This paper describes, for the human onchocerciasis focus of southern Venezuela, the age profiles of Onchocerca volvulus microfilarial (mf) and nodule prevalence, mf intensity, and mf aggregation for the whole examined population (836 Yanomami people) living in 20 villages, and for these communities classified according to endemicity levels (hypoendemic: < or = 20 %; mesoendemic: 21-59 %; hyperendemic: < or = 60 % infected). Mf prevalence and intensity increased with age, particularly in the hyperendemic areas, and there were no marked differences between the sexes. The prevalence of nodules followed the same age pattern. Fifty percent mf prevalence was reached in the 15-19 year age-class when the population was taken as a whole; nearly in the 10 to 14-year-olds for the hyperendemic level, in those aged 20-29 years in mesoendemic areas, and not reached at all in hypoendemic villages. The degree of mf aggregation was measured by the k value of the negative binomial distribution and by the variance to mean ratio (VMR). The relationship between the standard deviation (S.D.) of mf counts and the mean mf density was also explored. These 3 indices (k, VMR, and S.D.) showed a tendency to increase with both mean mf load and host age. Since infection intensity and host age were themselves positively related, it was not possible to draw definite conclusions about age-specific changes of parasite aggregation. There was not a significant decrease of mf intensity after an earlier peak neither was there a shift towards younger ages of the maximum no. of mf/mg reached as the endemicity level increased. These results are discussed in relation to detection of density dependence in the human host, selection of an indicator age-group for rapid epidemiological assessment (REA) methods, and strategies of ivermectin distribution in the Amazonian focus. It is recommended that, for the Amazonian onchocerciasis focus, the indicator group for REA consists of all those aged 15 years and over.

Introducción. Poblaciones naturales de Anopheles darlingi, principal transmisor de malaria en Colombia, han mostrado plasticidad fenotípica en algunos de sus caracteres diagnósticos.Objetivo. Caracterizar variaciones morfométricas en patrones alares y de pata posterior en poblaciones naturales de An. darlingi recolectados en localidades donde la malaria es endémica.Materiales y métodos. Se analizaron mediante morfometría lineal y geométrica, los patrones de manchas de la vena Costa del ala de hembras silvestres recolectadas en los departamentos de Chocó, Guaviare, Meta y Vichada. El segundo tarsómero posterior de las hembras se analizó por morfometría lineal.Resultados. Se encontraron 19 patrones de manchas de la vena Costa, los patrones I con 49 % (n = 118/240) y VI con 28 % (n = 66) correspondieron a los más frecuentes. La proporción DSIII2/TaIII2 constituyó un carácter diagnóstico robusto debido a representó el 89% (n = 213/240) del total de especímenes analizados. Se encontraron diferencias significativas para la forma (F = 1,65, gl = 50, p < 0,001) y el tamaño (F = 3,37, gl = 5, p = 0,005) del ala entre poblaciones de diferentes localidades. El tamaño del centroide más pequeño 2,64 mm se encontró en poblaciones de Chocó.Conclusiones. Se registraron once patrones nuevos para manchas de la vena Costa y se confirma la dominancia de los patrones alares I y VI para poblaciones de An. darlingi de Colombia. Se confirma que la relación DSIII2/TaIII2 constituye un carácter diagnóstico robusto para la taxonomía de la especie. Se encontraron diferencias en el tamaño corporal de las poblaciones evaluadas, lo que reviste importancia para el análisis de aspectos bionómicos de la especie.