T. cruzi is transmitted among its mammalian hosts by hematophagous triatomine insects, often called reduviid bugs. The insects become infected by sucking blood from animals or humans who have circulating parasites. It can also be transmitted through blood transfusion of infected blood, from the pregnant mother mother to her fetus, and in lab lab accidents. Chagas' disease is only a problem in the Americas (South America mainly).
The first signs of acute Chagas' disease develop at least 1 week after invasion by the parasites. When the organisms enter through a break in the skin, an indurated area of erythema and swelling (the chagoma), accompanied by local lymphadenopathy, may appear. Romana's sign -- the classic finding in acute Chagas' disease, which consists of unilateral painless edema of the palpebrae and periocular tissues. This results when the conjunctiva is the portal of entry.
This phase is usually followed by malaise, fever, generalized edema, a rash may develop as well as generalized lymphadenopathy and hepatosplenomegaly.
Usually the symptoms resolve spontaneously and patient enters the chronic phase.
In rare cases infection could be serious and lead to heart affection progressing to heart failure, achlasia and megacolon.
1. Acute Chagas' disease
Microscopic examination of fresh anticoagulated blood or of the buffy coat is the simplest way to see the motile organisms. Parasites also can be seen in Giemsa-stained thin and thick blood smears. When repeated attempts to visualize the organisms are unsuccessful, mouse inoculation, culture of blood in specialized media, or xenodiagnosis can be performed.
Serologic testing is of limited usefulness in diagnosing acute Chagas' disease.
2. Chronic Chagas' disease
The diagnosis of chronic Chagas' disease is made by the detection of antibodies that bind to T. cruzi antigens. Demonstration of the parasite is not of primary importance.
Therapy for Chagas' disease is unsatisfactory. Nifurtimox is the only drug active against T. cruzi that is available in the United States. In acute Chagas' disease, nifurtimox markedly reduces the duration of symptoms and parasitemia and decreases the mortality rate. Nevertheless, its efficacy at eradicating parasites is low. Limited studies have shown that only 70% of acute infections are cured parasitologically by a full course of treatment. Despite its limitations, nifurtimox treatment should be initiated as early as possible in acute Chagas' disease.
Adverse effects of nifurtimox include abdominal pain, anorexia, nausea, vomiting, and weight loss. Neurologic reactions to the drug may include restlessness, disorientation, insomnia, twitching, paresthesia, polyneuritis, and seizures.