Presentation of Quiz #67
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A 50-year-old male was admitted to the hospital for evaluation of increased shortness of breath. Although an examination several years earlier had revealed an enlarged heart, this did not seem to be a critical problem. He had been living in New York City for many years, but had grown up in La Paz, Bolivia (elevation 12,500 ft). Approximately 4 months before, he developed shortness of breath and general weakness, both of which began to interfere with his daily walks. He had no heart murmurs or history suggestive of rheumatic fever. The diagnosis of cardiomyopathy was made, including congestive heart failure, pleural effusion and conduction disturbances. The patient was treated for his cardiac problems and dramatically improved. However, about 5 months later, he died from other complications of the disease.
The following images were from his original workup and autopsy findings.
1. X-ray of enlarged heart (From a Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman).
2. Heart, gross section (note light under apex of heart, indicating ventricular aneurysm); also note the thickened wall of the heart
3. "Nests" of organisms
1. Please comment on the possible diagnosis related to the history, the patient’s clinical symptoms, and autopsy findings.
2. Does the history provide a clue to a possible infectious agent?
(Scroll Down for Answers and Discussions)
ANSWER AND DISCUSSION OF DIAGNOSTIC QUIZ #67
1. Cardiac X-ray of enlarged heart.
2. Thickened heart wall and apical left ventricular aneurysm
3. Nests of amastigotes of Trypanosoma cruzi (the cause of Chagas’ disease)
COMMENTS ON THE CASE:
If patients from Central or South America or Mexico present with a febrile illness (myocarditis or encephalitis may or may not be present), or a rash or localized swelling (particularly around the eyes (Romaña’s sign – see below), Chagas’ disease should be considered. Unfortunately, the trypomastigotes are only seen in the acute phases of the disease. Early treatment may prevent the advance to chronic disease (very difficult to treat).
COMMENTS ON THE ORGANISM:
This is a case of a man who was infected with Trypanosoma cruzi.
American trypanosomiasis (Chagas’ disease) is a zoonosis caused by T. cruzi discovered in Brazil in 1909 by Carlos Chagas, who described the entire life cycle in reservoir hosts. T. cruzi causes an acute or chronic parasitemia and invades the cells of many organs (e.g., heart, esophagus, and colon). Chagas’ disease is one of the major health problems in Latin American countries. It is estimated that there are 100 million persons at risk of infection, of whom 16 million to 18 million are actually infected. There are approximately 50,000 deaths per year due to Chagas’ disease. In certain endemic areas, approximately 10% of all adult deaths are due to Chagas’ disease.
The infective organism is transmitted to humans through the bite wound caused by the reduviid bugs (triatomids, kissing bugs, or conenose bugs) (See below). Humans are infected when metacyclic trypomastigotes are released with the feces while the insect is taking a blood meal, and the feces are rubbed or scratched into the bite wound or onto mucosal surfaces, an action stimulated by the allergic reaction to the insect’s saliva. Upon entry into the wound, the metacyclic forms invade local tissues, transform to the amastigote stage, and begin to multiply within the cells. In humans, T. cruzi can be found in two forms, amastigotes and trypomastigotes. The trypomastigote does not divide in the blood but carries the infection to all parts of the body. The amastigote form multiplies within virtually any cell, preferring cells of the reticuloendothelial system, cardiac muscle, skeletal muscle, smooth muscle, and neuroglia.
The trypomastigote is spindle shaped, approximately 20 mm long, and characteristically assumes a “C” or “U” shape in stained blood films. Trypomastigotes occur in the blood in two forms, a long slender form and a short stubby one. The nucleus is situated in the center of the body, with a large oval kinetoplast located at the posterior extremity. The kinetoplast consists of a small blepharoplast and a large oval parabasal body. A flagellum arises from the blepharoplast and extends along the outer edge of an undulating membrane until it reaches the anterior end of the body, where it projects as a free flagellum. When the trypomastigotes are stained with Giemsa stain, the cytoplasm stains blue and the nucleus, kinetoplast, and flagellum stain red or violet.
T. cruzi trypomastigote T. cruzi amastigotes in tissue
COMMENTS ON THE DISEASE:
In addition to contracting T. cruzi infections through the insect’s bite wound or exposed mucous membranes, one can be infected by blood transfusion, organ transplantation, placental transfer and accidental ingestion of parasitized reduviid bugs. The clinical syndromes associated with Chagas’ disease can be broken down into acute and chronic phases. The acute phase is the result of the first encounter of the patient with the parasite whereas the chronic phase is the result of late sequelae. In children under the age of 5, the disease is seen in its severest form, whereas in older children and adults, the disease is milder and is commonly diagnosed in the subacute or chronic form rather than in the acute form.
Acute-phase symptoms are usually seen in younger children and are less obvious in older individuals because of the nonspecific nature of the symptoms and the lack of availability to health care. Acute systemic signs occur around week 2 to 3 of infection and are characterized by the following: high fevers, which may be intermittent, remitting, or continuous; hepatosplenomegaly; myalgia; erythematous rash; acute myocarditis; lymphadenopathy; and subcutaneous edema of face, legs, and feet. There may be signs of CNS involvement including meningoencephalitis which has a very poor prognosis. Myocarditis is manifested by electrocardiographic changes, tachycardia, chest pain, and weakness. Amastigotes proliferate within the cardiac muscle cells and destroy the cells, which causes conduction defects and a loss of heart contractility. Death may occur due to myocardial insufficiency or cardiac arrest.
Symptoms of the chronic phase are related to the damage sustained during the acute phase of the disease. Chronic Chagas’ disease may develop years or decades after undetected infection or after the diagnosis of acute disease. The most frequent clinical sign of chronic Chagas’ disease is cardiomyopathy manifested by cardiomegaly and conduction changes. Because there are so few organisms isolated or seen in heart tissue, much of the cardiac tissue destruction is thought to be related to autoimmune antibodies possible due to cross reactivity to related T. cruzi antigens. The clinical course may vary from heart failure to a slow but continuing loss of cardiac function, with possible ventricular rupture and thromboemboli. Although it is less common than cardiac involvement, patients from certain areas are more likely to have dilation of the digestive tract with or without cardiomyopathy. These symptoms are most frequently seen in the esophagus and colon as a result of neuronal destruction. Megaesophagus characterized by dysphagia, chest pain, regurgitation and malnutrition is related to loss of contractility of the lower esophagus. Hypersalivation may occur leading to repeated bouts of aspiration pneumonia. Megacolon results in constipation, abdominal pain and the inability to discharge feces. In some individuals, there may be acute obstruction leading to perforation, septicemia and death.
COMMENTS ON DIAGNOSIS:
Trypomastigotes may be detected in blood by using thin and thick blood films or by buffy coat concentration techniques. T. cruzi trypomastigotes are usually “C” or “U” shaped on fixed blood films and have a large oval kinetoplast at the posterior end. Histologic examination of biopsies may also be done. Aspirates, blood, and tissues can also be cultured, which is valuable in detecting low-grade parasitemias. In endemic areas where reduviid bugs are readily available, xenodiagnosis can be used to detect light infections; this technique is most valuable for chronic infections when there are few trypomastigotes in the blood. Trypanosome-free bugs are allowed to feed on individuals suspected of having Chagas’ disease. If organisms are present in the blood meal, the parasites will multiply and be detected in the bug’s intestinal contents, which should be examined monthly for flagellated forms over a period of 3 months.
T. cruzi, xenodiagnosis T. cruzi in culture (epimastigotes)
In the chronic phase of Chagas’ disease, trypomastigotes are very rare or absent in the peripheral blood except during febrile exacerbations. Diagnosis depends primarily on culture xenodiagnosis or serologic tests. Some individuals with chronic Chagas’ disease may have a depressed humoral immune response, being serologically negative. This response has been correlated with specific zymodemes. Chronic disease should be considered in individuals from endemic areas who show signs of cardiomegaly, cardiac conduction defects, severe constipation, or dysphagia.
Serologic tests used for the diagnosis of Chagas’ disease include complement fixation (Guerreiro‑Machado test), indirect fluorescent‑antibody, and indirect hemagglutination tests and ELISA. The use of synthetic peptides and recombinant antigens has improved the sensitivity and specificity of these diagnostic techniques, particularly in the diagnosis of congenital disease by using IgM and IgA antibody detection and in the evaluation of cure. Depending on the antigens used, cross‑reactions have been noted to occur in patients with T. rangeli infection, leishmaniasis, syphilis, toxoplasmosis, hepatitis, leprosy, schistosomiasis, infectious mononucleosis, systemic lupus erythematosus, and rheumatoid arthritis. The Western blot method has been recommended for confirmatory serologic diagnosis of Chagas’ disease. Another potential confirmatory assay using preserved protein antigens of T. cruzi discriminates chagasic from nonchagasic infections and may be useful for elucidating inconclusive results obtained by standard serologic tests; this is particularly relevant to blood bank testing. Long‑lasting antibodies detected by a trans‑sialidase inhibition assay and antibody responses to certain heat shock proteins can serve as sensitive markers for previous T. cruzi infection in patients who are parasite free and serologically cured. ELISA procedures have also been used to detect specific antibodies in naturally infected dogs.
Although Bolivian donor screening studies using IHA, IFA, and four different ELISA tests demonstrated sensitivity from 96.5 to 100% and specificity from 87.0 to 98.9%, use of a single test results in unacceptable numbers of false-negative samples in highly endemic areas or in at risk populations. Use of two tests would only miss one infected unit per 10,000 screened; however, selection of tests depends on costs and feasibility.
Trypanosoma cruzi – KEY POINTS FOR DIAGNOSIS
1. Laboratory workers should use blood‑borne‑pathogen precautions when examining blood from Chagas’ disease patients, because the trypomastigotes are infective.
2. Trypomastigotes are prevalent in the blood in patients with acute Chagas’ disease; however, organism numbers are much smaller in the indeterminate and chronic stages of the infection.
3. T. rangeli (nonpathogen) cannot be differentiated from T. cruzi on the basis of parasite morphology; patient information regarding geographic exposure is required for more appropriate interpretation of laboratory results.
4. In addition to thin and thick blood smears, concentration methods should be used to concentrate the trypomastigotes in the blood.
5. Immunoassays for antigen detection are now available and are highly sensitive and specific. Alternative methods such as culture and serologic testing can be used; however, these approaches may not be feasible without the use of a reference laboratory.
6. Although culture is an option, it is rarely used in a routine diagnostic laboratory setting.
COMMENTS ON TREATMENT:
Although numerous drugs have been tried, including those used to treat African trypanosomiasis and leishmaniasis, few have proven to be effective for therapy of Chagas’ disease. In acute and congenital Chagas’ disease and infections caused by laboratory accidents, treatment should be administered as soon as possible, even though in some cases symptoms are self‑limited. Drug therapy has little effect on reducing the progression of chronic Chagas’ disease.
Nifurtimox (Bayer 205, Lampit), a nitrofurfurylidine derivative, is tolerated better in younger than older patients and should not be used during pregnancy. It reduces the duration and severity of illness and decreases mortality due to acute and congenital Chagas’ disease. Reversible gastrointestinal, cutaneous, and neurologic adverse effects are common. Treatment success varies from one country to another, possibly indicating differences in the susceptibility of strains of T. cruzi. There is no indication that treatment of patients with chronic Chagas’ disease is beneficial. Nifurtimox must be taken orally for prolonged periods, and there can be severe side effects including abdominal pain, nausea, vomiting, anorexia, and neurologic symptoms.
Benznidazole (RO‑7‑1051, Rochagan, Radanil), an imidazole derivative, is effective in reducing or suppressing parasites in the acute stages of disease but has limited capacity to produce a parasitic cure. It appears to be slightly more active and better tolerated than nifurtimox. Benznidazole is taken orally for prolonged periods and, similarly to nifurtimox, has little effect on changing clinical manifestations or reducing the progression of chronic Chagas’ disease. Side effects include peripheral polyneuropathy, abdominal pain, nausea, vomiting, and severe skin reactions.
Allopurinol, a purine analog, was found in limited clinical trials to be as effective as nifurtimox and benznidazole in treating Chagas’ disease. The drug is taken orally, and side effects include skin rashes in patients with renal impairment, epigastric pain, transient diarrhea, and pruritus. In a study using itraconazole or allopurinol in patients with chronic Chagas’ disease, parasitologic cure was evident in 44% of those treated with allopurinol and 53% or those treated with itraconazole. Electrocardiographic evaluation showed normalization in 36.5 and 48.2%, respectively, of patients with chronic or recent cardiopathy.
Symptoms associated with megaesophagus and megacolon may be treated with dietary measures or may require surgery. Patients with chronic chagasic heart disease may receive supportive therapy or be managed in some cases with pacemakers. With the use of a low cyclosporin dosage, 80% survival at 24 months has been reported for heart transplantation.
COMMENTS ON EPIDEMIOLOGY AND CONTROL:
Chagas’ disease is a zoonosis occurring throughout American continents and involves reduviid bugs living in close association with human reservoirs (dogs, cats, armadillos, opossums, raccoons, and rodents). The most ubiquitous sylvatic reservoir host is the opossum, Didelphus, which is found throughout much of the range of T. cruzi in the Americas. Multiple nesting or resting sites of the opossum encompass many types of triatomine habitat. High T. cruzi prevalence rates are partly due to the fact that opossums will eat triatomines and may also transmit infection via anal gland secretions. Sylvatic cycles of T. cruzi transmission extend from southern Argentina and Chile to northern California. Housing conditions are extremely important in transmission; the prevalence and incidence of infection are very high in human dwellings where the vector has adapted to living in the mud and in thatch walls and palm leaf roofs. The reduviid bug has easy access to humans to obtain blood meals and transmit the infection in this type of dwelling. A significant reduction in transmission was noted to occur in houses with walls made of plaster where cracks and crevices were covered, in contrast to houses with mud or thatch walls. Human infections occur mainly in rural areas where poor sanitary and socioeconomic conditions and poor housing provide excellent breeding places for reduviid bugs. These conditions allow maximum contact between the vector and humans. Although 12 species of reduviids occur within the United States, they have not adapted themselves to household habitation. Humans should avoid sleeping in thatch, mud, or adobe houses; bed nets should be used by persons sleeping in these types of houses. Travelers planning to stay in hotels, resorts, or other well‑constructed housing facilities are not at high risk for contracting Chagas’ disease. Insecticides can be used to kill the vectors and reduce the risk of transmission. Also, one must remember that in some countries, the blood supply may not always be screened for Chagas’ disease and so blood transfusions may carry a risk of infection. The severity of Chagas’ disease varies with the geographic area and may be related to strain differences in T. cruzi. Efforts have been made to characterize isolates based on enzyme profiles and have resulted in subpopulation classifications or schizodemes (zymodemes).
Transmission to humans is highly dependent on the defecation habits of the insect vector. In areas where the local species of reduviid bug does not ordinarily defecate while feeding, there are no human infections. This may explain why there are few human infections in the United States, even though sylvatic infections are known to occur in southern states. A number of autochthonous cases have been reported in the United States, in both Texas and California. The reduviid species involved in transmitting the infection to humans vary with the geographic area.
Until recently, control of Chagas’ disease has been mainly through the use of insecticides to eliminate the reduviid vector. In certain areas, insecticide resistance in triatomids has been noted. In addition to residual insecticide‑spraying programs, construction of reduviid‑proof dwellings and education are essential for effective control programs. Improvements in unsanitary living conditions, plastering of walls to obtain a smooth, crack‑free surface, and replacement of palm‑thatched roofs with metal roofing have been shown to considerably reduce the number of reduviids in houses. Although control of Chagas’ disease is feasible, few countries have initiated control programs because of both political and economic constraints.
Transmission can occur through organ transplants and blood transfusion. Some of the countries in areas where the disease is endemic have laws mandating serologic testing of blood donors. Financial constraints may hinder the implementation of these laws, and there is a lack of standardization of currently available serologic tests. An alternative approach to serologic screening in the United States, because of a lack of Food and Drug Administration‑approved tests, is the use of a questionnaire to identify prospective donors who may have resided in high‑risk areas. This approach may not be practical, since even in vector‑free areas in countries with endemic infection a significant portion of the donor blood units were positive for antibodies to Chagas’ disease. In areas where seroprevalence is high, rather than discarding all positive blood units, laboratorians add gentian violet to the units, which are stored at 4°C for 24 h before use, to kill the organism.
In evaluating electrocardiographic (ECG) changes among urban workers in Sao Paulo, Brazil, 2.2% positive sera for T. cruzi were found among 27,081 workers. A much higher percentage of workers with ECG abnormalities (42.7%) were seropositive for T. cruzi compared with the workers who were seronegative with ECG abnormalities (19.8%). Based on this data, it appears that the high frequency of ECG abnormalities emphasizes the importance of providing medical assistance to this group.
Freitas, J. M., E. Lages-Silva, E. Crema, S. D. Pena, and A. M. Macedo. 2005. Real time PCR strategy for the identification of major lineages of Trypanosoma cruzi directly in chronically infected human tissues. Int. J. Parasitol. 35:411-417.
Garcia, LS, 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, DC.
Garcia, L.S. 2009. Practical Guide to Diagnostic Parasitology, 2nd Ed., ASM Press, Washington, D.C.
Sartori, A. M. C., H. H Caiaffa-Filho, R. C. Bezerra, C. D. S. Guilherme, M. H. Lopes, and M. A. Shikanai-Yasuda. 2002. Exacerbation of HIV viral load simultaneous with asymptomatic reactivation of chronic Chagas’ disease. Am. J. Trop. Med. Hyg. 67:521-523.
Schmunis, G. A., and J. R. Cruz. 2005. Safety of the blood supply in Latin America. Clin. Microbiol. Rev. 18:12-29.
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Reference: Garcia, L.S. 2015. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, D.C.
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