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Table 2 Parameters used in the SEIRS + PI transmission model for B. melitensis

From: Vaccination control programs for multiple livestock host species: an age-stratified, seasonal transmission model for brucellosis control in endemic settings

Parameter (symbol) Equation/value Source
Age when susceptible to infection (a1) 9 months [3]
Age when infectious abortion (due to Brucellosis) possible (a2) 12 months Estimated from earliest conception date according to production data and earliest stage of pregnancy during which abortions due to brucellosis occur [3, 17, 18].
Age of death (a3) Sheep: 39 months Mean values of results of a survey of fifteen farmers in Jordan by co-author I. Musallam.
Cattle: 51.36 months
Duration of infectiousness (d1) 4 months Estimated from period that bacteria are shed plus maximum survival of bacteria in the environment [5, 19].
Duration of protective immunity (d2) 8 months Variability across reports and variability between animals [4].
Death and birth rate (m) 12/a3 (birth rate in sheep was adjusted for seasonality) Calculated
Annual rate at which animals mature from “young” to “juvenile” (m1) 12/a1 Calculated
Annual rate at which animals mature from “juvenile” to “adult” (m2) 12/a2 Calculated
Annual rate of loss of infectiousness (v) 12/d1 calculated
Annual rate of loss of immunity (g) 12/d2 calculated
Vaccine effectiveness (VE) Before intervention: 0. After intervention: 0.6, 0.8 and 0.9 Vaccine efficacy in experimental conditions: 80 % in ewes infected during first pregnancy and 62 % in ewes infected during second pregnancy.
Probability that a newborn is persistently infected given that the mother is seropositive (p) 0.01 [3]
Annual rate of abortion/giving birth (v) Cows: 0.26 Estimated from pregnancies per animal per year, recorded during seroprevalence study (statistical analysis described below)
Sheep: 0.33
Rate at which animals recover from infection (g) 12/d1 calculated
Rate at which animals lose protective immunity (z) 12/d2 Calculated
Ratio of cows: sheep on a typical seropositive farm 2.73 Estimated from data recorded during seroprevalence study (statistical analysis described below)