Defining the cost of the Egyptian lymphatic filariasis elimination programme

BACKGROUND: Ultrasonography (USG) is known to be a suitable tool for diagnosis in lymphatic filariasis as the adult filarial nematode Wuchereria bancrofti in scrotal lymphatic vessels of infected men can be detected by the characteristic pattern of movement, the Filaria Dance Sign. In onchocerciasis, moving adult worms have not yet been demonstrated by USG. In addition the verification of drug effects on living adult Onchocerca volvulus filariae in trials is hampered by the lack of tools for longitudinal observation of alterations induced by potentially macrofilaricidal drugs in vivo. The present study was carried out to determine the frequency of detection of moving adult filariae of O. volvulus by USG. METHODS: In an endemic region for onchocerciasis in Ghana, 61 patients infected with onchocerciasis were recruited by palpation and onchocercomas examined by USG using an ultrasound system equipped with a 7.5 - 10 MHz linear transducer. Onchocercomas were recorded on videotape and evaluated with regard to location, number and size, as well as to movements of adult filariae. RESULTS: In the 61 patients 303 onchocercomas were found by palpation and 401 onchocercomas were detected by USG. In 18 out of 61 patients (29.5%), altogether 22 nodules with moving adult O. volvulus filariae were detected and are presented in animated ultrasound images as mp-4 videos. CONCLUSION: Ultrasonographical examinations of onchocercomas where living adult filariae can be displayed may serve as a new tool for the longitudinal observation in vivo of patients with onchocerciasis undergoing treatment and as an adjunct to histological evaluation.     

Detection of Onchocerca volvulus (Nematoda: Onchocercidae) infection in vectors from Amazonian Brazil following mass Mectizan distribution

Detection of Onchocerca volvulus in Simulium populations is of primary importance in the assessment of the effectiveness of onchocerciasis control programs. In Brazil, the main focus of onchocerciasis is in the Amazon region, in a Yanomami reserve. The main onchocerciasis control strategy in Brazil is the semi-annually mass distribution of the microfilaricide ivermectin. In accordance with the control strategy for the disease, polymerase chain reaction (PCR) was applied in pools of simuliids from the area to detect the helminth infection in the vectors, as recommended by the Onchocerciasis Elimination Program for the Americas and the World Health Organization. Systematic sampling was performed monthly from September 1998 to October 1999, and a total of 4942 blackflies were collected from two sites (2576 from Balawaú and 2366 from Toototobi). The molecular methodology was found to be highly sensitive and specific for the detection of infected and/or infective blackflies in pools of 50 blackflies. The results from the material collected under field conditions showed that after the sixth cycle of distribution of ivermectin, the prevalence of infected blackflies with O. volvulus had decreased from 8.6 to 0.3% in Balawaú and from 4 to 0.1% in Toototobi.     

Onchocerciasis control and elimination: coming of age in resource-constrained health systems

During the past three decades, onchocerciasis control has been successful in reducing blindness and skin disease in Africa and the Americas. In this article, I review the control and elimination of Onchocerca volvulus as a public health problem. The success of onchocerciasis control has been the result of secure financing, generous drug donation, effective partnership between stakeholders, and focused operational and implementation research. The future challenges are to ensure sustainability of existing programmes and to increase the level of integration with other health interventions in resource-deficient health systems.     

Major sperm protein as a diagnostic antigen for onchocerciasis

Onchocerciasis, also known as river blindness, is the second leading infectious cause of blindness worldwide. In order to successfully control this disease, the development of efficient diagnostic tools as well as effective treatments is imperative. A number of proteins have been proposed as vaccine and diagnostic candidates, yet none have been successfully advanced to the point of general clinical use. We have prepared major sperm protein 2 (MSP2) from Onchocerca volvulus as a possible diagnostic antigen for onchocerciasis. Importantly, recombinant MSP2 is dimeric in solution, identical to alpha-MSP from the roundworm, Ascaris suum. A panel of sera obtained from Cameroonian individuals afflicted with onchocerciasis positively responded to the recombinant MSP2. Our data suggest that MSP2, like the previously described antigen Ov16, can be utilized as a diagnostic onchocerciasis antigen for monitoring the interruption of transmission.     

Final report of the Conference on the eradicability of Onchocerciasis

Sixty-four experts from a variety of disciplines attended a Conference on the Eradicability of Onchocerciasis at The Carter Center, in Atlanta GA, held January 22-24, 2002. The Conference, which was organized by The Carter Center and the World Health Organization, with funding from the Bill & Melinda Gates Foundation, addressed the question: "Is onchocerciasis (River Blindness) eradicable with current knowledge and tools?" Former US President Jimmy Carter attended part of the final plenary proceedings on January 24.The Conference consisted of a series of presentations by invited expert speakers (Appendix C) and further deliberations in four workgroups (Appendix D) followed by plenary discussion of major conclusions. The presentations underlined epidemiological and entomological differences between onchocerciasis in Africa and the Americas. Whilst onchocerciasis in Africa covers extensive areas and is associated with striking human and fly population migrations and remarkably efficient black fly vectors, in the Americas onchocerciasis is found in limited foci. Human and fly population migration are not major problems in the Americas, where most black fly species are inefficient, though some efficient black flies are also found there. Vector control has been effectively applied in the Onchocerciasis Control Program in West Africa (OCP) with remarkable results, interrupting transmission in most parts of the original Program area. The use of ivermectin has given variable results: while ivermectin treatment has been effective in all endemic areas in controlling onchocerciasis as a public health problem, its potential for interrupting transmission is more promising in hypo- and mesoendemic areas. The African Program for Onchocerciasis Control (APOC), which supports onchocerciasis control in endemic African countries outside the OCP, applies ivermectin, its principal control tool, to communities in high-risk areas as determined by rapid epidemiological mapping of onchocerciasis (REMO) and Geographic Information Systems (GIS). In the Americas, through support of the Onchocerciasis Elimination Program in the Americas (OEPA), a strategy of bi-annual ivermectin treatment of at least 85% of the eligible populations in all endemic communities is showing very good results and promises to be effective in eliminating onchocerciasis in the region.The Conference concluded that onchocerciasis is not eradicable using current tools due to the major barriers to eradication in Africa. However, the Conference also concluded that in most if not all the Americas, and possibly Yemen and some sites in Africa, transmission of onchocerciasis can be eliminated using current tools. The Conference recommended that where interruption of transmission is feasible and cost effective, programs should aim for that goal using all appropriate and available interventions so that the Onchocerca volvulus can eventually be eliminated and interventions halted. Although interruption of transmission of onchocerciasis cannot currently be achieved in most of Africa, the Conference recommended that efforts be made to preserve areas in West Africa made free of onchocerciasis transmission through the Onchocerciasis Control Program over the past 25 years. In the remaining hyper and mesoendemic foci in Africa, continued annual distribution of ivermectin will keep onchocerciasis controlled to a point where it is no longer a public health problem or constraint to economic development.     

Onchocerca volvulus: expression and immunolocalization of a nematode cathepsin D-like lysosomal aspartic protease

The N-terminal region of the cathepsin D-like aspartic protease from the human filarial parasite Onchocerca volvulus was expressed as His-tag fusion protein. Light and electron microscopic immunohistology using antibodies against the recombinant protein showed labeling of lysosomes in the hypodermis and epithelia of the intestine and the reproductive organs of Onchocerca. While developing oocytes were negative, mature oocytes and early morulae showed strong labeling. In older embryos and mature microfilariae, stained lysosomes were only found in a few cells. Cell death in degenerating microfilariae of patients untreated and treated with microfilaricidal drugs was associated with strong expression of aspartic protease. IgG1, IgG4, and IgE antibodies reactive with the recombinant protein were demonstrated in sera from onchocerciasis patients indicating exposure and recognition of the enzyme by the host's defence system. The aspartic protease of O. volvulus appears to function in intestinal digestion and tissue degradation of the filaria.     

The status of Simulium oyapockense and S.limbatum as vectors of human onchocerciasis in Brazilian Amazonia

In an attempt to explain the current distribution of onchocerciasis in the forests of northern Brazil (Moraes et al., 1979, 1986), and its potential for dispersal to other areas, this study compares the vector status of Simulium oyapockense Floch and Abonnenc, 1946 in both a hypoendemic and an onchocerciasis free area with that of S. limbatum Knab, 1915 in the latter area. Both species allowed the full development of Onchocerca volvulus (Leuckart) to the infective L3 stage after experimental infection with microfilariae. Their vector competence was significantly lower than for other efficient vector species in South America and Africa because of the lethal effect of the cibarial armature on ingested microfilariae. The low vector capacity of S. oyapockense, together with the low prevalence and intensity of infection of O. volvulus, probably explains why onchocerciasis has not significantly increased in intensity over the last 10 years in the hypoendemic part of the Amazonian focus. Omnipresence of both vector species in the adjacent savanna region, however, could facilitate the spread of onchocerciasis if human population movements continue from the hyperendemic part of the onchocerciasis focus.     

Efficiency of Simulium sanctipauli as a vector of Onchocerca volvulus in the forest zone of Ghana

The role of Simulium sanctipauli Vajime & Dunbar (Diptera: Simuliidae) as a vector of Onchocerca volvulus (Leuckart) (Spirurida: Onchocercidae) in the forest zone of central Ghana was studied in the Upper Denkyira district, where onchocerciasis is hyperendemic. Simulium sanctipauli was found to be a highly efficient vector, with a mean of 377 infective (L3) larvae in the heads of 1000 parous and 122 in the heads of 1000 biting flies. The overall infection rate of 44% of the parous flies with L1, L2 and L3 stages of O. volvulus (identity confirmed by polymerase chain reaction) demonstrates marked anthropophily. Female flies dispersed over a wide area and can transmit onchocerciasis up to at least 10 km away from their breeding sites. Annual community-directed treatments with ivermectin did not have a noticeable effect on the infection rates and parasitic loads of fly populations, which were as high 2 months after as 3 months before the distribution of ivermectin. This failure can be attributed to poor coverage, with treatment taken by only 24.4% of the population of the six study villages.     

Filariae of rodents useful for the experimental study of human onchocerciasis

In order to obtain skin and ocular lesions comparable to those which are found in human onchocerciasis, it is not necessary to use members of the genus Onchocerca which are found in large animals and difficult to use. Other Filariae with biological features comparable to Onchocerca volvulus can be used in which microfilariae are localized in capillaries and can escape from the walls and produce lesions similar to those in onchocerciasis. The life cycles of several filariae of rodents have been worked out and they are proposed as experimental models as the tick vectors and the rodent hosts are easily maintained in the laboratory.     

Pathogenesis and host responses in human onchocerciasis: impact of Onchocerca filariae and Wolbachia endobacteria

Onchocerca volvulus is a tissue-invasive parasitic nematode causing skin and eye pathology in human onchocerciasis. The filariae habour abundant intracellular Wolbachia bacteria, now recognised as obligatory symbionts, and therefore emerging as a novel target for chemotherapy. Recent research demonstrates that both the filariae and endobacteria contribute to the pathogenesis of onchocerciasis, and molecules have been identified that promote inflammatory or counter-inflammatory immune mechanisms, divert the host's immune response or procure evasion of the parasite.     

Onchocerca volvulus: limited heterogeneity in the nuclear and mitochondrial genomes

West African populations of Onchocerca volvulus endemic to the rain forest and savanna bioclimes of West Africa differ in their ability to induce ocular disease in infected individuals. In recent years, both clinical- and animal-model-based studies have implicated particular parasite antigens in the development of ocular onchocerciasis. To test the hypothesis that the difference in pathogenic potential of blinding and nonblinding parasites might be reflected in qualitative differences in antigens that have been implicated in the development of ocular onchocerciasis, we compared the sequences of two parasite antigens implicated in the development of ocular disease in blinding- and nonblinding-strain parasites. The results demonstrated a high level of homogeneity between the parasite strains in these genes. The study was extended to include additional nuclear genes encoding antigens that are commonly recognized by individuals infected with O. volvulus and to the mitochondrial genome of the parasite. The results demonstrate a high degree of homogeneity in both the nuclear and the mitochondrial genomes among O. volvulus isolates collected from several different sites in Africa and in the Americas. This high degree of genetic homogeneity may reflect the passage of the parasite through a recent genetic bottleneck.     

Combined Utilisation of Rapid Assessment Procedures for Loiasis (RAPLOA) and Onchocerciasis (REA) in Rain forest Villages of Cameroon

BACKGROUND: Individuals with high microfilarial loads of Loa loa are at increased risk of neurologic serious adverse (SAE) events following ivermectin treatment against onchocerciasis. RAPLOA (Rapid Assessment Procedure for loiasis), a newly developed rapid assessment procedure for loiasis that relates the prevalence of key clinical manifestation of loiasis (history of eye worm) to the level of endemicity of the infection (prevalence of high intensity), is a very useful tool to identify areas at potential risk of L. loa post ivermectin treatment encephalopathy. In a perspective of treatment decision making in areas of co-endemicity of loiasis/onchocerciasis, it would be advantageous (both in time and cost savings) for national onchocerciasis control programmes to use RAPLOA and the Rapid epidemiologic assessment for onchocerciasis (REA), in combination in given surveys. Since each of the two rapid assessment tools have their own specificities, the workability of combining the two methods needed to be tested. METHODS: We worked in 10 communities of a forest area presumed co-endemic for loiasis and onchocerciasis in the North-West Province of Cameroon where the mass-treatment with ivermectin had not been carried out. A four-step approach was used and comprised: (i) generating data on the prevalence and intensity of loiasis and onchocerciasis in an area where such information is scarce; (ii) testing the relationship between the L. loa microfilaraemia prevalence and the RAPLOA prevalence, (iii) testing the relationship between the O. volvulus microfiladermia prevalence and the REA prevalence, (iv) testing the workability of combining RAPLOA/REA by study teams in which a single individual can perform the interview for RAPLOA and the nodule palpation for REA. RESULTS: The microfilaraemia prevalence of loiasis in communities ranged from 3.6% to 14.3%. 6 (0.61%) individuals had L. loa microfilarial loads above 8000 mf/ml but none of them attained 30,000 mf/ml, the threshold value above which the risk of developing neurologic SAE after ivermectin treatment is very high. None of the communities surveyed had RAPLOA prevalence above 40%. All the communities had microfiladermia prevalence above 60%. The microfiladermia results could be confirmed by the rapid epidemiologic method (nodule palpation), with all the 10 communities having REA prevalence above 20%. For the first time, this study has demonstrated that the two rapid assessment procedures for loiasis and onchocerciasis can be carried out simultaneously by a survey team, in which a single individual can administer the questionnaire for RAPLOA and perform the nodule palpation for REA. CONCLUSION: This study has: (i) Revealed that the Momo valley of the North West province of Cameroon is hyperendemic for onchocerciasis, but is of lower level of endemicity for L. loa. (ii) Confirmed the previous relationships established between RAPLOA and the L. loa microfilaraemia prevalence in one hand and between the REA and the O. volvulus microfiladermia prevalence in another hand (iii) Shown that RAPLOA and REA could be used simultaneously for the evaluation of loiasis and onchocerciasis endemicity in areas targeted by the African Programme for onchocerciasis Control for community-directed treatment with ivermectin (CDTI).     

Longitudinal evaluation of repellent activity of Ocimum gratissimum (Labiatae) volatile oil against Simulium damnosum

To determine the repellent activity of Ocimum gratissimum volatile oil against Simulium damnosum (blackflies), a 12 month (January-December 2003) field study was conducted in three onchocerciasis endemic communities (Idomido, Obio camp, and Ikot Adaha) in Ini Local Government Area of Akwa Ibom State, Nigeria. The result revealed that topical application of 20% (v/v) concentration of the oil with liquid paraffin as a base, reduced the biting rate of S. damnosum by 90.2, 81.6, and 79.7%, in Idomido, Obiocamp, and Ikot Adaha respectively. The oil gave protection against the bite of S. damnosum for at least 3 h. A total of 710 adults S. damnosum were caught by individuals treated with Ocimum oil, as against 4296 caught by the control group. When the flies caught by the treated individuals were dissected none of them was infected with microfilariae of Onchocerca volvulus. Human-vector contact and onchocerciasis transmission could be reduced by the topical application of the volatile oil during the peak biting periods of the vector     

Models for the population biology and control of human onchocerciasis

The absence of animal models in which to reproduce successfully the complete life cycle of Onchocerca volvulus has hindered progress towards unravelling the processes involved in the regulation of parasite abundance in the vertebrate host. Mathematical frameworks have been developed to explore the consequences of such processes in determining parasite population dynamics and the effect on these of control interventions. Post-control predictions are strongly influenced by the assumptions concerning the reproductive life span of the adult female worm (the longest-lived parasite stage) and the distribution of its survival times, and this notion is important to all frameworks. Here, we review the development of models concerning onchocerciasis and discuss the various approaches that have been used, presenting a deterministic framework with parameter values estimated from the Mexican onchocerciasis control programme. This model is used to evaluate interventions combining the removal of adult worms (nodulectomy) and the microfilaricidal and possibly sterilizing effect of ivermectin.     

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.     

Chemokines and cytokines in patients with an occult Onchocerca volvulus infection

Repeated ivermectin treatment will clear microfilaria (Mf) of Onchocerca volvulus from skin and eyes of onchocerciasis patients while adult filaria remains alive and reproductive, and such occult O. volvulus infection may persist for years. To investigate the effect of residual adult filaria on the immune response profile, chemokines and cytokines were quantified 1) in onchocerciasis patients who developed an occult O. volvulus infection (Mf-negative) due to repeated ivermectin treatments, 2) patients who became Mf-negative without ivermectin treatments due to missing re-infection, and 3) endemic and non-endemic O. volvulus Mf-negative controls. With occult O. volvulus infection, serum levels of pro-inflammatory chemokines MCP-1/CCL2, MIP-1α/CCL3, MIP-1β/CCL4, MPIF-1/CCL23 and CXCL8/IL-8 enhanced and approached higher concentrations as determined in infection-free controls, whilst regulatory and Th2-type cytokines and chemokines MCP-4/CCL13, MIP-1δ/CCL15, TARC/CCL17 and IL-13 lessened. Levels of Eotaxin-2/CCL24, MCP-3/CCL7 and BCA-1/CXCL13 remained unchanged. At 3 days post-initial ivermectin treatment, MCP-1/CCL2, MCP-4/CCL13, MPIF-1/CCL23 and Eotaxin-2/CCL24 were strongly enhanced, suggesting that monocytes and eosinophil granulocytes have mediated Mf clearance. In summary, with occult and expiring O. volvulus infections the serum levels of inflammatory chemokines enhanced over time while regulatory and Th2-type-promoting cytokines and chemokines lessened; these changes may reflect a decreasing effector cell activation against Mf of O. volvulus, and in parallel, an enhancing inflammatory immune responsiveness.     

The variant Arg110Gln of human IL-13 is associated with an immunologically hyper-reactive form of onchocerciasis (sowda)

Onchocerca volvulus infection usually results in a predominantly immunopermissive reaction called generalized onchocerciasis and characterized by high microfilarial burden and immunological tolerance to the worms. Rarely, however, infection leads to the sowda form of the disease displaying low microfilarial numbers, i.e. microfilarial control, and a T helper 2 (Th2)-type immune response including high immunoglobulin (Ig)E levels, and interleukin (IL)-13 being one of the key cytokines. The aim of this study was to investigate a possible association of a variant of the IL-13 gene, which confers an IgE-independent risk for asthma and atopy, with the immunologically hyper-reactive sowda form of onchocerciasis. Genotyping for the IL-13 variant Arg110Gln revealed a highly significant association of Arg110Gln with the sowda form (relative risk of 2.98, n = 19 patients), whereas the frequency of the variant was significantly lower in patients with generalized onchocerciasis (n = 92 individuals). Sowda patients had higher IgE levels than those with generalized onchocerciasis. Logistic regression analysis revealed that IgE and IL-13 are independent variables, each increasing the relative risk for sowda. Arg110Gln has been suggested to lead to enhanced IL-13 signaling and thus may be involved in shifting the immune reaction towards the hyper-reactivity characteristic for the sowda form, thereby promoting defense mechanisms.     

Onchocerciasis in Canada

The first two cases of onchocerciasis seen in Canada are reported. The patients had come from West Africa to study in Canada several months prior to admission to hospital. The presenting symptom in each case was intense pruritus. One of the patients had early ocular involvement. The diagnosis was made by means of microscopic examination of a skin snip. The subcutaneous nodule excised from one of the patients showed the adult Onchocerca volvulus. Both patients also had urinary schistosomiasis. The clinical features, laboratory findings, treatment and public health aspects of onchocerciasis are discussed.     

Onchocerciasis-related epilepsy? Prospects at a time of uncertainty

Epilepsy and onchocerciasis (river blindness) constitute serious public health problems in several tropical countries. There are four main mechanisms that might explain a relationship between these two diseases: (i) the presence of Onchocerca volvulus in the central nervous system; (ii) the pathogenicity of various O. volvulus strains; (iii) immunological mechanisms involving cross-reactive immunization or cytokine production during infection; and (iv) the triggering role of insomnia due to itching.     

Drug activity against Onchocerca gutturosa males in vitro: a model for chemotherapeutic research on onchocerciasis

An in vitro system for chemotherapeutic research using adult male Onchocerca gutturosa has been developed as a model for O. volvulus. Using a culture system consisting of medium MEM + 10% heat inactivated foetal calf serum (IFCS) + LLCMK2 (monkey kidney) feeder cells in an atmosphere of 5% CO2 in air, we examined the effects of a range of antiparasitic drugs on worm motility. Ivermectin, levamisole, furapyrimidone, Mel W, chloroquine, metrifonate, flubendazole, amoscanate and the Ciba-Geigy compounds CGP 6140, CGP 20'376 and CGI 17658 either immobilized or significantly reduced motility levels at a concentration of 5 X 10(-5) M or less within a 7-day period. Worms were affected at very low concentrations by ivermectin (effective conc. to reduce motility levels to 50% of controls, 3.14 X 10(-8) M), levamisole (7.95 X 10(-8) M), CGP 6140 (8.87 X 10(-9) M) and CGP 20'376 (2.78 X 10(-8) M). Difficulties were experienced in accurately repeating the immotile endpoint for levamisole due to an inconsistent partial recovery of motility. Over a 7-day period diethylcarbamazine had little effect on motility levels, while suramin caused a slight increase in activity compared to controls at some timepoints. Subsequent experiments demonstrated some differences in drug efficacy depending on the presence or absence of serum and feeder cells in the culture system probably because of drug avidly binding to serum proteins. However, serum and cells were found to be essential ingredients of the culture system to maintain worms in good condition, indicating that new drugs should be evaluated both in the presence and absence of serum and cells. Comparisons were made between the responses of O. gutturosa and Brugia pahangi to certain drugs and these species were found to significantly differ in their sensitivities to ivermectin and a novel compound (Wellcome), indicating that Onchocerca parasites should be used wherever possible for compound identification and development intended for the treatment of onchocerciasis. The in vitro system described here, using male O. gutturosa, provides a basis for further research and a practical alternative to O. volvulus.