One Hundred Years After Its Discovery in Guatemala by Rodolfo Robles, Onchocerca volvulus Transmission Has Been Eliminated from the Central Endemic Zone

We report the elimination of Onchocerca volvulus transmission from the Central Endemic Zone (CEZ) of onchocerciasis in Guatemala, the largest focus of this disease in the Americas and the first to be discovered in this hemisphere by Rodolfo Robles Valverde in 1915. Mass drug administration (MDA) with ivermectin was launched in 1988, with semiannual MDA coverage reaching at least 85% of the eligible population in > 95% of treatment rounds during the 12-year period, 2000-2011. Serial parasitological testing to monitor MDA impact in sentinel villages showed a decrease in microfilaria skin prevalence from 70% to 0%, and polymerase chain reaction (PCR)-based entomological assessments of the principal vector Simulium ochraceum s.l. showed transmission interruption by 2007. These assessments, together with a 2010 serological survey in children 9-69 months of age that showed Ov16 IgG4 antibody prevalence to be < 0.1%, meeting World Health Organization (WHO) guidelines for stopping MDA, and treatment was halted after 2011. After 3 years an entomological assessment showed no evidence of vector infection or recrudescence of transmission. In 2015, 100 years after the discovery of its presence, the Ministry of Health of Guatemala declared onchocerciasis transmission as having been eliminated from the CEZ.

Elimination of Onchocerca volvulus Transmission in the Huehuetenango Focus of Guatemala

In Latin America, onchocerciasis is targeted for elimination by 2012 through twice-yearly mass treatment of the eligible population with ivermectin. In Guatemala, two of the four historical endemic foci have demonstrated elimination of transmission, following World Health Organization guidelines. Using established guidelines ophthalmological, serological, and entomological evaluations were conducted in 2007-8 to determine the transmission status of onchocerciasis in the Huehuetenango focus. The prevalence of Onchocerca volvulus microfilariae in the anterior segment of the eye in 365 residents was 0% (95% confidence interval [CI] 0-0.8%), the prevalence of infection of O. volvulus in Simulium ochraceum among 8252 flies collected between November 2007 and April 2008 was 0% (95% CI 0-0.02%), and the prevalence of antibodies to a recombinant O. volvulus antigen in 3118 school age children was 0% (95% CI 0-0.1%). These results showed transmission interruption; thus, in 2009 mass treatment was halted and posttreatment surveillance began. To verify for potential recrudescence an entomological evaluation (from December 2010 to April 2011) was conducted during the 2nd and 3rd year of posttreatment surveillance. A total of 4587 S. ochraceum were collected, and the prevalence of infection of O. volvulus was 0% (95% CI 0-0.04%). Transmission of onchocerciasis in the Huehuetenango focus has been eliminated.

Exposure of seasonal migrant workers to Onchocerca volvulus on coffee plantations in Guatemala

Onchocerciasis (river blindness), which is close to being eliminated from Guatemala through semiannual administration of ivermectin, is still transmitted in one area of the country that coincidentally receives an annual influx of migrant workers to harvest coffee. Migrant workers generally are not included in semiannual ivermectin treatments, but if infected could serve as a reservoir. We report on two studies undertaken to measure the exposure to onchocerciasis (presence of IgG4 antibodies to a recombinant Onchocerca volvulus antigen, OV-16) among migrant workers. During two coffee harvest seasons, 170 migrant workers with a history of working in the disease-endemic area were tested and 1 (0.6%, 95% confidence interval = 0-3.2%) was seropositive. This low rate of exposure in migrant workers indicates that they are unlikely to play a significant role in transmission of onchocerciasis and may indicate that transmission in the last remaining disease-endemic area of Guatemala is decreasing significantly.

Successful interruption of transmission of Onchocerca volvulus in the Escuintla-Guatemala focus, Guatemala

BACKGROUND

Elimination of onchocerciasis (river blindness) through mass administration of ivermectin in the six countries in Latin America where it is endemic is considered feasible due to the relatively small size and geographic isolation of endemic foci. We evaluated whether transmission of onchocerciasis has been interrupted in the endemic focus of Escuintla-Guatemala in Guatemala, based on World Health Organization criteria for the certification of elimination of onchocerciasis.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted evaluations of ocular morbidity and past exposure to Onchocerca volvulus in the human population, while potential vectors (Simulium ochraceum) were captured and tested for O. volvulus DNA; all of the evaluations were carried out in potentially endemic communities (PEC; those with a history of actual or suspected transmission or those currently under semiannual mass treatment with ivermectin) within the focus. The prevalence of microfilariae in the anterior segment of the eye in 329 individuals (> or =7 years old, resident in the PEC for at least 5 years) was 0% (one-sided 95% confidence interval [CI] 0-0.9%). The prevalence of antibodies to a recombinant O. volvulus antigen (Ov-16) in 6,432 school children (aged 6 to 12 years old) was 0% (one-sided 95% IC 0-0.05%). Out of a total of 14,099 S. ochraceum tested for O. volvulus DNA, none was positive (95% CI 0-0.01%). The seasonal transmission potential was, therefore, 0 infective stage larvae per person per season.

CONCLUSIONS/SIGNIFICANCE

Based on these evaluations, transmission of onchocerciasis in the Escuintla-Guatemala focus has been successfully interrupted. Although this is the second onchocerciasis focus in Latin America to have demonstrated interruption of transmission, it is the first focus with a well-documented history of intense transmission to have eliminated O. volvulus.

Elimination of Onchocercia volvulus transmission in the Santa Rosa focus of Guatemala

To eliminate transmission of Onchocerca volvulus, semiannual mass treatment with ivermectin (Mectizan; donated by Merck & Co) has been underway in Guatemala since 2000. We applied the 2001 World Health Organization (WHO) elimination criteria in the Santa Rosa focus of onchocerciasis transmission in Guatemala (10,923 persons at risk). No evidence of parasite DNA was found in 2,221 Simulium ochraceum vectors (one-sided 95% confidence interval [CI], 0-0.086%), and no IgG4 antibody positives to recombinant antigen OV16 were found in a sample of 3,232 school children (95% CI, 0-0.009%). We also found no evidence of microfilariae in the anterior segment of the eye in 363 area residents (95% CI, 0-0.08%). Our interpretation of these data, together with historical information, suggest that transmission of O. volvulus is permanently interrupted in Santa Rosa and that ivermectin treatments there can be halted.

The Carter Center's assistance to river blindness control programs: establishing treatment objectives and goals for monitoring ivermectin delivery systems on two continents

Periodic mass treatment with ivermectin in endemic communities prevents eye and dermal disease due to onchocerciasis. As part of an international global partnership to control onchocerciasis, The Carter Center's Global 2000 River Blindness Program (GRBP) assists the ministries of health in ten countries to distribute ivermectin (Mectizan, donated by Merck & Co.). The GRBP priorities are to maximize ivermectin treatment coverage and related health education and training efforts, and to monitor progress through regular reporting of ivermectin treatments measured against annual treatment objectives and ultimate treatment goals (e.g., full coverage, which is defined as reaching all persons residing in at risk villages who are eligible for treatment). Since the GRBP began in 1996, more than 21.2 million ivermectin treatment encounters have been reported by assisted programs. In 1999, more than 6.6 million eligible persons at risk for onchocerciasis received treatment, which represented 96% of the 1999 annual treatment objective of 6.9 million, and 78% of the ultimate treatment goal in assisted areas.

Transient changes in cytokine profiles following ivermectin treatment of onchocerciasis

Cytokine production by peripheral blood mononuclear cells after antigen or mitogen stimulation was assessed before and after semiannual ivermectin treatment of 27 patients with onchocerciasis. Before treatment, Onchocerca volvulus antigen (OvA) elicited interleukin (IL)-5 production but inhibited production of IL-10, granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor-alpha. Six months after the first dose of ivermectin, there were increases in the IL-2, IL-4, IL-5, and interferon-gamma responses to mitogen and in the GM-CSF and IL-10 responses to OvA. By 24 months (after four ivermectin doses), OvA-induced GM-CSF production and mitogen-induced IL-2 and IL-10 production remained elevated above pretreatment levels, whereas that of other cytokines returned to or below pretreatment levels. These transient changes in cytokine response profiles of patients with onchocerciasis following ivermectin treatment likely reflect changes in antigen load.

Comparison of the sensitivity of different geographical isolates of Onchocerca volvulus microfilariae to ivermectin: effects of exposure to drug on development in the blackfly Simulium ornatum

Four geographical isolates (Ghana forest, Ghana savannah, Cameroon forest, Guatemala) of Onchocerca volvulus microfilariae (mf) and O. lienalis mf (UK) were examined for their sensitivity to ivermectin by incubation in vitro in drug followed by assessing their ability to develop in the blackfly Simulium ornatum after intrathoracic injection. Parasites were incubated for 30 min in ivermectin (10(-6) to 10(-9) M), which resulted in a concentration dependent decrease in the numbers of parasites surviving and developing in the insect; there were significant reductions in parasite recoveries from all isolates in the 10(-6) M to 5 x 10(-8) M ivermectin groups, but no significant effect was seen following incubation in concentrations of 10(-8) M and below. Experiments consistently demonstrated that the 4 isolates of O. volvulus were similarly sensitive to ivermectin (in the 10(-7) M ivermectin groups there was a reduction of 76.3% to 85.1% in numbers of infective larvae, and 60.9% to 85.5% in numbers of all larval stages, compared to controls); O. lienalis mf were significantly more sensitive (100% reduction in infective larvae, 98.7% reduction in all larval stages). This baseline information on drug sensitivity and techniques should prove useful for examining populations of O. volvulus for possible development of drug resistance in the future.

Adverse reactions after community treatment of onchocerciasis with ivermectin in Guatemala

Male and female residents on a Guatemalan coffee plantation where Onchocerca volvulus infections were hyperendemic were offered oral ivermectin (100-200 micrograms/kg) as part of a community-wide treatment programme for onchocerciasis. Forty-five persons were treated and then questioned daily for 28 d about changes in their health. Those with complaints were monitored until all signs and symptoms had resolved. Sixty-seven percent complained of some adverse event after treatment; 60% developed observable adverse reactions attributed clinically to ivermectin. No reaction was life-threatening; the most common were oedema (53%) and fever (47%). Expulsion of intestinal helminths was reported by 38%. Almost all reactions began 24-48 h after treatment; their mean duration was 5 d, despite treatment with acetaminophen and antihistamines. Three patients had oedematous changes lasting over 2 weeks. Incidence, but not severity, of reactions was related to the pretreatment density of microfilariae in skin.

Ivermectin: reduction in prevalence and infection intensity of Onchocerca volvulus following biannual treatments in five Guatemalan communities

Residents of five hyperendemic communities located in the central focus of onchocerciasis in Guatemala were treated with ivermectin (Mectizan) or placebo every six months for 30 months. The effects of treatment on prevalence and the intensity of skin infection (microfilarial skin density [MFD]) were evaluated. Significant and persistent reductions in both of these indices were achieved by coverage of 80.7% of the eligible populations. The highest proportionate reductions in both indicators of infection occurred after the first treatment, followed by more gradual decreases through the fourth treatment. In one community in which the mean coverage was 92.7%, prevalence decreased from 74.0% at pretreatment to 34.9% after four treatments, while the MFD decreased from 7.8 to 2.0; reductions of 52.8% and 74.3% from pretreatment values, respectively. In every ivermectin-treated community except one, in which drug acceptance was low, the mean community MFD values were reduced to the level associated with low infectiousness for the vector, Simulium ochraceum. Moreover, the category of MFD associated with high vector infectiousness was reduced at least ten-fold over the pretreatment level. One community had low participation during the first two treatments (32.8% and 22.7% of those eligible). This increased to 55.2% at the third treatment because of implementation of an educational program describing both the disease and the beneficial effects of ivermectin and because skin biopsies and nodulectomies were not performed. Secondary reaction rates for all communities were 29.5%, 9.9%, 10.3%, 8.2%, and 7.1% for the first through fifth treatments, respectively. Pruritus was the most common (34.0%) secondary reaction, followed by facial edema (31.8%). All reactions were classified as mild to moderate. Recommendations for mass distribution of ivermectin in Guatemala are given.

The effects of repetitive community-wide ivermectin treatment on transmission of Onchocerca volvulus in Guatemala

The effects of biannual ivermectin treatment at the community level on transmission of Onchocerca volvulus during the dry season were measured over a 30-month period in Guatemala. In the Los Tarrales Transmission Zone, an area encompassing three villages, significant changes occurred in both the prevalence and quantity of infection in the Simulium ochraceum vector population. These included a 76% reduction in females with infective stage larvae (L3S) and an 80% reduction in number of L3S per 1,000 parous flies. Significant reductions in both the mean infective biting density (IBD) and mean transmission potential (TP) also occurred. In Santa Emilia, the prevalence of infection with L3S in S. ochraceum was significantly reduced by 77% from the baseline value. The number of O. volvulus L3S per 1,000 parous flies was also reduced by 92%. Changes in both the IBD and TP were substantial but not significant due to the high degree of variance in the occurrence of O. volvulus L3S in the vector population. This was due, in part, to the movement of infected migrant workers into the finca (coffee farm). In Los Andes, four recurrent treatments successfully blocked transmission of infective stage larvae. Prevalence (flies with all stages of developing larvae) in the vector population was reduced by 89% over the two-year period; yearly reductions in both the IBD and TP were also highly significant, ultimately ending in zero values. This finding is particularly striking since prior to treatment, Los Andes exhibited the highest IBD of the three study locations and the second highest TP.

Effects of three-month doses of ivermectin on adult Onchocerca volvulus

Onchocerca volvulus worms in nodules from Guatemalan patients treated with four, eight, or 11 single doses of ivermectin (150 micrograms/kg of body weight) that were given once every three months were examined by routine histologic techniques and compared with worms in control nodules from untreated persons living in the same location over the same time periods. All treated nodules were removed four months after the last dose of ivermectin, i.e., 13, 25, or 34 months after the start of the trial. At the 25th and 34th months, i.e., after the eighth or eleventh doses of ivermectin, there were excess mortalities in female worms of 25.5% and 32.6%, respectively, over and above the levels in controls. Furthermore, the proportions of live females still producing scanty embryos up to the gastrula stage were only 7.7% and 18.2%, and no females were producing microfilariae. Ivermectin given at 3-month intervals also reduced significantly the mean numbers of live male worms in nodules, as well as the proportions of inseminated females. This regimen was effective in preventing embryogenesis to the microfilarial stage while, at the same time, it caused a slow but steady attrition of the adult worms.

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.

Influence of food related to dose on the pharmacokinetics of amocarzine and of its N-oxide metabolite, CGP 13 231, after oral administration to 20 onchocerciasis male patients from Guatemala

Twenty male patients from Guatemala infected with Onchocerca volvulus received a 3 mg/kg oral dose of amocarzine twice daily for three days. The patients were randomly assigned to the sequence fasting/non-fasting and non-fasting/fasting for the morning administration on days 1 and 3. All other doses were given after food intake. Blood samples on days 1 and 3 and urine fractions from days 3 to 5 were collected for the determination of the unchanged drug and of its N-oxide metabolite, CGP 13 231. The absorption of amocarzine and CGP 13 231 was slower and sustained for longer time in fed patients than in fasting ones. The mean AUC of amocarzine was significantly higher (about 20%) in fed patients. No significant difference was found for CGP 13 231. The relative improvement of bioavailability of amocarzine due to food was less prominent than previously obtained after a high dose of 1200 mg which demonstrated a bioavailability improvement of a factor of three. Therefore, saturable dose dependent absorption processes are likely to be involved for the administration in fasting conditions. Conversely, the concentrations of amocarzine in fed patients after 150 and 1200 mg were dose proportional, thus indicating linear kinetics. The cumulative urinary excretions of CGP 6140 ranged from 0.1 to 3.8% of the daily dose. Those of CGP 13 231 ranged from 31 to 64%. This total excretion was larger than that previously recorded in fasting patients after a single oral dose. The present results confirm the improvement of the bioavailability of the drug administered after food intake.

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.

Immunologic responses to repeated ivermectin treatment in patients with onchocerciasis

To assess the effect of ivermectin treatment on the immunologic status of individuals with onchocerciasis, 27 patients from Guatemala were studied before and at 6-month intervals during 2 years of repeated semiannual treatment with ivermectin. T cell proliferative responses to onchocercal antigen increased transiently by 6 months (mean stimulation index [SI] rising from 4.17 to 12.81) but returned to preivermectin levels thereafter. Changes in SI to nonparasite antigen paralleled those induced by parasite antigen. There were also significant decreases in levels of blood eosinophils, polyclonal IgG and IgE, parasite-specific IgG antibody, and IgG subclass antibodies by the end of the study. This study emphasizes the apparent long-term safety of ivermectin by demonstrating the absence of immunopathogenic responses induced by repeated ivermectin treatments.

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.

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.

Guatemalan human onchocerciasis. II. Evidence for IgG3 involvement in acquired immunity to Onchocerca volvulus and identification of possible immune-associated antigens

Ag-specific isotypic differences in immune response to Onchocerca volvulus Ag were assessed for 778 long term residents of endemic Guatemalan areas by quantitative ELISA with 5-min incubation steps and immunoblot. The study population was separated into five groups based on clinical status: N+F+, N+F-, N-F+, N-F-H+, and N-F-H-, where N = O. volvulus adults (nodule), F = microfiladermia, and H = history of O. volvulus infection. A subset of 44 individuals with high exposure to onchocerciasis from the N-F-H- group were critically evaluated and designated as "putatively immune." IgG1 reactivity to O. volvulus Ag was elevated in the majority of infected persons, but not in putatively immune individuals. Specific IgG3 levels, however, were equally elevated in all groups. The majority of N+F- persons also had elevated IgG1 levels, but they were lower than those found in F+ persons. IgG3 reactivities to a group of antigens at 20 kDa (GP20) were seen in many uninfected persons and some N+F- persons. In contrast, most F+ persons, react to this Ag with IgG1 and not IgG3. A mangabey inoculated with the infectious larval stage of O. volvulus (L3), but showed no signs of infection, began to recognize GP20 at 2 wk postinoculation. Early recognition of GP20 was possibly elicited by the larval stage. Purified nodule Ag from N+F+ individuals contained GP20, however, identical nodule Ag prepared from N+F- individuals did not. These data suggest that GP20 Ag may be common to both uterine microfilaria and the infectious larval stages. The fact that GP20 is predominantly recognized by IgG3 in putatively immune persons and some N+F- persons suggests that this increased IgG3 activity may be important in acquired immunity to onchocerciasis.

Guatemalan human onchocerciasis. II. Evidence for IgG3 involvement in acquired immunity to Onchocerca volvulus and identification of possible immune-associated antigens

Ag-specific isotypic differences in immune response to Onchocerca volvulus Ag were assessed for 778 long term residents of endemic Guatemalan areas by quantitative ELISA with 5-min incubation steps and immunoblot. The study population was separated into five groups based on clinical status: N+F+, N+F-, N-F+, N-F-H+, and N-F-H-, where N = O. volvulus adults (nodule), F = microfiladermia, and H = history of O. volvulus infection. A subset of 44 individuals with high exposure to onchocerciasis from the N-F-H- group were critically evaluated and designated as "putatively immune." IgG1 reactivity to O. volvulus Ag was elevated in the majority of infected persons, but not in putatively immune individuals. Specific IgG3 levels, however, were equally elevated in all groups. The majority of N+F- persons also had elevated IgG1 levels, but they were lower than those found in F+ persons. IgG3 reactivities to a group of antigens at 20 kDa (GP20) were seen in many uninfected persons and some N+F- persons. In contrast, most F+ persons, react to this Ag with IgG1 and not IgG3. A mangabey inoculated with the infectious larval stage of O. volvulus (L3), but showed no signs of infection, began to recognize GP20 at 2 wk postinoculation. Early recognition of GP20 was possibly elicited by the larval stage. Purified nodule Ag from N+F+ individuals contained GP20, however, identical nodule Ag prepared from N+F- individuals did not. These data suggest that GP20 Ag may be common to both uterine microfilaria and the infectious larval stages. The fact that GP20 is predominantly recognized by IgG3 in putatively immune persons and some N+F- persons suggests that this increased IgG3 activity may be important in acquired immunity to onchocerciasis.

Guatemalan human onchocerciasis. I. Systematic analysis of patient populations, nodular antigens, and specific isotypic reactions

The population from five Guatemalan plantations in areas endemic for onchocerciasis was surveyed, and 1032 individuals were recruited to participate in our study. From physical examination, past clinical history (5 to 8 yr), laboratory evidence and sample availability, a group of 778 long term residents with confirmed disease status were selected for detailed examination. We were able to identify 268 long term residents of endemic areas who had never been infected, 44 of these are from hyper- and mesoendemic areas. The 44 uninfected individuals from the hyper- and mesoendemic areas, because of their considerable exposure to this disease, were classified as "putatively immune." Intact nodules containing adult worms of Onchocerca volvulus were homogenized in the presence of protease inhibitors and fractionated into particulate and aqueous isotonic soluble antigens. Systematic analysis of these Ag fractions showed considerable amounts of Ig, presumably associated with Ag in the form of immune complexes. Individual specific antibody reactions from all 778 patients to nodule Ag were examined. Reactions to O. volvulus antigens by antibodies from patients with confirmed parasitic infections were almost exclusively restricted to IgG1 and IgG4 isotypes. Antigenic activity appeared to be primarily associated with low molecular mass (14 to 29 kDa) components. Some competitive blocking of antibody activities of other isotypes by IgG1 was observed, most notable was that of IgG3 and IgA. IgG4 and IgM activities were not significantly blocked.

Guatemalan human onchocerciasis. I. Systematic analysis of patient populations, nodular antigens, and specific isotypic reactions

The population from five Guatemalan plantations in areas endemic for onchocerciasis was surveyed, and 1032 individuals were recruited to participate in our study. From physical examination, past clinical history (5 to 8 yr), laboratory evidence and sample availability, a group of 778 long term residents with confirmed disease status were selected for detailed examination. We were able to identify 268 long term residents of endemic areas who had never been infected, 44 of these are from hyper- and mesoendemic areas. The 44 uninfected individuals from the hyper- and mesoendemic areas, because of their considerable exposure to this disease, were classified as "putatively immune." Intact nodules containing adult worms of Onchocerca volvulus were homogenized in the presence of protease inhibitors and fractionated into particulate and aqueous isotonic soluble antigens. Systematic analysis of these Ag fractions showed considerable amounts of Ig, presumably associated with Ag in the form of immune complexes. Individual specific antibody reactions from all 778 patients to nodule Ag were examined. Reactions to O. volvulus antigens by antibodies from patients with confirmed parasitic infections were almost exclusively restricted to IgG1 and IgG4 isotypes. Antigenic activity appeared to be primarily associated with low molecular mass (14 to 29 kDa) components. Some competitive blocking of antibody activities of other isotypes by IgG1 was observed, most notable was that of IgG3 and IgA. IgG4 and IgM activities were not significantly blocked.

Immunity to onchocerciasis: recognition of larval antigens by humans putatively immune to Onchocerca volvulus infection

Immunoblot analyses were done using sera from 12 individuals without evidence of onchocerciasis and 16 with active infection from an area of Guatemala holoendemic for onchocerciasis. For adult antigens from Onchocerca volvulus, no differences in antigen recognition could be identified between the two groups. In contrast, when infective larval (L3) antigen preparations derived from the related animal parasite Onchocerca lienalis were used, IgG from the "immune" individuals preferentially recognized a 45- to 50-kDa triplet and a 22-kDa L3 antigen. When L3 antigens of Brugia malayi were used, sera from putatively immune individuals identified a high-molecular-weight triplet/quadruplet plus several additional antigens of lower molecular weights that were recognized by sera from few (or none) of the infected patients. These findings define some differences in antibody specificity in onchocerciasis patients and therefore might define potential target antigens of humoral host defense. The exact nature of such defenses is unknown.

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.

Experimental Onchocerca volvulus infections in mangabey monkeys (Cercocebus atys) compared to infections in humans and chimpanzees (Pan troglodytes)

Three chimpanzees, three mangabey monkeys (Cercocebus atys), and 14 patas monkeys (Erythrocebus patas) were inoculated with L3 Onchocerca volvulus of Guatemalan origin. One chimpanzee and two mangabey monkeys developed antibody activity to at least three different antigens. Both mangabey monkeys recognized a 20 kDa antigen 3.5-5 months post-inoculation, and the monkeys and the chimpanzee developed antibody activity to 14 and 22 kDa antigens 7.5-13 months post-inoculation. One mangabey monkey and the chimpanzee became microfilaria-positive in skin snips at 16 and 21 months post-inoculation, respectively. Antibody activity to the 20 kDa antigen in the mangabey monkeys is noteworthy because of the prominence of this antigen among putatively immune persons living in onchocerciasis-endemic areas. The two mangabey monkeys responded parasitologically in a manner comparable to immune humans. No microfilariae were detected in one monkey and only scant numbers of microfilariae were observed in the second. The mangabey monkey may be a good animal model for the study of onchocerciasis.

On the reproductive activity of the female Onchocerca volvulus

Onchocerca volvulus worms, extracted from nodules by collagenase digestion, stained with haematoxylin and cleared in glycerol, were unravelled for longitudinal examination and later embedded in brain blocks for study of serial transverse sections. A classification system for female worms is proposed, based on the reproductive status of 446 worms from Guatemala, 94 from Liberia and 125 from Mali. They were categorized into fecund, inseminated specimens; uninseminated, but potentially fertile specimens, shedding ova destined to degenerate; worms changing from the uninseminated to the inseminated state and vice versa, which were few in number; old worms, with degenerate ovaries, whose genital tracts were either empty or had disappeared; and moribund or dead worms, characterized by loss of turgor, collapse and degeneration, calcification, or invasion by polymorphic, basophilic cells. Potentially fertile worms shed oocytes continuously and, when they were inseminated, embryonic development ensured. No evidence was found of a periodic cycle of reproduction. Inseminated worms were found in nodules without a male worm, and uninseminated worms in nodules harbouring male worms. Measurements are recorded of portions of the female reproductive tract and of the length of uterus occupied by the various embryonic stages in fully fecund worms. A significant difference in the length of the body behind the first and second ovaries was observed as between worms from West African savanna (Mali) and forest (Liberia). Limited observations were also made on meiosis in the oocyte, penetration of the oocyte by sperm, formation of the ovum, syngamy and zygote formation.

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 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)

Onchocerca gutturosa and O. volvulus: studies on the viability and drug responses of cryopreserved adult worms in vitro

The viability and drug responses of cryopreserved adult Onchocerca have been examined in vitro. Male worms were cryopreserved in liquid nitrogen (-196 degrees C) using ethanediol as a cryoprotectant in a 2-step incubation procedure. After thawing, 85-90% of O. gutturosa males were normally motile. These motile worms were evaluated for viability using 4 measurements (long-term motility/survival in culture; [U-14C]adenine uptake and leakage; glucose utilization; MTT-formazan colorimetry) and were no different from unfrozen controls. Subsequent experiments demonstrated that the motility responses of cryopreserved worms exposed to the antifilarial drugs ivermectin, CGP 6140 and levamisole were virtually identical to unfrozen controls. Some success was also obtained with this technique in cryopreserving O. volvulus males, with 2 thawed specimens surviving in culture for 93 and 106 d respectively. Following collagenase isolation, female worms were cryopreserved in medium +10% serum without protectant at -79 degrees C. A batch of 8 female O. gutturosa were all motile when thawed 14 d later, with a mean survival time (based on 5 specimens) of 71 d (range 60-90). However, a batch of worms transferred from -79 degrees C to -196 degrees C were badly damaged when thawed. Female O. volvulus were cryopreserved at -79 degrees C in Guatemala and sent by air freight on solid CO2 to the UK. Most specimens were active when thawed. Survival of motile specimens ranged from 7 to 272 d in culture. It is concluded that these techniques are of practical value for the storage and transportation of adult Onchocerca.

Onchocerciasis and immunity in humans: enhanced T cell responsiveness to parasite antigen in putatively immune individuals

To identify possible immune mechanisms in human onchocerciasis, we compared a group of 12 individuals who had no clinical or parasitological evidence of infection, despite ongoing exposure to the parasite, with a group of 16 individuals from the same area who had active Onchocerca volvulus infection. Despite having less parasite-specific serum antibody, the infection-free ("putatively immune") individuals showed greater lymphocyte responsiveness, especially interleukin-2 (IL-2) production, to O. volvulus antigen (OVA) than did the infected subjects; lymphocyte responses (including IL-2 production) to mitogens and nonparasite antigen in both study groups were equivalent and normal. Our findings define differences in parasite-specific T cell subpopulations between infected and putatively immune subjects that could be a central element in developing or maintaining protective immunity to O. volvulus infection.