Onchocercomas in Guatemala, with special reference to appearance of new nodules and parasite content.

To determine the rate of appearance of new nodules during a specified period, a follow-up study on onchocercomas that had been removed was carried out in San Vicente Pacaya, Guatemala, between June 1976 and April 1977. Incidence rate, or rate of nodules appearing in initially negative subjects, was studied in relation to the degree of endemicity. Rates in a period of 7—8months in high, medium, and low endemic areas were 0.23 1, 0.083, and 0.022, respectively. The rate of nodule appearance in persons nodulectomized, or rate cfnodulesappearinginsubjectswhoweresurgicallyrenderednegativeduringthefirstsurvey, was 45.3%, 36.4%, and 4.5% in those areas. The highest rate of nodule appearance was observed in patients with microfilariae in both the skin and nodules, followed by patients with either microfilariae or nodules. In highly endemic areas, new nodules appeared in 13.2% of persons without microfilariae or nodules, while in low endemic areas even patients with nodules earlier were less likely to have developed new ones. The performance of the nodu lectomy teams (brigadas) was evaluated by confirming the worms in nodules. By gross ex amination alone, about 6% of nodules removed by brigadas did not contain worms. Nodules containing worms were examined for microfilariae to clarify their role as a source of micro filariae. Microfilariae were not detected in some of these nodules, especially in small ones. In contrast, microfilariae emerged from 80% of those larger than 10 mm. Number of worms per nodule, their sex, and the fecundity of female worms were examined by a collagenase tech nique. The average number of worms per nodule was 0.6 males and 1.2 females. The highest burden in any one nodule was seven worms, four females and three males. Most nodules had one female and either one male worm or none. Intrauterine microfilariae were found in most females from nodules shared with a male, while solitary females were not gravid. Solitary females were likely to be found in small nodules and large nodules were more likely to include both sexes. Since 1933 a nationwide nodulectomy campaign has been conducted in Guatemala as a control measure, but not as radical treatment, of oncho cerciasis;' all known endemic areas have been vis ited once or twice a year by paramedical nodulec tomy teams or “brigadas.―Although there is evidence of a reduced prevalence of onchocercal blindness,2 overall morbidity appears to have re mained unaffected.3 Romero and Wise questioned the effectiveness of mass nodulectomy as a means Accepted 16 August 1982. * This study was supported by the Ministry of Public Health,Guatemala,and Japan International Coopera tion Agency, Japan (ORCOP series, No. 53). of disease management, and stressed the need for a critical evaluation.4 Fuglsang and Anderson found that removal of head nodules was partially effective in reducing the microfilarial concentra tion in the cornea, but not in the skin, and was of some benefit to lesions of the anterior segment of the eyes.5 They noted, however, that removal of head nodules is far from sufficient as a curative measure in ocular onchocerciasis. Recently, Kale also reported that nodulectomy has no influence in microfilarial density.6 The general assumption that nodules, rather than worms free in the skin, are a significant source of microfilariae has not been examined thoroughly in Guatemala. In this investigation, we examined two major unanswered questions relevant to the value of no dulectomy as a control measure: the role of the