Inquiry Basket
Loading ......
Orientia Tsutsugamushi is the causative agent of scrub typhus and is a natural focal disease. Orientia Tsutsugamushi belongs to the class Proteobacteria, order α subgroup Rickettsiales, family Rickettsiaceae, and genus Rickettsia. Orientia Tsutsugamushi is short rod-shaped, with an average length of 1.2 μm and rarely exceeding 1.5 μm. Gimenez staining shows dark red; Gram staining, Giemsa staining and Macchiavello staining properties are the same as Rickettsia prowazekii.
Figure 1. Schematic representation of Orientia tsutsugamushi infection in vitro. (Jantana Wongsantichon, et al.; 2020)
Orientia Tsutsugamushi resides in chiggers and can be passed down through eggs. Chigger larvae need to suck the lymph fluid or blood of humans or animals to complete the development process from larvae to larvae. It is not pathogenic to guinea pigs, but mice are susceptible and can grow in chicken embryo yolk sacs and passage cells. Rickettsia tsutsugamushi has weak resistance to the external environment. After being cultured at 37°C for 2 to 3 hours, its vitality is greatly reduced. It loses its vitality in a few hours in a 0.1% formalin solution, but it does not survive at low temperatures or It can survive for a long time under vacuum drying conditions. Orientia Tsutsugamushi can cause scrub typhus in humans. Rickettsia tsutsugamushi isolated from different areas have varying degrees of virulence. The virulent strains can produce strong toxins, the properties of which are similar to the toxins of Rickettsia prowazekii and Rickettsia moschinii, but their antigenic structure and properties are different from other rickettsiae.
Chiggers are the vectors and reservoirs of Orientia Tsutsugamushi. Orientia Tsutsugamushi can be transmitted vertically among chiggers via eggs. Chiggers have a small activity range and generally live together in the form of mite islands in bushes. When host animals or people arrive at their activity areas, they can be bitten by chiggers, and Orientia Tsutsugamushi in their salivary glands is released into the tissues at the bite site, infecting host cells such as endothelial cells, macrophages, and dendritic cells. The local skin bitten by chiggers will first become congested, edema, and form small papules, then blisters, and then necrosis and bleeding, forming black scabs, called eschar. Infected macrophages and dendritic cells carry Orientia Tsutsugamushi and migrate to peripheral lymph nodes, and then infect multiple organs throughout the body, leading to systemic infection and systemic small vessel vasculitis. The incubation period of scrub typhus is generally 10 to 14 days, and the onset is acute. The main clinical features are fever (38.5 to 41.0°C), headache, specific eschar or ulcer, local or systemic lymphadenopathy, rash, and myalgia. This disease can involve multiple organs in the body, causing hepatosplenomegaly, focal or diffuse myocarditis in the myocardium, hemorrhagic pneumonia in the lungs, interstitial inflammation in the kidneys, and lymphocytic meningitis in the meninges.
Orientia Tsutsugamushi is an obligate intracellular parasitic Gram-negative bacterium. After Giemsa staining, it can be seen under a light microscope that there are purple dots in the cytoplasm near the nucleus with a size of (0.3~0.5) µm × (1.2~3.0) µm bacteria. Its genome is larger than that of other obligate intracellular parasitic bacteria. Other rickettsial genomes are generally 1.3Mbp, while the Orientia Tsutsugamushi genome is 2.1Mbp. Comparison of the genomes of Orientia Tsutsugamushi and other rickettsiae revealed that the genome of Orientia Tsutsugamushi possesses a large number of multi-copy repeat sequences, especially integration and conjugation originals. These originals were named amplified genetic originals of Orientia Tsutsugamushi. These repetitive sequences can account for up to 40% of the genome. These multi-copy repeated sequences can be used as targets for molecular detection of scrub typhus, thereby greatly improving detection sensitivity. Orientia tsutsugamushi enters cells through receptor-mediated endocytosis, is then released from endosomes, enters the cytoplasm, uses the host's microtubules to migrate to the vicinity of the nucleus, and replicates in the juxtanuclear region. Orientia Tsutsugamushi can be grown in sensitive animals, chicken embryos, and sensitive cell lines. Using the serum of clinical and experimental animals, it was found that there are four main dominant antigens of Orientia Tsutsugamushi, with molecular weights of 56kDa, 47kDa, 21kDa and 110kDa proteins respectively. Among them, the 56kDa protein is the most important and is the type-specific antigen (TSA). 56kDaTSA plays an important role in Orientia Tsutsugamushi' invasion of host cells and evasion of host immune recognition. Its amino acid sequence contains a conserved region and four highly variable variable regions. These four variable regions have dominant epitopes and can be recognized by clinical sera infected with the same type. There are many Oriental types of scrub typhus, and these types have great differences in virulence, genome and antigenicity. Currently, more than 100 strains of Orientia Tsutsugamushi have been isolated from clinical specimens, chiggers and rodents. However, there are large differences in antigenicity between strains and weak cross-protection, which has led to the development of vaccines and immunological diagnostic reagents R&D faces greater difficulties.
Because the clinical symptoms of scrub typhus are atypical and there are no abnormalities or specific abnormalities in routine blood, urine and biochemical test indicators, it is easy to cause misdiagnosis and missed diagnosis. The World Health Organization points out that scrub typhus is one of the most easily missed infectious diseases at present, so accurate and rapid laboratory diagnosis is of great significance for the diagnosis and treatment of scrub typhus. Laboratory diagnosis of scrub typhus includes three aspects: pathogen isolation and culture, serological detection and molecular biology detection. The most commonly used tests in laboratories are serology testing and molecular biology testing. Molecular biology testing is more sensitive within 10 days after the onset of clinical symptoms (fever), and serology testing is used for testing 10 days after the onset of clinical symptoms (fever).
At present, the main serological methods for detecting scrub typhus include Weil–Felix test, indirect immunofluorescence test, enzyme-linked immunosorbent assay and colloidal gold method.
Weil–Felix test is an agglutination test using Proteus OXK, which has a common antigen with Orientia tsutsugamushi, as an antigen. Weil–Felix test is simple and easy to operate, but its detection sensitivity and specificity are low.
The indirect immunofluorescence test is the gold standard for serological diagnosis of scrub typhus, which detects IgM and IgG antibody titers in serum by using Orientia tsutsugamushi -infected cells fixed on glass slides as antigens. When double sera are tested, if the IgG antibody titer of the convalescent serum is 4 times or more higher than that of the acute phase serum or seroconversion occurs, Orientia tsutsugamushi infection can be diagnosed.
Enzyme-linked immunosorbent assays initially measured serum IgM and IgG antibody titers using lysed Orientia tsutsugamushi thallus or recombinantly expressed single 56 kDa TSA as the coating antigen. Because there are also multiple serotypes of Orientia tsutsugamushi, detection may be missed. In order to expand the antigen spectrum, in recent years, 56 kDa TSA derived from multiple strains of Orientia tsutsugamushi has been used as a mixed antigen or chimeric antigen to conduct enzyme-linked immunosorbent assay to detect Orientia tsutsugamushi infection, and achieved good detection sensitivity and specificity.
The colloidal gold immunochromatographic test provides a rapid and simple serological method for detecting Orientia tsutsugamushi infection. The 56 kDa TSA of multiple strains of Orientia tsutsugamushi is used as a mixed antigen or chimeric antigen to detect anti-Orientia tsutsugamushi IgM and IgG in clinical serum. In order to increase the detection sensitivity, 21 kDa is also used as a detection antigen.
Reference
| Target | Cat. No. | Product Name | Expression System | Tag/Conjugate | Application | |
| O. tsutsugamushi | DAG-WT642 | Recombinant Orientia Tsutsugamuchi 56KDa Protein | E. coli | TBD | ELISA, CLIA | Inquiry |
Loading ......
