Risk analysis and prediction of visceral leishmaniasis dispersion in São Paulo State, Brazil

There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

Abstract

Visceral leishmaniasis (VL) is an important neglected disease caused by a protozoan parasite, and represents a serious public health problem in many parts of the world. It is zoonotic in Europe and Latin America, where infected dogs constitute the main domestic reservoir for the parasite and play a key role in VL transmission to humans. In Brazil this disease is caused by the protozoan Leishmania infantum chagasi, and is transmitted by the sand fly Lutzomyia longipalpis. Despite programs aimed at eliminating infection sources, the disease continues to spread throughout the Country. VL in São Paulo State, Brazil, first appeared in the northwestern region, spreading in a southeasterly direction over time. We integrate data on the VL vector, infected dogs and infected human dispersion from 1999 to 2013 through an innovative spatial temporal Bayesian model in conjunction with geographic information system. This model is used to infer the drivers of the invasion process and predict the future progression of VL through the State. We found that vector dispersion was influenced by vector presence in nearby municipalities at the previous time step, proximity to the Bolívia-Brazil gas pipeline, and high temperatures (i.e., annual average between 20 and 23°C). Key factors affecting infected dog dispersion included proximity to the Marechal Rondon Highway, high temperatures, and presence of the competent vector within the same municipality. Finally, vector presence, presence of infected dogs, and rainfall (approx. 270 to 540mm/year) drove the dispersion of human VL cases. Surprisingly, economic factors exhibited no noticeable influence on disease dispersion. Based on these drivers and stochastic simulations, we identified which municipalities are most likely to be invaded by vectors and infected hosts in the future. Prioritizing prevention and control strategies within the identified municipalities may help halt the spread of VL while reducing monitoring costs. Our results contribute important knowledge to public and animal health policy planning, and suggest that prevention and control strategies should focus on vector control and on blocking contact between vectors and hosts in the priority areas identified to be at risk.

Author summary

Visceral leishmaniasis [VL] is an important but neglected tropical disease that occurs worldwide. In areas where the disease is zoonotic, it is considered a serious public and animal health problem. In Brazil, despite the existing prevention and control programs, the disease is spreading, and in São Paulo State its dispersion presents a distinct temporal-geographic pattern. The goal of our study was to understand the landscape, climatic and economic factors that influence the dispersion of visceral leishmaniasis in Sao Paulo State, and then use these findings to predict its spread over time and space. To this end, we integrated data on the sand fly vector of the causative parasitic agent of VL, infected dogs and human cases. We find that landscape and climate were more important than economic factors in predicting competent vector, infected human and infected dog distributions, and the presence of the competent vector and infected dogs strongly influenced the dispersion of infected humans. Our study represents the first integrated investigation of vector and infected host invasion potential for individual municipalities, contributing to VL disease prevention and control planning in São Paulo State.

Related collections

Most cited references 33

Record: found
Abstract: found
Article: not found

Importance of worldwide asymptomatic carriers of Leishmania infantum (L. chagasi) in human.

Bernard Ferrua, Pierre Marty, Gregory Michel … (2011)

Leishmaniasis due to Leishmania infantum (syn. L. chagasi) infection is a zoonotic disease present mainly in Mediterranean basin, central Asia and Brazil. Besides a limited number of human cases of clinical visceral leishmaniasis, a great number of infections remains asymptomatic. In this review, the prevalence of asymptomatic carriers of L. infantum was evaluated worldwide using parasitological methods or indirect testing such as a skin test or serology. The consequences of the presence of asymptomatic carriers on parasite transmission by blood donation or the development of clinical visceral leishmaniasis in immunocompromised individuals and its possible role as reservoir are discussed. Copyright © 2011 Elsevier B.V. All rights reserved.

0 comments Cited 75 times – based on 0 reviews      Review now

Bookmark

Record: found
Abstract: found
Article: found

Is Open Access

Prevalence and Factors Associated with Leishmania infantum Infection of Dogs from an Urban Area of Brazil as Identified by Molecular Methods

Wendel Coura-Vital, Marcos José Marques, Vanja Veloso … (2011)

Introduction Human visceral leishmaniasis (HVL) constitutes a public health problem that affects millions of people throughout the world [1]. Over the past decade, there has been an average of 3379 cases of HVL per year in Brazil, with an incidence of 1.9 cases per 100,000 inhabitants [2]. During this period, however, an increase in the prevalence of the disease has been observed in several urban areas, and this phenomenon may be attributed to high population density, increased migration, environmental changes, inadequate living conditions and vector adaptation [1], [3]. In South America and Europe, the causative agent of HVL is Leishmania (Leishmania) infantum, a protozoan parasite transmitted by sand flies of the Phlebotominae family, which are widely distributed in both wild and domestic surroundings [4]. Dogs are the main urban reservoirs and represent the major source of contagion for the vector by virtue of their high prevalence of infection and intense cutaneous parasitism [5]. Furthermore, it has been estimated that more than 50% of seropositive dogs are asymptomatic [6] and may remain free of clinical symptoms for several years or even throughout life [7]. The prevalence of canine visceral leishmaniasis (CVL) in endemic areas of Brazil ranges between 5.9 and 29.8% [8]–[13], although the serological methods employed in the detection of CVL exhibit low sensitivities and may underestimate the true value [14]–[15]. The Brazilian Ministry of Health, through the Control Program of Visceral Leishmaniasis (CPVL), has instituted specific measures to control the dissemination of the disease, and these include early diagnosis and treatment of human cases, identification and elimination of seropositive infected dogs, control of insect vectors and health education [2]. To date, however, the actions of CPVL have had little impact, and this negative outcome has been ascribed to delays in detecting and eliminating infected dogs, the tendency to replace infected dogs by susceptible puppies, and the low sensitivity of the available serological methods [16]–[18]. Although serological techniques lack the sensitivity required to detect Leishmania in the initial stages of infection, polymerase chain reaction (PCR) based assays can disclose the presence of protozoan DNA very early on, even before seroconversion [19]–[20]. Epidemiological studies employing modern molecular techniques have revealed that the prevalence of CVL in endemic areas in Europe is far greater than serological methods had previously suggested [15], [21]–[22]. According to De Andrade et al. [14], it is possible that as many as 62% of Brazilian dogs showing negative serological and parasitological tests for L. infantum would be classified as CVL-positive according to PCR and restriction fragment length polymorphism (RFLP) assays. A cohort study conducted by Oliva et al. [20] showed that most of the animals had PCR-positive results months before seroconversion. In addition, experimentally infected dogs have been found to be positive by conjunctival PCR by 45 days of infection [23]. To understand the expansion and urbanization of VL, it is necessary to identify the risk factors associated with human and/or canine infection. A number of publications have considered the factors influencing HVL [24]–[26], but the potential risk factors of the canine disease have received far less attention. Information concerning animal susceptibility and its association with race, size, type of hair and age is available [8], [27]–[28]. However, factors relating to the domiciliary and peridomiciliary environment, the socioeconomic status of the owner, the type of care provided for the animal, and specific animal behavior must be investigated to explain the importance of dogs in the maintenance of CVL in urban areas. In view of the aforementioned problems an investigation was undertaken to look into the prevalence of L. infantum infection using PCR followed by RFLP and serological methods (ELISA). The factors associated with L. infantum infection among seronegative (determined by enzyme-linked immunosorbent assay - ELISA) and PCR-RFLP–positive dogs were also assessed. The L. infantum infection criterion proposed herein prioritizes CVL early onset. This study was conducted in Belo Horizonte, the capital of the State of Minas Gerais, located in Southeastern Brazil, which is considered an area of active transmission [29]. Methods Ethical statement The study was approved by the Committees of Ethics in Animal Experimentation of the Universidade Federal de Ouro Preto (protocol no. 083/2007), of the Universidade Federal de Minas Gerais (protocol no. 020/2007), and of the City Council of Belo Horizonte (protocol no. 001/2008). All procedures in this study were according to the guidelines set by the Brazilian Animal Experimental Collage (COBEA), Federal Law number 11794. Owners of the dogs participating in the project were informed of the research objectives and were required to sign the Informed Consent Form before sample and data collection. Study design The cross-sectional study was conducted in 2008 in the northwest sanitary district of Belo Horizonte, which covers an area of 36.874 km2 (Fig. 1). According to the census by the Instituto Brasileiro de Geografia e Estatística in 2007, the human population of this area is 360,000. The canine population comprised 20,883 animals, according to the Zoonosis Control Management of the northwest sanitary district. At the time of the study, the prevalences of CVL in Belo Horizonte and its northwest sanitary district were 7.6 and 7.8%, respectively [30]. With an expected prevalence of CVL in the study area of between 5 and 10%, the 95% confidence interval, and an estimated precision of 1.5%, the appropriate sample size for the study was calculated to be approximately 1500 animals. Because of the high prevalence of seropositive dogs and the presence of human cases, the activities of the CPVL, including canine surveys (diagnosis and culling seropositive dogs), have been carried out in the study area annually. The present field work was done in close collaboration with the Municipality Health Service, and the data were collected during the canine survey census, conducted by the health agents, as part of CVLP's routine. The studied area was selected within the northwest sanitary district by convenience and was chosen because at that moment (2008) a canine survey was beginning in this area. The households visited by the CVLP in an area that comprised of 37 census tracts (according to the Brazilian Institute of Geography and Statistics) [31] were included in the present study. A total of 918 households were included in this study, and all dogs within selected houses were sampled. 10.1371/journal.pntd.0001291.g001 Figure 1 Municipality of Belo Horizonte, state of Minas Gerais, Brazil, subdivided into sanitary areas. Collection of data A trained research team interviewed the owners of the study animals using a previously tested, structured questionnaire that sought information regarding the following groups of variables: (i) knowledge about the disease (i.e., form of transmission and clinical signs of HVL); (ii) knowledge about the vector (characteristics and presence in the domicile and peridomicile); (iii) knowledge about the host (epidemiological importance of the host, clinical signs of leishmaniasis, and care of the dog); (iv) socioeconomic characteristics of the owner (per capita/family income, and schooling); (v) characteristics of the domicile, annexes and surroundings [i.e., structure of roof, floor and walls; number of rooms, including bedrooms; number of residents; presence of trees (particularly banana trees); rubble; exposed garbage; dead leaves; and vegetable garden]; (vi) method of garbage disposal (collected, burnt or buried); and (vii) presence of other domestic animals (birds, cats and cattle). The knowledge about the disease was validated according to self-reporting of the mainly symptoms of LVC and LVH. Vector recognition was acknowledged by self-reporting and validated by the showing of different diptera species samples (Lutzomyia longipalpis and Aedes aegypti) to the participants. The following information on the dogs was collected on an appropriate form: age, sex, size, hair type, breed, behavior (habits related to the place where the dog sleeps spends most of its time, i.e. in the street, in the residence, in the backyard), dog care, clinical examinations, past history of vaccination and serological exams previous to leishmaniasis. Some characteristics were defined by the health agents, such as breed, dog size, hair type and clinical evaluation. These characteristics are routinely obtained and registered in a standardized form used by CPVL in the canine survey. The hair type was defined according to the breed, i.e., collie was classified as long-furred hair, Doberman as short-furred. Dog size also was defined according to the breed, i.e., pinscher was categorized as small size, poodle as medium size and German shepherd as large size. According to the absence/presence of clinical infection signs, the dogs were categorized as asymptomatic, with no signs suggestive of disease, and symptomatic, with characteristic clinical signs of visceral leishmaniasis, such as opaque bristles, severe loss of weight, onychogryphosis, cutaneous lesions, apathy and keratoconjunctivitis. Collection of blood samples A sample of peripheral blood (5 mL) was collected by puncture of the brachiocephalic vein and an aliquot transferred to a glass vial containing sufficient anticoagulant (ethylenediaminetetraacetic acid; EDTA) to give a final concentration of 1 mg/mL. The blood sample was centrifuged (1500–1800×g; 20 min), the buffy coat containing the leukocytes removed, resuspended in 10 mM Tris-HCl buffer (supplemented with 1 mM EDTA) in the proportion of 1∶1, and stored at −80°C until required for PCR-RFLP. The remaining portion of the blood sample was transferred to two separate filter papers for subsequent analysis by enzyme-linked immunosorbent assay (ELISA). Enzyme-linked immunosorbent assay ELISA was performed in parallel in the Laboratory of Immunopathology of Universidade Federal de Ouro Preto (LIMP) and the Laboratory of Zoonosis of the Prefeitura Municipal de Belo Horizonte (LZOON). The presence of IgG against Leishmania in blood samples was determined using an “in-house” ELISA procedure performed at the LIMP. Soluble Leishmania chagasi (MHOM/BR/1070/BH46) antigen (SLA) was prepared by the method of Reis et al. [32] from promastigotes harvested from stationary-phase liver infusion tryptose cultures. The concentration of protein in the SLA solution was determined as previously described [33] and adjusted to 1000 µg/mL. Diluted SLA was divided into small portions and stored at −70°C until required for assay. In the ELISA procedure, 96-well MaxiSorp™ microplates (Nalge Nunc Int., Rochester, NY, USA) were coated with SLA (2 µg/well) and maintained overnight at 4–8°C. Wells were then washed, and eluates from blood dried on filter paper were added at 1∶80 dilution. To perform the reaction, filter paper was thawed and 5-µm-diameter spots eluted in casein-PBS for testing by ELISA. The wells were washed again prior to the addition of peroxidase-conjugated sheep anti-dog IgG (anti-heavy chain specific; Bethyl Laboratories Inc., Montgomery, TX, USA). After further washes, chromogenic substrate (O-phenylenediamine; Sigma–Aldrich, St. Louis, MO, USA) was added, and the absorbance was read on an automatic EL 800G ELISA microplate reader (Bio Tek Instruments, Winooski, VT, USA) at 492 nm. The anti-IgG conjugate concentration employed (1∶16,000 dilution) was determined by a block titration method employing positive and negative standard sera. The cut-off value was established as the mean absorbance value +2 SD from 20 eluates from blood of uninfected dogs dried on filter paper. Duplicate filter papers were submitted to ELISA at LZOON using a kit developed by Fundação Oswaldo Cruz, EIE – Ensaio Imunoenzimático para diagnostico da leishmaniose visceral canina Bio-Manguinhos (Rio de Janeiro, RJ, Brazil) and applied according to the supplier's instructions. Molecular methods (PCR-RFLP) DNA was extracted from buffy coat fractions using Wizard™ Genomic DNA purification kits (Promega, Madison, WI, USA) according to the manufacturer's instructions. The primers used to amplify the conserved region of the Leishmania kDNA minicircle were as follows: forward: 5′-GGG (G/T)AG GGG CGT TCT (G/C)CG AA-3′; reverse: 5′-(G/C)(G/C)(G/C) (A/T)CT AT(A/T) TTA CAC CAA CCC C-3′ [34]. The reaction mixture consisted of 1× buffer [10 mM Tris-HCl, 50 mM KCl (pH 8.8)], 1.5 mM MgCl2, 2.0 µM dNTP, 1.0 pmol of each primer, 0.76 U of Taq polymerase (Sinapse, São Paulo, SP, Brazil), 2.5 µL DNA and Milli Q water to a final volume of 12.5 µL/well (MicroAmp® Fast Optical 96-Wells, Applied Biosystems, Foster City, CA, USA). PCR reactions were performed in a 96-well Verit Thermal Cycler (Applied Biosystems) using the following program: initial denaturation at 94°C for 1 min, followed by 40 cycles of 30 s at 93°C, 1 min at 64°C and 1 min at 72°C, with a final extension at 72°C for 7 min. DNA from L. chagasi (strain MHOM/BR/1972/BH46), obtained from the DNA reference library at LIMP, was used as positive control, while DNA from non-infected dogs, raised in the experimental kennels at UFOP, was used as negative control. PCR amplicons (5 µL) were digested for 3 h at 37°C in 1 U of Hae III (Invitrogen, Carlsbad, CA, USA) in 1× buffer [10 mM Tris-HCl, 10 mM MgCl2 (pH 7.5)] and Milli Q water to a final volume of 15.0 µL/well (MicroAmp® Fast Optical 96-Well, Applied Biosystems) [35]. Restriction fragments, together with a 25 bp DNA ladder (Invitrogen), were electrophoresed in 10% polyacrylamide gels at 40 mA in 89 mM Tris base (pH 8.0), 89 mM boric acid and 2 mM EDTA. Bands were detected by silver staining, and the patterns were compared with those obtained using DNA from L. (L.) amazonensis (MHOM/BR/1973/M2269), L. (Viannia) braziliensis (MHOM/BR/1975/M2903) and L. (L.) chagasi (MHOM/BR/1972/BH46) from the DNA reference library at LIMP. Samples with very faint bands in PCR were extracted again and assayed by PCR to obtain better bands in the RFLP profile. All samples that did not show similar profiles to L. infantum DNA were excluded from the present study. Animal groups Dogs were classified as seronegative if ELISA results were negative in both laboratories (LIMP and LZOON). The seronegative animals were categorized as (i) infected group: animals presenting positive PCR-RFLP for L. infantum; and (ii) non-infected group; animals presenting negative PCR-RFLP for L. infantum. These two groups were analyzed to identify factors associated with infection. Statistical analysis Databases were generated using EpiData version 3.2 (EpiData Association, Odense, Denmark) by double entry of the results, and they were subsequently corrected, compared and analyzed using STATA version 11.0 software (Stata Corp., College Station, TX, USA). To investigate the factors potentially associated with L. infantum infection, the infected and non-infected groups of animals were compared. A mixed logistic regression model [36] was employed to evaluate the association between the independent and dependent variables. This model was chosen on the basis that the sampling process included all dogs within a studied household, and it incorporated the underlying assumption that observations obtained from dogs in the same household were mutually dependent while observations from dogs in different households were independent. The xtmlogit function provide by Stata was used to perform the analysis and the household was included as a random effect. Univariate analysis using the mixed logistic regression model was conducted for all variables collected, and those that attained a p value 3 minimum salary), type of floor in the residence (other materials/tiles or wood), type of neighborhood (houses/houses with garden/lands), origin of dog (another district/present neighborhood), dog stays predominantly in the backyard (yes/no), where the dog sleeps (indoors/outdoors), and lack of previous CVL serological examination (no/yes). 10.1371/journal.pntd.0001291.t001 Table 1 Distribution of seronegative dogs (n = 1213) according to the characteristics of the animals, Brazil 2008. Variable PCR-RFLP Univariate analysisOdds Ratio(95% CI) ρ values Positiven (%) Negativen (%) Hair Short 173 (58.5) 491 (53.5) Long 123 (41.5) 426 (46.5) 1.2 (0.9–1.7) 0.17 Veterinary check ups Yes 151 (55.3) 527 (59.4) No 122 (44.7) 360 (40.6) 0.8 (0.6–1.1) 0.25 Symptomatic Yes 4 (1.4) 25 (2.7) No 292 (98.6) 890 (97.3) 0.4 (0.1–1.5) 0.20 Origin of the animal District of residence 154 (56.2) 459 (51.6) Other district 120 (43.8) 431 (48.4) 0.8 (0.6–1.1) 0.16 Dog staying predominantly in the backyard No 36 (13.1) 153 (17.2) Yes 238 (86.9) 737 (82.8) 1.4 (0.9–2.3) 0.10 Sleeping place Inside the house 51 (18.6) 208 (23.4) In the garden 223 (81.4) 682 (76.6) 1.4 (1.0–2.1) 0.08 CVL sorological examination previously Yes 183 (68.8) 662 (76.1) No 83 (31.2) 208 (23.9) 1.5 (1.1–2.2) 0.02 Age ≤24 months 108 (36.5) 292 (31.8) >24 and ≤84 months 116 (39.2) 411 (44.8) 0.7 (0.5–1.0) 0.08 >84 months 72 (24.3) 214 (23.3) 0.9 (0.6–1.3) 0.59 10.1371/journal.pntd.0001291.t002 Table 2 Distribution of owners (n = 918) of seronegative dogs according to the socioeconomic and environmental conditions and understanding of the disease, Brazil 2008. Variable PCR-RFLP Univariate analysisOdds Ratio (95%CI) ρ values Positive (%) Negative (%) Socioeconomic conditions Family income >3 minimum wages* 72 (54.1) 281 (65.8) 1 to 3 minimum wages 24 (18.1) 88 (20.6) 0.9 (0.6–1.5) 0.78 3 minimum wages* 2.4 (1.5–3.9) 2.3 (1.4–3.8) Knowledge of the owner regarding the vectoryes versus no 1.4 (0.9–2.2) 1.9 (1.1–3.4) Dog staying predominantly in the backyardyes versus no 1.4 (0.9–2.3) 2.2 (1.1–4.1) CVL serological examination previouslyno versus yes 1.5 (1.1–2.2) 1.5 (1.1–2.3) *Brazilian minimum wages (Brazilian monthly minimum wage = U$262). Discussion The results in the present investigation show that the prevalence of L. infantum infection in dogs as determined by PCR-RFLP (24.7%) is higher than that detected by serology (15.9%). Such divergent values are highly significant because they demonstrate that the magnitude of CVL in this study area, which is under constant CPVL intervention, has been underestimated. Factors associated with early L. infantum infection (PCR-RFLP+) were the socioeconomic conditions of the owner, the behavior of the dog, knowledge of the owner regarding the vector and the care the dogs had received. These results are relevant because they allow better understanding of the transmission of VL in a large city such as Belo Horizonte where leishmaniasis is expanding [29], [38]. Moreover, the diagnosis of canine infection by L. infantum was achieved through the application of PCR-RFLP, which indicated the early onset of CVL. Additionally, as the data originated directly from dog owners and their respective animals, it was possible to perform a detailed analysis of a range of information and to determine the factors associated with CVL. Studies in European endemic areas have also demonstrated an elevated prevalence of infection (typically 60–80%) by PCR in comparison with that indicated by serology (generally<30%) [15], [39]. Species identification was essential, especially because Belo Horizonte is an area of the simultaneous occurrence of cutaneous and visceral leishmaniasis and the dog can be host for both parasites [40]. Among the examined samples, only three showed molecular bands similar to L. braziliensis, and they were not included in the present study. Approximately a quarter of seronegative dogs were infected by L. infantum according to PCR-RFLP. These false-negative animals were likely within an “immunological window” that occurs prior to seroconversion, during which period B lymphocytes do not secrete polyclonal antibodies, and consequently, serological methods are less sensitive at this stage of the infection [41]. It is possible that false-negative dogs remain in the community as undisclosed reservoirs and, thus, interfere with the effectiveness of control measures. Indeed, despite recent intense efforts to eliminate seropositive dogs, no reduction in the incidence of HVL or CVL has been observed in urban areas [42]. Little is known if seronegative/PCR-positive dogs are immunologically resistant to Leishmania [43] or if they will develop the disease. However, it is possible to state that such animals have had previous contact with the parasite. Such information is relevant because canine positivity for Leishmania is included among the indicators for the prioritization of target control areas by the Ministry of Health. Although molecular biology methods are more promising in identifying infection, their use in the field requires further standardization and optimization. HVL is favored by precarious socioeconomic and housing conditions, migratory movements and the presence of vector and reservoir in the domestic environment [24]–[26], [44]. However, little is known about the risk factors that facilitate Leishmania infection in the main reservoir of the disease, namely, the domestic dog. To obtain a better understanding of these factors, comparisons were made between non-infected (seronegative/PCR-RFLP negative) animals and those infected (seronegative and PCR-RFLP positive). The decision to use PCR-RFLP–positive and seronegative animals was due to the detection of L. infantum in the initial stage of infection before seroconversion [19]–[20]. Regarding socioeconomic conditions of the owner, animals belonging to families with incomes of less than twice the minimum salary were twice as likely to be infected in comparison with dogs of higher-income families (three minimum salaries). In this context, family income is a proxy variable of socioeconomic status and is probably associated with the structure of the most vulnerable domiciles. Indeed, Oliveira et al. [26] demonstrated an association between HVL and family income following a study in the metropolitan area of Belo Horizonte. These data are also consistent with literature confirming that VL is more frequent in areas of precarious socioeconomic status [45]. In general, dog owners showed little knowledge of phlebotomine sand flies. Interestingly, however, dogs whose owners knew about the vector were twofold more likely to acquire the infection than those whose owners were not familiar with the insect. This variable can be understood as an indirect measure of exposure to phlebotomines and shows the importance of using proxy. A similar observation has been reported by Moreno et al. [44], who noted that in the metropolitan area of Belo Horizonte, the likelihood of being infected by Leishmania is six times greater for people who have seen the vector than for those who have not. A high density of Lu. longipalpis was observed in the present study area [38], so it is not surprising that the most respondents had noted the presence of the vector in their residences and neighborhood. Dogs that usually lived in the backyard were twice as likely to acquire the infection as those that remained inside the house. According to Galvez et al. [46], living outdoors is significantly associated with serological positivity for the parasite among canines. In the recent survey performed in Granada, Spain, dogs that slept outdoors were at greater risk than those sleeping indoors because of vector density [47]. On the other hand, Cabrera et al. [48] reported that the risk of infection by CVL is similar for dogs that live within the perimeter of a residence and those that wander the streets or woods. To reduce the risk of CVL, some preventive measures may be adopted, including the maintenance of dogs in closed kennels during periods of intense vector activity, the reduction of microenvironmental factors that favor the development of the vector in the residence, and the use insecticide-impregnated collars [22], [49]. However, the implementation of such measures depends not only on the degree of awareness of the dog owner about the disease but, mainly, on socioeconomic issues, because the most affected population could not afford to leave their dogs in kennels or buy impregnated collars. Only 35.5% of owners knew of the important role of dogs in the transmission of Leishmania, and 45.5% had knowledge of the symptoms of CVL, although 22.8% reported previous ownership of a dog that had contracted CVL. Animals serologically tested by the CPVL previously were less likely to be infected. This finding indicates that seropositive dogs have been removed regularly by the control measures and that dogs that remain seronegative in successive tests are more likely to be CVL-free. Unfortunately, however, the replacement of dogs within the study area is frequent, and these animals would be more susceptible to infection by L. infantum [50]. The mean age of infected dogs was 49.8 (SD 41.3) months, whereas the mean age of non-infected dogs was 54.5 (SD 39.0) months. One possible explanation for this result is that the CPVL had removed seropositive dogs during the canine survey. Therefore, PCR was detecting L. infantum infection early, in younger dogs. Although the univariate analysis was significant, dog age was not associated with L. infantum infection. Galvez et al.[46] examined the age at which seroprevalence showed a bimodal distribution, with one peak appearing in the young dogs (1–2 years) and a second, more evident, peak among the older dogs (7–8 years). On the other hand, França-Silva et al. [8] observed that the prevalence of infection was not correlated with dog age. The emergence of leishmaniasis in Belo Horizonte dates from the late 1980s, when the disease spread from areas marked by poor socioeconomic conditions [51]. At the present time, the disease is increasing, and VL has been detected in all regions of the city [38]. Indeed, the urbanization of VL is a current reality in many Brazilian cities. We tried to identify domiciles that were most vulnerable to the presence of the vector and occurrence of infection. However, no variable related to households was maintained in the final model. In a study conducted in Northeastern Brazil, the risk of HVL was greater in residences that lacked sewage services and garbage collection [25]. In the present study, no influence of such factors on the prevalence of CVL was found, as 99% of domiciles were served by a main sewage connection and nearly all received garbage collection. Even though our sampling procedure was not probabilistic, the studied households were sampled from a census survey, and the investigated blocks are representative of the northwest sanitary district. This study was not designed to evaluate a representative sample of Belo Horizonte but to assess the prevalence of infection by PCR-RFLP in seronegative dogs and identify risk factors for infection in these animals. However, the northwest sanitary district is representative of the city, with buildings, commerce, residences and green areas. Moreover, the main limitation of a cross-sectional study in identifying risk factors is that it does not permit causal inferences because time factors were not evaluated. Although it is not easy to attribute the associated factors with new measures that can be adopted by CPVL, it is necessary to better investigate the factors associated with VL expansion in urban areas. Improved understanding of urbanization processes in large cites such Belo Horizonte can help the CPVL to adopt measures that are more effective at controlling the spread of the disease. It is important to emphasize that the control of HVL depends on the management of CVL because dogs are the main urban reservoir of Leishmania and represent the main source of phlebotomine infection. The Control Program in Brazil used ELISA for screening and IFAT as a confirmatory test to identify seropositive dogs which are them euthanized. Due to the low level of humoral immune response, some of the infected dogs by L. infantum could not be detected. Therefore, using only seronegative dogs, this paper focuses on those animals that are positive by PCR and are not identified by the control program. Considering that the currently available serologic methods lack sufficient sensitivity and/or specificity to accurately identify all infected dogs, the employment of molecular diagnosis to detect the CVL infection before antibody production could be an efficient alternative. This study showed for the first time the identification of factors associated with early stage of CVL in animals seronegative with PCR-positive for L. infantum and therefore could contribute to better understanding of the involvement of this reservoir in urban-VL epidemiology. Additionally, for better investigation of the factors associated with VL expansion in urban areas further studies are required using a cohort study approach.

0 comments Cited 58 times – based on 0 reviews      Review now

Bookmark

Record: found
Abstract: found
Article: not found

Spatial analysis of American Visceral Leishmaniasis in Mato Grosso do Sul State, Central Brazil.

Suely Aparecida Correa Antonialli, Thais Gisele Torres, Antonio Paranhos Filho … (2007)

To map American Visceral Leishmaniasis (AVL) in Mato Grosso do Sul State (Central Brazil). The distribution of AVL was mapped, using the Geographic Information System. The disease was endemic to the Corumbá Region from 1913 to 1998. Spatial and temporal analysis indicated that the expansion route and dissemination through the State of the disease has been from west to east, coinciding with three different human interventions; two of them, a federal highway and a rail-road, were constructed in the early twentieth century, from east to west, from Bauru city, in São Paulo State, to Corumbá city, in Mato Grosso do Sul State. The third anthropogenic intervention was the construction of a gas pipeline that started in 1998, and attracted thousands of workers. This construction route has the same direction, west to east, and timescale as the observed expansion and dissemination of AVL. The results relate the expansion of the disease to intense human traffic along the route of spread.

0 comments Cited 58 times – based on 0 reviews      Review now

Bookmark

All references

Author and article information

Contributors

Edgar M Carvalho: Role: Editor

Journal

Journal ID (nlm-ta): PLoS Negl Trop Dis

Journal ID (iso-abbrev): PLoS Negl Trop Dis

Journal ID (publisher-id): plos

Journal ID (pmc): plosntds

Title: PLoS Neglected Tropical Diseases

Publisher: Public Library of Science (San Francisco, CA USA )

ISSN (Print): 1935-2727

ISSN (Electronic): 1935-2735

Publication date (Electronic): 6 February 2017

Publication date Collection: February 2017

Volume: 11

Issue: 2

Electronic Location Identifier: e0005353

Affiliations

[1 ]Department of Mathematics, University of Florida, Gainesville, Florida, United States of America

[2 ]Department of Preventive Veterinary Medicine and Animal Health, School of Veterinary Medicine and Animal Sciences, University of São Paulo, São Paulo, Brazil

[3 ]Department of Geography, University of Florida, Gainesville, Florida, United States of America

[4 ]Department of Epidemiology, School of Public Health, University of São Paulo, São Paulo, Brazil

[5 ]School of Forest Resources and Conservation, University of Florida, Gainesville, Florida, United States of America

Hospital Universitário Professor Edgard Santos, BRAZIL

Author notes

The authors have declared that no competing interests exist.

Conceptualization: AdPS DV.
Data curation: DV.
Formal analysis: AdPS DV.
Funding acquisition: AdPS.
Investigation: AdPS DV FGO LM.
Methodology: AdPS DV FGO LM.
Project administration: AdPS.
Resources: AdPS DV.
Software: AdPS DV.
Supervision: AdPS DV.
Validation: AdPS DV.
Visualization: AdPS DV JMTL FGO LM.
Writing – original draft: AdPS DV FGO JMTL.
Writing – review & editing: AdPS DV JMTL FGO LM.

* E-mail: anaiaps@ 123456usp.br

Author information

Anaiá da Paixão Sevá http://orcid.org/0000-0001-5203-012X

Article

Publisher ID: PNTD-D-16-01335

DOI: 10.1371/journal.pntd.0005353

PMC ID: 5313239

PubMed ID: 28166251

SO-VID: b24360a2-6b86-4162-bc80-616b3165e171

License:

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

History

Date received : 20 July 2016

Date accepted : 24 January 2017

Page count

Figures: 4, Tables: 1, Pages: 17

Funding

This project was co-funded by the National Council for Scientific and Technological Development - Brazil (CNPq, 205642/2014-4), the São Paulo Research Foundation - Brazil (FAPESP, 2011/23541-1), and the International Science and Technology Collaboration Project of Guangdong Province (#2014A050503053). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Custom metadata

PLOS Publication Stage vor-update-to-uncorrected-proof

Publication Update 2017-02-16

Data Availability All relevant data are within the paper and its Supporting Information files.

Risk analysis and prediction of visceral leishmaniasis dispersion in São Paulo State, Brazil

Read this article at

Abstract

Author summary

Related collections

Novel Coronavirus Disease COVID-19

Most cited references 33

Importance of worldwide asymptomatic carriers of Leishmania infantum (L. chagasi) in human.

Prevalence and Factors Associated with Leishmania infantum Infection of Dogs from an Urban Area of Brazil as Identified by Molecular Methods

Spatial analysis of American Visceral Leishmaniasis in Mato Grosso do Sul State, Central Brazil.

Author and article information

Contributors

Journal

Affiliations

Author notes

Author information

Article

History

Page count

Funding

Categories

Custom metadata

Comments

Comment on this article

Similar content 74

Cited by 34

Most referenced authors 498