African Swine Fever

What is African Swine Fever?

A contagious and tick-borne viral disease of swine that can be chronic. In its most recognizable acute form, the disease is characterized by high fever, reddened skin and extensive hemorrhages of lymphoid organs with high morbidity and high mortality

What kind of virus is African Swine fever?

DsDNA enveloped virus with an icosahedral shape and linear genome

What family does African Swine fever belong to?

Asfarviridae

What is the structure of the African Swine fever virus?

-Large, double stranded DNA virus

-175-210 nm in diameter

-170 Kbp

-151 open reading frames (evade host defenses, modulate host cell function)

What is the only known arthropod-vectored DNA virus of animals?

African Swine fever

What kind of ticks can carry African Swine fever?

Ornithodoros soft ticks

Are soft ticks a major mechanism of transmission for African Swine fever in Europe currently?

No

How resistant is African Swine fever in the environment?

Extremely

What secretions is African Swine fever found in?

Oral/nasal

How long does the African Swine fever virus survive in room temperature blood?

15 weeks

How long does the African Swine fever virus survive in raw meat?

3 months in raw meat, 1 year in dry meat and fat

How long does the African Swine fever virus stay in offal?

Temperature dependent

How long does the African Swine fever virus survive in urine?

15 days

How long does the African Swine fever virus survive in feces?

8 days

What is an important mechanical vector for African Swine fever?

Stable fly

How is soil contaminated with African Swine fever?

After body of infected animal is removed

What can serve as fomites for African Swine fever?

Cars, clothes, shoes, knives

African Swine fever infects species of what family?

Suidae

What species are infected by African Swine fever in Europe?

Only domestic pigs and wild boars (infected with genotype 2 with a very high case fatality rate. Severe hemorrhagic disease)

What was the primary source of infection for African Swine fever after 1957?

Airline waste fed to pigs

How long did African Swine fever remain endemic in the Iberian peninsula?

Until the mid-1990s

When was African Swine fever eradicated in South Brazil?

1978-1979

When did Brazil reach African Swine fever-free status?

In 1984

When was there an outbreak of African Swine fever in the Dominican Republic?

1978

When was there an outbreak of African Swine fever in Haiti?

1979

Describe African Swine Fever in the Dominican Republic in 1978

-Entered country in February 1978

-Not diagnosed until June

-100% of the pigs in infected herds were dying

-Virus disseminated throughout the country

-A total of 283 outbreaks occurred up to the end of January 1979

-The origin appears to have been food waste from international airlines

Describe African Swine fever in Haiti in 1979

-ASF diagnosed in the Dominican republic in 1978

-ASF moved to Haiti in 1979

-Haiti pig population at the time was around 2 million

-Small creole black pigs

-Mostly backyard operations

-86% of rural population owned pigs

-To stop the spread of ASF the government started a program to exterminate the pigs and replace them with European/U.S. pigs

-Mandatory depopulation of ALL pigs in the Dominican Republic and Haiti

-Eradication achieved in 1984

Has African Swine fever been documented in the US?

No

Is African Swine fever a reportable disease?

Yes

What are natural hosts for African Swine fever?

Warthogs, bushpigs, soft ticks (inapparent infection)

What countries have an increased risk of spread of African Swine fever since 2007?

Caucus region, Russia, Eastern Europe

What countries have had exposure to African Swine fever since August 2018?

-China + 12 Asian countries

-Belgium, Slovakia, Serbia, Germany, etc.

What are the two transmission pathways for ASF?

-Warthog-tick cycle (inapparent infection in warthogs)

-Sus scrofa pig to pig transmission (tick not required)

How is African Swine fever transmitted?

-Oronasal route by direct or indirect contact

-Bite of an infected soft tick

-Ingestion of uncooked pork in food waste

-Ingestion of contaminated feed

How long can shedding of the African Swine fever virus occur?

Up to 1 month in respiratory secretions and blood

How has African Swine fever transmission been controlled in China?

-Oct 2018 ban the feeding of kitchen waste to pigs

-Swill must be heated to a certain temperature but experts say that step is often skipped

What are the clinical signs of acute African Swine fever?

-High fever

-Decreased appetite and weakness

-Red, blotchy skin or skin lesions (hyperemia or cyanosis)

-Diarrhea (sometimes bloody) and vomiting

-Coughing and difficulty breathing

-Mild anorexia

-Abortions (due to high fever)

-Death

What is the primary route of infection for African Swine fever?

Oral or the upper respiratory tract

Describe the cellular pathogenesis of African Swine fever

-Severe disruption to blood clotting mechanism

-Destruction of macrophages (impaired hemostasis, release of cytokines and complement)

-Thrombocytopenia

-Lymphopenia

What is the incubation period for African Swine fever?

4-19 days

What are the forms of African Swine fever?

Peracute, acute, subacute, chronic, and subclinical

What are acute and lethal forms of African Swine fever accompanied by?

Hemorrhagic lesions, DIC, thrombocytopenia, increased vascular permeability, death within 5-10 days

What clinical signs are seen in the less acute form of African Swine fever?

Respiratory signs (coughing, sneezing, dyspnea) and gastrointestinal signs (diarrhea, constipation)

What clinical signs are seen in the chronic form of African Swine fever?

Emaciation, swollen joints, respiratory disease

What is the range of mortality for African Swine fever and what does it depend on?

Ranges from 0-100% (depends on strain virulence)

What lesions are seen in African Swine fever?

-Hyperemia and Hemorrhage on skin

-Generalized hyperemia of ears, abdomen, legs

-Edematously enlarged and hemorrhagic LN

-High-grade, acute, diffuse hemorrhage and enlargement of lymph nodes

-Lung hemorrhages

-ASFV predominately replicates in monocytes and macrophages

-High concentrations of virus found in spleen

-Paintbrush hemorrhage on gastric serosa

-Stomach filled with clotted blood, edematous wall

-Numerous acute petechiae on the renal cortex

-Hypopericardium, multifocal epicardial hemorrhage

-Urinary bladder, disseminated mucosal petechiae

Where does the African Swine fever virus predominately replicate in?

Monocytes and macrophages

What are the differentials for African Swine fever?

The same as classical swine fever

How is the African Swine fever virus detected?

-Whole blood, spleen, tonsil, lymph nodes, VI, PCR, ELISA, FA, ISH

How is African Swine fever detected via serology?

ELISA, IFA

How can African Swine fever be differentiated from Classical swine fever?

Samples should be submitted to laboratory for proper diagnosis since they have similar post-mortem lesions

Is there a vaccine for African Swine fever?

No

How can African Swine fever be prevented and controlled?

-Control of animal importations, decontamination and disposal of foreign garbage

-Cooking of food scraps for feeding pigs

-Tick vector controls

-Eradication typically depends on rapid diagnosis, slaughter and disposal of infected animals (controlled or stopped pig movement, treatment of food waste or ban of swill feeding

-Biosecurity and reducing exposure to wild suids