Borrelia (Borreliela) burgdorferi

Borrelia (Borreliella) burgdorferi is a bacterial pathogen transmitted by hard ticks of the genus Ixodes; it circulates in nature, through an enzootic cycle, between the ticks and a range of vertebrates that act as reservoirs. It is the causative agent of Lyme disease (LD)/Lyme borreliosis in humans, which is the fastest expanding vector-borne disease Northern Hemisphere. Borrelia spirochetes are flat wave in appearance with an undulating cell morphology. B. burgdorferi has a bundle of 7-11 helically shaped periplasmic flagella attached at each end of the cell cylinder. cells resemble Gram-negative bacteria in having both outer and inner membranes but the composition and structure of the outer membrane is significantly different and include lack of polysaccharide and the presence of numerous face-exposed lipoproteins. The 'virulence determinants' associated with infection by this bacterium are primarily proteins that enable the survival and growth of the pathogen within the mammalian host. The bacterium is unique ing a very expansive yet ordered system for antigenic variation. Segmental gene conversion events occur constantly, modifying VlsE, a surface-bound lipoprotein. Entirely different variants are generated effectively through unidirectional combination from unexpressed vls cassettes into the vlsE locus. This, and the downregulation of certain surface proteins, allow the spirochete to be always one step ahead of the acquired immune response and able to maintain a persistent infection. Although the genus name Borreliela has recently been designated for taxonomic use, the name Borrelia been associated with the LD pathogen from the time of its discovery and is being used here to avoid any confusion. This description of the LD spirochete in general refers to the B. burgdorferi sensu lato complex, which is made more than 23 different genospecies, five of them known to be pathogenic although currently at least eight of have been isolated from patients. Primary differences at the genomic level between the different LD Borrelia genospecies is in the presence or absence of certain plasmids, leading to differences in the range of hosts they can infect and gans to which they disseminate in humans. There is currently no vaccine against LD in humans. Early diagnosis of significant problem due to misdiagnoses as well as to diagnostically false-negative results.