lunes, 5 de noviembre de 2018

What is Chagas Disease?

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By Ananya Mandal, MDReviewed by Sally Robertson, B.Sc.

Chagas disease or American trypanosomiasis is a disease that is caught from infected triatomine bugs or "kissing bugs". The disease can cause serious damage to the heart and stomach.

Chagas disease is more common in certain regions of the world including Mexico, Central America and South American countries such as Argentina, Bolivia, Brazil, Chile, Costa Rica, El Salvador, Ecuador, Colombia, and Venezuela.

Cause and transmission of Chagas disease

The infection is transmitted through the bite of a triatomine bug that has been infected with the protozoan parasite Trypanosoma cruzi.. The strains of T.cruzi are mostly divided into two categories, T. cruzi I and T. cruzi II. These are then further subdivided into T.cruzi Ia, Ib etc.

When the triatomine insect feeds on the blood of a mammal infected with T. cruzi, it ingests extracellular nondividing forms of the parasites called trypomastigotes. After several weeks, these develop into infective metacyclic trypomastigotes.

After the insect bites a human and feeds, it defecates on the skin and releases these trypomastigotes which can then enter the blood stream by passing through mucous membranes or cracks in the skin.

The bite may itch and scratching the site can lead to transmission of the parasite through tiny skin abrasions. The infection can also spread from a mother to her unborn baby, through blood transfusion when contaminated or infected blood is administered or through transplant of an infected organ.

Symptoms of Chagas disease

Chagas disease has an incubation period of around 5 to 14 days before symptoms start to manifest. In the initial few weeks or months after being bitten, a person may develop a mild fever with body ache and swelling at the site of the bite called a chagoma.

Other symptoms that may manifest include fatigue, rash, headache, nausea, diarrhea, vomiting, enlargement of the spleen and swollen glands.

However, this phase of the disease can be symptomless and it often passes without causing long-term complications and without requiring treatment. Some individuals, however, may develop long-term consequences of the infection and these can be severe and sometimes life threatening.

It may take 5 to 40 years for these symptoms to manifest. The symptoms of this later phase include:

Irregular heartbeat that may lead to sudden cardiac arrest or sudden death
Heart failure
Enlarged heart that is unable to pump blood efficiently
Stroke
Problems with the digestive system such as enlargement of the food pipe (esophagus) or colon.

Diagnosis and treatment

Chagas disease can be diagnosed through isolation of the parasite in blood and examination under a microscope. Tissues, blood or cerebrospinal fluid samples are stained with Giemsa or Wright stain and examined under the microscope. T. cruzi may be detected in the heart, skeletal and smooth muscle cells as well as in cells of the nervous system.

The parasite is also sometimes detected in the chagomas that develop. Thick or thin blood smears can be examined under the microscope but the parasite can be viewed more clearly in thin smears. The parasite may also be cultured and grown from blood or tissues, which may take 1 to 6 months.

In long term cases, serology is usually used to diagnose infection. The most commonly used tests include indirect immunofluorescence (IFA), enzyme-linked immunosorbent assays (ELISAs) and hemagglutination. Polymerase chain reaction (PCR) and Western blotting may also be used.

Patients with acute Chagas disease may be treated with antiparasitic agents. Patients with chronic disease may have cardiomyopathy, heart failure or an enlargement in the digestive system that may require surgical treatment.

There are no available vaccines against Chagas disease. Precautions may be taken to reduce the risk of infection by preventing bites. The kissing bugs usually feed at night and therefore adequate protection should be used at night. Wearing long-sleeved shirts and trousers and using bed nets and insect repellents, for example, is recommended. Any blood or organ donations need to be screened to prevent transmission.