Chapter 35: Disease transmission at the interface between wild and domestic Suiform species395
and pigs are poorly connected (Müller et al. 2011; Chiari et al.
2015). However, this situation is highly dependent on pig hous-
ing and bio-safety: spillover from wild boar to DP is more likely
in areas were wild boars are endemically infected and DP are
reared in outdoor facilities (Wu et al. 2012). More studies using
biomolecular tools would be helpful for confirming the diversity
of situations between areas according to the degree of sympatry
between pigs and wild boars.
African Swine Fever and Wild Pigs
ASF is a viral disease, characterized by high mortality in all
forms of Sus scrofa (Blome et al. 2013). The virus originates
from sub-Saharan Africa where wild African suids and soft
ticks (Ornithodoros spp.) are considered natural reservoirs.
The different transmission cycles of the virus are presented
in Figure 35.1. The warthog–soft tick cycle, well described in
the literature, is able to maintain the virus in the environment
(Jori & Bastos 2009) and DP bitten with infected ticks will
become infected. Conversely, contacts with infected warthogs
are not considered infectious for DP, although they can facilitate
contacts between DP and infected ticks. For Potamochoerus spp.,
their role in the epidemiology of ASF remains unclear. In East
and Southern Africa, ASF virus has been isolated from bushpig
tissues on several occasions (Jori et al. 2013). However, data on
ASF prevalence in natural populations of Potamochoerus spp. are
limited to a single report of seropositivity (Stahl et al. 2014). It is
speculated that the production of antibodies against ASF virus
in Potamochoerus might be limited by a characteristic immuno-
logical process called apostosis (Oura et al. 1998; Jori et al. 2013).
In this regard, the case of P. larvatus, which occurs in large
numbers in the dry and tropical forested areas of Madagascar,
is quite particular. Since the introduction of ASF in 1998, the
disease has become endemic in the DP populations. However,
no scientific evidence has ever been found regarding the infec-
tion of P. larvatus populations with ASF virus (Ravaomanana
et al. 2011). In addition to Madagascar, in 2007, ASF spread into
Mauritius and also into Georgia (Rowlands et al. 2008), with
very different outcomes. In Mauritius, ASF managed to be erad-
icated two years later, while in Georgia, eradication efforts were
complicated by the spread of ASF virus into wild boar and feral
pig populations (Mannelli et al. 1998; Pérez et al. 1998; Mur et al.
2012), resulting in transboundary spread of ASF into neigh-
bouring countries such as Armenia, Azerbaijan, and the Russian
Federation (Sanchez-Vizcaino et al. 2013). Concurrent infection
of DP and wild boar populations led to persistence and furtherFigure 35.1 Schematic representation of the three types of cycles described for African swine fever.
Sylvatic cycle: The transmission of ASFV is maintained through a cycle between Ornithodoros ticks and warthogs in the burrows. Transmission of ASF from warthog to
DP occurs due to contact with the infected tick vector.
Domestic cycle: This is characterized by the perpetuation of the virus in a large population of pigs through direct contact via the oro-nasal route after contact with
excretions from infected pigs, through ingestion of pork or other contaminated products containing the virus, or indirectly through fomites. Argasid ticks adapted
to pigs can be involved in the transmission in some scenarios, e.g. Iberian Peninsula, East and Southern Africa.
Wild boar cycle (WB): In Eastern Europe, WB have been shown to play an increasingly important role in the spread of ASF as free-roaming pigs and WB may come
to inhabit and/or scavenge similar ranges. One should not ignore the threat of transportation of WB to hunting ranches and/or for management practices, or the
potential role played by hunters.
(Source: Daniel Beltrán Alcrudo & Scott Kramer, FAO)..03712:55:54