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Family: Asfarviridae

African Swine Fever (ASF)


Family: Asfarviridae - Properties

Virions are enveloped, nucleocapsid core, internal lipid layers, single molecule of linear double-stranded DNA, replication in the cytoplasm


ASF - Properties

- Only known DNA arbovirus that is able to replicate within an arthropod vector
- OIE List A Disease - Reportable Disease
- Remains viable for long periods in blood, feces, and tissues; especially infected, uncooked or undercooked pork products
- Produces cytopathic effects: synctia, intracytoplasmic inclusion bodies


ASF - Hemadsorption (HAD)

- Virus does not hemagglutinate
- This HAD is attributed to a virus specific protein that appears on plasma membrane of infected cells during late infection


ASF - Transmission - Sylvatic Cycle

- Reservoirs: warthog, giant forest hog, and bush pig
- Transmission of ASF virus between warthogs and soft ticks


ASF - Transmission - Domestic Cycle

- Bite of infected tick
- Direct contact with infected animal
- Indirect contact on fomites
- Virus spreads to new areas when pigs are fed uncooked scraps that contain infected pork
- Aerosol spread
- Mechanical transmission through biting flies


ASF - Transmission - Vector

- Soft ticks
- Ornithodorus spp., specifically O. moubata in Africa
- Virus replicates in the tick either trans-stadial or transovarial and sexual transmission


ASF - Hosts

All breeds and types of domestic pigs and European wild boar. Inapparent infection in warthogs, bush pigs, and giant forest hogs, which act as reservoirs.


ASF - Distribution

Endemic in sub-saharan Africa and island of sardninia (Italy)

(def. of endemic: regularly found among particular people or in a certain area.)


ASF - Pathogenesis

- The effects of ASF virus are primarily hemorrhages and apoptosis
- There is leukopenia, lymphopenia, thrombocytopenia


ASF - Site of Virus Replication

- Pharyngeal mucosa, tonsils, etc.
- Endothelial cells
- Megakaryocytes
- Macrophages


ASF - Apoptosis of host cells

- p54 protein (encoded by virus) directly induces apoptosis of host cells
- ASF infected macrophages release cytokines and apoptotic mediators
- Apoptosis of both lymphocytes and mononuclear phagocytic cells


ASF - Mechanisms related to Hemorrhages

- Vascular damage from degeneration of vascular endothelium
- Disseminated intravascular coagulation (DIC)
- Infection and necrosis of megakaryocytes
- Activation and extensive destruction of monocytes and macrophages
- Thrombocytopenia and coagulation defects


ASF - Clinical signs - Peracute

Pigs may die suddenly or 1-3 days course of high fever, hyperpnea, hyperemia before death


ASF - Acute

- High fever
- Moderate anorexia
- Erythema
- Cyanotic skin blotching on the ears, tails, lower legs or hams
- Respiratory distress
- Recumbency
- Vomiting
- Diarrhea: initially mucoid and later may become bloody
- Abortion: sometimes the first event seen in an outbreak
- Death


ASF - Chronic form

- Emaciation and stunting
- Swollen joints
- Ulcers and reddended or raised necrotic skin foci
- Pneumonia


ASF - Diagnosis

- Virus isolation: blood spleen, visceral lymph nodes, tonsils
- Hemadsorption
- Serology: FAT, immunodiffusion
- PCR to detect viral DNA


ASF - Immunity

-Infected pigs do not neutralize the virus, hence, humoral response does not seem to have substantial protective value
- Vaccine creations are unsuccessful