Onchocerciasis control: Moving towards the millennium

Neglected tropical disease control in post-war Sierra Leone using the Onchocerciasis Control Programme as a platform

Strategic investments in the control of neglected tropical diseases (NTD) spearheaded by the US Government, the British Government and other bilateral donors such as foundations and key pharmaceutical partners have enabled the treatment of millions of people for the five targeted debilitating diseases (lymphatic filariasis, onchocerciasis, schistosomiasis, soil-transmitted helminthiasis and trachoma), paving the way for the potential elimination as public health problems of some of these diseases. Like many other countries, Sierra Leone has a high burden of these major NTDs. Despite the fragile infrastructure of a health system emerging from a devastating 10-year civil war, the country has successfully implemented the National NTD Control Programme, reaching national coverage in 2010. The NTD Control Programme uses the existing Onchocerciasis Control Programme as a platform and involves primary health workers. The programme has provided extensive training opportunities to health workers at national, district and community levels. The country currently has 31 161 trained community volunteers treating a population of five million people. It is shown that the investments in NTD control are not only to control NTDs but also to strengthen health systems, particularly at the primary level, through extensive capacity building of frontline health workers and community-directed distributors.

Ocular onchocerciasis: current management and future prospects

This paper reviews the current management of onchocerciasis and its future prospects. Onchocerciasis is a disease affecting millions of people in Africa, South and Central America, and Yemen. It is spread by the blackfly as a vector and caused by the filarial nematode, Onchocerca volvulus. A serious attempt was made by the Onchocerciasis Control Program between 1975 and 2002 to eliminate the vector in eleven of the endemic countries in West Africa, and with remarkable success. Formerly, the treatment was with diethyl carbamazine for the microfilaria and suramin for the adult worm. These drugs are now known to be toxic and unsuitable for mass distribution. In particular, they precipitate optic nerve disease. With the discovery of ivermectin, a much safer microfilaricide, and the decision of Merck to distribute the drug free of charge for as long as needed, the strategy of control switched to mass drug administration through community-directed treatment with ivermectin. So far, millions have received this annual or biannual treatment through the African Program for Onchocerciasis Control and the Onchocerciasis Elimination Program for the Americas. However, the problem with ivermectin is that it is a monotherapy microfilaricide which has limited effect on the adult worm, and thus will need to be continued for the life span of the adult worm, which may last up to 15 years. There are also early reports of resistance. Serious encephalopathy and death may occur when ivermectin is used in subjects heavily infested with loiasis. It seems unlikely that a break in transmission will occur with community-directed treatment with ivermectin in Africa because of population migrations and the highly efficient vector, but in the Americas some countries such as Columbia and the Oaxaca focus in Mexico have reported eradication. Vector control is only now applicable in selected situations, and particularly to control the nuisance value of the blackfly. Trials are ongoing for alternatives to ivermectin. Candidate drugs include moxidectin, a macrofilaricide, doxycycline which targets the Wolbachia endosymbiont, and flubendazole, which shows promise with the newer oral cyclodextrin formulation.

Rates of microfilarial production by Onchocerca volvulus are not cumulatively reduced by multiple ivermectin treatments

Regular distribution of ivermectin reduces onchocerciasis transmission and morbidity by killing, within humans, the microfilarial stage of the parasite (microfilaricidal effect). In addition, ivermectin exerts a so-called embryostatic effect by which microfilarial production by the adult female worm becomes suppressed during a number of weeks after treatment. To assess the overall effect of ivermectin on onchocerciasis transmission and evaluate the likelihood of local elimination of the infection it is important to estimate the magnitude of the anti-fertility effect over the course of a treatment programme. Estimates of the effect of repeated drug treatments on the production of microfilariae by adult Onchocerca volvulus were obtained by developing a model that was fitted to data collected from three hyperendemic communities in Guatemala, where eligible residents received ivermectin twice per year for two and a half years. The data consist of microfilarial load measurements in the skin, collected just before each six-monthly treatment during the programme. The model that is developed describes the dynamics of an individual host's expected microfilarial load over the 30-month study period. We adopt a Bayesian approach and use Markov chain Monte Carlo (McMC) techniques to fit the model to the data. Combining estimates from the three villages, average microfilarial production in the first six months post-treatment was reduced by ~64% of its pre-treatment level, regardless of values chosen for the pre-ivermectin fertility rate within plausible ranges. Increased adult worm death rate after treatment (to mimic removal of macrofilariae via nodulectomy during the programme) resulted in a smaller estimated magnitude of the embryostatic effect (rate of microfilarial production was reduced by ~58% of pre-ivermectin value). After subsequent treatments, the rate of microfilarial production appeared to be similarly decreased. The data and analyses therefore do not support the hypothesis of a cumulative effect of multiple ivermectin treatments on microfilarial production by female worms.

After a decade of annual dose mass ivermectin treatment in Cameroon and Uganda, onchocerciasis transmission continues

OBJECTIVE

To evaluate the effectiveness of 10 years' annual single dose ivermectin treatment on onchocerciasis transmission in hyperendemic areas of Cameroon and Uganda.

METHODS

Baseline nodule and microfilaria ('skin snip') prevalence data were available from 10 hyperendemic sentinel communities in Cameroon (from 1996) and hyperendemic 20 sentinel communities in Uganda (from 1993). We returned to these villages in 2005, 10 months after the last annual ivermectin distribution, to repeat the cross-sectional surveys. Each sentinel community reported a mean interval treatment coverage of eligible persons of >88% (range 37-100%). Data were analyzed for more than 6200 person examinations. In Cameroon, 719 people >or=10 years were examined at the baseline survey in 1996 and 838 at the follow-up survey in 2005. In Uganda, 1590 people >or=10 years were examined at the baseline survey in 1993 and 2122 people at the follow-up survey in 2005. We also examined children under 10 in Cameroon (1996, n = 185; 2005, n = 448) and Uganda (1993, n = 177; 2005, n = 130). In Uganda, the vitality of worms was judged using standard histological criteria in 80 nodules excised in 2005.

RESULTS

The prevalence of microfilaria carriers among older children and adults (>or=10 years) in Cameroon sentinel communities dropped from 70.1% to 7.04% (P < 0.0001) over the 10-year treatment period; that of nodule carriers from 58% to 9.55% (P < 0.0001). Similarly, in Uganda, the prevalence of microfilaria carriers fell from 71.9% to 7.49% (P < 0.0001) over the 13-year treatment period, and that of nodule carriers from 53.21% to 9.66% (P < 0.0001). The number of microfilaria carriers among children <10 years in Cameroon decreased from 29.73% to 3.8% (P < 0.0001), and in Uganda from 33.89% to 3.1% (P < 0.0001). In 2005, worms excised from nodules in Uganda, 81.4% of males remained alive, and 64% of females, with 24% of them inseminated.

CONCLUSION

A decade or more of annual single dose ivermectin treatment in hyperendemic areas has reduced onchocerciasis to 'hypoendemicity', but onchocerciasis transmission persists. For now, annual treatment with ivermectin should be continued in formerly mesoendemic and hyperendemic zones.

UMF-078: A modified flubendazole with potent macrofilaricidal activity against Onchocerca ochengi in African cattle

BACKGROUND

Human onchocerciasis or river blindness, caused by the filarial nematode Onchocerca volvulus, is currently controlled using the microfilaricidal drug, ivermectin. However, ivermectin does not kill adult O. volvulus, and in areas with less than 65% ivermectin coverage of the population, there is no effect on transmission. Therefore, there is still a need for a macrofilaricidal drug. Using the bovine filarial nematode O. ochengi (found naturally in African cattle), the macrofilaricidal efficacy of the modified flubendazole, UMF-078, was investigated.

METHODS

Groups of 3 cows were treated with one of the following regimens: (a) a single dose of UMF-078 at 150 mg/kg intramuscularly (im), (b) 50 mg/kg im, (c) 150 mg/kg intraabomasally (ia), (d) 50 mg/kg ia, or (e) not treated (controls).

RESULTS

After treatment at 150 mg/kg im, nodule diameter, worm motility and worm viability (as measured by metabolic reduction of tetrazolium to formazan) declined significantly compared with pre-treatment values and concurrent controls. There was abrogation of embryogenesis and death of all adult worms by 24 weeks post-treatment (pt). Animals treated at 50 mg/kg im showed a decline in nodule diameter together with abrogated reproduction, reduced motility, and lower metabolic activity in isolated worms, culminating in approximately 50% worm mortality by 52 weeks pt. Worms removed from animals treated ia were not killed, but exhibited a temporary embryotoxic effect which had waned by 12 weeks pt in the 50 mg/kg ia group and by 24 weeks pt in the 150 mg/kg ia group. These differences could be explained by the different absorption rates and elimination half-lives for each dose and route of administration.

CONCLUSION

Although we did not observe any signs of mammalian toxicity in this trial with a single dose, other studies have raised concerns regarding neuro- and genotoxicity. Consequently, further evaluation of this compound has been suspended. Nonetheless, these results validate the molecular target of the benzimidazoles as a promising lead for rational design of macrofilaricidal drugs.

Onchocerca volvulus-specific antibody and cytokine responses in onchocerciasis patients after 16 years of repeated ivermectin therapy

The recommended control option against onchocerciasis is repeated ivermectin treatment, which will need to be implemented for decades, and it remains unknown how repeated ivermectin therapy might affect immunity against Onchocerca volvulus in the long term. O. volvulus-specific antibody reactivity and cellular cytokine production were investigated in onchocerciasis patients receiving ivermectin (150 microg/kg) annually for 16 years. In treated patients, the T helper type 2 (Th2) cytokine interleukin (IL)-5 and T regulatory IL-10 in response to O. volvulus antigen (OvAg) and bacteria-derived Streptolysin O (SL-O) diminished to levels found in infection-free endemic controls; also, cellular release of Th1-type interferon (IFN)-gamma at 16 years post initial ivermectin treatment (p.i.t.) approached control levels. In ivermectin-treated onchocerciasis patients, IL-5 production in responses to the mitogen phytohaemagglutinin (PHA) decreased, but IL-10 in response PHA increased, and neither attained the cytokine production levels of endemic controls. At 16 years p.i.t., O. volvulus-specific IgG1 and IgG4 subclass reactivity still persisted at higher levels in onchocerciasis patients than in O. volvulus exposed but microfilariae-free endemic controls. In addition, cytokine responses remained depressed in onchocerciasis patients infected concurrently with Mansonella perstans and Necator americanus or Entamoeba histolytica/dispar. Thus, long-term ivermectin therapy of onchocerciasis may not suffice to re-establish fully a balanced Th1 and Th2 immune responsiveness in O. volvulus microfilariae-negative individuals. Such deficient reconstitution of immune competence may be due to an as yet continuing and uncontrolled reinfection with O. volvulus, but parasite co-infections can also bias and may prevent the development of such immunity.

Repeated high doses of avermectins cause prolonged sterilisation, but do not kill, Onchocerca ochengi adult worms in African cattle

BACKGROUND

Ivermectin (Mectizan, Merck and CO. Inc.) is being widely used in the control of human onchocerciasis (Onchoverca volvulus) because of its potent effect on microfilariae. Human studies have suggested that, at the standard dose of 150 microg/kg an annual treatment schedule of ivermectin reversibly interferes with female worm fertility but is not macrofilaricidal. Because of the importance of determining whether ivermectin could be macrofilaricidal, the efficacy of high and prolonged doses of ivermectin and a related avermectin, doramectin, were investigated in cattle infected with O. ochengi.

METHODS

Drugs with potential macrofilaricidal activity, were screened for the treatment of human onchocerciasis, using natural infections of O. ochengi in African cattle. Three groups of 3 cows were either treated at monthly intervals (7 treatments) with ivermectin (Ivomec, Merck and Co. Inc.) at 500 microg/kg or doramectin (Dectamax, Pfizer) at 500 microg/kg or not treated as controls. Intradermal nodules were removed at 6 monthly intervals and adult worms were examined for signs of drug activity.

RESULTS

There was no significant decline in nodule diameter, the motility of male and female worms, nor in male and female viability as determined by the ability to reduce tetrazolium, compared with controls, at any time up to 24 months from the start of treatments (mpt). Embryogenesis, however, was abrogated by treatment, which was seen as an accumulation of dead and dying intra-uterine microfilariae (mf) persisting for up to 18 mpt. Skin mf densities in treated animals had fallen to zero by <3 mpt, but by 18 mpt small numbers of mf were found in the skin of some treated animals and a few female worms were starting to produce multi-cellular embryonic stages. Follow-up of the doramectin treated group at 36 mpt showed that mf densities had still only regained a small proportion of their pre-treatment levels.

CONCLUSION

These results have important implications for onchocerciasis control in the field. They suggest that ivermectin given at repeated high does may sterilise O. volvulus female worms for prolonged periods but is unlikely to kill them. This supports the view that control programmes may need to continue treatments with ivermectin for a period of decades and highlights the need to urgently identify new marcofiliaricidal compounds.

Genetic heterogeneity in Loa loa parasites from southern Cameroon: A preliminary study

Ivermectin (or Mectizan™) is widely used by onchocerciasis and lymphatic filariasis control programs worldwide. Generally, Mectizan™ is both safe and well tolerated. An exception to this general pattern is in some areas co-endemic for Onchocerca volvulus and Loa loa, where a number of severe adverse reactions to Mectizan™ have been noted in L. loa infected individuals. The vast majority of these severe adverse events have occurred in Southern Cameroon. This suggested the hypothesis that the parasites endemic to Southern Cameroon might form a distinct population that exhibited a phenotype of eliciting severe adverse reactions in Loa-infected individuals upon Mectizan™ exposure. To test this hypothesis, the DNA sequences of three potentially polymorphic loci were compared among L. loa parasites from Southern Cameroon and other endemic foci in Sub-Saharan Africa. Analysis of these data suggested that parasites from Southern Cameroon were at least as genetically diverse as those from other foci. Furthermore, no polymorphisms were noted that were unique to and shared among the parasite isolates from Southern Cameroon. Although a limited number of parasite isolates were tested, these results do not appear to support the hypothesis that L. loa parasites from Southern Cameroon represent a unique, genetically isolated population.

Association between microfilarial load and excess mortality in onchocerciasis: an epidemiological study

BACKGROUND

Infection with the parasitic filarial nematode Onchocerca volvulus can lead to severe visual impairment and ultimately blindness. Excess mortality has been noted among people with onchocerciasis, but it is not clear whether this effect is entirely due to blindness, or mediated by some more direct effects of the infection.

METHODS

We assessed the relations between infection with O volvulus, visual acuity, and host mortality with data obtained by the Onchocerciasis Control Programme in West Africa from 2315 villages in 11 countries.

FINDINGS

297,756 people were eligible for follow-up, and accumulated 2,579449 person-years of follow-up from 1971 through 2001. 24,517 people died during this period; 1283 (5.2%) of these deaths were due to onchocerciasis. Mortality of the human host was significantly and positively associated with increasing microfilarial burden (p<0.00001), but not with blindness after adjustment for microfilarial load and other variables. Overall, after adjustment for microfilarial load and other variables, female individuals had a risk of death about 7.5% lower than males (p<0.00001). Rates of mortality peaked in the mid 1980s but generally decreased thereafter.

INTERPRETATION

We have shown a direct relation between O volvulus microfilarial load and host mortality in a comprehensive dataset and in both sexes.

Cost-effectiveness of the use of vector control and mass drug administration, separately or in combination, against lymphatic filariasis

The costs and effects of two intervention strategies for the control of bancroftian filariasis-annual mass drug administrations (MDA) with a combination of diethylcarbamazine and ivermectin, with or without integrated vector control (VC)-were estimated in rural villages in South India. The aim was to compare the cost-effectiveness of MDA alone with that of MDA plus VC. Control of the local vector, Culex quinquefasciatus, was based on the application of polystyrene beads to cesspits, the treatment of drains with larvicidal Bacillus sphaericus and the stocking of wells with larvivorous fish. An itemized cost menu was used to cost MDA and MDA + VC, retrospectively. The annual transmission potential was used to assess the direct outcome of the disease-control methods, whereas the prevalence and intensity of microfilaraemia were used as indicators of the impact of each method. The per-capita costs were 1.49 U.S. dollars for two rounds of MDA, 1.70 U.S. dollars for 2 years of VC and, therefore, 3.19 U.S. dollars for 2 years of MDA + VC. Integration of VC with MDA did not appear to be cost-effective: it cost an estimated 1.80 U.S. dollars to stop an infective mosquito biting a villager using MDA alone but 3.32 U.S. dollars to achieve the same result using MDA + VC. Similarly, the cost to reduce the prevalence of microfilaraemia in a three-village group by 1% was only 96.62 U.S. dollars for MDA alone but 201.16 U.S. dollars when vector control was integrated. The implications of these results for the control and elimination of filariasis in Indian village communities, and the options for sharing and minimizing costs, are discussed.

Comparison between the skin snip test and simple dot blot assay as potential rapid assessment tools for Onchocerciasis in the postcontrol era in Ghana

Successful control of onchocerciasis through mass distribution of ivermectin needs to be coupled with reliable, sensitive, specific, yet affordable diagnostic methods to monitor and ensure the efficacy of such measures. The effort put into the development of diagnostic methods for onchocerciasis that can substitute for or work in combination with the present "gold standard," the skin snip test, has resulted in the discovery of a number of immunogenic proteins with potential use as diagnostic tools in the postcontrol era. Most of these proteins have now been produced through recombinant DNA techniques. However, when costs are not a trivial issue, none of them have yet found their way into the areas where the disease still exists. In the present study, we have evaluated the performance of a simple dot blot assay which uses a mixture of native proteins designated PakF as a serious contender in the quest for a less invasive and more sensitive method to detect Onchocerca volvulus infection in areas with diverse endemicities. Our results indicate that the assay we propose is more sensitive than the skin snip test and shows high specificity, both characteristics required for a suitable tool for the monitoring of onchocerciasis in the postcontrol era.

Resurgence in filarial transmission after withdrawal of mass drug administration and the relationship between antigenaemia and microfilaraemia--a longitudinal study

Seven village units endemic for filariasis were assigned randomly into three arms with different intervention strategies in the years 1995 and 1996. Villages in Group A received two annual mass drug administrations (MDAs) of diethylcarbamazine (DEC) plus ivermectin (IVR). Group B received the same MDAs in combination with vector control; in Group C only placebo was administered. Post-treatment evaluation in 1997 revealed marked reductions in microfilaraemia prevalences (MFP) and geometric mean intensities (GMI). Subsequently, vector control in Group B was continued by the community. Groups A and B received no MDAs between 1997 and 1999 and were re-evaluated in 1999. During this evaluation, antigenaemia prevalence (AGP) was estimated along with MFP, using immunochromatographic test (ICT) kits. The gains of the MDAs were sustained in Group B, while resurgences occurred in Group A, where annual transmission potential (ATP) rose from 21 to 631.6 and MFP doubled. Group C continued to have high ATPs (1057-1617), while Group B had very low ATPs (0-63). After Mulla's corrections, the reductions in MFP were 62.7 and 83.5% and for GMI 72.1 and 91.4% in Group A and B, respectively, compared with Group C. Vector control preserved the gains of MDAs and accounted for 55.8% and 67.1% reductions in MFP and GMI in Group B compared with Group A. The reductions in AGP were 29.4% in Group A and 39.2% in Group B against Group C. The differences between MFP and AGP were nearly uniform across all villages and there was a significant correlation (r=0.98) between the two variables. A similar significant relationship was observed between MFP and AGP values across age groups (r=0.95). Prediction of AGP values from MFP values was proposed with regression equations. We conclude that vector control would be useful as an adjuvant to chemotherapy to prevent resurgences.

Vector-borne infections in the tropics and health policy issues in the twenty-first century

Over the past 2 decades scientific advances and evolving strategies have significantly contributed to improved tools for control of vector-borne infections. These are: diagnostics--rapid assessment methods, non-invasive or minimally so yet sensitive and specific; new chemotherapeutics; pyrethroid insecticides and biological insecticidal products; refined strategies, such as combination therapy, rotation of insecticides for resistance management, community-directed treatment, standardized monitoring and evaluation to define programme progress; better epidemiological knowledge through improved identification of parasites and vectors; GIS, remote sensing and climate models which provide tools for epidemic prediction, planning control programmes and permit effective policy analysis; greater involvement of NGDOs (non-governmental development organizations) and CSOs (civil society organizations) in control; advent of donation programmes which involve community-based or directed mass drug distribution. Future problems could be: (1) the over-emphasis on inflexible financing by the insistence of donors on SWAps (sector-wide investment), (2) the over-reliance on pyrethroid pesticides, (3) the over-expectation that basic research will provide new drugs and vaccines for resource-poor settings in the necessary time scales, and (4) the failure to recognize that biological processes have an inherent capacity for change which outstrips the capacity of health services to respond. Malaria is a paradigm of an 'emerging disease'. (5) The challenge of implementing a 'vertical' approach to disease control within national health programmes, in the face of significant donor opposition to such programmes is a challenge even when such approaches will secure a 'public good'.

Topical application of diethylcarbamazine to detect onchocerciasis recrudescence in west Africa

The Onchocerciasis Control Programme in West Africa (OCP) has succeeded in eliminating blinding onchocerciasis as a public health problem throughout much of West Africa. The efforts of the OCP are now turning towards surveillance, with the goal of rapidly detecting and controlling outbreaks of infection in the onchocerciasis-free zone. With this goal in mind, cutaneous application of a solution of diethylcarbamazine (the DEC-patch test) was evaluated in 1996-99 as a method to detect patent Onchocerca volvulus infection in children and adolescents, a sentinel population for the detection of recrudescence. In an analysis of 1887 individuals in Côte d'Ivoire and Burkina Faso, the DEC-patch test produced prevalence estimates comparable to those obtained by skin snip. The sensitivity of the DEC-patch assay was marginally greater in children and adolescents than in adults, and was greater in individuals who had received prior Mectizan treatment. These data suggest that the DEC-patch test may be a useful tool for detecting recrudescence of O. volvulus infection in a sentinel population of children and young adults within the onchocerciasis-free zone created by the OCP.

Single-dose treatment of Wuchereria bancrofti infections with ivermectin and albendazole alone or in combination: evaluation of the potential for control at 12 months after treatment

The effect of single-dose ivermectin (150-200 micrograms/kg) and albendazole (400 mg) treatment alone and in combination on Wuchereria bancrofti microfilaraemia, antigenaemia and clinical manifestations was compared 12 months after treatment in a double-blind placebo-controlled field trial carried out in Ghana in 1996-98, to evaluate the potential of these treatments for control. Both ivermectin and combination treatments resulted in pronounced reductions in microfilaraemia among individuals who were microfilaria positive before treatment. Among individuals who were positive for circulating filarial antigen before treatment, antigen levels increased considerably over the 1-year period after treatment in the placebo group, whereas they decreased in the ivermectin and combination groups. However, the post-treatment difference reached statistical significance in neither microfilaraemia nor antigenaemia between the ivermectin and the combination groups. Albendazole treatment alone showed only a minor effect on microfilaraemia and antigenaemia. No effect of the treatments on the incidence of new cases of microfilaraemia or antigenaemia, or on clinical manifestations, was observed. Both ivermectin and combination treatment thus appeared effective for control of W. bancrofti infections, but the difference in efficacy between the 2 treatments after 12 months appeared to be minimal.

Macrofilaricidal activity of tetracycline against the filarial nematode Onchocerca ochengi: elimination of Wolbachia precedes worm death and suggests a dependent relationship

Filarial nematodes are important and widespread parasites of animals and humans. We have been using the African bovine parasite Onchocerca ochengi as a chemotherapeutic model for O. volvulus, the causal organism of 'river blindness' in humans, for which there is no safe and effective drug lethal to adult worms. Here we report that the antibiotic, oxytetracycline is macrofilaricidal against O. ochengi. In a controlled trial in Cameroon, all adult worms (as well as microfilariae) were killed, and O. ochengi intradermal nodules resolved, by nine months' post-treatment in cattle treated intermittently for six months. Adult worms removed from concurrent controls remained fully viable and reproductively active. By serial electron-microscopic examination, the macrofilaricidal effects were related to the elimination of intracellular micro-organisms, initially abundant. Analysis of a fragment of the 16S rRNA gene from the O. ochengi micro-organisms confirmed them to be Wolbachia organisms of the order Rickettsiales, and showed that the sequence differed in only one nucleotide in 858 from the homologous sequence of the Wolbachia organisms of O. volvulus. These data are, to our knowledge, the first to show that antibiotic therapy can be lethal to adult filariae. They suggest that tetracycline therapy is likely to be macrofilaricidal against O. volvulus infections in humans and, since similar Wolbachia organisms occur in a number of other filarial nematodes, against those infections too. In that the elimination of Wolbachia preceded the resolution of the filarial infections, they suggest that in O. ochengi at least, the Wolbachia organisms play an essential role in the biology and metabolism of the filarial worm.

A randomized double-blind placebo-controlled field trial of ivermectin and albendazole alone and in combination for the treatment of lymphatic filariasis in Ghana

The efficacy and safety of single-dose ivermectin (150-200 micrograms/kg) and albendazole (400 mg) treatment administered separately or in combination for Wuchereria bancrofti infections were assessed in 1996-98 in a randomized double-blind placebo-controlled field trial in Ghana: 1425 individuals from 4 lymphatic filariasis-endemic villages, 340 of whom were microfilaria (mf)-positive before treatment, were randomized into 4 groups to receive albendazole alone, ivermectin alone, combination of albendazole and ivermectin, or placebo, respectively. Individuals were followed for 5 days after treatment to record any adverse reactions, and the effect of treatment on microfilaraemia was monitored in night-blood samples after 3, 6 and 12 months. Treatment efficacy was analysed for 236 mf-positive individuals who had > or = 100 mf/mL of blood and who were also present for examination at 12 months after treatment. Compared to the placebo group, the ivermectin and combination groups both showed statistically significant reductions in geometric mean mf intensities at the follow-up examinations (to 6.7% and 0.9%, 9.9% and 6.9%, and 21.7% and 11.4% of pre-treatment levels, respectively, at 3, 6 and 12 months after treatment). Compared to the ivermectin group, however, the reduction in the combination group was significantly greater only at 3 months after treatment, but not after 6 or 12 months. The albendazole group showed a slow but non-significant reduction over the same period. Adverse reactions were few and mostly mild (no severe reactions were recorded), and no significant differences were observed between the treatment groups. Both ivermectin and combination treatment thus appeared effective and safe for treatment of lymphatic filariasis, but the difference in efficacy was minor and the study did not provide clear evidence for the combination drug therapy, as compared to ivermectin therapy alone, to be superior for control of lymphatic filariasis.

The control of the human filariases

There is a growing momentum for the global control and elimination of the major human filariases as public health problems worldwide. The renewed optimism for undertaking this objective reflects the development of simple and potentially cost-effective strategies for mass drug delivery in onchocerciasis and the availability of new extremely effective drug combinations to treat infection, and new methods of morbidity control in lymphatic filariasis. It also reflects the development and current availability of very effective diagnostic, surveillance and control modeling tools for both parasites. Control programming will also be aided by our greater understanding of the biology of transmission, host immunity and disease pathogenesis.

Onchocerciasis in pre-primary school children in Nigeria: lessons for onchocerciasis country control programme

There is limited data on the prevalence of onchocerciasis in young children in Nigeria, partly because treatment with the effective drug Ivermectin has been contra-indicated in children less than 5. As the risk of complications of onchocerciasis is related to duration and intensity of infection, it would be beneficial to know the prevalence in young children for design of control programmes. A study was therefore undertaken to determine the prevalence of onchocerciasis in 642 children 0-4 years old in a rain forest endemic community in South East Nigeria. The overall onchocerciasis prevalence (positive skin snips) for children 0-4 years old in three Local Government Areas in Enugu State, Eastern Nigeria was 15.7% with no significant difference in infection rates between male and female children. There was no detectable infection in children less than 1 year old. Characteristic onchocercal rash was identified in 11.1% of the children and presence of typical onchocercal subcutaneous palpable nodules in 4.6%. Total prevalence for adults in the same population was found to be 26.9%. This indicates that in onchocerciasis endemic communities, everybody may be at risk of infection irrespective of age.

Immunogenic glycoconjugates implicated in parasitic nematode diseases

Parasitic nematodes infect billions of people world-wide, often causing chronic infections associated with high morbidity. The greatest interface between the parasite and its host is the cuticle surface, the outer layer of which in many species is covered by a carbohydrate-rich glycocalyx or cuticle surface coat. In addition many nematodes excrete or secrete antigenic glycoconjugates (ES antigens) which can either help to form the glycocalyx or dissipate more extensively into the nematode's environment. The glycocalyx and ES antigens represent the main immunogenic challenge to the host and could therefore be crucial in determining if successful parasitism is established. This review focuses on a few selected model systems where detailed structural data on glycoconjugates have been obtained over the last few years and where this structural information is starting to provide insight into possible molecular functions.

Transmission control and drug resistance in malaria: a crucial interaction

Drug resistance is a major problem affecting progress on malaria control, while many current programmes are seeking to introduce impregnated bednets to reduce transmission and hence child mortality and morbidity. David Molyneux, Katherine Floyd, Guy Barnish and Eric Fèvre propose that more consideration should be given to the interaction between transmission control and the development of drug resistance, and that vector control as a means of reducing disease transmission is involved in reducing the rate of development, and the level, of resistance. Therefore, investment in vector control can have important benefits in reducing the future expenditure on drugs (as well as other costs, such as hospitalization, management of resistant cases and severe disease, drug development and household expenditure on malaria chemotherapy). Modelling the many parameters that impact on this complex relationship will better inform policy makers.

Vector-borne parasitic diseases--an overview of recent changes

This paper summarises the impact of different changes (environmental, ecological, developmental) on the one hand, with the impact of control measures on the other. The former group of changes have tended to exacerbate the incidence and prevalence of vector-borne parasitic diseases while the reduced public funds available for the health sector have reduced disease surveillance systems. However, some vector control/eradication programmes have been successful. Vector control in onchocerciasis and Chagas' disease and immediate host control in Guinea worm have reduced the public health importance of these disease. This contrasts, with malaria, where the complexity of different ecological situations and the variable vector ecology have made control difficult and epidemics frequent and unpredictable. Advances in our knowledge of how to implement and sustain insecticide-impregnated bednets which reduce morbidity and mortality in under 5-year olds will be a key issue for the coming years. In African trypanosomiasis and leishmaniasis, where control is dependent on effective diagnosis and surveillance followed by high-cost drug treatment, the health services are faced with major challenges--lack of drug availability and diagnostics no vector control--the diseases in some areas assuming epidemic status yet health services are unable to respond. Human African trypanosomiasis and visceral leishmaniasis are fatal if untreated, and require an emergency response approach. Changing vector distribution of Glossina is related to the ability of riverine flies of Glossina palpalis group to adapt to new vegetation patterns. In leishmaniasis changes have occurred in the distribution of the disease associated with development impact, urbanisation, civil unrest and changed agroforestry practice.

Traditional medicine to DNA vaccines: the advance of medical research in West Africa

West Africa has a rich medical history. Herbal medicine has been practiced for hundreds of years and the establishment of an effective herbal pharmacopoeia was probably the first medical research carried out in West Africa. Arabic medicine was practiced in the countries of the Sahel in the 15th and 16th centuries. The coming of the Europeans focused research on infectious diseases such as malaria, yellow fever and sleeping sickness, to which Europeans were very susceptible and which caused devastating epidemics among the populations of their new colonies. The end of the colonial era saw the establishment of a few large, well-equipped teaching hospitals but these proved too expensive for the newly independent states of West Africa to run effectively, and the second generation of West African medical schools was based on more modest government hospitals. This led to a change in the focus of research away from the more unusual conditions seen in a specialist referral hospital to an interest in conditions, such as the common infectious diseases, seen more frequently in district hospitals. The advent of the primary health care movement in the 1970s was followed by an increased emphasis on community studies. Molecular biology is likely to have an enormous impact on medicine in general in the coming years. One of the main challenges facing medical researchers in West Africa is how these new technologies can be used most effectively to improve health in countries with limited resources.