Question

Microbiology question!

"Sharon, the CEO of a start-up company, lives in Westchester County, a wooded community north of New York City. She spends her summer weekends e-mailing her managers from the outdoor deck of her home, shaded by tall oak trees. The acorns attract mice and deer, and the leaf litter is full of ticks (Ixodes scapularis) . One evening Sharon’s husband noticed a red rash on her back, consisting of a ring shape several centimeters across, surrounding another red spot in the middle. Sharon recalled seeing this “bull’s-eye” type of rash on the Internet. The rash was described as the hallmark of Lyme disease, or borreliosis, caused in the United States by the tick-borne bacterium Borrelia burgdorferi (in Europe, by the closely related species Borrelia afzelii ). The distinctive rash, erythema migrans (“migrating redness”), begins at the site of a tick bite and expands concentrically as the bacteria migrate outward. Sharon recalled that a neighbor’s child had suffered crippling arthritis caused by an undetected case of Lyme disease. Another neighbor who contracted Lyme disease had suffered from meningitis (inflammation of the brain lining) and neurological abnormalities, including facial paralysis, ultimately losing his job and his million-dollar home. The next day Sharon went to her doctor and was treated with the antibiotic doxycycline, a tetracycline derivative that targets the bacterial ribosome. Doxycycline is the antibiotic of choice for B. burgdorferi . Sharon was fortunate to make a full recovery before serious symptoms appeared. The bull’s-eye rash that is a hallmark of Sharon’s infection is associated with movement of the bacteria from the initial site of tick bite and infection. Discuss how these bacteria move and the cell structures associated with movement."

Answer 1

Sharon’s infection is associated with movement of the bacteria from the initial site of tick bite and infection. This is caused by B. burgdoferi which causes infection on the skin. Once it enters Sharon's skin, it tick bites, and thus the immune response of the host started. The spirochetes started replicating and can scattered away from the point of entry at a speed of 1-4 micron per second. Due to this reason, the bull's eye rash has two inflammatory reactions--  the salivary proteins and the bacteria that have been spread from the site of the bite. Since the microbes moved outward, there is expansion of redness of the rash, thus causing erythema migrans. Rash type can be determined by observing the motility patterns and how fastly macrophages are spread from the infection site. The homogeneous rash surrounding the site of the tick bite is due to the strong immune response of the host given at the center of the rash. The bacteria in the center can be cleared within a week whereas bacteria on the edge go on spreading outward, thus causing the immune response to follow. Major changes occured during infection like phagocytosis, chemotaxis etc. They can even exploit IFN pathways to inhibit T-lymphocyte function to suppress immune. Moreover, connective tissue become less adhesive and cell viability. These makes them easier to swim through and invade the skin. Therefore, if there is slow in clearing the macrophages from the infection site, then the rash will appear more. Sharon was lucky that she went to doctor on time, and fully recovered before serious symptoms appeared.