What is Chagas Disease?
Chagas disease stems from an infection with the protozoan parasite Trypanosoma cruzi, principally transmitted by triatomine bugs. Poor housing conditions are a primary region for vector-borne transmission in the Americas, where an estimated 8 to 10 million people are infected. The epidemiology of the disease is changing due to successful reduction of transmission in endemic areas as well as migration of individuals within and outside of endemic areas. Hundreds of thousands of infected individuals live in cities across Latin America and in the United States, Spain, and other European countries.
How Does Chagas Disease Parasite Get in the Body?
The infective trypomastigote form of the T. cruzi parasite is present in large numbers in the feces of infected triatomine bugs. During or immediately after a blood meal, the triatomine bug defecates on the host’s skin, allowing the organism to enter through the bite wound or via intact conjunctiva or mucous membranes. The risk of infection in the setting of short-term exposure is low. It has been estimated that 1000 to 2500 contacts with infected vectors were needed to result in infection.
Who is Most Affected by Chagas Disease?
In endemic areas, T. cruzi infection is usually acquired in childhood and persists for life. Therefore, the seroprevalence in an area with sustained vector-borne transmission increases with age. Before widespread vector control was instituted, more than 60 percent of adults were infected with T. cruzi in some endemic communities. About 70 to 80 percent of infected individuals have lifelong asymptomatic infection. The prevalence of clinical disease increases with age, reflecting onset of cardiac and gastrointestinal manifestations in early adulthood with progression over a period of years to decades.
Chagas disease transmission can also occur vertically from mother to fetus, transfusion of infected blood components, organ transplantation from an infected donor, ingestion of contaminated food or drink, or laboratory exposure. In the United States, voluntary blood bank screening was initiated in 2007 and is estimated to cover 75 to 90 percent of the blood supply.
Most congenitally infected infants are asymptomatic or have non-specific signs; specific laboratory screening is needed to detect congenital infections in infants. Several endemic countries have congenital Chagas disease screening programs; however, only a small proportion of at-risk infants complete all steps of the algorithm.
Diagnoses of Chagas Disease
The initial evaluation of patients with suspected chronic T. cruzi infection consists of thorough medical history with an emphasis on symptoms suggestive of cardiac arrhythmia or conduction system defect, early congestive heart failure, thromboembolism, and gastrointestinal disease. Additionally, social history should include details related to potential means of exposure to the parasite in endemic areas. Reactivation of chronic T. cruzi infection can occur in patients with immunosuppression due to malignancy, chemotherapy, immunosuppressive regimens for solid organ or bone marrow transplantation, or HIV/AIDS. The diagnosis of reactivation requires detection of circulating trypomastigotes in the peripheral blood; quantitative polymerase chain reaction (PCR) on serial specimens is a useful technique to show rising parasite load. A positive result on conventional PCR does not prove reactivation, but quantitative PCR assays that indicate rising parasite numbers over time provide the earliest and most sensitive indicator of reactivation. Organ transplant recipients who receive an organ from a donor infected with T. cruzi may develop acute T. cruzi infection, although transmission under these circumstances is rare.
Treatment of Chagas Disease
The approach to antitrypanosomal therapy for Chagas disease varies by phase and form of disease. Antitrypanosomal therapy is recommended during acute infection, congenital infection, and chronic infection among patients ≤18 years of age [(Grade 1A) for patients ≤12 years; (Grade 1B) for patients 13 to 18 years]. Antitrypanosomal therapy is also recommended in the setting of reactivated infection (Grade 1B). However, antitrypanosomal therapy is not recommended for patients with advanced Chagas cardiac disease (Grade 2C).
Limitations of Current Treatments for Chagas Disease
The available drugs are not effective for reversal of existing pathology; in such patients, the focus of management is supportive care for heart failure, arrhythmia, and thromboembolism.