: 266  Logographic writing systems, such as Chinese characters, have extensive symbol use; and these also pose problems for dyslexic learners. Pathophysiology
For most people who are right-hand dominant, the left hemisphere of their brain is more specialized for language processing. With regard to the mechanism of dyslexia, fMRI studies suggest that this specialization is less pronounced or absent in people with dyslexia. In other studies, dyslexia is correlated with anatomical differences in the corpus callosum, the bundle of nerve fibers that connects the left and right hemispheres.Data via diffusion tensor MRI indicate changes in connectivity or in gray matter density in areas related to reading and language. Finally, the left inferior frontal gyrus has shown differences in phonological processing in people with dyslexia. Neurophysiological and imaging procedures are being used to ascertain phenotypic characteristics in people with dyslexia, thus identifying the effects of dyslexia-related genes. Dual route theory
The dual-route theory of reading aloud was first described in the early 1970s. This theory suggests that two separate mental mechanisms, or cognitive routes, are involved in reading aloud. One mechanism is the lexical route, which is the process whereby skilled readers can recognize known words by sight alone, through a "dictionary" lookup procedure. The other mechanism is the nonlexical or sublexical route, which is the process whereby the reader can "sound out" a written word. This is done by identifying the words constituent parts (letters, phonemes, graphemes) and applying knowledge of how these parts are associated with each other, for example, how a string of neighboring letters sound together.
Typhus, also known as typhus fever, is a group of infectious diseases that include epidemic typhus, scrub typhus, and murine typhus. Common symptoms include fever, headache, and a rash. Typically these begin one to two weeks after exposure.The diseases are caused by specific types of bacterial infection. Epidemic typhus is due to Rickettsia prowazekii spread by body lice, scrub typhus is due to Orientia tsutsugamushi spread by chiggers, and murine typhus is due to Rickettsia typhi spread by fleas.Vaccines have been developed, but none are commercially available. Prevention is achieved by reducing exposure to the organisms that spread the disease. Treatment is with the antibiotic doxycycline. Epidemic typhus generally occurs in outbreaks when poor sanitary conditions and crowding are present. While once common, it is now rare. Scrub typhus occurs in Southeast Asia, Japan, and northern Australia. Murine typhus occurs in tropical and subtropical areas of the world.Typhus has been described since at least 1528. The name comes from the Greek tûphos (τῦφος) meaning fever or delusion, describing the state of mind of those infected. While "typhoid" means "typhus-like", typhus and typhoid fever are distinct diseases caused by different types of bacteria. Note, however, that in some languages such as German, typhus does mean "typhoid fever". Signs and symptoms
These signs and symptoms refer to epidemic typhus, as it is the most important of the typhus group of diseases.Signs and symptoms begin with sudden onset of fever and other flu-like symptoms about one to two weeks after being infected.