Medicine for the Outdoors
Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Chagas Disease

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A reader asks me for a brief discussion of Chagas disease (also known as American trympanosomiasis), which is named after the Brazilian physician Carlos Chagas. The disease was discovered in 1909 and is caused by the parasite Trypanosoma cruzi. Infection usually occurs by contact with the feces of infected triatomine (or triatomid) bugs (“kissing bugs”). These are blood-sucking insects that feeds on humans and animals.

Chagas disease is endemic throughout much of Mexico, Central America, and South America. In fact, Chagas disease kills more Latin Americans than does any other parasitic illness. It has been estimated that up to 11 million people are infected. Chagas disease is as much or more an urban phenomenon than a wilderness disease. The kissing bugs dwell "in poverty" and in rural areas - mud walls and thatched roofs - so it is in these environments that people are most risk. Like certain other infectious diseases, it is possible to acquire Chagas disease from blood products, transplanted organs, or congenitally. Screening donated blood for Chagas disease is an important process to prevent transfusion-acquired disease.

It is extremely important to recognize and diagnose Chagas disease, because if it is not treated, infection is lifelong.

Acute Chagas disease occurs immediately after acquisition of the parasite, and may last up to a few weeks or months. Sometimes parasites are found in the circulating blood. Infection may be mild or asymptomatic. Occsionally there is fever and sometimes there is swelling around the site where the parasite entered the skin or mucus membrane. Rarely, acute infection may cause severe inflammation of the heart muscle or the brain and lining around the brain (meningoencephalitis).

The acute phase of the disease is often not recognized for what it is, so the Chagas disease remains undiagnosed. After the acute phase has passed, most infected persons enter into a prolonged asymptomatic form of disease (technically called “chronic indeterminate”). During this phase, few or no parasites are found in the blood, so most people do not realize that they are infected and the diagnosis is quite difficult. Fortunately, many individuals never develop symptoms for the remainder of their lives. However, approximately 30% of infected people go on to develop debilitating and sometimes life-threatening medical problems at various times during their lives.

The severe medical problems caused by chronic Chagas disease are abnormal heart rhythms and inflammation of the heart muscle, a dilated and ineffective (as a pump) heart, and a dilated esophagus or colon, which causes difficulty eating and having bowel movements.

The diagnosis of Chagas disease can be made by observation of the parasite in a blood smear viewed under the microscope. Examining a blood smear generally only works well during in the acute phase of infection when parasites are more likely to be circulating in blood in sufficient quantity to be noticed. The diagnosis of chronic Chagas disease is made by testing using with at least two different serologic tests. The polymerase chain reaction (PCR)-based assay for Chagas disease has revolutionized testing because it is rapid and portable.

Treatment for Chagas disease is recommended for all people diagnosed with an acute infection, congenital infection, and for those with suppressed immune systems, and for all children with chronic infection, because they benefit from treatment. Adults with chronic infection may also benefit from treatment.

In the United States, medication (benznidazole and nifurtimox) for Chagas disease is available only through the Centers for Disease Control (CDC).

The goals of therapy in persons with T. cruzi infection are to eliminate the parasites with specific drug treatment and to manage the signs and symptoms, although it should be noted that once significant pathophysiologic changes have occurred to organs (e.g., heart), they may be permanent.

Both benznidazole and nifurtimox are limited in their capacity to cause a parasitologic cure, especially in chronically infected patients. Because of this fact, the use of these drugs in such patients is still controversial. The current recommendation is to treat all patients with either benznidazole or nifurtimoxacute if they have acute Chagas disease, including congenital infection or reactivation of chronic infection due to immunosuppression.

As noted before, the younger the patient and the sooner the treatment after acquisition of the parasite, the higher the probability of parasitologic cure (elimination of the parasite from the blood stream and body).

For indeterminate-phase Chagas disease, all children with chronic infection should be treated. Unfortunately, the probability of parasitologic cure for adults with long-standing infection, is less than 10%. Furthermore, there is not evidence that treatment of chronic infection in women prior to pregnancy reduces the probability of congenital transmission. In addition, it is not known if there is any value in prophylactically treating persons with chronic infection if they are about to become immunosuppressed (such as for an organ transplant) or have acquired immunosuppression (e.g., cancer or HIV). If a person has chronic Chagas disease, even if he or she has symptoms, there is not support for treatment with antiparasitic drugs.

This is a terrible disease that can lead to fatal heart and bowel problems. Given the non-trivial nature of the illness, it is essential to adhere to proper preventive measures which are all directed at avoiding kissing bugs.

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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.

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