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92 CHAPTER 4

at risk for becoming infected by this parasite. Infection
may also occur through blood transfusions of infected
blood donors, because the parasite is found in the blood.
T. cruzi has also been implicated as the causative agent
for encephalitis and as an opportunistic infection in im-
munocompromised patients such as those with HIV in-
fections and other chronic illnesses. Victims may suffer Source: Centers for Disease Control and Prevention (CDC)
from chronic infection by T. cruzi with serious medical
consequences because no effective medication is avail-
able for an effective cure for the disease.

Morphology
FIGURE 4-11 Chagas’s disease is due to a protozoan,
Trypanosoma cruzi is a flagellate of the family Trypano-
T. cruzi, transmitted by the true bug
somatidae. The organism possesses one flagellum and
a single mitochondrion in which the kinetoplast is situ-
ated, consisting of a specialized DNA-containing organ- T. cruzi infection and also proved that the trypanosome
elle. The identification of this parasite by morphological T. cruzi is transmitted by the previously mentioned “kiss-
and biological features does not offer difficulties. Differ- ing bugs.” These transient infective forms of the trypano-
entiation between Trypanosoma rangeli, a nonpathogenic some organism circulate in the bloodstream and are taken
flagellate that infects humans in some areas of Central up by the bloodsucking bugs as they feed on a mammalian
and South America, and pathogenic strains is necessary. host. After the parasites multiply in the gut of the bug, the
The organisms are transmitted by some of the same vec- infective forms are passed in the feces of the insect.
tors that transmit T. cruzi.
Disease Transmission
Symptoms
Chagas’s first observation that the bloodsucking bugs
Most frequently the disease ranges from mild to no infesting the poorly constructed houses harbored these
symptoms, and usually the symptoms are confined to flagellates appeared to be a well-reasoned possibility as
fever, facial edema, and hepato- and splenomegaly. But a host for the T. cruzi protozoan. He also determined
the infection is sometimes accompanied by myocarditis, that the disease organism is not mechanically spread
cardiomyopathy, megaesophagus, megacolon (massive merely through a bite but is accomplished through the
dilation of the colon), and eventually death may ensue. liquid feces that is excreted around a bite mark by the
insect. A stage called the epimastigote state migrates to
Life Cycle the anus of the bug and is deposited with its feces as the
reduviid bug feeds on the victim (Figure 4-12) often in
The trypanosomes of T. cruzi, found in the Western the mouth region. Organisms are able to enter the host
Hemisphere, are now known to be spread mainly by by passing through the bite wounds and the victim rubs
one of the “true” bugs (not all insects are correctly la- or scratches the bitten area, allowing the organism to
beled as “bugs”). Various triatomid species belong to the enter the body of the potential victim. Although Chagas
order Hemiptera and include the reduviid bug, the in- thought that without a doubt the link between the bites
sect responsible for transmitting the parasite in the of the bugs and contraction of the parasitic infection
Americas (Figure 4-11). These insects have efficient was indisputable, his thesis was later supported by the
biting and piercing mouthparts and are often called “kiss- French parasitologist, Emile Brumpt. Brumpt, in 1909,
ing bugs,” commonly known by this name because of definitively demonstrated the transmission of the disease
their tendency to bite the lips and face. During the time through contamination of the area with the feces of the
period between 1907 and 1912 the Brazilian scientist bug. He proved that transmission of the protozoan did
Carlos Chagas, gave the common name of the disease to not occur during the biting process itself, but instead
the world. His research shows that the disease is from a the organism entered the wound the bite left behind.