Effect of semiannual treatments of ivermectin on the prevalence and intensity of Onchocerca volvulus skin infection, ocular lesions, and infectivity of Simulium ochraceum populations in southern Mexico.

The effect of semiannual ivermectin treatment along with nodulectomy on filarial transmission levels were estimated during the three dry seasons of 1991-1993 in a hyperendemic village in southern Mexico. Parasitologic and ophthalmologic examinations were carried out every six months until five drug treatments were completed. Ivermectin mass treatment with a coverage of approximately 80% had a significant impact (P < 0.05) on the prevalence of skin infection and the mean microfilarial skin density (CMFL), which were reduced 38% and 89%, respectively. A gradual and significant (P < 0.05) decrease in the mean microfilariae number in the anterior chamber of the eye and in corneal opacities was also observed as the CMFL was reduced. After three treatments, these were reduced 84% and 69%, respectively. However, after two years of continuous intervention, no significant differences (P > 0.05) were observed in either the daily mean infective biting density and the daily mean transmission potential. This was probably due to the remaining microfilarial load provided by the untreated resident population and migrant groups. On the whole, our results confirm both the efficacy of ivermectin to alleviate the clinical manifestations of the disease and its minimal impact on Onchocerca volvulus transmission, and indicate the need both to achieve higher levels of drug coverage and to incorporate other measures to stop transmission until a macrofilaricide drug is found.

[Problems in the investigation of the control of Onchocerca volvulus in Mexico]. / Algunos problemas en la investigación para el control de la transmisión de Onchocerca volvulus en México.

The treatment and control of onchocerciasis in Mexico has been supported only on the administration of diethylcarbamazine and the removal of adult worms, which are in the onchocercomata. These actions seems to have diminished the prevalence and incidence of blindness in those individuals who are affected by this parasitosis. However, there has not been an important impact on onchocerciasis transmission. The objective of this paper is to critically analyze and discuss subjects related to diagnosis, treatment and control of onchocerciasis transmission in Mexico. Chemical vector control has been successfully achieved in other world regions; however, in Mexico, it has not been fully accepted as part of the integral onchocerciasis control due to several causes. Moreover, there has been few scientific research activities toward the search of new options for vector control. Recently, results of research on ivermectin (a microfilaricide agent) have indicated that this drug is effective and safe for the treatment of onchocerciasis. Additionally, it has been reported that ivermectin has an effect on the onchocerciasis transmission. However, there are several unanswered questions about the efficacy of ivermectin in stopping onchocerciasis transmission. In this report, the main efforts carried out in Mexico against onchocerciasis are analysed and problems related with diagnosis, treatment and control are also discussed. Some parameters for the correct evaluation of onchocerciasis control, with entomological emphasis, are proposed.

[Changes in the peripheral leukocytes of onchocerciasis patients treated with consecutive doses of ivermectin]. / Modificaciones en los leucocitos periféricos de pacientes oncocercosos tratados con dosis consecutivas de ivermectina.

The purpose of this investigation, which utilized a single-blind study with placebo, was to evaluate the peripheral leukocyte count in onchocerciasis patients treated with ivermectin. Eighty-three male patients between the ages of 12 and 60, all with moderate or severe onchocerciasis infections (but otherwise in general good health), were selected from three villages from the southern onchocerciasis endemic area of Chiapas, Mexico. All onchocerciasis patients were randomly assigned to either the ivermectin group or a placebo group in a three to one ratio, respectively. Sixty-two patients from the ivermectin group received five single oral doses of ivermectin between 150 and 220 mcg/kg (one every six months), and placebo pills of identical appearance were given to 21 patients from the placebo group. Physical, ophthalmological, and laboratory exams were performed on all patients in this study. Skin and ocular microfilaria were stimulated in all patients. Results have indicated that ivermectin induced a decrease in the total number of peripheral leukocytes to the extent of about 300 to 500 cells after each drug intake. In the majority of the cases, the reduction was due to a decrease in the total number of eosinophils; the number of neutrophils, lymphocytes, and monocytes remained at the same level after treatment. These results strongly suggest that the eosinophilia observed in the prestudy of those individuals with onchocerciasis could have induced leukocytosis (the eosinophilia decreasing significantly after administering ivermectin).

[The correlation between onchocercomas and positivity for microfilaria in onchocerciasis]. / Correlación entre oncocercomas y positividad para microfilarias en oncocercosis.

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.

Antigen detection in onchocerciasis: correlation with worm burden.

Detection of O. volvulus antigen by indirect ELISA test in the serum and the urine of 169 individuals with residence in the southeast onchocerciasis endemic focus in Chiapas, Mexico was performed. Every individual under study was physically examined for signs of onchocerciasis in particular for subcutaneous nodules, dermic lesions, ocular damage and history of Mazzotti reaction. Of the total cases, 91.7% were positive for skin microfilariae. Only 32.2% of the microfilariae positive cases carried at least one palpable nodule. The sensitivity of the ELISA test was 92.3% for serum and 85.9% for urine. A good correlation between the transformed numbers of skin microfilariae (square root of x + 1) and the positivity of the ELISA test for serum and for urine was found. It was also observed that the ELISA test values for the sera and for the urine showed a good correlation with r = 0.76 and Z0.95 less than 0.005. This serological test can be used for seroepidemiological surveys and for orientating the activity of massive onchocerciasis treatment campaigns.

Morphological characteristics and isoenzyme patterns of an Onchocerca sp. found in cattle in Southern Mexico.

An Onchocerca sp. was isolated from the nuchal ligaments of 78 out of 79 naturally infected cattle in Southern Mexico. Infections were moderate to heavy, averaging 20-30 parasites per nuchal ligament. Microfilariae were concentrated in the skin of the head and neck, although small numbers were found in the skin of the withers, brisket and medial abdomen. High numbers of microfilariae were found in the skin around the eye, but not in the ocular tissues themselves a situation dissimilar to that found in human onchocerciasis. Morphologically, adult females, males and microfilariae were identified as being O. gutturosa. Analysis of the isoenzyme patterns of LDH, MDH, PGM, GPI, PGD and ES of adult female worms, showed the Mexican parasite to be the same as O. gutturosa from England and Australia.