Background In Kazakhstan, a live plague vaccine EV 76 NIIEG has been used for plague prophylaxis since the mid-1930s. Vaccination is administered yearly among people living in plague-enzootic areas. Similar practices are used in other former Soviet Union countries. Yet, to this day, the effectiveness period of the vaccine is unknown. It is also not clear how different factors can affect the effectiveness of the vaccine over time. Methods We surveyed changes in antibody levels specific for F1 antigens of Yersinia pestis among vaccinated people 4, 8, and 12 months post- vaccination. Blood samples were taken from the participants of the study for producing sera, which was later analyzed using indirect hemagglutination reaction with antigenic erythrocyte assay (micromethod) for identifying antibodies to F1 Y . pestis . Results In first-time-receivers of the plague vaccine, antibody titer reached the highest level of antibody that represents a conditionally protective titer after 4 months, dropped drastically after 8 months, and dropped again after 12 months. Similar results were obtained among those who have been vaccinated previously. However, in that group, the percentage of people with a level of antibody that represents a conditionally protective titer remained statistically significant even after 8 and 12 months. Conclusion Based on the results of this study, we recommend initiating vaccination campaigns for the medical and veterinary staff, as well as the general population four months prior to the springtime epizootics of plague among wild rodents.
The Sari-Dzhas natural mountain focus of plague with an area of 5000 sq. km is located mainly in Kyrgyzstan. This enzootic area belongs to a group of Tien-Shan mountain plague foci and crosses the boundaries of Kazakhstan, Kyrgyzstan, and China. After collapse of Soviet Union, this area was not investigated fully, thence we have estimated current status of hosts and vectors comparing to 1977 in the Sari-Dzhas focus. For period 1977-2014, the number of the gray marmot (Marmota baibacina) as main host of plague has decreased twice due to regular chemical suppression of focal area, but now there is a tendency for population recovery. If negative impact of human activity (hunting, livestock, and tourism) will be minimized, the population density should rise in the near future, related to high reproduction score of animals. Significant increase of number of narrow-skulled vole (Microtus gregalis) observed on focus area in 1977-2017 can effort a risk of pathogen transmission in cross-populations of marmots provided by recovery of vector number between different hosts. For whole observation period in the Sari-Dzhas focus were described 33 species of marmot fleas with dominated Oropsylla silantiewi (67% from whole amount of fleas) and Radinopsilla li ventricosa (6.5%). Deep dustation of marmot burrows by 10% dichlorodiphenyltrichloroethane (DDT) conducted in 1980s caused significant decrease of ectoparasite abundance: the number of specific fleas is strongly diminished, while recovery of ticks and lice number is faster. At the same time, Yersinia pestis constantly circulates in the focal area, which is comfortable for interacting of human populations and pathogen hosts. Last plague epizootic was recorded in 1983 and recent outbreaks among gray marmot and its vectors with varying intensity are registered again starting from 2012. Thus, the Sari-Dzhas natural plague focus remains active with all links of plague epizootic cycle (marmot-vector-rodent) and needs strong monitoring every year.
The main purpose of this study was to clarify the role of gray marmots ( Marmota baibacina ) in the long-term maintenance of highly virulent strains of Yersinia pestis in two plague endemic foci of the Tien Shan Mountains in Kyrgyzstan. We present data from regular observations of populations of M. baibacina and small rodents cohabiting with marmots in the mountainous grasslands of the Sari-Dzhas (east of Issyk-Kul Lake) and the Upper-Naryn (south of Issyk-Kul Lake) natural foci. During 2012–2017, an abundance of marmots and their ectoparasites (fleas and ticks) was significantly higher in Upper-Naryn comparing to Sari-Dzhas, although there were no differences in a number and diversity of small rodents cohabiting with marmots. The plague bacterium was detected either in marmots or in their ectoparasites collected during 4 of 6 years of observation in Sari-Dzhas and during 2 of 4 years of observation in Upper-Naryn. Plague was found in three sectors situated closely to each other in Sari-Dzhas and in 1 of 8 repeatedly surveyed sectors in Upper-Naryn. During 6 years, we isolated 9 strains of Y. pestis from marmots, two from their fleas Oropsylla silantiewi , one from an unidentified tick, and one from the gray hamster ( Cricetulus migratorius ). All plague strains isolated from the rodents and their ectoparasites in this study were similar to Antiqua biovar specific for marmots. The results indicate that plague can circulate continuously in the Tien Shan Mountains in populations of gray marmots and their ectoparasites with a facultative involvement of other rodent species after significant changes in rodent communities that happened in Kyrgyzstan during the previous two decades. The simultaneous field survey of two natural foci of plague, Sari-Dzhas, and Upper-Naryn, would be important for further analysis of circulation of Y. pestis strains belonging to Antiqua biovar in the Tien Shan Mountains.
ASSESSMENT OF THE VULNERABILITY OF THE POPULATION ON SARI-DZHAS AUTONOMOUS FOCUS OF PLAGUE, KYRGYZSTAN
Контакты: Абдел Зият Жумадилулы, канд. мед. наук, заведующий лабораторией микробиологии и эпидемиологии чумы на ПХВ «Казахский научный центр карантинных и зоонозных инфекций им. М. Айкимбаева» МЗ РК, г. Алматы, ул. Капальская, 14, индекс 050054.
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