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LACK OF RESISTANCE AFTER RE-EXPOSURE OF CATTLE CURED OF ONCHOCERCA OCHENGI INFECTION WITH OXYTETRACYCLINE

Although vector control and ivermectin chemotherapy have led to a dramatic reduction in the incidence of river blindness (onchocerciasis), there is a consensus that additional control tools are required to sustain and extend this success. The recognition of endosymbiotic bacteria (Wolbachia) in filariae and their targeting by antibiotics constitutes the most significant and practicable opportunity for a macrofilaricidal therapy in the short-to-medium-term. Using Onchocerca ochengi in cattle, an analog of human onchocerciasis, we have previously shown that oxytetracycline is macrofilaricidal, and protective immunity exists naturally in a subset of animals termed putatively immune. Here, we report that although 24 weeks of weekly oxytetracycline treatment eliminated adult worms, cured animals remained susceptible to re-infection by natural challenge when compared with putatively immune cattle. However, their susceptibility was not significantly different from that of concurrently exposed, heavily infected animals. Thus, cattle cured by oxytetracycline are neither hypo-susceptible nor hyper-susceptible.

Received July 27, 2006. Accepted for publication September 17, 2006.

Acknowledgments: We thank the herdsmen, watchmen, and technical staff of the Institut de Recherche Agricole pour le Développement for invaluable assistance. We are grateful to Pfizer (Tadworth, United Kingdom) and Merial (Lyon, France) for donating Terramycin® LA and Cymelarsan® free of charge, respectively.

Financial support: This study was supported by the European Union (INCO-DEV contract no. ICA4-CT-1999-10002). Leo M. Njongmeta received a research training grant from WHO-TDR (No. M8/181/4/N.194).

^* Address correspondence to Alexander J. Trees, Liverpool School of Tropical Medicine and Faculty of Veterinary Science, University of Liverpool, Liverpool, L3 5QA, United Kingdom. E-mail: trees{at}liv.ac.uk

Authors’ addresses: Charles K. Nfon, Benjamin L. Makepeace, Leo M. Njongmeta, and Alexander J. Trees, Liverpool School of Tropical Medicine and Faculty of Veterinary Science, University of Liverpool, Liverpool, L3 5QA, United Kingdom, Telephone: 44-151-705-3118, Fax: 44-151-705-3373, E-mails: nfonck{at}yahoo.fr, blm1{at}liv.ac.uk, lmnjongm{at}utmb.edu, and trees{at}liv.ac.uk. Vincent N. Tanya, Institut de Recherche Agricole pour le Développement, Regional Centre of Wakwa, BP 65 Ngaoundéré, Cameroon, Telephone: 237-223-7720, E-mail: vntanya{at}yahoo.com.