Factors Associated with Visceral Leishmaniasis in the Americas: A Systematic Review and Meta-Analysis

Abstract

BackgroundStill today, more than 30 years after the beginning of the process of visceral leishmaniasis' urbanization, there is little knowledge about the risk factors for its occurrence, despite their relevance to the control and understanding of disease dynamics. The present study is the first systematic review with meta-analysis about factors associated with Leishmania infantum infection in humans in the Americas.Methods and FindingsAfter searching different databases, consultations to the reference lists of articles and to experts in the field, 51 studies were reviewed. Theoretical discussions or meta-analysis of p-values or of effect sizes were used to pool information about each variable. The Q test and the I2 statistic were used to assess heterogeneities among the studies. Male sex was associated with visceral leishmaniasis in studies which used the leishmanin skin test for diagnosis and in those where the outcome was the clinical disease; the opposite occurred when serological diagnosis was applied. Younger individuals were less frequently infected than adults, but were more prone to illness. Although with different levels of evidence and of heterogeneity, the presence of dogs at home, higher dog seropositivity in nearby areas, lower socioeconomic status and highly vegetated areas were associated with L. infantum infection. This was not noticed for the presence of chickens in the house and with nutritional status. Susceptibilities to bias and limitations in the analysis and in the description of results were often identified in the studies analyzed.ConclusionsResults showed the existence of consistent patterns for some of the factors analyzed and should be taken into account in developing more effective and well-targeted control measures. Studies must be conducted in new areas of the continent, with improved methodological quality and prioritizing the investigation of the patterns identified and their causes, as well as variables for which knowledge is poor.

Fatores ambientais associados à ocorrência de leishmaniose visceral canina em uma área de recente introdução da doença no Estado do Rio de Janeiro, Brasil

“…Meanwhile, there was no statistically significant association between dense vegetation and L. infantum infection. The fact that no association was found with the presence of dense vegetation or proximity to it, which various studies of human and canine VL have highlighted 11,43,44 , may be due to the fact that this type of land cover was highly abundant, covering at least 40% of the area in the squares. Thus, all the squares were under the influence of favorable conditions for the vector's existence due to the presence and abundance of dense vegetation.…”

Dificuldades na execução das diretrizes do Programa de Vigilância e Controle da Leishmaniose Visceral em grandes municípios brasileiros

“…De acordo com o citado em vários estudos, cães reagentes podem atuar como bons reservatórios, com grande poder de infectar o vetor da doença, mesmo não apresentando sinais clíni- cos 32,33,34 . Assim, quanto mais tempo o animal é mantido no ambiente, maior a chance de transmitir a parasitose aos vetores e maior o risco de transmissão da doença ao homem 26,27,35 . Todos os coordenadores relataram terem tido dificuldades na condução das diretrizes do PVCLV também por interferências de clínicos veterinários.…”

EVIDENCE OF Leishmania (Leishmania) infantum INFECTION IN DOGS FROM JUIZ DE FORA, MINAS GERAIS STATE, BRAZIL, BASED ON IMMUNOCHROMATOGRAPHIC DUAL-PATH PLATFORM (DPP®) AND PCR ASSAYS

“…Among the countries of the Americas, Brazil accounts for the highest number of human VL cases and is the third largest VL focus globally (ALVAR et al, 2012;BELO et al, 2013). Despite having presented a typical rural and wild pattern of VL until the 80's (WERNECK, 2008), current data show that the numbers have increased considerably, thus creating a new epidemiological profile, due to the spread of the disease to urban centers of the North, South and West regions of the country (JERONIMO et al, 2004;ROMERO & BOELAERT, 2010;HARHAY et al, 2011).…”

“…The Brazilian Ministry of Health recommends both the immunoenzymatic assay (ELISA) and the indirect immunofluorescence antibody test (IFAT) as the chosen tests for dogs screening and culling campaigns. However, the moderate sensitivity and specificity of these tests together with the complexity of their implementation have been cited as factors of limited impact for the control of CVL (HARHAY et al, 2011;BELO et al, 2013).…”

“…This disease is endemic in 88 countries with approximately 0.2 to 0.4 million cases each year in Europe, South America, Africa and Asia (ALVAR et al, 2012). Anthroponotic transmission caused by L. donovani is present in the Indian subcontinent and in Central Africa, and zoonotic transmission caused by L. infantum is present in the Americas, Mediterranean basin, Middle East and Central Asia, and parts of Africa (HARHAY et al, 2011, PALATNIK-DE-SOUSA & DAY, 2011.Among the countries of the Americas, Brazil accounts for the highest number of human VL cases and is the third largest VL focus globally (ALVAR et al, 2012;BELO et al, 2013). Despite having presented a typical rural and wild pattern of VL until the 80's (WERNECK, 2008), current data show that the numbers have increased considerably, thus creating a new epidemiological profile, due to the spread of the disease to urban centers of the North, South and West regions of the country (JERONIMO et al, 2004;ROMERO & BOELAERT, 2010;HARHAY et al, 2011).…”