Chagas disease, predominantly found in Latin America, typically manifests with findings of myocardial inflammation and fibrosis on histopathology, and megacolon or megaesophagus on imaging.
Description
Chagas disease, also known as American trypanosomiasis, is a parasitic infection caused by the protozoan Trypanosoma cruzi. This zoonotic disease is primarily transmitted by triatomine bugs, commonly known as “kissing bugs,” and is a significant cause of morbidity and mortality in Central and South America.
Pathogenesis
The infection begins when an infected triatomine bug defecates on the skin of a mammalian host and the host scratches the bite site, introducing the faeces and the trypanosomes into the bloodstream. The trypanosomes then invade local cells, where they replicate and eventually burst the cells, releasing more parasites into the bloodstream. The parasites can invade a variety of tissues but have a predilection for cardiac and smooth muscle cells.
There are two main phases of Chagas disease:
- Acute phase: Lasts for a few weeks or months after infection. Patients may experience mild symptoms or none at all. Parasites may be observed in the circulating blood.
- Chronic phase: The parasites are hidden mainly in the heart and digestive muscles. Up to 30% of patients suffer from cardiac disorders and up to 10% suffer from digestive (typically enlargement of the oesophagus or colon), neurological or mixed alterations.
Epidemiology, Risk Factors & Associations
- Endemic in Central and South America (estimated 6-7 million people infected)
- Increasing prevalence in non-endemic areas due to global travel and migration (e.g., United States, Europe, Australia)
- Poverty and living in a mud, adobe, or thatch house (risk of contact with triatomine bugs)
Clinical Features
Acute phase symptoms include fever, malaise, swelling at the site of inoculation (chagoma) or unilateral periorbital swelling (Romaña’s sign). Chronic phase can be asymptomatic (indeterminate form) or present with cardiac (e.g., arrhythmias, heart failure) or gastrointestinal symptoms (dysphagia or constipation due to megaesophagus and megacolon respectively).
Complications
Major complications of chronic Chagas disease are heart failure, arrhythmias, cardiac arrest, and gastrointestinal complications due to megaesophagus and megacolon.
Pathological Features
Histopathology
- Macroscopic: Cardiomegaly, segmental or diffuse wall thinning, dilated chambers in the heart. Megacolon or megaesophagus can be seen in the gastrointestinal tract.
- Microscopic: Chronic myocarditis with mononuclear cell infiltration and fibrosis. In the GI tract, there’s neuronal loss in the myenteric plexus.
Serology
- Positive serology for Trypanosoma cruzi antibodies (ELISA, immunofluorescence, or western blot).
Biochemistry
- Non-specific findings. During acute phase, mild anaemia and leukocytosis can be seen.
Radiological Features
General Features
- Cardiac involvement leads to cardiomegaly, segmental wall motion abnormalities, and possible aneurysm formation.
- Gastrointestinal involvement manifests as megaesophagus or megacolon.
Cardiac Imaging
XR
- Enlargement of the cardiac silhouette may be seen in cases of cardiomegaly.
CT
- Non-contrast: May show myocardial thinning and dilation of cardiac chambers. In late stages, mural thrombus can be seen.
- C+ Arterial: Enhancement may help delineate myocardial fibrosis and wall motion abnormalities.
MRI
- T1: Myocardial inflammation and fibrosis can be seen as hyperintense areas.
- T2: Edema due to inflammation appears hyperintense.
Gastrointestinal Imaging
XR
- Abdominal X-ray may show dilated bowel loops in case of megacolon or fluid levels in case of megaesophagus.
CT
- Non-contrast: Dilated oesophagus or colon can be seen.
- C+ Venous: Can aid in demonstrating the extent of dilation of the oesophagus and colon, as well as any secondary complications (such as bowel obstruction).
US
- B-mode: May show dilated sections of the colon or oesophagus.
- Colour: Non-specific and is not typically used for the diagnosis or management of Chagas disease.
NM
- PET FDG: Not typically used in the evaluation of Chagas disease.
Grading and Staging
There is no universal grading or staging system for Chagas disease. However, the chronic phase can be divided into indeterminate, cardiac, digestive, and cardiodigestive forms based on the organ system involvement.
Diagnosis
Diagnosis is based on positive serological tests (two different tests should be positive due to possibility of cross-reactivity). In the acute phase, parasites can be directly observed in the blood.
Differential Diagnosis
- Other causes of cardiomyopathy: e.g. Ischemic cardiomyopathy typically involves the coronary artery distribution and is associated with atherosclerotic disease.
- Other causes of megaesophagus or megacolon: e.g. Achalasia can also present with megaesophagus, but is not associated with cardiac findings.
Management
Antiparasitic treatment is most effective early in the course of infection. Drugs like benznidazole and nifurtimox are commonly used. Cardiac and gastrointestinal complications are managed symptomatically.