A cross-sectional study on canine Leishmania (L) infantum chagasi infection in Amazonian Brazil ratifies a higher prevalence of specific IgG-antibody response than delayed-type hypersensitivity in symptomatic and asymptomatic dogs

Abstract

This was a cross-sectional study which analyzed the prevalence and the clinical and immunological spectrum of canine Leishmania (L.) infantum chagasi infection in a cohort of 320 mongrel dogs living in an endemic area of American visceral leishmaniasis in the Amazonian Brazil by using, mainly, the indirect fluorescence antibody test (IFAT-IgG) and the delayed-type hypersensitivity (DTH), and the parasite research by the popliteal lymph node aspiration. The IFAT and DTH reactivity recognized three different immune response profiles: (1) IFAT((+))/DTH((-)) (107 dogs), (2) IFAT((-))/DTH((+)) (18 dogs), and (3) IFAT((+))/DTH((+)) (13 dogs), providing an overall prevalence of infection of 43 per cent (138/320). Thus, the specific prevalence of IFAT( (+) )/DTH( (-) ) 33.4 per cent (107/320) was higher than those of IFAT( (-) )/DTH( (+) ) 5.6 per cent (18/320) and IFAT( (+) )/DTH( (+) ) 4.0 per cent (13/320). Moreover, the frequency of these profiles among 138 infected dogs showed that the IFAT( (+) )/DTH( (-) ) rate of 77.5 per cent (107/138) was also higher than those of 13.0 per cent (18/138) of IFAT( (-) )/DTH( (+) ) and 9.5 per cent (13/138) of IFAT( (+) )/DTH( (+) ) rates. The frequency of asymptomatic dogs (76 per cent-105) was higher than those of symptomatic (16.6 per cent-23) and oligosymptomatic ones (7.4 per cent-10). A total of 16 (11.6 per cent) L. (L.) i. chagasi isolates were obtained from infected dogs, all from the IFAT( (+) ) /DTH( (-) ) profile: 41 per cent (9/22) from symptomatic, 33.3 per cent (3/9) from oligosymptomatic, and 5.2 per cent (4/76) from asymptomatic dogs. These findings strongly suggested that despite the higher frequency of asymptomatic dogs (76 per cent-105), the majority (72.4 per cent-76) was characterized by the IFAT( (+) ) /DTH( (-) ) profile with a doubtful immunogenetic resistance against infection.