Strong Hearts

Introduction

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Chagas disease is called “the most neglected of the neglected tropical diseases” by the World Health Organization. It affects almost exclusively low-income people, so markets for diagnostic and therapeutic modalities were not judged commercially attractive by major industry entities. This disease is the third most prevalent parasitic infection in the world, despite its restriction to the Western hemisphere. The Centers for Disease Control estimate 300,000 infected people in the United States, and 3,000 in Massachusetts. Many questions remain insufficiently researched at present. The following FAQ are answered based on current literature and expert opinion.

 

What causes Chagas disease?

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Human infection with the Trypanosoma cruzi parasite causes Chagas disease. After percutaneous or mucuous membrane inoculation by an insect vector, the parasite circulates in the bloodstream and invades myocardial and gastrointestinal smooth muscle cells, where it continues to persist for the lifetime of the infected person. Both the parasites’ replication, and the immune response to its presence, contribute to inflammation and scarring of the infected tissues.

 

How is Chagas disease transmitted?

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The parasite is transmitted by triatomine bugs in Mexico, Central and South America but not the Caribbean islands. Other common modes of transmission are blood transfusion and vertical (mother-to-child) transmission. Screening of the blood supply for Chagas was introduced in most affected countries by 2005 and in the US in 2007 so that this mode of transmission is now rare. Organ transplantation is a potential transmission mode. More than one-fifth of new cases of Chagas disease are due to mother-to-child transmission. Thee is no person-to-person transmission through mucous membrane or body fluid exposures, e.g. through household- or sexual contact.

 

Who is at risk of Chagas disease?

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Any person who has lived in Mexico, Central or South America where the triatomine bug is endemic is at risk of having acquired this infection. The bug lives in substandard housing in rural and periurban areas. In each country, the occurrence of the vector is limited to specific areas. Children born to mothers with Chagas disease and any person who received a blood transfusion in an endemic area prior to screening of the blood supply may be at risk.

 

What is the natural history of Chagas disease?

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There are no disease manifestations over the lifetime of 70-80% of infected individuals, though a recent study suggests a higher risk of death from all causes in Chagas-parasite infected individuals. In 20-30% of infected people, heart or gsastrointestinal disease manifests 2-3 decades after infection. Once heart disease appears, antiparasitic treatment has not been shown to slow progession of the disease to death due to cardiomyopathy, arrhythmias or stroke.

 

How is infection with the Chagas disease parasite diagnosed?

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Antibody production against the T. cruzi parasite is measured by different assays, none of which have satisfactory sensitivity or specificity. For this reason, an initial serologic screening test must be followed by confirmatory testing at the Centers for Disease Control to make the diagnosis. PCR is used to confirm congenital infection in newborns.

 

What treatment is available for Chagas disease?

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The only drugs with proven efficacy against the T. cruzi parasite are benznidazole and nifurtimox, which are both given for 60 days. Benznidazole is better tolerated and thus generally favored as the first-line treatment for Chagas disease. Neither medication has been approved by the FDA however both are available through the Centers for Disease Control and Prevention (CDC)'s Division of Parasitic Diseases. Benznidazole has been shown to be effective even in imunocompromised individuals, suggesting good antiparasitic efficacy. Rashes, nausea and GI disturbance, and neuropathy are the most frequent adverse effects of both medications. Laboratory monitoring is recommended for patients on therapy.

 

Who should be treated for infection with the Chagas parasite?

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The younger the infected person, the less frequently adverse effects appear. Newborns with congenital Chagas disease, seropositive children and women of childbearing age who are not pregnant should be treated. We expect that treating asymptomatic adults age 50 and under who are asymptomatic will prevent the disease. Older infected adults are thought to be less likely to develop the disease, but there is no reason other than adverse effects of the medications, to withhold treatment if they request it.

 

How do I refer a patient for treatment?

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Dr. Huanuco facilitates referral to BMC Infectious Disease, but any provider can refer. Also please feel free to email julia.koehler@childrens.harvard.edu.

 

How do I contact the CDC if I have further questions?

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You can contact the CDC Division of Parasitic Diseases Public Inquiries line (404-718-4745 or parasites@cdc.gov) for consultations on Chagas disease and requests for benznidazole and nifurtimox.