Table 1.
Epidemiological parameters for the transmission of African horse sickness virus (AHSV). BTV, bluetongue virus.
| description | symbol | estimate or range | comments | |
|---|---|---|---|---|
| probability of transmission from vector to host | b | beta (7.38,2.12) | based on an analysis of data on the transmission of BTV to sheep presented in [26] (cf. [27]); full details are presented in the electronic supplementary material | |
| probability of transmission from host to vector | β | beta (1.05,39.6) | based on experimental infection of field-caught Culicoides imicola with a number of different strains of AHSV [28]; full details are presented in the electronic supplementary material | |
| reciprocal of the time interval between blood meals | a | — | depends on temperature, T, such that: a = 0.0002T (T − 3.7)(41.9 − T)1/2.7 [29] | |
| duration of viraemia | mean | 1/rH | uniform (4,8) | assumed to follow a gamma distribution with mean (1/rH) and variance (1/nHrH2 ); estimates for the mean were obtained from [30] |
| scale parameter | nH | uniform (7,15) | ||
| disease-associated mortality rate | dH | uniform (0.28,0.52) | based on a case fatality of 75–90% [30]; full details are presented in the electronic supplementary material | |
| maximum vector-to-host ratio | only horses | m | uniform (0,10 000) | based on a maximum host biting rate (ma) of 2500 bites per host per day [31], and light trap catches of up to 10 000 individuals per night [32]; the vector-to-host ratio varies seasonally as mδ(t), where δ(t) is the seasonal vector activity (see below). In general, the ratio is rescaled by a factor f depending on the density of other non-susceptible hosts. Other regimens (table 2) are also considered |
| horses and non-susceptible hosts | m | uniform (0,10 000)f
|
||
| extrinsic incubation period (EIP) | mean | 1/ν | — | follows a gamma distribution with mean (1/ν) and variance (1/nν
ν
2 ); the mean EIP depends on temperature, T, so that:  [25] |
| scale parameter | nν | 17 | ||
| vector mortality rate | μ | — | depends on temperature: μ = 0.009exp(0.16T) [33] | |
| seasonal vector activity | δ | — | given by  ; note that this function was normalized, so that the maximum value is equal to 1; parameters are: b0 =−1.71, a1 =−1.56, a2 =−1.49, b1 =−3.74, b2 =−1.00 [34] |