Prevalence of asymptomatic Leishmania infection and associated risk factors, after an outbreak in the south-western Madrid region, Spain, 2015

Abstract

Background A large outbreak of leishmaniasis with 758 cutaneous and visceral leishmaniasis cases occurred in 2009 in Fuenlabrada, in the south-west of the Madrid region of Spain. Aim We aimed to determine the prevalence of asymptomatic Leishmania infection after this outbreak, and its associated risk factors. Methods A cross-sectional study of 804 healthy individuals living in Fuenlabrada who had no history of leishmaniasis, was conducted between January and July 2015. Asymptomatic infections were sought by either a combination of PCR, immunofluorescent antibody titre, and direct agglutination tests, or by whole blood stimulation assay (WBA) with interleukin-2 (IL-2) quantification. Results Using the first approach, prevalence of asymptomatic individuals was 1.1% (9/804), while the second returned a value of 20.7% (143/804). Older age, being male, proximity to the park where the focus of infection was identified, and living in a detached house, were all strongly associated with the prevalence of asymptomatic infection. Conclusions The true number of infected individuals may be underestimated if only serological methods are used. The combination of WBA with IL-2 quantification may allow to better determine the prevalence of asymptomatic Leishmania infection, which would be useful in establishing control measures and in quantifying their impact. In our study, the use of WBA with IL-2 quantification also helped establish the risk factors that influence exposure to and infection by Leishmania .

Asymptomatic Leishmania infantum infection in blood donors living in an endemic area, northeastern Italy

“…Our results are in line with previous evidence reporting that many cases of Leishmania infection are asymptomatic in the Mediterranean Europe. 2,[9][10][11][12][13][14]16,17,[19][20][21][22] Some patients with subclinical infection can harbor viable parasites throughout life and may develop reactivation to full-blown visceral leishmaniasis if immunosuppression occurs thereafter. 23 Visceral and cutaneous leishmaniasis are compulsory notifiable diseases in Italy and confirmed cases are obligatorily reported by local public health departments to the regional health authorities.…”

Role of asymptomatic and symptomatic humans as reservoirs of visceral leishmaniasis in a Mediterranean context

“…Although asymptomatic infection with the Leishmania parasite was recently reported in a large percentage of the population in Fuenlabrada by whole blood stimulation assay with interleukin-2 quantification [30], no CPA-SLA positive asymptomatic donor was able to infect PLOS NEGLECTED TROPICAL DISEASES sand flies, including the two donors with positive serology for Leishmania. These results agree with those obtained by direct xenodiagnosis in Brazil in which no sand fly was found to be infected by microscopy, although the detection of L. infantum DNA by PCR in some L. longipalpis females fed on a few asymptomatic subjects was reported [11,18].…”

Implications of asymptomatic infection for the natural history of selected parasitic tropical diseases

“…These values reflect not only differences in the virulence of the strain involved and the characteristics of the host but also differences in the design of the studies and the methods used to identify asymptomatic infections. In addition, levels of parasite transmission fluctuate greatly within an endemic area, with a gradient of prevalence for asymptomatic L. infantum infection ranging from 8-12% to 35-38% [44,45].…”

“…On the contrary, a positive cellular test means a very low risk of subsequent VL [48,49]. In a recent cross-sectional survey done in a post-outbreak area in Spain, 164 out of 804 (20.7%) individuals were identified as asymptomatic by using a cellular test (whole blood stimulation assay, WBA) and none of these subjects developed visceral leishmaniasis after 4 years of follow-up [45].…”