Chagas Disease

I. EPIDEMIOLOGY
The protozoan Trypanosoma cruzi causes Chagas disease,
which affects more than 30 million individuals, with
approximately 100 million at risk in Latin America.
Figure 1 shows the distribution of Chagas disease in the
Americas. This disease is prevalent only in Central and
South America, particularly in Argentina, Chile, Brazil,
and Bolivia. It also occurs in the southern United States,
however, where more than 90,000 Latin Americans are
believed to be infected. The risk of transmission in the
United States is mainly by blood transfusion by this
immigrant population.

A. Transmission
Chagas disease is transmitted to children and young adults
less than age 20 through the bite of a bug (reduviid,
subfamily Triatominae). The bug becomes infected by
feeding on infected animals such as the armadillo,
opossum, raccoon, and skunks. Domestic dogs and cats
also provide an extensive reduviid reservoir for infecting
entire families.

The biting bug unfortunately dwells in the roofs and
walls of houses. During the night the bug drops onto the
sleeping individual and inflicts bites around the eyes.
Infection is transferred when the trypanosomes in the
animals excrement enters the wounded skin or penetrates
the conjunctiva. The protozoa multiplies and then
migrates through most organs of the body including the
myocardium, pericardium, liver, spleen, and brain. Chagas
disease is primarily transmitted through blood transfusions,
and unfortunately screening of blood is financially
not possible in the affected countries. The simple
accomplishment of screening blood, building better
homes, and screening cats and dogs would prevent the
majority of infections.

II. SYMPTOMS AND SIGNS
A. Acute Phase
The bite of the bug around the eyes allows the
trypanosomes to gain entry through the conjunctiva.
This often results in one-sided swelling around the eye
(periorbital edema) and swelling of the eyelid (Romana
sign). If the entry is through the skin, a lesion called a
chagoma appears. The initial lesion may go unrecognized,
however, and no symptoms may appear until after more
than 15 years when symptoms of chronic disease emerge.
In about 10% of infected individuals acute symptoms
such as muscle aches and pains, fever, sweating, and
enlargement of the liver and spleen occur. If the parasitic
infection involves the cardiac muscle, an acute myocarditis
and heart failure may supervene causing death. Lesions
may spread to involve the endocardium and stimulate the
flowing blood to form a clot that may embolize. The
pericardium may be involved causing pericardial effusions.
Young children become more seriously ill than young
adults, and in more than 10% the acute disease is fatal.
Many patients recover, however, and symptoms disappear
over 1–2 years. More than 40% of infected patients after
a relatively symptom-free interval of several years reveal
signs and symptoms of chronic Chagas disease.

B. Latent and Chronic Phase
Cardiac involvement is mainly due to a cardiomyopathy
that manifests about 20 years after the trypanosomal
infection. At this point, the heart muscle is uniformly
destroyed and replaced by fibrous tissue. The weakened
heart muscle is stretched, the left ventricular chamber
dilates, the pumping function is severely deranged, and
heart failure supervenes. Heart failure produces changes
in the heart, circulation, and veins that can be detected
on examination by the physician. A chest x-ray confirms
dilation of the heart and presence of fluid in the
spongework of the lungs and fluid within the pleural
space (pleural effusions).

The main manifestation of heart failure is increasing
shortness of breath on mild activity and with severe heart
failure, shortness of breath occurs at rest. Heart failure
describes the signs and symptoms that occur when the left
or right ventricles are unable to eject an adequate amount
of blood into the aorta to fulfill the needs of organs and
tissues. Thus blood remains longer in the lungs and salt
and water escapes into the air sacs (the alveoli), causing
oxygen lack and severe shortness of breath. In heart
failure, salt and water are retained by the kidneys as a
compensatory mechanism and extra fluid exudes into
tissues in dependent parts of the legs causing bilateral
leg edema. The legs are not waterlogged, they are brine
logged (see the chapter Heart Failure).

The pathologic findings include hypertrophy and
dilatation of cardiac chambers in keeping with a dilated
cardiomyopathy. The left ventricle apex becomes thin and
bulges into an aneurysm. Clot formation often occurs
within the aneurysm and thromboembolism to other
organs occurs.

The electrical bundles of the heart, particularly the right
bundle branch and the anterior fascicle of the left bundle
branch, are commonly involved by the inflammatory
process causing the ECG to show a typical pattern of
right bundle branch block and left anterior fascicular
block hemiblock. The large left bundle branch is really
involved.

Symptoms of cardiomyopathy include shortness of
breath, chest pain, syncope, and sudden death caused by
heart block due to involvement of the electrical conducting
system. In many patients the left ventricle fails, but
manifestations are mainly of right heart failure. Thus, the
shortness of breath from left ventricular failure may
diminish and signs of right heart failure may become more
prominent. These signs include fluid retention that causes
swelling of the abdomen (ascites) and bilateral leg edema.
The trypanosome in Brazil often involves the esophagus,
stomach, and colon resulting in a dilated esophagus
(megaesophagus and megacolon). This is uncommon in
Central America and Mexico because it is caused by a
different strain of trypanosome.

In the acute phase of the disease, trypanosomes are
found in the cardiac fibers accompanied by marked cellular
infiltrate around cells that have ruptured and released the
parasites. It is not unusual, however, to be unable to find
parasites in the cardiac tissue at autopsy. An autoimmune
mechanism is believed to explain the lack of correlation
of parasitemia with disease severity. T. cruzi antigen is
frequently found in biopsy specimens.

III. DIAGNOSTIC INVESTIGATIONS
A. Chest X-ray
The chest x-ray shows a dilated heart that increases to
severe proportions as the disease progresses. The lungs
may show evidence of fluid accumulation with pleural
effusions, but the lung fields may be relatively clear if
mainly right heart failure occurs.

B. Blood Tests
In Chagas disease the serum aldolase is usually elevated.
A complement fixation test (Machado-Guerreiro test) that
has high specificity and sensitivity is used to identify
chronic Chagas disease. Xenodiagnosis is the preferred test
in endemic areas. With this test reduviid bugs bred in the
laboratory are allowed to bite the patient. The parasites are
then found in the intestine of the insect proving infection
in the patient.

C. Echocardiography
Echocardiography shows enlargement of all four heart
chambers in Chagas patients. There is also a reduction in
the ejection fraction. On echo, the appearance of Chagas is
distinctive: there is hypokinesis, poor contractility of the
left ventricular posterior wall, relatively preserved intraventricular
septal wall motion, and poor movement of the
apical segment of the heart with dilatation and aneurysmal
formation.

IV. MANAGEMENT
A. Prevention
Vector control and interruption of transmission of the
parasites to humans remain crucial. In endemic areas
individuals should avoid having dogs or cats in the home.
Improved housing conditions, repair of walls and ceilings,
and added fresh paint should deter bugs from these areas.
The use of nets for sleeping should prevent bugs from
falling from ceilings onto the exposed face at night.

B. Medications
Antiparasitic agents such as benzimidazole, itraconazole,
and nifurtimox reduce parasitemia in the acute phase, but
they do not have any effect on the autoimmune-mediated
chronic form of the disease. Anticoagulants are necessary in
patients with left ventricular aneurysm or thrombi detected
in the ventricle and those who have sustained embolism.
Arrhythmias often require treatment with antiarrhythmics
such as amiodarone. This drug is used for symptomatic
relief and does not appear to prolong life.

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