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African Swine Fever: An Expanding
Threat To American Hogs
African swine fever (ASF) is a contagious, usually fatal viral
disease of swine. It can be the most deadly of all foreign
diseases of hogs. The acute form kills almost all hogs that
Other species of animals are not susceptible to the
disease. It does not affect humans.
Since the 1960's, a milder form of ASF has been in-
creasingly reported. Because this chronic strain has a lower
death rate than the acute form, it is more difficult to
diagnose and thus is harder to eradicate.
Both the milder form and acute ASF are often confused
with hog cholera. The signs are almost identical, although
the viruses are not related. ASF also can be confused with
other swine diseases.
No effective vaccine has been developed for ASF, and no
effective treatment is known.
Where It Occurs:
African swine fever has probably infected several kinds of
wild pigs in Africa for many years. It was first recognized
among domestic European swine in Kenya in 1909.
The global threat of the disease became apparent when
ASF invaded Portugal in 1957. It spread to Spain in 1960,
and to France in 1964. France reported further outbreaks in
1967 and 1974, but successfully eradicated the disease
through quarantine and slaughter. Outbreaks have also
occurred on mainland Italy and on the islands of Malta,
Sardinia, the Canary Islands, and Madeira since the
In 1971, ASF penetrated the Western Hemisphere for the
first time. The disease struck Cuba, and the swine population
of Havana province had to be slaughtered before the disease
Further outbreaks in the Western Hemisphere were
confirmed in Brazil and the Dominican Republic in 1978
and in Haiti in 1979.
If An Outbreak Should Occur In The United States:
If an outbreak should occur in the United States, it is
probable that-unless immediate steps were taken to control
the disease-ASF would spread rapidly to all sections of the
country. It is also probable that most exposed hogs would
develop ASF, and either die or become unprofitable as
Plans for a U.S. emergency eradication program against
ASF have already been developed. State and Federal animal
health authorities will begin eradication immediately upon
confirmation of an outbreak.
Sows with ASF may abort at any stage ofpregnancy and all
feti will be at a similar stage of development. Hemorrhage is
often apparent on feti and fetal membranes (left). Economic
losses with ASF result not only from death and abortion
in swine, but also from slow-gaining or stunted survivors of the
disease (top right).
In African swine fever, skin may become reddish on belly,
hams, legs (top left, bottom), ears, and snout. Typically
seen only in white pigs, this characteristic color also occurs in
African swine fever spreads rapidly in both its acute and
Infected pigs are a primary source of the disease. Hogs
that recover from ASF can still transmit the virus for a long
period of time. The virus of ASF is present in all excretions
and secretions of the infected pig and may persist outside of
its hosts for long periods of time.
In Africa, wild pigs are carriers. Though they show no
signs of illness, infected wart hogs and wild bush pigs
transmit the disease to domestic swine.
ASF can be spread by:
Contact between infected and susceptible hogs.
Contaminated garbage, feed, or water.
Infected ticks (particularly soft ticks).
Contaminated insects-lice, biting flies.
Contaminated premises, clothing, footwear, equipment.
Improper disposal of infected carcasses.
Aerosol transmission within the herd.
Recent studies indicate that certain soft ticks may actually be
natural hosts of ASF, and are capable of transmitting the
virus from one generation to the next. Thus, ticks on ASF-
infected farms may carry the virus for longer than 6 months
and could infect reintroduced swine. The virus is highly
resistant to environmental conditions, such as high tem-
peratures. Only certain disinfectants are effective for the
Many outbreaks have been traced directly to uncooked
garbage fed to hogs.
ASF may resemble hog cholera and other common swine
diseases. It is almost impossible to tell the difference by
observing sick pigs.
Susceptible hogs will develop ASF 5 to 15 days after
exposure. Some may die before the signs are apparent.
In ASF, an infected pig first undergoes an abrupt rise in
temperature, from a normal 101 F (38.3 C) to
1050 F (40.60 C) or higher. The animal may seem to "burn
up" with fever.
Swine with acute ASF ordinarily die 4 to 7 days after the
onset of fever. The temperature usually falls quickly a day or
two before death.
In the sub-acute form of ASF, 50 percent or more of the
herd may survive the acute phase of the disease. Survivors
are often stunted and make poor gains.
In ASF, sqme or all of the following signs may be seen:
* Tendency to lie down.
* Discolorations-blotchy or diffuse redness-on ears,
snout, tail, legs, abdomen, and flanks of white-skinned
* Labored breathing.
One difference between ASF and hog cholera may be the
appetite of the infected hog. Pigs with ASF often continue to
eat and drink limited amounts of food and water until near
death, while pigs with hog cholera usually go off feed and die
without regaining their appetites.
Post Mortem Lesions:
African swine fever produces lesions similar to those caused
by hog cholera, salmonellosis, erysipelas, and various toxins.
Edema, ascites, and hemorrhage are the most frequently
observed lesions in ASF.
Hemorrhages, varying from small pinpoints of blood in
tissues to massive amounts of free blood, may involve almost
any organ of the body. The following organs are most
* Skin-reddening on ears, snout, abdomen, and hind-
* Lungs-hemorrhages plus edema and pneumonia.
* Lymph nodes-hemorrhages may be minute and
diffused, or entire node may resemble a blood clot.
* Liver-often enlarged and discolored.
* Kidney-hemorrhage ranges from pinpoint to entire
* Spleen-may be enlarged or occasionally infarcted.
* Heart-hemorrhages in heart muscles.
Excessive fluid may be present in body cavities and joints.
Occasionally, death is sudden and no obvious lesions are
Hogs dying from the milder, chronic strains may also
have secondary infections, which complicate the clinical and
post mortem picture.
As milder forms emerge, it is becoming more difficult to
distinguish between ASF and other swine diseases at
Spleen of pig with Afjican swinefever is .., 'ad, enlarged and
dark-almost black-in color (bottom left).
Mesenteric lymph nodes- normally lr .... *' I q''. a' as
blood clots in African swine fever ltop)
"Clumping of red blood cells around infected white cells in
test tube proves African swine fever virus is present. This test.
developed by USDA scientists employed by Plum Island
Animal Disease Laboratory. is used to diagnose the disease
A provisional diagnosis of ASF may be made on the basis of
the clinical signs, gross lesions, and history of the swine
population in the area. However, since the disease so closely
resembles many other swine diseases, a laboratory con-
firmation must be made.
Report any suspicious case immediately to your
veterinarian, State or Federal animal health officials, or
your county agricultural agent.
Every report will be investigated. Several tests are
available to differentiate between ASF and other diseases.
If tests confirm either ASF or hog cholera, eradication
measures will be started at once.
The U.S. Department of Agriculture-to prevent the
introduction of African swine fever or the reintroduction of
hog cholera-prohibits the importation of live hogs and
uncooked pork from any country known to be infected with
these diseases. The only pork products allowed from such
countries are those that have been commercially canned,
hermetically sealed, and fully sterilized to produce a shelf-
stable product without refrigeration. Strict inspection and
quarantines are conducted at U.S. ports of entry.
What You Can Do:
Watch your herds. Be alert to abnormal conditions.
If any hogs show signs of African swine fever or hog
cholera, notify your veterinarian, State or Federal
animal health officials, or your county agricultural
agent at once.
* Isolate hogs showing signs of disease. Do not move them
from your premises.
* Restrict movement of all livestock on your premises if
you suspect an outbreak.
* Restrict movement of persons, vehicles, and equipment
to and from your premises until you are notified of the
Animal and Plant Health Inspection Service
Revised June 1979 Slightly revised June 1980
U.S. GOVERNMENT PRINTING OFFICE : 1980 0-322-713 : QL 2
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402