Development and evaluation of an ITS1 "Touchdown" PCR for assessment of drug efficacy against animal African trypanosomosis
Global Alliance for Livestock Veterinary Medicines (GALVmed), Doherty Building, Pentlands Science Park, Bush Loan, Edinburgh EH26 0PZ, United Kingdom; Institute of Tropical Medicine, Nationalestraat 155, B-2000 Antwerp, Belgium; ClinVet International (Pty) Ltd., Uitzigweg, Bainsvlei, Bloemfontein, South Africa
Animal African trypanosomoses (AAT) are caused by flagellated protozoa of the Trypanosoma genus and contribute to considerable losses in animal production in Africa, Latin America and South East Asia. Trypanosoma congolense is considered the economically most important species. Drug resistant T. congolense strains present a threat to the control of AAT and have triggered research into discovery of novel trypanocides. In vivo assessment of trypanocidal efficacy relies on monitoring of treated animals with microscopic parasite detection methods. Since these methods have poor sensitivity, follow-up for up to 100 days after treatment is recommended to increase the chance of detecting recurrent parasitaemia waves. Molecular techniques are more amendable to high throughput processing and are generally more sensitive than microscopic detection, thus bearing the potential of shortening the 100-day follow up period. The study presents a "Touchdown" PCR targeting the internal transcribed spacer 1 of the ribosomal DNA (ITS1 TD PCR) that enables detection and discrimination of different Trypanosoma taxa in a single run due to variations in PCR product sizes. The assay achieves analytical sensitivity of 10 parasites per ml of blood for detection of T. congolense savannah type and T. brucei, and 100 parasites per ml of blood for detection of T. vivax in infected mouse blood. The ITS1 TD PCR was evaluated on cattle experimentally infected with T. congolense during an investigational new veterinary trypanocide drug efficacy study. ITS1 TD PCR demonstrated comparable performance to microscopy in verifying trypanocide treatment success, in which parasite DNA became undetectable in cured animals within two days post-treatment. ITS1 TD PCR detected parasite recrudescence three days earlier than microscopy and had a higher positivity rate than microscopy (84.85% versus 57.58%) in 66 specimens of relapsing animals collected after treatments. Therefore, ITS1 TD PCR provides a useful tool in assessment of drug efficacy against T. congolense infection in cattle. As the assay bears the potential for detection of mixed infections, it may be applicable for drug efficacy studies and diagnostic discrimination of T. vivax and T. congolense against other pathogenic trypanosomes, including T. brucei, T. evansi and T. equiperdum. © 2014 The Authors. Published by Elsevier B.V.
antitrypanosomal agent; internal transcribed spacer 1; ribosome DNA; animal experiment; article; cattle; controlled study; diagnostic test accuracy study; dog; drug efficacy; experimental infection; female; goat; hematocrit centrifugation technique; horse; human; intermethod comparison; male; microscopy; mouse; nagana; nonhuman; parasite identification; polymerase chain reaction; process development; sensitivity analysis; sensitivity and specificity; touchdown polymerase chain reaction; Trypanosoma; Trypanosoma brucei; Trypanosoma congolense; trypanosoma equiperdum; Trypanosoma gambiense; Trypanosoma rhodesiense; trypanosoma theileri; Trypanosoma vivax; Animalia; Bos; Mastigophora (flagellates); Trypanosoma; Trypanosoma brucei; Trypanosoma congolense; Trypanosoma equiperdum; Trypanosoma evansi; Trypanosoma vivax; Trypanozoon; Cattle; ITS1; Touchdown PCR; Trypanosoma congolense; Trypanosoma vivax; Trypanozoon; Animals; Cattle; Cattle Diseases; DNA, Ribosomal Spacer; Drug Resistance; Mice; Polymerase Chain Reaction; Sensitivity and Specificity; Trypanocidal Agents; Trypanosomiasis, African