[The correlation between onchocercomas and positivity for microfilaria in onchocerciasis]

The objective of this work is to evaluate the palpation sensitivity of onchocercomata for the diagnosis of onchocerciasis in individuals residents of the locality of Nueva Costa Rica, Mapastepec, in the south endemic area of the state of Chiapas, Mexico. Every one of the 243 individuals who voluntarily participate in this study was interrogated and physical examined for the detection of nodules. The positivity and the worm burden to the Onchocerca volvulus infections was estimated by the presence of one or more microfilariae in any of the for skin snips taken from both suprascapular and gluteal regions, and by the mean of the Dmf/mg of each skin snip. From the total number of individual studied, 131 (53.9%) were positives to microfilariae and 37 (15.2%) to onchocercomata. Only 23 (17.6%) of the microfilariae positive individuals carried nodules. The distribution of positive individuals to nodules in relation to age, was similar in all the age groups. In relation to the intensity of the infection was found that, the mean of the Dmf/mg of all individuals was 6.67, there was not significant differences (p greater than 0.001) between males and females; being the Dmf/mg of 6.35 and 6.99, respectively. The age group between 21 and 30 years old showed the higher mean of Dmf/mg than the rest of the groups (p greater than 0.001). However, there was a high microfilariae positivity in the oldest groups than in the young. The prevalence for onchocerciasis in this locality, estimated by the positivity to either microfilariae or nodules, was 59.9 per cent. It is concluded that, the onchocercomata detection sensitivity for the diagnosis of onchocerciasis was very low, probably due to the nodulectomy activity of the onchocerciasis control program, which has been operating since 1930 and therefore, there are an important number of individuals positive to microfilariae without detectable nodules.