Factors associated with Leishmania spp. infection in domestic dogs from an emerging area of high endemicity for visceral leishmaniasis in Central-Western Brazil

Global Distribution of Canine Visceral Leishmaniasis and the Role of the Dog in the Epidemiology of the Disease

Visceral leishmaniasis is a disease caused by protozoa of the species Leishmania (Leishmania) infantum (syn = Leishmania chagasi) and Leishmania (Leishmania) donovani, which are transmitted by hematophagous insects of the genera Lutzomyia and Phlebotomus. The domestic dog (Canis familiaris) is considered the main urban reservoir of the parasite due to the high parasite load on its skin, serving as a source of infection for sandfly vectors and, consequently, perpetuating the disease in the urban environment. Some factors are considered important in the perpetuation and spread of canine visceral leishmaniasis (CVL) in urban areas, such as stray dogs, with their errant behavior, and houses that have backyards with trees, shade, and organic materials, creating an attractive environment for sandfly vectors. CVL is found in approximately 50 countries, with the number of infected dogs reaching millions. However, due to the difficulty of controlling and diagnosing the disease, the number of infected animals could be even greater. In the four continents endemic for CVL, there are reports of disease expansion in endemic countries such as Brazil, Italy, Morocco, and Tunisia, as well as in areas where CVL is not endemic, for example, Uruguay. Socio-environmental factors, such as migration, drought, deforestation, and global warming, have been pointed out as reasons for the expansion into areas where it had been absent. Thus, the objective of this review is to address (i) the distribution of CVL in endemic areas, (ii) the role of the dog in the visceral leishmaniasis epidemiology and the factors that influence dog infection and the spread of the disease, and (iii) the challenges faced in the control of CVL.

Re-emergence and influencing factors of mountain-type zoonotic visceral leishmaniasis in the extension region of Loess Plateau, China

OBJECTIVE

To understand the epidemiological distribution characteristics of mountain-type zoonotic visceral leishmaniasis (MT-ZVL) in Yangquan City, Shanxi Province, China, from 2006 to 2021, to explore the influencing factors leading to the re-emergence of the epidemic, and to provide a basis for the formulation of targeted control strategies.

METHODS

Case information spanning from 2006 to 2021 in Yangquan City was collected for a retrospective case-control study conducted from June to September 2022. A 1:3 matched ratio was employed. A questionnaire was utilized to gather data on basic information, demographic characteristics, awareness of MT-ZVL knowledge, residence, and dog breeding and living habits. The study employed a multifactorial conditional stepwise logistic regression model to analyze the influencing factors.

RESULTS

A total of 508 subjects was analyzed. Risk factors for MT-ZVL included the use of soil/stone/concrete as building materials (OR = 3.932), presence of nearby empty/stone stack houses (OR = 2.515), dog breeding (OR = 4.215), presence of stray dogs (OR = 2.767), and neighbor's dog breeding (OR = 1.953). Protective factors comprised knowledge of MT-ZVL (OR = 0.113) and using mosquito repellents (OR = 0.388). The findings indicate significant associations between environmental and behavioral factors and MT-ZVL incidence in Yangquan City, Shanxi Province, China, from 2006 to 2021. These results underscore the importance of public awareness campaigns and targeted interventions aimed at reducing exposure to risk factors and promoting protective measures to mitigate the re-emergence of MT-ZVL outbreaks.

CONCLUSION

House building materials, presence of neighboring empty houses, breeding domestic dogs and distribution of stray dogs surrounding the home are risk factors for MT-ZVL. Awareness of MT-ZVL and implementation of preventive measures during outdoor activities in summer and autumn are protective and may reduce the risk of MT-ZVL.

Socioeconomic Status of Guardians as a Risk Factor for Canine Visceral Leishmaniasis: A Cohort Study in an Endemic Area of the Federal District, Brazil

Current control measures of canine visceral leishmaniasis (CVL), a chronic and fatal zoonosis with potential transmission to humans, are not efficient enough to reduce its spread. The search for improved control measures should include studies of risk factors for infection and illness. This study aimed to identify the risk factors for CVL in an endemic locality of the Federal District, Brazil, from June 2016 to December 2018. Biologic samples and data on dog characteristics, owner household characteristics, and dog care were collected. A combination of serological and molecular tests was used to identify infected animals. The 248 dogs screened for inclusion were predominantly asymptomatic/oligosymptomatic. The baseline prevalence of infection was 27.5%. One hundred six of 162 susceptible dogs were monitored for an average period of 10.7 months. The estimated CVL incidence was 1.91 cases/100 dog-months. The multivariate analysis using a proportional Cox model included the potential risk factors, with P ≤ 0.25 in the univariate analyses. Greater purchasing power (hazard ratio [HR], 1.04; 95% CI, 1.01-1.06; P = 0.03) and paved yard (HR, 0.19; 95% CI, 0.13-1.01; P = 0.05) remained in the final model as risk and protection factors, respectively. The use of repellent collars in dogs was associated moderately (P = 0.08) with protection against CVL. Our findings reflect the challenge of identifying strong interventions for reducing CVL incidence. Increased owner wealth had a counterintuitive effect on CVL, making the intervention scenario more complex for a zoonosis traditionally associated with poverty.

First molecular-based detection study of Leishmania infantum in the Tapirapé indigenous population in the Brazilian Amazon

Species of the genus Leishmania parasitize mammals and have life cycles that alternate between vertebrate and invertebrate hosts. Most species develop in a hematophagous arthropod and infect a specific vertebrate host that may belong to diverse orders and families. Visceral leishmaniasis is a chronic zoonosis with a wide geographic distribution, affecting 350 million people globally, mostly in areas with a high risk of infection. In Brazil, this disease not only has a high incidence but is also expanding to new areas, both in urban centers and rural areas, including territories with tribal communities, due to increasing human intervention. The objective of this study was to perform cathepsin L-like gene-based molecular diagnosis of Leishmania infantum in the indigenous Tapirapé ethnic group in the state of Mato Grosso. From the 372 individuals assessed, only 0.8% (3/372) tested positive for L. infantum, all from the same village (Urubu Branco). Despite the small number of infected individuals, this study demonstrates the first human cases of Leishmania infantum infection in this population, suggesting the need for regular monitoring of visceral leishmaniasis in the area and leading to a broad discussion on the planning and implementation of public health measures for the indigenous population, while respecting their distinctive territories and culture.

Passive case detection for canine visceral leishmaniasis control in urban Brazil: Determinants of population uptake

BACKGROUND

In Brazil, the transmission of Leishmania infantum in urban settings is closely related to infection among dogs, with occasional transmission to humans. Serological screening of dogs for Leishmania spp. infection on requests of their owners (passive case detection) represents a frequent, but little studied, practice within the scope of Brazilian public health. This study identified factors associated with canine visceral leishmaniasis (CVL) diagnosis-seeking behavior of dog owners in Rondonópolis (236,000 inhabitants), a municipality in Central-Western Brazil where VL is endemic. Also, we evaluated the profile of dog owners and their animals screened on free demand.

METHODOLOGY/PRINCIPAL FINDINGS

Using mixed effects negative binomial regression, we modelled the number of dogs screened for Leishmania infection on free demand per neighborhood from 2011 to 2016 as a function of time-dependent predictors (current or recent canine seropositivity and human VL incidence), distance to the screening site, and demographic variables. We assessed potential delays in the effect of time-dependent predictors on the outcome. Among 12,536 dogs screened for Leishmania infection, 64.2% were tested during serosurveys and 35.8% were tested on free demand. Of these, 63.9% were positive. Uptake of screening under free demand was strongly associated with higher levels of canine seropositivity in the neighborhood (current or recent) and decreasing distance to the screening site. A subsample of dog owners (n = 93) who sought CVL screening between 2016 and 2017 were interviewed in more detail. Owners with better socioeconomic status and dogs with apparent CVL clinical manifestations prevailed among them.

CONCLUSIONS/SIGNIFICANCE

To support timely CVL management, passive case detection along with awareness activities aimed at dog owners should be encouraged in endemic areas. Screening sites should be prioritized in accessible zones, as well as in socio-economically disadvantage areas. In parallel, CVL active case detection should be continued as a surveillance tool to guide control actions.

Human visceral leishmaniasis in Central-Western Brazil: Spatial patterns and its correlation with socioeconomic aspects, environmental indices and canine infection

In this ecological study, we investigated spatial patterns of human visceral leishmaniasis (VL) incidence, its correlation with socioeconomic aspects, environmental indices (obtained through remote sensing) and canine VL during 2011-2016 in the municipality of Rondonópolis, a relevant endemic area for VL in Central-Western Brazil. Human VL cases were georeferenced and point patterns were analyzed by univariate Ripley's K function and Kernel density estimation (KDE). Poisson-based scan statistics were used to investigate spatial and spatiotemporal clusters of human VL incidence at the neighborhood level. Socioeconomic and environmental characteristics were compared between neighborhoods within and outside spatial human VL clusters. Also, we assessed the correlation between smoothed human VL incidence and canine VL seropositivity rates within and between neighborhoods. Human VL cases were clustered up to 2000 m; four hotspots were identified by KDE in peripheral areas. Spatial and spatiotemporal low-risk clusters for human VL were identified in central and southern areas. Neighborhoods within spatial low-risk cluster presented higher mean income, literacy rate, sanitary sewage service coverage and lower altitude, compared to the rest of the municipality. A positive correlation was found between the occurrence of human and canine VL. On the northern outskirts, high human VL incidence was spatially correlated with high canine VL seropositivity in surrounding neighborhoods. In conclusion, human VL demonstrated a heterogeneous, aggregated and peripheral spatial pattern. This distribution was correlated with intra-urban socioeconomic differences and canine VL seropositivity at the neighborhood level.

A cross-sectional study of Leishmania spp. in draft horses from the Distrito Federal, Brazil: Seroprevalence, spatial distribution, and associated factors

Equine leishmaniasis is a neglected tropical disease caused by the protozoan of the Leishmania genus, and it has been reported in several countries around the world, especially Brazil. Therefore, the present investigation aims to conduct a cross-sectional study to determine the prevalence, spatial distribution, and associated factors with seropositivity for Leishmania spp. in draft horses from the Distrito Federal, Brazil. The serological survey was conducted on 411 animals, employing the Indirect Immunofluorescence Test (IFA) and Enzyme-Linked Immunosorbent Assay (ELISA). The Kappa (κ) and gross agreement indexes evaluated the Leishmania spp. seropositivity by IFA and ELISA test. The statistical analysis was performed using the Chi-square test and logistic regression. The spatial analysis showed the areas with the highest number of seropositive and the Moran autocorrelation analyses between the spatial distribution and the epidemiological model's explanatory variables. A 27.01 % co-positivity was observed with a κ index of 52.64 %. The final model considered the variables: access to water bodies (p-value = 0.008, Odds Ratio (OR) = 2.26, Confidence Interval (CI) = 1.24-4.13), the absence of the use of ectoparasiticide (p-value = 0.008, OR = 1.93 CI = 1.18-3.15) and traveling animal (p-value = 0.059, OR = 1.54, CI = 0.98-2.41). The Kernel map showed hot areas with a high concentration of nine positive animals per area and some lighter areas ranging from five to seven positive animals per area where control measures should be performed. The Moran autocorrelation analysis was significant for the variables: traveling animal (Moran's I = 0.540 and pseudo-p-value = 0.001) and the absence of use ectoparasiticide (Moran's I = 0.259 and pseudo-p-value = 0.005). The current study exposes a high seroprevalence of Leishmania spp. in horses in the Distrito Federal, Brazil. Moreover, it proposes that traveling animal, the access to water bodies and the absence of the use of ectoparasiticide are significantly associated with seropositivity for Leishmania spp. in draft horses, which may contribute to the implementation of prophylactic and controls measures where leishmaniasis is already stalled.

Basic knowledge about visceral leishmaniasis before and after educational intervention among primary health care professionals in Midwestern Brazil

Health education and training of primary health care (PHC) professionals are highly recommended to reduce the occurrence and lethality of visceral leishmaniasis (VL). This study assessed the impact of an educational intervention on the basic knowledge about visceral leishmaniasis (VL) among PHC professionals from the Brazilian municipality of Rondonopolis, an important endemic area for VL. Responses provided by physicians, nurses, nursing technicians and community health agents from 12 PHC facilities were recorded through the application of self-completed and semi-structured questionnaires before (n=92) and after (n=64) an in-person health training course covering various aspects of VL. Closed- and open-ended responses were compared by the chi-square test and analyses of word clouds, respectively. The proportion of professionals aware of the correct etiological agent (p<0.001) and transmission route (p<0.001) of VL increased post-intervention. In addition, they increased their ability to recognize fever (p<0.001), weakness (p<0.001), weight loss (p<0.001), pallor (p<0.001) and abdominal distention (p=0.013) as clinical manifestations of human VL, and weakness (p<0.001), alopecia (p<0.001) and weight loss (p=0.019) as signs of canine VL. Analyses of word clouds suggested that the participants became more aware of the role of dogs in VL transmission and the role of environmental management in the prevention of VL. In conclusion, the intervention positively impacted the baseline knowledge concerning VL among the professionals. This can support the planning of educational activities for the PHC team regarding early case detection, prevention and control of VL in endemic areas.

Are backyard characteristics relevant factors for the occurrence of human visceral leishmaniasis in Central-Western Brazil?

BACKGROUND

This retrospective case-control study aimed to investigate the factors associated with the occurrence of human visceral leishmaniasis (VL) in the municipality of Rondonópolis, which is a highly endemic area for VL in Central-Western Brazil.

METHODS

All VL cases reported in Rondonópolis from 2011 to 2016 were included. For each case, two neighborhood- and age-matched controls with the absence of past and present history of VL and negative rk39-based immunochromatographic test, were recruited. Data were retrospectively collected through interviews that assessed socioeconomic aspects, housing features, backyard characteristics, presence of animals and daily habits. A multivariate conditional logistic regression analysis was used to identify factors associated with human VL.

RESULTS

During the study period, 81 VL cases were reported in Rondonópolis, of which 37 (45.7%) were included in this study. Seventy controls were also included. The variables associated with VL occurrence were the outdoor location of a bathroom and/or kitchen separated from the rest of the house (OR 7.8; 95% CI 2.1 to 29.5), the presence of a vegetable garden (OR 5.3; 95% CI 1.3 to 21.2) and the presence of decaying fruits (OR 10.7; 95% CI 2.0 to 52.1) in the backyard.

CONCLUSIONS

Our findings suggest an association between backyard characteristics and VL. This may be useful in guiding preventive and control measures against zoonotic VL worldwide.

Detecting antibodies to Leishmania infantum in horses from areas with different epizooticity levels of canine leishmaniosis and a retrospective revision of Italian data

Background

Leishmania infantum is a vector-borne pathogen endemic in countries in the Mediterranean basin, including Italy. Dogs act as the primary reservoir for this parasite, but other animal species may also be infected. Low-to-moderate seroprevalence levels of infection have been reported in apparent healthy equine populations in southern Europe, reinforcing the importance of exploring those species, including horses, that act as a food source for vectors and may thus participate in the epizoological scenario of canine leishmaniosis (CanL) and zoonotic visceral leishmaniosis (ZVL). Since little is known regarding the exposure to L. infantum in horses in Italy, we assessed the seroprevalence in healthy equine populations from different CanL endemic areas.

Methods

The survey was conducted on 660 apparently healthy horses distributed throughout central and northern regions of Italy between 2016 and 2019. Blood samples were collected and the presence of anti-Leishmania antibodies (IgG) was investigated by the immunofluorescence antibody test. Information on the location and altitude of the stables, along with the horses’ breed, age, sex, and reproductive status was obtained by filling in a questionnaire. This was then used for statistical analysis by generalized linear models to explore risk factors associated with seroreactivity to L. infantum.

Results

An average seroprevalence of 13.9% was detected for L. infantum in the equine populations investigated, with statistically significant associations between seroprevalence, geographical variables (northern vs central Italy, origin and altitude) and individual factors (i.e. age and breed morphotype).

Conclusions

Our results highlight that horses are frequently exposed to L. infantum. Further prevalence surveys in horses, also using direct methods (e.g. PCR), are warranted to clarify the role of these hosts in the epidemiology of Leishmania in Italy.

Where, when, and how the diagnosis of human visceral leishmaniasis is defined: answers from the Brazilian control program

BACKGROUND

Timely diagnosis is recommended by the Brazilian Visceral Leishmaniasis (VL) Surveillance and Control Program to reduce case fatality. Attempts at assessing this topic in Brazil are scarce.

OBJECTIVE

This study aimed to describe where, when, and how the diagnosis of VL has been performed in a Brazilian endemic setting.

METHODS

Data of all autochthonous cases confirmed between 2011 and 2016 (N = 81) were recorded. The care-seeking itinerary until the confirmation of VL diagnosis was assessed among 57 patients.

FINDINGS

The majority of VL cases (79.1%) were reported by referral hospitals. The patients mainly sought primary health care centres at the onset of symptoms. However, they had to visit seven health services on average to achieve a confirmed diagnosis. The time from the onset of symptoms to the diagnosis of VL (T_D) ranged from 1-212 (median, 25) days. The T_D was longer among adult patients. There was a direct correlation between the patient’s age and T_D (r = 0.22; p = 0.047) and a higher occurrence of deaths due to the disease among older patients (p = 0.002). Almost all the patients (98.9%) underwent laboratory investigation, and the VL diagnosis was mainly confirmed based on clinical-laboratory criteria (92.6%). Positive results for the indirect fluorescence antibody test (22.7%) and parasitological examination plus rk39-based immunochromatographic tests (21.3%) were commonly employed.

MAIN CONCLUSIONS

VL diagnosis was predominantly conducted in hospitals with a long T_D and wide application of serology. These findings may support measures focused on early diagnosis, including a greater involvement of the primary health care system.