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. 2018 Jan 4;11(1):7.
doi: 10.1186/s13071-017-2587-5.

Antibody response to sand fly saliva is a marker of transmission intensity but not disease progression in dogs naturally infected with Leishmania infantum

Affiliations

Antibody response to sand fly saliva is a marker of transmission intensity but not disease progression in dogs naturally infected with Leishmania infantum

Rupert J Quinnell et al. Parasit Vectors. .

Abstract

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.

Keywords: Antibody; Brazil; Dogs; Exposure; Leishmania infantum; Leishmaniasis; Saliva; Sand fly; Transmission.

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Conflict of interest statement

Ethics approval and consent to participate

Canine samples were collected with fully informed consent from dog owners. Sampling was performed in accordance with UK Home Office guidelines.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1
Fig. 1
The initial acquisition of anti-sand fly saliva antibody responses in sentinel dogs. a The antibody response before exposure, 2 and 4 months after being placed in the field of each cohort of dogs (geometric mean ± SE). Sample sizes for each cohort are 11, 13, 15, 2 and three dogs; three further cohorts of a single dog each are not illustrated. b Seasonal changes in the estimated incidence of infection (dotted line) and numbers of Lutzomyia longipalpis sand flies caught in 10 chicken sheds (data from [31])
Fig. 2
Fig. 2
Seasonal variation in anti-sand fly saliva antibody responses. a Antibody responses (geometric mean ± SE). b Estimated incidence of infection (per day) in study dogs (solid line) and monthly rainfall in mm (dotted line) during the study period
Fig. 3
Fig. 3
The relationship between the mean anti-saliva antibody responses of individual dogs and their incidence of infection. Incidence for each dog (n = 58) was assessed as the inverse of the number of days in the field to patent infection with Leishmania infantum
Fig. 4
Fig. 4
The relationship between the mean parasite load of individual dogs and their anti-saliva antibody responses 2 months before patent infection with Leishmania infantum. Parasite load was assessed as the mean log number of parasites in bone marrow biopsies of infected dogs (n = 55)
Fig. 5
Fig. 5
Variation in mean anti-saliva IgG responses (a), mean anti-Leishmania IgG responses (b) and median clinical score through time (c). Dogs were classified as severe infections (filled circles, n = 23), recovered (crosses, n = 6) and mild infections (open circles, n = 18). Estimated time of patent infection is indicated by the vertical dotted line. Asterisks indicate a significant difference between groups after sequential Bonferroni correction by ANOVA (IgG) or Kruskal-Wallis test (clinical score) *P < 0.05, **P < 0.01, ***P < 0.001

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