Chagas disease, also called American or South American trypanosomiasis, is a potentially life-threatening infection with the parasitic protozoan Trypanosoma cruzi, which is transmitted to animals and humans by blood-sucking insects. Chagas disease is endemic to the Americas and is considered a neglected tropical disease.
Chagas disease is transmitted by triatomine bugs that resemble cockroaches. They are also called kissing bugs, because they tend to bite the face, or assassin or cone-nose bugs. Triatomine bugs are in the Reduviidae family and are sometimes called reduviid bugs. Several species can transmit Chagas disease. They take in T. cruzi when they bite and suck the blood of infected mammals, birds, reptiles, or humans. During the day, they hide in cracks or holes in the walls and roofs of mud, adobe, straw, or palm-thatch homes. At night, they crawl across and bite sleeping people, usually on their exposed faces, but sometimes on their arms, legs, or trunk. As they feed on human blood, they deposit their T. cruzi-infected feces or urine, which people often instinctively rub into the bite. The parasite also can enter the bloodstream through cuts, open sores, or mucous membranes of the mouth, eyes, or nose. T. cruzi causes a chronic disease that is a major cause of heart failure and sudden death. Some experts have called Chagas the new AIDS of the Americas, because it has a long incubation period, can be difficult or impossible to cure, and can be transmitted by pregnant women to their babies. African trypanosomiasis or sleeping sickness is caused by two other Trypanosoma species that are transmitted by flies.
Chagas disease is closely associated with poor housing and poverty. The major risk factor is living in substandard housing infested with triatomine bugs in Central or South America. The bugs can also live outdoors near their hosts' homes: in kennels and chicken coops; between rock structures; under porches, cement, or bark; or in piles of rock, wood, or brush. Transfusion with infected blood is also a risk factor for Chagas disease.
Chagas is the third most common parasitic disease worldwide. It infects 6–8 million people in the Western Hemisphere, mostly in rural and suburban areas from Mexico to Argentina. It is not endemic to the Caribbean. Chagas disease is a leading cause of heart failure in Latin America and is responsible for about 10,000 deaths annually from complications to the heart, digestive system, or nervous system, or from multi-system effects.
Widespread human migration has spread Chagas disease to the United States and other continents, as well as to urban areas of Latin America. Although more than 90% of T. cruzi infections go undiagnosed, there are an estimated 238,000–300,000 cases in the United States. A 2017 study reported that more than 1% of Latin American-born residents of Los Angeles County tested positive for T. cruzi. There are more than 50,000 Chagas disease cases in Spain, where there were 75 confirmed cases of congenital Chagas due to motherto-fetus transmission between 2007 and 2016; however, this is believed to be only about 10% of the true number.
There are 11 species of triatomine bugs in the United States, mostly in the South. About 40% of triatomine bugs in Arizona are reported to be infected with T. cruzi; however, the risk of Chagas disease transmission is very low. This is because the Arizona bugs fly away before defecating, rather than depositing feces on their hosts. U.S. homes are rarely infested with the bugs because they generally have plastered walls and sealed entries. When triatomine bugs are inside, they tend to be in and around beds and bedrooms, pet sleeping areas, or rodents. There is some local T. cruzi transmission in Texas, and Chagas disease is predicted to spread in the United States as climate change makes regions more hospitable to these insect vectors.
In endemic regions, Chagas disease is mainly transmitted from animals to humans and between humans by T. cruzi-infected triatomine bug vectors. Other modes of transmission include:
Chagas disease is not transmitted through casual contact with infected people or animals or through breastfeeding unless the mother has cracked nipples or blood in her breast milk. However, a 2017 study suggested that the parasite can be transmitted through sexual intercourse.
Chagas disease occurs in two phases, acute and chronic, which can vary from symptom-free to life-threatening. A few hours after infection, a raised red spot appears at the site of the bite. The initial acute phase begins a few weeks later and lasts for a few weeks or months, during which large numbers of parasites circulate in the blood; however, symptoms are usually absent or mild and nonspecific. Rarely, infants, young children, or people with weakened immune systems develop meningoencephalitis (brain swelling). Fewer than half of infected people have acute-phase symptoms that may include:
Untreated infections enter the chronic phase, with the parasites hiding in the heart and digestive muscles. Chronic symptoms may occur decades after infection or not at all. Up to 30% of infected people develop heart problems. Destruction of heart muscle and its nerves can cause a pounding or racing heart, enlarged heart, progressive heart failure, or sudden death from cardiac arrhythmia. Up to 10% of infected people have enlargement of the esophagus or colon, causing trouble swallowing or digestive problems, including constipation and abdominal pain, neurological damage, or multiple disorders.
Much of what is known about Chagas disease is from people infected as children via vector-borne transmission. Thus, the severity and course of the disease may differ in people infected by other means, at different ages, or by different T. cruzi strains.
Chagas disease has a prevalence rate of 1.2–1.3% in the United States, making it increasingly common. Diagnosis is essential for pregnant women and their newborns and other children. Romaña's sign is diagnostic of acute Chagas disease. A physical exam may reveal local swelling (chagoma), swollen lymph glands, and/or mild enlargement of the liver or spleen. During the acute phase, the parasite can be seen under a microscope in a peripheral blood smear. A blood culture also can detect the parasite. Family members of a diagnosed patient should be tested.
Signs of chronic Chagas disease may include an irregular or rapid heartbeat or heart-muscle disease. Diagnosis may include:
Acute-phase, congenital, reactivated, and early chronic-phase Chagas disease require treatment with one of two available drugs: benznidazole or nifurtimox. Infected adults without symptoms should be offered treatment to potentially prevent or curb disease progression and prevent congenital transmission during pregnancy. Chronic-phase Chagas disease also may be treated with drugs in children and most adults. Treatment with either drug lasts up to three months and sometimes requires hospitalization. Up to 40% of patients, especially older adults, suffer severe side effects from the drugs. Patients are observed for at least two years following treatment for any signs of continued infection. The drugs cannot be used by pregnant women or patients with kidney or liver failure. Nifurtimox is contraindicated for patients with neurologic or psychiatric disorders.
Cardiac and gastrointestinal manifestations of chronic-phase Chagas disease require specific treatments; for example, a pacemaker may be required for certain heart conditions. As of 2018, the only U.S. clinic that specifically treated Chagas disease was the Olive View-UCLA Medical Center in Sylmar, California. However, most major medical centers in border areas, along with those in Florida and New York, are familiar with and treat Chagas. Healthcare providers can consult with the Centers for Disease Control and Prevention (CDC) about treatment options.
WHO has identified remaining challenges for Chagas disease control, including the following:
With the goals of eliminating Chagas transmission and providing care for infected patients worldwide, WHO aims to do the following:
As of 2018, there were the beginnings of a public health response to Chagas disease outside Latin America, including large-scale clinical trials funded by governments and drug companies. In 2015, the University of Texas and the CDC established the Texas Chagas Taskforce, a 100-plus group of experts for raising awareness of the disease. Still, healthcare providers in the United States and other non-endemic regions need more information about Chagas disease at a time when its epidemiology is changing rapidly due to large-scale human migration worldwide as well as from rural to urban areas in Latin America. In the United States and other countries where Chagas is increasingly more common, there is a need for early detection, treatment, and prevention of congenital, transfusion, and organ-transplantation transmission.
At the onset of acute infection, both benznidazole and nifurtimox are nearly 100% effective in destroying T. cruzi, including congenital transmissions. Fewer than 5% of young infected children die from severe inflammation/infection of the heart muscle or brain. However, treatment failures do occur, and drug resistance has been identified. Furthermore, as of 2018, fewer than 1% of infected patients were receiving treatment, and the effectiveness of both drugs diminishes with increased length of infection. About 30% of infected patients eventually develop serious cardiac disease and are at risk for so-called silent death from heart failure. A 2015 Latin American trial reported that trypanocidal therapy with benznidazole did not significantly affect cardiac deterioration from Chagas. About 10% of patients with chronic Chagas disease develop gastrointestinal or neurological disorders or multiple problems, including an enlarged colon or an enlarged esophagus that causes difficulty swallowing and can lead to malnutrition.
Because of the large wild-animal reservoir of T. cruzi in the Americas, it is impossible to eradicate the parasite, and there are no drugs or vaccines that prevent infection. Thus, the best prevention of Chagas disease is vector control with insecticides and sealing of homes. Synthetic pyrethroid sprays have proved effective in Latin America although, as of 2018, none had been specifically approved in the United States for use against triatomine bugs. So-called roach hotels and other baits are ineffective. In endemic regions, WHO recommends:
Measures for preventing infestations with triatomine bugs include:
Travelers to T. cruzi-endemic areas should do the following:
See also Tropical disease ; Zoonoses .
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Margaret Alic, PhD