Overview:

Today’s lecture revolves around the discussion of Chagas disease, signs and symptoms, its manifestations and treatment.

Chagas disease is an infectious disease caused by Trypanosoma cruzi, a parasite transmitted through the bite of Reduviid bug. The parasite is present in the feces of the bug.

Chagas disease is predominantly found in South America, Central America, and Mexico. The Reduviid bugs hide in the crevices of the walls and roof during the day and come out at night to feed on the sleeping host.

Most of the people who are infected with Trypanosoma cruzi don’t even know that they are infected. This disease is not transmitted from person to person like a number of contagious diseases.

There are two phases of Chagas disease; acute and chronic. The acute phase may last for a few weeks or even months while the chronic phase can continue for decades or for the entirety of someone’s lifetime.

An infected person may be asymptomatic or may present with a number of symptoms ranging from fever, fatigue, rash, body aches, cardiac complications or gastrointestinal complications.

Treatment of Chagas disease involves getting rid of the parasite in acute infection or managing signs and symptoms in chronic phases. Steps should be taken to prevent the infection too. When left untreated, Chagas disease can lead to chronic lifelong and sometimes life-threatening manifestations.

 

Trypanosoma Cruzi (the culprit of Chagas disease) :

Before moving on to the detailed discussion about Chagas disease, let us first go through the life cycle of Trypanosoma cruzi.

Trypanosoma cruzi is a protozoan that can live in humans, mammals and Reduviid bug (whose nickname is “kissing bug”.)

 

Trypanosoma cruzi circulates in the blood of infected mammals in the form of   “trypomastigotes”.  When Reduviid bug bites and feeds on the infected mammal’s blood, it ingests the parasite. This parasite then subsequently matures in the bug’s intestine before being eliminated in its feces. When the bug bites the next mammal, the bug generally defecates near the site of the bite, allowing trypomastigotes in the feces to enter the host through a wound, intact skin or mucous membrane. Once the parasite gains entry into the host, it develops into an intracellular form called “amastigote”. The amastigote then multiplies producing trypomastigotes which are released in circulation, thus infecting other cells and tissues.

This was briefly the life cycle of Trypanosoma cruzi parasite, now we continue with our discussion of Chagas disease.

 

Risk factors

There are several risk factors that increase the risk of transmission of the parasite. Some of the risk factors which increase the incidence of Chagas disease are described below:

  • Living in an area that contains the bug
  • Living in poor housing conditions e.g mud walls, thatched roofs, adobe huts in parts of the country residing the bug
  • Infection can also occur through infected transplanted organ
  • Transfusion of contaminated blood products
  • Vertical transmission from mother to child may also occur
  • And very rarely as a result of laboratory accident or contaminated food or drink

Signs and symptoms

Chagas disease has an acute phase and a chronic phase as mentioned earlier. Symptoms range from mild to severe or the person might even not be aware of the symptoms at all.

Acute phase

The acute phase lasts for the first few weeks or months of infection. The clinical features of acute phase include:

  • Fever
  • Fatigue
  • Body aches
  • Muscle pain
  • Headache
  • Rash
  • Loss of appetite
  • Diarrhea
  • Nausea
  • Vomiting
  • Mild enlargement of liver or spleen
  • Swollen glands
  • Swelling at the site of the bite

Clinical features presented in this phase may go away but if left untreated, the infection persists and may progress to the chronic phase.

Chronic phase

The chronic phase of Chagas disease may continue for 10-20 years or even for the lifetime of a person. In severe cases, the chronic phase may present with:

  • Irregular heartbeat
  • Congestive heart failure due to dilated heart
  • Sudden cardiac arrest
  • Difficulty swallowing due to the dilated esophagus
  • Abdominal pain or constipation due to dilated colon

Chronic “indeterminate” phase

Along with the above-mentioned phases of Chagas disease, some of the infected people, following the acute phase of infection enter into an asymptomatic phase, known as chronic “indeterminate” phase. In this phase, few or no parasites are found in the blood.

Most of the people are thus unaware of their infection as they are asymptomatic. Among them, many people remain asymptomatic throughout their lives but some may progress to develop the complications of chronic Chagas disease.

Having mentioned the clinical features of Chagas disease let us understand the pathophysiology of this disease.

 

Pathophysiology of Chagas disease :

The main event destroying the peace in Chagas disease is the inflammatory process occurring as a response to the parasite.

Dilated cardiomyopathy, the principal cardiomyopathy of Chagas disease starts with inflammation. Following inflammation, cellular damage occurs. The body attempts to recover from the cellular damage by causing fibrosis of cardiac tissue.

Conduction abnormalities also accompany Trypanosoma cruzi infection. The inflammatory and non-inflammatory response of the heart leads to parasympathetic denervation of cardiac tissues.

Cardiac manifestations may cause death in a person by producing arrhythmias, stasis of blood with embolism in a dilated heart, thrombi affecting several organs, or sudden cardiac death due to severe cardiac failure.

Parasympathetic denervation due to inflammation also occurs in esophagus and colon. The esophagus is dilated because of loss of parasympathetic innervation (known as “megaesophagus”) and thus leading to swallowing difficulty. Dilation of the colon (known as “megacolon”) leads to abdominal pain and constipation producing complications of Chagas disease. 

 

Diagnosis :

After the host comes in contact with the feces of Reduviid bug, the incubation period of infection is about 5-14 days. Tests are used to diagnose a patient to begin treatment and prevent complications from occurring and include the following:

  • Microscopic examination:

During the acute phase of infection, parasites may be seen circulating in the blood. Thick and thin blood smears stained with Giemsa stain are used for direct visualization of parasites.

  • Immunoassays:

Test including complement fixation, indirect haemagglutination, indirect fluorescence assays, radioimmunoassays, ELISA and polymerase chain reaction (PCR) can be used to differentiate between the different strains of Trypanosoma. These immunoassays are usually used for the diagnosis of chronic Chagas disease.

 

Treatment :

Treatment is recommended for patients diagnosed early in the course of their disease (acute phase), babies with congenital infection (through vertical transmission), patients with reduced immunity (due to increased risk of aggressive disease) and many patients with chronic infection.

Two approaches are used to treat Chagas disease; antiparasitic treatment (to kill the parasite) and symptomatic management (to manage the signs and symptoms of infection).

  • Medications:

Antiparasitic medications are usually effective early in the course of the disease. Drugs of choice include azole or nitro derivatives such as benznidazole or nifurtimox. The parasitological cure of these drugs is high in children and low in adults. The reason might be the resistance of drugs or longer periods of infection in adults.

  • Symptomatic management:

Symptomatic management involves managing the clinical features of the disease. For example for irregular heartbeats, pacemaker or medications may be used. Surgical procedures like subtotal colectomy are used to manage megacolon. Similarly, surgical procedures can also be used for the treatment of megaesophagus.

 

Prevention and Control :

No vaccines are available against Trypanosoma cruzi. Certain preventive measures that can be used in high-risk areas include:

  • Vector control by using insecticides to remove bugs from the residence
  • Insect repellent sprays or lotions can be used on exposed skin
  • Wearing protective clothing
  • Avoid sleeping in mud, thatch or adobe house
  • Screening of blood donations to prevent the spread of disease through blood transfusion

Control strategies are directed towards transmission prevention through organ donation, blood donation, and mother to child transmission.

 

References :

  1. First Aid for USMLE Step-1
  2. Robbins and Cotran Pathological basis of disease
  3. http://www.infochagas.org/en_GB/ciclo-de-vida-del-parasito
  4. https://en.wikipedia.org/wiki/Trypanosoma_cruzi
  5. https://www.cdc.gov/parasites/chagas/diagnosis.html
  6. https://www.mayoclinic.org/diseases-conditions/chagas-disease/symptoms-causes/syc-20356212
  7. https://en.wikipedia.org/wiki/Chagas_disease