Control of onchocerciasis today: status and challenges

Dual RNA-seq in filarial nematodes and Wolbachia endosymbionts using RNase H based ribosomal RNA depletion

Lymphatic filariasis is caused by parasitic nematodes and is a leading cause of disability worldwide. Many filarial worms contain the bacterium Wolbachia as an obligate endosymbiont. RNA sequencing is a common technique used to study their molecular relationships and to identify potential drug targets against the nematode and bacteria. Ribosomal RNA (rRNA) is the most abundant RNA species, accounting for 80-90% of the RNA in a sample. To reduce sequencing costs, it is necessary to remove ribosomal reads through poly-A enrichment or ribosomal depletion. Bacterial RNA does not contain a poly-A tail, making it difficult to sequence both the nematode and Wolbachia from the same library preparation using standard poly-A selection. Ribosomal depletion can utilize species-specific oligonucleotide probes to remove rRNA through pull-down or degradation methods. While species-specific probes are commercially available for many commonly studied model organisms, there are currently limited depletion options for filarial parasites. Here, we performed total RNA sequencing from Brugia malayi containing the Wolbachia symbiont (wBm) and designed ssDNA depletion probes against their rRNA sequences. We compared the total RNA library to poly-A enriched, Terminator 5'-Phosphate-Dependent Exonuclease treated, NEBNext Human/Bacteria rRNA depleted and our custom nematode probe depleted libraries. The custom nematode depletion library had the lowest percentage of ribosomal reads across all methods, with a 300-fold decrease in rRNA when compared to the total RNA library. The nematode depletion libraries also contained the highest percentage of Wolbachia mRNA reads, resulting in a 16-1,000-fold increase in bacterial reads compared to the other enrichment and depletion methods. Finally, we found that the Brugia malayi depletion probes can remove rRNA from the filarial worm Dirofilaria immitis and the majority of rRNA from the more distantly related free living nematode Caenorhabditis elegans. These custom filarial probes will allow for future dual RNA-seq experiments between nematodes and their bacterial symbionts from a single sequencing library.

Identification and Characterization of Onchocerca volvulus Heat Shock Protein 70 (OvHSP70) as Novel Diagnostic Marker of Onchocerciasis in Human Urine

Despite several decades of mass drug administration and elimination-related activities, human onchocerciasis still represents a major parasitic threat in endemic regions. Among the challenges encountered by the elimination program is the lack of a suitable diagnostic tool that is accurate and non-invasive. Currently used methods are either invasive or not suitable for monitoring large numbers of patients. Herein, we describe the identification and characterization of Onchocerca volvulus heat shock protein 70 (OvHSP70) as a novel diagnostic biomarker for human onchocerciasis, which can directly be detected in urine samples of infected patients. This nematode-specific antigen was identified through LC-MS after differential SDS-PAGE using urine-derived protein extracts from O. volvulus-infected patients in Cameroon. Polyclonal antibodies generated in rabbits after cloning and expression of OvHSP70 in Escherichia coli reliably differentiated between urine samples from infected- and uninfected patients in a hypoendemic area of human onchocerciasis. These results provide an excellent basis for further development of a non-invasive and scalable diagnostic assay for human onchocerciasis using urine samples. Such a urine-based diagnostic assay will be of major importance for the elimination program of human onchcerciasis in endemic countries.

Improved metagenome assemblies through selective enrichment of bacterial genomic DNA from eukaryotic host genomic DNA using ATAC-seq

Genomics can be used to study the complex relationships between hosts and their microbiota. Many bacteria cannot be cultured in the laboratory, making it difficult to obtain adequate amounts of bacterial DNA and to limit host DNA contamination for the construction of metagenome-assembled genomes (MAGs). For example, Wolbachia is a genus of exclusively obligate intracellular bacteria that live in a wide range of arthropods and some nematodes. While Wolbachia endosymbionts are frequently described as facultative reproductive parasites in arthropods, the bacteria are obligate mutualistic endosymbionts of filarial worms. Here, we achieve 50-fold enrichment of bacterial sequences using ATAC-seq (Assay for Transposase-Accessible Chromatin using sequencing) with Brugia malayi nematodes, containing Wolbachia (wBm). ATAC-seq uses the Tn5 transposase to cut and attach Illumina sequencing adapters to accessible DNA lacking histones, typically thought to be open chromatin. Bacterial and mitochondrial DNA in the lysates are also cut preferentially since they lack histones, leading to the enrichment of these sequences. The benefits of this include minimal tissue input (<1 mg of tissue), a quick protocol (<4 h), low sequencing costs, less bias, correct assembly of lateral gene transfers and no prior sequence knowledge required. We assembled the wBm genome with as few as 1 million Illumina short paired-end reads with >97% coverage of the published genome, compared to only 12% coverage with the standard gDNA libraries. We found significant bacterial sequence enrichment that facilitated genome assembly in previously published ATAC-seq data sets from human cells infected with Mycobacterium tuberculosis and C. elegans contaminated with their food source, the OP50 strain of E. coli. These results demonstrate the feasibility and benefits of using ATAC-seq to easily obtain bacterial genomes to aid in symbiosis, infectious disease, and microbiome research.

Prevalence of epilepsy in Ndom Health District (Littoral Region, Cameroon) after long-term ivermectin-based preventive chemotherapy for the control of onchocerciasis

Assuming the causality relationship between Onchocerca volvulus infection and epilepsy onset, preventive chemotherapy for the control onchocerciasis can result to a significant impact on epilepsy burden. This study aimed at assessing the prevalence of epilepsy in an onchocerciasis endemic area under annual CDTI for 16 years. A cross-sectional survey was conducted in two communities (Kelleng and Nkonkwalla) located in the Ndom Health District (Littoral Region, Cameroon) to assess the prevalence of epilepsy using a standardized questionnaire for non-specialists in tropical areas. Data on the nuisance of onchocerciasis vector and distance of surveyed households to the river were also collected. Epilepsy status was collected from 367 participants (sex ratio (M/F): 1.13). The crude prevalence of epilepsy was estimated at 8.4 % (95 % CI: 5.8-11.8); the highest prevalence was found in females (13.8 %; 95 % CI: 8.8-20.3) compared to males (5.0 %; 95 % CI: 2.4-9.04)) (p-value = 0.02) and in Nkonkwalla (9.0 %; 95 % CI: 5.5-13.6) (p-value = 0.82) compared to Kelleng (7.7 %; 95 % CI: 4.06-13.13). After 16 years of CDTI in Kelleng, crude prevalence of epilepsy decreased from 10.2 % to 7.2 % (p-value = 0.19), whereas the age sex-standardized prevalence dropped from 13.5 % to 7.7 % between 2004 and 2020 (p-value = 0.05). The median age of epilepsy cases shifted from 24 (IQR: 20-30) in 2004 to 28 years (IQR: 23-34) in 2020. The shift in age-specific prevalence over the years suggests a decreasing incidence of epilepsy in areas under long-term CDTI and a significant impact of onchocerciasis control on the prevalence of epilepsy.

Development of a recombinant vaccine against human onchocerciasis

INTRODUCTION

Human onchocerciasis caused by the filarial nematode parasite Onchocerca volvulus remains a major cause of debilitating disease infecting millions primarily in Sub-Saharan Africa. The development of a prophylactic vaccine, along with mass drug administration, would facilitate meeting the goal of onchocerciasis elimination by 2030.

AREAS COVERED

Models used to study immunity to Onchocerca include natural infection of cattle with Onchocerca ochengi and O. volvulus infective third-stage larvae implanted within diffusion chambers in mice. A vaccine, comprised of two adjuvanted recombinant antigens, induced protective immunity in genetically diverse mice suggesting that it will function similarly in diverse human populations. These antigens were recognized by immune humans and also induced protective immunity against Brugia malayi. We describe the development of a fusion protein composed of the two vaccine antigens with the plan to test the vaccine in cows and non-human primates as a prelude to the initiation of phase 1 clinical trials.

EXPERT OPINION

The adjuvanted O. volvulus vaccine composed of two antigens Ov-103 and Ov-RAL-2 was shown to be consistently effective at inducing protective immunity using multiple immune mechanisms. The vaccine is ready for further evaluation in other animal models before moving to clinical trials in humans.

Antiparasitic antibiotics from Japan

Antibiotics are microbial secondary metabolites and they are important for the treatment of infectious diseases. Japanese researchers have made a large contribution to studies of antibiotics, and they have also been important in the discovery of antiparasitic antibiotics. Satoshi Ōmura received the Nobel Prize in 2015 for the "discoveries concerning a novel therapy against infections caused by roundworm parasites", which means discovery of a new nematocidal antibiotic, avermectin. Here, I review the many antiparasitic antibiotics and their lead compounds that have been discovered for use in human and veterinary medicine.

Determinants of community-led ivermectin treatment adherence for onchocerciasis control in Western Ethiopia: a case-control study

Background

Onchocerciasis is an infection of a filarial worm which is endemic in Sub-Saharan Africa, including Ethiopia. Annual mass treatment with high coverage over for a long period of time should lead to a complete interruption of transmission and the ultimate elimination of the parasite. However, in Ethiopia, the required coverage levels were not achieved. Thus, the aim of this study was to identify the possible determinants of onchocerciasis treatment adherence in Assossa District.

Methods

A case-control study was conducted among 528 respondents (176 cases and 352 controls). Cases were respondents who took all five doses of treatments, and controls were those who took at most four does of ivermectin treatments (missed at least one or more doses). Structured questionnaire was used for data collection. Each possible factor for treatment adherence, with a P value < 0.2 obtained in the bi-variable logistic regression was entered into the multivariable logistic regression models to control the confounding factors. p value < 0.05 was used as cut-off-point for a variable to become a significant determinant of treatment adherence in multivariable logistic regression.

Results

Participation in selecting drug distributers [AOR = 2.7, 95%CI (1.7–4.1)], measuring height for dose determination [AOR = 3.6, 95%CI (1.9–6.7)], perceived risk of getting onchocerciasis [AOR = 2.1, 95%CI (1.6–2.7)], living near running water [AOR = 1.7, 95%CI (1.1–2.8)], and perceived needs of support for intake of ivermectin [AOR = 3.2, 95%CI(2.1–4.9)] were independent predictors for t treatment adherence.

Conclusions

Treatment adherence was influenced by participation in selecting drug distributers, measuring height for dose determination, perceived risk of getting onchocerciasis, living near running water and perceived needs of support for intake of ivermectin. To improve intake of the drug and its adherence, the community should be empowered to make decisions, and counseling family members and sensitizing those living far from river sides is commendable. Health information about onchocerciasis should be strengthening to increase risk perception.

Hidden biodiversity revealed by DNA barcoding in black fly genus Simulium

BACKGROUND & OBJECTIVES

The black fly genus Simulium Latreille is one of the most important medical insect group of the family Simuliidae (Diptera) and many species of this genus are important pests of human and animals, while some of them also represent vectors of pathogens. Correct species identification is essential to the implementation of control measures for species of medical or agricultural importance.

METHODS

In this study, the usefulness of DNA barcoding was discussed in distinguishing species of Simulium.

RESULTS

Analysis showed hidden biodiversity, usually referred to in Simuliidae as cryptic species, which was detected in 15 species. Firstly, intraspecific divergences of eleven species was unexpectedly high and the maximum distances of them ranged from 5.1-16.8%. Based on the differential of K2P (Kimura 2-Parameter) distances, sequences were subdivided into two or three groups, respectively. Secondly, extremely low interspecific divergences were detected in eight groups of species, and shared haplotypes were also found among them. Furthermore, the subdivision within species and shared haplotypes among some species were all supported by the NJ (Neighbour-Joining) analysis.

INTERPRETATION & CONCLUSION

Our results confirmed that DNA barcoding was a powerful tool for revealing hidden species diversity of black flies. Further work is needed to reveal ambiguous species delimitation in some problematic species groups.

Reaching the last mile: main challenges relating to and recommendations to accelerate onchocerciasis elimination in Africa

BACKGROUND

Onchocerciasis (river blindness), caused by the filarial worm species Onchocerca volvulus, is a serious vector-borne neglected tropical disease (NTD) of public health and socioeconomic concern. It is transmitted through the bite of black flies of the genus Simulium, and manifested in dermal and ocular lesions. Ninety-nine percent of the total global risk and burden of onchocerciasis is in Africa. This scoping review examines the key challenges related to the elimination of onchocerciasis by 2020-2025 in Africa, and proposes recommendations to overcome the challenges and accelerate disease elimination. To find relevant articles published in peer-reviewed journals, a search of PubMed and Google Scholar databases was carried out.

MAIN TEXT

Rigorous regional interventions carried out to control and eliminate onchocerciasis in the past four decades in Africa have been effective in bringing the disease burden under control; it is currently not a public health problem in most endemic areas. Notably, transmission of the parasite is interrupted in some hyperendemic localities. Recently, there has been a policy shift from control to complete disease elimination by 2020 in selected countries and by 2025 in the majority of endemic African countries. The WHO has published guidelines for stopping mass drug administration (MDA) and verifying the interruption of transmission and elimination of human onchocerciasis. Therefore, countries have revised their plans, established a goal of disease elimination in line with an evidence based decision to stop MDA and verify elimination, and incorporated it into their NTDs national master plans. Nevertheless, challenges remain pertaining to the elimination of onchocerciasis in Africa. The challenge we review in this paper are: incomplete elimination mapping of all transmission zones, co-endemicity of onchocerciasis and loiasis, possible emergence of ivermectin resistance, uncoordinated cross-border elimination efforts, conflict and civil unrest, suboptimal program implementation, and technical and financial challenges. This paper also proposes recommendations to overcome the challenges and accelerate disease elimination. These are: a need for complete disease elimination mapping, a need for collaborative elimination activities between national programs, a need for a different drug distribution approach in conflict-affected areas, a need for routine monitoring and evaluation of MDA programs, a need for implementing alternative treatment strategies (ATSs) in areas with elimination anticipated beyond 2025, and a need for strong partnerships and continued funding.

CONCLUSIONS

National programs need to regularly monitor and evaluate the performance and progress of their interventions, while envisaging the complete elimination of onchocerciasis from their territory. Factors hindering the targeted goal of interruption of parasite transmission need to be identified and remedial actions should be taken. If possible and appropriate, ATSs need to be implemented to accelerate disease elimination by 2025.

Economic evaluations of onchocerciasis interventions: a systematic review and research needs

OBJECTIVE

To provide a systematic review of economic evaluations that has been conducted for onchocerciasis interventions, to summarise current key knowledge and to identify research gaps.

METHOD

A systematic review of the literature was conducted on the 8th of August 2018 using the PubMed (MEDLINE) and ISI Web of Science electronic databases. No date or language stipulations were applied to the searches.

RESULTS

We identified 14 primary studies reporting the results of economic evaluations of onchocerciasis interventions, seven of which were cost-effectiveness analyses. The studies identified used a variety of different approaches to estimate the costs of the investigated interventions/programmes. Originally, the studies only quantified the benefits associated with preventing blindness. Gradually, methods improved and also captured onchocerciasis-associated skin disease. Studies found that eliminating onchocerciasis would generate billions in economic benefits. The majority of the cost-effectiveness analyses evaluated annual mass drug administration (MDA). The estimated cost per disability-adjusted life year (DALY) averted of annual MDA varies between US$3 and US$30 (cost year variable).

CONCLUSIONS

The cost benefit and cost effectiveness of onchocerciasis interventions have consistently been found to be very favourable. This finding provides strong evidential support for the ongoing efforts to eliminate onchocerciasis from endemic areas. Although these results are very promising, there are several important research gaps that need to be addressed as we move towards the 2020 milestones and beyond.

Review of the National Program for Onchocerciasis Control in the Democratic Republic of the Congo

Here, we review all data available at the Ministry of Public Health in order to describe the history of the National Program for Onchocerciasis Control (NPOC) in the Democratic Republic of the Congo (DRC). Discovered in 1903, the disease is endemic in all provinces. Ivermectin was introduced in 1987 as clinical treatment, then as mass treatment in 1989. Created in 1996, the NPOC is based on community-directed treatment with ivermectin (CDTI). In 1999, rapid epidemiological mapping for onchocerciasis surveys were launched to determine the mass treatment areas called "CDTI Projects". CDTI started in 2001 and certain projects were stopped in 2005 following the occurrence of serious adverse events. Surveys coupled with rapid assessment procedures for loiasis and onchocerciasis rapid epidemiological assessment were launched to identify the areas of treatment for onchocerciasis and loiasis. In 2006, CDTI began again until closure of the activities of African Program for Onchocerciasis Control (APOC) in 2015. In 2016, the National Program for Neglected Tropical Diseases Control using Preventive Chemotherapy (PNMTN-CP) was launched to replace NPOC. Onchocerciasis and CDTI are little known by the population. The objective of eliminating onchocerciasis by 2025 will not be achieved due to the poor results of the NPOC. The reform of strategies for eliminating this disease is strongly recommended.

Upon entering an age of global ivermectin-based integrated mass drug administration for neglected tropical diseases and malaria

Ivermectin mass drug administration (MDA) in humans to reduce malaria vectors is yet another use for this remarkable medicine whose discoverers shared the 2015 Nobel Prize in Medicine with the discoverer of artemisinin. The malaria community should join those who have long used ivermectin MDA in an integrated battle to break transmission of three vector-borne parasitic diseases.

River Blindness: Mathematical Models for Control and Elimination

Human onchocerciasis (river blindness) is one of the few neglected tropical diseases (NTDs) whose control strategies have been informed by mathematical modelling. With the change in focus from elimination of the disease burden to elimination of Onchocerca volvulus, much remains to be done to refine, calibrate and validate existing models. Under the impetus of the NTD Modelling Consortium, the teams that developed EPIONCHO and ONCHOSIM have joined forces to compare and improve these frameworks to better assist ongoing elimination efforts. We review their current versions and describe how they are being used to address two key questions: (1) where can onchocerciasis be eliminated with current intervention strategies by 2020/2025? and (2) what alternative/complementary strategies could help to accelerate elimination where (1) cannot be achieved? The control and elimination of onchocerciasis from the African continent is at a crucial crossroad. The African Programme for Onchocerciasis Control closed at the end of 2015, and although a new platform for support and integration of NTD control has been launched, the disease will have to compete with a myriad of other national health priorities at a pivotal time in the road to elimination. However, never before had onchocerciasis control a better arsenal of intervention strategies as well as diagnostics. It is, therefore, timely to present two models of different geneses and modelling traditions as they come together to produce robust decision-support tools. We start by describing the structural and parametric assumptions of EPIONCHO and ONCHOSIM; we continue by summarizing the modelling of current treatment strategies with annual (or biannual) mass ivermectin distribution and introduce a number of alternative strategies, including other microfilaricidal therapies (such as moxidectin), macrofilaricidal (anti-wolbachial) treatments, focal vector control and the possibility of an onchocerciasis vaccine. We conclude by discussing challenges, opportunities and future directions.

A community-based cross-sectional study of the epidemiology of onchocerciasis in unmapped villages for community directed treatment with ivermectin in Jimma Zone, southwestern Ethiopia

BACKGROUND

Human onchocerciasis is a neglected tropical parasitic disease caused by Onchocerca volvulus (O. volvulus) that may result in devastating skin and eye morbidity. Even though the disease is targeted for elimination, there was little or no information on the level of onchocerciasis endemicity for implementation of community directed treatment with ivermectin (CDTI) in the current study area. Thus, this study aimed at investigating the epidemiology of onchocerciasis and the level of awareness towards the disease among communities living close to CDTI area, Jimma Zone, southwestern Ethiopia.

METHODS

A community based cross-sectional study was conducted from April 23 to May 22, 2012. Data on socio-demographic characteristics, knowledge, attitude and practice towards onchocerciasis were collected using semi-structured questionnaires. Clinical examination was undertaken for onchocercal skin diseases by experienced health professionals. Moreover, two skin snip samples were collected from the right and left gluteal folds. Study participants found positive for O. volvulus infection during the study were treated individually with standard dose of ivermectin as per WHO guideline.

RESULTS

The overall prevalence of O. volvulus infection was 22.5 % while the prevalence of onchocercal skin diseases was 29.8 %. The community microfilarial (mf) load was 5.70 mf per skin snip. Age, sex, educational status, occupation and duration of stay in the villages showed significant association with onchocerciasis (P < 0.05). But sex (OR = 0.565, 95 % CI = 0.335, 0.952), educational status (OR = 0.545, 95 % CI = 0.310, 0.958) and duration of stay in the village (OR = 5.933, 95 % CI = 1.017, 34.626) were the independent predictors for O. volvulus infection. Three hundred eighty eight (88.2 %) of the study participants reported that they didn't know about onchocerciasis.

CONCLUSIONS

There was moderate prevalence of onchocercal infection and onchocercial skin diseases (OSD) in the study area. Result of this study may suggest that the endemicity level of onchocerciasis in the study area was mesoendemic. Hence, intervention using ivermectin treatment should be implemented to reduce the burden of onchocerciasis. Since the majorities of the population had poor knowledge, attitude and practice towards onchocerciasis, inclusion of health education in the intervention package is crucial.

Predictors of compliance with community-directed treatment with ivermectin for onchocerciasis control in Kabo area, southwestern Ethiopia

Background

Compliance with annual ivermectin treatment is a major challenge in community-directed treatment with ivermectin (CDTI) implementation. There are individuals who do not comply with the annual mass treatment, which contributes to the continuity for disease transmission. Hence, ensuring high treatment coverage and sustained compliance should be given due emphasis in the control of onchocerciasis. The aim of this study was to determine CDTI compliance rate and predictors of compliance where the CDTI was in its 9^th round in Kabo area, southwestern Ethiopia.

Methods

Community-based cross-sectional study was conducted in Kabo area, three weeks after the 9th round of annual ivermectin distribution. Systematic random sampling was used to select head of households and structured, pre-tested questionnaire was used to interview the study participants. Data was analyzed using SPSS version 16. Descriptive statistics was used to compute mean and standard deviation of continuous variables and frequency for categorical variables, while bivariate and multivariate logistic regressions were used to assess the effects of independent variables on the outcome variable. Variables which showed association in multivariate analysis were considered as final predictors of compliance and strength of association was measured through adjusted odds ratio (AOR).

Results

A total of 308 respondents (age range 18-70, mean age ± SD, 32.21 ± 9.64) participated in the study. Of these, 249 (80.8%) reported that they took ivermectin during the 9^th round annual treatment. Significantly higher rate of treatment compliance was reported by participants age ≥35 years (AOR = 5.48, 95% CI; 1.97 - 15.23), participants who stayed in the area for more than ten years (AOR = 3.86, 95% CI; 1.83- 8.11), participants who perceive that they are at risk of contracting the disease(AOR = 7.05, 2.70- 18.43), participants who perceive community drug distributors (CDDs) are doing their work well (AOR = 2.35 95% CI; 1.15- 4.83) and participants who know at least one CDD in their village (AOR = 2.83, 95% CI; 1.26- 6.40).

Conclusion

The majority of the study participants in the present study area complied with ivermectin treatment. Nevertheless, intervention packages should consider factors such as age, residence duration and community’s perception of the disease to improve compliance and make drug distribution sustainable.

Localization of a filarial phosphate permease that is up-regulated in response to depletion of essential Wolbachia endobacteria

Wolbachia of filarial nematodes are essential, obligate endobacteria. When depleted by doxycycline worm embryogenesis, larval development and worm survival are inhibited. The molecular basis governing the endosymbiosis between Wolbachia and their filarial host is still being deciphered. In rodent filarial nematode Litomosoides sigmodontis, a nematode encoded phosphate permease gene (Ls-ppe-1) was up-regulated at the mRNA level in response to Wolbachia depletion and this gene promises to have an important role in Wolbachia-nematode endosymbiosis. To further characterize this gene, the regulation of phosphate permease during Wolbachia depletion was studied at the protein level in L. sigmodontis and in the human filaria Onchocerca volvulus. And the localization of phosphate permease (PPE) and Wolbachia in L. sigmodontis and O. volvulus was investigated in untreated and antibiotic treated worms. Depletion of Wolbachia by tetracycline (Tet) resulted in up-regulation of Ls-ppe-1 in L. sigmodontis. On day 36 of Tet treatment, compared to controls (Con), >98% of Wolbachia were depleted with a 3-fold increase in mRNA levels of Ls-ppe-1. Anti-Ls-PPE serum used in Western blots showed up-regulation of Ls-PPE at the protein level in Tet worms on day 15 and 36 of treatment. Immunohistology revealed the localization of Wolbachia and Ls-PPE in the embryos, microfilariae and hypodermis of L. sigmodontis female worms and up-regulation of Ls-PPE in response to Wolbachia depletion. Expression of O. volvulus phosphate permease (Ov-PPE) studied using anti-Ov-PPE serum, showed up-regulation of Ov-PPE at the protein level in doxycycline treated Wolbachia depleted O. volvulus worms and immunohistology revealed localization of Ov-PPE and Wolbachia and up-regulation of Ov-PPE in the hypodermis and embryos of doxycycline treated worms. Ls-PPE and Ov-PPE are upregulated upon Wolbachia depletion in same tissues and regions where Wolbachia are located in untreated worms, reinforcing a link between Wolbachia and this nematode encoded protein. The function of nematode phosphate permease in the endosymbiosis is unknown but could involve transportation of phosphate to Wolbachia, which encode all the genes necessary for de novo nucleotide biosynthesis. Electron microscopic localization of PPE and Wolbachia and RNAi mediated knock-down of PPE in filarial nematodes will bring further insights to the functions of PPE in the Wolbachia-nematode symbiosis.

Molecular phylogeny of black flies in the Simulium tuberosum (Diptera: Simuliidae) species group in Thailand

Black flies are medically and ecologically significant insects. They are also interesting from an evolutionary standpoint regarding the role of chromosomal change and ecological adaptation. In this study, molecular genetic markers based on multiple gene sequences were used to assess genetic diversity and to infer phylogenetic relationships for a group of cytologically highly diverse black flies of the Simulium tuberosum species group in Thailand. Ecological affinities of the species were also investigated. High levels of genetic diversity were found in cytological species complexes, S. tani and S. doipuiense, and also in S. rufibasis, which was cytologically nearly monomorphic. The results highlight the necessity of integrating multilevel markers for fully understanding black fly biodiversity. Phylogenetic relationships based on multiple gene sequences were consistent with an existing dendrogram inferred from cytological and morphological data. Simulium tani is the most distinctive taxa among the members of the S. tubersosum species group in Thailand based on its divergent morphological characters. Molecular data supported the monophyletic status of S. tani, S. weji, and S. yuphae, but S. doipuiense and S. rufibasis were polyphyletic, most likely due to incomplete lineage sorting and inadequate phylogenetic signals. Ecological analyses revealed that members of the S. tuberosum species group have clearly different ecological niches. The results thus supported previous views of the importance of ecology in black fly evolution.

New strategies to combat filariasis

Two of the major filarial infections, lymphatic filariasis (LF) and onchocerciasis, affect 150 million people, while 1 billion living in endemic areas are at risk of infection. Public health programs to control these infections have successfully existed for years and have evolved from activities driven by the WHO into global programs with public-private partnerships. Currently, these programs use yearly mass application of drugs that mainly kill the larval stages (the microfilariae), with the aim of preventing uptake by the transmitting insect vectors and thus, to block transmission and reduce the infections to such levels that in 15-30 years from now, they will no longer pose a public health problem. While the programs have been very successful in general, there are drawbacks such as coverage being too low within the population, reappearance of infection by migration of infected people into controlled areas, targeting of a stage (the microfilaria) that does not induce pathology in LF and thus lowers compliance, and the potential development of drug resistance, first indications of which have been clearly observed in onchocerciasis. In addition, even without drawbacks, program scopes are not the eradication of filarial infections, which is, however, an ultimate goal of control activities. There is therefore an unequivocal call for the development of higher efficient, complementary chemotherapeutical approaches that lead to a long-lasting reduction of the pathology-inducing worm stages; that is, microfilariae in onchocerciasis and adult worms in LF, or to a macrofilaricidal effect. The recent discovery that depletion of Wolbachia endosymbionts by tetracycline antibiotics leads to long-lasting sterility of adult female worms in onchocerciasis and a macrofilaricidal effect in LF fulfils these requirements. Successful regimens have already been published and agreed upon for use by expert panels. While these regimens are still too long for mass application, the antiwolbachial chemotherapy can currently be applied in the form of a suitable doxycycline regimen for 6 weeks for the treatment of individuals, and exploited in the future for the development of new drugs suitable for mass application. In addition, first data suggest that Wolbachia may also be major mediators of lymphangiogenesis and that their depletion is associated with reduction of lymph vessel-specific vascular endothelial growth factors and reduced lymph vessel size.

The cost of annual versus biannual community-directed treatment of onchocerciasis with ivermectin: Ghana as a case study

BACKGROUND

It has been proposed that switching from annual to biannual (twice yearly) mass community-directed treatment with ivermectin (CDTI) might improve the chances of onchocerciasis elimination in some African foci. However, historically, relatively few communities have received biannual treatments in Africa, and there are no cost data associated with increasing ivermectin treatment frequency at a large scale. Collecting cost data is essential for conducting economic evaluations of control programmes. Some countries, such as Ghana, have adopted a biannual treatment strategy in selected districts. We undertook a study to estimate the costs associated with annual and biannual CDTI in Ghana.

METHODOLOGY

The study was conducted in the Brong-Ahafo and Northern regions of Ghana. Data collection was organized at the national, regional, district, sub-district and community levels, and involved interviewing key personnel and scrutinizing national records. Data were collected in four districts; one in which treatment is delivered annually, two in which it is delivered biannually, and one where treatment takes place biannually in some communities and annually in others. Both financial and economic costs were collected from the health care provider's perspective.

PRINCIPAL FINDINGS

The estimated cost of treating annually was US Dollars (USD) 0.45 per person including the value of time donated by the community drug distributors (which was estimated at USD 0.05 per person per treatment round). The cost of CDTI was approximately 50-60% higher in those districts where treatment was biannual than in those where it was annual. Large-scale mass biannual treatment was reported as being well received and considered sustainable.

CONCLUSIONS/SIGNIFICANCE

This study provides rigorous evidence of the different costs associated with annual and biannual CDTI in Ghana which can be used to inform an economic evaluation of the debate on the optimal treatment frequency required to control (or eliminate) onchocerciasis in Africa.

Uncertainty surrounding projections of the long-term impact of ivermectin treatment on human onchocerciasis

Background

Recent studies in Mali, Nigeria, and Senegal have indicated that annual (or biannual) ivermectin distribution may lead to local elimination of human onchocerciasis in certain African foci. Modelling-based projections have been used to estimate the required duration of ivermectin distribution to reach elimination. A crucial assumption has been that microfilarial production by Onchocerca volvulus is reduced irreversibly by 30–35% with each (annual) ivermectin round. However, other modelling-based analyses suggest that ivermectin may not have such a cumulative effect. Uncertainty in this (biological) and other (programmatic) assumptions would affect projected outcomes of long-term ivermectin treatment.

Methodology/Principal Findings

We modify a deterministic age- and sex-structured onchocerciasis transmission model, parameterised for savannah O. volvulus–Simulium damnosum, to explore the impact of assumptions regarding the effect of ivermectin on worm fertility and the patterns of treatment coverage compliance, and frequency on projections of parasitological outcomes due to long-term, mass ivermectin administration in hyperendemic areas. The projected impact of ivermectin distribution on onchocerciasis and the benefits of switching from annual to biannual distribution are strongly dependent on assumptions regarding the drug's effect on worm fertility and on treatment compliance. If ivermectin does not have a cumulative impact on microfilarial production, elimination of onchocerciasis in hyperendemic areas may not be feasible with annual ivermectin distribution.

Conclusions/Significance

There is substantial (biological and programmatic) uncertainty surrounding modelling projections of onchocerciasis elimination. These uncertainties need to be acknowledged for mathematical models to inform control policy reliably. Further research is needed to elucidate the effect of ivermectin on O. volvulus reproductive biology and quantify the patterns of coverage and compliance in treated communities.

Studies in Mali, Nigeria, and Senegal suggest that, in some settings, it is possible to eliminate onchocerciasis after 15–17 years of ivermectin distribution. Computer models have been used to estimate the required duration of ivermectin distribution to reach elimination. Some models assume that annual ivermectin treatment reduces the fertility of the causing parasite, Onchocerca volvulus, by 30–35% each time the drug is taken. Other analyses suggest that ivermectin may not have such an effect. We explore how assumptions regarding: a) treatment effects on microfilarial production by female worms (fertility), b) proportion of people who receive the drug (coverage), c) proportion of people who adhere to treatment (compliance), and d) whether people are treated once or twice per year (frequency) affect temporal projections of infection load and prevalence in highly endemic African savannah settings. We find that if treatment does not affect parasite fertility cumulatively, elimination of onchocerciasis in highly endemic areas of Africa may not be feasible with annual ivermectin distribution alone. If two areas have equal coverage but dissimilar compliance, they may experience very different infection load, prevalence and persistence trends. Projections such as these are crucial to help onchocerciasis control programmes to plan elimination strategies effectively.

Human ocular onchocerciasis caused by Onchocerca lupi (Spirurida, Onchocercidae) in Iran

Cases of canine onchocerciasis caused by Onchocerca lupi are increasingly reported from Europe and the western United States of America. The zoonotic role of this parasite had already been suspected in Europe as the clinical signs and histopathology seen in two ocular cases from Albania and the Crimean region were very similar to those of canine ocular onchocerciasis. In the most recent reports of human onchocerciasis, O. lupi has been morphologically and molecularly identified as the causative agent of ocular infestation in two patients from Turkey, and one patient from Tunisia. Here, we report an additional case of nodular lesions involving two, and possibly more, immature worms in a patient from Iran. The parasite was found to belong to the genus Onchocerca based on morphological features and the species was confirmed as O. lupi from a partial sequence analysis of 12S ribosomal DNA.

Putative filariosis outbreak in white and black rhinoceros at Meru National Park in Kenya

BACKGROUND

Habitat and food supply loss and disruption, together with man's pursuit of the animal's unique horn pose significant threats to the charismatic rhinoceros. Filarial worms have been thought to cause cutaneous lesions in black rhinoceros (Diceros bicornis) in Kenya and South Africa, but never in white rhinoceros (Ceratotherium simum) in the wild, despite the fact that the two species live often in close proximity. Stephanofilaria dinniki has been implicated in the past as the causal agents for such lesions.

FINDINGS

In this paper we report a putative filariosis outbreak in both black and white rhinos at Meru National Park in Kenya. Four black and five white rhinos were affected by various degrees of filarioid-like lesions, while apparently all sympatric wild and domestic animals were filarial worm-free. Affected rhinos were captured and successfully treated. Comparison between the epidemiological aspects of white and black rhinoceros filariosis, and the possible relations between this outbreak and annual seasons, the presence of oxpeckers and other host species are discussed.

CONCLUSIONS

Our study highlights (i) that filarial infection is not restricted to black rhinos, but it affects both rhinoceros species, and (ii) the importance of the earlier detection and immediate treatment (capture-treat and release) of filarioid infections, which is of pivotal interest for wildlife conservation, and especially the endangered and isolated white and black rhinoceros populations.

Ophthalmic parasitosis: a review article

Ocular parasitosis in human is more prevalent in geographical areas where environmental factors and poor sanitary conditions favor the parasitism between man and animals. Lesions in the eye can be due to damage directly caused by the infectious pathogen, indirect pathology caused by toxic products, or the immune response incited by infections or ectopic parasitism. The epidemiology of parasitic ocular diseases reflects the habitat of the causative parasites as well as the habits and health status of the patient. An ocular examination may provide clues to the underlying disease/infection, and an awareness of the possibilities of travel-related pathology may shed light on an ocular presentation. This paper is a comprehensive review of the parasitic diseases of the eye. The majority of the clinically important species of parasites involved in eye infection are reviewed in this paper. Parasites are discussed by the disease or infection they cause.

Human ocular filariasis: further evidence on the zoonotic role of Onchocerca lupi

Background

Among ocular vector-borne pathogens, Onchocerca volvulus, the agent of the so-called “river blindness”, affects about 37 million people globally. Other Onchocerca spp. have been sporadically reported as zoonotic agents. Cases of canine onchocerciasis caused by Onchocerca lupi are on the rise in the United States and Europe. Its zoonotic role has been suspected but only recently ascertained in a single case from Turkey. The present study provides further evidence on the occurrence of O. lupi infesting human eyes in two patients from Turkey (case 1) and Tunisia (case 2). The importance of obtaining a correct sample collection and preparation of nematodes infesting human eyes is highlighted.

Methods

In both cases the parasites were identified with morpho-anatomical characters at the gross examination, histological analysis and anatomical description and also molecularly in case 1.

Results

The nematode from the first case was obviously O. lupi based on their morphology at the gross examination, histological analysis and anatomical description. In the second case, although the diagnostic cuticular characters were not completely developed, other features were congruent with the identification of O. lupi. Furthermore, the morphological identification was also molecularly confirmed in the Turkish case.

Conclusions

The results of this study suggest that O. lupi infestation is not an occasional finding but it should be considered in the differential diagnosis of other zoonotic helminths causing eye infestation in humans (e.g., D. immitis and Dirofilaria repens). Both cases came from areas where no cases of canine onchocerciasis were previously reported in the literature, suggesting that an in depth appraisal of the infestation in canine populations is necessary. Physicians and ophthalmologists are advised on how to preserve nematode samples recovered surgically, to allow a definitive, correct etiological diagnosis.

Density-dependent mortality of the human host in onchocerciasis: relationships between microfilarial load and excess mortality

Background

The parasite Onchocerca volvulus has, until recently, been regarded as the cause of a chronic yet non-fatal condition. Recent analyses, however, have indicated that in addition to blindness, the parasite can also be directly associated with human mortality. Such analyses also suggested that the relationship between microfilarial load and excess mortality might be non-linear. Determining the functional form of such relationship would contribute to quantify the population impact of mass microfilaricidal treatment.

Methodology/Principal Findings

Data from the Onchocerciasis Control Programme in West Africa (OCP) collected from 1974 through 2001 were used to determine functional relationships between microfilarial load and excess mortality of the human host. The goodness-of-fit of three candidate functional forms (a (log-) linear model and two saturating functions) were explored and a saturating (log-) sigmoid function was deemed to be statistically the best fit. The excess mortality associated with microfilarial load was also found to be greater in younger hosts. The attributable mortality risk due to onchocerciasis was estimated to be 5.9%.

Conclusions/Significance

Incorporation of this non-linear functional relationship between microfilarial load and excess mortality into mathematical models for the transmission and control of onchocerciasis will have important implications for our understanding of the population biology of O. volvulus, its impact on human populations, the global burden of disease due to onchocerciasis, and the projected benefits of control programmes in both human and economic terms.

Human onchocerciasis (River Blindness) is a parasitic disease leading to visual impairment including blindness. Blindness may lead to premature death, but infection with the parasite itself (Onchocerca volvulus) may also cause excess mortality in sighted individuals. The excess risk of mortality may not be directly (linearly) proportional to the intensity of infection (a measure of how many parasites an individual harbours). We analyze cohort data from the Onchocerciasis Control Programme in West Africa, collected between 1974 and 2001, by fitting a suite of quantitative models (including a ‘null’ model of no relationship between infection intensity and mortality, a (log-) linear function, and two plateauing curves), and choosing the one that is the most statistically adequate. The risk of human mortality initially increases with parasite density but saturates at high densities (following an S-shape curve), and such risk is greater in younger individuals for a given infection intensity. Our results have important repercussions for programmes aiming to control onchocerciasis (in terms of how the benefits of the programme are calculated), for measuring the burden of disease and mortality caused by the infection, and for a better understanding of the processes that govern the density of parasite populations among human hosts.

Elimination of human onchocerciasis: history of progress and current feasibility using ivermectin (Mectizan(®)) monotherapy

We review and analyze approaches over a 65 year period that have proven successful for onchocerciasis control in several different epidemiological settings. These include vector control with the goal of transmission interruption versus the use of mass drug administration using ivermectin (Mectizan(®)) monotherapy. Ivermectin has proven exceedingly effective because it is highly efficacious against Onchocerca volvulus microfilariae, the etiological agent of onchocercal skin and ocular disease and the infective stage for the vector. For these reasons, the drug was donated by the Merck Company for regional control programs in Africa and the Americas. Recurrent treatment with ivermectin at semi-annual intervals also impacts adult worms and result in loss of fecundity and increased mortality. Using a strategy of 6-monthly treatments with high coverage rates, the Onchocerciasis Elimination Program for the Americas has interrupted transmission in seven of the thirteen foci in the Americas and is on track to eliminate onchocerciasis in the region by 2015. Treatments given annually or semi-annually for 15-17 years in three hyperendemic onchocerciasis foci in Mali and Senegal also have resulted in a few infections in the human population with transmission levels below thresholds postulated for elimination. Follow-up evaluations did not detect any recrudescence of infection or transmission, suggesting that onchocerciasis elimination could be feasible with Mectizan(®) treatment in some endemic foci in Africa.

Cryptic biodiversity and phylogenetic relationships revealed by DNA barcoding of Oriental black flies in the subgenus Gomphostilbia (Diptera: Simuliidae)

Understanding the medical, economic, and ecological importance of black flies relies on correct identification of species. However, traditional taxonomy of black flies is impeded by a high degree of morphological uniformity, especially the presence of cryptic biodiversity, historically recognized by details of chromosomal banding patterns. We assess the utility of DNA barcoding, based on cytochrome c oxidase subunit 1 (COI) sequences, for identifying 13 species of Oriental black flies in the subgenus Gomphostilbia. Samples of larvae fixed in Carnoy's solution were used to gather molecular and chromosomal data from the same individual. We found that larvae refrigerated in Carnoy's fixative for as long as 11 years can be used for DNA study. Levels of intraspecific genetic divergence, based on the Kimura-2 parameter, range from 0% to 9.28%, with a mean of 2.75%, whereas interspecific genetic divergence ranges from 0.34% to 16.05%. Values of intraspecific and interspecific genetic divergence overlap in seven species owing to incomplete lineage sorting and imperfect taxonomy, implying that DNA barcoding to identify these species will be ambiguous. Despite a low level of success, we found that DNA barcoding is useful in revealing cryptic biodiversity, potentially facilitating traditional taxonomy. Phylogenetic analyses indicate that species groups currently recognized on morphological criteria are not monophyletic, suggesting a need to reevaluate the classification of the subgenus Gomphostilbia.

Case report: First evidence of human zoonotic infection by Onchocerca lupi (Spirurida, Onchocercidae)

In the past decades, cases of canine ocular onchocercosis have been reported worldwide, particularly in the United States and Europe. Onchocerca lupi, originally described from a wolf, has been implicated in some of these cases, and its zoonotic role has been hypothesized on the basis of the reexamination of two cases of human ocular onchocerciasis. In the present study, we describe, for the first time, the occurrence of O. lupi in the subconjunctival region of the human eye in a patient from Turkey. The nematode was identified as O. lupi based on its morphology and molecular phylogenetic analysis of partial cox1 and 12S ribosomal DNA genes. The results suggest that O. lupi should be considered in the differential diagnosis of other eye parasitic infections in humans. The role of dogs as natural hosts of O. lupi and the vectors of this zoonotic parasite need to be investigated.

Control of onchocerciasis in Africa: threshold shifts, breakpoints and rules for elimination

Control of onchocerciasis in Africa is currently based on annual community-directed treatment with ivermectin (CDTI) which has been assumed to be not efficient enough to bring about elimination. However, elimination has recently been reported to have been achieved by CDTI alone in villages of Senegal and Mali, reviving debate on the eradicability of onchocerciasis in Africa. We investigate the eradicability of onchocerciasis by examining threshold shifts and breakpoints predicted by a stochastic transmission model that has been fitted extensively to data. We show that elimination based on CDTI relies on shifting the threshold biting rate to a level that is higher than the annual biting rate. Breakpoints become relevant in the context of when to stop CDTI. In order for the model to predict a good chance for CDTI to eliminate onchocerciasis, facilitating factors such as the macrofilaricidal effect of ivermectin must be assumed. A chart predicting the minimum efficacy of CDTI required for elimination, dependent on the annual biting rate, is provided. Generalisable recommendations into strategies for the elimination of onchocerciasis are derived, particularly referring to the roles of vectors, the residual infection rate under control, and a low-spreader problem originating from patients with low parasite burdens.

To give is better than to receive: compliance with WHO guidelines for drug donations during 2000-2008

OBJECTIVE

to assess drug donations in terms of their adherence to the drug donation guidelines put forth by the World Health Organization (WHO).

METHODS

in 2009 we searched the academic and lay literature - journal articles, media articles and industry and donor web sites - to identify reports about drug donations made from 2000 to 2008. Publications focusing on molecular mechanisms of drug action, general descriptions of guidelines or specific one-time drug donations before 2000 were excluded. For cases with sufficient information, we assessed compliance with each of the 12 articles of WHO's guidelines.

FINDINGS

we found 95 articles describing 96 incidents of drug donations between 2000 and 2008. Of these, 50 were made in response to disaster situations, 43 involved the long-term donation of a drug to treat a specific disease and 3 were drug recycling cases. Disaster-related donations were less likely to comply with the guidelines, particularly in terms of meeting the recipient's needs, quality assurance and shelf-life, packaging and labelling, and information management. Recipient countries were burdened with the costs of destroying the drugs received through inappropriate donations. Although long-term donations were more likely to comply with WHO guidelines related to quality assurance and labelling, they did not consistently meet the needs of the recipients. Furthermore, they discouraged local drug production and development.

CONCLUSION

drug donations can do more harm than good for the recipient countries. Strengthening the structures and systems for coordinating and monitoring drug donations and ensuring that these are driven by recipient needs will improve adherence to the drug donation guidelines set forth by WHO.

Metabolomics-based discovery of diagnostic biomarkers for onchocerciasis

Background

Development of robust, sensitive, and reproducible diagnostic tests for understanding the epidemiology of neglected tropical diseases is an integral aspect of the success of worldwide control and elimination programs. In the treatment of onchocerciasis, clinical diagnostics that can function in an elimination scenario are non-existent and desperately needed. Due to its sensitivity and quantitative reproducibility, liquid chromatography-mass spectrometry (LC-MS) based metabolomics is a powerful approach to this problem.

Methodology/Principal Findings

Analysis of an African sample set comprised of 73 serum and plasma samples revealed a set of 14 biomarkers that showed excellent discrimination between Onchocerca volvulus–positive and negative individuals by multivariate statistical analysis. Application of this biomarker set to an additional sample set from onchocerciasis endemic areas where long-term ivermectin treatment has been successful revealed that the biomarker set may also distinguish individuals with worms of compromised viability from those with active infection. Machine learning extended the utility of the biomarker set from a complex multivariate analysis to a binary format applicable for adaptation to a field-based diagnostic, validating the use of complex data mining tools applied to infectious disease biomarker discovery and diagnostic development.

Conclusions/Significance

An LC-MS metabolomics-based diagnostic has the potential to monitor the progression of onchocerciasis in both endemic and non-endemic geographic areas, as well as provide an essential tool to multinational programs in the ongoing fight against this neglected tropical disease. Ultimately this technology can be expanded for the diagnosis of other filarial and/or neglected tropical diseases.

Onchocerciasis, caused by the filarial parasite Onchocerca volvulus, afflicts millions of people, causing such debilitating symptoms as blindness and acute dermatitis. There are no accurate, sensitive means of diagnosing O. volvulus infection. Clinical diagnostics are desperately needed in order to achieve the goals of controlling and eliminating onchocerciasis and neglected tropical diseases in general. In this study, a metabolomics approach is introduced for the discovery of small molecule biomarkers that can be used to diagnose O. volvulus infection. Blood samples from O. volvulus infected and uninfected individuals from different geographic regions were compared using liquid chromatography separation and mass spectrometry identification. Thousands of chromatographic mass features were statistically compared to discover 14 mass features that were significantly different between infected and uninfected individuals. Multivariate statistical analysis and machine learning algorithms demonstrated how these biomarkers could be used to differentiate between infected and uninfected individuals and indicate that the diagnostic may even be sensitive enough to assess the viability of worms. This study suggests a future potential of these biomarkers for use in a field-based onchocerciasis diagnostic and how such an approach could be expanded for the development of diagnostics for other neglected tropical diseases.

Factors associated with compliance with community directed treatment with ivermectin for onchocerciasis control in Southwestern Ethiopia

Background

Although ivermectin is distributed free of charge through the African Programme for Onchocerciasis Control (APOC), not all eligible individuals within communities receive the annual treatment. This poses a serious threat to efforts aimed to control onchocerciasis. This study attempts to determine factors associated with compliance to Community Directed Treatment with Ivermectin (CDTI) and provides a basis for trying to understand how best to sustain long-term compliance in order to achieve success in the control of onchocerciasis.

Methods

An unmatched case-control study was conducted in Bebeka coffee plantation southwest Ethiopia. Cases were, compliant i.e., those individuals who had been registered on the relevant treatment registers and had taken all the five annual doses of Ivermectin. Controls were non-compliant, i.e. those individuals who had been recorded in the relevant treatment registers during the first treatment round(2003), and did not take at least two doses of which one being in the last treatment round (2007). Data were collected using a pre-tested interviewer administered structured questionnaire. Data were edited, cleaned, coded and analyzed using SPSS version 12.0.1 for Microsoft Windows. Multiple logistic regression models was used to identify factors associated with compliance to ivermectin.

Results

From the total of 456 individuals selected for administration of the survey questionnaire, 450(225 cases and 225 controls) were contacted and completed the study 2 refused and 4 were unavailable. Five factors associated with compliance were identified: high risk perception [Adjusted Odds Ratio(AOR) = 1.98, 95% Confidence Interval (CI), 1.32-2.95], one's family support [AOR = 1.86, 95% CI, 1.22-2.84], perceiving that the Community Drug Distributors (CDDs) are doing their work well [AOR = 2.84, 95% CI, 1.50-5.37] and perceiving measuring height is the best way to determine a person's treatment dose [AOR = 6.37, 95% CI, 2.10-19.29] are positive predictors of compliance to ivermectin.

Conclusion

Interventions to improve compliance in the area should focus on health education using epidemiological data in order to increase risk perception and dispelling misconceptions. Motivation and continued support to improve CDD's performance including training and incentives are crucial.

Mapping, monitoring, and surveillance of neglected tropical diseases: towards a policy framework

As national programmes respond to the new opportunities presented for scaling up preventive chemotherapy programmes for the coadministration of drugs to target lymphatic filariasis, onchocerciasis, schistosomiasis, soil-transmitted helminthiasis, and trachoma, possible synergies between existing disease-specific policies and protocols need to be examined. In this report we compare present policies for mapping, monitoring, and surveillance for these diseases, drawing attention to both the challenges and opportunities for integration. Although full integration of all elements of mapping, monitoring, and surveillance strategies might not be feasible for the diseases targeted through the preventive chemotherapy approach, there are opportunities for integration, and we present examples of integrated strategies. Finally, if advantage is to be taken of scaled up interventions to address neglected tropical diseases, efforts to develop rapid, inexpensive, and easy-to-use methods, whether disease-specific or integrated, should be increased. We present a framework for development of an integrated monitoring and evaluation system that combines both integrated and disease-specific strategies.

Onchocerca-Simulium interactions and the population and evolutionary biology of Onchocerca volvulus

Parasite-vector interactions shape the population dynamics of vector-borne infections and contribute to observed epidemiological patterns. Also, parasites and their vectors may co-evolve, giving rise to locally adapted combinations or complexes with the potential to stabilise the infection. Here, we focus on Onchocerca-Simulium interactions with particular reference to the transmission dynamics of human onchocerciasis. A wide range of simuliid species may act as vectors of Onchocerca volvulus, each exerting their own influence over the local epidemiology and the feasibility of controlling/eliminating the infection. Firstly, current understanding of the processes involved in parasite acquisition by, and development within, different Simulium species in West Africa and Latin America will be reviewed. A description of how Onchocerca and Simulium exert reciprocal effects on each other's survival at various stages of the parasite's life cycle within the blackfly, and may have adapted to minimise deleterious effects on fitness and maximise transmission will be given. Second, we describe the interactions in terms of resultant (positive and negative) density-dependent processes that regulate parasite abundance, and discuss their incorporation into mathematical models that provide useful qualitative insight regarding transmission breakpoints. Finally, we examine the interactions' influence upon the evolution of anthelmintic resistance, and conclude that local adaptation of Onchocerca-Simulium complexes will influence the feasibility of eliminating the parasite reservoir in different foci.

A four-antigen mixture for rapid assessment of Onchocerca volvulus infection

Background

Onchocerciasis, an infection caused by the filarial nematode Onchocerca volvulus, is a major public health concern. Given the debilitating symptoms associated with onchocerciasis and concerns about recrudescence in areas of previous onchocerciasis control, more efficient tools are needed for diagnosis and monitoring of control measures. We investigated whether luciferase immunoprecipitation systems (LIPS) may be used as a more rapid, specific, and standardized diagnostic assay for Onchocerca volvulus infection.

Methods

Four recombinantly produced Onchocerca volvulus antigens (Ov-FAR-1, Ov-API-1, Ov-MSA-1 and Ov-CPI-1) were tested by LIPS on a large cohort of blinded sera comprised of both uninfected controls and patients with a proven parasitic infection including Onchocerca volvulus (Ov), Wuchereria bancrofti (Wb), Loa loa (Ll), Strongyloides stercoralis (Ss), and with other potentially cross-reactive infections. In addition to testing all four Ov antigens separately, a mixture that tested all four antigens simultaneously was evaluated in the standard 2-hour incubation format as well as in a 15-minute rapid LIPS format.

Findings

Antibody responses to the four different Ov antigens allowed for unequivocal differentiation between Ov-infected and uninfected control sera with 100% sensitivity and 100% specificity. Analysis of the antibody titers to each of these four antigens in individual Ov-infected sera revealed that they were markedly different and did not correlate (r_S = –0.11 to 0.58; P = 0.001 to 0.89) to each other. Compared to Ov-infected sera, patients infected with Wb, Ll, Ss, and other conditions had markedly lower geometric mean antibody titers to each of the Ov 4 antigens (P<0.0002 for each antigen). The simplified method of using a mixture of the 4 Ov antigens simultaneously in the standard format or a quick 15-minute format (QLIPS) showed 100% sensitivity and 100% specificity in distinguishing the Ov-infected sera from the uninfected control sera. Finally, the QLIPS format had the best performance with 100% sensitivity and specificity values of 76%, 84% and 93% for distinguishing Ov from Wb, Ll and Ss-infected sera.

Conclusions

The multi-antigen LIPS assay can be used as a rapid, high throughput, and specific tool to not only to diagnose individual Ov infections but also as a sensitive and potentially point-of-care method for early detection of recrudescent infections in areas under control and for mapping new areas of transmission of Ov infection.

Caused by the filarial parasite Onchocerca volvulus, onchocerciasis is a neglected tropical disease associated with blindness and severe dermatitis. Available diagnostic methods are either invasive, require hours or days to perform, and/or need sophisticated equipment to be conducted. Thus, there is an urgent need for simple and rapid technologies for the specific diagnosis of Onchocerca volvulus infection. Here we investigated whether luciferase immunoprecipitation systems (LIPS) can produce a more rapid and specific test for diagnosis of O. volvulus infection. Using modified versions of previously identified Onchocerca-specific antigens, LIPS tests detected antibodies to all four O. volvulus antigens and easily distinguished the O. volvulus-infected samples from uninfected samples. We also tested these four different antigens in a simpler format as a combined mixture and distinguished 100% of the confirmed cases from the uninfected controls. A rapid 15-minute version of this mixture test (QLIPS) also allowed distinction of 100% of the cases from those uninfected and performed even better in identifying Onchocerca from other cross-reactive parasitic infections. This study suggests that this rapid LIPS test (QLIPS) has the potential to be used in point-of-care detection of onchocerciasis and thereby may provide a new tool for diagnosis and the monitoring of transmission control measures.

Malaria in India: challenges and opportunities

India contributes about 70% of malaria in the South East Asian Region of WHO. Although annually India reports about two million cases and 1000 deaths attributable to malaria,there is an increasing trend in the proportion of Plasmodium falciparum as the agent. There exists heterogeneity and variability in the risk of malaria transmission between and within the states of the country as many ecotypes/paradigms of malaria have been recognized. The pattern of clinical presentation of severe malaria has also changed and while multi-organ failure is more frequently observed in falciparum malaria, there are reports of vivax malaria presenting with severe manifestations. The high burden populations are ethnic tribes living in the forested pockets of the states like Orissa, Jharkhand, Madhya Pradesh, Chhattisgarh and the North Eastern states which contribute bulk of morbidity and mortality due to malaria in the country. Drug resistance,insecticide resistance,lack of knowledge of actual disease burden along with new paradigms of malaria pose a challenge for malaria control in the country. Considering the existing gaps in reported and estimated morbidity and mortality, need for estimation of true burden of malaria has been stressed. Administrative, financial,technical and operational challenges faced by the national programme have been elucidated. Approaches and priorities that may be helpful in tackling serious issues confronting malaria programme have been outlined.

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.

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.

Impact of long-term treatment of onchocerciasis with ivermectin in Ecuador: potential for elimination of infection

BACKGROUND

Onchocerciasis is a leading cause of blindness worldwide, hence elimination of the infection is an important health priority. Community-based treatment programs with ivermectin form the basis of control programs for the disease in Latin America. The long-term administration of ivermectin could eliminate Onchocerca volvulus infection from endemic areas in Latin America.

METHODS

A strategy of annual to twice-annual treatments with ivermectin has been used for onchocerciasis in endemic communities in Ecuador for up to 14 years. The impact of ivermectin treatment on ocular morbidity, and O. volvulus infection and transmission was monitored in seven sentinel communities.

RESULTS

Over the period 1990-2003, high rates of treatment coverage of the eligible population were maintained in endemic communities (mean 85.2% per treatment round). Ivermectin reduced the prevalence of anterior segment disease of the eye to 0% in sentinel communities and had a major impact on the prevalence and transmission of infection, with possible elimination of infection in some foci.

CONCLUSION

The distribution of ivermectin in endemic communities in Ecuador might have eliminated ocular morbidity and significant progress has been made towards elimination of the infection. A strategy of more frequent treatments with ivermectin may be required in communities where the infection persists to achieve the objective of elimination of the infection from Ecuador. The elimination of the infection from an endemic country in Latin America would be a major public health achievement and could stimulate the implementation of elimination strategies in other endemic countries.

Advances in drug discovery and biochemical studies

Japanese researchers continue to discover new means to combat parasites and make important contributions toward developing tools for global control of parasitic diseases. Streptomyces avermectinius, the source of ivermectin, was discovered in Japan in the early 1970s and renewed and vigorous screening of microbial metabolites in recent years has led to the discovery of new antiprotozoals and anthelminthics, including antimalarial drugs. Intensive studies of parasite energy metabolism, such as NADH-fumarate reductase systems and the synthetic pathways of nucleic acids and amino acids, also contribute to the identification of novel and unique drug targets.

Environmental effects on parasitic disease transmission exemplified by schistosomiasis in western China

Environmental effects on the transmission of many parasitic diseases are well recognized, but the role of specific factors like climate and agricultural practices in modulating transmission is seldom characterized quantitatively. Based on studies of Schistosoma japonicum transmission in irrigated agricultural environments in western China, a mathematical model was used to quantify environmental impacts on transmission intensity. The model was calibrated by using field data from intervention studies in three villages and simulated to predict the effects of alternative control options. Both the results of these interventions and earlier epidemiological findings confirm the central role of environmental factors, particularly those relating to snail habitat and agricultural and sanitation practices. Moreover, the findings indicate the inadequacy of current niclosamide-praziquantel strategies alone to achieve sustainable interruption of transmission in some endemic areas. More generally, the analysis suggests a village-specific index of transmission potential and how this potential is modulated by time-varying factors, including climatological variables, seasonal water-contact patterns, and irrigation practices. These time-variable factors, a village's internal potential, and its connectedness to its neighbors provide a framework for evaluating the likelihood of sustained schistosomiasis transmission and suggest an approach to quantifying the role of environmental factors for other parasitic diseases.

The Mectizan Donation Program - highlights from 2005

Through the Mectizan^® Donation Program, Merck & Co., Inc. has donated Mectizan (ivermectin, MSD) for the treatment of onchocerciasis worldwide since 1987. Mectizan has also been donated for the elimination of lymphatic filariasis (LF) since 1998 in African countries and in Yemen where onchocerciasis and LF are co-endemic; for LF elimination programs, Mectizan is co-administered with albendazole, which is donated by GlaxoSmithKline. The Mectizan Donation Program works in collaboration with the Mectizan Expert Committee/Albendazole Coordination, its scientific advisory committee. In 2005, a total of 62,201,310 treatments of Mectizan for onchocerciasis were approved for delivery via mass treatment programs in Africa, Latin America, and Yemen. Seventy-seven percent and 20% of these treatments for onchocerciasis were for countries included in the African Programme for Onchocerciasis Control (APOC) and the former-Onchocerciasis Control Programme in West Africa (OCP), respectively. The remaining 3% of treatments approved were for the six onchocerciasis endemic countries in Latin America, where mass treatment is carried out twice-yearly with the goal of completely eliminating morbidity and eventually transmission of infection, and for Yemen. All 33 onchocerciasis endemic countries where mass treatment with Mectizan is indicated have ongoing mass treatment programs. In 2005, 42,052,583 treatments of co-administered albendazole and Mectizan were approved for national Programs to Eliminate LF (PELFs) in Africa and Yemen. There are ongoing PELFs using albendazole and Mectizan in nine African countries and Yemen; these represent 35% of the total number of countries expected to require the co-administration of these two chemotherapeutic agents for LF elimination. In Africa, the expansion of existing PELFs and the initiation of new ones have been hampered by lack of resources, technical difficulties with the mapping of LF endemicity, and the co-endemicity of LF and loiasis. Included in this review are recommendations recently put forward for the co-administration of albendazole and Mectizan in areas endemic for LF, loiasis, and onchocerciasis.

River blindness: a success story under threat?

The success of the Onchocerciasis Control Programme is undeniable and exemplary, say the authors, but it is too early to claim victory against river blindness.