among the population was carried out between 1959 and 1962, covering most of the territory (Kondratjeva et al. 1963). In that survey, the prevalence of ascariosis given is 5.2%, indicating a possibly higher prevalence of the infection among the population.
For Latvia, the available data begin from 1967 with 5.5% prevalence although the control programme was introduced in 1948.
The control measures over these last 50 years have had significant effect on the prevalence of ascariosis in all three countries. In 1995, the following prevalence were reported: 0.029% for Estonia, 0.3% for Latvia, and 0.79% for Lithuania. As the initial level of prevalence in Lithuania was very high, it took about 35 years to achieve prevalence lower than 1% of the population. In Estonia, with the lowest initial proportion of the population infected, it took only eight years. The situation stabilized in Estonia to lower than 0.1% in mid-1970s and has been around 0.03% in the 1990s. The situation in Latvia is apparently similar, although the initial prevalence seems to have been higher. In Lithuania, the prevalence declined below 1% in mid-1980s and the lowest level was recorded in 1990 (0.37%). Beginning from 1991, a mild rise, both in Latvia and Lithuania has taken place: 0.3% in Latvia and 0.79% in Lithuania in 1996. This change might be attributed to the significant decrease in the overall number of people tested and paying more attention to the risk groups.
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