• View in gallery
    Figure 1.

    Location of the former onchocerciasis hyperdemic communities, province of Esmeraldas, Ecuador.

  • 1.

    World Health Organization, 2017. Progress report on the elimination of human onchocerciasis, 2016–2017. Weekly Epidemiol Rec 45: 681700.

    • Search Google Scholar
    • Export Citation
  • 2.

    Sauerbrey M, Rakersb LJ, Richards FO Jr., 2018. Progress toward elimination of onchocerciasis in the Americas. Int Health 10: i71i78.

  • 3.

    Lovato R, Guevara A, Guderian R, Proaño R, Unnasch T, Criollo H, Hassan HK, Mackenzie CD, 2014. Interruption of infection transmission in the onchocerciasis focus of Ecuador leading to the cessation of ivermectin distribution. PLoS Negl Trop Dis 8: e2821.

    • Search Google Scholar
    • Export Citation
  • 4.

    Guevara Á, Lovato R, Proaño R, Rodriguez-Perez MA, Unnasch T, Cooper PJ, Guderian RH, 2018. Elimination of onchocerciasis in Ecuador: findings of post-treatment surveillance. Parasit Vectors 11: 265.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5.

    WHO, 2016. Guidelines for Stopping Mass Drug Administration and Verifying Elimination of Human Onchocerciasis. Geneva, Switzerland: World Health Organization. WHO/HTM/NTD/PCT/2016.1.

    • Search Google Scholar
    • Export Citation
  • 6.

    Vieira JC, Cooper PJ, Lovato R, Mancero T, Rivera J, Proaño R, López AA, Guderian RH, Guzmán JR, 2007. Impact of long-term treatment of onchocerciasis with ivermectin in Ecuador: potential for elimination of infection. BMC Med 5: 9.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7.

    Lobos E, Weiss N, Karam M, Taylor HR, Ottesen EA, Nutman TB, 1991. An immunogenic Onchocerca volvulus antigen: a specific and early marker of infection. Science 251: 16031605.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 8.

    Lipner EM, Dembele N, Souleymane S, Alley WS, Prevots DR, Toe L, Boatin B, Weil GJ, Nutman TB, 2006. Field applicability of a rapid-format anti-Ov-16 antibody test for the assessment of onchocerciasis control measures in regions of endemicity. J Infect Dis 194: 216221.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9.

    Fernández-Santos NA, Unnasch TR, Rodríguez-Luna IC, Prado-Velasco FG, Adeniran AA, Martínez-Montoya H, Rodríguez-Pérez MA, 2020. Post-elimination surveillance in formerly onchocerciasis endemic focus in southern Mexico. PLoS Negl Trop Dis 30: e0008008.

    • Search Google Scholar
    • Export Citation
Past two years Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 895 263 10
PDF Downloads 482 180 7
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

 

 

Use of Ov16-Based Serology for Post-Elimination Surveillance of Onchocerciasis in Ecuador

Ángel GuevaraInstituto de Biomedicina, Carrera de Medicina, Universidad Central, Quito, Ecuador;

Search for other papers by Ángel Guevara in
Current site
Google Scholar
PubMed
Close
,
Esteban SalazarInstituto de Biomedicina, Carrera de Medicina, Universidad Central, Quito, Ecuador;
Distrito Calderón Ministerio de Salud Pública del Ecuador, Quito, Ecuador;
Infectious and Tropical Diseases Group (e-INTRO), IBSAL-CIETUS (Biomedical Research Institute of Salamanca-Research Centre for Tropical Diseases at the University of Salamanca), Faculty of Pharmacy, University of Salamanca, Salamanca, Spain;

Search for other papers by Esteban Salazar in
Current site
Google Scholar
PubMed
Close
,
Yosselin VicuñaInstituto de Biomedicina, Carrera de Medicina, Universidad Central, Quito, Ecuador;

Search for other papers by Yosselin Vicuña in
Current site
Google Scholar
PubMed
Close
,
Hassan K. HassanCenter for Global Health Infectious Diseases, University of South Florida College of Public Health, Tampa, Florida;

Search for other papers by Hassan K. Hassan in
Current site
Google Scholar
PubMed
Close
,
Antonio MuroInfectious and Tropical Diseases Group (e-INTRO), IBSAL-CIETUS (Biomedical Research Institute of Salamanca-Research Centre for Tropical Diseases at the University of Salamanca), Faculty of Pharmacy, University of Salamanca, Salamanca, Spain;

Search for other papers by Antonio Muro in
Current site
Google Scholar
PubMed
Close
,
Ronald GuderianHospital Vozandes, Quito, Ecuador;

Search for other papers by Ronald Guderian in
Current site
Google Scholar
PubMed
Close
,
Philip J. CooperFacultad de Ciencias Médicas de la Salud y la Vida, Universidad Internacional del Ecuador, Quito, Ecuador;
Institute of Infection and Immunity, St. George’s University of London, London, United Kingdom

Search for other papers by Philip J. Cooper in
Current site
Google Scholar
PubMed
Close
, and
Thomas R. UnnaschCenter for Global Health Infectious Diseases, University of South Florida College of Public Health, Tampa, Florida;

Search for other papers by Thomas R. Unnasch in
Current site
Google Scholar
PubMed
Close

Onchocerciasis is a blinding disease caused by the filarial parasite Onchocerca volvulus, with a worldwide distribution. Onchocerciasis has been targeted for regional elimination based on annual and semiannual mass drug administration (MDA) with ivermectin in endemic communities over several years. This strategy in Ecuador led to the interruption of transmission and suspension of ivermectin MDA in 2009 with certification of elimination in 2014. In the present study, we analyzed sera collected in 2018 from 123 children aged 5–9 years from formerly hyperendemic communities in the Esmeraldas focus, Ecuador, for the presence of antibodies to Ov16 antigen. All samples were negative, indicating no evidence of transmission since MDA was stopped. Ov16-based serology offers an economic and practical alternative for measuring vector infectivity for post-certification surveillance in formerly endemic countries where expertise and capacity to reliably measure fly infectivity rates are costly to maintain.

Onchocerciasis, caused by the filarial parasite Onchocerca volvulus, infects an estimated 17 million people in endemic areas of Africa, the Americas, and the Eastern Mediterranean region, and 205 million people are considered to be at risk of infection.1 Onchocerciasis is a neglected tropical disease targeted for regional elimination and eventual global elimination.1 In Latin America, a strategy of community-based periodic mass drug administrations (MDAs) with ivermectin has led to certification of elimination in endemic foci in Colombia, Ecuador, Mexico, and Guatemala, although transmission is still active in an isolated rain forest focus on the Brazil–Venezuela border.2 In Ecuador, annual or semiannual ivermectin was administered to endemic communities in the endemic foci in Esmeraldas Province from 1991 to 2009 when treatments were stopped following interruption of transmission.3,4 Posttreatment surveillance (PTS) of black flies by PCR to detect O. volvulus DNA (O-150 PCR) in 2012 showed no evidence of active transmission,4 and elimination of onchocerciasis in Ecuador was certified in 2014. Measurement of infectivity rates in vectors by O-150 PCR is considered the key parameter for the detection of interruption of and resurgence in transmission, but useful also is the evaluation of exposure to O. volvulus by measurement of antibodies to an O. volvulus–specific antigen, Ov16.5

In the present study carried out in June 2018, almost 4 years after certification of elimination, we collected 123 blood samples from children aged 5–9 years living in four formerly hyperendemic communities for onchocerciasis in Esmeraldas Province in Ecuador (Figure 1): Zapallo Grande (n = 34), San Miguel (n = 24), El Tigre (n = 30), and Corriente Grande (n = 35). The mean age of the 123 children sampled was 7.5 years (range 5–9 years), and 53.7% were male.6 Sera were tested for the presence of IgG4 antibodies to Ov16 antigen using an ELISA test as described.7,8 In brief, ELISA plates were coated with 100 μL of 2.0 μg/mL Ov16 antigen. Between each step, the plates were washed with phosphate-buffered saline containing 0.1% Tween 20 (PBS-T), used also as diluent. Plate wells were incubated sequentially with 50 μL of sera (diluted 1/50 in PBS-T containing 5% [w/v] bovine serum albumin) or negative or positive controls and incubated at room temperature (RT) for 2 hours. Then, the plates were incubated with antihuman IgG4–biotin conjugate (1:1,000) for 1 hour at RT and streptavidin–alkaline phosphatase (1:2,000) for 1 hour at RT. The plates were developed with p-nitrophenyl phosphate until the positive control had reached an optical density (OD) of 1.1. Reactions were stopped with 25 μL of 3 M NaOH and read after 5 minutes at 405 nm. All samples were tested in duplicate and considered putatively positive if the OD in duplicate wells differed by less than 10% and the mean OD of the wells from the sample was equal to or greater than the signal obtained from a 1/1,280 dilution of a pool of known positive sera. Putatively positive samples were retested using the same procedure. A sample was classified as a confirmed positive if it gave a positive result in the confirmatory assay and in the initial assay. None of the 123 samples were positive for Ov16-specific IgG4 antibodies (95% CI: 0–3).

Figure 1.
Figure 1.

Location of the former onchocerciasis hyperdemic communities, province of Esmeraldas, Ecuador.

Citation: The American Journal of Tropical Medicine and Hygiene 103, 4; 10.4269/ajtmh.20-0082

Ov16-based serological assays in young children can be used to monitor resurgence of transmission of O. volvulus: young children born following suppression and interruption of transmission in black fly vectors would be expected to be negative for Ov16 antibodies. This study, carried out in formerly hyperendemic communities for onchocerciasis in Ecuador, which were the last to receive ivermectin MDA and which would be the first in which resumption of transmission of onchocerciasis would be detected, confirms the absence of O. volvulus transmission in these communities for at least 9 years (i.e., since the oldest child was born in 2009 around the time that ivermectin MDA was stopped in these communities). These findings are consistent with previous serological studies using the same assay in the Esmeraldas focus, where large samples of children aged up to 15 years were shown to be negative up to 2008.3

Current guidelines for the use of the Ov16 assay are to confirm the interruption of transmission as part of PTS when the results of fly infectivity rates show levels close to the threshold for the interruption of transmission. Recommendations for post-elimination surveillance include periodic testing of fly infectivity by O-150 PCR until elimination is verified in all endemic countries in the same region.5 However, conducting black fly collections and O-150 PCR following certification of elimination is a challenge for most formerly endemic countries including Ecuador with multiple competing demands for scarce health resources: maintaining such capacity requires continued investment in infrastructure and personnel. In the case of the latter, effective vector surveillance requires experience and expertise as well as historical knowledge of where and when to sample vectors to detect transmission. In the specific case of Ecuador, following certification of elimination, the program’s entomological expertise was lost because of reassignment or loss of experienced staff and lack of an assigned budget for post-certification activities. The measurement of Ov16 antibodies offers potential advantages over studies of fly infectivity. First, it is much less costly and time-consuming to collect, transport, and test sera from schoolchildren than to conduct black fly collections that require maintaining specialized teams in isolated settings for prolonged periods. Furthermore, Ov16-based surveillance is not dependent on maintaining highly specialized personnel and infrastructure. Finally, measures of immunologic exposure by detection of specific IgG4 antibodies may be a more sensitive measure to detect indirect transmission occurring over extended periods (particularly when transmission rates are low) than point estimates of black fly infectivity that may be greatly affected by vector–parasite variability in terms of time and site of sampling. The only previous report of post-certification surveillance was from a former focus in southern Chiapas in Mexico in which ≥ 60% of inhabitants of three communities were examined annually for onchocercomas (with surgical removal of suspicious masses) for 4 years after certification,9 another setting where pool screening of black flies was presumably not viable: skin snips were taken from contacts of the only person found to have a viable female adult and from young children in the three communities who had never received ivermectin—the snips were examined by microscopy and O-150 PCR, and were found to be negative. The detection and removal of onchocercomas is time-consuming and expensive and carries the risk of complications relating to a surgical procedure. Ov16-based surveillance is, thus, likely to be preferable as well as being a more sensitive tool for monitoring recrudescence of transmission, albeit indirect, because many adult females are not found in palpable nodules and because of the delay between infection and nodule formation.

In conclusion, we have used Ov16-based serology to monitor potential resurgence of transmission of O. volvulus in formerly hyperendemic communities following the certification of elimination of onchocerciasis in Ecuador. Our data show no evidence of O. volvulus transmission since 2009 when MDA was stopped. We believe that Ov16-based surveillance offers practical advantages over measurements of vector infectivity for post-certification surveillance in resource-limited settings.

REFERENCES

  • 1.

    World Health Organization, 2017. Progress report on the elimination of human onchocerciasis, 2016–2017. Weekly Epidemiol Rec 45: 681700.

    • Search Google Scholar
    • Export Citation
  • 2.

    Sauerbrey M, Rakersb LJ, Richards FO Jr., 2018. Progress toward elimination of onchocerciasis in the Americas. Int Health 10: i71i78.

  • 3.

    Lovato R, Guevara A, Guderian R, Proaño R, Unnasch T, Criollo H, Hassan HK, Mackenzie CD, 2014. Interruption of infection transmission in the onchocerciasis focus of Ecuador leading to the cessation of ivermectin distribution. PLoS Negl Trop Dis 8: e2821.

    • Search Google Scholar
    • Export Citation
  • 4.

    Guevara Á, Lovato R, Proaño R, Rodriguez-Perez MA, Unnasch T, Cooper PJ, Guderian RH, 2018. Elimination of onchocerciasis in Ecuador: findings of post-treatment surveillance. Parasit Vectors 11: 265.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5.

    WHO, 2016. Guidelines for Stopping Mass Drug Administration and Verifying Elimination of Human Onchocerciasis. Geneva, Switzerland: World Health Organization. WHO/HTM/NTD/PCT/2016.1.

    • Search Google Scholar
    • Export Citation
  • 6.

    Vieira JC, Cooper PJ, Lovato R, Mancero T, Rivera J, Proaño R, López AA, Guderian RH, Guzmán JR, 2007. Impact of long-term treatment of onchocerciasis with ivermectin in Ecuador: potential for elimination of infection. BMC Med 5: 9.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7.

    Lobos E, Weiss N, Karam M, Taylor HR, Ottesen EA, Nutman TB, 1991. An immunogenic Onchocerca volvulus antigen: a specific and early marker of infection. Science 251: 16031605.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 8.

    Lipner EM, Dembele N, Souleymane S, Alley WS, Prevots DR, Toe L, Boatin B, Weil GJ, Nutman TB, 2006. Field applicability of a rapid-format anti-Ov-16 antibody test for the assessment of onchocerciasis control measures in regions of endemicity. J Infect Dis 194: 216221.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9.

    Fernández-Santos NA, Unnasch TR, Rodríguez-Luna IC, Prado-Velasco FG, Adeniran AA, Martínez-Montoya H, Rodríguez-Pérez MA, 2020. Post-elimination surveillance in formerly onchocerciasis endemic focus in southern Mexico. PLoS Negl Trop Dis 30: e0008008.

    • Search Google Scholar
    • Export Citation

Author Notes

Address correspondence to Ángel Guevara, Instituto de Biomedicina, Carrera de Medicina, Universidad Central del Ecuador, Iquique N14-121 y Sodiro, Quito 170136, Ecuador. E-mail: agguevara@uce.edu.ec

Authors’ addresses: Ángel Guevara and Yosselin Vicuña, Instituto de Biomedicina, Carrera de Medicina, Universidad Central del Ecuador, Quito, Ecuador, E-mails: agguevara@uce.edu.ec and yavicuna@uce.edu.ec. Esteban Salazar, Distrito Calderón Ministerio de Salud Pública del Ecuador, Quito, Ecuador, E-mail: essalazar15@gmail.com. Hassan K. Hassan and Thomas R. Unnasch, Center for Global Health Infectious Diseases, University of South Florida College of Public Health, Tampa, FL, E-mails: hhassan@usf.edu and tunnasch@usf.edu. Antonio Muro, Infectious and Tropical Diseases Group (e-INTRO), IBSAL-CIETUS (Biomedical Research Institute of Salamanca-Research Centre for Tropical Diseases at the University of Salamanca), Faculty of Pharmacy, University of Salamanca, Salamanca, Spain, E-mail: ama@usal.es. Ronald Guderian, Hospital Vozandes, Quito, Ecuador, E-mail: r.guderian@frontier.com. Philip J. Cooper, Facultad de Ciencias Médicas, de la Salud y la Vida, Universidad Internacional del Ecuador, Quito, Ecuador, and Institute of Infection and Immunity, St George’s University of London, London, United Kingdom, E-mail: pcooper@sgul.ac.uk.

Save