Schulz-Key H (1990) Acta Leiden "Observations on the reproductive biology of Onchocerca volvulus."

Schulz-Key H

[Acta Leiden, 1990]

This study compiles observations on the reproductive capacity of O. volvulus. Adult parasites enzymatically isolated from excised onchocercomata of untreated and chemotherapeutically treated patients, and from inhabitants living in areas with long vector control, were investigated to assess their fecundity. Changes of microfilaria development in utero and microfilaria release were assessed or estimated after treatment of patients with micro-filaricidal drugs that interfered with the development of intra-uterine stages. Intra-uterine production of microfilariae: After treatment of patients with ivermectin a daily development of 2500 to 4000 uterine microfilariae per female worm was observed. Actual output of microfilariae: Microfilariae left actively the female worms. The daily microfilaria release in vivo was 700 to 900 microfilariae, assessed after treatment of patients with mebendazole. In vitro most worms isolated from untreated patients shed between 500 to 1500 microfilariae per day.-The microfilarial load of 56 adult patients calculated from microfilarial skin counts was 12 million on the average. Taken for granted a mean life span of a microfilaria of 1.0 to 1.5 years, 22 to 47 female worms per patient would suffice to maintain this microfilarial load on a constant level. Excision of all palpable nodules showed a geometric mean of 15.9 female worms in these patients. It is suggested that factors intrinsic in the host and the adult worms partially operate together to regulate and maintain a stable microfilarial density.

Schulz-Key H et al. (1977) Tropenmed Parasitol "Isolation of living adult Onchocerca volvulus from nodules."

Buttner DW, Albiez EJ, Schulz-Key H

[Tropenmed Parasitol, 1977]

A technique for the isolation of adult Onchocerca volvulus from excised onchocercomata is described. The nodules are incubated in medium 199 containing 1-5 mg collagenase and 0.2 mg gentamicin per ml for 6-48 hours in a waterbath at 30-37 degrees C. A proportion of the worms can be isolated alive.

Schulz-Key H et al. (1984) Trans R Soc Trop Med Hyg "Quantitative assessment of microfilariae and adults of Onchocerca volvulus in ethanol-fixed biopsies and nodules."

Schulz-Key H, Karam M

[Trans R Soc Trop Med Hyg, 1984]

Ethanol-fixed Onchocerca nodules and skin snips were successfully digested with collagenase to assess the parasite load. The importance of this technique for investigations in the field is discussed.

Engelbrecht F et al. (1984) Trans R Soc Trop Med Hyg "Observations on adult Onchocerca volvulus maintained in vitro."

Schulz-Key H, Engelbrecht F

[Trans R Soc Trop Med Hyg, 1984]

Adult Onchocerca volvulus were enzymatically isolated with collagenase from excised nodules and kept in TC medium 199 with Hank's salts supplemented with various sera. Male and female worms survived in the culture medium and 10% human serum on average for about 11 days (maximum 28 days) and 14.5 days (maximum 42 days). Up to 4,000 microfilariae were expelled by each female per day, but the production of new oocytes or development of embryos could not be observed in vitro.

Albiez EJ et al. (1984) Tropenmed Parasitol "Studies on nodules and adult Onchocerca volvulus during a nodulectomy trial in hyperendemic villages in Liberia and Upper Volta. II. Comparison of the macrofilaria population in adult nodule carriers."

Buttner DW, Albiez EJ, Schulz-Key H

[Tropenmed Parasitol, 1984]

In the Liberian rain-forest and the savanna of Upper Volta 189 adult nodule carriers were operated on. From 2231 extirpated nodules 3327 male and 5713 female macrofilariae were isolated. About 98% of the male worms and 88% of the female worms were found alive. The sex ratio of the live male and female worms was 1:1.5 in Liberia and 1:1.6 in Upper Volta. Less than 1% of all live macrofilariae were immature in both countries. 22% of the live male worms in Liberia were regarded as old. The percentage of old male and female worms in Upper Volta and that of the old female worms in Liberia were similar (5-7%). The portion of old worms was independent of the age of the patients in Liberia. Dead worms were found in 66% of the Liberians and in 85% of the Voltaics. The percentage of patients with dead worms increased with the age. About 0.5% of all male and 8% of all female worms were calcified. In Liberia the percentage of calcified worms increased with the age of the patients. In both countries the highest number of live and dead worms were found on the pelvic girdle. On the thorax many more macrofilariae were found in Upper Volta than in Liberia. This may contribute to the severe eye lesions in this savanna area. The presented findings provide some basic information for the planning and performance of trials with macrofilaricidal drugs in hyperendemic areas of West Africa. However, the striking differences between individual worm burdens have to be considered.

Franz M et al. (1987) Parasitol Res "Electron-microscopic observations on the female worms of six Onchocerca species from cattle and red deer."

Copeman DB, Franz M, Schulz-Key H

[Parasitol Res, 1987]

The midbody regions of female worms of six Onchocerca species (O. flexuosa, O. tarsicola, O. lienalis, O. gutturosa, O. armillata, O. gibsoni) were studied by transmission electron microscopy. The cuticular layering was rather similar in all species with the ridges built up by the cortical layers and the inner cuticular striations by the median or basal layers. Differences in the epicuticular morphology were considerable. O. flexuosa and O. lienalis had a thin epicuticle without protuberances, the epicuticle of O. armillata carried small knobs, and O. tarsicola, O. gutturosa, and O. gibsoni had a thick trilaminar epicuticle with long protuberances. Extreme hypertrophy of hypodermis and reductions of somatic musculature were observed in O. flexuosa and O. gibsoni. Less extended thickenings of the hypodermis were observed in the other species. No degenerative alterations were found in the muscle cells of O. gutturosa and O. lienalis. The intestinal lumen of most of the species was in a central position, but in O. tarsicola and O. gibsoni the lumen was reduced to small clefts between the intestinal cells. In these species, numerous electron-dense, concentric granules were observed in the cytoplasm of the intestinal cells. The proportions of the various organs differed considerably from species to species, e.g., the uteri contained the embryos filed one behind the other in O. tarsicola, whereas 50 or more embryos were found beside one another in cross-sections of the uterus of O. gibsoni. The comparative study showed that O. gibsoni and O. volvulus have many derived morphological characteristics in common and that in the other species more primitive stages of development of these morphological marks can be observed.

Karam M et al. (1987) Acta Trop "Population dynamics of Onchocerca volvulus after 7 to 8 years of vector control in West Africa."

Karam M, Schulz-Key H, Remme J

[Acta Trop, 1987]

In an attempt to describe the changing population dynamics of Onchocerca volvulus during a period of vector control, nodulectomies were undertaken in 256 patients from ten villages in the Onchocerciasis Control Programme (OCP) and in 74 patients from two villages in an area with ongoing transmission. A total of 1198 nodules were excised and 4350 adult worms were isolated and examined for viability and productivity. In the OCP villages, the worm population is ageing and dying without replacement by new generations of parasites and various findings signal a breakdown of the worm population after about 12 years interruption of transmission. The sexual activity of the worms was significantly reduced. A Productivity Index was developed to measure the microfilariae production at the nodule level. The reduction in this index for the OCP villages correlates closely with the decline over the control period in the community microfilarial loads in the skin. The results show that it is not only the longevity of the parasite which will determine the duration of vector control, but that the reduced productivity of the ageing parasite population is of equal importance.

Duerr HP et al. (2001) Parasitology "A stochastic model for the aggregation of Onchocerca volvulus in nodules."

Duerr HP, Schulz-Key H, Dietz K, Buttner DW

[Parasitology, 2001]

A model is presented which describes the aggregation of female Onchocerca volvulus in nodules and their distribution in the human population. The basic model is based on a single parameter, the formation probability q, which represents the probability with which incoming larvae form a new nodule. This parameter describes parasite behaviour which cannot easily be recognized in available data without modelling. The estimate for the average formation probability of muq = 0.39 suggests an attraction of the invading infective larvae to already existing nodules or resident worms with probability 0.61. No significant difference in muq was found between the forest and savanna parasite strains. The model can be used inversely to estimate the worm burden of persons from palpation data. The observed variance in the number of nodules per person requires the assumption of a variance-increasing mechanism which was implemented by heterogeneity within the host population (extended model with 2 parameters). Possible reasons for this heterogeneity are presented and its implications concerning the reproductive biology of the parasite are discussed.

Awadzi K et al. (1990) Trop Med Parasitol "The chemotherapy of onchocerciasis. XIV. Studies with mebendazole citrate."

Awadzi K, Edwards G, Breckenridge A, Orme M, Gilles H, Schulz-Key H

[Trop Med Parasitol, 1990]

Twenty patients from an area of vector control in the savannah region of northern Ghana with moderate to heavy infection with Onchocerca volvulus were randomised to receive two priming doses of levamisole 150 mg on two occasions followed either by mebendazole-citrate (500 mg) given daily or twice daily for 14 days. The two dose levels produced a similar effect on skin microfilariae (80-88% reduction) with a very mild systemic clinical reaction: low levels were maintained over 42 weeks. Both regimes were embryotoxic for O. volvulus; an effect which was transient in the single dose group but persisted for more than three months in the twice daily dose group. Mebendazole-citrate appeared to be absorbed more predictably than has been observed previously for mebendazole. The degree of systemic exposure as determined by measurement of AUC (0-24 h) was 2.5 times greater for the twice daily dose as compared to the single dose and this fact was reflected in the efficacy of the two dose regimes against the adult female worms at three months.

Singhal NS et al. (2020) J Cell Biol "Neuronal GDPGP1 and glycogen metabolism: friend or foe?"

Ma DK, Singhal NS, Lee EM

[J Cell Biol, 2020]

The adult brain consumes glucose for energy needs and stores glucose as glycogen mainly in astrocytes. Schulz et al. (2020. J. Cell Biol.https://doi.org/10.1083/jcb.201807127) identify the stress-regulated metabolic enzyme GDPGP1 that promotes neuronal survival likely through glycogen reserves in mouse and C. elegans neurons.