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Superorder Xenarthra

Xenarthrans were previously classified in an order termed Edentata, found to be polyphyletic and that also included ant-eating Pangolins. With the reclassification of the latter to the Pholidota order, the orders Cingulata (armadillos) and Pilosa

(anteaters and sloths) were classified together in the superorder Xenarthra (odd joints). Xenarthra display fascinating biological peculiarities such as fused pelvic bones, spine reinforcing bones, and a peculiar blood vessel structure that allows energy sparing by an extremely low metabolic rate. These adaptations did not prevent a massive extinction of a huge number of representatives of this taxon so that the current extant genera represent only a minor part of those found in the Tertiary. In modern times the specific niche destruction due to human action certainly contributed, but the overall causes of this massive extinction are still under debate.

Armadillos, sloths, and anteaters, currently the main representatives of this superorder, have a long coevolutionary history with trypanosomatids. So, besides the bizarre genus Endotrypanum, sloths may harbor several Leishmania and Trypanosoma species.35 These mammals represent, beside marsupials, ancient hosts of T. cruzi. The first description of a wild reservoir of this parasite was made by Carlos Chagas, in 1912, when he found tripomastigote forms similar to Trypanosoma cruzi in the wild nine-banded armadillo Dasypus novemcinctus, which he classified as a “depository of the agent of Brazilian trypanosomiasis in the outside world.”36 This definition of Carlos Chagas shows clearly what was understood at that time as a reservoir. The term “depository” means preservation and not a living dynamic system that exerts and undergoes selective pressures all the time. In its underground refuges, armadillos are usually associated with triatomines from the Panstrongylus genus and some studies suggest an association between this mammalian host and the parasite DTU TcII—TcVI (currently nomenclature).18 Nevertheless, these animals have also been found infected with DTU TcI, showing its putative importance in the maintenance of distinct transmission cycles in nature.33,37

Armadillos are widely distributed and found infected by T. cruzi in a prevalence of infection that ranges from 4% to 50%, from the southern United States to Uruguay. In Louisiana, USA, infection by T. cruzi was detected in 26% of 80 armadillos.38 In the same state, but in another region, only 3.9% of 415 D. novemcinctus were infected.39 In a retrospective study conducted in French Guiana, Dasypus novemcinctus were identified as an important reservoir of Trypanosoma cruzi, following Didelphis marsu- pialis40 Other species found to be infected by Trypanosoma cruzi are Cabassous unicinctus, Chaetophractus vellorosous, Tolypeutes matacus, and Euphractus sexcinc- tus41 (Fig. 11.2). It is worth mentioning that, in rural areas, E. sexcinctus regularly invade chicken facilities to prey on eggs and/or chicks. This behavior favors the nearness of this armadillo species with peridomestic areas, where it can be a source of infection for triatomine bugs that nest there.

Concerning the arboreal xenarthrans, sloths are usually associated to triatomines from the genera Belminus, Panstrongylus, and Rhodnius42 and some sloth species, such as the three-toed sloth (Bradypus torquatus) have been found naturally infected.22 Two different species of anteaters, the lesser anteater (Tamandua tetradactyla) and the silky anteater (Cyclops didactylus) have also been considered natural hosts of Trypanosoma cruzi.18,43 It is worth mentioning that one Tamandua tetradactyla found infected by Trypanosoma cruzi in Para State, Brazil, showed a mixed infection with two other trypanosomatids, Trypanosoma rangeli and Leishmania infantum.44

Armadillo Euphractus sexcinctus from Axixa, Brazil. Photo

Figure 11.2 Armadillo Euphractus sexcinctus from Axixa, Brazil. Photo: Ana Maria Jansen.

The epidemiological importance of these mammalian species is enhanced as sloths, anteaters, and armadillos are hunted and eaten in some areas of South America, such as the Amazon region. The careless handling of the carcass or the ingestion of undercooked meat from infected animals can be a source of T. cruzi infection for humans.

 
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