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The Worm Institute for Research and Medicine

Diagnostics

The filarial disease onchocerciasis, commonly referred to as “river blindness”, afflicts approximately 37 million people in Africa, Central and South America and Yemen, with 90 million more at risk and is the second most common cause of preventable blindness in sub-Saharan Africa.  Approximately 99% of O. volvulus infections occur in 28 countries in Africa with the remaining 1% found in six countries of the Americas, and Yemen on the Arabian Peninsula (Figure 1).

Figure 1: Countries with Onchocerciasis (River Blindness)
Symptoms of the disease include acute dermatitis and blindness, the result of which is the loss of 1 million disability adjusted life years (DALYs) annually.  The causative agent, the filarial nematode Onchocerca volvulus, is transmitted in its larval stage between human hosts through the bite of a Simulium (sp.) black fly (Figure 2).

Figure 2:  Life Cycle of Onchocerca volvulus
Onchocerciasis and other neglected tropical diseases (NTDs) are generally classified as a group of medically disparate diseases afflicting the poorest people of the world's developing nations and resulting in acute illness, long-term disability and early death.  Estimates attribute twelve of the NTDs together as causing 162,000 deaths annually with 14.8 million years lost to disability, causing a total burden of 19.0 million DALYs.  Diagnostic tools currently in use for the detection of the NTDs are insufficient for measuring the extent of infection making it difficult to distribute the appropriate therapies to those who need them.  Within WIRM our approach applies mass spectrometric based metabolomic technologies to the creation of diagnostic tests for identifying and classifying these diseases by measuring the blood of infected patients.  In addition to serving a diagnostic purpose, relevant biomarkers could be a valuable means of understanding the complexity of pathogenic infection and may serve as chemical leads for therapeutic development. 

In Africa, where onchocerciasis control programs have been in place since the founding of the Onchocerciasis Control Programme in West Africa (OCP, 1974-2002) and are currently being conducted by the African Programme for Onchocerciasis Control (APOC, 1995-present), diagnosis is an essential aspect of the determination of treatment and distribution of medication.  In the Western hemisphere, accurate and robust diagnostics are essential for attaining the goal of disease elimination.  Twice yearly dosage of ivermectin, through the efforts of the Onchocerciasis Elimination Program for the Americas (OEPA, 1992-present), has lead to a minimization of infection to 13 foci within 6 countries in Central and South America.  Although mass treatment of onchocerciasis foci in the Western hemisphere is slated to be suspended in 2012, achieving the goal of elimination is contingent upon continued surveillance of the disease.  The achievement of the goals of elimination and eradication of onchocerciasis and of the neglected tropical diseases in general, ultimately depends upon the ability to measure and track the progress of disease elimination and recrudescence. Thus, at WIRM we see advantages of a metabolomics based diagnostic over onchocerciasis diagnostics currently implemented including: sensitivity, reproducibility, invasiveness, and the potential for multiplexing with biomarkers for other filarial and/or neglected tropical diseases.

In the discovery phase of WIRM’s research, 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 (Figure 3).  Further analysis of these markers applied 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 has allowed WIRM to extend 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.

Figure 3:  Analysis of Onchocerca volvulus Biomarkers
Currently mass spectrometry has gained wide acceptance for its use in determining metabolic diseases in newborns and mass spectrometers are now found in hospital and clinical settings in the developed world.  This success however has not developed to a wider use of the technology for the diagnosis of other diseases. Ultimately, the optimized biomarker analysis can be ported into mass spectrometry based and/or field amenable technologies (e.g., immunochromatographic or micro-fluidic based tests) for use as a point of care diagnostic.