An international study co-ordinated by IRD and the Research centre for filariases and other tropical diseases (CRFilMT, Cameroon), shows the efficacy of a new mass treatment strategy for onchocerciasis in central Africa. Referred to as “test and treat”, it is based on a rapid diagnosis thanks to a device connected to a mobile phone, the “LoaScope”. These results, which offer hope that this neglected tropical illness can be eliminated, were recently published in The New England Journal of Medicine, on 8 November 2017.
Onchocerciasis, or “river blindness” is a parasitic infection caused by a roundworm (Onchocerca volvulus) transmitted to humans by biting flies known as simulium. Their larvae are found in fast-flowing rivers. Adult worms produce larvae (microfilariae) which cause skin lesions and severe eye problems that can lead to irreversible blindness. Until the 1970s, onchocerciasis was a public health problem and a major socio economic-affliction in intertropical Africa.
From 1974, the World Health Organisation (WHO) introduced programmes to combat the problem, based initially on simulium elimination, then on the mass distribution of the drug ivermectin from the 1990s. With over 110 million people treated in 2015, onchocerciasis is no longer considered a public health problem. These advances have led the WHO to redefine its objectives, to eliminate the infection. To achieve this, it is necessary to also treat onchocerciasis in regions where it was relatively infrequent (“hypo-endemic” zones).
One of the main problems facing the disease-fighting programmes is the risk of severe side-effects (possibly death) after taking ivermectin, in subjects also infected with Loiasis, another endemic filariasis in central Africa. These incidents thwart hopes of eliminating onchocerciasis.
In this study, IRD and CRFilMT researchers showed the feasibility and efficacy of a new strategy for combating onchocerciasis. Referred to as “test and treat”, it is based on a test done before treatment with ivermectin. To this end, the researchers have developed the LoaScope, a rapid, low-cost tool allowing on-site identification of people with a density of Loa loa in their blood of over 20,000 microfilariae per millilitre, who are at risk of serious side effects if treated with ivermectin.
A true “pocket microscope”, the LoaScope consists of a smartphone equipped with an optical device and an LED light source, allowing the analysis of a very small amount of blood taken from the patient’s finger. “The optical system of the smartphone camera serves as a lens, and using films lasting a few seconds, an algorithm for recognising images can detect and count the embryonic forms of the Loa loa parasitic worm present in the blood,” explains Sébastien Pion, IRD epidemiologist and author of the study.
If no Loa loa infection is detected by the LoaScope, or if the parasite density is below 20,000 per millilitre of blood (as for 95 % of the population), the patient can be treated with ivermectin. However, if the person shows a higher Loa loa infection level, an alternative treatment method can be offered on an individual basis (using such a treatment, which is administered over four weeks, cannot be envisaged for the whole population).
From August to October 2015, researchers evaluated the “test and treat” strategy using the LoaScope in 92 villages of the Okola district in Cameroon, where ivermectin treatment was abandoned in 1999, following severe side-effects in certain patients. Out of over 16,250 people tested, 95.5% could be treated with ivermectin, and 2.1% were excluded from the distribution of ivermectin because their density of Loa loa microfilariae was above the risk threshold. The results of the LoaScope tests have been confirmed by microscope analysis of blood samples. The researchers also introduced a monitoring protocol for post-treatment side-effects, which revealed no severe adverse effects among the patients who had received ivermectin.
Researchers have recently demonstrated the effectiveness of the “test and treat” strategy, which allows them to envisage risk-free mass distribution ivermectin, in the hopes of eliminating onchocerciasis in zones where Loiasis is also endemic. Quick and cheap, the LoaScope test also facilitates communication between patients and care staff, as well as acceptance of the treatments, by allowing the person tested to see the microfilariae detected in their blood via the mobile telephone.
A new “test and treat” campaign has been introduced by the Ministry of Public Health in Cameroon, in the Soa district (Central region), with support from IRD, the CRFilMT, American teams from the National Institutes of Health (NIH), Michigan State University and The University of Berkeley.