Chaga's Disease, American Trypanosomiasis

Chaga's disease is caused by infection with a protozoa of the genus Trypanosoma, which affect all domestic animals. Domestic animals can be a source of human infection. The disease occurs in Central and South America and some areas of southern United State. Chaga's disease is the most important parasitic infection in Latin America. Eighteen million people are currently infected, with up to 100 million at risk of the disease. It is caused by Trypanosoma cruzi and is characterized-in its chronic stage-by extensive myocarditis, cardiac arrhythmia, and ultimately death. The parasite multiplies inside cells, particularly of heart and smooth muscle. Congenital infection occurs in a small proportion of newborns from infected mothers. Dogs are mostly infected by blood-sucking insects, such as Triatoma infestans, a nocturnal predator.

Trypanosoma cruzi is a protozoan species from the same genus that produces cardiac disease in dogs and is a significant veterinary problem from Argentina north to the southwest United States. Dogs are domestic reservoir hosts of Trypanosoma cruzi. Although T. cruzi may be transmitted by a range of triatomine bug species, cats and dogs have consistently been shown to be the main domestic reservoir throughout the range of Chaga's disease. Elimination of infected dogs from a household with infected people could be sufficient to almost extinguish transmission of T. cruzi, barring reintroduction of infected dogs or bugs.

Signs of American Trypanosomiasis

Affected dogs may die suddenly or have long- or short-term inflammation of the heart muscle. Two clinical forms of the disease are recognized, acute and chronic. During the acute stage pathological damage is related to the presence of the parasite, whereas in the chronic stage few parasites are found.

Diagnosis of American Trypanosomiasis

In most areas where Chaga's disease is present, the diagnosis of T. cruzi infection in humans or domestic animals relies on ELISA and IFAT tests. The diagnosis and treatment of this infection are active areas of investigation. New serological and molecular biological techniques have improved the diagnosis of chronic infection.

Treatment of American Trypanosomiasis

Current therapy for Chaga's disease is not always effective and is limited by frequent and severe side effects. In one study, the effect of deltamethrin-treated dog collars (DTDCs) were evaluated over time on the population dynamics of Triatoma infestans, a main T. cruzi insect that transmits the protozoan infection. Bugs exposed to dogs wearing those collars became extinct 77-196 days after study initiation. Even a single exposure of bugs to dogs wearing deltamethrin-treated dog collars (DTDCs) significantly reduced feeding success of triatomine bugs. Thus, DTDCs could represent a novel tool to prevent and control canine and (hence) human Chaga's disease. Tested collars could not only be a potential tool to prevent Chaga's disease in endemic areas of human disease but also in areas where human disease is scarce and Chaga's disease is mainly of veterinary importance (e.g., in the United States, where canine T. cruzi infections are regularly reported. Deltamethrin-treated collars have also been shown to protect dogs from sand flies and zoonotic .

Deltamethrin is a comparatively safe insecticide, with reportedly few systemic side effects that are usually reversible (e.g., neuroexcitation, gastroenteritis). It is heavily used in agriculture and public health to control crop pests or insect vectors of disease, and the consensus is that the gain in reduction of disease morbidity and mortality caused by its use outweigh the potential adverse events experienced by people exposed to it. As with any potentially toxic product, care should be taken to minimize required contact (e.g., not letting young children play with the collar, touch it, or put it in their mouth).

Chaga's Disease in Humans

Chagas disease can be mild in the acute stages: the victim might not realize they have been infected. Often the only irritation is the bite mark of the vector, and typical symptoms are indistinguishable from those of other conditions. But, like many parasitic infections, Chagas disease lingers. In around one-third of those infected, the disease resurfaces in a chronic manifestation often decades after the acute stage, with devastating consequences.³

Infection occurs when an infected reduvid bug (also called kissing bug) bites a human. At the time of the bite, the insect excretes trypomastigotes of T. cruzi. As the saliva of the insect is irritating, the human will commonly scratch or rub the bite site, thereby introducing the trypomastigotes into the lesion. Once introduced, the trypomastigotes circulate throughout the body with a preference for invading muscle cells, neural tissue, and the reticuloendothelial system. Once intracellular, the trypomastigote divides to become an amastigote which, in turn, continues to divide, ultimately leading to the destruction of the cell with release of amastigotes and trypomastigotes. The T. cruzi life cycle is completed with the ingestion of trypomastigotes during a blood meal by the reduvid bug.

Once introduced to the body, T. cruzi may cause a nodule called chagoma. If the initial bite is near the orbit of the eye, the patient may experience significant inflammation and swelling (edema, or Romana's sign), with the chagoma lasting several months. This is a hallmark clue to the identification of Chaga's disease. The edema is painless and is frequently followed by symptoms of fever, malaise, and loss of appetite. While there are no long-term symptoms developing as a consequence of the Romana's sign, there are a number of potentially severe complications of chronic Chaga's disease, including cardiomyopathy, enlarged esophagus, and enlarged colon.

Diagnosis of acute Chaga's disease is made by the detection of trypomastigotes in the bloodstream by direct examination of uncoagulated blood. Likewise, trypomastigotes and amastigotes may be demonstrated on aspiration near the site of initial bite or chagoma. The feces are then examined for the presence of trypomastigotes 10 to 20 days later. Serologic testing is of little value in the diagnosis of acute Chaga's disease as antibodies do not usually appear for 2 to 40 days following the onset of symptoms.

Treatment of Chaga's Disease

Therapy of Chaga's disease with antitrypanosome therapy is most successful in the acute stage. Two medications are available: nifurtimox and benznidazole. Therapy is usually extended for a period of months, and cure rates are somewhat disappointing. Both medications carry a long list of significant side effects.

References:
1. Extinction of experimental Triatoma infestans populations following continuous exposure to dogs wearing deltamethrin-treated collars by R. Reitinger, L. Ceballos, R. Stariolo, C. R. Davies, and R. E. Gurtler 2. Fungal and Parasitic Infections of the Eye by Stephen A. Klotz, Christopher C. Penn, Gerald J. Negvesky, and Salim I. Butrus
3. Chagas disease. Michelle Grayson. In: Nature Volume 465, Page S3, Date published 24 June 2010, DOI: doi:10.1038/465S3a