Chagas Disease Facts
- About 6 to 7 million people are infected with Chagas disease in 21 Latin American countries. The Centers for Disease Control and Prevention (CDC) estimates that over 300,000 infected people are living in the U.S. and are unaware of their infection. Because the long-term complications cause disability, this number of infected people is a serious economic and health-care burden.
- Chagas disease is not considered curable. Some victims develop disabling heart and intestinal complications over time. However, investigators in Argentina suggest a 90% parasitologic cure rate in babies if treatment is given within the first year of life.
- Chagas disease is also known as American Trypanosomiasis to differentiate it from African Trypanosomiasis (African sleeping sickness), which is caused by a different species (variety or type) of Trypanosoma parasite. Various species of reduviid or triatomine bugs transmit it. These bugs are found in Latin America and in the southern U.S. The insect prefers impoverished rural areas without modern housing.
- Public-health experts are concerned that Chagas disease may spread further north in coming years due to warmer temperatures with climate change. Blood-sucking triatomine bugs may begin to populate northern states and pose a risk of exposure to humans.
- The risk of Chagas disease in the U.S. is low, however, because the required human living conditions for the insects to transmit T. cruzi are uncommon.
What Is Chagas Disease?
Chagas disease is caused by an infection with a blood parasite called Trypanosoma cruzi. Chagas disease is incurable. Those who have Chagas disease are usually symptom-free. Some people who have been infected for a long time may develop symptoms of heart failure, trouble swallowing, or trouble moving the bowels. Chagas disease is named after Dr. Carlos Chagas. While evaluating railroad workers for malaria, this Brazilian doctor discovered the disease and the parasite that causes it in 1909. The disease is "endemic" (native) to these countries. Due to population movements, cases are diagnosed in the United States, Europe, Australia, and Japan, but it is not endemic outside of Latin America. The CDC estimates that over 300,000 infected people are living in the U.S. and are unaware of their infection.
Chagas disease has not been common in the U.S. because the bugs that transmit it do not survive in cooler climates. However, the parasite has been documented in blood-sucking triatomine bugs and animals from California to Pennsylvania, and these bugs have been found in several areas of Florida (see map, Fig. 1, below) and detected in 28 states. Infected animals can maintain the parasite life cycle in nature. A very few cases of locally acquired Chagas disease have been documented in Texas, Louisiana, California, and Tennessee. There is a concern, however, that the human impact in the U.S. may be underestimated.
Figure 1: U.S. map showing states where blood-sucking triatomine bugs have been found, as of Dec. 1, 2015. SOURCE: CDC.
Researchers have discovered that triatomine bugs in Arizona are both feeding on humans and are carrying T. cruzi parasites. Using DNA testing, they found human blood in the bugs' guts; half of those bugs also contained T. cruzi DNA. (Fig. 1) Still, the majority of cases in the U.S. are diagnosed in people who acquired it while living in affected parts of Latin America -- and only when they have heart or intestinal complications that lead to a diagnosis.
What Are the Causes and Risk Factors for Chagas Disease?
Trypanosoma cruzi must enter the flesh, and it can only be transmitted in the feces of a species of triatomine bug that prefers to feed on blood at night. The life cycle of T. cruzi includes a bug stage and a human or animal stage. First, the bug sucks the blood of an infected person or animal, and its gut becomes filled with T. cruzi. The insect defecates as it is feeding. The feces contain the T. cruzi in an infective form. The parasites are transmitted when feces contaminate the bite wound or the moist lining of the eye, nose, or mouth. After multiplying in the tissues, the parasites develop into a swimming form and enter the blood. From the blood, they can infect other tissues and repeat this cycle over and over. Another triatomine bug can now ingest this person's blood and continue the chain of transmission. Some of the parasites do not burst into the blood but remain in the tissues, especially the muscles and nerves of the heart, esophagus (swallowing tube between the mouth and stomach), and intestines (gut).
These bugs prefer biting on the face, so bites around the mouth and eyes are very common. This has earned them the nickname "kissing bugs." About half of the time, the person awakens with a swollen area near the bite called a "chagoma." If the person awakens with a purple swelling of the eyelid near the bite, it is called Romaña's sign. This is a classic sign of T. cruzi infection.
Rarely, infection happens by blood transfusion or an accidental injury in a laboratory worker or organ transplantation. Mothers may transmit Trypanosoma cruzi to an unborn child (congenital Chagas). Chagas disease is not spread by contact with people or animals.
In a natural jungle habitat, triatomine bugs hide in dark crevices during the day and come out to suck the blood of sleeping animals at night. Lumber or rock piles, barns or animal quarters (such as dog, goat or chicken pens), and houses built of mud or wood in rustic areas offer good places to hide near a blood source. Risk factors for Chagas disease include sleeping outdoors or in poorly constructed housing in rural areas where the right species of triatomine bugs live. The highest risk of exposure is in rural, impoverished areas where houses are built with mud bricks, dirt flooring, and thatched roofs.
Is Chagas Disease Contagious?
It is not contagious from person to person, from person to animal, either by direct contact with the infected individual or through the air. Only the feces of the triatomine bugs may be contagious, and only if they are accidentally rubbed into a bite, scratch, or the moist membranes of the mouth, nose, or eyes. Handling or crushing the bug with the hands can also expose a person to the parasite in the feces, which can be rubbed into a wound or moist membrane. The parasite cannot get into unbroken skin. It is not typically food-borne.
What Is the Incubation Period for Chagas Disease?
The incubation period (the period between infection and symptoms) may be up to 14 days; it is not clear because most cases are diagnosed in areas where people are constantly being bitten. People who are infected by blood transfusion or transplanted organ may have an incubation period up to four months.
What Are Chagas Disease Symptoms and Signs?
The symptoms and signs happen in an acute (early) phase and a chronic (later) phase. For about half of victims, the first symptom is the Romaña's sign. Other than this, most people have no symptoms or signs. Those who do get early symptoms or signs may have fever, headache, swollen lymph glands, fatigue, muscle pain, or body aches. They may have swelling and difficulty breathing, and they may have chest or abdominal pain, which is due to swelling of the liver and spleen. Most of these symptoms and signs are a reaction to a large amount of parasites in the bloodstream. The acute phase is most serious in the young. Up to 8% of children die. This phase lasts about eight weeks, then the level of parasites in the blood drops to low levels.
The chronic phase of Chagas disease occurs when the parasites continue to multiply in the tissues of the nervous system and in the muscles of heart and digestive system. The parasites progressively destroy these tissues over years. The patient may remain without symptoms for 10 or more years, up to lifelong. This is called the "indeterminate form" of chronic Chagas. About one out of three patients go on to develop symptomatic disease with heart problems, such as congestive heart failure from a dilated heart or even sudden death. About one in 10 patients develop a dilated esophagus or dilated colon. This is called the "determinate" form of Chagas. The heart is the organ that is affected the most, and chronic heart failure is called Chagas cardiomyopathy. Worldwide, Chagas disease is the common infectious cause of heart failure. Any triatomine bug that feeds on a person with acute or chronic Chagas disease can pick up the infection and transmit it to others. People with chronic infection can reactivate the disease (develop high blood levels again) if they develop a condition that weakens their immune defenses.
Triatomine bites may cause allergic reactions with hives, itching, sometimes severe swelling, or even anaphylaxis. These are not signs of T. cruzi infection or Chagas disease but are signs of an allergic reaction.
How Do Health-Care Professionals Diagnose Chagas Disease?
During the acute phase, parasites can be seen with a microscope in fresh or specially stained blood smears. The blood may be cultured in a specialty lab to grow the parasite. There are newer, more sensitive tests called "polymerase chain reaction assays" or PCR, which can detect T. cruzi in blood. People with chronic phase Chagas disease who develop weakened immunity, or who are suspected to have received an infected organ or blood exposure, are screened regularly by PCR or microscope tests, since they are likely to have detectable levels of blood parasites.
Blood PCR is not as sensitive in chronic disease, because the parasites are mostly in the tissues. Chronic Chagas disease is diagnosed by testing for antibodies against the parasite. There are multiple and varied tests, so usually two or more different tests are performed. If at least two tests are positive, the diagnosis is confirmed. Patients with weakened immunity are screened with PCR assay.
What Is the Treatment for Chagas Disease?
The treatments for T. cruzi are medicines called nifurtimox (Lampit) and benznidazole (Rochagan, Ragonil). Unfortunately, they must be taken for up to three months and have many side effects, so many patients cannot complete the treatment. They are better tolerated by children, but they cannot be taken during pregnancy or with kidney or liver dysfunction. Treatment is focused on those under 50 who are most likely to benefit with fewer side effects. Side effects of benznidazole include skin rashes, poor appetite, numbness of hands and feet, and rarely weakened bone marrow function. Side effects of nifurtimox include nausea, poor appetite, loss of weight, difficulty sleeping, tremors, and numbness of hands and feet. They work best for acute phase infection, but they may also stop progression of damage from chronic infection. As recently as 2011, there was no form of these medicines made for children; benznidazole is now used in children. Several agencies are working to find more effective, safer, and easier to use medicines for both phases of Chagas disease.
These medications have been used for over 30 years outside of the U.S., but they are only available in the U.S. from the CDC Drug Service for compassionate use under an Investigational New Drug (IND) protocol. The doctor must call CDC and provide information to the CDC expert for review. The CDC then provides the drug at no cost.
There is no test that can tell whether the parasite has been cured.
What Kinds of Doctors Treat Chagas Disease?
A general doctor who is aware of a patient's history of residing in an area with endemic Chagas disease can perform basic annual physicals and an EKG (heart rhythm test) to look for signs and symptoms of chronic phase infection. Patients should be asked about their residence conditions and travel history as a matter of routine, but if they immigrated very young, they may not know. Once a patient develops more serious or complicated organ symptoms, they are usually managed along with a heart specialist (cardiologist) and/or gastrointestinal specialist (gastroenterologist). An infectious diseases specialist may be consulted to assist in the diagnosis and treatment of the parasite infection.
Are There Home Remedies for Chagas Disease?
There are no effective home remedies for Chagas disease.
What Are Complications of Chagas Disease?
Most of the complications happen in the chronic phase of Chagas disease. The heart becomes inflamed as the immune system continues to fight the parasites, and damage occurs to all of the heart muscle and the nerves (electrical system) of the heart. Abnormal heartbeat sensations and patterns may occur. This can progress to dangerous rhythms and sudden death. The heart muscle may dilate, and blood clots may form. These can cause dangerous blockage of blood flow to lungs ("pulmonary embolus"). Heart failure occurs when blood flow "backs up." The heart is too weak to pump, and fluids may pool in the lungs and legs. This causes trouble breathing and swelling in the feet.
Gastrointestinal disease is caused by damage to the nerves that control the muscles that move food along. The esophagus muscles weaken and dilate ("mega-esophagus"), and foods may pool there or back up into the mouth or airway. Pain and difficulty swallowing may occur, and the patient may lose weight. Pneumonias occur from breathing esophageal contents into the lungs (aspiration). Cancer of the esophagus can occur from chronic inflammation. The same things happen to the colon, and symptoms include belly pain and severe constipation due to "mega-colon." The floppy bowel may twist on itself and cut off blood flow, which may cause the bowel to die if not immediately corrected.
What Is the Prognosis of Chagas Disease?
It is important to remember that the majority of infected people live normal lives and never know they are infected. Very generally, the worse the symptoms, the shorter the life span of the patient from that point onward. The prognosis of a person diagnosed with Chagas disease can only be determined from the medical evaluation of each individual.
Is It Possible to Prevent Chagas Disease?
Yes, Chagas disease is highly preventable if basic steps are taken to isolate people from the vectors, triatomine bugs. In areas where Chagas disease is endemic, preventive measures include eliminating the triatomine bugs in and around homes with pyrethrin insecticides and paints that slowly release insect repellent. Housing problems must be repaired. Effective methods include sealing cracks in walls, installing or repairing window and door screens, clearing away wood or rock piles near the house, and moving lights away from the house that can attract the insects at night. Holes leading to attic or crawl spaces should be sealed. Pets should sleep indoors and any outdoor animal pens should be kept free of clutter. When camping outdoors in the southern U.S., use zippered tents or other sleep accommodations that keep biting insects out. Using insect repellents every night on skin or clothes is not recommended or necessary if the above steps are taken. Identifying a blood-sucking triatomine bug is not necessary if barrier precautions are taken. It can be difficult for the nonexpert to identify the bug because there are many harmless and common insects that appear very similar. Modern, tight construction will keep most insects out and does not offer the habitat needed by triatomine bugs.
Children of infected mothers and pregnant women should be screened for blood antibodies to T. cruzi. The family members of a person with Chagas disease should be tested if they lived in an endemic area.
The U.S. blood supply has been screened since tests became available in 2012. Blood banks test for T. cruzi and discard infected blood. They screen donors for blood antibodies and prohibit them from donating, even if they have been treated. It is estimated that one in every 27,500 donors in the U.S. tests positive for Chagas disease. Very few cases of Chagas disease have been transmitted from an infected organ transplant. Less than 20 have been documented worldwide.