Identification of asymptomatic Leishmania infections: a scoping review

Abstract

Background Asymptomatic Leishmania infection may play an important role in the transmission of the parasite in endemic areas. At present there is no consensus on the definition of asymptomatic Leishmania infection, nor is there a safe and accessible gold standard test for its identification. Methods This paper presents a scoping review to summarize definitions of asymptomatic Leishmania infection found in the literature, as well as to detail the approach (molecular, serological, cellular, and/or parasitological tests) used by researchers to identify this asymptomatic population. A scoping review of published and gray literature related to asymptomatic Leishmania infection was conducted; retrieved citations were screened based on predefined eligibility criteria, and relevant data items were extracted from eligible articles. The analysis is descriptive and is presented using tables, figures, and thematic narrative synthesis. Results We conducted a screening of 3008 articles, of which 175 were selected for the full review. Of these articles, we selected 106 that met the inclusion criteria. These articles were published between 1991 and 2021, and in the last 5 years, up to 38 articles were reported. Most of the studies were conducted in Brazil (26%), Spain (14%), India (12%), Bangladesh (10%), and Ethiopia (7%). Of the studies, 84.9% were conducted in the immunocompetent population, while 15.1% were conducted in the immunosuppressed population (HIV, immunosuppressive drugs, and organ transplantation population). We report 14 different techniques and 10 strategies employed by researchers to define asymptomatic Leishmania infection in an endemic area. Conclusions The definition of asymptomatic Leishmania infection is not unified across the literature, but often includes the following criteria: residence (or extended stay) in a Leishmania-endemic area, no reported signs/symptoms compatible with leishmaniasis, and positive on a combination of serological, molecular, cellular, and/or parasitological tests. Caution is recommended when comparing results of different studies on the subject of asymptomatic infections, as the reported prevalence cannot be confidently compared between areas due to the wide variety of tests employed by research groups. More research on the importance of asymptomatic immunosuppressed and immunocompetent Leishmania-positive populations in leishmaniasis epidemiology is required. Graphical Abstract

Multiparametric analysis of host and parasite elements in new world tegumentary leishmaniasis

“…Our results showed the correlation of pro-inflammatory cytokines, especially IFN-γ, was predominant in all groups, independently of the clinical status ( Maspi et al., 2016 ). This was more evident in the case of asymptomatic patients, which corroborates the results found by Ibarra-Meneses et al., 2022 ., and confirms that IFN-γ release is critical to Leishmania clearance and is associated with host protection against TL. Furthermore, IFN-γ response has already been observed in asymptomatic patients from endemic areas in Peru, which was associated with the exposure time to Leishmania ( Best et al., 2018 ).…”

Detection of specific antibodies against Leishmania infantum in canine serum and oral transudate using an in-house ELISA

“…The incidence rate of human leishmaniosis in Spain was 0.62 cases per 100,000 inhabitants between 2005 and 2017, with cases mainly distributed throughout the Mediterranean region [ 42 ]. However, asymptomatic infections are also common in humans in Spain and Mediterranean basin countries as recently reviewed elsewhere [ 43 ].…”

Identi̇fi̇cati̇on of Lei̇shmani̇a Tropi̇ca From Pedi̇atri̇c Vi̇sceral Lei̇shmani̇asi̇s i̇n Southern Mediterranean Region of Turkey.

“…In addition, the asymptomatic VL patients may serve as a silent reservoir of parasites, presenting a risk to public health through infection of the phlebotomine vector. 29 Although most of our patients in our study had a history of being in rural areas and having contact with sandflies, some lived in the city and whose risks were not defined.…”