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Rickettsia typhi is a small, aerobic, obligate intracellular, rod shaped gram negative bacterium. It belongs to the typhus group of the Rickettsia genus, along with R. prowazekii. R. typhi has an uncertain history, as it may have long gone shadowed by epidemic typhus (R. prowazekii). This bacterium is recognized as a biocontainment level 2/3 organism. R. typhi is a flea-borne disease that is best known to be the causative agent for the disease murine typhus, which is an endemic typhus in humans that is distributed worldwide. As with all rickettsial organisms, R. typhi is a zoonotic agent that causes the disease murine typhus, displaying non-specific mild symptoms of fevers, headaches, pains and rashes. There are two cycles of R. typhi transmission from animal reservoirs containing R. typhi to humans: a classic rat-flea-rat cycle that is most well studied and common, and a secondary periodomestic cycle that could involve cats, dogs, opossums, sheep, and their fleas. R. typhi was once one of the most prevalent causes of rickettsial diseases worldwide, but has since experienced a drop in case reports with the implementation of pest control programs. The microorganism is concentrated in warmer climate and coastal ports where there is an abundance of rats and their fleas, which are the preferred hosts for the pathogen. R. typhi  is transmitted between competent flea and mammalian hosts through flea bites and contact with infected feces and tissues. There are several laboratory tests available for the diagnosis of Rickettsial species, with the traditional diagnosis based on serology. However, newer laboratory techniques such as real-time PCR and microimmunofluorescence can be used to identify Rickettsia faster and down to the Rickettsia typhi species level. History and taxonomy In the early 20th century epidemic typhus (R. prowazekii) ran rampant throughout many parts of the world. It was associated with high mortality, high virulence, and thought to be transmitted via louse. During this period, less severe and untraceable cases began appearing. These cases were characterized by fever, rash, headache, as well as musculoskeletal and gastro intestinal signs. Epidemiologist Kenneth F Maxy recognized this and began questioning and isolating the presence of another typhus within the United States aside from R. prowazekii, he detailed this in an article released in 1926. Maxy speculated the presence of another arthropod vector transmitting this new form of typhus, which would later be discovered as R. typhi. It is thought that R. typhi has historically been under diagnosed compared to its typhus group member R. prowazekii. The discovery of R. typhi lead to the creation of the typhus group Rickettsia, which contains R. typhi and R. prowazekii. Rickettsia species are generally broken into 3 groups, the spotted fever group, typhus group and scrub typhus group. Cellular morphology and motility Rickettsia typhi is a small, aerobic, obligate intracellular, rod shaped, gram negative bacterium. R. typhi is a zoonotic bacterium that is recognized as a biocontainment level 2/3 organism (dependent upon the tissue being worked with). As obligate intracellular pathogens, R. typhi can be difficult to isolate, and are not able to be cultured using standard plating methods seen with most other organisms. R. typhi are motile, creating movement through actin based motility, with little control over directionality and speed, and are often seen moving in a circular pattern. Virulence Rickettsia typhi is a flea-borne disease organism and is widely distributed throughout the world. There are two cycles in R. typhi transmission from animal reservoirs to human: a classic rat-flea-rat cycle, and a peridomestic cycle involving cats, dogs, opossums, sheep, and their fleas. Classic rat-flea-rat cycle R. typhi circulates amongst rats (Rattus rattus or Rattus norvegicus) and rat fleas (Xenopyslla cheopis), but other rodents and their ectoparasites also play a role in maintaining R. typhi in nature. While the rat flea is the main vector of R. typhi, P. h. humanus, Polypax lice and bloodsucking mites of rats have been reported to be capable of acquiring R. typhi, either naturally or experimentally. Transmission of R. typhi from the rat flea is affected by contact with rickettsia-containing flea feces during or after blood feeding, as well as via flea bite. The rickettsiae have no harmful effects on the fitness of either the vector or the rat, showing a true mutual relationship. Infected fleas can maintain R. typhi for life, giving them potential for infecting large number of susceptible hosts. Peridomestic cycle Thus far, there have not been many studies on the periodomestic animal cycle of transmission, with the majority that have been done focusing on cats. It has been shown that R. typhi can be present in cats and the cat flea, Ctenocephalides felis, which is a flea species that readily bites humans. So far, there has been no direct human R. typhi infections from cats, but instead an association between high rates of infected cats related to human cases of murine typhus in the same geographical location. There is also some evidence that other domestic animals such as dogs and sheep, as well as opossums, could be involved in the R. typhi transmission cycle, but studies are currently limited. Pathogenesis Rickettsia spp. including R. typhi enter the skin and spread through the bloodstream to infect the endothelium lining the blood vessels. This leads to vascular inflammation, damage to vascular integrity, and compromised vascular permeability, which is collectively known as 'Rickettsial vasculitis' Disease Murine typhus (endemic typhus) in humans Rickettsia typhi is a causative agent of murine typhus (endemic typhus) in humans and is distributed worldwide. It is an acute, febrile illness that is mainly transmitted by the fleas of rodents, commonly associated with cities and ports where urban rats (Rattus rattus and Rattus norvegicus) are abundant. Humans acquire infection by inhalation or by self-inoculating infected fleas or flea feces into skin when they visit disease-endemic areas infested with rats. Most patients present with a fever, and many have a rash and headache, although it can also lead to disseminated, multisystem disease including infections of the brain, lung, liver, kidney, and heart endothelia. As these signs and symptoms are similar to those produced by other diseases, including other rickettsiae, murine typhus is difficult to diagnose clinically. In addition to non-uniform and non-specific symptoms, there is a lack of diagnostic tests effective during the acute stages of the illness, leading to delayed appropriate treatment. Murine typhus may generally be clinically mild, but severe and even fatal cases have been reported. The severity of murine typhus infection has been associated with age, race, and delayed diagnosis. Doxycycline is the antibiotic of choice as it is shown to s.... Discover the George Muntau popular books. Find the top 100 most popular George Muntau books.