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Chagas Disease

Overview

Chagas disease (American trypanosomiasis)is a protozoan infection caused by the parasite, Trypanosoma cruzi. It is endemic to Latin America but has been increasingly detected in the USA, Canada, Western Pacific countries and parts of Europe due to population mobility. Chagas disease infections are estimated to affect between six to seven million people per year, with 12500 cases resulting in death. The disease is curable if treated soon after infection. Without treatment the person remains infected for life which can be fatal as Chagas progressively damages the heart, nervous and digestive systems.

 

Symptoms

Chagas disease is presented in two phases; acute and chronic.

 

The initial acute phase occurs for four to eight weeks after the initial infection, during which, a large number of parasites circulate in the bloodstream. The acute phase can be difficult to diagnose due to mild symptoms similar to those of other diseases, and some patients remain asymptomatic. Acute symptoms can be severe in those who are immunocompromised.

Acute phase symptoms include:

  • Swelling and/or redness at the infection site (chagoma)

  • Romaña sign (unilateral painless oedema of tissue around eye)

  • Fever

  • Vomiting

  • Headache

  • Enlarged lymph glands

  • Muscle pain

  • Fatigue

  • Pallor

After the acute phase, Chagas enters a remission stage where no symptoms of the infection present. Chronic symptoms will develop in 10-30% of those infected after a remission period of ten to twenty years. This period may last a person’s entire life, meaning around 70% of infected people will be unaware they were ever infected.

 

During the chronic phase, the parasites remain mainly in the heart and digestive muscles; hence symptoms vary depending on the organ affected. Symptoms occur due to the persistent presence of the parasites causing irreversible damage to the tissues of these organs and chronic inflammation develops as the body reacts to the parasites. Parasites damage nerve cells and neurons, resulting in electrical conduction changes in the heart and poor muscle tone in the intestines.

Chronic phase symptoms include:

  • Irregular heartbeat

  • Palpitations

  • Fainting

  • Cardiomyopathy

  • Congestive heart failure

  • Dyspnoea

  • Emphysema

  • Stroke

  • Chronic abdominal pain

  • Chronic constipation

  • Dilated colon

  • Difficulty with digestion

  • Difficulty swallowing due to oesophageal inflammation

  • Cardiac arrest

 

Causes

Trypanosoma parasites are transmitted via the urine or faeces of infected triatomine insects, which feed on human blood during the night. Triatomine insects thrive under poor housing conditions such as in the walls and roofs of mud and straw housing, common to the rural areas and urban slums of Latin America. The infected insect bites an exposed area of skin, usually the face, and then defecates on the surrounding or nearby area. Parasites enter the bloodstream when the bitten person accidentally rubs or wipes the faeces into the bite wound. Chagas can also occur via vector-borne transmission through entering mucous membranes such as the conjunctiva or via broken skin or open wounds. Chagas cannot be transmitted from person to person, nor through casual contact with infected people or animals.

 

Less common methods of infection include:

  • Congenital transmission

  • Blood transfusion from an infected donor

  • Organ transplantation from an infected donor

  • Consumption of inadequately cooked food contaminated with infected triatomine faeces (rare)

  • Accidental laboratory exposure

 

Risk factors / at risk groups

Risk groups include those who live in or visit the endemic areas of Latin America, particularly the rural parts. There is an increased risk of infection in persons staying in poor quality housing, as triatomine insects typically inhabit the cracks of walls and ceilings, thatched roofs and dirt floors. Farmers and owners of livestock in Latin America are at high risk due to triatomine insects thriving in chicken coops, pig pens and stables. Children are more prone to scratching bites and hence are at a higher risk for introducing the parasite into the bloodstream. Chronic phase infections are more prevalent in adults and the elderly as the infection has undertaken the remission period.

 

Treatment

Anti-parasitic treatment is indicated for all infections in the acute phase, in reactivated infections, and for chronic infections in children up to the age of 18. Reactivated infections include those due to immunosuppression, infants with congenital infection, and patients during the early chronic phase. To kill the parasite, Chagas disease can be treated with benznidazole or nifurtimox. Both medicines are almost 100% effective in curing the disease if given at the onset of the acute phase, soon after infection. Both medicines have reduced efficacy the longer the person has been infected for. Infected adults, especially those who are asymptomatic, should be offered treatment to prevent or halt disease progression. Treatment is strongly recommended for adults up to 50 years old with chronic infection and absent cardiomyopathy. For adults older than 50, the treatment decision should be individualized. Physicians should consider factors such as age, clinical status, preference, and overall health.

 

The potential benefits of preventing or delaying the development of Chagas disease should be weighed against the long duration of treatment (up to 2 months) and possible adverse reactions (occurring in up to 40% of treated patients). Benznidazole and nifurtimox are both contra-indicated in pregnancy, renal and hepatic impairment. Nifurtimox is also contra-indicated for people with a background of neurological or psychiatric disorders. Specific treatment for cardiac or digestive manifestations may be required if the infected person has entered the chronic phase.

 

Vaccines / preventative measures

There is currently no vaccine for Chagas disease and anti-parasitic treatment has only proven effective in the acute and asymptomatic stages. Prevention is therefore favourable to cure.

Simple preventative measures include:

  • Avoiding staying in poor housing

  • Sealing any faults to prevent infestation

  • Using screens on doors and windows

  • Personal preventative measures such as bed nets

  • Screening of blood and organ donors

  • Screening of newborn babies of infected mothers

  • Maintaining good hygiene practices in food preparation

  • Spraying houses with residual insecticides

  • Checking areas for infestation

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