Amocarzine investigated as oral onchocercacidal drug in 272 adult male patients from Guatemala. Results from three dose regimens spread over three days

The clinical investigations with three types of a three days regimen of amocarzine permitted to adjust the fixed dosing to the body weight related dosing and subsequently the administration of amocarzine from fasting state to drug intake after food. The main objective to reach a dose with predictable and sustained absorption was achieved, and this in turn proved to be onchocercacidal and safe. A combined clinicopharmacokinetic study showed enhancement and consistency of amocarzine absorption after food. Quantitative assessment of the urinary excretion confirmed the presence of the N-oxide metabolite, which qualitatively was visible by a urine colorimetry. This assay proved useful for drug monitoring. Ultrasonography of onchocercal skin nodules detected changes within the nodules following amocarzine therapy. Histology after nodul-ectomy at four months post-therapy showed that 57% of the female worms were dead, 24% necrobiotic, and 19% alive; male worms were more necrobiotic. Skin microfilariae were reduced within one week to about 10% of the initial level and after one year they remained at about 20%. Skin punch biopsies on day 5 showed that most microfilariae were dead or moribund. Ocular reduction of microfilariae was also observed, although it was slower than in the skin. The visual acuity improved within the one year's observation time. Ocular and clinical tolerability was good, with one exception of neurological disturbance, which was fully reversible. Sequential testing of the liver function showed average values within the normal range. In conclusion, a repeat low dose regimen of amocarzine (3 mg/kg twice daily post-prandially for three consecutive days) was well absorbed with predictable plasma levels, macro- and microfilaricidal with good local and systemic tolerability in patients with moderate to heavy onchocerciasis. Amorcarzine is recommended for further clinical investigations, particularly in females and juveniles. Urine colorimetry and nodular ultrasonography are recommended for optional monitoring of amocarzine.

Fine structure of microfilariae in the skin of onchocerciasis patients after exposure to amocarzine

Transmission electron microscopy was used to demonstrate the effects of amocarzine (CGP 6140) on the fine structure of Onchocerca volvulus microfilariae (mf) in skin biopsies from patients treated orally in Guatemala or transepidermally exposed in Liberia. After 6-10 hours exposure to the drug most mf did not show any alterations and only a few mf contained increased numbers of vacuoles in the cytoplasm and clefts between cuticle and hypodermis. At 20-48 hours after treatment most of the mf showed distinct signs of damage. Most frequently seen was disintegration of the cytoplasm of the afibrillar portion of the muscle cells. Some mf showed also disintegration of the myofilaments and of the internal structure of the mitochondria in the muscle cells. Other signs were progressive separation of the cuticle from the hypodermis, increase of intracellular vacuoles and clefts and in some mf condensation of the cytoplasm. The type and the site of the morphological alterations were the same after both forms of amocarzine administration. The degree of morphological changes increased with the length of time of exposure to the drug. Microfilariae with morphological alterations were nearly always surrounded by adherent host cells, mostly eosinophils and macrophages.

The effect of antimalarial chloroquine therapy and prophylaxis on concurrent infection with Onchocerca volvulus in Ecuador

The effect of chloroquine phosphate on Onchocerca volvulus in vivo was studied in Ecuadorians undergoing treatment for malaria. All persons with a diagnosis of acute malaria and treated with 2500 mg of chloroquine over 3 d showed a 100% reduction of dermal O. volvulus microfilariae 7 d after treatment. However, 28 d after treatment the microfilarial densities returned to their pre-treatment levels and at 35 d they had increased to 121.6% of their pre-treatment values. Treatment did not appear to have any effect on the adult O. volvulus examined histologically in extirpated nodules. Patients treated for acute malaria and subsequently kept on a prophylactic regimen of 500 mg chloroquine weekly showed a reduction of 56.7% from pre-treatment microfilarial density after 27 weeks. Patients who underwent nodulectomy as well as treatment for acute malaria and were given 500 mg of chloroquine prophylactically for 27 weeks showed a reduction in dermal microfilarial density of 93.6%. Symptoms of onchocerciasis were reduced in the latter group of patients, with the elimination of all acute dermatological changes within 6 weeks. Ocular examination of these surgically and chemotherapeutically treated individuals revealed reductions of 94.9% of microfilariae in the anterior chamber, 95.9% of live microfilariae in the cornea, and 95.1% of dead microfilariae in the cornea. There was a reduction of 69.8% in corneal fluffy opacities. No alteration in the visual acuity or in visible lesions in the posterior segment was recorded. The results suggest that a complex interaction between chloroquine and O. volvulus takes place in vivo, which can be beneficial to the patient over a long period.(ABSTRACT TRUNCATED AT 250 WORDS)

Microfilaricidal effect of amocarzine in skin punch biopsies of patients with onchocerciasis from Latin America

Skin punch biopsies were performed in 54 selected patients with onchocerciasis participating in a clinical trial with amocarzine (CGP 6140) in Ecuador and Guatemala. Skin snipping for counting microfilariae of Onchocerca volvulus was done before treatment (day 0) and day 4 and 8 following start of the therapy which consisted of 3 mg/kg amocarzine postprandially twice daily for three consecutive days. The mean microfilarial skin density has been reduced by 45% on day 4 and 95% on day 8. Skin punch biopsies were taken on day 5, within 1 cm from the snip site on the iliac crest. Histopathologic examination revealed that the vast majority of the microfilariae in the upper as well as in the deeper dermis were degenerated or necrotic, surrounded often (57%) by minute foci of fibrinoid change of the collagen. There was usually slight, less frequently moderate eosinophilic, lympho-plasmocytic and initial histocytic inflammatory reaction in the vicinity. Microfilariae were frequently (69%) found at the dermal-epidermal junction and in the epidermis. Occasionally (7%) intra-epidermal microabscesses were noted. Microfilariae were detected also in the lumen of some dermal lymphatic vessels. Therefore it is concluded that amocarzine showed marked microfilaricidal effects in the skin of patients with onchocerciasis as evidenced histologically by mainly destroyed or moribund microfilariae which induced a mild to moderate inflammatory cell reaction.

Onchocercacidal effect of three drug regimens of amocarzine in 148 patients of two races and both sexes from Esmeraldas, Ecuador

The objective of this multidisciplinary clinical investigation was to test whether amocarzine was absorbed effectively and safely in patients of two races and either sex infected with Onchocerca volvulus while living in the holoendemic area of Esmeraldas Province, Ecuador. The prerequisite for a systemic onchocercacidal effect is the regular absorption of orally administered amocarzine. Single dosing after overnight fasting proved to produce irregular absorption of amocarzine, although some microfilaricidal effect was achieved. A pilot study with repeated low dose and postprandial administration of amocarzine showed a regular and predictable absorption with acceptable tolerability and a microfilaricidal effect lasting up to one year post-therapy. Since amocarzine and its major N-oxide metabolite are coloured agents, urine colorimetry was used to assess the urinary excretion of the N-oxide qualitatively. For the postprandial drug regimens plasma concentrations of amocarzine and its metabolite were determined at two selected time points in patients of two races and either sex; the results showed no major differences. Excision of onchocercal nodules was performed four months post-therapy. The pooled results of the histologic analysis of 100 patients with the same drug regimen read under blinded condition showed that 65% of the adult female worms were dead, 20% necrobiotic and 15% alive. The male worms were fewer and mainly necrobiotic. Control worm populations in Esmeraldas without chemotherapy showed that on the average 81.5% were alive and 18.5% dead. Amocarzine was also microfilaricidal producing a reduction of skin dwelling microfilariae to about 10% of the initial value within the first week after start of therapy and lasting for half a year at a 20% level. The reduction of ocular microfilarial was slower and reached 35-40% after one year. The general tolerability was acceptable to good. Reversible dermal reactions were usually mild and peaked as a rash in 57% of the patients on day 6. No prohibitive ocular intolerance was observed. Mild and reversible dizziness peaked on day 4 in 74% of patients. A positive reversible Romberg sign was found in 12 patients on day 4. Amocarzine, the first oral micro- and macrofilaricidal agent administered as a low dose repeat regimen (3 mg/kg twice daily and postprandial for three consecutive days) can be recommended for oral onchocercacidal therapy in adult patients. Clinical trials in juveniles should be encouraged.

Longterm follow-up of onchocerciasis patients in Latin America after treatment and retreatment with amocarzine. Preliminary results

Amocarzine has been reported to have onchocercacidal effects. Four months posttherapy the majority of adult worms were dead or moribund. The effect of skin microfilariae lasted up to one year as reflected by markedly reduced microfilaridermia. Since the duration of the onchocercacidal effect of amocarzine beyond one year was unknown and since such an effect may influence the planning of future control strategies, efforts were made to follow-up the already treated amocarzine patients for a second year. The present study from Latin America showed that various amocarzine drug regimens produced a prolonged reduction of microfilaridermia at the end of the second year following the initial therapy, the best levels were about 7-17% of the initial parasite load in the skin for some three days amocarzine regimens. Such an effect occurring in a transmission area of onchocerciasis in Latin America provides additional, although indirect, evidence of a macrofilaricidal effect of amocarzine. Similar experiences of a prolonged amocarzine effect on skin microfilariae has also been observed in West Africa (Ghana, Mali). Preliminary results of retreatment schedules at the start of the third year post-initial therapy showed that simplified postprandial dose regimen of one or two days were well tolerated. It is premature at the time of this report to judge upon their ultimate efficacy, but they had significantly reduced levels of moderate microfilaridermia.

The embryogenesis of Onchocerca volvulus over the first year after a single dose of ivermectin

Adult Onchocerca volvulus, extracted from nodules before, and at intervals of two weeks to 12 months after, a single 150 micrograms/kg dose of ivermectin, were examined longitudinally and by sequential transverse sections. The mean number of male worms per nodule fell, and the proportion of nodules with no male worm rose, within two weeks of ivermectin and remained so for 12 months. In female worms, at intervals after ivermectin, the percentages of the length of the lower genital tracts occupied by embryos at each stage of development, or by degenerating ova, embryos and microfilariae (mfs), were recorded: (a) in un(re-)inseminated worms whose original embryogenesis was continuing and in those in which it was completed; and (b) in worms, reinseminated post-ivermectin, in which a new embryogenesis had begun. The results indicated that: (a) the time needed for the zygotes of O. volvulus to develop to mfs is 8-12 weeks; (b) nearly 40 percent of females had not resumed mf production by 12 months after treatment; (c) many intrauterine mfs had not degenerated within the first two weeks of ivermectin; (d) some of the last embryos to mature to mfs did not degenerate but accumulated temporarily in the anterior uteri 8-16 weeks after ivermectin.

Use of an ophthalmologic ultrasoundscanner in human onchocercal skin nodules for non-invasive sequential assessment during a macrofilaricidal trial with amocarzine in Guatemala. The first experiences

Ultrasonography of onchocercal skin nodules was performed with an ophthalmologic real time linear scanner with a B probe of 10 MHz. A clinical trial in Guatemala with amocarzine (CGP 6140)--a new oral macrofilaricidal compound--investigated three repeat dose regimens and one placebo control group, each group consisting of six patients. Onchocercal nodules were scanned before treatment and on day 10, 30 and 60 after start of amocarzine. A total of 28 treated and 8 additional untreated nodules were analysed and compared with the histologic findings following nodulectomy at day 60. Of the 28 treated nodules, 21 were of onchocercal origin and seven were lymph nodes. The correlation between ultrasonography and histology was good in 25 patients, but did not match in three. In 20 out of 21 treated nodules a progressive ultrasonographic change over two months was seen. Of the eight additional untreated nodules, five were of onchocercal origin, one was a lymph node, one an epidermoid cyst and in one only fibrous tissue was detected. The ultrasonography correlated well to histology in seven nodules but not in one. In five onchocercal nodules no change was observed over two months. For initial control purposes six nodules were excised around day 10, four were of onchocercal origin and two were lymph nodes. The correlation was good in four. The present results indicate that an ophthalmologic real time linear scanner can be used in the bidimensional mode as a non-invasive method to assess sequentially the events in superficial onchocercal nodules following chemotherapy with amocarzine. This is the first objective non-invasive method permitting sequential assessment of the content of onchocercal nodules and it is far superior than subjective sequential manual palpation.

Comparison of the effects of a single dose and of four six-monthly doses of ivermectin on adult Onchocerca volvulus

Adult Onchocerca volvulus worms, extracted from nodules of Guatemalans by collagenase digestion, were examined whole and by histological techniques. One group of persons received a single 150 micrograms/kg dose of ivermectin; two other groups (one with older and one with younger nodules) received four similar doses of ivermectin at 6-month intervals. For each group, there were comparable untreated controls. All nodules were removed six months after the last dose. After a single dose, the only significant difference from the controls was in the decreased proportion of female worms producing live microfilariae. After four doses, there were significant increases in the proportions of moribund/dead female worms and of live uninseminated females, when compared with the corresponding controls. There were also fewer male worms present, but this difference was not significant. Six months after the conclusion of the 4-dose regimen, the proportion of female worms producing live microfilariae was significantly lower than in the groups that had received a single dose.

2-acetylpyridine thiosemicarbazones. 13. Derivatives with antifilarial activity

Several members of a series of 2-acetylpyridine thiosemicarbazones possess in vivo and in vitro macrofilaricidal properties. The most promising of the group tested is N4-(2-aminophenyl)-2-[1-(2-pyridinyl)ethylidene]-hydrazinecarbothioam ide (4), which suppressed 100% of the macrofilariae of Brugia pahangi and 94% of those of Acanthocheilonema viteae in the jird at a dose of 25 mg/kg per day x 5. Compounds 4 and 14 were also shown to inactivate or kill Onchocerca gutturosa and Onchocerca volvulus adult worms as measured by the loss of their motility or the inhibition of the conversion by the worms of the dye MTT to formazan.

Onchocercacidal effects of amocarzine (CGP 6140) in Latin America

An open clinical trial of amocarzine was carried out in onchocerciasis patients in Ecuador and Guatemala. Administration after food was more effective than that during fasting. The most effective and best tolerated regimen, 3 mg/kg twice daily after food for 3 days (in 312 patients), killed 73% of 1477 female worms at nodulectomy 4 months after treatment. The mean microfilarial skin count was greatly reduced within a week (6-11% Of day 0 value on day 8) and it remained low at least 6 months (14-18% on day 180). Follow-up of a higher dose 3 day regimen taken while fasting showed microfilaridermia of 7-9% of the day 0 value 2 years after treatment.

The use of monoclonal antibody-based ELISAs to monitor chemotherapeutic effects in the bovine-Onchocerca gibsoni drug screen

Three monoclonal antibodies directed towards antigens of Onchocerca gibsoni were used in antigen detection ELISAs to detect parasite antigens in sera from 100 cattle infected with O. gibsoni, in trials with the filaricidal compounds CGP 6140, CGP 20309, CGP 20376, CGP 21833, CGP 24589 and CGP 26702. Measurable levels of parasite antigens were highly variable, both within and between treatment and control groups of animals, with no consistent trends which related to time after treatment, micro or macrofilaricidal effects against O. gibsoni, or dose rate for any of the compounds used. It was concluded that these assays were unsuitable as a method of identifying drug-induced damage to O. gibsoni following the administration of these compounds. A detailed protocol for selecting suitable assays is discussed.

The use of monoclonal antibody-based ELISAs to monitor the efficacy of drugs against male Onchocerca gibsoni in vitro

Four monoclonal antibodies directed against antigens of Onchocerca gibsoni were used in antigen detection ELISAs to monitor the efficacy of CGP 20309, CGP 20376, CGP 21833, CGP 24589 and CGP 26702 at 5 micrograms/ml against male O. gibsoni in vitro. No significant differences (P less than 0.05) in antigen output between treated and control groups of parasites were recorded. However, consistently higher levels of antigen from treated (CGP 21833) as compared to control parasites were measured with all four assays, with differences being higher in the first 2 to 3 days post treatment than subsequently. The sensitivity of comparisons between groups was reduced by the high variability in output of antigen both between worms and also from the same worm, in part as a result of mechanical damage to worms sustained during collection or manipulation in vitro. This problem was reduced by zero handling once worms were established in vitro and it is recommended that future work should include a 24 to 48 hour period before treatment commences to detect raised antigen levels associated with physically damaged parasites so they can be excluded. It was concluded that this type of assay has no intrinsic technical or logistical advantage over other published methods of assessing drug-related damage in in vitro filarial screens. Nevertheless, further work using antigen detection ELISAs in this context is justified since these assays, unlike all other methods of assessing drug-induced damage in vitro, have direct application for use in identifying chemotherapeutic effects against similar parasites in vivo.

The effects of ivermectin on the viability of Onchocerca lienalis microfilariae in vitro and on their subsequent development in the blackfly vector, Simulium ornatum

Experiments examined the sensitivity of Onchocerca lienalis microfilariae (mf) to ivermectin in vitro using a range of parameters to measure viability. Incubation in drug (1 x 10(-4) and 5.71 x 10(-8) M) caused an immediate decrease in motility levels in a concentration dependent fashion with a continuing decline over 24 h; the inclusion of a monkey kidney cell (LLCMK2) feeder layer in the culture system partially abrogated drug effects. The use of feeder cells allowed the longer-term culture of mf; incubation in drug at low concentrations (5.71 x 10(-8) and 1 x 10(-10) M) significantly reduced motility levels during a 17 day trial. Using MTT colorimetry it was found that 10,000 untreated mf per replicate sample were required to produce a sufficient quantity of formazan to make comparisons, and that formazan formation was most rapid during the first 30 min of incubation in MTT but continued up to 3-4 h. Following incubation of mf in ivermectin (1 x 10(-4) and 5.71 x 10(-8) M) for 24 h, only the higher concentration inhibited formazan formation (51%), while motility levels were reduced by 94% and 45% respectively. Using the same drug concentrations, mf viability was assessed by measuring the uptake of [3H]2-deoxy-D-glucose; uptake was only significantly reduced (40%) by the higher concentration, while motility levels were reduced by 77% and 63% respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of multiple monthly doses of ivermectin on adult Onchocerca volvulus

This paper assesses the effects on adult Onchocerca volvulus of monthly doses of ivermectin (150 micrograms/kg) given over 4, 8, and 12 months to patients in Guatemala. Nodules were removed 4 months after the last dose; the adult O. volvulus were extracted by collagenase digestion, studied by histological techniques, and compared with worms from untreated patients. Twelve monthly doses killed a proportion of the adult worms (12% of males and 22% of females), leaving the remainder relatively unaffected and the females slowly resuming embryogenesis. After 8 and 12 doses, a number of female worms had resumed embryogenesis in 1 genital tract only, and in 1 female a total degeneration of 1 ovary was seen. Ivermectin also led to a marked drop in the number of male worms in nodules. No serious adverse reactions occurred and the treatment was well accepted.

The chemotherapy of onchocerciasis. XIV. Studies with mebendazole citrate

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.

Morphological alterations of male Onchocerca volvulus after in vitro exposure to mel w and milbemycin a confirming the results of viability tests

The suitability of two viability parameters used for screening of antifilarial activities of new compounds was examined by parallel observation of the morphology. Male Onchocerca volvulus were exposed in vitro to 10 mumol mel w and milbemycin a and examined by light and transmission electron microscopy. The viability was assessed by measurement of the motility, using a micromotility meter and by determination of tetrazolium reduction. Already twelve hours after exposure to mel w the muscles of the body wall showed severe damage. After 36 hours the other tissues revealed degenerative changes and after 60 hours disintegration of all tissues was observed. Effects on the morphology caused by milbemycin a were seen earliest after 60 hours. Condensed cytoplasm in the hypodermal layer and beginning degeneration of spermatogenic stages indicated drug activity. The time-point of appearance of these drug induced morphological alterations was in accordance with the decrease of the motility indices and the degree of tetrazolium reduction. Morphological alterations indicating irreversible damage of worm tissues are a reliable parameter to detect macrofilaricidal activity. The good agreement between the results of the morphological examination and the assessment of the motility and the tetrazolium reduction confirms the suitability of the latter two assays for in vitro drug screening with O. volvulus.

Efficacy of avermectin B1 given orally against equine intestinal strongyles and Onchocera microfilaria

Three groups of horses and ponies (N = 13, 13 and 12) were treated with ivermectin paste (0.2 mg/kg p.o.), avermectin B1 solution (0.2 mg/kg p.o.), or fenbendazole suspension (10 mg/kg via nasogastric tube). The avermectin B1 was a 1% solution in a propylene glycolglycerol formal base. Faecal strongyle egg counts were performed before, and 14, 28, 42, 56 and 70 d, after treatment. Full-thickness skin biopsies from the neck, pectoral and umbilical regions were examined for Onchocera microfilaria before treatment, and again 14 and 70 d later. Ivermectin therapy produced a significant (P less than 0.01) decrease in mean strongyle egg counts 14, 28, 42 and 56 d after treatment. Avermectin B1 therapy resulted in significant (P less than 0.01) decreases in mean strongyle egg counts 14, 28 and 42 d after treatment. All horses given ivermectin or avermectin B1 had zero strongyle egg counts 14 and 28 d after treatment. Fenbendazole failed to significantly decrease strongyle egg counts. Both ivermectin and avermectin B1 resulted in zero microfilaria counts in all horses 14 d after treatment. On day 70 the percentage decrease in microfilaria counts were 100% and 99.6% respectively. Fenbendazole failed to significantly decrease microfilaria counts. The oral administration of this formulation of avermectin B1 appeared to be highly efficacious against intestinal strongyles and Onchocera microfilaria. The duration of anti-strongyle activity was, however, significantly (P less than 0.01) shorter than that of ivermectin paste.

Hydrogen peroxide is the most toxic oxygen species for Onchocerca cervicalis microfilariae

The toxicity of the active oxygen species hydrogen peroxide, superoxide radical, hydroxyl radical and singlet oxygen to microfilariae (mf) has been studied in vitro, using active oxygen-generating systems and scavengers/inhibitors. Mf viability was monitored by uptake of the radiolabel, [3H]2-deoxy-D-glucose. Hydrogen peroxide and singlet oxygen, but not superoxide radical or hydroxyl radical, are toxic for mf. Hydrogen peroxide was toxic for mf within 2 h at concentrations as low as 5 microM, an amount eosinophils have been shown to release in vitro (Weiss et al. 1986). Catalase and thiourea, but not inactivated catalase, superoxide dismutase (SOD), singlet oxygen scavengers, or hydroxyl radical scavengers, protected mf. Mf have relatively high levels of endogenous SOD but no measurable glutathione peroxidase and low levels of catalase when compared with other parasites (Callahan, Crouch & James, 1988). The low levels of hydrogen peroxide-scavenging enzymes correlate well with mf sensitivity to hydrogen peroxide and the protective effect of exogenous catalase.

Effect of ivermectin on the vertical distribution of Onchocerca volvulus microfilariae in the skin

A new technique for assessing vital and degenerative microfilariae (mf) in different skin layers of onchocerciasis patients is described. Vertical sections at least 5 mm deep were collected from the surgical nodulectomy wounds before and 2, 4 and 28 days after treatment with ivermectin and fixed in ethanol. Skin biopsies were punched horizontally with trephines and digested enzymatically with collagenase. In untreated biopsies 80% of the mf were located in the uppermost layer of 1 mm and only 1.2% were degenerated. After treatment with ivermectin the total number of mf was significantly reduced, and the distribution of living and remnant mf in the different skin layers had changed. The proportion of degenerated mf had increased markedly, but did not exceed 6% of the total pre-treatment mf level, i.e., the vast majority of the mf had actually disappeared from the skin. It is suggested that ivermectin reduces microfilarial motility slightly, and that mf are then attacked by adhering immunocompetent cells of the host and cleared by the lymphatic drainage.

The effects of ivermectin used in combination with other known antiparasitic drugs on adult Onchocerca gutturosa and O. volvulus in vitro

The effects of ivermectin at a concentration of 3.13 x 10(-6) M used in combination with other antiparasitic drugs on the viability of adult Onchocerca in vitro were assessed using MTT colorimetry and worm motility levels. When ivermectin was used against male O. gutturosa over a 7 d period in combination with suramin (5 x 10(-5) M), CGP 6140 (3.13 x 10(-6) M), CGP 20376 (1.95 x 10(-7) M), mefloquine (3.13 x 10(-6) M), levamisole (3.13 x 10(-6) M), mebendazole (5 x 10(-5) M), flubendazole (5 x 10(-5) M) and albendazole (5 x 10(-5) M), there was either no increased effect or only a marginally increased effect on motility levels when compared with the use of ivermectin alone. MTT colorimetry revealed that in most cases there was a cumulative effect of the 2 drugs used in combination but not a synergistic effect. In a trial extended to 26 d it was demonstrated that the combination of ivermectin and suramin did not produce a greater inhibition of motility than ivermectin alone. Using female O. volvulus, the activity of ivermectin, CGP 6140 and the 2 drugs combined was examined. The motility of all 3 groups exposed to drug(s) was suppressed by 24 h compared with controls. MTT colorimetry performed on day 7, using the pre-weighed anterior end of each worm, illustrated that ivermectin alone produced a 43.4% inhibition of formazan formation compared with controls, CGP 6140 alone produced 50.6% inhibition, while the drug combination produced a 72% inhibition, equivalent to the heat-killed control.(ABSTRACT TRUNCATED AT 250 WORDS)

A preliminary assessment of the feasibility of evaluating promising antifilarials in vitro against adult Onchocerca volvulus

The suitability of motility indices and tetrazolium-based colorimetric assays for the determination of the viability of adult Onchocerca volvulus after in vitro exposure to potential macrofilaricides has been examined. Experimentation showed that both techniques could be applied to adult O. volvulus, although the variability between individual worms necessitated the use of large experimental groups. The potential of using cut anterior tips of female O. volvulus for screening was also investigated. These were shown to give reasonably consistent motility indices, and drug effects were discernible even after 72 h in vitro culture. Application of these viability criteria to studies on the short-term in vitro survival of intact male and female O. volvulus incubated in Eagles MEM plus serum, under 5% CO2 in air, showed this medium to be suboptimal with a greater than 50% loss of worm viability within 144 h of nodulectomy. Males isolated by the collagenase technique were shown to be significantly less viable than dissected males, by both motility indices and tetrazolium reduction. The results highlight the need to use either dissected males, or in the case of females, the need to minimize exposure to collagenase solution. A possible mechanism for selecting a more uniformly viable female worm population is discussed. Examination of the in vitro effects of CGP 20376 using these viability criteria/assay systems showed some delayed suppression of worm motility, but after 120 h in vitro CGP 20376 was not macrofilaricidal against male or female O. volvulus. Male worms were also implanted subcutaneously into gerbils.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of intermediary metabolites and electron transport inhibitors on action of chloroquine on Brugia pahangi and Onchocerca volvulus

We examined the possibility that chloroquine is interfering with aerobic energy-generating processes in the adult filarial parasites, Brugia pahangi and Onchocerca volvulus. Using motility of these parasites as an assay of drug effect, we found that micromolar concentrations of chloroquine caused significant paralysis, but only in alkaline medium (pH 8.4). The addition of 12 mM glutamine or 10 mM albizziin to the medium completely antagonized drug-induced paralysis. In addition, in B. pahangi, all of the tricarboxylic acid cycle intermediates (10 mM) except citrate and pyruvate antagonized the effect of chloroquine on motility; in O. volvulus, oxaloacetate as well as glutamine inhibited the effect of the drug. The effect of chloroquine on both parasites was enhanced when it was used in combination with 10 microM acivicin, a glutamine antimetabolite. Here motility of B. pahangi was reduced significantly within 24-48 hr at acidic (6.8) neutral (7.4) and alkaline (8.4) pH. This effect was partially reversible by glutamine (12 mM). Motility of O. volvulus was reduced to near zero within 4 hr with this drug combination. Antimycin A and rotenone, both electron transport inhibitors, also synergized with chloroquine at any pH to produce paralysis in B. pahangi. The effects of the rotenone and chloroquine combination were reversed in the presence of 10 mM succinate. However, glutamine (12 mM) was unable to antagonize the effects of chloroquine plus antimycin A on the motility of B. pahangi. These findings suggest that chloroquine may be inhibiting aerobic energy metabolism in the filariae, possibly at the level of electron transport. Furthermore, since chloroquine is well-tolerated but only weakly filaricidal in vivo, the data indicate that use of this drug in combination with other inhibitors of aerobic energy metabolism may be a chemotherapeutically useful approach to the treatment of filariases.

A community trial of ivermectin in the onchocerciasis focus of Asubende, Ghana. I. Effect on the microfilarial reservoir and the transmission of Onchocerca volvulus

A community trial of the microfilaricide ivermectin was undertaken in an isolated focus of hyperendemic savanna onchocerciasis in Ghana. One of the objectives was to determine the effect of mass treatment on the microfilarial reservoir and on the transmission of Onchocerciasis volvulus. Since 1978 the focus has been under entomological surveillance. This was intensified from 1 September 1987 till 11 February 1988 with daily vector collection and dissection of over 30,000 flies. A total of 14,991 people were treated with ivermectin on 7-10 October 1987. Skin snip surveys were done pre-treatment, and at two and four months after treatment. The mean skin microfilarial load in treated persons had fallen by more than 96% two months after treatment. During the next two months there was an increase in microfilaria loads which appeared to be faster than reported in the clinical trials. The total reservoir of skin microfilariae available for transmission had been reduced by an estimated 68%-78% two months after treatment. This was consistent with the entomological results which indicated a reduction in transmission of 65%-85% during the first three post-treatment months. The present study has shown for the first time that mass chemotherapy can significantly reduce onchocerciasis transmission. However, the remaining level of transmission was still unacceptably high and further studies are required to predict the long term impact of repeated mass treatment.