[Entomology of onchocerciasis. I. Entomological factors in the transmission of onchocerciasis in Mexico].
Explore the source record for details and available documents.
Animals↗
SEARCH · Search PubMed
Results for “Onchocerciasis”
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Visual field defects in onchocerciasis.
Lesions in the posterior segment of the eye in onchocerciasis may give visual field defects, but so far no detailed investigation has been done to determine the functional visual loss. Examination of the visual fields in 18 selected cases of onchocerciasis by means of a tangent screen test revealed important visual field defects associated with lesions in the posterior segment of the eye. Involvement of the optic nerve seemed to be important, giving rise to severely constricted visual fields. Cases of postneuritic optic atrophy showed a very uniform pattern of almost completely constricted visual fields, with only 5 to 10 degree central rest spared. Papillitis gave a similar severe constriction of the visual fields. The pattern of visual fields associated with optic neuropathy in onchocerciasis indicates that a progressive lesion of the optic nerve from the periphery may be responsible for the loss of vision. The visual field defects in onchocerciasis constitute a serious handicap, which must be taken into consideration when estimating the socioeconomic importance of the disease.
Adolescent↗
[Sudan-savanna and rain-forest onchocerciasis in West Africa: an epidemiological problem (author's transl)].
A Sudan-savanna and a rain forest onchocerciasis have been described in West Africa. These two patterns of onchocerciasis have in common many epidemiological features but in hyperendemic areas there is a very essential difference between the two. In savanna the prevalence of serious ocular lesions and blindness due to onchocerciasis are much higher than in forest. Therefore attempting to explain these differences five groups of factors (or working hypothesis) are reviewed: --factors related to the vectors; --onchocerca-simulium couples; --different Onchocerca volvulus strains; --factors related to the human-host; --other varied factors: nutritional factors, concomitant ocular infections, luminousness of savanna, periods of transmission... A critical examination of these hypothesis brings to the conclusion that according to our present knowledge the main difference between savanna and rain-forest onchocerciasis may be due to degrees in pathogenicity of different strains of O. volvulus but these hypothesis have not been proved formally. More the part of concomitant factors (co-factors), themselves related to bioclimactic zones must not be ruled out.
Adolescent↗
Serum vitamin A levels of patients with onchocerciasis from two areas of the Sudan.
Two areas of the Sudan known to be endemic to onchocerciasis were surveyed for skin and ocular changes, and serum vitamin A levels in patients and normal controls. In Southern Sudan severe eye lesions and blindness are common complications. In Northern Sudan skin lesions predominate, and no case of blindness was recorded. Serum vitamin A levels were found to be adequate in all groups studied. However, patients from Southern Sudan with both eye and skin lesions due to onchocerciasis had the lowest mean serum vitamin A level. The significance of these findings is discussed in relation to the possible aetiological role of vitamin A deficiency in the pathogenesis of ocular complications of onchocerciasis.
Adolescent↗
[Aspects of the development of ocular onchocerciasis in West-Africa after three years of simulium control (authors transl)].
In four rural West-African communities with different degrees of ocular affection the development of ocular onchocerciasis has been evaluated after three years of vector control. In the area of a successful disruption of the transmission the population with a slight degree of ocular onchocerciasis before control operations started, did not show an aggravation of the lesions. In those groups severely affected at the beginning of vector control the lesions showed no progression in the majority of the cases. The diminuition of the ocular parasite load, resulting from the reduced transmission, appears to be an important factor in the change of the incidence of blindness and severe ocular lesions attributable to onchocerciasis. Contrary to this the aggravation of ocular lesions was found to be more severe in a community situated in the area reinvaded by the vector than in those that did not experience a reinvasion of the fly.
Adolescent↗
The use of an Onchocerca volvulus microfilarial antigen skin test in an epidemiological survey of onchocerciasis in Guatemala.
Onchocerca volvulus microfilariae obtained from onchocercal nodules were used as antigenic material for a skin test. This antigen is as specific as those previously employed in skin tests, detecting 85.2% of the persons with positive diagnostic signs of onchocerciasis in endemic areas. A low rate of false positives was found in the control group in nonendemic areas. The positive rate of reactions in the persons without positive signs in the endemic areas might be due to the presences of cases not detected as a result of palpation for nodules and two skin biopsies. In the examination of the residents of several populations, a close correlation was found between the positive rates of skin tests and the presence of infection. From these findings, we conclude that the skin test using the microfilarial antigen is a suitable procedure for the diagnosis of onchocerciasis. The skin test could also be useful as an epidemiological tool in assessing the effectiveness of control programmes.
Adolescent↗
Displacements of Simulium damnosum and strategy of control against onchocerciasis.
Regular aerial treatment of 14 000 km of watercourses has achieved and maintained, over an area of 700 000 km2 of West African savannah, a very high degree of control of the larvae of Simulium damnosum sensu stricto and S. sirbanum, the vectors of onchocerciasis in this area. However, particular and relatively restricted parts of this area, mainly in northern Ivory Coast and neighbouring parts of Upper Volta, experience regular and prolonged reinvasions by parous female vectors, which have already taken bloodmeals (and many of them carrying the parasites) and arrive from unknown sources probably hundreds of kilometres away, from directions probably between southwest and north. This reinvasion, now experienced in three successive years, represents the outstanding scientific, epidemiological and logistic problem still facing the WHO Onchocerciasis Control Programme. An outline is presented of the multidisciplinary investigations being undertaken to find a solution.
Africa, Western↗
Evaluation of microfilaricidal effects in the cornea from topically applied drugs in ocular onchocerciasis: Trials with levamisole and mebendazole.
Increasing concentrations of levamisole and of mebendazole were applied to 1 eye in groups of 4 patients with ocular onchocerciasis in northern Cameroon. No effect resulted from up to 3.0% mebendazole suspensions, but 3.0% levamisole solutions rapidly caused entry of microfilariae, straightening out and subsequent opacification of previously curled-up living microfilariae, the rapid formation of typical limbal globular infiltrates, and the subsequent formation of fluffy opacities around the microfilariae. These changes are typical of all other drugs so far studied that have a microfilaricidal action on O. volvulus--diethlycarbamizine citrate (DEC), suramin, and metrifonate. The efficacy of 3.0% levamisole approximated to that of 0.03% DEC. This is in keeping with published observations on the filaricidal activity of these 2 compounds. It is suggested that this system of drug testing should be considered for systematic use in the search for more effective and safer drugs for onchocerciasis.
Cornea↗
Onchocerciasis in San Vicente Pacaya, Guatemala.
An epidemiological survey for onchocerciasis was carried out in the San Vicente Pacaya area of Guatemala. A total of 2,153 inhabitants were examined by a single skin snip, and 664 (30.8%) were positive for microfilariae. Slit lamp examination of the anterior chamber of the eye revealed microfilariae in 6.2%; the positive rate for microfilariae in the anterior chamber was proportional to the microfilarial density in the skin. The altitude-dependent character of onchocercal infection was shown in this mountainous area, suggesting that transmission occurs principally between 600 and 1,300 m. Of, 1,217 persons examined simultaneously by skin snip and by palpation for nodules, 587 were positive by one or both methods; 101 infections were detected by onchocercal nodules only and these were usually in children or persons living in areas of low endemicity. It was concluded that both the skin snip and a search for nodules are required for accurately determining the prevalence of onchocerciasis in Guatemala.
Adolescent↗
The microfilarial load in the anterior segment of the eye. A parameter of intensity of onchocerciasis.
The presence of microfilariae of Onchocerca volvulus in the eye is associated with an increased risk of deterioration of existing eye lesions. An opthalmological and parasitological examination of 630 persons was carried out in a hyperendemic focus of onchocerciasis in northern Togo. The prevalence of microfilariae increased in the cornea as well as the anterior chamber up to the age of 40-50 years, then decreased. The prevalence of onchocercal punctate keratitis, on the other hand, showed a peak for the age group 10-20 years. In two-thirds of the cases microfilariae were present in the anterior chamber as well as in the cornea. The relative distribution of microfilariae between the anterior chamber and the cornea did not change with the development of severe anterior lesions but in cases with severe posterior lesions relatively more microfilariae were found in the anterior chamber than in the cornea. In all cases of severe ocular lesions the numbers of microfilariae both in the anterior chamber and in the cornea were increased. The average number of microfilariae in the eye can be used as a parameter to enumerate the severity of ocular onchocerciasis.
Adolescent↗
Epidemiological aspects of intraocular pressure in an onchocerciasis endemic area.
A field investigation of intraocular pressure in populations in onchocerciasis endemic areas of West Africa revealed a normal pressure distribution in individuals without signs of ocular onchocerciasis or with only microfilariae or reversible lesions in the eye. Females showed a significantly higher mean ocular tension, and in both sexes tension decreased with age. Patients with irreversible onchocercal ocular lesions and signs of anterior uveitis showed a significantly lower and abnormally distributed intraocular pressure. The prevalence of glaucoma was significantly higher in this group, thus indicating that a high intensity of onchocercal infection may be associated with a risk of secondary glaucoma. The presence of microfilariae in the ocular tissues and consequent inflammatory reactions may possibly give rise to an abnormal distribution of ocular tension.
Adolescent↗
Immunological studies on onchocerciasis. Varying skin hypersensitivity and leucocyte migration inhibition in a clinical spectrum of the disease.
Soluble antigen was prepared from adult worms and microfilariae of Onchocerca volvulus. In 27 patients clinically characterized as having generalized type (17) and localized reaction type (10) onchocerciasis, the response to this antigen was assessed in vivo by skin testing and in vitro by leucocyte migration inhibition assay. Three varieties of skin hypersensitivity were observed: Immediate, Arthus-type and delayed or type IV hypersensitivity. The first 2 occurred in all patients, but type IV hypersensitivity was noted only in 10, eight of whom had localized reactive type onchocerciasis, whilst the other 2 had mild generalized lesions which had for the most part healed with treatment. The leucocyte migration inhibition assay showed a spectrum of responsiveness with significant inhibition in the presence of antigen in 8 patients with localized lesions and in 2 others with mild generalized disease which had largely healed.--The specificity of the skin reaction and leucocyte migration inhibition to the antigen used was confirmed by the results obtained when a control group of 18 subjects, with no evidence of previous filarial infection, was similarly tested. 16 of them showed no skin hypersensitivity and 2 had a doubtful immediate reaction. No significant inhibition of leucocyte migration in the presence of antigen was noted in this group.
Adolescent↗
A histological investigation of skin lesions in onchocerciasis patients from Southern Togo.
Specimens from unselected populations in an area of hyperendemic onchocerciasis were used to describe and quantify histological changes in the upper layers of the dermis and the findings were compared with the macroscopical lesions observed. 553 persons, the inhabitants of two villages in Southern Togo, were examined. 502 biopsies were processed histologically. Onchocerciasis prevalence was over 75% and macroscopical skin lesions were evident in 30--40% of the population examined. Histological changes typical for the infection existed in the dermis in 68.5%. A cellular infiltration was seen in 49%, changes in the elastic or collagenous fibrils in 28.9% of the specimen. The observations are described in detail. Signs of inflammatory as well as primary degenerative changes were seen in biopsies from all age-groups. When microscopic and macroscopic findings are compared, it can be noticed that atrophy may start at an early age without preceeding dermatitis and that inflammatory reactions may occur at all ages. After submersion in saline for 24 hours not all microfilariae had emerged from the skin snips as evidenced by the histological examination. In 12.1% of those that otherwise would have been diagnosed as negative, microfilariae were identified in the sections.
Adolescent↗
Onchocerciasis treated with diethylcarbamazine.
One hundred patients with onchocerciasis were treated with diethylcarbamazine: a single course of treatment led to clinical cure in 48% of the patients; no means of anticipating which patients might require only a single course of treatment was found.
Adolescent↗
Effects of various concentrations of diethylcarbamazine citrate applied as eye drops in ocular onchocerciasis, and the possibilities of improved therapy from continuous non-pulsed delivery.
Diethylcarbamazine was given as eye drops in varying concentrations in a half-log dilution series from 1.0 to 0.0001% to patients with ocular onchocerciasis. Migration of microfilariae into the cornea, followed by their straightening and disintegration, was observed with delivery rates as low as 0.1 microgram/hour. Dose-related adverse inflammatory reactions, including the development of globular limbal infiltrates with itching and redness, were seen with delivery rates as low as 0.6 microgram/hour, but substantial inflammatory reactions, including severe vasculitis, were seen only with delivery rates of or above 1.0 microgram/hour. This suggests that it should be possible to achieve beneficial clearing of the microfilarial load, without adverse reactions, by continuous non-pulsed delivery of the drug. Technology exists for such delivery, either directly into the eye or systemically by a transdermal system that could give 3 to 7 days' treatment from each application. The observations reported suggest that after preliminary clearing of the microfilarial load by carefully controlled delivery of DEC it may be possible to maintain therapy by less strictly controlled delivery in DEC-medicated salt, or to use treatment with suramin, without incurring substantial adverse reactions, such as a deterioration in vision in cases in which the optic nerve is already compromised. Continuous non-pulsed DEC delivery systems could have a place in the management of onchocercal sclerosing keratitis. The unique opportunities for using the ocular model to define the requirements for beneficial non-damaging therapy with DEC should be explored in further field trials.
Adult↗
Aspects of corneal changes in onchocerciasis.
The distribution of living and dead microfilariae in 160 cases of ocular onchocerciasis has been studied. A model for coding the densities in 9 different areas of the cornea has been used. The average numbers of microfilariae and onchocercal punctate opacities per square millimetre were assessed. The highest densities were found in the superficial one-third of the corneal stroma at the periphery of the nasal and temporal parts of the cornea. Sclerosing keratitis was also recorded, and the average age of the patients in this group was significantly higher than in the group with non-sclerosing onchocercal involvement. Corneal thickness measurement showed that the presence of microfilariae or onchocercal punctate opacities or a faint uveitis did not influence the values. In sclerosed areas the corneal thickness varied greatly and was dependent on the degree of the vascularisation. The routes of entry of microfilariae into the eye are discussed on the basis of the distribution patterns of microfilariae and onchocercal opacities.
Cornea↗
Ocular onchocerciasis.
Well over 20 million people in the world are infected with Onchocerca volvulus and it is probable that 200 000-500 000 people are blind as a result of this infection, which is the most important cause of blindness in certain areas of Africa and Latin America.Treatment of the disease is difficult and often produces serious adverse reactions in the patient. Combined use of diethylcarbamazine citrate and suramin is still the most suitable form of treatment. Screening for the early detection of cases at high risk of ocular manifestations must be organized, and their treatment undertaken, if blindness is to be avoided.Prevention of ocular onchocerciasis is feasible, using vector control methods to reduce transmission, but the procedures are costly and may have to be maintained for many years.Research is needed to improve treatment and to find a chemoprophylactic agent or a preventive vaccine.
Diethylcarbamazine↗
The risk of optic atrophy following suramin treatment of ocular onchocerciasis.
Treatment of onchocerciasis with suramin in an area of vector control led to an increased incidence of optic atrophy in treated patients compared to an untreated group.
Eye Diseases↗