Leishmaniasis in Bolivia. I. Lutzomyia longipalpis (Lutz & Neiva, 1912) as the vector of visceral leishmaniasis in Los Yungas

Visceral Leishmaniasis in Bolivia: Current Status

INTRODUCTION

In Bolivia, before 1982 there were no records of visceral leishmaniasis (VL) cases that would allow us to review and describe the temporospatial occurrence of VL by ecoregions in provinces and departments of Bolivia to evaluate its impact on public health, risk of outbreaks, or dispersion.

METHODS

This update on VL in Bolivia is based on research, reviews, and retrospective literature analyses of online data and libraries and institutional reports, from 1939 to the present.

RESULTS

In Bolivia, 56 cases of VL have been reported. Until 2014, only three endemic departments had been identified (La Paz, Santa Cruz, and Tarija). Since then, further cases have been recorded in Pando, Cochabamba, and Beni, and in Chuquisaca in 2015. In Yungas, a VL focus was confirmed by isolating and comparing parasites from human and dog cases, and from the Lu. longipalpis vector. VL cases from seven departments, involving 12 different ecoregions were located within the Amazon and Plata basins.

CONCLUSIONS

We confirmed that dogs are its primary reservoir, and Lutzomyia longipalpis is its main vector (currently dispersed in six departments). The primary vectors in areas where Lutzomyia longipalpis is absent are Migonemyia migonei and Lutzomyia cruzi.

Detection of multiple circulating Leishmania species in Lutzomyia longipalpis in the city of Governador Valadares, southeastern Brazil

Leishmaniasis encompasses a group of diverse clinical diseases caused by protozoan parasites of the Leishmania genus. This disease is a major public health problem in the New World affecting people exposed in endemic regions. The city of Governador Valadares (Minas Gerais/Brazil) is a re-emerging area for visceral leishmaniasis, with 191 human cases reported from 2008 to 2017 and a lethality rate of 14.7%. The transmission of the parasite occurs intensely in this region with up to 22% of domestic dogs with positive serology for the visceral form. Lu. longipalpis is one of the most abundant sand fly species in this area. Despite this scenario, so far there is no information regarding the circulating Leishmania species in the insect vector Lutzomyia longipalpis in this focus. We collected 616 female Lutzomyia longipalpis sand flies between January and September 2015 in the Vila Parque Ibituruna neighborhood (Governador Valadares/MG), which is located on a transitional area between the sylvatic and urban environments with residences built near a preserved area. After DNA extraction of individual sand flies, the natural Leishmania infections in Lu. longipalpis were detected by conventional PCR, using primers derived from kDNA sequences, specific for L. (Leishmania) or L. (Viannia) subgenus. The sensitivity of these PCR reactions was 0.1 pg of DNA for each Leishmania subgenus and the total infection rate of 16.2% (100 positive specimens). Species-specific PCR detected the presence of multiple Leishmania species in infected Lu. longipalpis specimens in Governador Valadares, including L. amazonensis (n = 3), L. infantum (n = 28), L. (Viannia) spp. (n = 20), coinfections with L. infantum and L. (Viannia) spp. (n = 5), and L. (Leishmania) spp (n = 44). Our results demonstrate that multiple Leishmania species circulate in Lu. longipalpis in Governador Valadares and reveal a potential increasing risk of transmission of the different circulating parasite species. This information reinforces the need for epidemiological and entomological surveillance in this endemic focus, and the development of effective control strategies against leishmaniasis.

Ecological niche modelling and predicted geographic distribution of Lutzomyia cruzi, vector of Leishmania infantum in South America

In some transmission foci of Leishmania infantum in Brazil, Lutzomyia cruzi could be considered the main vector of this pathogen. In addition, L. cruzi is a permissive vector of L. amazonensis. Its geographical distribution seems to be restricted and limited to Cerrado and Pantanal biomes, which includes some areas in Brazil and Bolivia. Considering that predicting the distribution of the species involved in transmission cycles is an effective approach for assessing human disease risk, this study aims to predict the spatial distribution of L. cruzi using a multiscale ecological niche model based in both climate and habitat variables. Ecological niche modelling was used to identify areas in South America that are environmentally suitable for this particular vector species, but its presence is not recorded. Vector occurrence records were compiled from the literature, museum collections and Brazilian Health Departments. Bioclimatic variables, altitude, and land use and cover were used as predictors in five ecological niche model algorithms: BIOCLIM, generalised linear model (logistic regression), maximum entropy, random forests, and support vector machines. The vector occurs in areas where annual mean temperature values range from 21.76°C to 26.58°C, and annual total precipitation varies from 1005 mm and 2048 mm. Urban areas were most present around capture locations. The potential distribution area of L. cruzi according to the final ecological niche model spans Brazil and Bolivia in patches of suitable habitats inside a larger climatically favourable area. The bigger portion of this suitable area is located at Brazilian States of Mato Grosso do Sul and Mato Grosso. Our findings identified environmentally suitable areas for L. cruzi in regions without its known occurrence, so further field sampling of sand flies is recommended, especially in southern Goiás State, Mato Grosso do Sul (borders with Mato Grosso, São Paulo and Minas Gerais); and in Bolivian departments Santa Cruz and El Beni.

First Record of Lutzomyia (Lutzomyia) longipalpis (Diptera: Psychodidae: Phlebotominae) on the Trinational Frontier (Brazil-Peru-Bolivia) of South-Western Amazonia

In South America, the main sand fly species involved in the transmission of Leishmania infantum chagasi (Cunha & Chagas, 1937), etiological agent of the visceral leishmaniasis (VL), is Lutzomyia longipalpis (Lutz & Neiva, 1912). The species has been recorded in Colombia, Venezuela, Bolivia, Argentina, Paraguay, Uruguay, and Brazil, where it is recorded in 24 of the 27 Brazilian states, except Acre, Amazonas, and Santa Catarina. Collections were carried out for one year (April 2013 to March 2014) using modified CDC light traps in different environments in Assis Brasil municipality, state of Acre. Two males of Lu. longipalpis were found in peridomiciliary location in a peri-urban area. This is the first record of the species in Acre. This finding may be considered by the health agencies located in the trinational frontier, and new collections are needed to evaluate the real distribution of the species.

The first record of Lutzomyia longipalpis in the Argentine northwest

In 2004, the urban presence of Lutzomyia longipalpis was recorded for the first time in Formosa province. In 2006, the first autochthonous case of human urban visceral leishmaniasis (VL) was recorded in Misiones in the presence of the vector, along with some canine VL cases. After this first case, the vector began to spread primarily in northeast Argentina. Between 2008-2011, three human VL cases were reported in Salta province, but the presence of Lu. longipalpis was not recorded. Captures of Phlebotominae were made in Tartagal, Salta, in 2013, and the presence of Lu. longipalpis was first recorded in northwest Argentina at that time. Systematic sampling is recommended to observe the distribution and dispersion patterns of Lu. longipalpis and consider the risk of VL transmission in the region.

Active surveillance of American tegumentary leishmaniasis in endemic areas in rural Bolivia

INTRODUCTION

American tegumentary leishmaniasis (ATL), including mucocutaneous leishmaniasis (MCL) and localized cutaneous leishmaniasis (LCL), is endemic in Bolivia. We describe the results of active surveillance of ATL from 2001 to 2006 and assess demographic data related to ATL epidemiology in the Yungas valleys.

METHODS

Community-based active ATL surveillance was performed by the institutions SERVIR, CÁRITAS, and the Health Services Department of La Paz, whose files were reviewed retrospectively. A cross-sectional survey was carried out to assess demographic data in two communities.

RESULTS

Two thousand nine hundred nine cases of ATL were detected from 2001 to 2006: 2,488 (85.5%) corresponded to LCL and 421 (14.5%) to MCL. A reduction in the proportion of mucosal cases was observed between 2001 and 2006. The proportion of MCL cases increased with age and was higher among males (15.5% versus 12.1%, p=0.018). The rate of positivity via direct observation of the parasite in dermal scrapings and in parasite cultivation was significantly higher for LCL than for MCL (p<0.001 and p=0.009, respectively). The rate of reactivity in the leishmanin skin test was higher in the group with mucosal lesions (p=0.012). The cross-sectional survey showed that 40% of the families had emigrated from the Altiplano.

CONCLUSIONS

It is necessary to undertake continuous case detection of ATL in the area, where the disease presents a high rate of mucosal cases. Increasing incidence seems to be associated with immigration and continuous deforestation to expand the crop-growing areas.

Sand fly fauna in Chapare, Bolivia: an endemic focus of Leishmania (Viannia) braziliensis

Data on the distribution and abundance of Lutzomyia spp. (Diptera: Psychodidae) in Bolivia is scarce. Sand flies from an area of Leishmania (Viannia) braziliensis endemicity in the Isiboro-Secure National Park in the Department of Cochabamba were captured and identified to species. In total, 945 sand flies (789 females and 156 males) belonging to 15 species were collected from the four collection points in two study villages in 2007. With 549 (58.1%) specimens, Lutzomyia shawi was the most abundant species, followed by Lutzomyia (Trichophoromyia) sp. (22.2%), Lutzomyia llanosmartinsi (8.3%), Lutzomyia antunesi (4.3%), and Lutzomyia olmeca (2.1%). Abundance and species composition varied between rainy and dry seasons, with 99.3% of all sand flies being collected outdoors. Because of species abundance and confirmed Leishmania infection in previous entomological collections, we believe Lu. shawi is the vector of L. (Viannia) braziliensis in Isiboro-Secure National Park.

Lutzomyia longipalpis in Clorinda, Formosa province, an area of potential visceral leishmaniasis transmission in Argentina

Phlebotomine captures were performed during 2004 in Clorinda, Argentina. Clorinda is located across the branches of the Paraguay river in front of Asunción city, Paraguay. Reports of canine and human visceral leishmaniasis in Asunción have been increasing since 1997, however neither leishmaniasis cases nor sand flies were ever recorded from Clorinda. Light traps were located in migration paths (bridges, port), and peridomestic environments of Clorinda and surrounding localities. Lutzomyia longipalpis was found in Clorinda and Puerto Pilcomayo, first report in a potential visceral leishmaniasis transmission area for Argentina. Active surveillance is required immediately in the localities involved and the surrounding area.

Comparative vectorial efficiency of Lutzomyia evansi and Lu. longipalpis for transmitting Leishmania chagasi

The infection rates and development of Leishmania chagasi in two sandfly species, Lutzomyia evansi and Lutzomyia longipalpis, were evaluated under natural and experimental conditions. Natural infection rates of Lu. evansi in San Andrés de Sotavento (Colombia) and Montañas de Peraza (Venezuela) (0.05 and 0.2%, respectively) were similar to those previously recorded for this species in Colombia and Venezuela and for Lu. longipalpis in many foci of American Visceral Leishmaniasis (AVL). Both sand fly species were able to support the development of two Colombian strains of L. chagasi experimentally acquired from dogs, hamsters or membrane feeders. However, the experimental infection rates and the sequence of parasite development in the guts of these sand flies revealed that parasite colonisation, differentiation, migration and attachment were more frequent and uniform in Lu. longipalpis than in Lu. evansi. This is consistent with a more recent association between L. chagasi and Lu. evansi, and these results might help to explain the irregularity of AVL outbreaks in foci where Lu. evansi has been reported as the sole vector.

Wing geometry as a tool for studying the Lutzomyia longipalpis (Diptera: Psychodidae) complex

Toro Toro (T) and Yungas (Y) have been described as genetically well differentiated populations of the Lutzomyia longipalpis (Lutz & Neiva, 1912) complex in Bolivia. Here we use geometric morphometrics to compare samples from these populations and new populations (Bolivia and Nicaragua), representing distant geographical origins, qualitative morphological variation ("one-spot" or "two-spots" phenotypes), ecologically distinct traits (peridomestic and silvatic populations), and possibly different epidemiological roles (transmitting or nor transmitting Leishmania chagasi). The Nicaragua (N) (Somotillo) sample was "one-spot" phenotype and a possible peridomestic vector. The Bolivian sample of the Y was also "one-spot" phenotype and a demonstrated peridomestic vector of visceral leishmaniasis (VL). The three remaining samples were silvatic, "two-spots" phenotypes. Two of them (Uyuni and T) were collected in the highlands of Bolivian where VL never has been reported. The last one (Robore, R) came from the lowlands of Bolivia, where human cases of VL are sporadically reported. The decomposition of metric variation into size and shape by geometric morphometric techniques suggests the existence of two groups (N/Y/R, and U/T). Several arguments indicate that such subdivision of Lu. longipalpis could correspond to different evolutionary units.

[Phlebotomines (Diptera: Psychodidae) focusing visceral leishmaniasis in the State of Mato Grosso do Sul, Brazil]

INTRODUCTION

In the Americas, Lutzomyia longipalpis has been incriminated as the vector of visceral leishmaniasis in almost all the areas in which this disease has been reported. The notification of human cases of visceral leishmaniasis and the presence of dogs with an appearance suggestive of the disease in the country of Corumbá, Mato Grosso do Sul State, Brazil, led us to undertake an entomological investigation in this area, for the purpose of identifying the phlebotomine vector.

MATERIAL AND METHOD

The county of Corumbá is located in the Pantanal region and its urban area is situated at 18 degrees 59' 44" South and 57 degrees 39' 16" West. The research project was carried out in peri and intradomiciliary environments, in three urban districts, one of which was central and the other two on the outskirts, and in a cave situated outside the urban perimeter. Most of the captures were made weekly with light automatic traps, in the period from February 1984 to December 1986. Meteorological data for this period were obtained from the city's meteorological station and those for the period from 1925 to 1982 from the literature.

RESULTS

The urban phlebotomine fauna consisted of eight species and was similar to that of the cave, except that in the latter the species were more abundant. Lutzomyia cruzi was predominant in the peri and intradomiciliary environments. Its prevalence in the central district was of 90.3% and lower in the outskirts. Lu. forattinii presented considerable prevalence (39.0%) in one of the outlying districts too. In the cave, Lu. corumbaensis was the predominant species, followed by Lu. sordellii, Lu. forattinii, Lu. peresi and Lu. cruzi. The impact of the climatic condition and the action of insecticides in the urban area on the frequency of the species, as well as the use of the cave as a breeding ground by the phlebotomines, in view of the changes in the sex rate, are commented. Data on anthropophily and captures of Lu. forattinii using dog bait have been added.

CONCLUSION

The predominance of Lu. cruzi in the urban area; the great prevalence of Lu. forattinii in most of the outlying areas studied and the anthropophily of this latter species, as well as the strong affinity of these species with Lu. longipalpis, the main vector of visceral leishmaniais in other areas of the Americas, suggest the participation of both in the transmission of the disease in Corumbá.

Saliva of Lutzomyia longipalpis sibling species differs in its composition and capacity to enhance leishmaniasis

Leishmania donovani chagasi parasites, transmitted by sandflies of the Lutzomyia longipalpis species complex, normally cause visceral leishmaniasis. However, in Central America infections frequently result in cutaneous disease. We undertook experiments to investigate the possible influence of sandfly saliva on the course of infection. Erythemas caused by feeding sandflies correlated well with the levels of the erythema-inducing peptide, maxadilan, in their saliva. Saliva of Brazilian flies was the most potent, that of Colombian flies less so, and Costa Rican saliva had very little maxadilan and lacked activity. Nucleotide sequence differences in the maxadilan gene of the three species were detected by 'single strand conformational polymorphism' electrophoresis. Leishmania infections proliferated fastest when coinjected with the saliva of Costa Rican flies. Brazilian flies had less influence, and Colombian flies only a slight effect. Thus Costa Rican Lutzomyia longipalpis, vectors of non-ulcerative cutaneous disease, have very low vasodilatory activity and very little maxadilan, but their saliva strongly enhances cutaneous proliferation of Leishmania infections. Conversely, flies from Colombia and Brazil, vectors of visceral disease, have more maxadilan, but exacerbate cutaneous infections to a lesser degree. These coincidental observations suggest that species of Lutzomyia longipalpis differ in their propensity to modulate the pathology of the disease they transmit.