Molecular and cellular mechanisms related to pathogenesis of Rickettsia helvetica infection and how it evades immune response in humans.

Rickettsia helvetica is a gram-negative coccobacillus, an obligate parasite that cannot grow outside living cells. A tick Ixodes ricinus is the natural reservoir of the bacteria and its bite causes a febrile illness called Rocky Mountain spotted fever in humans. R.helvetica also can cause meningitis and few cases have been reported in Europe, primarily France and Sweden. Seventeen cases of Rickettsial meningitis are also reported from Sri Lanka, where two elderly patients died because of that. IgG Antibodies against rickettsia are formed but they cannot cross blood brain barrier. Rickettsia species has more than 105 strains and genomes of more than 40 percent of the strains have been fully typed and others have been partially typed. The genome of R.helvetica was completely sequenced in 2012 with a total length of some 1.36 million base pairs. Rickettsia has some important genes very well-known namely; outer membrane protein A (ompA), outer membrane protein (ompB), citrate synthase (gltA), 16S ribosomal RNA (rrs), 23S ribosomal RNA, and Gene D. OmpA and citrate synthase are known for pathogenicity, while 16S rRNA and 23S rRNA are frequently PCR amplified from cerebrospinal fluid (CSF) for diagnostic reasons. Rickettsia can be successfully cultivated in green monkey kidney (Vero) cells, tick cell lines and chicken embryo cells. Its actin tail is void of Arp2/3, a seven subunit trans-membrane protein that plays a significant role in eukaryotic actin cytoskeleton. Its surface has proteins OmpA, OmpB, RickA and ActA, which activate WASH, Wiskott-Aldrich syndrome protein and its scar homologue. WASH and activated Arp2/3 help rickettsial entry into mammalian cells. Actin nucleation proteins are needed to enter the host cells of the arthropod. Once it enters mammalian cells then within 50 minutes post infection it transcribes the genes that are related with tlyC (hemolysin C) and pld (phospholipase D) and they play significant role in the lysis of the phagosomes walls. Lysis of phagosomes is critical to the survival of the Rickettsia.