Trypanosoma cruzi (Chagas´ disease): IgG and IgM antibodies; Microscopic exam; Culture; Molecular diagnosis (PCR).
Chagas´ disease, also called American trypanosomiasis, owes its name to the Brazilian doctor Carlos Chagas, who discovered it in 1909. This disease is caused by a parasite, Trypanosoma cruzi, which is transmitted between animals and humans by vector insects located only in America, especially in rural areas. It is estimated that about 8 million people are infected in Mexico, Central America and South America, but most of them are unaware. If left untreated, the infection is chronic and can sometimes be fatal.
Trypanosoma cruzi is a protozoan of the class Kinetoplastida, family Trypanosomatidae, characterized by the presence of a single flagellum and a single mitochondrion, whose genome is located in a complex and compact region near the base of the flagellum, called the kcinetoplast. It is an intracellular parasite with a life cycle that involves vertebrates and invertebrates. From the morphological point of view, in the vertebrate host the parasite is found in the blood in the form of trypomastigote, in the reticuloendothelial system and in the tissues it adapts to the amastigote form, and in the transmitting insect (vector) it presents the morphology of epimastigote and metacyclic trypomastigote. In man, the most frequent location of the parasite is in the reticuloendothelial cells of the spleen, liver, lymph nodes and myocardium.
The disease is practically limited to South and Central America, including Mexico (but not the Caribbean islands), although some isolated cases have been described in the US and Canada, as well as the existence of reservoirs (small rodents) in various southern states. from this country. WHO estimates that there are more than 25 million people at risk and between 7 and 8 million infected by T. cruzi, mainly in Latin America. The prevalence is high in Brazil, Venezuela, Chile, Argentina, Uruguay, Bolivia and Peru, as well as throughout Central America, preferably in rural areas, with adobe houses and poor environmental sanitation. The insects that act as vectors of this parasite are bugs (not bedbugs) and among them the most common species are Triatoma infestans, Rhodnius prolixus and Panstrongylus megistus, although there are more than 122 potentially transmitting species. The first two species are the main vectors in Central America and Venezuela, and the last is the most frequent transmitter in South America.
It is important to note that this disease is no longer exclusive to the Americas. Chagas´ disease has become a health problem in several non-endemic countries, due to migratory movements and mechanisms of vertical transmission or by donation of blood and organs of immigrants with chronic infection from endemic areas. Cases of Chagas´ disease have been detected in North America (Canada and the United States), in the Western Pacific (mainly Australia and Japan) and, more recently, in Europe.
The reservoir are humans and 150 other species of mammals, domestic and wild animals. Triatomids (bugs) become infected by biting a previously infected reservoir. The life cycle of the parasite in the vector takes place in the intestine, where it evolves from the trypomastigote form to metacyclic trypomastigote, which is the form that is eliminated with its feces and is already infective to man and animals. The transmission is caused by contamination of the wound caused by the bite of the vector with its feces, which contain the infective forms. This happens easily since the transmitting arthropod, when it bites its host, defecates in the vicinity of the bite it causes, and with scratching the feces can enter the wound. The insect preferably bites at the mucocutaneous junctions, such as the external eyelid angle and the corners of the mouth. Hence, they are commonly known as "kissing bugs."
However, T. cruzi has other routes of transmission: from mother to child by transplacental route (congenital), by blood transfusions or organ transplants in which donors are infected, by consumption of food or beverages contaminated with feces from infected triatomids, or in laboratory accidents.
Once the metacyclic tripomastigotes penetrate the host, they invade cells near the site of inoculation, where they differentiate into intracellular amastigotes, which multiply and release trypomastigotes back into the bloodstream, invading new cells. Triatomids become infected by feeding on human or animal blood that contains circulating trypomastigotes. Ingested trypomastigotes are transformed into epimastigotes in the middle intestine of the vector. Here the parasites multiply and differentiate into infectious metacyclic trypomastigotes in the posterior intestine, thus closing the cycle.
Chagas´ disease occurs in two phases: acute and chronic phase. During the acute phase, parasites can be found in the circulating blood. This phase of the infection is usually mild or asymptomatic, presenting symptoms usually in children younger than 10 years. In this case, it is characterized by high fever, chills, headaches and myalgias, lack of appetite and the appearance of an intense non-suppurative eyelid edema, called the Romaña sign, which indicates the pathway of the parasite into the body. This eyelid edema is the earliest sign of the disease and is almost pathognomonic, but it is only seen in 4% of parasitized individuals. The establishment of this sign is abrupt and there is an elastic, hard and painless edema usually in a single eyelid, which ends up becoming purple and causes generalized facial edema. The edema tends to disappear after 2 or 3 months, but in the area where it has occurred remains a characteristic pigmentation for many years. In addition, the thyroid, submaxillary glands, lymph nodes, liver and spleen are enlarged and the central nervous system is affected, causing anxiety, irritability and mental dullness.
After the acute phase, most infected people enter a form of prolonged asymptomatic disease (called "chronic indeterminate") during which few or no parasites are found in the blood. During this time, most people are unaware that they are infected. Many may remain asymptomatic for the rest of their life and never manifest symptoms. However, it is estimated that between 20 and 30% of infected individuals will develop serious and sometimes life-threatening medical problems throughout their lives.
The chronic phase is diagnosed more frequently than the acute one, and the most notable symptoms are dilated cardiomyopathy (with conduction disturbances and heart failure) and digestive complications, where the destruction of the wall plexuses causes visceral dilation (megaesophagus or megacolon), being able to become clogged and/or perforated. Over the years, the infection can cause sudden death from cardiac arrhythmias, progressive heart failure or ventricular rupture. In immunosuppressed patients (for example, due to HIV infection or chemotherapy), Chagas´ disease can be reactivated and blood parasites appear again. This reactivation can cause a potentially serious illness.
The diagnosis of the disease in the acute phase is made by the clinic and the presence of epidemiological antecedents (residence or travel to endemic areas) and is confirmed with the demonstration of blood parasites, usually after hemoconcentration, and sometimes with the use of cultures; by xenodiagnostic a procedure in which triatomids free of the parasite that suck blood are used and in which it is subsequently observed if there are parasites in their feces; or by molecular diagnosis (PCR). These methods are only valid in the acute phase of the infection, because it is when there is a large number of trypomastigotes circulating in blood, especially in the first 6 to 10 weeks of infection, or in immunosuppressed patients in the chronic phase of the disease because there may be exacerbations
In chronic forms there is a low and intermittent degree of parasitemia, so it is usual to indirectly detect the parasite with serological techniques to detect antibodies (ELISA, IFI, IHA). In this phase the anti-T. cruzi IgG antibody titer is elevated. According to the WHO diagnostic criteria, at least two serological tests that use different parasite antigens to establish the diagnosis of infection should be positive.
Tests performed in IVAMI:
- Microscopic examination of peripheral blood samples.
- Blood culture in liquid medium.
- IgG, IgM and/or total antibodies by indirect immunofluorescence.
- Total antibodies by enzyme immunoassay (ELISA).
- Molecular diagnosis (PCR).
- For microscopic exam, culture and molecular diagnosis (PCR): whole blood drawn with EDTA (5 mL).
- For the determination of antibodies: blood (5 mL) or serum (2 mL).
Storage and shipment of the sample:
- Refrigerated (preferred) for less than 2 days.
- Frozen (not for microscopic exam): more than 48 hours.
Schedule for results:
- Microscopic exam: 24 hours
- Culture: 4 to 5 working days
- Molecular diagnosis (PCR): 48 to 72 hours.
- Detection of IgG and/or IgM antibodies: 5 working days.
Cost of the test:
- Microscopic exam: Consult to firstname.lastname@example.org..
- Blood culture in liquid medium: Consult to email@example.com.
- IgG antibodies by indirect immunofluorescence: Consult to firstname.lastname@example.org.
- IgM antibodies by indirect immunofluorescence: Consult to email@example.com.
- Total antibodies by indirect immunofluorescence: Consult to firstname.lastname@example.org.
- Total antibodies by enzyme immunoassay: Consult to email@example.com.
- Molecular diagnosis (PCR): Consult to firstname.lastname@example.org.