Volume 68, Issue 2
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645


The prevalence of infected and infective black flies was estimated by pool screen polymerase chain reaction (PCR) amplification in the three river basins in Ecuador endemic for onchocerciasis. Mass distribution of ivermectin (Mectizan™) resulted in dramatic declines in the prevalence of infected and infective flies. In the Rio Santiago river basin, no infections were detected, suggesting that transmission had ceased. The ratio of infected to infective flies in was 10-fold lower than the corresponding ratio for , suggesting that is a more-competent vector for than . However, the prevalence of infective flies in the two species was not different, suggesting that may play an important vectorial role where it is the dominant human-biting species. The data demonstrate that pool screen PCR is an efficient way to monitor transmission in areas subject to control, and to certify an area as free of transmission


Article metrics loading...

Loading full text...

Full text loading...



  1. Richards FO, Boatin B, Sauerbrey M, Seketeli A, 2001. Control of onchocerciasis today: status and challenges. Trends Parasitol 17 : 558–563.
  2. Hougard JM, Alley ES, Yameogo L, Dadzie KY, Boatin BA, 2001. Eliminating onchocerciasis after 14 years of vector control: a proved strategy. J Infect Dis 184 : 497–503.
  3. Walsh JF, Davies JB, LeBerre R, Garms R, 1978. Standardization of criteria for assessing the effects of Simulium control in onchocerciasis control programs. Trans R Soc Trop Med Hyg 72: 675–676.
  4. Garms R, 1975. Observations on filarial infections and parous rates of anthropophilic blackflies in Guatemala, with reference to the transmission of Onchocerca volvulus. Tropenmed Parasitol 26 : 169–182.
  5. Cheke RA, Avissey HS, Sowah SA, Walsh JF, Garms R, 1992. The vectorial efficiency of Simulium yahense populations in south-eastern Ghana. Trop Med Parasitol 43 : 62–64.
  6. Cheke RA, Denke AM, 1988. Anthropophily, zoophily and roles in onchocerciasis transmission of the Djodji form of Simulium sanctipauli and S. squamosum in a forest zone of Togo. Trop Med Parasitol 39 : 123–127.
  7. Meredith SEO, Lando G, Gbakima AA, Zimmerman PA, Unnasch TR, 1991. Onchocerca volvulus: application of the polymerase chain reaction to identification and strain differentiation of the parasite. Exp Parasitol 73 : 335–344.
  8. Zimmerman PA, Dadzie KY, DeSole G, Remme J, Alley ES, Unnasch TR, 1992. Onchocerca volvulus DNA probe classification correlates with epidemiological patterns of blindness. J Infect Dis 165: 964–968.
  9. Zimmerman PA, Toè L, Unnasch TR, 1993. Design of onchocerca DNA probes based upon analysis of a repeated sequence family. Mol Biochem Parasitol 58 : 259–269.
  10. Katholi CR, Toé L, Merriweather A, Unnasch TR, 1995. Determining the prevalence of Onchocerca volvulus infection in vector populations by PCR screening of pools of black flies. J Infect Dis 172: 1414–1417.
  11. Yamèogo L, Toè L, Hougard J-M, Boatin BA, Unnasch TR, 1999. Pool Screen PCR for estimating the prevalence of Onchocerca volvulus infection in Simulium damnosum sensu lato: results of a field trial in an area subject to successful vector control. Am J Trop Med Hyg 60 : 124–128.
  12. Rodríguez-Pérez MA, Danis-Lozano R, Rodríguez MH, Unnasch TR, Bradley JE, 1999. Detection of Onchocerca volvulus infection in Simulium ochraceum sensu lato: comparison of a PCR assay and fly dissection in a Mexican hypoendemic community. Parasitology 119 : 613–619.
  13. Guderian RH, Shelley AJ, 1992. Onchocerciasis in Ecuador: the situation in 1989. Mem Inst Oswaldo Cruz 87 : 405–415.
  14. Collins RC, Lehmann T, Vieira Garcia JC, Guderian RH, 1995. Vector competence of Simulium exiguum for Onchocerca volvulus: implications for the epidemiology of onchocerciasis. Am J Trop Med Hyg 52 : 213–218.
  15. Arzube M, Shelley AJ, 1990. Seasonal variation in onchocerciasis transmission in the Santiago focus of Ecuador. Trop Med Parasitol 41 : 286–288.
  16. Shelley AJ, Arzube M, 1985. Studies on the biology of Simuliidae (Diptera) at the Santiago onchocerciasis focus in Ecuador, with special reference to the vectors and disease transmission. Trans R Soc Trop Med Hyg 79: 328–338.
  17. Guderian RH, Anselmi M, Espinel M, Mancero T, Rivadeneira G, Proano R, Calvopina HM, Vieira JC, Cooper PJ, 1997. Successful control of onchocerciasis with community-based Mectizan™ distribution in the Rio Santiago focus in Ecuador. Trop Med Int Health 2 : 982–988.
  18. Blanks J, Richards F, Beltran F, Collins R, Alvarez E, Zea Flores G, Bauler B, Cedillos R, Heisler M, Brandling-Bennett D, Baldwin W, Bayona M, Klein R, Jacox M, 1998. The Onchocerciasis Elimination Program for the Americas: a history of partnership. Rev Panam Salud Publica 3 : 367–374.
  19. Davies JB, Seketeli A, Walsh JF, Barro T, Sawadogo R, 1981. Studies on biting Simulium damnosum s.l. at a breeding site in the Onchocerciasis Control Programme area during and after an interruption of insecticidal treatments. Trop Med Parasitol 32 : 17–24.
  20. Unnasch TR, Meredith SEO, 1996. The use of degenerate primers in conjunction with strain and species oligonucleotides to classify Onchocerca volvulus. Clapp JP, ed. Species Diagnostic Protocols: PCR and Other Nucleic Acid Methods. Totowa, NJ: Humana Press, 293–303.
  21. Woodring JL, Higgs S, Beaty BJ, 1996. Natural cycles of vector-borne pathogens. Beaty BJ, Marquardt WC, eds. The Biology of Disease Vectors. Niwot, CO: University Press of Colorado, 51–72.
  22. Trpis M, Childs JE, Fryauff DJ, Greene BM, Williams PN, Munoz BE, Pacque MC, Taylor HR, 1990. Effect of mass treatment of a human population with Mectizan™ on transmission of Onchocerca volvulus by Simulium yahense in Liberia, West Africa. Am J Trop Med Hyg 42 : 148–156.
  23. Cupp EW, Ochoa JO, Collins RC, Cupp MS, Gonzales-Peralta C, Castro J, Zea-Flores G, 1992. The effects of repetitive community-wide Mectizan™ treatment on transmission of Onchocerca volvulus in Guatemala. Am J Trop Med Hyg 47 : 170–180.
  24. Basanez MG, Remme JH, Alley ES, Bain O, Shelley AJ, Medley GF, Anderson RM, 1995. Density-dependent processes in the transmission of human onchocerciasis: relationship between the numbers of microfilariae ingested and successful larval development in the simuliid vector. Parasitology 110 : 409–427.
  25. Reid GD, 1994. Structure and function of the cibarial armature in Simuliidae. Med Vet Entomol 8 : 295–301.

Data & Media loading...

  • Received : 05 Jun 2002
  • Accepted : 22 Jul 2002

Most Cited This Month

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error