Laboratory research into the pathogenesis of ocular onchocerciasis

Despite its importance as a cause of blindness, there is still much to be learned about the way in which onchocerciasis damages ocular tissues. Much of the difficulty encountered in investigating the problem is due to the lack of an adequate laboratory model amenable to study outside the endemic areas of O. volvulus infection. An attempt has been made to reproduce the ocular effects of O. volvulus in humans by infecting rabbits and guinea-pigs and bovine (O. gutturosa) and equine (O. cervicalis) strains of Onchocerca. The subconjunctival inoculation of rabbits with microfilariae of O. volvulus can produce a keratitis comparable to that seen in the naturally occurring disease and there is evidence that the intensity of the inflammatory response can be modified by pre-immunization. Injecting microfilariae into the posterior segment is equally able to produce choroido-retinal lesions, but evidence that immunological mechanisms are involved is less obvious.

[Studies on the serological manifestation of the hepatitis B-virus-infections in the Republic of Liberia (author's transl)]

The prevalence of hepatitis B virus infections was examined in four groups from Liberia using radioimmunoassays for HBsAg, anti-HBs and anti-HBc. At the age of 15-19 years 90% have been infected, at the age of 40 years 100%. In a rubber plantation 30% had HBsAg, in the remaining 3 groups only 13% were HBsAg-positive. In the first group onchocerciasis was also a more frequent finding. However the parasitic infection was not the cause of the HBs-antigenemia. The HBsAg-concentration is mostly lower in the positive Liberians than in German HBsAg-carriers. Apparently the HBV caused frequently latent infections with low production of viral antigens in Liberia.

Adolescent breast masses in Nigerian Igbos

In the Igbos of Nigeria, most adolescent breast masses were due to gynecomastia in males and to fibroadenoma in females. The peak ages for both diseases differed from those reported in a recent American series. An exotic finding was a mammary mass due to onchocerca worms. Curiously, there were as many as two cases of a rare tumor, namely, alveolar soft part sarcoma.

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.

Avoidable blindness: a world problem

There are four billion people in the world. Forty million of them are blind. If the link between population growth and blindness is not broken, the number will double by the turn of the century.

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.

Onchocercal lymphadenitis: Clinicopathologic study of 34 patients

Clinicopathological studies on lymph nodes of 32 Africans with onchocerciasis--some complicated by hanging groin and elephantiasis of the genitalia--revealed atrophic lymphoid tissue, lymphoedema, chronic inflammation and fibrosis. We identified microfilariae of Onchocerca volvulus in nodes of 24 of 32 Africans (75%). There microfilariae were most numerous in the capsule and in the fibrous tissue of the medulla, but smaller numbers were also found within lymphoid tissue, in dilated lymphatics and in blood vessels. We believe that in Africians, antigens released from microfilariae of O. volvulus lead to the deposition of immune complex in tissues, which in turn causes inflammation and fibrosis and eventually obstructive lymphadenitis. This causes hanging groin and, possibly, also elephantiasis. A distinctive pattern of perivascular fibrosis contains "fibrinoid material" that we interpret as immune complexes involving microfilarial antigens. In contrast, nodes from two Yemenites with severe onchocercal dermatitis of the lower limbs (sowda) had hyperplastic follicles, minimal fibrosis and no microfilariae.

Studies on onchocerciasis in the United Cameroon Republic. IV. A four-year follow-up of six rain-forest and six savanna villages. The incidence of ocular lesions

After an interval of four years the same observers re-examined six rain-forest and six savanna villages, using the same standardized techniques. The results of these surveys have previously been reported by area, i.e. rain-forest and savanna. The present paper analyses the incidence of ocular changes by village. In the rain-forest the concentrations of microfilariae in the skin were similar in the six villages and there was, in general, little difference in the incidence and/or deterioration of ocular lesions between these villages. In the savanna the corresponding quantities were much higher in the three more heavily infected villages compared with the three less heavily infected ones. The implications of these findings for the control of blindness due to onchocerciasis in the savanna are discussed.

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.