Table 1.
Parameter values used to model the spread of rabies and canine distemper virus (CDV) in island foxes on San Clemente Island, California. MDS = maritime desert scrub. N (, variance) = normal distribution from which parameter value was sampled.
| Parameter | Value | Source | |
|---|---|---|---|
| Home range radius (meters; based on fox density) | High density:
N (252.31, 2.28) Medium-high density: N (282.09, 1.56) Medium-low density: N (504.63, 2.02) Low density: N (713.65, 1.59) |
Field data (Sanchez and Hudgens 2015) | |
| Proportion of home range overlap | ≤ 0.75 | Maximum overlap between non-related pairs (Sanchez and Hudgens 2015) | |
| Contact rate | Rabies (number of
contacts/day): N (0.02+0.88m,
0+0.25m) CDV (seconds in contact/day): N (1.42+58.57m, 0+2594.03m) m = home range overlap |
Field data (Sanchez and Hudgens 2015) | |
| Transmissibility | Rabies:
0.49c c = contact rate |
Farrell et al. 1955, Hampson et al. 2009 | |
| Transition probabilities1 | Rabies: latent to infectious
class: 1/42 (max 90
days) infectious to dead class: 1/4 (max 14 days) CDV: latent to infectious class: 1/5 (max 14 days) infectious to dead class (no recovery): 1/21 (max 60 days) infectious to dead class (recovery): 1/60 (max 90 days) |
Gorham and Brandly 1953, Gillespie 1962, Appel 1987, Blancou et al.1991, Kitala et al. 1997, Greene and Vandevelde 2012, Rhodes et al. 1998, Gorham 1999, Deem et al. 2000, Headley and Graça 2000, Hampson et al. 2009 | |
| Background transmission rate2 | 1 − (1 −
f )(# of infectious
foxes) f = 0.000001 = probability per time-step of pathogen transmission between two foxes with non-overlapping home ranges |
Reed-Frost equation; Abbey 1952 | |
Transition probabilities calculated as the average number of days a fox is in each disease class.
During the 206-day study period (Sanchez 2012) only one fox out of 40 made a foray outside its study site. The probability of transmission between a focal fox and a fox on a foray was set to the arbitrarily low value of 1% because contact rates among foxes outside their home ranges are not known. The resulting daily risk each focal fox had of encountering a fox on a foray outside its home range and contracting a pathogen was approximately (1 ÷ 40 ÷ 206) × 0.01 ≈ 0.000001.