Chagas’ Disease – Characteristics and History
Chagas’ disease (also American trypanosomiasis or trypanosomiasis cruzi) can be either an acute febrile infection or a chronic process. The cause is a protozoan, Trypanosoma cruzi, harbored by domestic and wild animals. When transmitted to humans by insects, this essentially untreatable disease presents with fever, edemas, and lymph node enlargement and can cause dilation in the digestive tract, leading to megacolon and megaesophagus as well as cardiac enlargement and failure. In parts of South America, Chagas’ disease is the leading cause of cardiac death in young adults.
Probably originating in Brazil, the disease is limited to the Western Hemisphere, with heavy concentrations in Brazil, Argentina, Chile, and Venezuela. Cases are also reported in Peru, Mexico, and most other American countries, including the Caribbean islands and the United States. T. cruzi has over 100 vertebrate hosts, including dogs, cats, armadillos, opossums, monkeys, and humans. Unlike other trypanosomes, which multiply in the bloodstream, it lives within various tissues of the host and reproduces by binary fission. It is transmitted by reduvid bugs that ingest it from a host during a blood meal.
The trypanosomes develop in the intestines of the bug. They neither enter its saliva nor are injected when it bites but do pass out in its feces. Thus the infection is transmitted when the infected insect defecates following its blood meal, thereby contaminating the site of the bite. Infection can also occur when feces are rubbed into the eyes or reach oral mucosa, and possibly via contaminated foods as well. The insect vector flourishes in huts in poor rural areas, where it lives in cracks in the walls and in thatching and mats used as roofing. Cases may be few de-spite large numbers of infected bugs, if the bugs are not adapted to living in houses.
The disease takes several different forms, but, in all cases, no effective treatment exists. The acute form ends in death in 10 percent of cases, and, although the chronic form may last as long as 40 years, few individuals remain asymptomatic for life. Chronic cardiac disease, mega-colon, and megaesophagus all can shorten life.
The acute form of the disease, occurring primarily in young children, is usually a febrile illness. When death occurs, it is generally caused by myocarditis or a complicating broncho-pneumonia. The latent form is seen in patients who have recovered from the acute form, as well as others who have harbored the parasite without displaying symptoms. Examinations of-ten reveal changes in esophageal and peristaltic motility as well as electrocardiographic changes. The subacute form is normally seen in young adults, who suffer a rapidly progressive cardiac failure.
The chronic form of the illness is the lead-ing cause of death in endemic areas. The heart becomes tremendously enlarged, and in about 30 percent of cases, parasites are found within pseudocysts in muscle fibers. Although survival may be as long as 5 years, death usually intervenes within 6–12 months.
The digestive form of Chagas’ disease presents as megacolon or megaesophagus. victims suffer degeneration and diminution of nerve cells in the muscular layers of these organs, leading to their enlargement. The condition by itself is normally not fatal, but patients often experience difficulty swallowing because of the enlarged esophagus, and constipation normally accompanies megacolon. These difficulties in turn can promote other illnesses that are life-threatening. The congenital form of the disease has long been known. The fetus is infected transplacentally, resulting in premature fetal death or a newborn with Chagas’ disease in its acute stage.
Chagas’ disease is unusual in that its etiological agent, its vector, and major features of its epidemiology were described before the first human case was ever reported. Brazilian physician Carlos Chagas accomplished this in a series of publications beginning in 1909, and the disease appropriately bears his name. The ill-ness, however, is not new. Studies of mummies from northern Chile have revealed megacardia, megacolon, and megaesophagus in several individuals who lived more than 2,000 years ago. The same area today is endemic for Chagas’ disease.
Nineteenth-century visitors to Brazil reported instances of megaesophagus and the presence of the cone-nosed bug vectors of Chagas’ dis-ease. Most interesting is the case of Charles Darwin, who wrote that he was bitten by a huge Triatoma bug while in South America. It has been suggested that Darwin’s mysterious chronic illness dated from this time, and some believe that Darwin was afflicted with Chagas’ disease.
Although similar to African trypanosomiasis (“sleeping sickness”), Chagas’ disease most likely evolved independently. Its cradle is believed to be the Bahia-Minas-Gerais area of Brazil, although it has subsequently spread throughout the Americas and has a notable presence in Argentina. In fact, a mid-twentieth century Argentine study established that the disease was much more widespread than previously believed and stimulated other studies, leading to recognition that Chagas’ disease was a serious health threat in South America. In-deed, since the 1950s, it has become increasingly common in southern Peru, although the vector (called chirimacha) is known throughout all of Peru.