Critical medicine topic-CMT 004
CHAGAS' DISEASE
(AMERICAN TRYPANOSOMIASIS)
Definition
Chagas' disease is a parasitic infection caused by the
protozoan Trypanosoma cruzi. The major cardiovascular
manifestation is extensive myocarditis, which eventually leads to dilated
cardiomyopathy and congestive heart failure. The disease usually
becomes clinically evident 20–30 years after the initial infection.
Epidemiology
- Endemic in Central
and South America.
- Approximately 10–20
million people are infected.
- The disease is an
important cause of non-ischemic dilated cardiomyopathy in endemic
regions.
Etiology
- Caused by the
protozoan parasite Trypanosoma cruzi.
- Transmitted to
humans by the bite of the reduviid bug (kissing bug) during the
acute phase of infection.
Phases of Chagas' Disease
1. Acute Phase
- Infection occurs
following the bite of the kissing bug.
- Protozoa multiply
rapidly and spread throughout the body.
- The acute illness is
often mild or asymptomatic.
2. Latent (Indeterminate) Phase
- Parasites persist
within the host with few or no clinical manifestations.
- This phase may last
for several decades.
3. Chronic Phase
- Develops in
approximately 30% of infected individuals.
- Characterized by
progressive myocardial damage, arrhythmias, and heart failure.
- Interestingly, many
individuals with a high parasite burden never develop chronic disease,
while parasites may not be detectable in patients dying from Chagas'
disease, suggesting that an autoimmune mechanism contributes to
cardiac injury.
Pathogenesis
- Chronic myocarditis
causes progressive destruction of myocardial tissue.
- Cardiac dysfunction
may result from both:
- Persistent
infection with Trypanosoma cruzi, and
- An autoimmune-mediated
myocardial injury.
- Cardiac parasympathetic
denervation is a characteristic pathological feature.
Pathology (Autopsy Findings)
Typical autopsy findings include:
- Extensive
myocarditis.
- Cardiac
parasympathetic denervation.
- Marked cardiomegaly.
- Dilatation and
hypertrophy of all cardiac chambers.
- Thin, bulging left
ventricular apical aneurysm.
- Frequent mural
thrombus formation, particularly within the left ventricular apex.
Clinical Features
Heart Failure
- Chronic progressive congestive
heart failure.
- Predominantly right-sided
heart failure in advanced disease.
- Severe cardiomegaly
is usually present.
Arrhythmias
- Ventricular
arrhythmias are a prominent feature.
- Conduction
abnormalities are common.
Electrocardiographic (ECG) Findings
The most common ECG abnormalities include:
- Right bundle branch
block (RBBB).
- Left anterior
hemiblock (left anterior fascicular block).
- T-wave
abnormalities.
- Atrioventricular
(AV) block.
- Ventricular
arrhythmias.
Diagnosis
Diagnosis is established by:
- Complement-fixation
test (Machado–Guerreiro test).
Treatment
- No clinically
effective treatment is available
for advanced chronic Chagas' cardiomyopathy.
- Current management
is mainly supportive, including treatment of heart failure and
arrhythmias.
- Immunoprophylaxis
with a vaccine remains a future
hope.
Key Points
- Caused by Trypanosoma
cruzi.
- Transmitted by the kissing
bug (reduviid bug).
- Endemic in Central
and South America.
- Clinical disease
usually appears 20–30 years after infection.
- Only about 30%
of infected individuals develop chronic Chagas' disease.
- Major cardiac
manifestation is dilated cardiomyopathy with congestive heart failure.
- Characteristic
pathology includes left ventricular apical aneurysm and mural
thrombus.
- Common ECG findings
are RBBB, left anterior hemiblock, AV block, and ventricular
arrhythmias.
- Diagnosis is by the Machado–Guerreiro
complement-fixation test.
- No definitive
curative therapy is currently available for chronic disease.
DR.C.GANESAN
M.D.,
PROFESSOR
OF MEDICINE
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