RESUMEN
Phlebotomine sand flies (Diptera: Psychodidae) were captured in an area of Argentina endemic for American cutaneous leishmaniasis (ACL). A total of 44,944 flies were collected during a 130-wk interepidemic period from 1990 through 1993. These sand flies included Lutzomyia neivai (Pinto) (97.8%), Lutzomyia migonei (Franca) (1.2%), Lutzomyia cortelezzii (Brèthes) (0.8%), Lutzomyia shannoni (Dyar) (0.1%), and Lutzomyia punctigeniculata (Floch and Abonnenc) (0.1%). Lutzomyia neivai was more abundant in secondary forests and peridomestic environments associated with human cases than in primary forest or xeric thorn scrub areas. Time series analyses of species densities suggested a bimodal or trimodal annual pattern related to rainfall peaks, a 5-wk reproductive cycle, and peridomestic local populations that were located adjacent to secondary forests. In general, sand fly abundance was correlated with the rainfall of the previous year. Lutzomyia neivai spatial distributions were consistent with ACL incidence patterns during the study and in the recent outbreaks in Argentina. However, Lu. migonei also may be involved in peridomestic transmission. Our results suggest that there is a need for improved, long-term surveillance of sand flies and ACL cases, as well as development of effective intervention strategies.
Asunto(s)
Leishmaniasis Cutánea/transmisión , Phlebotomus/clasificación , Animales , Argentina/epidemiología , Geografía , Humanos , Incidencia , Control de Insectos/métodos , Insectos Vectores/clasificación , Leishmaniasis Cutánea/epidemiología , Phlebotomus/patogenicidad , Población , Psychodidae/clasificación , Psychodidae/patogenicidadRESUMEN
Polyacrylamide gel electrophoresis was used to elucidate genetic variation at 13 isozyme loci among forest populations of Lutzomyia shannoni from three widely separated locations in Colombia: Palambí (Nariño Department), Cimitarra (Santander Department) and Chinácota (Norte de Santander Department). These samples were compared with a laboratory colony originating from the Magdalena Valley in Central Colombia. The mean heterozygosity ranged from 16 to 22%, with 2.1 to 2.6 alleles detected per locus. Nei's genetic distances among populations were low, ranging from 0.011 to 0.049. The estimated number of migrants (Nm=3.8) based on Wright's F-Statistic, F ST, indicated low levels of gene flow among Lu. shannoni forest populations. This low level of migration indicates that the spread of stomatitis virus occurs via infected host, not by infected insect. In the colony sample of 79 individuals, the Gpi locus was homozygotic (0.62/0.62) in all females and heterozygotic (0.62/0.72) in all males. Although this phenomenon is probably a consequence of colonization, it indicates that Gpi is linked to a sex determining locus.
Asunto(s)
Variación Genética , Psychodidae/genética , Animales , Colombia , Electroforesis en Gel de Poliacrilamida/métodos , Femenino , Frecuencia de los Genes , Masculino , Psychodidae/enzimologíaRESUMEN
Baseline biological growth data of Lutzomyia shannoni (Dyar) were compared under two experimental conditions within insulated styrofoam chests and in standard laboratory incubators. The developmental time from egg to adult was 67 and 52 days, respectively. Based on cohorts of 100 females in each experiment, horizontal life tables were constructed. The following predictive parameters were obtained under each of the two conditions: net rate of reproduction (23.5 and 18.0 females per cohort female), generation time (11.4 and 9.4 weeks), intrinsic rate of population increase (0.27 and 0.30), and finite rate of population increment (1.31 and 1.36). The reproductive value for each class age of the cohort females was calculated. The observed parameters were obtained under each experimental condition: net rate of reproduction (1.9 and 2.5 females per cohort female), generation time (11.7 and 9.6 weeks), intrinsic rate of population increase (0.05 and 0.09), and finite rate of population increment (1.06 and 1.10). Vertical life tables were elaborated and mortality was described for every generation in each cohort. In addition, for two successive generations, additive variance and heritability for fecundity were estimated.
Asunto(s)
Estadios del Ciclo de Vida , Psychodidae/crecimiento & desarrollo , Animales , Interpretación Estadística de Datos , Femenino , Fertilidad , Óvulo , Reproducción , Tiempo (Meteorología)RESUMEN
A cross-sectional serosurvey of a rural community near Iquitos, Peru was conducted to determine Oropouche (ORO) virus antibody prevalence and risk factors for human infection. Venous blood samples, and demographic, social, and risk factor data were obtained from people age five years of age and older who lived in the village of Santa Clara on the Nanay River, a tributary of the Amazon River. Sera were tested for ORO viral antibody by an ELISA. The specificity of viral antibody reactivity was determined by a standard plaque-reduction neutralization test. Interview data were analyzed by univariate and multiple logistic regression to determine which variables were statistically associated with previous ORO viral infection, as indicated by the presence of IgG antibody. Final models were evaluated based on log-likelihood and Wald chi-square. Clustering of seropositive residents within houses was analyzed by the method of Walter. Among 1,227 persons sampled, 33.7% (n=414) were positive for ORO viral IgG antibody. Overall, antibody prevalence was similar for males (33.9%) and females (33.6%), and increased significantly with age for both sexes to include more than half of persons more than 25 years of age. The length of residence in the village was positively associated with serologic status; persons who had moved to the village within the past 15 years were less likely to be seropositive than life-long residents of the same age. Antibody prevalence among immigrants who had lived in Santa Clara more than 15 years was similar to that in life-long residents. The activity most predictive of previous ORO viral infection was travel to forest communities and travel to Iquitos. No evidence of spatial heterogeneity in ORO virus antibody distribution was observed. Results suggested that endemic transmission of ORO virus in this region has been ongoing during many decades, and that people are at considerable risk of infection.
Asunto(s)
Infecciones por Bunyaviridae/epidemiología , Infecciones por Bunyaviridae/transmisión , Virus Simbu , Adolescente , Adulto , Anciano , Anticuerpos Antivirales/sangre , Infecciones por Bunyaviridae/inmunología , Niño , Preescolar , Estudios Transversales , Femenino , Humanos , Inmunoglobulina G/sangre , Masculino , Persona de Mediana Edad , Perú/epidemiología , Factores de Riesgo , Estudios Seroepidemiológicos , Virus Simbu/inmunología , Factores de Tiempo , ViajeRESUMEN
The phlebotomine sand fly, Lutzomyia longipalpis, is the vector of visceral leishmaniasis in the New World. Variability in its tergal spot morphology has led to conflicting interpretations of the species status of the various forms. An L. longipalpis field population from eastern Brazil was found with three co-occurring morphological variations--1-spot, 2-spot, and an intermediate form. Genetic profiles were established for each form. Fifteen isoenzyme loci provided the data matrix for comparison of genetic variation among the forms. Spot patterns and isoenzyme frequencies fit Hardy-Weinberg expectations, and no significant differences in isoenzyme frequencies were associated with morphological phenotype. The spot phenotype appears to be a polymorphic character not related to genetic isolation or differentiation at the species level.
Asunto(s)
Psychodidae/anatomía & histología , Alelos , Animales , Brasil , Femenino , Frecuencia de los Genes , Variación Genética , Masculino , Polimorfismo Genético , Psychodidae/genética , Psychodidae/metabolismoRESUMEN
The life cycle of Lutzomyia shannoni (Dyar), was described for laboratory conditions with maximum daily temperature of 27-30 degree C, minimum daily temperatures of 22-27 degree C and relative humidity between 87-99%. Life cycle in each stage was as follows: egg 6-12 days (ave, 8.5 days); first stage larva 5-13 days (ave. 9.6 days); second stage larva 4-13 days (ave. 9.2 days); third stage larva 5-19 days (ave. 11.8 days); fourth stage larva 7-37 days (ave. 19.9 days); pupa 7-32 days (ave. 15.2 days). The life expectancy of adults ranged from 4 to 15 days (ave. 8.6 days). The entire egg to adult period ranged from 36 to 74 days (ave. 54.6 days). On average, each female oviposited 22.7 eggs; the average egg retention per female was 24.3 eggs.
Asunto(s)
Fertilidad/fisiología , Estadios del Ciclo de Vida/fisiología , Psychodidae/anatomía & histología , Psychodidae/crecimiento & desarrollo , Animales , Femenino , Humedad , Masculino , Caracteres Sexuales , TemperaturaRESUMEN
Lutzomyia longipalpis (Lutz & Neiva), the sand fly vector of American visceral leishmaniasis in the New World tropics, has a broad but discontinuous geographical distribution from southern Mexico to Argentina. A baseline for population genetic structure and genetic variability for this species was obtained by analyzing 5 local, peridomestic populations at the approximate center of its distribution, the Magdalena River Valley of central Colombia. Three populations of L. longipalpis from El Callejón, a small rural community, were compared with 2 populations from neighboring areas 12 and 25 km distant for genetic variation at 15 isoenzyme loci. The mean heterozygosity ranged from 11 to 16%, with 1.2 to 2.3 alleles detected per locus. Nei's genetic distances among the populations were very low, ranging from 0.001 to 0.007. Gene flow estimates based on FST indicated high levels of gene flow among local L. longipalpis populations, with minimal population substructuring.
Asunto(s)
Psychodidae/genética , Alelos , Animales , Colombia , Polimorfismo Genético , PoblaciónRESUMEN
The phlebotomine sand fly Lutzomyia longipalpis is the insect vector of visceral leishmaniasis, a protozoan disease of increasing incidence and distribution in Central and South America. Electrophoretic allele frequencies of 15 enzyme loci were compared among the L. longipalpis populations selected across its distribution range in Brazil. The mean heterozygosity of two colonized geographic strains (one each from Colombia and Brazil) were 6% and 13% respectively, with 1.6-1.9 alleles detected per locus. In contrast, among the seven widely separated field populations, the mean heterozygosity ranged from 11% to 16% with 2.1-2.9 alleles per locus. No locus was recovered that was diagnostic for any of the field populations. Allelic frequency differences among five field strains from the Amazon basin and eastern coastal Brazil were very low, with Nei's genetic distances of less than 0.01 separating them. The two inland and southerly samples from Minas Gerais (Lapinha) and Bahia (Jacobina) states were more distinctive with genetic distances of 0.024-0.038 and 0.038-0.059, respectively, when compared with the five other samples. These differences were the consequence of several high frequency alleles (glycerol-3-phosphate dehydrogenase [Gpd1.69] and phosphoglucomutase [Pgm1.69]) relatively uncommon in other strains. The low genetic distances, absence of diagnostic loci, and the distribution of genes in geographic space indicate L. longipalpis of Brazil to be a single, but genetically heterogeneous, polymorphic species.
Asunto(s)
Insectos Vectores/genética , Leishmaniasis/transmisión , Psychodidae/genética , Animales , Brasil , Femenino , Variación Genética , MasculinoRESUMEN
The genetic qualities of laboratory colonies of phlebotomine sand flies have not been compared with field specimens despite 1) probable genetic shifts due to the colonization process and 2) the problems associated with the extrapolation of experimental data derived from colonized organisms to field populations. The present study compared the genetic profiles of five laboratory colonies of geographic strains of the New World sand fly Lutzomyia longipalpis, and contrasted them with field populations. The profiles were based on the variability exhibited with polyacrylamide gels at 14 enzyme loci. A general pattern of a loss of infrequent alleles and decreased heterozygosity emerged as an apparent consequence of colonization. The average number of alleles per locus ranged from 1.2 to 1.6, and the average heterozygosity ranged from 4% to 11%. The field collection from Lapinha Caves (near Belo Horizonte, Brazil) averaged 2.1 alleles with a heterozygosity of 16%. In contrast, the LAPINHA laboratory colony established from that site 24 years earlier showed very low values (1.2 alleles/locus and 4% heterozygosity) and fixation for alleles not present or rare in the field collection from the same site. The genetic differences between the other Brazilian colonies and the Lapinha Caves field samples were due to presence of both different alleles and highly diverged allelic frequencies. Biological inferences based on colonized sand flies must be tempered by recognizing that the colony may represent a highly skewed genetic subsample of the L. longipalpis field genome.