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Visceral leishmaniasis (VL) is one of the most important reemerging parasitic disease in the world. The domestic dog is the main reservoir in urban environments. The aim of this work was to extend the knowledge on canine Leishmania infection in the city of Fortaleza in northeastern Brazil, identifying the risk factors inherent in dog susceptibility to the infection. Two populations were analyzed, domestic dogs from clinics and the Veterinary Hospital Unit of Ceará State University and stray dogs captured by the Center for Zoonosis Control in Fortaleza. Blood samples were collected and centrifuged and the sera were stored at -20 degrees C. ELISA, with soluble crude Leishmania chagasi antigens (LTCC - WDCM731) was used for diagnosis. A total of 1,381 samples were tested, 750 from domestic and 631 from stray dogs. The seroprevalence of canine VL was 21.4% (135/631) in stray dogs and 26.2% (197/750) in domestic dogs. The seroprevalence of Leishmania infection in the six administrative regions of the city (Secretarias Executivas Regionais, or SER) among stray dogs was highest in SER V, representing 31.4% of the cases, with large dogs more infected (27.7%). Among domestic dogs Leishmania infection was most prevalent in SER V (38.5%) and VI (37.6%). The dogs' age (1-6 years), large size, environment with dense vegetation and presence of clinical signs compatible with Leishmania infection were associated with the illness in domestic dogs. The frequency of the infection varied seasonally. The seroprevalence was greatest in July and December. These results confirm Fortaleza is an endemic area for canine VL and suggest some variables associated with increasing infection risk in dog populations.

The prevalence of Mal de Cadeiras--Portuguese for Trypanosoma (T.) evansi infections in horses--as well as the prevalence of T.evansi infections in cattle, dogs and free-ranging capybaras (Hydrochaeris hydrochaeris) was investigated in Pantanal de Poconé (Mato Grosso, Brazil). In 0.3, 8.6 and 8.0% of the horses, dogs and capybaras, respectively, infection was detected using standard parasitological methods. A seroprevalence of 4.1, 2.3, 7.1 and 22.0% was found in horses, cattle, dogs and capybaras, respectively, using an enzyme-linked immunosorbent assay for the detection of T.evansi antigen (Ag-ELISA), whereas 9.6, 4.2, 18.6 and 14.0% of the animals investigated were reactive in a T.evansi antibody (Ab-) ELISA. Positive ELISA results ('high responders') were identified using computer-assisted mixture analysis (C.A.MAN). Agglutinating antibodies were detected by the T.evansi card agglutination test for trypanosomiasis (CATT/T.evansi) in 14.6%, 1.3%, 15.7% and 22.0% of the horses, cattle, dogs and capybaras, respectively. A moderate but significant (kappa test; p < 0.05) agreement beyond chance level was observed between Ab-ELISA and CATT results but generally not between antibody and antigen detection tests. Therefore, in an attempt to maximize the information yield of the three serodiagnostic tests, their results were numerically scored (negative = 0, intermediate = 1, positive = 2) and added up to a total score (TS) which was considered indicative for infection when TS > or = 4 (results of the Ag-ELISA received double weight). Estimates of seroprevalence according to TS were 13.2, 4.7, 30.0 and 24.0% for horses, cattle, dogs and capybaras, respectively. Identical isoenzyme profiles, known as zymodeme 58 (T.evansi MCAN/BR/86/H), were found in all T.evansi stocks isolated in the study area (six from dogs, one from a horse and one from a capybara). From the results of this study it can be inferred that Mal de Cadeiras is endemic in Pantanal de Poconé. Although clinical and parasitological findings support the possible role of the capybara as a reservoir host of T.evansi, dogs and cattle--due to their close contact with horses--should rather be regarded as efficient reservoir hosts for Mal de Cadeiras in the study area.

In the serodiagnosis of tropical infectious diseases, cut-off values are often established by using sera from individuals living under moderate climatic conditions, not exposed to the risk of infection (non-endemic controls). This approach guarantees the disease-free status of the individuals within that control group but leads to an assembly of samples which are not representative for the disease-free individuals of the target population (selection bias). Using data from an epidemiological study of Trypanosoma evansi infection in dogs, two alternative methods to construct cut-off values for a T. evansi antibody ELISA are described which are solely based on a distribution analysis of the data from the endemic animals. By cluster analysis these data could be divided into 'high', 'intermediate' and 'low responders'. High responders could also be identified by using the computer-assisted analysis of mixtures (C.A.MAN). Conventional cut-offs were calculated from a group of non-endemic individuals. A receiver operating characteristic (ROC) analysis was performed to demonstrate the impact of the choice of cut-offs on the test specificity and on the estimated seroprevalence among the endemic population. The data indicate that distribution analysis, especially the mixture analysis (C.A.MAN), are valuable tools for the unbiased estimation of seroprevalence when representative negative controls are not available.