Lutzomyia longipalpis abundance in the city of Posadas, northeastern Argentina: variation at different spatial scales.

SANTINI MS; FERNÁNDEZ MS; PÉREZ AA; SANDOVAL E; STAINHOST I; SALOMÓN OD

Kasadasi

Simposio; 7th International Symposium on Phlebotomine Sandflies; 2011

In Argentina, the first autochthonous human case of visceral leishmaniasis was recorded in the City of Posadas (northeastern Argentina) in 2006, currently with 49 cases. A previous study in this urban environment showed that the spatial distribution of Lutzomyia longipalpis abundance was heterogeneous, scattered throughout the city, but with a pattern of high abundance areas (HAA) in a matrix of low abundance areas (LAA). In this work, we show preliminary results on the variation in Lu. longipalpis abundance in individual peridomestic environments (micro-scale: houses), and areas of 400 x 400 m (meso-scale: squares), and its association with environmental variables and canine infection in the city of Posadas. Samplings were carried out during January-March 2009, in three to 10 houses from 11 squares of HAA and 11 squares of LAA. CDC light minitraps were placed in environments according to the “worst scenario” criteria from 5.00 p.m. to 9.00 a.m.,Lutzomyia longipalpis abundance was heterogeneous, scattered throughout the city, but with a pattern of high abundance areas (HAA) in a matrix of low abundance areas (LAA). In this work, we show preliminary results on the variation in Lu. longipalpis abundance in individual peridomestic environments (micro-scale: houses), and areas of 400 x 400 m (meso-scale: squares), and its association with environmental variables and canine infection in the city of Posadas. Samplings were carried out during January-March 2009, in three to 10 houses from 11 squares of HAA and 11 squares of LAA. CDC light minitraps were placed in environments according to the “worst scenario” criteria from 5.00 p.m. to 9.00 a.m.,Lu. longipalpis abundance in individual peridomestic environments (micro-scale: houses), and areas of 400 x 400 m (meso-scale: squares), and its association with environmental variables and canine infection in the city of Posadas. Samplings were carried out during January-March 2009, in three to 10 houses from 11 squares of HAA and 11 squares of LAA. CDC light minitraps were placed in environments according to the “worst scenario” criteria from 5.00 p.m. to 9.00 a.m.,cording to the “worst scenario” criteria from 5.00 p.m. to 9.00 a.m., for two consecutive nights. Environmental variables, usually associated with phlebotomine distribution, were recorded at houses and squares. In order to analyze the variation in Lu. longipalpis abundance at both scales, we computed a nested-ANOVA analysis and estimated the variance component. To explore which are the environmental variables that better explain the differences between houses and squares of HAA and LAA, we computed a Manova/ Discriminant analysis. Results showed that the houses within areas contributed significantly to the variability in the observed abundance of Lu. longipalpisLu. longipalpis abundance at both scales, we computed a nested-ANOVA analysis and estimated the variance component. To explore which are the environmental variables that better explain the differences between houses and squares of HAA and LAA, we computed a Manova/ Discriminant analysis. Results showed that the houses within areas contributed significantly to the variability in the observed abundance of Lu. longipalpisLu. longipalpis (p<0.0001), while the variability between squares was not significant (p>0.05). In turn, the variability between houses was higher than among sampling nights (72.3% vs 24.6%). In relation to LAA vs HAA for squares, “proportion of infected dogs (rK39+)” was higher in HAA and “number of unpaved streets by block” was higher in LAA (p=0.01), while for houses, “area occupied by land or grass” was greater in peridomestic environments belonging to LAA, and “number of pots”, “number of tree species” and “distance to watercourse” were higher in houses from HAA (n=128, houses, “area occupied by land or grass” was greater in peridomestic environments belonging to LAA, and “number of pots”, “number of tree species” and “distance to watercourse” were higher in houses from HAA (n=128, belonging to LAA, and “number of pots”, “number of tree species” and “distance to watercourse” were higher in houses from HAA (n=128, p<0.0001). These results show that Lu. longipalpis at micro-scale would increase its abundance in areas with vegetation that provides shadow, moist soil and humidity. Further research should be carried out to take into account the variability in the abundance of the vector between houses from HAA and LAA. At meso-scale level the results lacked robustness, perhaps due to the low sampling size. However, the higher proportion of RK+ dogs in HAA may evidence that transmission is taking place in these areas and that this transmission is related to the abundance of the vector.Lu. longipalpis at micro-scale would increase its abundance in areas with vegetation that provides shadow, moist soil and humidity. Further research should be carried out to take into account the variability in the abundance of the vector between houses from HAA and LAA. At meso-scale level the results lacked robustness, perhaps due to the low sampling size. However, the higher proportion of RK+ dogs in HAA may evidence that transmission is taking place in these areas and that this transmission is related to the abundance of the vector.