Early reduction of Leishmania infantum-specific antibodies and blood parasitemia during treatment in dogs with moderate or severe disease

Background: Leishmania infantum-specific antibodies are used extensively for the diagnosis and monitoring of treatment in canine leishmaniosis. Different views have been described for the measurement of L. infantum antibody levels for the monitoring of anti-leishmanial treatment. In addition, molecular techniques using blood are frequently employed in the clinical setting. However, there are not enough studies to prove the usefulness of PCR in diagnosis, treatment monitoring and in assessing the prognosis of the disease. The objectives of this study were to evaluate L. infantum-specific antibodies and blood parasitemia at the time of diagnosis and during treatment and to correlate these with the dog's clinical status. Methods: Thirty-seven dogs were diagnosed and followed-up during treatment (days 30, 180 and 365). The treatment protocol consisted of a combination of meglumine antimoniate for one month and allopurinol for at least one year. Leishmania infantum-specific antibodies and blood parasitemia were assessed by an end point sera dilution ELISA and by real-time PCR, respectively. Results: The majority of dogs were classified as LeishVet stage II (moderate disease) at the time of diagnosis (86 %) and the rest as stage III. Results showed variable levels of specific antibodies at the time of diagnosis [median +/- interquartile range (IQR): 1372 +/- 8803 ELISA units (EU)]. Twenty-three seropositive dogs (64 %) were detected as PCR-positive at the time of diagnosis. Interestingly, a rapid significant antibody level reduction was observed by day 30 of treatment (median +/- IQR: 604 +/- 2168 EU). A continuing significant decrease of specific antibodies was also found at days 180 (median +/- IQR: 201 +/- 676 EU) and 365 (median +/- IQR: 133 +/- 329 EU) in association with clinical improvement. A significant blood parasitemia reduction was also observed at all time points studied. Mean parasites/ml +/- SD were 19.4 +/- 79.1 on day 0, 2.2 +/- 11.7 on day 30, 0.9 +/- 2.9 on day 180, and 0.3 +/- 0.7 on day 365. Conclusions: This study reports a significant reduction of L. infantum antibodies measured by an end point sera dilution ELISA method after 30 days of treatment associated with clinical improvement. A low proportion of sick dogs with moderate disease were negative by blood real-time PCR at the time of diagnosis.