In Southern Nigeria Loa loa Blood Microfilaria Density is Very Low Even in Areas with High Prevalence of Loiasis: Results of a Survey Using the New LoaScope Technology

Emmanuel Emukah The Carter Center, Owerri, Nigeria;

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Lindsay J. Rakers The Carter Center, Atlanta, Georgia;

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Barminas Kahansim The Carter Center, Jos, Nigeria;

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Emmanuel S. Miri The Carter Center, Jos, Nigeria;

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Bertram E. B. Nwoke Parasitology Department, Imo State University, Owerri, Nigeria;

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Emily Griswold The Carter Center, Atlanta, Georgia;

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Yisa Saka Federal Ministry of Health, Abuja, Nigeria;

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Ifeoma Anagbogu Federal Ministry of Health, Abuja, Nigeria;

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Emmanuel Davies Federal Ministry of Health, Abuja, Nigeria;

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Cephas Ityonzughul The Carter Center, Jos, Nigeria;

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Michael D’Ambrosio University of California Berkeley, Berkeley, California;

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Matthew Bakalar University of California Berkeley, Berkeley, California;

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Daniel A. Fletcher University of California Berkeley, Berkeley, California;

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Thomas Nutman National Institute of Health, Bethesda, Maryland;

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Joseph Kamgno Centre for Research on Filariasis, Yaoundé, Cameroon;
Faculty of Medicine and Biomedical Sciences, University of Yaounde I, Yaoundé, Cameroon

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Frank O. Richards Jr. The Carter Center, Atlanta, Georgia;

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Ivermectin treatment can cause central nervous system adverse events (CNS-AEs) in persons with very high-density Loa loa microfilaremia (≥ 30,000 mf/mL blood). Hypoendemic onchocerciasis areas where L. loa is endemic have been excluded from ivermectin mass drug administration programs (MDA) because of the concern for CNS AEs. The rapid assessment procedure for L. loa (RAPLOA) is a questionnaire survey to assess history of eye worm. If ≥ 40% of respondents report eye worm, this correlates with ≥ 2% prevalence of very high-density loiasis microfilaremia, posing an unacceptable risk of CNS-AEs after MDA. In 2016, we conducted a L. loa study in 110 ivermectin-naïve, suspected onchocerciasis hypoendemic villages in southern Nigeria. In previous RAPLOA surveys these villages had prevalences between 10% and 67%. We examined 10,605 residents using the LoaScope, a cell phone–based imaging device for rapidly determining the microfilaria (mf) density of L. loa infections. The mean L. loa village mf prevalence was 6.3% (range 0–29%) and the mean individual mf count among positives was 326 mf/mL. The maximum individual mf count was only 11,429 mf/mL, and among 2,748 persons sampled from the 28 villages with ≥ 40% RAPLOA, the ≥ 2% threshold of very high Loa mf density could be excluded with high statistical confidence (P < 0.01). These findings indicate that ivermectin MDA can be delivered in this area with extremely low risk of L. loa–related CNS-AEs. We also concluded that in Nigeria the RAPLOA survey methodology is not predictive of ≥ 2% prevalence of very high-density L. loa microfilaremia.

Author Notes

Address correspondence to Lindsay J. Rakers, The Carter Center, 453 Freedom Parkway, One Copenhill Ave., Atlanta, GA 30307. E-mail: lindsay.rakers@cartercenter.org

Financial support: D. A. F. reports grants from Bill & Melinda Gates Foundation, during the conduct of the study; In addition, Fletcher has a patent High Numerical Aperture Telemicroscopy Apparatus (US Patents 8,743,194 and 8,786,695) licensed to Thermo Fisher Scientific; CellScope, Inc., and a patent Automated Hardware and Software for Mobile Microscopy (US Patent pending). M. D. reports grants from Bill & Melinda Gates Foundation, during the conduct of the study; In addition, D’Ambrosio has a patent Automated Hardware and Software for Mobile Microscopy (US Patent pending).

Authors’ addresses: Emmanuel Emukah, Carter Center, Owerri, Nigeria, E-mail: emmanuel.emukah@cartercenter.org. Lindsay J. Rakers, Emily Griswold, and Frank O. Richards, Carter Center, Atlanta, GA, E-mails: lindsay.rakers@cartercenter.org, emily.griswold@cartercenter.org, and frank.richards@cartercenter.org. Barminas Kahansim, Emmanuel S. Miri, and Cephas Ityonzughul, Carter Center, Jos, Nigeria, E-mails: barminas.kahansim@cartercenter.org, emmanuel.miri@cartercenter.org, and cephas.Ityonzughul@cartercenter.org. Bertram E. B. Nwoke, Parasitology Department, Imo State University, Owerri, Nigeria, E-mail: bebndie@yahoo.com. Yisa Saka, Ifeoma Anagbogu, and Emmanuel Davies, Federal Ministry of Health, Abuja, Nigeria, E-mails: yisaasaka@yahoo.com, ifechuba@yahoo.co.uk, and enimed2003@yahoo.com. Michael D’Ambrosio, Matthew Bakalar, and Daniel A. Fletcher, University of Berkeley, Berkeley, CA, E-mails: mdambrosio@berkeley.edu, matthew.bakalar@gmail.com, and fletch@berkeley.edu. Thomas Nutman, National Institute of Health, Bethesda, MD, E-mail: tnutman@niaid.nih.gov. Joseph Kamgno, Centre for Research on Filariasis, Yaoundé, Cameroon and Faculty of Medicine and Biomedical Sciences, University of Yaounde I, Yaoundé, Cameroon, E-mail: kamgno@crfilmt.org.

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