title: Transition models to assess risk factors for new and persistent trypanosome infections in cattle-analysis of longitudinal data from the Ghibe Valley, southwest Ethiopia.
abstract: The objective of this study was to apply transition models to distinguish between factors associated with both incident and persistent trypanosome infections. Data collected from 1561 cattle were analyzed from a long-term study involving 8 herds in which both trypanosome infections (a total of 56,931 cattle sampling-months) and tsetse (Glossina spp.) challenge were monitored monthly from March 1986 to March 1998. Both pour-on and insecticide-target tsetse control programs and mass treatment with diminazene aceturate before tsetse control were associated with significant decreases in both incidence and persistence of trypanosome infection relative to noncontrol periods, as were seasonal and sex effects. The magnitudes of the effects were, however, often different for new and persistent infections. For persistence of infection, there were 2 trends. In general, the duration of infection increased during the study, despite the regular treatment with diminazene aceturate. The transition model had 2 major benefits. The first was to identify an increasing duration of infections with time, taking into account other factors associated with increasing infection risk. The second was to highlight different patterns in the effects of certain factors on new and persistent trypanosome infections.
authors.affiliation: Department of Population Medicine and Diagnostic Sciences, S3119 Schurmann Hall, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA. yhs2@cornell.edu
authors.forename: Y H
authors.initials: YH
authors.lastname: Schukken
authors.forename: G
authors.initials: G
authors.lastname: van Schaik
authors.forename: J J
authors.initials: JJ
authors.lastname: McDermott
authors.forename: G J
authors.initials: GJ
authors.lastname: Rowlands
authors.forename: S M
authors.initials: SM
authors.lastname: Nagda
authors.forename: Woudyalew
authors.initials: W
authors.lastname: Mulatu
authors.forename: G D M
authors.initials: GD
authors.lastname: d'Ieteren
mesh_terms: D000367:Age Factors; D000818:Animals; D002417:Cattle; D004133:Diminazene / Q000008:administration & dosage / Q000031:analogs & derivatives*; D005002:Ethiopia / Q000453:epidemiology; D005260:Female; D015994:Incidence; D007300:Insect Control / Q000379:methods; D007303:Insect Vectors / Q000254:growth & development* / Q000469:parasitology; D008137:Longitudinal Studies; D008297:Male; D008954:Models, Biological; D016017:Odds Ratio; D015995:Prevalence; D012008:Recurrence; D012307:Risk Factors; D012621:Seasons; D012680:Sensitivity and Specificity; D012737:Sex Factors; D014344:Trypanocidal Agents / Q000008:administration & dosage; D014353:Trypanosomiasis, African / Q000453:epidemiology / Q000517:prevention & control / Q000662:veterinary; D014354:Trypanosomiasis, Bovine / Q000453:epidemiology* / Q000517:prevention & control; D014370:Tsetse Flies / Q000254:growth & development* / Q000469:parasitology
chemical_list: D014344:Trypanocidal Agents; C003915:diminazene aceturate; D004133:Diminazene