Chagas disease, the illness caused by the bite of the kissing bug, sometimes called the assassin bug, is an important cause of morbidity and mortality in Central and South America. Like so many diseases not native to North America, however, immigration and travel is slowly making this a problem for the southern United States.
Chagas disease is responsible for approximately 50,000 deaths a year in Central America, and costs these countries approximately $8 billion a year. The causative organism is the parasite known as Trypanosoma cruzi, transmitted by the insect vector, the reduviids or triatomines. T. cruzi are single-celled flagellates, which were discovered in the early 20th century by Carlos Chagas, a Brazilian physician. (Infect Dis Clin NA 2004;18:247.)
THE ANTIBIOTICS NIFURTIMOX AND BENZNIDAZOLE ARE USED TO TREAT CHAGAS DISEASE
The insects live in thatched roofs and cavities of mud walls. This disease, also know as American trypanosomiasis, is related to African sleeping sickness and Leishmaniasis. Although the vast majority of the cases of Chagas disease occur in Central and South America, the extreme southern United States is at risk of endemic disease, and with immigration, any site in North America is at risk of seeing a patient with Chagas.
The primary sites of pathogenesis are muscle tissue and the esophagus. Parasites also can be found in the cerebrospinal fluid of some patients. Transmission via blood transfusion, organ transplantation, and transplacental routes are possible; approximately five percent of infants born to women with Chagas are infected. Interestingly, approximately 70 percent of these infants are asymptomatic. (Mandell GL, et al. Mandell's Principles and Practices of Infectious Disease. Philadelphia, PA: Elsevier, 2008.)
The parasite will infect many mammalian hosts besides humans, including dogs, rats, squirrels, raccoons, foxes, and armadillos. The vectors in the United States, which can be found from Texas and New Mexico to Maryland, are a different species than the type of triatomine in Central and South America. The paucity of human cases in the United States is attributed to several factors: better housing, more nonhuman blood meals, and the delayed defecation of the species of insects in the United States compared with the South and Central American species.
Although endemic Chagas disease is rare in the United States (fewer than 10 reported cases), there are an estimated 12 million people living in the United States who come from countries, mostly Mexico, with Chagas disease. These data suggest that approximately 80,000 to 100,000 people living in the United States are infected with Chagas, and eight million people in Latin America are carriers. (Lancet Infect Dis 2007;7:572.) Although there is a very low likelihood of vector transmission here, there is a small but real risk of transfusion or organ transplantation transmission, with seven cases in North America reported from transfusions. (Lancet Infect Dis 2007;7:380.)
Heart Most Affected
Acute Chagas disease, usually affecting children, occurs shortly after the entry of the organism into the host. After the insect feeds, it defecates, usually at night. The parasite, which is present in the feces, then has the opportunity to enter the body. If the portal is a break in the skin (abrasions, for example), a chagoma, an area of swelling, is formed, followed by erythema and local lymphadenopathy. A classic finding in the acute stage of the disease is Romaña's sign, which is painless lid swelling when the parasite enters through the conjunctiva.
If untreated after a few weeks or months, the patient's symptoms resolve and the disease then enters the indeterminate phase. Years or decades later, the disease enters the chronic phase in approximately 30 percent of acutely infected patients (MMWR 2007;56:141), and cardiac and GI symptoms develop. The heart is the most commonly affected organ, with the esophagus and colon as potential sites. Cardiomyopathy is the classic cardiac finding, with congestive heart failure, arrhythmias (usually ventricular), and emboli as causes of morbidity and mortality. (Libby P, et al. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 8th ed. Philadelphia, PA: Saunders, 2008.)
The cardiomyopathy preferentially affects the right ventricle, with right heart failure the most common symptom. Chagas-induced conduction delays are the most common reason for pacemaker implantation in Venezuela. (Lancet Infect Dis 2005;5:470.) When the esophagus is affected, a resultant megaesophagus develops, with symptoms similar to achalasia, GERD, chronic cough, chest pain, and dysphagia. A megacolon also can develop, with constipation, bloating, and sometimes a volvulus occurring.
The diagnosis begins with suspicion using epidemiological criteria, as often is the case in tropical diseases in North America. Although the incidence in tourists who have visited endemic countries is low, immigrants from South and Central America with symptoms of acute or chronic Chagas should prompt a search. In acute Chagas, parasites seen on blood smear confirm the diagnosis. In chronic Chagas, the diagnosis is made by detecting IgG in the serum.
The FDA recently approved an ELISA assay for blood screening of blood donors. In a recent American Red Cross study, blood from California and Arizona donor centers were screened for T. cruzi antibodies; one in 2,365 tested positive for antibodies. Beginning in January 2007, the American Red Cross and Blood Systems, Inc., began screening all donated blood for T. cruzi antibodies. (MMWR 2007;56:141.)
Treatment of Chagas disease is mainly based around two antibiotics, nifurtimox and benznidazole. The former is a derivative of nitrofurantoin, the latter a relative of metronidazole. Treatment with nifurtimox achieves approximately a 70 percent parasite clearance rate. Data on benznidazole, seen as the drug of choice by physicians in Central and South America, are scant. Both of these drugs have many side effects, and can be difficult to tolerate. There are actually few data supporting the treatment of chronic Chagas, according to a Cochrane review in 2002. (Villar JC, et al. Trypanocidal drugs for chronic asymptomatic Trypanosoma cruzi infection. Cochrane Database of Systematic Reviews, 2002.)
The treatment for the specific organ dysfunction depends on the issue; cardiomyopathy is treated like non-Chagasic cardiomyopathy, conduction defects with pacemaker placement. Treatment for megaesophagus is similar to that of idiopathic achalasia, beginning with balloon dilatation. Treatment of the megacolon, constipation/fecal impaction, and volvulus are again no different from non-Chagasic disease.