smuggled into the U.S., and remnants
are consumed by domestic or feral
swine. The feral swine could then communicate directly with farmed swine
through a fence, or provide infected
ticks that migrate to pastures where
farmed swine graze.
The preferred management of ASF is
prevention through monitoring in the
country of origin and surveillance of
swine overseas, along with import and
vector control, biosecurity measures
including double fencing, control of
ectoparasites, and elimination of feral
swine. 3 Denmark has proposed a boar-proof wall on its border with Germany
to prevent entry of infected animals.
A proposal to eliminate the wild boar
population in Poland, however, sparked
protests over ecological disruption and
loss of the major component of the European wolf’s diet.
Perhaps the only certain outcome of
an ASF outbreak in the U.S. is that all
pork exports (approximately 2. 45 million metric tons) would be curtailed at a
loss of $6.5 to $7 billion. The duration
of import bans would vary based on
the time the U.S. needed to eradicate
the disease, as well as the time required
for complete decontamination of the
agricultural premises. Additional time
would be required for restocking and to
resume production of feeder hogs.
However great the efforts at eradication, there is the distinct chance that
pockets of infected animals would persist. Although ASF was eradicated from
Haiti in 1984 and Cuba in 1980, it has
become endemic in Sardinia since its
introduction in 1982. Thus, the threat
of a newly introduced disease becoming
a feature of swine agriculture in the U.S.
cannot be dismissed.
Consequences of ASF
Within the U.S., loss of pork production would depend on the extent of the
outbreak, based on location and season.
Swine-raising operations of more than
5,000 head are found in every state, and
the major producers are collocated with
the feed sources in the Midwestern grain
belt. The southern edge of the dense
U.S., with increased biosecurity efforts on swine-rearing operations and widespread
public notification about the disease. ASF threatens U.S. swine rearing and export
and also serves as a model of the complex challenges of disease control in a global-
ized market subject to the changes wrought by global warming.
European swine were brought to North America with Hernando de Soto in 1537,
and escapees may have founded the feral swine population in the U.S. Feral swine
number approximately 5 million and cause more than $1.5 billion in damage and
crop losses each year. Feral swine are smart, cautious, and destructive, and no effective controls for them have been approved. Populations of feral swine inhabit much
of the same territory as the soft ticks capable of spreading ASF. 2
Why Is ASF Such a Threat?
The U.S. markets about 115 million hogs each year, for a gross income of about
$20 billion. Pork exports were valued at $6.45 billion in 2017, amounting to 2. 45
million metric tons. Domestic hog markets were devastated in 2013 by a pandemic
of porcine epidemic diarrhea, which spread from Asia and Europe and demonstrated
U.S. susceptibility to transboundary diseases. Five percent fewer hogs were slaughtered, although most of the production loss was recovered by growing the hogs longer and slaughtering them at a larger size.
ASF is spread by infected ticks of the genus Ornithodorus spp. 2 Recent discovery
of the Asian longhorned tick in states along the Atlantic, as well as the discovery in
the U.S. of Heartland and Bourbon viruses (also tick-borne) and the increased spread
of Lyme borreliosis, suggests greater survival of ticks due to milder winters.
ASF is a hemorrhagic disease seen in swine of European origin, Sus scrofa, caused
by a virus found in African swine such as the warthog, bush pig, and giant forest
hog. None of these African swine show signs of clinical infection, nor do the native
suids of North America (species of peccary). Clinical ASF presents in swine of any
age with fever, rapid breathing, vomiting, diarrhea, and reddened patches on the
skin, ears, or tail. Death can occur as a first sign or within 24–48 hours of onset of
fever. In the U.S., the expected outcome would be death of all members of the herd,
although a small number might survive and become silent carriers. Thus, depopulation of infected and contiguous premises is a required step in control.
The ASF virus survives in tissues, including some preserved meats, for as long
as 30 days. The virus can be spread from pig to pig, tick to pig, or food/feed to pig.
Thus, a possible scenario for establishment of ASF in the U.S. might look like this:
An infected animal is used to produce sausage or chorizo overseas, the product is
Table 2. Some tick-vectored diseases in the U.S., recognized (R) or emerging (E). Native ticks
already serve as vectors of many old and emerging diseases in the U.S.
Lyme borreliosis R
Powassan fever (rare) E
Bourbon virus (rare) E
Heartland virus (rare) E
Rocky Mountain spotted fever R
Northeast, WI, MN
Northeast, WI, MN
AR, MO, NC, OK, TN
Midwest to TX
Table 3. Distribution of soft, argasid ticks in the U.S. Tick distribution overlaps the distribution
of feral swine and could, as a consequence of an outbreak, serve to establish a reservoir of
ASF in the U.S.
Ornithodoros parkeri (can be infected; not
CA south into Mexico
AZ, CA, CO, FL, KS, NM, OK, TX, UT
Rocky Mountains west to CA, OR, WA
Caribbean basin including U.S. territories