Latin America: Many mammals including humans can be infected with Chagas Disease

Reported from promedmail.org – American trypanosomiasis (Chagas disease) is an important cause of heart disease, megaesophagus, and megacolon among people in Mexico, Central and South America. Many mammals can be infected with the parasite that causes this disease; however, among animals, clinical cases have been reported mainly in dogs. Chagas disease is transmitted by the bite of triatomine insects, or “kissing bugs.” Some infected insects occur in sylvatic environments, where humans are exposed only occasionally. These “sylvatic cycles” are found from the US through South America. From Mexico through South America, triatomine insects have also become adapted to human dwellings, particularly substandard housing where the insects hide in cracks during the day and emerge to feed on humans and animals at night. Most human cases are acquired from insects in these “domestic cycles,” and campaigns to eliminate the bugs, together with testing to prevent congenital cases and transmission in blood transfusions, have significantly reduced the incidence of Chagas disease. Antiparasitic treatment is most effective early, before irreversible damage occurs to the heart or gastrointestinal tract.

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Chagas disease results from infection with the protozoan parasite _Trypanosoma cruzi_, a member of the family Trypanosomatidae. Most strains of this parasite can be classified into 2 major groups, _T. cruzi_ I and _T. cruzi_ II, which can be separated further into various lineages (eg, _T. cruzi_ IIa). Lineages tend to be associated with certain host species, although this relationship is not absolute.

Chagas disease is a vector-borne disease transmitted primarily by triatomine insects, which are also called reduviid insects, “kissing beetles/bugs,” or “assassin bugs.” More than 130 species of these insects appear to be capable of transmitting _T. cruzi_, with the most important species in the genera _Triatoma_, _Rhodnius_, and _Panstrongylus_. The parasite usually completes its life cycle by cycling between an insect species and a mammalian species with which the insect lives in close association. The mammalian hosts include wildlife, domesticated animals, and humans.

_Trypanosoma cruzi_ occurs in more than 100 species of mammals throughout the Americas; infections have been reported among carnivores including dogs and cats, as well as in pigs, goats, lagomorphs, rodents, marsupials, bats, xenarthra (anteaters, armadillos, and sloths) and non-human primates. In the US, opossums, armadillos, raccoons, coyotes, rats, mice, squirrels, dogs, and cats are among the most frequent hosts. Birds, reptiles, and fish are not susceptible to infection.

The incubation period for acute disease in dogs appears to be 5 to 42 days; in experimental infections, symptoms of acute heart disease are usually reported after 2 to 4 weeks. Like humans, some dogs may not develop clinical signs until the chronic stage, which occurs after a few years; the exact length of this period is not known.

Dogs
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Acute, latent, and chronic stages of infection occur in experimentally infected dogs. Clinical signs reported in the acute stage include fever, anorexia, lethargy, an unkempt hair coat, lymphadenopathy, hepatomegaly, and splenomegaly. Anorexia, diarrhea, ascites, and/or weight loss may also be seen. Some dogs may have palpebral edema. Chagomas appear to be rare, but they have been reported in a few dogs inoculated with a South American strain of _T. cruzi_. Cardiac dysfunction can occur during the acute phase; acute myocarditis may cause arrhythmias or sudden collapse and death. After the acute phase, infected dogs enter the indeterminate (latent) stage, during which the parasites are difficult to find and the animal is asymptomatic. The indeterminate stage can be as short as 27 days in some experimentally infected animals, but it seems to last for years in some natural infections. Congestive heart failure is the most common sign during the chronic stage. Right-sided heart failure usually occurs first. Eventually, dogs with heart disease develop chronic myocarditis with cardiac dilatation and arrhythmias. Sudden death can occur.

Chagas disease is not contagious during casual contact, but the parasite can be transmitted in blood or by contact with tissues. Carnivores can be infected if they eat _T. cruzi_-contaminated tissues. Many species of animals, including dogs, can serve as amplifying hosts, and infect the insect vectors. Vertical transmission can also occur in some animals.

Chagas disease can be diagnosed by microscopy, isolation of the parasite, serology, and molecular techniques.

Occasionally, dogs have been treated with anti-parasitic drugs. These drugs appear to be more effective in the early stages; by the time of diagnosis, treatment may be too late to prevent the progression of the disease.

Dogs and cats should not be allowed to eat tissues from potentially infected wild animals. Strict indoor housing in well-constructed homes or other facilities reduces the risk of infection. Housing animals indoors at night, when triatomine insects are active, may also be helpful. Residual insecticides sprayed regularly in kennels and surrounding structures may decrease the number of insect vectors. In breeding kennels, testing bitches for _T. cruzi_ might also decrease the incidence of Chagas disease by reducing vertical transmission. No vaccines are available.

The disease has been known in Texas for over 25 years. However, there is an increased awareness of it now, as well as better tools for diagnosis. Consequently, we may have had the disease in Texas at higher levels than were previously recognized. Now with improved tools providing more accurate and more rapid testing, an increase in diagnoses is expected.

Portions of this comment have been extracted from http://www.cfsph.iastate.edu/Factsheets/pdfs/trypanosomiasis_american.pdf

Photos of triatomine bugs may be found at http://www.cals.ncsu.edu/course/ent425/text18/humanvectors.html and http://www.cdc.gov/parasites/chagas/gen_info/vectors/triatomine_stages_lg.html. – Mod.TG

The life cycle of the parasite can be seen at http://www.dpd.cdc.gov/dpdx/HTML/TrypanosomiasisAmerican.htm. – Sr.Tech.Ed.MJ]
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