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The objective of this study was to examine nodules from Mexico, Guatemala, and Ecuador collected over a one-year period (2001) to determine the effects of semi-annual ivermectin treatments on Onchocerca volvulus macrofilarial populations. Nodules were sectioned, stained with hematoxylin and eosin, and histologic findings were compared between countries and with historical data prior to the introduction of ivermectin into the region. Nodules from Ecuador had 10 times more dead or moribund worms than the historical control (66.6% versus 6.5%); nodules from patients from Mexico and Guatemala did not differ from the control. More than 80% of the female worms in each country were uninseminated and producing unfertilized oocytes. Nodules containing males differed in each country from the historical control (P < 0.0001), with presence of males ranging from 19.7% in Mexico to 13.6% in Ecuador versus 73% in the control. Nodules with females producing active microfilariae ranged from 7.8% (Mexico) to 2.7% (Ecuador) versus 60% in the historical control (P < 0.0001). Nodules from Ecuador and Mexico were significantly smaller in size than those from Guatemala or historical controls (P < 0.0005). These results depict a deteriorating condition of adult O. volvulus populations in Mexico, Guatemala and Ecuador, indicating that semi-annual ivermectin treatment of 
6 years has had a profound effect on survival and reproduction of this species.
Received March 24, 2004. Accepted for publication April 29, 2004.
Acknowledgments: We thank Dr. Carlos Gonzales-Peralta for administrative assistance during the initial phase of this work and Dr. Richard Collins for reading an earlier version of the manuscript. We acknowledge the technical assistance of Kurtis Hunsberger, Jeff Muston, and Stephanie Benton in the preparation of histologic material.
Financial support: This study was supported by the International Development Bank and the Ministries of Health of Mexico, Guatemala and Ecuador.
Authors’ addresses: Eddie W. Cupp and Mary S. Cupp, Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849-5413, E-mail: ecupp{at}acesag.auburn.edu. Brian O. Duke, River Blindness Foundation, 2 Hillside, Lancaster LA1 1YH, United Kingdom. Charles D. Mackenzie, Filarial Diseases Unit, Michigan State University, East Lansing, MI 48824. Jose Rumbea Guzmán and Juan Carlos Vieira, National Program for the Elimination of Onchocerciasis from Ecuador, Guayaquil, Ecuador. Jorge Mendez-Galvan, Vector-Borne Diseases Program, Secretariat of Health, Mexico City, Mexico. Julio Castro, Vector-Borne Diseases Program, Ministry of Public Health and Social Assistance, Guatemala City, Guatemala. Frank Richards, Epidemiology Branch, Centers for Diseases Control and Prevention, Atlanta, GA 30341. Mauricio Sauerbrey and Alfredo Dominguez, Program for the Elimination of Onchocerciasis in the Americas, Guatemala City, Guatemala. Rob R. Eversole, Biologic Imaging Center, Western Michigan University, Kalamazoo, MI 49008.
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  F. O. Richards Jr., J. Amann, B. Arana, G. Punkosdy, R. Klein, C. Blanco, B. Lopez, C. Mendoza, A. Dominguez, J. Guarner, et al. No Depletion of Wolbachia from Onchocerca volvulus after a Short Course of Rifampin and/or Azithromycin Am J Trop Med Hyg, November 1, 2007; 77(5): 878 - 882. [Abstract] [Full Text] [PDF]
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E. W. CUPP and M. S. CUPP IMPACT OF IVERMECTIN COMMUNITY-LEVEL TREATMENTS ON ELIMINATION OF ADULT ONCHOCERCA VOLVULUS WHEN INDIVIDUALS RECEIVE MULTIPLE TREATMENTS PER YEAR Am J Trop Med Hyg, December 1, 2005; 73(6): 1159 - 1161. [Abstract] [Full Text] [PDF]
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