Detection of Leishmania infantum by PCR, serology and cellular immune response in a cohort study of Brazilian dogs

The sensitivity and specificity of PCR, serology (ELISA) and lymphoprolifer ative response to Leishmania antigen for the detection of Leishmania infant um infection were evaluated in a cohort of 126 dogs exposed to natural infe ction in Brazil. For PCR, Leishmania DNA from bone-marrow was amplified wit h both minicircle and ribosomal primers. The infection status and time of i nfection of each dog were estimated from longitudinal data. The sensitivity of PCR in parasite-positive samples was 98 %. However, the overall sensiti vity of PCR in post-infection samples, from dogs with confirmed infection, was only 68%. The sensitivity of PCR varied during the course of infection, being highest (78-88 %) 0-135 days post infection and declining to around 50 % after 300 days. The sensitivity of PCR also varied between dogs, and w as highest in sick dogs. The sensitivity of serology was similar in parasit e-positive (84%), PCR-positive (86%) and post-infection (88 %) samples. The sensitivity of serology varied during the course of infection, being lowes t at the time of infection and high (93-100%) thereafter. Problems in deter mining the specificity of serology are discussed. The sensitivity and speci ficity of cellular responsiveness were low. These data suggest that PCR is most useful in detecting active or symptomatic infection, and that serology can be a more sensitive technique for the detection of all infected dogs.