Orientia tsutsugamushi
"O. tsutsugamushi" causes a complex and dangerous infection scrub typhus. Infection starts when chiggers bite on the skin during their feeding. The bacteria are deposited at the site of feeding (inoculation), where they multiply. They cause progressive tissue damage (necrosis). Necrosis progresses to inflammation of the blood vessels called vasculitis. This in turn causes inflammation of the lymph nodes, called lymphadenopathy. Within a few days, vasculitis extends to various organs including liver, brain, kidney, meninges and the lung. The disease is responsible for nearly a quarter of all the febrile (high fever) illness in endemic areas. Mortality in severe case or due to improper treatment or misdiagnosis may be as high as 30-70%. About 6% of infected people die untreated, and 1.4% of the patients die even with medical treatment. Moreover, death rate can be as high as 13% where medical treatment is not properly handled. In cases of misdiagnosis and failure of treatment, systemic complications rapidly develop including acute respiratory distress syndrome, acute kidney failure, encephalitis, gastrointestinal bleeding, hepatitis, meningitis, myocarditis, pancreatitis, pneumonia, septic shock, sub-acute thyroiditis, and multi-organ dysfunctions. Harmful symptoms involving multiple organ failure and neurological impairment are difficult to treat, and can be lifelong debilitation or directly fatal. The central nervous system is often affected and result in various complications including cerebellitis, cranial nerve palsies, meningoencephalitis, plexopathy, transverse myelitis, neuroleptic malignant syndrome, and Guillan-Barré syndrome. Death rates due to complications can be up to 14% in brain infections, and 24% with multiple organ failure. It is the major cause of acute encephalitis syndrome in India, where viral infection Japanese encephalitis has been regarded as the main factor.
Orientia tsutsugamushi
"O. tsutsugamushi" has four major surface-membrane proteins (antigens) having molecular weights 22 kDa, 47 kDa, 56 kDa and 110 kDa. A 56-kDa protein is the most important because it is not produced by any other bacteria, and is responsible for making the genetic diversity in different strains. It accounts for about 10–15% of the total cell protein. The 22-kDa, 47-kDa or 110-kDa antigens are not normally detected by sophisticated diagnostic tests. But clinical tests easily detect the 56-kDa protein, making it the main target in diagnosis. The protein assists the adhesion and entry of the bacterium into host cells, as well as evasion of the host's immune reaction. It varies in size from 516 to 540 amino acid residues between different strains, and its gene is about 1,550 base pairs long. It contains four hypervariable regions, indicating that it synthesise many antigenically different protein but of the same kind. There are also 11-kDa and 60-kDa protein inside the bacterium which are very similar to GroES and GroEL of the bacterium "Escherichia coli", but not that of "Rickettsia" species. GroES and GroEL are heat shock proteins belonging to the family of molecular chaperones in bacteria. DNA analysis have shown that the "GroES" and "GroEL" genes are indeed present in "O. tsutsugamushi" with slight variation in different strain and they produce the 11-kDa and 60-kDa proteins.