Viable Leishmania parasites in the absence of an in vitro IFN-γ response in asymptomatic carriers

Asymptomatic infection (the absence or inapparent signs and symptoms) has been observed in many endemic areas of leishmaniasis, however, little is known about the parasitological and immunological factors associated with this type of infection. This study aimed to identify the in vitro expression of IFN-γ in asymptomatic carriers of viable Leishmania parasites. Asymptomatic infection was identified using the Montenegro skin test in an at-risk population from Yucatan, Mexico. Parasite viability was evinced in the blood by 7SL RNA transcripts amplification. The expression of mRNA IFN-γ was analyzed in peripheral blood mononuclear cells stimulated with soluble Leishmania antigen, using RT-qPCR. Parasite viability was observed in 33.3 % (5/15) of asymptomatic subjects. No differences were found in the expression of IFN-γ between asymptomatic and healthy subjects, and no correlation was found between the presence of viable parasites and the expression of IFN-γ. This study demonstrates the persistence of Leishmania parasites in the absence of an in vitro IFN-γ response in asymptomatic carriers from Mexico

Frecuencia serológica y molecular de Leishmania spp y Trypanosoma cruzi y factores asociados en perros con signos sugestivos de infección por tripanosomátidos en Quintana Roo, México

A cross-sectional study was conducted with a sample of 40 dogs with clinical signs suggestive of infection by Leishmania spp and Trypanosoma cruzi in the municipality of Lázaro Cárdenas, Quintana Roo, Mexico. Blood, skin and bone marrow samples were taken. Indirect immunofluorescence (IFI) tests for detection of anti-Leishmania infantum and immunochromatic test for the detection of anti-Trypanosoma cruzi antibodies in serum were performed. In addition, molecular analyses were performed using PCR to detect Leishmania spp in bone marrow and skin and T. cruzi in bone marrow. Histopathological analyses of the skin and cytology of the bone marrow were carried out in search of lesions and trypanosomatid agents. The results showed that 3 (7.5%) and 6 (15%) dogs with anti-L. infantum and T. cruzi antibodies were detected, respectively. Molecular analyses detected 17 dogs positive for infection by T. cruzi (42.5%) and none for infection by Leishmania spp. Dogs with low body condition showed greater seropositivity to T. cruzi using Fisher’s exact test (p<0.05). Parasites of the genus Leishmania did not actively participate in the pathological processes of the animals; however, a high frequency of animals infected with T. cruzi was observed.Se realizó un estudio transversal con una muestra de 40 perros con signos clínicos sugestivos de infección por Leishmania spp y Trypanosoma cruzi en el municipio de Lázaro Cárdenas, Quintana Roo, México. Se tomaron muestras de sangre, piel y médula ósea. Se realizaron las pruebas de inmunofluorescencia indirecta (IFI) para detección de anticuerpos anti-Leishmania infantum e inmunocromática para detección de anticuerpos anti-Trypanosoma cruzi en suero. Además, se realizaron análisis moleculares, mediante PCR para la detección de Leishmania spp en médula ósea y piel y T. cruzi en médula ósea. Se realizaron análisis histopatológicos de piel y citológicos de médula ósea en busca de lesiones y agentes tripanosomátidos. Se detectaron 3 (7.5%) y 6 (15%) perros con anticuerpos anti-L. infantum y T. cruzi, respectivamente. En los análisis moleculares se detectaron 17 perros positivos a la infección por T. cruzi (42.5%) y ninguno a la infección por Leishmania spp. Los perros con baja condición corporal presentaron mayor seropositividad a T. cruzi mediante la prueba exacta de Fisher (p<0.05). Los parásitos del género Leishmania no participaron activamente en los procesos patológicos de los animales estudiados; sin embargo, se observa una alta frecuencia de animales infectados por T. cruzi

ANIMAL MODELS FOR THE STUDY OF LEISHMANIASIS IMMUNOLOGY

Leishmaniasis remains a major public health problem worldwide and is classified as Category I by the TDR/WHO, mainly due to the absence of control. Many experimental models like rodents, dogs and monkeys have been developed, each with specific features, in order to characterize the immune response to Leishmania species, but none reproduces the pathology observed in human disease. Conflicting data may arise in part because different parasite strains or species are being examined, different tissue targets (mice footpad, ear, or base of tail) are being infected, and different numbers (“low” 1×102 and “high” 1×106) of metacyclic promastigotes have been inoculated. Recently, new approaches have been proposed to provide more meaningful data regarding the host response and pathogenesis that parallels human disease. The use of sand fly saliva and low numbers of parasites in experimental infections has led to mimic natural transmission and find new molecules and immune mechanisms which should be considered when designing vaccines and control strategies. Moreover, the use of wild rodents as experimental models has been proposed as a good alternative for studying the host-pathogen relationships and for testing candidate vaccines. To date, using natural reservoirs to study Leishmania infection has been challenging because immunologic reagents for use in wild rodents are lacking. This review discusses the principal immunological findings against Leishmania infection in different animal models highlighting the importance of using experimental conditions similar to natural transmission and reservoir species as experimental models to study the immunopathology of the disease

Asymptomatic infection with American cutaneous leishmaniasis: epidemiological and immunological studies

American cutaneous leishmaniasis (ACL) is a major public health problem caused by vector-borne protozoan intracellular parasites from the genus Leishmania, subgenera Viannia and Leishmania. Asymptomatic infection is the most common outcome after Leishmania inoculation. There is incomplete knowledge of the biological processes explaining the absence of signs or symptoms in most cases while other cases present a variety of clinical findings. Most studies of asymptomatic infection have been conducted in areas of endemic visceral leishmaniasis. In contrast, asymptomatic ACL infection has been neglected. This review is focused on the following: (1) epidemiological studies supporting the existence of asymptomatic ACL infection and (2) immunological studies conducted to understand the mechanisms responsible for controlling the parasite and avoiding tissue damage

Preliminary epidemiological findings of Leishmania infection in the municipality of Tinum, Yucatan State, Mexico

Localized cutaneous leishmaniasis (LCL) is endemic in Mexico, mainly in the states of Campeche and Quintana Roo, hyperendemic areas of Leishmania (Leishmania) mexicana transmission. In this report, epidemiological features of Leishmania infections in the municipality of Tinum, Yucatan State, Mexico are presented. Nine cases of LCL were diagnosed in 2015. Patients were men between 30 and 74 years of age, without a history of living or traveling to endemic areas (Quintana Roo or Campeche). Due to asymptomatic infection is the most common outcome after Leishmania inoculation, between November 2017 to June 2018, 47 men working in the forest were tested by Montenegro skin test (MST). Thirteen of them (27.6%) were identified MST positive, in absence of either lesion or typical scar, and evidence of exposure to vector. Findings in Tinum, Yucatan, supported the presence of specific environmental conditions that seem to favor Leishmania transmission in this region. Thus, active surveillance for the detection of new cases in the municipality of Tinum as well as the eco-epidemiological characterization to identify all the transmission components (parasite, vector, and reservoir species) are urgently needed. Keywords: Asymptomatic infection, Leishmania, Localized cutaneous leishmaniasis, Tinum, Yucata

Nitric oxide production by Peromyscus yucatanicus (Rodentia) infected with Leishmania (Leishmania) mexicana

Peromyscus yucatanicus (Rodentia: Cricetidae) is a primary reservoir of Leishmania (Leishmania) mexicana (Kinetoplastida: Trypanosomatidae). Nitric oxide (NO) generally plays a crucial role in the containment and elimination of Leishmania. The aim of this study was to determine the amount of NO produced by P. yucatanicus infected with L. (L.) mexicana. Subclinical and clinical infections were established in P. yucatanicus through inoculation with 1 x 10 2 and 2.5 x 10 6 promastigotes, respectively. Peritoneal macrophages were cultured alone or co-cultured with lymphocytes with or without soluble Leishmania antigen. The level of NO production was determined using the Griess reaction. The amount of NO produced was significantly higher (p ≤ 0.0001) in co-cultured macrophages and lymphocytes than in macrophages cultured alone. No differences in NO production were found between P. yucatanicus with subclinical L. (L.) mexicana infections and animals with clinical infections. These results support the hypothesis that the immunological mechanisms of NO production in P. yucatanicus are similar to those described in mouse models of leishmaniasis and, despite NO production, P. yucatanicus is unable to clear the parasite infection