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 % (138/320). Thus, the specific prevalence of IFAT⁽⁺⁾/DTH⁽⁻⁾ 33.4 % (107/320) was higher than those of IFAT⁽⁻⁾/DTH⁽⁺⁾ 5.6 % (18/320) and IFAT⁽⁺⁾/DTH⁽⁺⁾ 4.0 % (13/320). Moreover, the frequency of these profiles among 138 infected dogs showed that the IFAT⁽⁺⁾/DTH⁽⁻⁾ rate of 77.5 % (107/138) was also higher than those of 13.0 % (18/138) of IFAT⁽⁻⁾/DTH⁽⁺⁾ and 9.5 % (13/138) of IFAT⁽⁺⁾/DTH⁽⁺⁾ rates. The frequency of asymptomatic dogs (76 %—105) was higher than those of symptomatic (16.6 %—23) and oligosymptomatic ones (7.4 %—10). A total of 16 (11.6 %) L. (L.) i. chagasi isolates were obtained from infected dogs, all from the IFAT⁽⁺⁾ /DTH⁽⁻⁾ profile: 41 % (9/22) from symptomatic, 33.3 % (3/9) from oligosymptomatic, and 5.2 % (4/76) from asymptomatic dogs. These findings strongly suggested that despite the higher frequency of asymptomatic dogs (76 %—105), the majority (72.4 %—76) was characterized by the IFAT⁽⁺⁾ /DTH⁽⁻⁾ profile with a doubtful immunogenetic resistance against infection.