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222 CHAPTER 10

Source: Centers for Disease Control and Prevention (CDC)

FIGURE 10-13 Morphologic changes experienced by a flea during its life cycle, from an egg to an adult insect

hundreds of thousands of Europeans in the Middle Ages by this vector usually involve pigs, dogs, and humans
was simply called “the plague,” which refers in general who traditionally go barefoot as the groups most suscep-
to bubonic plague. This disease is caused by a bacterial tible to attacks by this organism. These fleas are found in
bacillus called Yersinia pestis, and was spread from rats the tropical and subtropical parts of America and Africa
to humans via the rat flea, although there is some argu- (Figure 10-14). In humans the pregnant female burrows
ment regarding the link of flea bites and the development into the spaces between the toes where she causes a pain-
of bubonic plague. The term bubonic comes from the ful and open sore. The gravid (pregnant) flea must be re-
word bubo, which indicates swollen and enlarged lymph moved with a sterile needle and the wound treated with
nodes, main sign of the disease. iodine to destroy any remaining fleas and eggs. This pen-
Humans can allegedly contract plague, Y. pestis, etration causes intense itching and irritation that some-
when bitten by a rodent flea that is carrying the plague times results in ulcerations and if left untreated, extreme
bacterium or by handling an infected animal. “Murine” cases may result in amputation of the affected limb as a
typhus, due to Rickettsia typhi bacteria, can also be medical necessity.
transmitted by rodent fleas to man. Four stages, with
changing morphology in the flea’s life cycle, include
the egg, followed by a larva that becomes a pupa, and OTHER LESS COMMON
then finally metamorphoses into an adult organism ECTOPARASITES
(Figure 10-13).
Although they may be less common than many of the
Tropical Chigoes or Jiggers other organisms that infest the skin and hair of humans
and other mammals, those who become infected by
The term jigger, or chigo, is the common name for a par- these lesser-known ectoparasites may suffer from irri-
asitic flea called Tunga penetrans. Parasitic infestations tating and exacerbated conditions. Serious infections