Phlebotomine sand flies (Diptera: Psychodidae) in the municipality of Várzea Grande: an area of transmission of visceral leishmaniasis in the state of Mato Grosso, Brazil

Vol. 102(8): 913-918, December 2007

Nanci Akemi Missawa, Edelberto Santos Dias*/+

Laboratório de Entomologia, Secretaria Estadual de Saúde de Mato Grosso, Cuiabá, MT, Brasil *Laboratório de Leishmanioses, Instituto de Pesquisas René Rachou-Fiocruz, Av. Augusto de Lima 1715, 30190-002 Belo Horizonte, MG, Brasil

Visceral leishmaniasis (VL) has been naturally transmitted in periurban areas due to the emergence and reemergence of its vectors in such areas. Aimed to further knowledge on ecological aspects affecting the occurrence of phlebotomine sand flies in VL transmission areas in the municipality of Várzea Grande, state of Mato Grosso (MT), Brazil, sand fly captures were carried out. Monthly collections of sand flies were undertaken with CDC light-traps, which were left in both intradomiciliary and peridomiciliary areas of ten residences during four consecutive days between January 2004 and June 2006. Twenty-two species of genus Lutzomyia and one of Brumptomyia were captured. The most abundant species was Lutzomyia longipalpis (65.23%), followed by L. evandroi (16.26%), L. lenti (7.69%), L. whitmani (4.92%), L. sallesi (2.34%) and L. termitophila (1.32%). The highest density of the main VL vector, L. longipalpis, was found in peridomiciliary areas, mostly males. No significant correlation was found between environment (temperature, air relative humidity and rain fall) and phlebotomine density; although a slight increase in sand fly density has been observed in the period following rainfalls, particularly L. longipalpis. No correlation was observed between distribution and density of L. longipalpis, prevalence of human VL cases and the presence of serologically positive dogs. The presence of infected dogs, increased vector density, susceptibility rate and interruption of epidemiological surveillance may raise the risk of VL transmission to man in Várzea Grande.

Key words: Phlebotomine - Lutzomyia longipalpis - Várzea Grande - Mato Grosso

Leishmaniases are regarded as one of the main world zoonosis, and visceral leishmaniasis (VL), particularly, constitutes an important anthroponosis or anthropozoonosis when man acts as a reservoir. The disease is worldwide spread and is found in Americas, Africa, Southern Europe, Asia and Midwestern countries (Lainson & Shaw 1987). In Americas, VL is prevalent from Mexico to Argentina, and Brazil accounts for 90% of the cases in the continent (Soares & Turco 2003). Changes in human behavior and the environment may exert greater impact in the prevalence and pattern of VL transmission.

In Brazil, VL was previously known as a rural disease in several states, including Goiás, Tocantins and Mato Grosso do Sul (MS) (Marzochi & Marzochi 1994), and the first report of the disease in the country was made in 1913 in Mato Grosso (MT) (Alencar & Dietze 1991). Despite the fact that VL prevalence is underestimated, Brazil has recorded increasing incidences of the disease in the last 20 years (Dantas-Torres & Brandão-Filho 2006). Approximately 3,000 clinical cases a year have been recorded in the country with average mortality between 8% and 10% (Gontijo & Melo 2004).

Urbanization conditions of the disease and environmental changes influencing VL transmission can be of natural or anthropogenic origin (Barata et al. 2005, Monteiro et al. 2005), including human activities expansion, habitat fragmentation and deforestation, which have led to an increasing adaptation of the parasite, as well as of phlebotomine sand flies (Marzochi & Marzochi 1994). Thus, this metaxenic disease has been naturally transmitted in periurban areas due to the emergence and reemergence of its vectors in such areas (Tauil 2006). Recent data have confirmed urbanization of the disease in large urban centers (Silva et al. 2001, Bevilacqua et al. 2001, Souza et al. 2004, Monteiro et al. 2005, Barata et al. 2005); add to this the fact that some investigators (Bevilacqua et al. 2001) have suggested that socio-economical factors may be one of the determinant factors for VL transmission in Brazil.

Dogs are regarded as important reservoirs in several VL foci in both rural and periurban areas (Marzochi & Marzochi 1994, Silva et al. 2001). Several reports have correlated human VL with the presence of high canine seroprevalence (Deane & Deane 1955, Lainson & Shaw 1987, Oliveira et al. 2001); in addition, the disease occurrence has been associated with the sheer abundance of vectors (Vieira & Coelho 1998).

In Brazil, VL transmission is associated with a variety of sand fly species, and Lutzomyia longipalpis is the main vector species (Lainson & Rangel 2003). L. cruzi has been implicated in VL transmission in MS (Santos et al. 1998), being found naturally infected in the municipality of Jaciara, in MT (unpublished observations). Other phlebotomine species, such as L. forattini and L. almerioi, may also be associated with the disease in MS, both anthropophilic, although has not been evidenced its vectorial ability (Galati et al. 1997, Galati et al. 2006), whereas in the state of Para, L. antunesi is considered an alternative VL vector (Lainson & Rangel 2003). In Colombia, L. evansi has been reported to be the most likely VL vector (Travi et al. 1990). The VL etiological agent is a protozoan parasite of the family Tripanosomatidae, species Leishmania (Leishmania) infantum chagasi (Lainson & Rangel 2005, Shaw 2006).

Most environmental factors affecting the epidemiology of leishmaniases provide evidence on the adaptation of parasites and their vectors to ecological changes due to socio-environmental processes such as deforestation and urbanization. Because these parasites and vectors adapt to modified environmental conditions in order to survive, the epidemiological profile of the disease has also undergone modifications (Marzochi & Marzochi 1994).

Hence, the present study was aimed at furthering knowledge on ecological aspects influencing density, seasonal fluctuation, endophilia and exophilia of phlebotomine sand flies in a VL transmission area in the municipality of Várzea Grande, MT.

MATERIALS AND METHODS

RESULTS

DISCUSSION

ACKNOWLEDGEMENTS

To technicians of the Laboratory of Entomology and the Regional Office of the State Secretary of Health of Mato Grosso, and the residents of the dwellings surveyed in the municipality of Várzea Grande for their collaboration, friendship and support.

REFERENCES

Fig. 1 | Fig. 2 | Fig. 3 | Table I | Table II

Financial support: Instituto René Rachou/Fiocruz

⁺Corresponding author: edel@cpqrr.fiocruz.br

Received 6 June 2007

Accepted 20 December 2007

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