Onchocerciasis

Neglected tropical diseases: survey and geometry of randomised evidence

OBJECTIVE

To assess the quantity and distribution of evidence from randomised controlled trials for the treatment of the major neglected tropical diseases and to identify gaps in the evidence with network analysis.

DESIGN

Systematic review and network analysis.

DATA SOURCES

Cochrane Central Register of Controlled Trials and PubMed from inception to 31 August 2011.

STUDY SELECTION

Randomised controlled trials that examined treatment of 16 neglected tropical diseases or complications thereof published in English, French, Spanish, Portuguese, German, or Dutch.

RESULTS

We identified 971 eligible randomised trials. Leishmaniasis (184 trials, 23,039 participants) and geohelminth infections; 160 trials, 46,887 participants) were the most studied, while dracunculiasis (nine trials, 798 participants) and Buruli ulcer (five trials, 337 participants) were least studied. Relative to its global burden of disease, lymphatic filariasis had the fewest trials and participants. Only 11% of trials were industry funded. Either a single trial or trials with fewer than 100 participants comprised the randomised evidence for first or second line treatments for Buruli ulcer, human African trypanosomiasis, American trypanosomiasis, cysticercosis, rabies, echinococcosis, New World cutaneous leishmaniasis, and each of the foodborne trematode infections. Among the 10 disease categories with more than 40 trials, five lacked sufficient head to head comparisons between first or second line treatments.

CONCLUSIONS

There is considerable variation in the amount of evidence from randomised controlled trials for each of the 16 major neglected tropical diseases. Even in diseases with substantial evidence, such as leishmaniasis and geohelminth infections, some recommended treatments have limited supporting data and lack head to head comparisons.

Characterization of an immunodominant Onchocerca volvulus antigen with patient sera and a monoclonal antibody

Adult Onchocerca voluvlus and infective larvae, but not microfilariae contain an immunodominant antigen (33,000 and 21,000 Mr in females, 39,000, 33,000, and 21,000 Mr in males, 133,000 Mr in infective larvae) which is recognized by an Onchocerca-specific mAb. The component is part of the reproductive organs and muscles. 96.2% of onchocerciasis sera contained antibodies detectable by immunoblotting against it. Antigen purified by immunoaffinity chromatography was specifically recognized in immunoblots by onchocerciasis sera, but not by sera from other filarial infections. The high immunogenicity, the specificity, and the occurrence in infective larvae of this antigen indicate an immunodiagnostic potential and a possible role in the immunobiology of the parasite.

Characterization of an Onchocerca-specific DNA clone from Onchocerca volvulus

A genomic library of a savanna isolate of Onchocerca volvulus was screened to detect recombinant plasmids containing highly repeated DNA sequences of this parasite. Four recombinant plasmids were identified which hybridized specifically to Onchocerca DNA, but not to DNA from humans, black flies, Brugia malayi, B. pahangi, or Wuchereria bancrofti. The recombinant plasmids had a low level of homology to Dirofilaria immitis. All recombinant plasmids contain related DNA sequences based on Southern hybridization analysis. Sequences related to these recombinant plasmids are present in different geographic isolates of O. volvulus and O. ochengi, an animal parasite. Two of the recombinant plasmids contain sequences also found in O. lienalis. One recombinant plasmid, puOvs3, has been characterized in detail, including DNA sequence determination. Radiolabeled puOvs3 is able to detect 100 pg of genomic DNA isolated from O. volvulus worms from both savanna and forest regions. It can differentiate O. volvulus from O. ochengi by Southern blot analysis.

The effects of ivermectin on transmission of Onchocerca volvulus

Ivermectin, given to onchocerciasis patients as a single oral dose of 200 micrograms per kilogram of body weight, substantially reduced the uptake of Onchocerca volvulus microfilariae by Simulium yahense, an efficient black fly vector of the parasite in the tropical rain forests of West Africa. Three months after treatment, patients given ivermectin infected flies at a significantly lower rate than those who had received diethylcarbamazine or placebo, thereby reducing the number of developing larvae in the vector population. This diminished rate of infectiousness was also evident 6 months after treatment. These results strongly suggest that ivermectin could be effective in interrupting transmission of Onchocerca volvulus for epidemiologically important periods of time.

Onchocerciasis in Sierra Leone. I. Studies on the prevalence and transmission at Gbaiima village

A longitudinal survey--parasitological, clinical, immunological and entomological--of onchocerciasis is being conducted in Gbaiima village in Sierra Leone. The estimated Annual Transmission Potential (ATP) is 5863. More than 80% of the annual transmission occurs between October and December. Four species of the Simulium damnosum complex are known to breed in a nearby river. The relative role of these species as vectors has yet to be determined. The total population (598 persons) aged one year and over were examined. Based on microfilarial and nodular rates the prevalence of onchocerciasis was 68.6%. In persons above 15 years of age this prevalence was 88.9%. Microfilarial and nodular rates were related to age. Severe skin lesions occurred in 1.0% of persons. 24 adults (7.5%) were blind (but the cause of the blindness was not determined).

Implications of heterophile antigens in immunological infertility in males

Immunological study was conducted on serum and hydrocel fluids from males belonging to an equatorial African population heavily contaiminated by Filaria and Schistosoma. Anti-spermatozoa antibodies were detected by agglutination in 31 of 64 sera and 24 of 60 fluids, and by cytotoxicity in 19 of 64 sera and 8 of 60 fluids. Antinuclear antibodies were detected in 21 of 64 sera and 8 of 60 fluids. However, the titers of these antibodies were low, as were the frequency and titers of other tissues antibodies. The appearance of antispermatozoa antibodies is also correlated with extensive skin burns and infection by Pseudomonas aeruginosa or severe Candidiasis.

Onchocerciasis treated with diethylcarbamazine

One hundred patients with onchocerciasis were treated with diethylcarbamazine: a single course of treatment led to clinical cure in 48% of the patients; no means of anticipating which patients might require only a single course of treatment was found.

Pathology of ocular onchocerciasis: human and experimental

Involvement of the outer eye in Onchocerca volvulus infection is characterized by an inflammatory process around degenerating microfilariae. Individual microfilariae in the cornea may be associated with localized punctate lesions or, especially when present in large numbers, may provoke a sclerosing keratitis due to invasion by fibrovascular pannus from the limbal conjunctiva. Anterior uveitis develops in some patients and can be either granulomatous, probably as a result of direct microfilarial invasion of the iris and ciliary body, or non-granulomatous, in which case the inflammation is likely to be a response to free microfilarial antigens. Posterior segment involvement takes the form of either inflammatory or atrophic lesions, or both. It is possible that the marked atrophy of the retina and choriocapillaris seen in some cases is largely attributable to preceding choroiditis and that the optic nerve atrophy has a similar pathogenesis.