Abstract. The role of reinfection in the evolution of Chagas' disease was evaluated in dogs alternately infected with the 147 and SC-1 strains of Trypanosoma cruzi. A parasitologic, serologic, clinical, and electrocardiographic follow-up was carried out on the infected and noninfected dogs. The dogs were reinfected five times over a period of 38 months. No deaths were observed during the experiment. They presented a brief oligosymptomatic acute phase. The level of parasitemia decreased progressively with the number of reinfections. Bloodstream parasites were not detectable after the fifth reinfection. All parasite samples isolated during the follow-up were zymodeme B, corresponding to strain 147, irrespective of the strain with which the dogs were first infected and of the triatomine species used for isolation. Conversely, amplification by the polymerase chain reaction of a segment of the T. cruzi mini-exon gene showed the simultaneous presence of both strains in three of the eight reinfected animals. Antibody titers were greater among the dogs successively infected than those infected only once. Neither amastigotes nor T. cruzi DNA were detected in the tissues of the infected dogs. Alterations related to Chagas' disease were identified only in the heart and consisted of chronic focal and discrete myocarditis, compatible with the indeterminate form of Chagas' disease. All infected dogs developed this form of the disease, which was independent of the number of infections.

A morphometric study of the circular colon musculature was performed, in which the mast cell count was determined and the connective fibrous tissue in this layer was measured. The objective was to gain better understanding of Chagas megacolon morphology and contribute towards the knowledge of fibrosis pathogenesis in Chagas megas. An evaluation was made of 15 distal sigmoid rings from Chagas patients with megacolon (MCC), 15 without megacolon (CSMC) and 15 non-Chagas patients (NC). The rings were fixed in formol, embedded in paraffin, and 7mm thick sections were cut and stained using Azan-Heidenhain and Giemsa. The mast cell count and fibrosis were greater in the MCC group than in the CSMC and NC groups (p < 0.05; Kruskal-Wallis test) and there was no significant difference between the latter two. The fibrosis and increased mast cell count in the colon musculature of the MCC group possibly indicates that there is a relationship between mastocytosis and fibrosis, as has already been demonstrated in other pathologies.

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Melanotic neuroectodermal tumor of infancy (MNTI) is a rare neoplasia and it occurs almost exclusively in infants of up to age 1, regardless of sex. 1,7,8 There are few reports of the cytological aspects of this entity in the literature, one of them published by Rege et al. 9 in Diagnostic Cytopathology, 1999. Since it was first described by Krompecher in 1918, it has been given 23 different names, which reflect the uncertainty surrounding its histogenesis. 1,6 However, electron microscopy, laboratory data, and immunohistochemistry indicate its neuroectodermal origin. [1][2][3][4][5]7 We had a case in a 7-mo-old male child, displaying rapid progressive tumor development in the maxilla for 4 mo. The patient was first submitted for a fine-needle aspiration biopsy (FNAB) and the MNTI diagnosis was not made immediately following the aspirated biopsy, possibly due to the rarity of pigmented cells and the thickness of the microscope smear, which made the distinction of the two characteristic cell types of this neoplasia difficult. Later, an incisional biopsy was performed and MNTI diagnosed, since the neoplasia was composed of a biphasic cellular population, either in an irregular alveolar pattern, or forming tubular structures composed of small round cells, similar to neuroblasts, disposed centrally, surrounded by large epithelioid polygonal or dendritic cells, with cytoplasms containing melanin. The alveolar structures were separated by stroma.The lesion was surgically removed. The specimen was nodular, bossed, and ulcerated, measured 3.5 ϫ 2.5 ϫ 2.0 cm, and weighed 10 g. The external surface was smooth, grayish white, and elastic; when cut, it displayed a darkened center and grayish surrounding area.Its microscopic features were identical to those described for the incisional biopsy with the hematoxylineosin technique. In the immunohistochemical study, the epithelioid cells displayed positivity for cytokeratin and HMB-45; the small cells were positive for NSE, chromogranin, and CD99, and were weak for HMB-45. Negative results were obtained for proteins S-100, HHF35, GFAP, and desmin.The review of the microscope smear from the FNAB showed that there were elements of an MNTI diagnosis, with a double-cell population, sometimes with small round cells with hyperchromatic nuclei (Fig. 1), sometimes with larger cells occasionally containing melanin (Fig. 2).In the electron photomicrography there were small cells, similar to lymphocytes. The nuclei were round and condensed. The nucleocytoplasm ratio was high and the cytoplasm small compared to its nucleus, with few mitochondrions and many ribosomes. Different types of electrondense melanin grains were observed, some of which were amorphous and some laminated.The evolution at 2 yr after surgery is good and the neoplasia displays no signs of recurrence or metastasis.MNTI is a neoplasia of neural crest origin, 5,6 with polyphenotypic differentiation: neural, epithelial, melanogenic, and occasionally glial and myogenic cells. 7 It was considered by Raju et al. 7 to belong to ...

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