Morphometric analysis of nodules in human onchocerciasis collected in communities of the southern Chiapas focus, México.

Human onchocerciasis is a disease that remains as an important public health problem. The morphometric and physical characteristics of 363 Onchocerca volvulus nodules collected in the major endemic focus of onchocerciasis in Southern Chiapas (Soconusco), was assessed. In the present work we found that treatment the morphometry of 363 onchocercal nodules preserved in a 67% glycerol solution was determined by measuring the length, width and thick of each nodule with a Vernier caliper. The mass was determined with an analytical balance and the volume by measuring the water displacement, while the specific gravity was calculated by dividing mass over the volume. Statistical analysis was calculated for each parameter. The results showed that the nodules were rather longer than wider or thicker. Morphometric characteristics were 9.87 +/-3.70 (mean +/- standard deviation), 7.52 +/- 2.81, and 4.62 +/-+/- 2.06 mm for length, width and thick respectively. In regard to the shape, 62.81% of the nodules showed a lenticular shape, while 18.18% were spherical and 19.01% were ovoid. Based on the distribution of frequencies of the length, the nodules were classified in three groups: the "small" (5.77 +/- 0.73 mm; n = 104, 28.65%), the "medium" group (9.86 +/- 2.05 mm; n = 203 nodules, 55.92%), and the group of the "big" ones (16.03 +/- 1.91 mm; n = 56, 15.43%). Moreover, the physical characteristics were: for the mass 0.33 +/- 0.24 g, the volume of displaced water was 0.28 +/- 0.26 ml, and the specific gravity was 1.10 +/- 0.55 g/ml. The results indicated that most of the Mexican Onchocerca nodules have a lenticular shape with average size of 10x7x5 mm, which is useful in the knowledge of the genus biodiversity and can be taken as a parameter in clinical or epidemiological trials, where onchocerciasis remains as a public health problem.