RESUMEN
Transmission of Onchocerca volvulus at 4 locations with different prevalences of human onchocerciasis in the Atitlán region of Guatemala is described in relation to vector density and infection rates. The percentages of residents with skin biopsies positive for microfilariae of O. volvulus at these locations were 13.8%, 33.3%, 65.4%, and 89.6%. The following variables associated with transmission were calculated from our observations (the values are presented in an order that corresponds with the above prevalence rates): frequency of third-stage larvae (calculated on an annual basis) in parous Simulium ochraceum, 0, 0.004, 0.005, and 0.004; estimated daily biting density of S. ochraceum, 23, 24, 254, and 1,509 flies per day; and estimated annual infective biting density (based on S. ochraceum), 0, 18, 185, and 1,101 potentially infective bites per year. The frequencies of third-stage larvae are very small compared with those observed in Africa, and suggest that transmission of O. volvulus in Guatemala depends on high vector density. Locations with low, and perhaps tolerable, levels of onchocerciasis (less than 15% of female residents with skin biopsies positive for microfilariae) have mean daily biting densities for S. ochraceum of less than or equal to 24 flies, and infected residents normally have mean microfilarial densities of less than or equal to 3 microfilariae per mg of skin. Stratification of prevalence rates by age group proved useful for assessing current transmission within a village.
Asunto(s)
Insectos Vectores/parasitología , Onchocerca/crecimiento & desarrollo , Oncocercosis/transmisión , Simuliidae/parasitología , Adolescente , Adulto , Animales , Niño , Preescolar , Femenino , Guatemala , Humanos , Lactante , Insectos Vectores/crecimiento & desarrollo , Masculino , Oncocercosis/epidemiología , Simuliidae/crecimiento & desarrolloRESUMEN
The usual pattern of onchocercal dermatitis in Africans and Guatemalans is a generalized and symmetrical dermatitis located on legs, arms and trunk. These patients appear to be anergic, with depressed immune responses and numerous microfilariae in the skin. In contrast, "sowda" is an unusual type of onchocercal dermatitis found in Yemenites and in a minority of African patients. Here the dermatitis is localized and asymmetrical - typically confined to one limb or one region of the body. Patients with sowda appear to be hypergic, with active humoral and cellular immune responses; microfilariae are rare or absent. This study describes two Guatemalan patients with sowda-type dermatitis. The diagnosis in these two patients is based on the asymmetrical papular pruritic dermatitis, rare or absent microfilariae, a positive Mazzotti reaction, and histopathologic changes characteristic of the sowda-type onchocercal dermatitis.
Asunto(s)
Dermatitis/patología , Oncocercosis/patología , Adulto , Biopsia , Dermatitis/diagnóstico , Dermatitis/parasitología , Diagnóstico Diferencial , Guatemala , Humanos , Masculino , Oncocercosis/diagnóstico , Oncocercosis/parasitología , Piel/patologíaRESUMEN
Ten Simulium ochraceum were allowed to feed at 10 different sites on 12 Guatemalans with onchocerciasis, and skin snips were taken from six of these sites. Numbers of microfilariae (mff) ingested by the flies and mff emerging from skin snips were highly correlated and showed that concentrations were greatest on the torso and decreased peripherally. S. ochraceum ingested the number of mff present in 1.0 mg or under 1.5 mm2 of skin. Numbers of mff in skin snips from the head, shoulder and upper arm correlated with over-all levels of infection but were frequently negative in subjects with light infections. Two or more skin snips were best able to detect and quantify infections.
Asunto(s)
Onchocerca/aislamiento & purificación , Oncocercosis/parasitología , Piel/parasitología , Animales , Dípteros/parasitología , Humanos , Insectos Vectores , Masculino , Microfilarias , Oncocercosis/transmisiónRESUMEN
To provide quantitative information on the epidemiology of infection with Onchocerca volvulus and to define the association between indicators of infection and onchocercal eye disease, skin snips were obtained and skin and ocular examinations were performed on 892 persons living on seven Guatemalan coffee plantations. Skin-snip positivity and the density of microfilariae in the skin increased with age, reaching highest levels at 15-19 years, and both were greater in males than females. A history of nodulectomy was given by 67% of long-term residents and this percentage also increased with age. Over 90% of skin-snip positive subjects and 39% of skin-snip negative subjects had previous or present nodules. Microfilariae were detected in the cornea of 35.1% and in the anterior chamber of 18.9% of all persons examined and the frequencies increased with age, reaching peak levels at 10-19 years. Onchocercal eye lesions were found in 52 persons, causing bilateral blindness in six. Skin-snip positivity, microfilarial skin density, number of nodules, eye infection, and onchocercal eye lesions all correlated significantly with each other. Onchocercal blindness in one or both eyes was found only on fincas with a high prevalence (greater than 80%) and intensity of infection (greater than 22 microfilariae/mg skin).