Distribution of Lutzomyia longipalpis chemotype populations in São Paulo state, Brazil

Abstract

Background: American visceral leishmaniasis (AVL) is an emerging disease in the state of São Paulo, Brazil. Its geographical expansion and the increase in the number of human cases has been linked to dispersion of Lutzomyia longipalpis into urban areas. To produce more accurate risk maps we investigated the geographic distribution and routes of expansion of the disease as well as chemotype populations of the vector.

Methodology/principal findings: A database, containing the annual records of municipalities which had notified human and canine AVL cases as well as the presence of the vector, was compiled. The chemotypes of L. longipalpis populations from municipalities in different regions of São Paulo State were determined by Coupled Gas Chromatography - Mass Spectrometry. From 1997 to June 2014, L. longipalpis has been reported in 166 municipalities, 148 of them in the Western region. A total of 106 municipalities were identified with transmission and 99 were located in the Western region, where all 2,204 autochthonous human cases occurred. Both the vector and the occurrence of human cases have expanded in a South-easterly direction, from the Western to central region, and from there, a further expansion to the North and the South. The (S)-9-methylgermacrene-B population of L. longipalpis is widely distributed in the Western region and the cembrene-1 population is restricted to the Eastern region.

Conclusion/significance: The maps in the present study show that there are two distinct epidemiological patterns of AVL in São Paulo State and that the expansion of human and canine AVL cases through the Western region has followed the same dispersion route of only one of the two species of the L. longipalpis complex, (S)-9-methylgermacrene-B. Entomological vigilance based on the routes of dispersion and identification of the chemotype population could be used to identify at-risk areas and consequently define the priorities for control measures.

Fig 1. Study area.

São Paulo and neighboring states.

Fig 2. Expansion route of Lutzomyia longipalpis.

Distribution of Lutzomyia longipalpis, in municipalities of São Paulo State, according to the first record, from the 1970’s to June 2014. In negative municipalities, the entomological collections have not recorded the presence of L. longipalpis.

Fig 3. Annual new records of Lutzomyia longipalpis.

Annual distribution of municipalities which reported Lutzomyia longipalpis for the first time in São Paulo State, from 1970’s to June 2014.

Fig 4. Expansion route of canine cases.

Distribution of American visceral leishmaniasis in São Paulo State, according to the record of the first canine case, from 1998 to 2013.

Fig 5. Expansion route of human cases.

Distribution of American visceral leishmaniasis in São Paulo State, according to the record of the first human case, from 1999 to April 2013.

Fig 6. Spatial distribution of chemotype populations.

Distribution of (S)-9-methylgemacrene-B and cembrene-1 pheromone producing population in São Paulo State. Map shows only municipalities sampled for chemical analysis.