Activity of Natural Tularemia Foci in West Ukraine

摘要

Objective Stady the activity of natural foci of tularemia and identify the main types of reservoirs and vectors of Francisella tularensis. Introduction Annually sporadic cases of tularemia in humans are registered in Ukraine and new enzootic areas are found. Monitoring of tularemia natural foci is important given the potential significant financial losses in case of tularemia outbreaks and taken into account that this pathogen can be used as a bioterrorist agent. Methods 1. Light microscopy of smears of organs and tissues of animals, bacterial suspension (Gram staining) - the study of morphological and tinctorial properties of the pathogen. 2. Immunofluorescence method for detection of antibody (IFA) - detection of tularemia bacterial cells using specific fluorescent immunoglobulin. 3. Biological method - subcutaneous infection of laboratory animals (white mice) with material from environmental samples and bacterial suspension (for accumulation of tularemia agent in organs and tissues of laboratory animals). 4. Bacteriological method - inoculation of samples of wild and laboratory animals in differential diagnostic nutrient media (for isolation of a pure culture of tularemia agent). 5. Serological method: - Indirect reaction of agglutination - detection of antibodies to tularemia agent in blood of humans, wild rodents (liquid tularemia antigen erythrocyte diagnostic agent). - Indirect reaction of agglutination - detection of tularemia agent and its antigen in suspensions of organs, swabs of substrate from nests of rodents, pellets of birds (liquid tularemia immunoglobulin erythrocyte diagnostic agent). - Reaction of agglutination - detection of tularemia agent and its antigen (dry tularemia diagnostic serum). Results Tularemia in Lviv oblast has been studied for more than 40 years, 69 enzootic localities in 14 administrative districts have been registered. More than 200 cultures of Francisella tularensis have been isolated, mostly from ticks (58.3%) and Myomorphic rodents (24.5%), the rest from water, straw, other rodents, and patients. In 2012-2015, 210 suspected patients were studied for tularemia, negative results were obtained. 22,320 ticks, 1,810 Myomorphic rodents, 282 water samples, 15 straw samples, and 3 bird nests were tested for tularemia. Tularemia cultures have not been isolated bacteriologically over the last few years. Pathogen circulation in natural foci was confirmed by immuno-serological studies of field material. Antibodies to the pathogen were detected in 6.5% out of 630 samples from Myomorphic rodents of seven species studied by Indirect Hemagglutination test. Most of the positive results were obtained from the samples of striped field mouse (46.3%), red-backed vole (17.0%), and common vole (14.6%). Francisella tularensis antigen was detected in 32 samples out of 14,600 ticks D. reticulatus collected in natural biotopes and in 8.9% out of 289 samples of pellet. Conclusions No incidence registered in Lviv oblast and difficulty of isolation of Francisella tularensis cultures over the last years in other oblasts (the last one happened in 2006) may indicate the decrease of foci activity under the influence of anthropogenic and environmental factors or changes in parasitic systems. But there are some evidence of agent circulation in the oblast, so some precautions should be taken, especially considering the fact that there have been no specific preventive measures taken over the last years.