[Show abstract][Hide abstract] ABSTRACT: A detailed follow-up investigation of the major parasitological, serological and phenotypic features in dogs experimentally infected with metacyclic (MT) and blood (BT) trypomastigotes of Trypanosoma cruzi strain Berenice-78, typifying vectorial and transfusional transmission of human Chagas disease, has been conducted. Although there were no changes with respect to the window of patent-parasitaemia, significant differences between MT- and BT-infected dogs in both the prepatent period (days 23 and 19, respectively) and the day of maximum parasitaemia (days 26 and 22, respectively) were recorded. A progressive enhancement in the level of T. cruzi-specific antibodies accompanied infection by both MT and BT forms, although higher IgG titres developed on days 14 and 21 following infection with MT forms. Higher Thy-1(+)/CD21(+) and lower CD4(+)/CD8(+) cell ratios, occasioned by increased levels of Thy-1(+) and CD8(+) T-cells and reduced frequencies of CD4(+) T-cells and CD21(+) B-lymphocytes, were observed in both MT- and BT-infected animals. The reduced frequency of CD14(+) leukocytes was revealed as the most relevant phenotypic feature intrinsic to T. cruzi infection independent of inoculum source. BT-specific phenotypic features included an early reduction in the percentage of circulating CD21(+) and CD14(+) leukocytes, together with a higher Thy-1(+)/CD21(+) cell ratio on day 42. On the other hand, higher levels of CD8(+) T-cells, together with a lower CD4(+)/CD8(+) cell ratio on day 28, were characteristic of MT infection. These findings emphasise the importance of inoculum source and suggest that vectorial or transfusional routes of T. cruzi infection may trigger distinct parasite-host interactions during acute Chagas disease.
[Show abstract][Hide abstract] ABSTRACT: In this study, the polymerase chain reaction (PCR) was compared with parasitological and serological methods to detect the infection in dogs, 5-12 years after experimental infection with Trypanosoma cruzi. The ability of parasitological methods to identify a positive animal was 22 and 11% by hemoculture and xenodiagnosis/xenoculture, respectively. On the other hand, the serological tests, including conventional serology and anti-live trypomastigote antibodies (ALTA) were positive in all infected dogs. Despite its low sensitivity, if considering only one reaction, the PCR analysis showed 100% of positivity, demonstrating the presence of parasite kDNA in all infected dogs. To identify a positive dog required at least two blood samples and up to nine repeated reactions using the same sample. Serial blood sample collection, ranging from 1 to 9, revealed that the percentage of dogs with positive PCR ranged from 67 to 100%. These findings suggested that, although the PCR is useful to detect the parasite in infected hosts, it should not be used isolated for the diagnosis of Chagas' disease and warn for the necessity of serial blood collection and re-tests. Moreover, these data validate once more the dog as a model for Chagas' disease since they demonstrate the permanence of infection by PCR, parasitological and serological methods, reaching relevant requisites for an ideal model to study this disease.