Geostatistical modelling enables efficient safety assessment for mass drug administration with ivermectin in Loa loa endemic areas through a combined antibody and LoaScope testing strategy for elimination of onchocerciasis

Abstract

The elimination of onchocerciasis through community-based Mass Drug Administration (MDA) of ivermectin (Mectizan) is hampered by co-endemicity of Loa loa, as individuals who are highly co-infected with Loa loa parasites can suffer serious and occasionally fatal neurological reactions from the drug. The test-and-not-treat strategy of testing all individuals participating in MDA has some operational constraints including the cost and limited availability of LoaScope diagnostic tools. As a result, a Loa loa Antibody (Ab) Rapid Test was developed to offer a complementary way of determining the prevalence of loiasis. We develop a joint geostatistical modelling framework for the analysis of Ab and Loascope data to delineate whether an area is safe for MDA. Our results support the use of a two-stage strategy, in which Ab testing is used to identify areas that, with acceptably high probability, are safe or unsafe for MDA, followed by Loascope testing in areas whose safety status is uncertain. This work therefore contributes to the global effort towards the elimination of onchocerciasis as a public health problem by potentially reducing the time and cost required to establish whether an area is safe for MDA.

Colorimetric and Real-Time Loop-Mediated Isothermal Amplification (LAMP) for Detection of Loa loa DNA in Human Blood Samples

“…Microscopy is time-consuming, labor-intensive, requires skilled laboratory personnel and examines a small amount of blood, making it variable in terms of sensitivity and impractical for mass screening [6]. In an attempt to overcome the problems of traditional microscopy, the LoaScope, a smartphone-based video-microscope has been extensively validated to quantify Loa loa mf in fingerstick blood without the need for sample processing or staining [11][12][13][14][15]. However, LoaScope is calibrated to detect high-density Loa loa microfilaremia, and values under 150 mf/mL are considered unreliable [13,15].…”

“…In an attempt to overcome the problems of traditional microscopy, the LoaScope, a smartphone-based video-microscope has been extensively validated to quantify Loa loa mf in fingerstick blood without the need for sample processing or staining [11][12][13][14][15]. However, LoaScope is calibrated to detect high-density Loa loa microfilaremia, and values under 150 mf/mL are considered unreliable [13,15]. In addition, the specificity on other filariae such as Mansonella spp.…”

Low Diagnostic Performance of Thick Blood Smears of 50 µL in Comparison with Blood Direct Examination of 10 µL and Leukoconcentration Techniques among Loiasis-Suspected Patients with Low Microfilaremia in Gabon, Central Africa, using the STARD-BCLM Guidelines

“…There are other diagnostic tools, such as LoaScope, that have 100.0% sensitivity and 94.0% speci city when compared to a TBS [42]. This test was developed to quickly diagnose (~ 2 minutes) hypermicro laremic loiasis in rural areas during the Mass Drug Administration with ivermectin, where no technical platform is available for the realization and reading of the TBS.…”

“…As an alternative, blood collection on a microscope slide could be performed in the eld, and staining and reading of the TBS-50 would be carried out later in the laboratory. The diagnostic indicators of LoaScope were obtained in comparison with a thick blood smear of the same volume, namely, 2.59 µL [42]. It would be interesting to compare this point-of care with a technique using a high volume of 10 µL, 50 µL or 5 mL of blood.…”