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

Abstract

Background In the Mediterranean basin, Leishmania infantum is the causative agent of visceral leishmaniasis (VL), a zoonosis in which the dog is the primary domestic reservoir, although wildlife may have a leading role in the sylvatic cycle of the disease in some areas. Infections without disease are very frequent. There is limited information regarding the role that VL patients and asymptomatic infected individuals could be playing in the transmission of L. infantum. Xenodiagnosis of leishmaniasis has been used in this descriptive study to explore the role of symptomatic and asymptomatic infected individuals as reservoirs in a recent focus of leishmaniasis in southwestern Madrid, Spain. Methodology and main findings Asymptomatic blood donors (n = 24), immunocompetent patients who were untreated (n = 12) or treated (n = 11) for visceral leishmaniasis (VL), and immunocompromised patients with VL (n = 3) were enrolled in the study. Their infectivity to Phlebotomus perniciosus was studied by indirect xenodiagnosis on peripheral blood samples. Quantitative polymerase chain reaction of blood samples from immunocompetent patients untreated for VL and immunocompromised untreated, treated and under secondary prophylaxis for VL was performed. Antibodies against Leishmania were studied by indirect fluorescent antibody and rK39-immunochromatographic tests. A lymphoproliferative assay with a soluble Leishmania antigen was used to screen for leishmaniasis infection in the healthy population. Sixty-two xenodiagnostic tests were carried out and 5,080 sand flies were dissected. Positive xenodiagnosis was recorded in four patients, with different sand fly infection rates: 1 immunosuppressed HIV / L. infantum coinfected asymptomatic patient, 1 immunosuppressed patient PLOS NEGLECTED TROPICAL DISEASES

Leishmaniasis in the United States: Emerging Issues in a Region of Low Endemicity

“…This raises the spectre that introduction of L. infantum (possibly by asymptomatic, previously deployed U.S. military servicemembers, or infected hunting and companion dogs) could lead to vector borne transmission of VL within the U.S. To better understand the risk that persons with AVL may pose with regard to anthroponotic spread, several studies have been performed within endemic countries using xenodiagnosis. Molina et al in the wake of the aforementioned Madrid outbreak identified four groups of persons with current or previous VL: asymptomatic immunocompetent persons (14 with AVL, 10 with no evidence of prior VL), untreated persons with symptomatic VL, formerly symptomatic VL patients post-treatment, and three immunocompromised patients with VL (two persons with HIV, one on therapy for multiple myeloma) [ 150 ]. None of the 14 asymptomatic VL individuals were found on xenodiagnosis to transmit infection to the sand flies.…”

“…The risk of transmission correlated with parasite burden, with transmission frequency reaching as high as 30.6% in the patient with hematologic malignancy whose parasite load was 4360/µL prior to VL treatment, and 48.6% in one of the two HIV/VL co-infected individuals (608 parasites/µL). Strikingly, this latter individual continued to have detectable parasitemia and showed anthroponotic transmission potential even while taking anti-retroviral therapy and following treatment and institution of secondary prophylaxis for his Leishmania infection [ 150 ]. Previous work in six HIV-VL infected persons showed an association between low CD4 count and infectivity to sand flies [ 151 , 152 ].…”

“…Although the final analysis concluded that both symptomatic disease and HIV infection were associated with an increased ability to transmit infection to sand flies, perhaps the most interesting finding was that 5.4% of sand flies fed on asymptomatic, HIV-uninfected persons were found Leishmania PCR positive. Though sand fly infection could not be confirmed by microscopy, this finding suggests that humans with AVL and no underlying immunosuppression may be able to act as reservoirs, with the potential for low levels of anthroponotic spread [ 150 ].…”

Properties of virulence emergence ofLeishmania infantumisolates fromPhlebotomus perniciosuscollected during the human leishmaniosis outbreak in Madrid, Spain. Hepatic histopathology and immunological parameters as virulence markers in the mouse model

“…Scientists have not fully revealed how the outbreak isolates have been able to affect middle-aged people with adequate levels of immunocompetence in this outbreak, the largest human VL outbreak in Europe. The results of the present study may help guide future research on this topic (Molina et al, 2020).…”

Asymptomatic Leishmania infection in HIV-positive outpatients on antiretroviral therapy in Pernambuco, Brazil

“…Asymptomatic Leishmania infected individuals, despite the typically low parasite load, might contribute to maintaining the transmission cycle of Leishmania parasites in endemic regions during episodes of increased parasite load and disease relapse [ 16 , 17 ]. In Brazil, due to the high prevalence of HIV- Leishmania coinfection observed in previous studies [ 10 , 15 , 18 ], and due to the other potential implications (e.g.…”