Background: Antibody responses to
sand fly saliva have been suggested to be a useful marker of exposure to
sand fly bites and
Leishmania infection and a potential tool to monitor the
effectiveness of entomological interventions. Exposure to
sand fly bites before
infection has also been suggested to modulate the severity of the
infection . Here, we test these hypotheses by quantifying the anti-
saliva IgG response in a
cohort study of
dogs exposed to natural
infection with
Leishmania infantum in
Brazil .
Methods: IgG responses to crude salivary
antigens of the
sand fly Lutzomyia longipalpis were measured by
ELISA in longitudinal
serum samples from 47 previously unexposed sentinel
dogs and 11 initially uninfected resident
dogs for up to 2 years.
Antibody responses were compared to the intensity of
transmission , assessed by variation in the
incidence of
infection between
seasons and between
dogs .
Antibody responses before patent
infection were then compared with the severity of
infection , assessed using
tissue parasite loads and clinical symptoms.
Results: Previously unexposed
dogs acquired anti-
saliva antibody responses within 2 months, and the rate of acquisition increased with the intensity of seasonal
transmission . Over the following 2 years,
antibody responses varied with seasonal
transmission and
sand fly numbers, declining rapidly in periods of low
transmission .
Antibody responses varied greatly between
dogs and correlated with the intensity of
transmission experienced by individual
dogs , measured by the number of days in the field before patent
infection . After
infection , anti-
saliva antibody responses were positively correlated with anti-
parasite antibody responses . However, there was no evidence that the degree of exposure to
sand fly bites before
infection affected the severity of the
infection .
Conclusions: Anti-
saliva antibody responses are a marker of current
transmission intensity in
dogs exposed to natural
infection with
Leishmania infantum , but are not associated with the outcome of
infection .