Tutorial 08 Objetivos Estudar a Doena de Chagas

Doena de ChagasTrypanosoma cruzi is endemic in South, Central and parts of North America (also Mexico and possibly South Texas). T. cruzi infection occurred mainly in rural areas where humans live in poorly constructed dwellings and in close contact with potential vectors. However, rural-to-urban and international migrations have changed the epidemiology of CD affecting peri-urban, urban, endemic and non-endemic areas alike. The prevalence and incidence of the disease are decreasing. Eradicating transmission of T. cruzi by the main domiciliary vector species, Triatoma infestans, from three endemic countries (Uruguay in 1997; Chile in 1999; and Brazil in 2006)According to the most recent estimates, there are currently 7.6 million people infected with T. cruzi in Latin America.

Pathogenesis and Pathology

Tissue damage appears to be caused both by direct parasite effects and secondary to the hosts immune response. Cross-reactivity between T. cruzi antigens and auto-antigens, and an imbalance between CD4+ and CD8+ T lymphocyte responses leading to excessive production of inflammatory cytokines may have roles in immune-mediated tissue damage.During the acute phase of infection (usually corresponding to the first 23 months after infection), all types of nucleated cells may be infected and inflammatory changes are especially marked close to ruptured infected cells. Lesions reveal localized inflammatory reactions, acute diffuse myocarditis with myocyte necrosis, interstitial edema and inflammatory cell infiltrates. Inflammatory lesions may also be found in the smooth muscle of the esophagus and colon, and the central and peripheral nervous systems. In nearly all infected individuals, an effective host immune response, involving T helper-1, CD4+ and CD8+ lymphocytes and the production of interferon-, tumor necrosis factor- and interleukin-12, develops within 60 days of infection which controls the parasitemia. However, in the absence of effective treatment, tissue infection persists for the life of the host. In the indeterminate form of the chronic phase, isolated inflammatory foci may be found in tissues.Sensitive methods of parasite detection, such as immunohistochemistry and polymerase chain reaction (PCR). Evidence exists for multiple hypotheses to explain the aetiology of chronic cardiac lesions implicating the parasite directly, the immune reaction to the parasite and autoimmunity elicited either directly by the parasite (mimicry) or indirectly (bystander activation).7,8 The end-product of these lesions is varying degrees of necrosis, neuronal damage, microvascular damage and fibrosis.

There is evidence of both functional and anatomical parasympathetic neuronal damage. Patients with CD lack the tonic inhibitory parasympathetic action on the sinus node and thus the chronotropic mechanism to respond to changes in blood pressure or venous return. Neuronal loss is occur during the acute stage of the disease; the extent of neuronal damage however, does not correlate with disease stage. Therefore, despite possible contributions of parasympathetic impairment to the impact of CHD cardiac dysautonomia is unlikely to explain the main pathogenic mechanism underlying CHD.

Microcirculatory changes leading to ischaemia also were implicated in the pathogenesis of chronic CHD. Diffuse collapse of intramyocardial arterioles has been observed in the hearts of chronically infected patients. Occlusive platelet thrombi in small epicardialand intramural coronary arteries and increased production of cytokines and mediators that promote vasospasm and platelet aggregation have been demonstrated in experimental models of CD.

The inflammatory infiltrate in chronic Chagasic cardiomyopathy has a predominance of macrophages, CD8+ and CD4+ lymphocytes (in a 2 : 1 ratio) and in some instances has been shown to correlate with more advanced stages of the disease. Persistence of parasites and antigens is thought to be involved in recruitment of T. cruzi-specific CD8+ T lymphocytes which predominate in the myocardial infiltrate of chronic myocarditis. The cytokine profile associated with this myocarditis is also shifted toward Th1 cytokines so that elevated INF- levels and decreased IL-10 levels may potentially perpetuate an existent, ongoing inflammatory process. However, the exact mechanism responsible for the turning point from immunoprotection to immune-mediated aggression leading to irreversible tissue damage remains elusive: not only is parasite persistence true for both symptomatic and asymptomatic patients, but presence of the parasite in heart tissue does not always correlate with inflammation.Autoimmunity has also been postulated as a plausible aetiology for the chronic myocarditis observed in T. cruzi-infected patients. Several T. cruzi antigens that cross-react with cardiac and non-cardiac host components have been identified, but only some have been shown to have functional activity. Among these, attention has focused on antibodies that cross-react with cardiac myosin and the immunodominant T. cruzi antigen B13 initially because they were detected in 100% of patients with chronic Chagasic cardiomyopathy in contrast to 14% of asymptomatic infected individuals, and later because T-cell clones derived from lesions of chronic CHD were found to be simultaneously reactive to cardiac myosin heavy chain and the B13 T. cruzi protein. Opponents to the molecular mimicry theory with specific relevance to anti B13-cardiac myosin crossreactive antibodies and derived cellular autoimmunity contend that these antibodies do not bind to intact myocytes, are not unique to T. cruzi infection, Are present in asymptomatic patients without heart lesions, and that myosin autoimmunity is not essential for cardiac inflammation in experimental models. Arguing against autoimmunity developing as a result of parasite-specific immune responses, antigen exposure after tissue damage may also sensitize autoreactive T cells to selfantigens given a proinflammatory environment. The question, therefore, is not whether autoimmunity is present, but whether it is a primary cause or merely a contributing factor to the pathogenesis of chronic myocarditis. Further evidence is required from experiments to prove an association between the development of similar cardiac lesions with transfer of autoantibodies and/or autoreactive cells to susceptible hosts.

Although the effects of both autonomic and microvascular disturbances in CHD may play an important role in potentiating and perpetuating cardiac muscle damage, persistent inflammation in the setting of continuous antigenic stimulation is perhaps the common pathway for tissue damage.Multiple mechanisms seem to explain this chronic inflammation (including anti-parasite immunity and possibly autoimmunity), which are not necessarily mutually exclusive. The course to progression to chronic CHD and other forms of the disease has been suggested to be related to genetic properties of both host and parasite. However, the molecular mechanisms underlying tissue tropism and the initial trigger or determinant of the course of chronic disease are not yet known.

Clinical FeaturesACUTE CHAGAS DISEASE

ACUTE TRYPANOSOMA CRUZI INFECTIONThe incubation period is 12 weeks, after which the acute phase of infection begins. The acute phase lasts 812 weeks and is characterized by circulating trypomastigotes detectable by microscopy of fresh blood. Most patients are asymptomatic or have mild, nonspecific symptoms, such as fever, lymphadenopathy and/or hepatosplenomegaly, and do not come to clinical attention during the acute phase. In some patients, acute infection is associated with inflammation and swelling at the site of inoculation, known as a chagoma. Chagomas typically occur on the face or extremities, and parasites may be demonstrable in an aspirate of the lesion. Inoculation via the conjunctiva leads to the characteristic unilateral swelling of the upper and lower eyelid known as the Romaa sign. Severe acute disease occurs in less than 1% of patients; manifestations include acute myocarditis pericardial effusion, and/or meningoencephalitis. Acute Chagas disease carries an estimated risk of mortality in the range of 1 in 200 to 1 in 400 cases. Orally-transmitted T. cruzi infection appears to be associated with more severe acute morbidity and higher mortality than vector-borne infection.

CHRONIC TRYPANOSOMA CRUZI INFECTIONEight to 12 weeks after infection, parasitemia levels become undetectable by microscopy and, in the absence of effective anti-trypanosomal treatment, the individual passes into the chronic phase. Persons with chronic T. cruzi infection can transmit the parasite to the vector and directly to other humans through blood components, organ donation and congenitally. Persons with chronic T. cruzi infection, but without signs or symptoms of Chagas disease, are considered to have the indeterminate or asymptomatic form. An estimated 2030% of people who initially have the indeterminate form of Chagas disease progress over a period of years (to decades) to clinically-evident cardiac and/or gastrointestinal disease.

CHRONIC CHAGAS HEART DISEASECardiac involvement is the most frequent and most severe manifestation of chronic CD. Transition from the indeterminate form to the cardiac form of chronic CD is usually manifested by the appearance of ECG changes such as incomplete or complete right bundle branch block (RBBB), left anterior fascicular block (LAFB), minimal ST-T changes, and monomorphic premature ventricular contractions (PVCs) mostly in asymptomatic or oligosymptomatic patients. As the disease advances, associated intraventricular conduction defects (usually RBBB with LAFB), polymorphic PVCs, bradyarrhythmias, high-grade atrioventricular blocks, q-waves, nonsustained or sustained ventricular tachycardia and ultimately atrial flutter or fibrillation may ensue. Symptoms such as palpitations, atypical chest pain, presyncope, syncope, dyspnoea on exertion and oedema are usually observed throughout the course of CHD. Findings on physical examination vary according to the stage of the disease and the presence of conduction system abnormalities. They include: cardiac rhythm irregularities; displaced point of maximal impulse; gallop rhythms; a loud second heart sound implying pulmonary hypertension; mitral or tricuspid regurgitation murmurs; an increase in the systemic venous pressure with liver enlargement and oedema; and borderline low systolic blood pressure with a reduced radial pulse implying systolic dysfunction.

The clinical course of CHD is diverse and difficult to predict, with some patients remaining asymptomatic lifelong, despite electrocardiographic and/or echocardiographic evidence of the disease; some presenting with signs, symptoms and complications of progressive heart failure or advanced cardiac arrhythmias; and others dying unexpectedly without prior symptoms.Currently, several staging systems of CHD are available. They can help to identify patients at different degrees of risk, facilitate choices among treatment alternatives and aid patient counselling. Most systems classify patients into four or five stages, based on their functional capacity, ECG findings and the presence or absence of heart enlargement and/or systolic dysfunction on echocardiogram. Systemic and pulmonary embolism arising from mural thrombi in the cardiac chambers is relatively frequent. Although the brain is by far the most common clinically recognized site of embolisms (followed by limbs and lungs), at necropsy, embolisms are found more frequently in the lungs, kidneys and spleen. CD is an independent risk factor for stroke in endemic areas. Mortality in CHD is due to sudden cardiac arrest in 5565% of patients, congestive heart failure in 2530% of patients and thromboembolic phenomena in 1015%.

Chronic Gastrointestinal Chagas Disease (Megadisease) Dysfunction of the GI tract is the second most common consequence of chronic T. cruzi infection.89,90 As in the case of chagasic cardiopathy, GI Chagas disease usually occurs years or even decades after infection with T. cruzi is acquired. Dysfunction related to megaesophagus (Fig. 99.7) is the most typical clinical manifestation, but symptoms due to megacolon are also frequent. The process underlying megadisease is a loss of neurons in the gut.91 Quantitative assessments of this degenerative process have shown that in severely affected patients as many as 85% of the neurons in the esophagus and 50% of those in the colon may be lost. The factors that determine the rate and pattern of the neuronal destruction are not known. Pathologic examination of esophageal specimens obtained surgically or at autopsy from patients with megaesophagus have shown dilatation and varying degrees of thickening of the muscular wall. As in the case of cardiac tissue, microscopic examination shows mononuclear cell infiltration and fibrosis, but finding parasites is unusual. The most common symptom associated with chagasic megaesophagus is dysphagia. Many patients experiencing this sense the accumulation of swallowed food in the esophagus and take in water or more food, or even eat in a standing position, to facilitate its passage into the stomach. Pain, typically starting in the lower substernal area and spreading upward, is also a frequent symptom in patients with megaesophagus. In patients with severe degrees of megaesophagus, regurgitation can become a problem, and if the underlying problem is not treated, it can lead to intermittent aspiration with associated chronic cough, bronchitis, and pneumonia. As in the case of chagasic megaesophagus, colonic disease is manifested by dilatation and typically the sigmoid colon is the most affected segment. As the disease progresses, the colon can become markedly enlarged in both length and diameter, and the thickening of the wall can become less pronounced. The pathologic changes evident on microscopic examination of affected colonic tissue are similar to those found in the esophagus. The cardinal symptom associated with Chagas disease of the colon is constipation. Pain is also a common symptom, resulting from accumulation of feces and flatus, as well as ineffective and recurrent colonic contractions. Other GI and urinary viscera can be affected in persons with chronic Chagas disease, but this is much less common.92 The most frequent occurrence is hypertrophy of the parotid glands, which is present in as many as 25% of patients with chagasic megaesophagus. The stomach may also be affected, and hypoperistalsis, hypotonia, decreased acid secretion, and delayed emptying of the stomach have been documented in patients with megaesophagus, but dilatation of the stomach is not found frequently.93 The pathogenesis of the cardiac and GI lesions of chronic Chagas disease has been debated for decades. Recently, convincing evidence has accumulated supporting the concept that the low-level presence of parasites in chronically affected cardiac tissue, detectable by molecular methods, stimulates a chronic inflammatory response that over time leads to the pathologic changes observed microscopically.OTHER CLINICAL MANIFESTATIONSAmong some immunosuppressed hosts such as HIV-infected individuals and transplant recipients, reactivation of infection and de novo infection (including transmission with transplanted organs among transplant patients) have been reported.1,12 With reactivation in HIV-positive patients, myocarditis has been reported in up to 45% of cases.12 Reactivation of CD among heart transplant patients has been estimated to occur in approximately 30% of cases. However, not all these cases are accompanied by florid symptoms or diagnosed by endomyocardial biopsy and therefore, the true incidence of myocarditis with reactivation is difficult to estimate. Acute T. cruzi infection can also result as a consequence of donor-related transmission, which has been reported after kidney, heart, liver and multi-organ transplants. Involvement in this setting can range from asymptomatic parasitaemia that easily responds to treatment without further complications to severe, fulminant disease despite therapy (including death directly attributable to Chagasic myocarditis). Approximately 1 in 20 T. cruzi infections in pregnant women is passed vertically to the unborn fetus.1 In congenitally infected infants, the most common symptoms, which may be apparent at birth or develop within weeks after delivery, are hypotonicity, fever, hepatosplenomegaly and anemia. Other findings include prematurity and low birth weight. In utero infections are also associated with abortion and placentitis. Serious manifestations, including myocarditis,meningoencephalitis and pneumonitis, are uncommon, but carry a high risk of death.1,5 Finally, reactivation of latent CD may present with dermatological manifestations including indurated erythematous plaques with necrosis, erythematous papules and nodules, panniculitis or skin ulcers.13 Some of these lesions may resemble erythema migrans due to Lyme disease borreliosis.

DiagnosisDiagnosis of acute and early congenital T. cruzi infection requires demonstration of the parasite in blood by microscopy, PCR or hemoculture. Diagnosis of chronic infection relies on serologic tests (e.g. ELISA) to detect IgG antibodies to T. cruzi

DIAGNOSISAppropriate diagnostic testing for T. cruzi infection varies depending on the phase of the disease and the status of the patient DIAGNOSIS OF ACUTE TRYPANOSOMA CRUZI INFECTIONBecause the parasitemia level is high during the acute phase, motile trypomastigotes can be detected by microscopy of fresh preparations of anti-coagulated blood or buffy coat [3]. Parasites may also be visualized by microscopy of blood smears stained by Giemsa or other standard stains. Even without treatment, the parasitemia level decreases within 90 days of infection and is undetectable by microscopy in the chronic phase. PCR is a sensitive diagnostic tool in the acute phase of Chagas disease and to monitor for acute T. cruzi infection in the recipient of an infected organ, or after accidental exposure .

DIAGNOSIS OF CONGENITAL TRYPANOSOMA CRUZI INFECTIONIn the first months of life, congenital Chagas disease is an acute T. cruzi infection and similar diagnostic methods are employed.Concentration methods give better sensitivity than direct examination of whole blood. The most widely used technique in Latin American health facilities is the microhematocrit method. In this technique, cord or neonatal blood is collected and sealed in 46 heparinized microhematocrit tubes, centrifuged and the buffy coat layer examined by microscopy. Repeated sampling on several occasions during the first months of life increases sensitivity, but may not be acceptable to the parents of a neonate. Hemoculture can increase sensitivity, but the technique is not widely available, and results are not available for3060 days. Molecular techniques have higher sensitivity and detect congenital infections earlier in life compared with the microhematocrit method [29]. Transient detection of parasite DNA has occasionallybeen reported in specimens from infants who subsequently are found to be uninfected [4]. For this reason, positive PCR results on two samples drawn on separate occasions are sometimes required for confirmation of congenital infection. PCR is increasingly used for the early diagnosis of congenital Chagas disease in Latin America and is the method of choice in industrialized countries. For infants not diagnosed at birth, conventional IgG serology (as outlined below for chronic T. cruzi infection) is recommended after nine months of age, when transferred maternal antibody has disappeared and the congenital infection has passed into the chronic phase.DIAGNOSIS OF CHRONIC TRYPANOSOMA CRUZI INFECTIONDiagnosis of chronic infection relies on tests to detect IgG antibodies to T. cruzi, most commonly the ELISA and immunofluorescent antibody assay (IFA). No single serologic assay has sufficient sensitivity and specificity to be relied on alone; two tests based on different antigens (e.g. whole parasite lysate and recombinant antigens) and/ or techniques (e.g. ELISA, IFA, immunoblot) are used in parallel to increase the accuracy of the diagnosis [3]. Published data suggest that the sensitivity of serologic assays varies by geographical location, possibly because of T. cruzi strain differences and resulting antibody responses [30, 31]. Inevitably, a proportion of individuals tested by two assays will have discordant serologic results and need further testing to resolve their infection status. The status of some individuals remains difficult to resolve, even after a third test, because there is no true gold standard assay for chronic T. cruzi infection [32]. Assays such as the radioimmune precipitation assay (RIPA) and trypomastigote excreted-secreted antigen immunoblot (TESA-blot) are promoted as reference tests but even these do not have perfect sensitivity and specificity, and may not be capable of resolving the diagnosis.UTILITY OF PCR FOR DIAGNOSIS OR MONITORINGMolecular techniques currently provide the most sensitive tools to diagnose acute phase and early congenital Chagas disease and to monitor for acute T. cruzi infection in the recipient of an infected organ or after accidental exposure (Table 98-3). PCR assays usually show positive results days to weeks before circulating trypomastigotes are visible by microscopy of peripheral blood [29]. In chronic T. cruzi infection, PCR is used as a research tool, but is not generally a useful diagnostic test. Although PCR results will be positive for a proportion of patients, the sensitivity is highly variable depending on characteristics of the population tested, as well as the PCR primers and methods used. Quantitative PCR assays (e.g. real-time PCR) are useful for monitoring for reactivation in immunosuppressed patients with chronic T. cruzi infection, such as an organ recipient or HIV-coinfected patient. In these patients, a positive result on conventional PCR does not prove reactivation, but quantitative PCR assays showing rising parasite numbers over time provide the earliest and most sensitive indicator of reactivation [33]. The Centers for Disease Control (CDC) currently performs several conventional and real-time PCR assays with primers targeting kinetoplast and nuclear DNA.

PATIENT EVALUATIONThe initial evaluation of a patient diagnosed with T. cruzi infection should begin with the complete medical history and physical examination.Details on family history, potential exposure to the vector and history of blood transfusion in endemic areas should be recorded. A detailed review of systems should focus on cardiovascular and gastrointestinal symptoms. Screening should be offered to other family members, including children of seropositive mothers, and the patient should be advised regarding possible transmission routes (such as blood and organ donation). An HIV test and/or evaluation for other causes of immunosuppression should be considered, as management of Chagas disease in these patients merits special attention.Every patient should have a resting 12-lead ECG with a 30-second rhythm strip; other tests should be ordered if warranted by signs and symptoms elicited during the history and examination. In the strict sense, the indeterminate form is defined by positive anti-T. cruzi serology in an asymptomatic person with a normal physical examination, a normal 12-lead ECG and normal radiologic examination of the chest, esophagus and colon. However, patients with a normal ECG and no cardiovascular and gastrointestinal symptoms have a favorable prognosis and yearly follow-up may be sufficient without having to perform any additional tests.Patients with cardiovascular symptoms and/or ECG abnormalities suggestive of Chagas cardiac disease (Tables 98-1 and 98-4) should undergo further evaluation, including two-dimensional (2-D) ECG, exercise testing and 24-hour ambulatory ECG monitoring. The need for additional cardiac studies should be assessed on an individual basis. A barium swallow or enema should be performed in patients with upper or lower gastrointestinal symptoms respectively. Esophageal manometry may be of use for patients with suggestive symptoms in whom the barium swallow is inconclusive. Patients with megaesophagus may be at increased risk for esophageal cancer and an upper gastrointestinal endoscopy may be indicated, especially in patients with new, or progressive, symptoms. An increased risk of colorectal cancer has not been found in patients with megacolon.Additional procedures may have a role in patient evaluation in the future. Segmental cardiac wall motion abnormalities detected by 2-D ECG and areas of myocardial fibrosis demonstrated by delayedenhancement magnetic resonance imaging (MRI) have been found in patients with normal ECGs; research studies suggest that minor abnormalities of ventricular contractility may be predictive of future deterioration in function. Diastolic dysfunction and elevated blood levels of brain natriuretic peptide (BNP) appear to correlate with prognosis in patients with cardiomyopathy owing to a variety of etiologies, including Chagas disease [41]. 2-D echo and 24-hour ambulatory ECG monitoring results are used to assess risk in some prognostic scores for Chagas disease

Management and TreatmentIndication for anti-parasitic therapy depends on the phase of the disease and the clinical status and age of the patient. There are currently only two available drugs: benznidazole and nifurtimox ANTITRYPANOSOMAL THERAPYSPECIFIC ANTI-PARASITIC DRUGSNifurtimox, a nitrofuran compound, acts through production of nitrogenated free radicals (e.g. superoxide, hydrogen peroxide) for which parasites have much lower detoxification capacity than vertebrates [42]. Benznidazole, a nitroimidazole derivative, is thought to act through the mechanism of reductive stress by covalent binding of nitroreduction intermediates to parasite molecules [42]. Both drugs are rapidly absorbed from the gastrointestinal tract (plasma levels peak at 1 hour after a single oral dose); the average biological half-life is 12 hours. Nifurtimox is rapidly and extensively metabolized in the liver using cytochrome P-450 and P-450 reductase. Interindividual variability suggests that metabolism of nifurtimox may be under genetic control. Elimination of both drugs is predominantly renal. Hepatic or renal function impairment increase blood concentrations of the medication, increasing the risk of side effects. Concurrent alcohol intake may enhance the occurrence of side effects. In tissue other than the liver (testicles, ovaries, adrenal glands, colon, esophagus), the reducing activity is variable. Both drugs are mutagenic and have been reported to increase the risk of lymphomas in experimental animals but no increase in incidence of human lymphoma has been reported among treated populations. The drugs are known to be teratogenic in experimental animals and their use in pregnant women is contraindicated. Risk for significant infant exposure to drugs through breast milk seems small and below the level of exposure of infants with Chagas disease receiving nifurtimox treatment. This potential degree of exposure may not justify discontinuation of breastfeeding.Recent trials have all used benznidazole and this drug is usually better tolerated than nifurtimox; for these reasons benznidazole is viewed by most experts as the first line treatment. Nevertheless, individual tolerance variesif one drug must be discontinued, the other can be used as an alternative. Nifurtimox is indicated for a patient in the acute phase with documented benznidazole treatment failure.

IndicationsTreatment has been recommended for all cases of acute and congenital infection, reactivated infection, and in early chronic CD (particularly children/adolescents