Interruption of infection transmission in the onchocerciasis focus of Ecuador leading to the cessation of ivermectin distribution.
BACKGROUND
A clinically significant endemic focus of onchocerciasis existing in Esmeraldas Province, coastal Ecuador has been under an ivermectin mass drug administration program since 1991. The main transmitting vector in this area is the voracious blackfly, Simulium exiguum. This paper describes the assessments made that support the decision to cease mass treatment.


RESULTS
Thirty-five rounds of ivermectin treatment occurred between 1991-2009 with 29 of these carrying >85% coverage. Following the guidelines set by WHO for ceasing ivermectin distribution the impact on parasite transmission was measured in the two vector species by an O-150 PCR technique standard for assessing for the presence of Onchocerca volvulus. Up to seven collection sites in three major river systems were tested on four occasions between 1995 and 2008. The infectivity rates of 65.0 (CI 39-101) and 72.7 (CI 42-116) in 1995 dropped to zero at all seven collection sites by 2008. Assessment for the presence of antibodies against O. volvulus was made in 2001, 2006, 2007 and 2008 using standard ELISA assays for detecting anti-Ov16 antibodies. None of total of 1810 children aged 1-15 years (between 82 and 98% of children present in the surveyed villages) tested in the above years were found to be carrying antibodies to this antigen. These findings were the basis for the cessation of mass drug treatment with ivermectin in 2009.


CONCLUSIONS
This fulfillment of the criteria for cessation of mass distribution of ivermectin in the only known endemic zone of onchocerciasis in Ecuador moves the country into the surveillance phase of official verification for national elimination of transmission of infection. These findings indicate that ivermectin given twice a year with greater than 85% of the community can move a program to the final stages of verification of transmission interruption.
Ecuadorian Onchocerciasis Program, Ministerio de Salud Pública, Quito, Ecuador.
Raquel
R
Lovato
Centro de Biomedicina, Laboratorio de Parasitología Molecular, Escuela de Medicina, Universidad Central del Ecuador, Quito, Ecuador.
Angel
A
Guevara
Hospital Vozandes, Quito, Ecuador.
Ronald
R
Guderian
Ecuadorian Onchocerciasis Program, Ministerio de Salud Pública, Quito, Ecuador.
Roberto
R
Proaño
GHIDR Program, Department of Global Health, College of Public Health, University of South Florida, Tampa, Florida, United States of America.
Thomas
T
Unnasch
Centro de Biomedicina, Laboratorio de Parasitología Molecular, Escuela de Medicina, Universidad Central del Ecuador, Quito, Ecuador.
Hipatia
H
Criollo
GHIDR Program, Department of Global Health, College of Public Health, University of South Florida, Tampa, Florida, United States of America.
Hassan K
HK
Hassan
Department of Pathobiology and Diagnostic Investigation, Michigan State University, East Lansing, Michigan, United States of America.
Charles D
CD
Mackenzie
D000293:Adolescent; D000818:Animals; D000909:Antibodies, Helminth / Q000097:blood; D002648:Child; D002675:Child, Preschool; D004484:Ecuador / Q000453:epidemiology; D005369:Filaricides / Q000008:administration & dosage*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007303:Insect Vectors / Q000469:parasitology*; D007559:Ivermectin / Q000008:administration & dosage*; D009855:Onchocerciasis / Q000453:epidemiology / Q000469:parasitology / Q000628:therapy / Q000635:transmission*; D011314:Preventive Health Services / Q000379:methods; D012843:Simuliidae / Q000469:parasitology*
D000909:Antibodies, Helminth; D005369:Filaricides; D007559:Ivermectin