Heterogeneities in Leishmania infantum Infection: Using Skin Parasite Burdens to Identify Highly Infectious Dogs

Abstract

BackgroundThe relationships between heterogeneities in host infection and infectiousness (transmission to arthropod vectors) can provide important insights for disease management. Here, we quantify heterogeneities in Leishmania infantum parasite numbers in reservoir and non-reservoir host populations, and relate this to their infectiousness during natural infection. Tissue parasite number was evaluated as a potential surrogate marker of host transmission potential.MethodsParasite numbers were measured by qPCR in bone marrow and ear skin biopsies of 82 dogs and 34 crab-eating foxes collected during a longitudinal study in Amazon Brazil, for which previous data was available on infectiousness (by xenodiagnosis) and severity of infection.ResultsParasite numbers were highly aggregated both between samples and between individuals. In dogs, total parasite abundance and relative numbers in ear skin compared to bone marrow increased with the duration and severity of infection. Infectiousness to the sandfly vector was associated with high parasite numbers; parasite number in skin was the best predictor of being infectious. Crab-eating foxes, which typically present asymptomatic infection and are non-infectious, had parasite numbers comparable to those of non-infectious dogs.ConclusionsSkin parasite number provides an indirect marker of infectiousness, and could allow targeted control particularly of highly infectious dogs.

Progress in the Mathematical Modelling of Visceral Leishmaniasis

“…Of 42 infected dogs (18 infectious) in the Brazilian cohort study, 7 (17%) highly infectious dogs were responsible for >80% of the transmission events (Courtenay et al, 2002b), and other studies show that 15-44% of infected dogs are responsible for >80% of transmission (Travi et al, 2001;Molina et al, 1994). These results have been corroborated by studies of tissue parasite burdens across dogs, which show similarly high levels of heterogeneity (Courtenay et al, 2014).…”

“…kDNA for preparing qPCR standards) varies between amastigotes and promastigotes, and even between strains . Studies suggest that there exists a parasite density threshold above which canine and human infections are disproportionately infectious (Courtenay et al, 2014;Miller et al, 2014). In contrast, natural wildlife hosts (e.g.…”

“…Clinical signs are not sufficient for diagnosis due to their low specificity. Distinguishing infectious from non-infectious dogs is also difficult, though parasite burden assessed by qPCR may provide a useful measure of the level of infectiousness (Courtenay et al, 2014).…”

“…Current diagnostics through sera or blood eluates are able to detect latent and asymptomatic infections (though with reduced sensitivity compared to infectious dogs (Courtenay et al, 2002b)). Current tests cannot reliably identify infectious dogs, though both the anti-parasite IgG antibody level and the parasite load have been shown to be highly correlated with probability of infection in sandflies during xenodiagnostic studies (Courtenay et al, 2002b(Courtenay et al, , 2014. infected…”

La leishmaniose canine à Leishmania Infantum : actualités épidémiologiques – applications

“…La quantité de leishmanies dans le derme croît avec l'ancienneté et la sévérité de la maladie, et constitue un marqueur fiable du pouvoir infectant du chien pour le vecteur (Courtenay et al 2014).…”