Forgotten People, Forgotten Diseases by Peter J. Hotez

Author:Peter J. Hotez
Language: eng
Format: epub
ISBN: 9781555818746
Publisher: Wiley
Published: 2013-11-05T00:00:00+00:00

Figure 7.7Triatomine bug, Rhodnius prolixus. (Courtesy of Erwin Huebner, University of Manitoba, Winnipeg, Canada.)

The possibility that the triatomine bug could transmit American trypanosomiasis was demonstrated by Carlos Chagas. As a young physician and a member of one of Brazil’s first biomedical research institutes, the Institute of Experimental Pathology of Manguinhos (later named Instituto Oswaldo Cruz and now a major component of FIOCRUZ [the Oswaldo Cruz Foundation], Brazil’s largest and most extensive biomedical and research organization devoted to infectious diseases and other conditions), Chagas had developed a reputation for his ability to organize and lead antimalaria campaigns in the interior of the country.20 While he was on assignment, a railway company engineer brought to the young Chagas’s attention the vinchucas inhabiting the poor dwellings of the region and their nocturnal biting behavior. Chagas began to examine vinchucas and identified trypanosomes, which he named in honor of Oswaldo Cruz, his institute director.20 He subsequently found a trypanosome in the blood of a 22-month- old girl named Bernice who was suffering from fever with enlargement of the liver, spleen, and lymph nodes, as well as facial edema (swelling of the face). He also identified the trypanosomes in a cat that lived in the same house. Ultimately, Bernice recovered from her acute illness, and 52 years later (27 years after the death of Chagas), Bernice was rediscovered as a grandmother of three living on a farm in Minas Gerais State. Blood tests conducted at a major university teaching hospital at that time subsequently confirmed a diagnosis of Chagas disease. Bernice ultimately died in 1981 at the age of 73.20

Humans become infected with T. cruzi in an interesting way (Fig. 7.8). Unlike metacyclic African trypanosomes, which live in the insect salivary glands and enter through a bite, the metacyclic American trypanosome lives in the hindgut of the triatomine bug. While working in Brazil around the same time as Chagas, the eminent French parasitologist Emile Brumpt demonstrated that T. cruzi infection first occurs by the process of autoinoculation. This transmission phenomenon occurs when the triatomine bug defecates as it feeds; during sleep, the unsuspecting victim of the assassin bug rubs the trypanosome-infected bug feces into either the puncture wound caused by the bug or the mucous membranes of the eyes or mouth. Once the metacyclic trypanosomes invade the mucous membranes, they continue to behave quite differently from T. brucei. Rather than invade the bloodstream immediately and multiply as the trypomastigote form, the metacyclic T. cruzi trypomastigotes exhibit the ability to invade cells and multiply as intracellular pathogens.27 Initially, this stage of invasion results in inflammation near the site of entry, causing swelling around the eye and face (known as Romana’s sign) or some other region of the skin, where it is known as a chagoma. Once inside cells, the parasite replicates as a rounded, so-called amastigote form, but subsequently the cells burst and release of a new round of trypomastigote forms of the parasite, which then invade the bloodstream before besieging multiple organs. Initially, organ invasion

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