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Ticks 15 *
This 2005 image depicted a male “brown dog tick”, Rhipicephalus sanguineus from a superior, or dorsal view looking down on this “hard tick’s” scutum, or keratinized “shield” which entirely covers its back, identifying it as a male. In the female, the dorsal abdomen is only partially covered, thereby, offering room for abdominal expansion when she becomes engorged with blood while ingesting her blood meal obtained from her host.
Though not the primary vector for Rocky Mountain spotted fever (RMSF) like the “American dog tick”, Dermacentor variabilis, and the “Rocky Mountain wood tick” D. andersoni, R. sanguineus has been found to be a less-common vector as well. This tick is distributed throughout the world. It also is known to transmit diseases to animals including canine babesiosis, bovine anaplasmosis, East Coast fever and Texas cattle fever. It can also spread tularemia, and tick-borne typhus to human beings.
RMSF is caused by Rickettsia rickettsii, a small bacterium that grows inside the cells of its hosts. These bacteria range in size from 0.2µm x 0.5µm to 0.3µm x 2.0µm. They are difficult to see in tissues by using routine histologic stains, and generally require the use of special staining methods.
In the human body, rickettsiae live and multiply primarily within cells that line small- to medium-sized blood vessels. Spotted fever group rickettsiae can grow in the cytoplasm or in the nucleus of the host cell. Once inside the host the rickettsiae multiply, resulting in damage and death to these cells. This causes blood to leak through tiny holes in vessel walls into adjacent tissues. This process causes the rash that is traditionally associated with Rocky Mountain spotted fever and also causes damage to organs and tissues.
Content Providers(s): CDC/ James Gathany; William Nicholson
Picture & text from CDC/PHIL. For more information on source & for information on color coding used above for different types of ticks, see Tick Pictures from CDC