How do genetic relatedness and spatial proximity shape African swine
fever infections in wild boar?
Abstract
The importance of social and spatial structuring of wildlife populations
for disease spread, though widely recognized, is still poorly understood
in many host-pathogen systems. In particular, system specific kin
relationships among hosts can create contact heterogeneities and
differential disease transmission rates. Here, we investigate how
distance-dependent infection risk is influenced by genetic relatedness
in a novel wild boar ( Sus scrofa) - African swine fever (ASF)
system. We hypothesized that the infection risk would correlate
positively with proximity and relatedness to ASF-infected individuals
but expected those relationships to weaken with distance between
individuals due to decay in contact rates and genetic similarity. ASF
infection risk was shaped by the number of infected animals throughout
the zone of potential contact (0-10 km) but not beyond it. This effect
was the strongest at close distances (0-2 km) and weakened further on
(2-10 km), consistent with decreasing probability of contact. Overall,
there was a positive association between genetic relatedness to
infectees and infection risk within the contact zone but this effect
varied in space. In the high-contact zone (0-2 km), infection risk was
not influenced by relatedness when controlled for the number of
ASF-positive animals. However, infections were more frequent among close
relatives indicating that familial relationships could have played a
role in ASF transmission. In the medium-contact zone (2-5 km), infection
risk and frequency of paired infections were associated with
relatedness. Relatedness did not predict infection risk in low- and
no-contact zones (5-10 and >10 km, respectively). Together,
our results indicate that the number of nearby infected individuals
overrides the effect of relatedness in shaping ASF transmission rates
which nevertheless can be higher among close relatives. Highly localized
transmission highlights the possibility to control the disease if
containment measures are employed quickly and efficiently.