African Swine Fever in Pigs

Epidemiology

Contributing factors:

• infected swill is likely culprit

  • scraps (meat products, plant products that you would give to animals)

  • pigs

• movement of infected individuals across borders

Etiology

• large virus

• capsid contains genetic material (dsDNA) for immune system evasion, cell process modulation and virulence

  • contributes to virulence of pathogen within host

• 23 genotypes (versions)

  • all 23 are present in Africa (endemic)

  • I and II are present in other parts of the world

• Cytoplasmic virus

  • causes huge macrophage loss within host, dampening its ability to fight off any pathogen

Current endemic areas

Transmission

1. direct contact with infected individual

• virus can be found in all fluids, especially oronasal (lungs, nose, tracts, cough, sneeze) secretions and excretions

  • airborne virus

• persistent in the blood and lymph

  • head, face, neck

• persistent in tissues after death

  • necropsy

2. indirect contact with contaminated fomites

• highly stable in proteinaceous (meat) resources

  • consumption or handling of infected meat that has not been cooked properly is a key factor in transmission)

• can persist stably on surfaces

  • things we use to handle/transport pigs

3. infected tick bite (Ornithodoros spp. → soft tick)

• competent vectors of ASFV can be found globally

• ticks can maintain the virus transstadially (virus can be passed through each stage, egg → larva → nymph → adult), transovarially (female tick → eggs), and sexually (mating on host)

Vector role- ornithodoros ticks

• nidicolous

  • hand out with host

    • their bedding, nesting, burrowing areas

    • not found on the host like hard ticks

• feed often and frequently

• maintain virus across generations

Host- family suidae (come down with clinical signs/are reservoirs)

Warthog

• Phacochoerus africanus

• resistant to clinical signs

Bush pig

• Potamochoerus larvatus

• resistant to clinical signs

Wild Boar & Domestic Pig

• Sus scrofa

• Sus scrofa (domestical)

  • come down with clinical disease the worst

Host- warthog, bush pig

Warthog

• young develop significant viremia and show no clinical disease

  • reservoir host

  • if a tick were to bite, warthogs would most definitely take in the virus

• adults show no clinical signs and are infected/tive for life

  • -ed: containing virus

  • -tive: having the virus & being able to give it to a tick

• only ticks contribute to transmission

Bush pig

• resistant to clinical disease despite high viremia for extended time

• capable of transmission to other swine

  • more readily transmit pathogen

Host- peccary (family teyassuidae)

• not true pigs

• resistant to infection

• peccary macrophages are not compatible to the virus

Clinical disease- wild pig, domestic pig

Acute Hemorrhagic Fever

• caused by highly virulent strains

• almost always 100% mortality

• signs: high fever, lethargy, weakness, diarrhea, hemorrhagic signs

• death occurs 1-4 days post signs

• most common in disease free regions (areas where it is not endemic)

Chronic Infection

• caused by lesser virulent strains

• low mortality

• signs: intermittent fever, loss of appetite, depression and fatality (if prolonged)

• domestic pigs are MOST infectious during incubation period and can shed virus up to one month after clearing signs

  • period b/w acquiring pathogen and showing signs

• prolonged infected = disease persistence

Diagnosis

Best tissues: spleen, kidney, and lymph nodes

• organ/tissues involved in clearing a pathogen

Vaccine

• currently no vaccine available

• WHY??? It’s complicated!!

1. diversity of viral strains (23 genotypes)

2. inadequate understanding of virus-host-cell interaction

3. inadequate understanding of protective antigens

4. genetic diversity of the host (diff. genuses)

Housing domestic swine in the U.S. (not endemic)

• maintenance is a highly regulated closed system

• housed indoors

• high biosecurity measures from birth to slaughter

• frequent sanitation of slaughter materials, feed and transportation devices

Contributing factors to geographic spread

Legal

• movement of domestic swine from neighboring countries

• imported animals, animal biproducts, and feed from endemic areas that were poorly treated… required permit upon entry

Illegal

• improper border security

  • into non-endemic areas

• bioterrorism

  • pathogen is stable in frozen products

major consequences?

crippling economic loss!

Complications if introduced to US

1. role of soft ticks species is generally unknown (10 to 12 known species)

2. virus can persist in a range of climates (flexible, cold/hot)

3. backyard and feral swine could contribute to short term outbreaks

wild hogs susceptible to disease in same way as domestic

The problem with feral hogs

• feral hogs are free roaming and can contribute to disease spread

• >6 million in US (3-4 million in Texas)

• males are free roaming

• reproductive females live in small communities (sounders)

• contact rate study (US 2012): Sounder interaction is reduced by at least 2km which reduced transmission

• using bait stations to study behavior

• home range studies are necessary

  • Texas study in 2012 found range up to 22.23 square km

• culling events are most effective (prophylactic culling as well)

  • eliminate threats

Estimations