Probability of infection
We found a positive relationship between the probability of ASF
infection and the proportion of infected individuals in high-, medium-,
and low-contact zones (0-2km, 2-5km, and 5-10 km, respectively)
(Supplementary Information, Table S1, Fig. S2). The strongest effect of
the proportion of infectees was observed in the high-contact zone, where
infection risk increased from 2.5 % if no infected individuals were
present to 96 % if all other individuals were ASF-positive. Proportion
of infected individuals at distances over 10 km did not influence the
probability of infection (Table S1, Fig. S2). Relatedness was a positive
predictor of infection risk within 10 km but had no effect at larger
distances (Table S1, Fig. S2). Probability of infection among kin (i.e.
presumably group members) across the study area was on average 77 ±
1.5% (min-max: 69-87) within 10 km, while infection risk among non-kin
averaged 52 ± 0.9% (min-max: 28-68) within 10km (Fig. S2a). Models
combining relatedness and proximity to infected individuals (Table 2)
showed that the relative contribution of relatedness and proportion of
infected individuals to explaining variation in infection probability
varied with distance. In the high-contact zone, variation in infection
risk was shaped overwhelmingly by the proportion of infected individuals
and not by relatedness (Table 2, Fig 3). However, infection risk among
kin within 2 km distance was high. All of the animals which were
surrounded by ASF-positive kin (n = 17) tested positive, while none of
the animals surrounded by ASF-negative kin (n = 7) tested positive.
Among animals surrounded only by infected non-kin between 0 and 2 km (n
= 18), the proportion of ASF-positive individuals was 83%, indicating
they were 17% less likely to become infected by non-kin relative to kin
on average. At further distances of 2-5 km (medium-contact zone)
infection risk increased with both relatedness and proportion of
ASF-positive individuals at this distance (Table 2, Fig.3), indicating
that ASF transmission was significantly more likely between related
individuals. In the medium-contact zone, infection risk averaged 84 ±
3.5% (min-max: 58-93) among kin and 47 ± 2.5% (min-max: 16-81) among
non-kin. At even further distances of 5-10 km (low-contact zone),
probability of infection increased with the number of ASF-positive
individuals while relatedness to infectees did not shape infection risk.
Here, infection risk increased from 38 % if at least one infected
individual was present to 75 % if all other individuals were
ASF-positive (Fig. 3). At distances >10 km (no-contact
zone), neither relatedness to infected individuals nor their number
influenced infection risk (Table 2, Fig.3).