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MEM INST OSWALDO CRUZ, RIO DE JANEIRO, 97(2) March 2002
PAGES: 163-168 DOI: Full paper
Ecological Aspects of Phebotomine (Diptera, Psychodidae) in an Endemic Area of Tegumentary Leishmaniasis in the Northeastern Argentina, 1993-1998

Oscar D Salomón +, Gustavo C RossiI, Gustavo R SpinelliII

Centro Nacional de Diagnóstico e Investigación en Endemo-Epidemias, Av. Paseo Colón 568, 1063, Buenos Aires, Argentina
ICentro de Estudios Parasitológicos y de Vectores, La Plata, Argentina
IIFacultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina

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Abstract

The first epidemic tegumentary leishmaniasis´ outbreak in the province of Misiones was recorded in 1998, in the locality of Puerto Esperanza. Phlebotominae collected in the region, previously or simultaneously to the outbreak (September 1993-December 1998) showed that the species Lutzomyia intermedias. l. was prevalent (94%, n 6,150) at all the sites sampled with miniature light trap (10) and Shannon trap (3). L. pessoaiL.whitmaniL. migonei, L. shannoni, L. fischeri, L. misionensis, Brumptomyia avellari andB. guimaraesi were also captured. Sand fly distribution in time and space suggests that in the province of Misiones (1) the species already present before 1990 could give rise to the epidemic by the density/dispersion fluctuation of their local populations; (2) the abundance of L. intermedia s. l. was associated with environments with ecotones of primary-secondary vegetation, close to water bodies and with moderate human disturbance; (3) this species showed, towards the end of 1997, peaks of exceptional abundance, subsequent to rainfall peaks in 1996. This increase in abundance of potential vector sand fly populations close to houses with colonizable surroundings could have generated the 1998 epidemic outbreak.

 

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The first autochthonous cases of tegumentary leishmaniasis were recorded in Argentina in 1916 (Bernasconi 1928, Villalonga 1963). Until 1980, 43 cases/year, coming from the territory north of parallel 28º, were reported in the whole country (Bernasconi 1930, Cedillos & Walton 1988). In 1985, an epidemic outbreak due to Leishmania (Viannia) braziliensis in the province of Salta, NW of Argentina, occurred, followed by outbreaks in the rest of the endemic territory (Villafañe et al. 1988, Grimaldi et al. 1989, Campanini et al. 1993, Salomón 1993, 1998, Sosa Estani et al. 1993, 1998, Salomón et al. 1995, Sosa Estani 1998). The province of Misiones is located in the NE of Argentina, on the frontier with Brazil and Paraguay, the primary vegetation belongs to the subtropical forest (Cabrera 1971). Mean cases/year in the province of Misiones were 7.2 for the period 1954/1974, 0.25 in 1975/1995, 5.5 in 1996/1997 and 205 cases in 1998 (incidence rate 25.6/100,000). In 1998, 98% of these cases came from Puerto Esperanza, Department of Iguazú (Epid Dir, pers. commun.).

Sporadic captures of Phlebotominae, carried out in Misiones before 1960, demonstrated the presence of Lutzomyia alphabetica, L. intermedia, L. longipalpis, L. migonei, L. misionensis, L. monticola, L. pascalei, L. pessoai, L. quinquefer, L. shannoni, and L. whitmani (Romaña & Abalos 1949, Bejarano & Duret 1950, Duret 1952, Castro 1959a,b, Del Ponte 1960). According to Marcondes et al. (1998a,b) the taxon that occur in Argentina is L. neivai instead of L. intermedia, so in this text L. intermedia means actuallyL. intermedia s. l.

This study shows the results of captures of Phle-botominae carried out in Misiones between 1993 and 1998, at sites with and without records of previous cases. Probable entomological causes of the epidemic outbreak are inferred from the results with the objective of contributing to the design of possible control strategies. Characteristics of the epidemic outbreak will be the subject of a future article.

 

MATERIALS AND METHODS

Phlebotominae were collected at 10 sites along the Paraná river (Fig. 1), corresponding to greatly modified environments with open vegetation (A, D, E, J), modified environments with secondary vegetation and isolated specimens of primary vegetation (C, F, H, I), and less modified environments or transitional environments with thickly vegetation (B, G). Two CDC miniature light traps were used in parallel per site, both with CO2 (500 ml/h), one of them dry and the other with 70% alcohol, placed 1.5 m above the ground. Captures were carried out monthly, uninter-rumptedly during 24 h, from September 1993 to December 1998. The objective of the design was not a longitudinally study of Phlebotominae but to sample other insects, so that the captures were discontinuous and, the effort different among sites. In February 1998, captures in Eldorado (26º23'LS - 54º39'LW), Andresito (25º40'LS - 54º03'LW) and Cerro Azul (27º43'LS - 55º29'LW) were carried out for two consecutive days per site, using a modified Shannon trap, from 6.30 pm to 9 pm (Salomón et al. 1995, Salomón 1997). Andresito had recorded human cases of leishmaniasis in 1996/1997 and Cerro Azul in 1990/1995. Phlebotominae were processed and identified according to Young and Duncan (1994).

Meteorological data were obtained from the forest stations of APSA Libertad, INTA Cerro Azul and EBY Ituzaingó. APSA data were the only overplotted as the data did not show any significant differences among sources.

For their statistical analysis, monthly capture data, by station or by species, were transformed into proportions of total captures.

 

RESULTS

Phlebotominae (n 6,150) were captured using light minitraps at the 10 sampled sites, and in 36.6% of the 232 nights/capture (Table I). L. intermedia wasrepresented in 98.7% of the captures, with at least one individual in each of them. At Corpus station 91% of the 5,781 specimens of this species were captured (Table II). The annual collections and records of mean temperature and rainfall were plotted per site (Fig. 2). Mean temperature was relatively uniform over the year and during the years studied, with a minimum between June and July (May in 1995). Rainfall was trimodal in 1992-1994 and 1996, and bimodal in 1995, 1997 and 1998. In November 1994 and October 1996, accumulated monthly rainfall higher than 400 mm was recorded.

No specimens of Phlebotominaewere captured between September 1993 and February 1994 at the stations sampled. In Montecarlo, Posadas and Ituzaingó (Fig. 2), maximum captures of L. intermedia took place in May-July and another capture, significantly more important, occurred in August 1995 (in Ituzaingó, in January and March 1996). Santa Tecla had more uniform captures during the study period, but again with a maximum in August 1995. Results in Corpus were qualitatively different from the others: from February 1996 to 1998 captures of L. intermedia s. l. exceeded 200 specimens/month in five occasions, reaching a maximum of 1,508 specimens in November 1997. Corpus presented captures in all months without a rainfall peak, except during the abnormal profile of 1997 (with rains in August).

The other collected species were L. pessoai, L. whitmani, L. migonei, L. shannoni, L. fischeriL. misionensisBrumptomyia avellari and B. guimaraesi. These species were found together with L. intermedia on 24 occasions, and only in two captures, those made at Santa Tecla and Posadas (Mártires Stream), B. guimaraesi and L. pessoai were found alone. Captures of L. intermediasimultaneously with other species were customary in Corpus and Santa Tecla (Table I), but only ocurred once in Mártires (L. pessoai), Itaembé (L. whitmani), Candelaria and Ituzaingó (B. avellari).

Using the modified Shannon trap in Eldorado, on the banks of the Paraná river, without any records of previous cases, and in Cerro Azul, with historical records, no Phlebotominae were obtained. On the other hand, in Andresito, in a thickly forested peridomicile close to a recent human case, 35 Phlebotominae, 23 L. intermedia s. l. (65.7%) (male: female 1:1), 9 L. whitmani(25.7%) (male: female 1:2) and 3 females of L. shannoni (8.6%) were captured.

 

DISCUSSION

Phlebotominae are cited by 11 species in the literature for the provinces of Misiones and Corrientes, captured mainly between 1947 and 1951 (Bejarano & Duret 1950, Castro 1959a,b, Del Ponte 1960, Borda et al. 1998). Six of these species are reported in this study; another four of them (L. longipalpis, L. quinquefer, L. monticola and L. cortelezzii) were collected after 1998 (unpublished), and the other two, cited for single specimens from 1948, were not found (L. pascaleiL. alphabetica). Captures of L. fischeri, B. avellari and B. guimaraesi are recent (Spinelli et al. 1999); the rarity of the first and the little attraction for light and null anthropophily of Brumptomyia (Young & Arias 1992), would be the cause of their absence in previous records.

The presence of L. intermedia was observed throughout the year, showing peaks in later autumn (1994), others of higher magnitude associated to relatively scarce rainfall (1995, 1996, 1997, March - 1998), and maximum peaks related to exceptional rainfall in the season or in the previous years (1996 and 1997). Regarding the lower thermic amplitude and the more temperate winter of Misiones, the annual pattern was consistent with that obtained for this species in the focus of leishmaniasis in the province of Salta. In this latter, abundance was associated to temperate seasons with moderate rain, to the years after one of exceptional precipitation, and to the fact that the risk of transmission of leishmaniasis is higher in autumn (Salomón 1997).

The historical area of dispersion of Phlebotominae in Misiones has suffered, in the last decades, an intense process of deforestation and reforestation, as well as environmental modifications due to dam construction, both phenomena associated in the literature with vector concentration, microfoci of parasite circulation and epidemic outbreaks (Lainson 1989, Gomes et al. 1990, Mott et al. 1990, Walsh et al. 1993, Tolezano 1994). Captures were carried out on environment associated with the gallery forest of the Paraná river or smaller streams and in ecotones between the primary forest and deforested areas, where the concentration/abundance of vectors could be increased by periodic inundations (Salomón 1997). In the greatly modified environment with open vegetation (Montecarlo, Candelaria, Posadas) few captures were obtained (the most productivity being obtained in the residual forest of Candelaria and Itaembé), with peaks in dry winters. Unseasonable peaks in Ituzaingó could be due to anthropic action or to a non-recorded local meteorological phenomenon. In the less modified environment or transitional environment with thick vegetation (Corpus, Santa Tecla) the captures were more numerous, and because there was very little human interference the meteorological variables could be better observed. The better preserved forest and the greater distance from human settlements could explain the higher magnitude of the captures in Corpus. The abundance of B. guimaraesi in Santa Teclarequires a focal investigation into potential host dynamics and spacial distribution.

The literature records isolations of L. (V.) braziliensis from L. whitmani, L. intermedia, L. migonei and L. pessoai (Young & Arias 1992). Captures in Andresito allow one to obtain a profile of anthropophagic species at a site of transmission prior to the outbreak, simultaneously with captures with the light trap. The prevalent species was L. intermedia, followed by L. whitmaniL. intermediawas considered as a possible vector of L. (V.) braziliensis during recent outbreaks in modified environments; L. whitmani has been its primary vector, responsible for the traditional sporadic transmission, and associated with work in the forest (Lainson & Shaw 1979, Gomes et al. 1990, Pereira & Hoch 1990, Rangel et al. 1990, 1992, Stolf et al. 1993, Gomes 1994, Queiroz et al. 1994, Tolezano 1994, Salomón 1997, Salomón & Zaidemberg 1997).

Results of sand fly captures have been evaluated from historical, meteorological, anthropic and microecological variables. In conclusion, the fauna of Phlebotominae of the province of Misiones has not suffered qualitative changes at a macrogeographical level, which would lead to an epidemic outbreak. However, metapopulations of already present species can colonize new environments or even became extinct which would modify their local density and spacial distribution. L. intermedia, possible vector of L. (V.) braziliensis, was the prevalent species in the captures in Misiones, and its abundance was associated with thickly forested environments of primary secondary ecotones and the proximity of bodies of water. These conditions can be heightened or nullified by microecological characteristics provoked by anthropic activity. L. intermedia, in proper environments, showed peaks of exceptional abundance, subsequent to rainfall peaks in the previous season/year, as has already been observed in the epidemic focus of the northwestern Argentina (Salomón 1997). This phenomenon, observed in Misiones towards the end of 1997, if it occurred in vector populations infected with Leishmania close to a human settlement, with ecological conditions which allowed colonization of the surroundings of the house, could have generated the 1998 epidemic outbreak.

 

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