Chagas Disease, American Trypanosomiasis

Chagas dChagasisease is infection with the protozoan parasite Trypanosoma cruzi that affects all domestic animals. It is named after the Brazilian physician Carlos Chagas, who discovered the parasite. The disease occurs in Central and South America and some areas of southern United State. Texas is a high-risk state for transmission of T. cruzi to dogs and shelter dogs have widespread exposure to T. cruzi across 7 ecologic regions in Texas. Domestic animals can be a source of human infection. Chagas disease is the most important zoonotic parasitic infection in Latin America. Eighteen million people are currently infected, with up to 100 million at risk of the disease. In its chronic stage the disease is characterized by extensive myocarditis, cardiac arrhythmia, and ultimately death. Affected dogs may die suddenly or have long- or short-term inflammation of the heart muscle.

Dogs are domestic reservoir hosts of Trypanosoma cruzi. Although T. cruzi may be transmitted to humans by a range of triatomine bug species, cats and dogs have consistently been shown to be the main domestic reservoir throughout the range of Chagas 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.



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. In most areas where Chagas disease is present, the diagnosis of T. cruzi infection in humans or domestic animals relies on ELISA and IFAT tests. Current therapy for Chagas 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 on Triatoma infestans, a main T. cruzi insect vector that transmits the 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 significantly reduced feeding success of triatomine bugs. Thus, DTDCs could represent a tool to prevent and control canine and human Chagas disease. Tested collars could not only be a potential tool to prevent Chagas disease in endemic areas of human disease but also in areas where human disease is scarce and Chagas 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 leishmaniasis. Deltamethrin is a comparatively safe insecticide, with reportedly few systemic side effects that are usually reversible. 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 mortality caused by its use outweigh the potential adverse effects experienced by people exposed to it. As with any potentially toxic product, care should be taken to minimize required contact by not letting young children play with the collar, touch it, or put it in their mouth.

Kissing bug, the vector of Chagas Disease or American Trypanosomiasis
Kissing bug, the vector of Chagas Disease or American Trypanosomiasis
Source: CDC

Chagas Disease In Humans

Chagas disease, an infection with the parasite Trypanosoma cruzi, is increasingly diagnosed among humans in the southern United States. Estimates of human infection range from 300,000 to >1 million. The parasite can be passed through consumption of infected bugs or contaminated food products, through blood transfusions, and congenitally. The 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. If the initial bite is near the orbit of the eye, the patient may experience significant edema (swelling) and inflammation (Romana's sign), with the chagoma lasting several months. This is a hallmark clue to the identification of Chagas 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 Chagas disease, including cardiomyopathy, enlarged esophagus, and enlarged colon.

Diagnosis of acute Chagas 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 Chagas disease as antibodies do not usually appear for 2 to 40 days following the onset of symptoms. Therapy of Chagas 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. No vaccine is available for humans or dogs.

References

  1. R. Reitinger, L. Ceballos, R. Stariolo, C. R. Davies, and R. E. Gurtler. Extinction of experimental Triatoma infestans populations following continuous exposure to dogs wearing deltamethrin-treated collars
  2. Stephen A. Klotz, Christopher C. Penn, Gerald J. Negvesky, and Salim I. Butrus. Fungal and Parasitic Infections of the Eye
  3. Chagas disease
  4. Shelter Dogs as Sentinels for Trypanosoma cruzi Transmission across Texas




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