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) |