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A group of 150 persons living in the Lublin province of eastern Poland and occupationally exposed to tick bite were examined by the immunoenzymatic ELISA test for the presence of antibodies against tick-borne Spotted Fever Group (SFG) rickettsiae. The group consisted of 75 forestry workers employed in 3 forest inspectorates and 75 agricultural workers living in 2 villages. As a control group, 43 urban dwellers living in the city of Lublin and not occupationally exposed to tick bite were examined. Among 150 persons occupationally exposed to tick bite, the presence of antibodies against SFG rickettsiae was found in 54 (36.0% of the total). In the control group, the frequency of positive findings was only 4.7%, being significantly smaller compared to the exposed group (p=0.0001). Within the exposed group, the percentage of positive results in forestry workers (50.7%) was greater than in agricultural workers (21.3%); the difference was statistically significant (p=0.0002). Also within this group, the frequency of positive findings in males(46.5%) was significantly greater than in females (21.9%) (p=0.0029). In the exposed group, the positive results tended to increase with the age of the examined persons. However, a significant relationship between age and positive findings was found only in forestry workers (c2=14.207, p=0.00264), but not in agricultural workers and total exposed workers. The frequencies of positive results in forestry workers varied significantly depending on place of work (c2=11.271, p=0.00357). Similarly, the difference between the positive reactions in agricultural workers living in 2 villages proved to be significant (34.2% vs. 8.1%; p=0.0074). The obtained results indicate that people occupationally exposed to tick bite and living in the area of eastern Poland where over half of Dermacentor reticulatus ticks harbour SFG rickettsiae, are under significantly increased risk of infection with these rickettsiae.
Rickettsia spp. transmitted by ticks are classified mostly in the Spotted Fever Group Rickettsiae (SFGR). Numerous species of this group have been identified in Eurasia as emerging pathogens, but still little is known about their occurrence, effects on human health, and co-incidence with other tick-borne pathogens. The aim of the presented study was to determine the prevalence of Rickettsia spp. in adult Dermacentor reticulatus (Acari: Amblyommidae) ticks collected in Lublin province of eastern Poland using the PCR method. The infection rate of D. reticulatus with Rickettsia spp. was 53.0%. All except one rickettsial isolates showed 100% homology with Rickettsia raoultii. A high prevalence of R. raoultii in Dermacentor reticulatus ticks from eastern Poland suggests that the SFGR species should be considered as potential causative agents of tick-borne diseases in this area.
Prokaryotic or gan isms are ex posed in the course of evo lu tion to var i ous im pacts, re­sult ing of ten in dras tic changes of their ge nome size. De pending on cir cum stances, the same lin eage may di verge into spe cies hav ing sub stan tially re duced genomes, or such whose genomes have un der gone con sid er able en large ment. Ge nome re duc tion is a con se quence of ob li gate intracellular life style ren der ing nu mer ous genes ex pend able. An other con se quence of intracellular life style is re duc tion of ef fec tive pop u la- tion size and lim ited pos si bil ity of gene ac quire mentvia lat eral trans fer. This causes a state of re laxed se lec tion re sult ing in ac cu mu la tion of mildly del e te ri ous mu ta tions that can not be cor rected by re com bi na tion with the wild type copy. Thus, gene loss is usually irreversible. Additionally, constant environment of the eukaryotic cell ren­ders that some bac te rial genes in volved in DNA re pair are ex pand able. The loss of these genes is a prob a ble cause of mutational bias re sult ing in a high A+T con tent. While causes of genome reduction are rather indisputable, those resulting in ge­nome ex pan sion seem to be less ob vi ous. Pre sum ably, the ge nome en large ment is an indirect consequence of adaptation to changing environmental conditions and re­quires the ac qui si tion and in te gra tion of nu mer ous genes. It seems that the need for a great number of capabilities is common among soil bacteria irrespective of their phylo gen etic re la tion ship. How ever, this would not be pos si ble if soil bac te ria lacked in dig e nous abil i ties to ex change and ac cu mu late ge netic in for ma tion. The lat ter are con sid er ably fa cil i tated when house keep ing genes are phys i cally sep a rated from adaptive loci which are useful only in certain circum stances.
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