Elsevier

Acta Tropica

Volume 137, September 2014, Pages 118-122
Acta Tropica

Distribution of Lutzomyia ayacuchensis, the vector of Andean-type cutaneous leishmaniasis, at different altitudes on the Andean slope of Ecuador

https://doi.org/10.1016/j.actatropica.2014.05.006Get rights and content

Highlights

  • Lutzomyia ayacuchensis, the vector of Leishmania mexicana, was surveyed through Andean slope.

  • The distribution of Lu. ayacuchensis was identified at higher altitude and the ratio is increased with increasing altitude.

  • A haplotype analysis showed no apparent genetic divergence among populations at different localities.

  • The result suggests that Lu. ayacuchensis in Andean slope areas have a potential to transmit L. mexicana.

Abstract

Distribution of the vector species is a major risk factor for the endemicity of leishmaniasis. In the present study, the vertical distribution of Lutzomyia (Lu.) ayacuchensis, the vector of Leishmania (Leishmania) mexicana in the Ecuadorian Andes, was surveyed at different altitudes (300–2500 m above sea level) of the Andean slope. The vector species Lu. ayacuchensis was identified at an altitude of 650 m and a higher areas, and higher distribution ratio of the species was observed at higher altitudes. In addition, high ratios of L. (L.) mexicana infection were detected in higher areas, but none in lower populations of sand flies. Since an association between sand fly populations and vector competence is suggested in Lu. ayacuchensis, haplotype analysis was performed on the species from different altitudes of the study areas; however, no apparent difference was observed among populations. These results suggested that Lu. ayacuchensis in Andean slope areas of Ecuador has the potential to transmit L. (L.) mexicana and spread leishmaniasis in these areas.

Introduction

Leishmaniasis is a vector-borne parasitic disease caused by an obligate intracellular protozoan of the genus Leishmania. The disease is one of the most neglected diseases worldwide, having strong and complex associations with poverty, and it affects at least 12 million people (Alvar et al., 2012). Approximately 20 species of Leishmania are reported to be pathogenic to humans, and the parasites produce a wide range of clinical infections in both humans and vertebrate animals as zoonoses. In humans, the disease occurs in three distinct manifestations, cutaneous, mucocutaneous and visceral forms, and these clinical forms are largely associated with the Leishmania species responsible. The parasites are transmitted by female sand flies of the genus Phlebotomus in the Old World and Lutzomyia in the New World. At present, approximately 800 sand fly species have been recorded; however, less than 10% of them transmit each particular Leishmania species (Munstermann, 2004, Bates, 2007, Kato et al., 2010). Therefore, investigations on the prevalent parasite and vector species at given endemic areas is important for risk assessment and appropriate treatment of the disease.

Since 1982, we have been conducting epidemiological studies in the New World, especially in Ecuador. In this country, transmission of cutaneous and mucocutaneous leishmaniases occurs in rural populations living in bilateral regions of the Andes Mountains from the lowlands to the highlands up to an elevation of 2500 m. The disease is widely spread in most provinces and is a considerable public health problem in Ecuador (Gomez and Hashiguchi, 1991). In the endemic areas, however, adequate epidemiological studies have not been done on a community basis, and no control measures have been applied to reduce or interrupt the transmission of the disease.

During our research activities, we have discovered a form of the disease in people living on the Andean plateau/valleys; the disease form is very similar to ‘Peruvian uta’ but the causative agent and vector are completely different (Takaoka et al., 1990, Hashiguchi et al., 1991, Gomez and Hashiguchi, 1991, Kato et al., 2005, Kato et al., 2008a). These findings have increased the known distribution of Andean leishmaniasis in the Andes regions. Until very recently, the only form of leishmaniasis in the Andes was thought to be ‘Peruvian uta’ caused by Leishmania (Viannia) peruviana. In Peru, the causative agent of the disease is L. (V.) peruviana and the suspected vectors are Lutzomyia (Lu.) verrucarum, Lu. peruensis, and Lu. ayacuchensis (Davies et al., 1993, Perez et al., 1991, Perez et al., 2007, Caceres et al., 2004, Kato et al., 2008a, Kato et al., 2011). In Ecuador, on the other hand, two species of the genus Leishmania, Leishmania (Leishmania) mexicana and L. (L.) major-like, seemed to be involved in Andean highland leishmaniasis (Hashiguchi et al., 1991). The only incriminated vector species is Lu. ayacuchensis, and the ratio infected by L. (L.) mexicana is high (1–8%) in highland areas, which is uncommon in most endemic areas of Ecuador (Takaoka et al., 1990, Gomez and Hashiguchi, 1991, Hashiguchi et al., 1991, Kato et al., 2005, Kato et al., 2008a). Therefore, distribution of the vector species is a major risk factor for the endemicity of leishmaniasis. In the present study, the vertical distribution of Lu. ayacuchensis and other man-biting sand fly species were surveyed at different altitudes (300–2500 m above sea level (a.s.l.)) of the Andean slope, and the genetic divergence of Lu. ayacuchensis was analyzed by targeting the cytochrome oxidase I gene.

Section snippets

Study sites

The main study sites are located in Chimborazo Province on the south east of Ecuador, and located on the Andean slope, ranging from 300 m to 2500 m a.s.l. along a railway, which was recently reconstructed and restarted after an approximately 20-year break (Fig. 1). The study area Canton Alausi has a population of ca. 4000 and lies at 2300–2500 m a.s.l. (Fig. 1). A small village, Chanchan, has only 37 villagers in total, and Canton Huigra has a population of ca. 2000 at an altitude of 1200–1300 m

Vertical distribution of sand flies along the Andean slope

Eight man-biting species of the genus Lutzomyia, Lu. ayacuchensis, Lu. maranonensis, Lu. robusta, Lu. hartmanni, Lu. gomezi, Lu. trapidoi, and Lu. panamensis were identified at different altitudes/sites of the present study areas (Table 1 and Fig. 2). The vector species of Andean-type cutaneous leishmaniasis, Lu. ayacuchensis, was identified at altitude of 650 m and higher areas, and a higher distribution ratio of the species was observed at higher altitudes; from 23.4% in Ochoa (650 m a.s.l.) to

Discussion

In the present study, sand fly species were surveyed at different altitudes of an Andean slope, and vertical distribution of Lu. ayacuchensis, the vector of L. (L.) mexicana in the Ecuadorian Andes, was elucidated. The distribution pattern was similar to that of 20 years ago. A haplotype analysis of Lu. ayacuchensis targeting the COI gene showed no apparent difference among populations at different localities where the infection ratio of the sand flies by L. (L.) mexicana is markedly different.

Funding

This study was financially supported by the Ministry of Education, Culture and Sports, Science and Technology (MEXT) of Japan (Grant nos. 23256002 and 25257501), and the Prometeo Project of the Secretaria Nacional de Educacion Superior, Ciencia, Tecnologia e Innovacion (SENESCYT), Ecuador.

Conflict of interest

The authors have no conflicts of interest to declare.

Acknowledgements

We are indebted to Flavio-Valeriano Zambrano C. (Servicio Nacional de Erradicacion de la Malaria, Guayaquil, Ecuador), Kazue Hashiguchi (Centro de Biomedicina, Universidad Central del Ecuador, Quito, Ecuador), and Roberto Sud A. (Ministerio de Salud Publica y Asistencia Social, Guayaquil, Ecuador) for their technical assistance during the field phase of the present study.

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    Molecular mass screening to incriminate sand fly vectors of Andean-type cutaneous leishmaniasis in Ecuador and Peru

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