Chapter 35: Disease transmission at the interface between wild and domestic Suiform species393
Bushpigs (Potamochoerus spp) are elusive species difficult to
capture and sample in the wild. As a result, information on patho-
gens circulating in their populations is very limited (Table 35.2).
Experimental and field studies have shown that they are natu-
rally infected with ASF virus but they do not develop clinical
disease. A recent study using metagenomic analysis reported the
presence of variants of porcine parvovirus and Torque tenovirus
(Blomström et al. 2012). However, these findings were not asso-
ciated with any signs of disease. Equally, increased mortalities
of bushpigs have been observed and suspected to be associated
with outbreaks of Ebola virus in Central Africa, but without any
supportive laboratory confirmation (Lahm et al. 2007). Finally,
some diseases affecting livestock have been described in captive
individuals such as a case of post-weaning multisystemic wast-
ing syndrome (Woodger & Hosegood 2011).
Interactions between DP and bushpigs are suspected to be
more common than with warthogs. Oral and written reports
of bushpig × DP hybrids are common across their distribution
range. They generally describe cases of domestic sows mating
with male bushpigs and giving birth to cross-bred offspring (Jori
& Bastos 2009; Leslie & Huffman 2015). Despite there being no
scientific evidence based on genetic analysis, circumstantial evi-
dence suggests that hybridization can occasionally occur when
domestic sows are sexually receptive. However, considering the
genetic distance between both species (34 pairs of chromosome
for bushpigs and 38 for DP), it seems unlikely that those hybrids
can produce offspring. Nevertheless, these reports suggest that
cross-breeding can occur in specific circumstances and allow
pathogen transmission (Okoth et al. 2013). A recent study in
northern Uganda suggested that direct interactions between
those species were unlikely while indirect interactions around
crops or water sources were reported more frequently (Kukielka
et al. 2015). Equally, a recent study monitoring macroparasites
among DP, giant forest hogs and bushpigs in Uganda showed
that several species of worms were shared between the three
sympatric pig species, suggesting a certain level of contact
between them which allowed a certain level of interspecific par-
asite exchange (A. Tumukunde, personal communication). In
any case, further research is needed to assess if this level of inter-
actions between wild and DP in Africa, occurs in other locations
and if it allows the exchange of other pathogens.
Case Studies of Disease Transmission
between Sympatric Species of Wild and
Domestic Pigs
This part of the chapter focuses on descriptions of case studies
in which the circulation of specific pathogens between wild and
domestic pig populations has been assessed in different loca-
tions and ecosystems in Europe, Africa, and the Neotropics.
Classical Swine Fever in Wild Boar
CSF is caused by a Pestivirus specific to pigs and associated with
a wide range of symptoms, from acute haemorrhagic fever to
subclinical carriage. Biomolecular studies showed that viruses
isolated from European wild boar over the last 30 years were
moderately virulent and belonged to the same ‘genogroup’
(Paton et al. 2000). Wild boar can perpetuate foci of CSF infec-
tions for several years, especially when the virus is introduced
among large connected populations in continuous forested hab-
itats. Wild boar strains have been found circulating within back-
yard pigs in eastern European countries (Artois et al. 2002; Rossi
et al. 2015). CSF viruses may be transmitted by direct contact,
meat consumption, or environmental contaminations. Thus,
the confinement of pig farms and the control of swill have been
the main key points for preventing CSF transmission from wild
boar to DP or between pig farms. In Europe, the deployment
of oral vaccination using a live attenuated vaccine has brought
satisfactory results for controlling wild reservoirs of CSF, com-
pared to other strategies (Rossi et al. 2015) and since the early
2010s, CSF circulation in those locations appears much more of
a problem linked to backyard pigs than to wild boars (Monger
et al. 2016).Brucellosis in Wild Boar
Porcine brucellosis is mainly associated with B. suis strains
having different pathogenic effects among mammal hosts and
humans. Among feral pig populations, B suis biovar 1, iso-
lated in Australia, is extremely pathogenic to humans, while
B. abortus, isolated in the USA, does not represent a zoonotic
risk. B. suis biovar 2, reported in wild boar and/or brown hare
populations from many European countries (Godfroid et al.
2013; Kreizinger et al. 2014), is moderately pathogenic to
humans (Algers et al. 2009) and has a low impact on wild boar
demography. Conversely, it is known to cause epizootics in DP
populations previously unexposed to the bacteria. To prevent
transmissions between DP farms, EU legislation recommends
stamping out when a farm is declared infected. Outdoor pig
farming is considered the main risk factor for B. suis biovar 2
outbreaks because it facilitates transmissions between wild pigs
and DP. The fact that hybrid piglets have been reported in many
infected farms suggests that sexual interactions facilitate bacte-
rial transmission (Algers et al. 2009; Wu et al. 2012). B. suis has
not been confirmed in African wild pigs, although antibodies
have been detected.Aujeszky’s Disease (AD) in Wild Boar
Wild swine and DP are natural hosts of AD virus, which may
also (incidentally) infect a large number of mammal species,
with lethal consequences for carnivores (Muller et al. 2011).
AD virus causes respiratory and reproductive symptoms in
DP, and can generate important economic losses to the pig
industry. Morbidity seems lower in wild boar, possibly due to
the coevolution of wild virus types and wild boar resulting in
mild infections (Müller 2012). During the last two decades, AD
has been eradicated in most of the indoor pig farms using vac-
cination and sanitary measures (Chiari et al. 2015). However, it
remains present in wild boars and feral pigs in the Old and New
Worlds, and is considered as a potential threat for pigs in areas
having acquired an AD-free status (Rossi et al. 2008; Boadella
et al. 2012a; Meier et al. 2015). Studies performed in Europe
suggest that different strains are circulating in wild pigs and DP
and that AD spatial and temporal dynamics between wild boars.03712:55:54