Date Published: March 17, 2015
Publisher: Public Library of Science
Author(s): Claudio Casanova, Fernanda E. Colla-Jacques, James G. C. Hamilton, Reginaldo P. Brazil, Jeffrey J. Shaw, Paul Andrew Bates. http://doi.org/10.1371/journal.pntd.0003620
Abstract: BackgroundAmerican 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 FindingsA 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/SignificanceThe 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.
Partial Text: Recording the geographic distribution and identifying the possible routes of expansion of both arthropod-borne diseases and their associated vectors is essential information for surveillance as well as the execution and elaboration of control strategies .
Before 1997, L. longipalpis had been found only in the rural areas of six municipalities of São Paulo State, all of which are in the East and Northeast regions of the state. The first report of the vector in an urban area was in 1997 in the municipality of Araçatuba, in the Western region near the border with Mato Grosso do Sul State (Fig. 2). From 1998 to June 2014, L. longipalpis has been reported in another 164 municipalities (Fig. 2, S1 Database). During this period, between 2 and 21 new municipalities per year reported the presence of L. longipalpis, with more than 45 reporting the presence of the vector in the last 3 years (Fig. 3). The biggest expansion in the distribution of L. longipalpis happened in the western part of Sao Paulo where 146 municipalities have recorded their presence in urban areas during this 17.5 year period.
The argument in favour of the hypothesis of the recent introduction of L. longipalpis into the Western region of São Paulo State can be supported by its absence, for decades, from various sporadic rural collections of sand flies [28–30]. These collections were done in areas where autochthonous cases of cutaneous leishmaniasis, caused by Leishmania (Viannia) braziliensis, had been reported. The contrary hypothesis, that L. longipalpis has always been there, hidden in the primitive natural vegetation habitat, could be supported because of the existence of several areas where collections have never been done [28–30] Therefore, there are gaps in our knowledge of its distribution and in future, it would be interesting to collect samples from the few natural vegetation areas of São Paulo State.