Temporal trend, space risk and factors associated with the occurrence of dengue in northeast Brazil, 2009-2018.

BACKGROUND: Dengue is an acute viral disease of major relevance and impact on public health, causing major epidemics around the world, especially in tropical regions. Here we aimed to analyse the temporal trend and spatial risk, as well as social vulnerability factors, associated with the occurrence of dengue in the state of Bahia, Brazil between 2009 and 2018. METHODS: This is an ecological study carried out with all suspected cases of dengue in Bahia between 2009 and 2018. The data were obtained from the National Notifiable Diseases Information System, available on the website of the Health Department of the State of Bahia, and from the Brazilian Institute of Geography and Statistics. We used the Joinpoint regression model, local empirical Bayesian model for smoothing, global and local Moran statistics and spatial scanning statistics. The relationship between the dengue incidence rate and social determinants was tested using Moran's bivariate correlation. RESULTS: During the study period, 451 847 probable dengue cases were registered in Bahia. A declining trend was observed in 39.28% (n=11) of the state's health regions and 60.71% (n=17) showed a stationary tendency. The spatiotemporal scanning statistic showed nine clusters of dengue occurrence. The largest cluster had a radius of 342.14 km, consisting of 160 municipalities, 120 094 cases (710.20 cases/100 000 inhabitants) and a relative risk of 2.80. In the multivariate regression model, 11 variables showed a significant association: Social Vulnerability Index (SVI), Municipal Human Development Index (MHDI), SVI urban infrastructure, SVI human capital, MHDI longevity, MHDI education, proportion of people living in households with per capita income less than half the minimum wage (in 2010) and who spend more than 1 h commuting, proportion of mothers who are heads of household who did not complete elementary school and with children <15 y of age, activity rate of persons ages 10-14 y and per capita income. CONCLUSIONS: In the analysis of the spatial distribution, areas of risk of disease transmission throughout the state were identified. These results can provide subsidies for the strategic planning of actions, as well as for the implementation of programs and/or public policies in order to control the incidence of dengue in the population.

Genetic characterization of residual Triatoma infestans populations from Brazil by microsatellite.

In spite of long-term efforts to eliminate Triatoma infestans (Klug 1834) from Brazil, residual foci still persist in the states of Bahia and Rio Grande do Sul. Data on the genetic variability and structuring of these populations are however lacking. Using nine microsatellite loci, we characterized one residual T. infestans population from Bahia and four from Rio Grande do Sul, and compared them with bugs originally from an older focus in São Paulo; 224 bugs were genotyped. The number of alleles per locus ranged from 5 to 11. Observed and expected heterozygosities per locus ranged, respectively, from 0 to 0.786 and from 0 to 0.764. Significant departures from Hardy-Weinberg equilibrium, mainly due to heterozygote deficits, were detected in all loci and in most populations. Global indices estimated by AMOVA were: Fis was 0.37; Fst was 0.28; and Fit was 0.55; overall indices with p = 0.00 indicated substantial differentiation. Inter-population Fst ranged from 0.118 to 0.562, suggesting strong genetic structuring and little to no gene flow among populations. Intra-population Fis ranged from 0.301 to 0.307. Inbreeding was apparent in all populations except that from Bahia-which might be either linked by gene flow to nearby unsampled populations or part of a relatively large local population. The overall pattern of strong genetic structuring among pyrethroid-susceptible residual T. infestans populations suggests that their persistence is probably due to operational control failures. Detection and elimination of such residual foci is technically feasible and must become a public health priority in Brazil.

Susceptibility characterization of residual Brazilian populations of Triatoma infestans Klug, 1834 (Hemiptera: Reduviidae) to deltamethrin pyrethroid.

INTRODUCTION: Despite years of efforts towards the elimination of Triatoma infestans in Brazil, residual foci still persist in some areas of the States of Bahia and Rio Grande do Sul. The persistence of these T. infestans populations in the country has two different origins of equal concern: operational failures or insecticide resistance. Thus, the objective of this study was to characterize the susceptibility profile of the residual Brazilian populations of T. infestans to deltamethrin. METHODS: The susceptibility reference lineage was derived from Cipein/Argentina. The populations studied were manually collected using a dislodging agent in peridomiciles in the States of Bahia (Novo Horizonte) and of Rio Grande do Sul (Santa Rosa and Doutor Maurício Cardoso). Serial dilutions of deltamethrin were prepared and applied at the dorsal abdomen of first instar nymphs. The control group received only pure acetone. Mortality was evaluated after 72h. Qualitative tests assessed the mortality of a diagnostic dose of 1xLD99 (2.76ng a.i./nymph) determined for the susceptibility reference lineage. RESULTS: The susceptibility profile characterization of the T. infestans populations revealed an RR50 ranging from 1.73 to 3.26. The mortality percentage in response to a diagnostic dose was 100%. The results obtained in the quantitative and qualitative assays corresponded for all populations. CONCLUSIONS: The results of this study indicate that the persistence of residual foci of T. infestans in Bahia and Rio Grande do Sul is not related to insecticide resistance but may be associated with operational failures. In Rio Grande do Sul, we must consider the possibility of continuous reinfestation by Argentinian individuals, which justifies active and efficient epidemiological surveillance.

Susceptibility characterization of residual Brazilian populations of Triatoma infestans Klug, 1834 (Hemiptera: Reduviidae) to deltamethrin pyrethroid

INTRODUCTION: Despite years of efforts towards the elimination of Triatoma infestans in Brazil, residual foci still persist in some areas of the States of Bahia and Rio Grande do Sul. The persistence of these T. infestans populations in the country has two different origins of equal concern: operational failures or insecticide resistance. Thus, the objective of this study was to characterize the susceptibility profile of the residual Brazilian populations of T. infestans to deltamethrin. METHODS: The susceptibility reference lineage was derived from Cipein/Argentina. The populations studied were manually collected using a dislodging agent in peridomiciles in the States of Bahia (Novo Horizonte) and of Rio Grande do Sul (Santa Rosa and Doutor Maurício Cardoso). Serial dilutions of deltamethrin were prepared and applied at the dorsal abdomen of first instar nymphs. The control group received only pure acetone. Mortality was evaluated after 72h. Qualitative tests assessed the mortality of a diagnostic dose of 1xLD99 (2.76ng a.i./nymph) determined for the susceptibility reference lineage. RESULTS: The susceptibility profile characterization of the T. infestans populations revealed an RR50 ranging from 1.73 to 3.26. The mortality percentage in response to a diagnostic dose was 100%. The results obtained in the quantitative and qualitative assays corresponded for all populations. CONCLUSIONS: The results of this study indicate that the persistence of residual foci of T. infestans in Bahia and Rio Grande do Sul is not related to insecticide resistance but may be associated with operational failures. In Rio Grande do Sul, we must consider the possibility of continuous reinfestation by Argentinian individuals, which justifies active and efficient epidemiological surveillance. .