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Author: Marie Hartley, Staff Writer, 2009.
The protozoa Trypanosoma is responsible for two distinct diseases in humans.T. cruzi causes American trypanosomiasis, also known as Chagas disease, and is found predominantly in the tropical Americas (described on this page). T. brucei causes Human African trypanosomiasis, also known as sleeping sickness, in Africa, and is described elsewhere.
American trypanosomiasis or Chagas disease is caused by the protozoan parasite Trypanosoma cruzi, which is transmitted to humans via insect vectors called triatomine bugs (also known as reduviid or kissing bugs). These blood-sucking insects get infected by biting an infected human or other mammal. Once infected the insect bites other humans and mammals and deposits parasite-laden faeces near the wound. The parasites enter the body via contact with mucosal surfaces, conjunctivas, or breaks in the skin. Less common routes of transmission of American trypanosomiasis are:
T. cruzi infection is endemic (i.e. constantly present with low levels of infection) throughout most of the Americas and is a leading cause of parasitic death in Latin America. Among the Americas, there are nearly 20 million persons with Chagas disease, most of who do not know they are infected. If untreated, infection is life-long.
Chagas disease has an acute phase and a chronic latent stage that may result in heart or gastrointestinal disease.
The acute phase lasts for the first few weeks or months. Because it is often asymptomatic or mimics other common viral illnesses, acute Chagas disease may go undetected. Symptoms include:
|Dermatological manifestations of acute Chagas disease|
|Chagomas||Skin lesions (called chagomas) are sometimes seen when T. cruzi enters the patient through a break in the skin. Chagomas are boil-like, indurated (hardened), violet lesions with central oedema (swelling) that may persist for several weeks. Chagomas may be accompanied by swollen lymph nodes.|
|Romaña sign||If the parasites enter via the conjunctivae (e.g. by the patient accidentally rubbing triatomine insect faeces into their eye), an eyelid swelling, known as the Romaña sign, may form. This is a painless swelling of the upper and lower eyelid of the affected eye, with accompanying conjunctivitis. The Romaña sign may persist for several weeks and be accompanied by swollen lymph nodes. The inflammation and infection can also spread to the skin around the eye (periorbital cellulitis) and produce metastatic (spreading) chagomas. The Romaña sign is a classic sign of acute Chagas disease, but develops in few newly infected persons.|
|Schizotripanides||This is a transient, non-itchy skin rash that resembles the rash of measles.|
Following the acute phase, the infection may remain silent for decades or even for life (known as the indeterminate stage of Chagas disease). These people are still infected with T. cruzi and are capable of transmitting it to others. Approximately 30% of infected people will develop chronic symptoms after a latency period of 10 to 30 years. In people who have impaired immunity (for example, due to AIDS or chemotherapy), Chagas disease can reactivate.
Chronic Chagas disease causes cardiac and gastrointestinal disease:
Various methods can be used to diagnose Chagas disease depending on the stage of the disease.
Acute Chagas disease
The diagnosis of acute Chagas disease is based on direct detection of the parasites in the blood e.g. centrifugation blood culture, thick and thin blood smears, and direct light microscopy.
Indeterminate and chronic Chagas disease
Few parasites circulate in the blood in this phase of the disease. Therefore methods such as ELISA (enzyme-linked immunosorbant assay to detect antibodies) are most helpful.
Any stage of Chagas disease
There are two approaches to therapy of Chagas disease: antiparasitic treatment and symptomatic treatment.
Antiparasitic treatment is most effective when given early, however acute Chagas disease often goes undetected. Two antiparasitic agents are currently recommended, nifurtimox or benznidazole (neither of which are registered in New Zealand). All patients with acute Chagas disease and those with reactivated infection due to impaired immunity should receive antiparasitic treatment. Children with indeterminate-phase Chagas disease may also benefit from antiparasitic treatment. It is thought that adults with long-standing indeterminate-phase disease are unlikely to benefit from antiparasitic treatment, although more scientific studies are needed. Antiparasitic medications have significant side effects and offer no benefits in patients with established cardiac or gastrointestinal complications of chronic Chagas disease.
Symptom-specific supportive measures are used to treat chronic disease, such as:
Vaccines against T. cruzi are still being researched and are not yet available
Triatomine insects infest poor-quality dwellings and are most active at night. Travellers who sleep indoors, in well-constructed facilities (e.g. air-conditioned or screened hotel rooms) are at low risk of exposure and infection.
Travellers should be aware of bloodborne and foodborne routes of transmission
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