354 Microbes and You 



out imbedded ticks. Some part, usually the head or mouthpart, 

 may remain in the skin and set up a severe irritation which may 

 become infected. 



Ticks are important in the spread of the rickettsial disease 

 ROCKY MOUNTAIN SPOTTED FEVER, the Spirochete disease relapsing 

 FEVER, and the bacterial disease tularemia. Ticks are also im- 

 portant from the standpoint of their bites which are slow to heal 

 and cause intense local irritation. These arthropods are widespread 

 throughout the tropics, subtropics, and the temperate zones. 



FLEAS 

 Fleas are small insects without wings, but they are endowed 

 with great jumping ability. They thrive in dark and damp (not 

 wet) places. Fleas are of medical importance since some species 

 can transmit bubonic plague, which is caused by a gram negative 

 bacterium, Pasteurella pestis, and endemic typhus which is caused 

 by Rickettsia mooseri (Rickettsia typhi). The most important 

 species is the tropical rat flea, Xenopsijlla cheopis, which, although 

 primarilv a parasite of the rat, during epidemics can transmit 

 plague from rat to rat, from rat to man, and from man to man. 

 Endemic typhus and plague may also be maintained in the 

 temperate zone rat flea, Nosopsi/IIus fasciatus, which is found in 

 the United States. Fortunately, the dog and the cat fleas are not 

 of general medical importance. 



MITES 



Mites in general are extremely small, almost invisible to the 

 naked eve. Sarcoptes scabiei is the common itch mite which 

 causes the skin disease scabies, usually between the fingers. Itch- 

 ing is severe and scratching frequently results in secondary bac- 

 terial infections. 



The larvae of mites are parasites on various animals. American 

 chiggers or redbugs bite into the skin not to obtain blood but to 

 obtain Ivmph. A highlv fatal disease called tsutsugamushi disease 

 is caused bv Rickettsia tsutsugamushi, and it is transmitted bv a 

 lai-val mite belonging to the genus Trombicula. In the Philippines 



