Diseases

African Swine Fever

Download as PDF Download as XLS Download summary

Chapter select

Control Tools

  • Diagnostics availability

  • Commercial diagnostic kits available worldwide

    ELISA TESTS:

    For  antibody detection

    o  INGEZIM PPA COMPAC K3 (INGENASA)→ blocking ELISA assay which uses a monoclonal antibody (MAb) specific of VP73 ASFV protein o  SVANOVIR® ASFV-Ab → indirect ELISA based on a recombinant antigen - the p30 (screening format) o  ID Screen® ASF → Indirect Multi-antigen indirect ELISA kit for the detection of antibodies against P32, P62 and P72 ASFV proteins.

    For antigen detection

    o  INGEZIM PPA DAS 1.PPA.K2, commercial kit (Ag-ELISA).  

    • PCR TESTS

      o   Tetracore real-time PCR kit based on primers and probes designed by Zsak et al., 2005.

    •  PENSIDE TEST FOR ANTIBODY DETECTION 

             o  INGEZIM PPA CROM (INGENASA) based on the technique of  Direct Immunochromatography which uses a Monoclonal Antibody (MAb) specific of VP72 of ASFV.

    GAPS:

    -        Field validation data need to be expanded for all tests.

    -        Penside tests for Antigen detection

    -        Worldwide distribution of existing commercial tests

    -     Need for developments of new commercial assays for ASF virus and antibody detection.

  • Commercial diagnostic kits available in Europe

    ·      ELISA TESTS:

    For ASF antibody detection

    - INGEZIM PPA COMPAC K3 (INGENASA) blocking ELISA assay which uses a monoclonal antibody (MAb) specific of VP73 ASFV protein

    - SVANOVIR® ASFV-Ab indirect ELISA based on a recombinant antigen - the p30 (screening format)

    - ID Screen® ASF Indirect Multi-antigen indirect ELISA kit for the detection of antibodies against P32, P62 and P72 ASFV proteins.

     

    For ASF antigen detection

    - INGEZIM PPA DAS 1.PPA.K2, commercial kit (Ag-ELISA). 

     

    ·      PCR TESTS

    Tetracore real-time PCR kit for ASF; real time PCR based on primers and probes designed by Zsak et al., 2005.

    INgene q PPA real-time PCR kit (INGENASA) based on the use of a  Universal Probe Library (UPL) labelled with FAM (Fernández et al., 2013)

    ·      PENSIDE TEST FOR ANTIBODY DETECTION

    INGEZIM PPA CROM (INGENASA) based on the technique of Direct Immunochromatography which uses a Monoclonal Antibody (MAb) specific of VP72 of ASFV.

     

     

    GAPS:

    - Field validation data need to be expanded for all tests.

    - Penside tests for Antigen detection

    - Need for developments of new commercial assays for ASF virus and antibody detection

  • Diagnostic kits validated by International, European or National Standards

    Identification of the agent

    • VI (Virus Isolation) and HA (Haemadsorption) test based on the inoculation of sample material (blood or tissue suspension from suspect pigs) into susceptible primary leukocyte cultures of porcine origin. It is the reference virological test for confirmation of positive virus detection techniques results in primary outbreaks.  Described in the OIE Manual of ASF diagnosis (OIE, 2012) and by the EURL (http://asf-referencelab.info/asf/en/).
    • Antigen detection by fluorescent antibody test (FAT) described in the OIE Manual of diagnosis (OIE, 2012).
    • Detection of ASF virus genome by polymerase chain reaction (PCRs);
      • OIE conventional PCR described by Agüero et al., 2003 (OIE 2012).
      • OIE real time PCR described by King et al., 2003.
      • UPL real time PCR described by Fernández et al., 2013. Highest sensitivity for the detection of chronically infected animals.
      • Taqman real time PCR described by Tignon et al., 2011. Highest sensitivity for the detection of chronically infected animals.
      • TETRACORE commercial real time PCR (Zsak et al., 2005) which includes all reagents dried down, rehydration buffer and controls.
      • INgene q commercial real time PCR kit (INGENASA) based on the use of a Universal Probe Library (UPL) labelled with FAM (Fernández et al., 2013).
    • Multiplex detection of ASF/CSF virus genome by conventional and real time PCRs (Agüero et al. 2004; Haines et al 2013) useful for surveillance in free areas with high risk of entrance of CSF and/or ASF, and in case of co-circulation of both viruses. It is important to remain that ASF diagnostic sensitivity drops slightly than the single assay.
    Serological tests
    • OIE-ELISA Indirect ELISA based of ASFV semipurified antigen. Described in the OIE Manual of ASF diagnosis (OIE, 2012) and by the EURL (http://asf-referencelab.info/asf/en/). Is the prescribed test for international trade) according to the OIE Manual.
    • Commercial ELISA tests such us the INGEZIM PPA COMPAC K3 (INGENASA) and the ID Screen® ASF (IDVET)
    • Immunoblotting (IB) for the confirmation of positive and inconclusive ELISA results. Described in the OIE Manual of ASF diagnosis (OIE, 2012) and by the EURL (http://asf-referencelab.info/asf/en/).
    • Indirect fluorescent antibody test (IFA) for the confirmation of positive and inconclusive ELISA results and for tissue exudates analyses. Described in the OIE Manual of ASF diagnosis (OIE, 2012)
    • Immunoperoxidase test (IPT) for the confirmation of positive and inconclusive ELISA results and for tissue exudates analyses. Described in the OIE Manual of ASF diagnosis (OIE, 2012) and by the EURL (http://asf-referencelab.info/asf/en/).

     

    ASFV genotyping: i) sequencing of the C- terminal end of VP72 gene,which differentiates up to 22 distinct genotypes; ii) full genome sequence of the p54-gene and iii) analysis of the central variable region (CVR) to distinguish between closely related isolates and identify virus subgroups within the 22 p72 genotypes. Described in the OIE Manual of ASF diagnosis (OIE, 2012) and by the EURL (http://asf-referencelab.info/asf/en/).

    GAPS:

    -        Update of the EU and OIE Manual of diagnosis for ASF.

  • Diagnostic method(s) described by International, European or National standards

    Identification of the agent

    • VI (Virus Isolation) and HA (Haemadsorption) test based on the inoculation of sample material (blood or tissue suspension from suspect pigs) into susceptible primary leukocyte cultures of porcine origin. It is the reference virological test for confirmation of positive virus detection techniques results in primary outbreaks.  Described in the OIE Manual of ASF diagnosis (OIE, 2012) and by the EURL (http://asf-referencelab.info/asf/en/).
    • Antigen detection by fluorescent antibody test (FAT) described in the OIE Manual of diagnosis (OIE, 2012).
    • Detection of virus genome by conventional (Agüero et al., 2003) and real time (King et al., 2003 and Fernández et al., 2013) polymerase chain reaction (PCR) described in the OIE Manual of ASF diagnosis (OIE, 2012) and by the EURL (http://asf-referencelab.info/asf/en/).

    o   Serological tests

    • OIE-ELISA Indirect ELISA based of ASFV semipurified antigen. Described in the OIE Manual of ASF diagnosis (OIE, 2012) and by the EURL (http://asf-referencelab.info/asf/en/). Is the prescribed test for international trade) according to the OIE Manual.
    • Immunoblotting (IB) for the confirmation of positive and inconclusive ELISA results. Described in the OIE Manual of ASF diagnosis (OIE, 2012) and by the EURL (http://asf-referencelab.info/asf/en/).
    • Indirect fluorescent antibody test (IFA) for the confirmation of positive and inconclusive ELISA results and for tissue exudates analyses. Described in the OIE Manual of ASF diagnosis (OIE, 2012)
    • Immunoperoxidase test (IPT) for the confirmation of positive and inconclusive ELISA results and for tissue exudates analyses. Described in the OIE Manual of ASF diagnosis (OIE, 2012) and by the EURL (http://asf-referencelab.info/asf/en/).

     

    ASFV genotyping: i) sequencing of the C- terminal end of VP72 gene,which differentiates up to 22 distinct genotypes; ii) full genome sequence of the p54-gene and iii) analysis of the central variable region (CVR) to distinguish between closely related isolates and identify virus subgroups within the 22 p72 genotypes. Described in the OIE Manual of ASF diagnosis (OIE, 2012) and by the EURL (http://asf-referencelab.info/asf/en ).

    GAPS:

    -        Update of the EU and OIE Manual of diagnosis for ASF.

  • Commercial potential for diagnostic kits in Europe

    High potential to date, due to the current situation.

  • DIVA tests required and/or available

    None available but would be required of vaccines were available
  • Opportunities for new developments

    GAPS:

    • Lack of epidemiology information about what is going on, limit capability for new developments.

  • Vaccines availability

  • Commercial vaccines availability (globally)

    None

  • Commercial vaccines authorised in Europe

    None

  • Marker vaccines available worldwide

    None

  • Marker vaccines authorised in Europe

    None

  • Effectiveness of vaccines / Main shortcomings of current vaccines

    No vaccines available

  • Commercial potential for vaccines in Europe

  • Regulatory and/or policy challenges to approval

    Needs for authorisation in country to be used in.

  • Commercial feasibility (e.g manufacturing)

    Until vaccines developed difficult to assess.

  • Opportunity for barrier protection

    Not at present.

  • Opportunity for new developments

    Attempts over many years to develop inactivated or attenuated vaccines to ASF have failed. Inactivated vaccines have conferred no protection. Attempts to attenuate the virus through passage in cell culture have not been successful:

    - DNA vaccine strategies have not been successful to date. - Deletion mutant’s strategies have not been successful to date.

    GAPS:

    -        Knowledge/molecular basis and understanding immune mechanisms of surviving pigs to resist a challenge with the homologous virus.

    -        Knowledge of inhibition mechanisms for virus replication.

    -        New developments based on new , non-conventional,  strategies.

    -     Characterization of the mechanisms/Identification of genes related to virulence of the isolates.  

  • Pharmaceutical availability

  • Current therapy (curative and preventive)

    None.

  • Future therapy

    Some studies are on-going. Preliminary results obtained by “in-vitro” experiments using antiviral substances that antivirals might be used as an additional tool in ASF control.

    GAP:

    -        Lack of knowledge on antivirals therapy for ASF.

  • Commercial potential for pharmaceuticals in Europe

    None at present.

  • Regulatory and/or policy challenges to approval

    Not applicable.

  • Commercial feasibility (e.g manufacturing)

    Low.

  • Opportunities for new developments

    None.

  • New developments for diagnostic tests

  • Requirements for diagnostics development

    Currently there are very good tools in terms of sensitivity and specificity  for ASF diagnosis, however some limitations should be considered:

    -        Few commercial kits are currently available.

    -        Less sensitivity of current Ab ELISA tests for early detection of the disease compared to that obtained using the confirmatory tests (IPT/IFI).

    -        Virus isolation and haemadsorption identification is based mainly on the use of primary cell cultures, which difficult the standardisation of the technique at international level.

    -        A number of PCR tests have been validated for ASFV genome detection in different pig samples. However, virus detection in ticks is carried out by using in-house PCR procedures that are frequently not validated for this target.

    -        Standardised methods for molecular characterization of ASFV isolates allow the differentiation of at least 22 genotypes and further subtyping analysing some specific genome regions (p72 and p54 coding genes and B602L gene). However, DNA viruses’ variation rate is very low and this approach seems to be not enough to follow deeply an epidemic evolution. A very small number of full genome sequences are available. 

    -        A penside test for antibody detection is commercially available, while the development of a penside test for antigen detection is ongoing.

    A different behaviour against the virus of the varied host breeds has been proposed to influence in the disease diagnosis.

    GAPS:

    -        Understanding of viral replication at genome and protein level.

    -        Validated diagnostic tests ready for a fast upgrade to a high-throughput application in case of emergency would be desirable.

    -        An increased number of commercial kits should be very convenient. Lack of any confirmatory serological test commercially available.

    -        Improvement of screening ELISA tests for antibody detection.

    -        Standardisation of virus isolation methods using stablished cell lines cultures.

    -        Standardisation and international harmonisation of virus detection in ticks by appropriate PCR tests.

    -        A wide number of full genome sequences of diverse ASFV isolates is required to identify new genetic markers useful for further molecular characterization purposes.

    -        Penside test and front line diagnostic tests - useful for a very rapid application in case of sanitary emergency.

    -     Understanding the behaviour of different host breeds to the virus and the kinetics of antibody response.

  • Time to develop new or improved diagnostics

    GAPS: Some gaps that could delay the development of new or improved diagnostics tests:

    -        More information on host/pathogen characteristics and interaction coming from basic research.

    -     The availability of field samples from different disease scenarios.

  • Cost of developing new or improved diagnostics and their validation

    Medium at Laboratory.

    GAP:

    -    Support of programmes for sampling in Africa regions, and European countries     through collaboration with the affected countries and international        organisations. 

  • Research requirements for new or improved diagnostics

    See section "Requirements for diagnostics development" above.

    GAP:

    -        Determine the potential carrier status of surviving animals infected with different viral isolates and the changes in virulence of the ASFV. See section 18.1 above

  • New developments for vaccines

  • Requirements for vaccines development / main characteristics for improved vaccines

    -       Identify candidate vaccines or components of the genome which should be effective against the mild and acute variants of ASF. Identify candidate vaccines or recombinant DNA based on analysis of the ASFV genome. Production of a molecularly-attenuated ASFV vaccine offers a challenging research project.

    -        Conventional strategies for a vaccine have not been   useful to date. New strategies should be attempted.

    GAP:

          -     Conventional strategies for a vaccine have not been useful to date. New              strategies should be attempted.
  • Time to develop new or improved vaccines

    10 years.

  • Cost of developing new or improved vaccines and their validation

    High.

  • Research requirements for new or improved vaccines

      -        Develop better understanding of the immune response to infection and the humoral and cellular basis for the lifelong immunity post infection. Identification of target proteins or genes

      -        Understanding of the host-pathogen interactions and whether immunity is humoral or cell mediated.

      -        Assessment whether antibodies alone can passively protect pigs against ASF virus, has demonstrated not complete protection .There is not protection induced by passively acquired antibodies.

      • New developments for pharmaceuticals

      • Requirements for pharmaceuticals development

        None at present.

      • Time to develop new or improved pharmaceuticals

        Not applicable.

      • Cost of developing new or improved pharmaceuticals and their validation

        Not applicable.

      • Research requirements for new or improved pharmaceuticals

        None at present.

      Disease details

      • Description and characteristics

      • Pathogen

        ASF (ASFV) is a complex large icosahedral enveloped DNA virus that exhibits many features common to both Iridovirus and Poxvirus families. This virus is currently classified as the only member of the family Asfarviridae. DNA structure is based on two variable ends  and a conserved central region of about 125 kbp.The left and right variable ends of the genome  encodes five multigene families (MGF).  MGF are involved in the variability of the genome size within isolates, due to deletions and insertions of copies within MGF genes. In addition some MGF are involved in determining virulence and tick host-range.

        GAPS:

          -        Identification and role of viral genes interfering with host gene transcription.

          -        Persistence mechanisms of the virus in the host. 

          -        The role of the MGF in the generation of antigenic variabilility and evasion of the immune system.

          -        Role of ASFV proteins and induced proteins for an effective   and protective immune mechanism in surviving infected animals, after challenge with homologous isolate. 

          • Variability of the disease

            Suids, wild and domestic, are the natural host of ASFV. Several species of soft ticks have been shown to be ASFV reservoirs and vectors.

             

            ASFV don’t induce neutralising antibodies and this is why non serotype classification can be performed.  ASFV genotyping based on the partial nucleotide genome sequence of  the B646L gene, encoding  the p72 protein allow to   differentiate up to 22 distinct genotypes. The complete genome sequence of the E183L gene, encoding the p54 protein might be used also for subtyping.  Enhanced discrimination between isolates can be obtained through the analysis of the central variable region (CVR) within B602L gene by characterization of the tandem repeats sequences (TRS). Different isolates belonging the same ASFV genotype vary in their ability to cause disease with some causing severe acute disease and high mortality while  others exhibits  subacute and chronic forms resulting in seroconversion.

            22 different genotypes of ASF virus are already described.

            GAPS:

            -        Biological and molecular characterization of current circulating isolates.

            -        Evolution  of circulating viruses in  endemic regions

            -        Genome markers related to virulence

          • Stability of the agent/pathogen in the environment

            T°: Highly resistant to low temperatures. Heat inactivated by 56°C/70 min; 60°C/30 min

            pH: Inactivated by pH <3.9 or >11.5 in serum-free medium. Serum increases the resistance of the virus, e.g. at pH 13.4 - resistance lasts up to 21 hours without serum, and 7 days with serum

            Chemicals: Susceptible to ether and chloroform.

            Disinfectants: Inactivated by 8/1,000 sodium hydroxide (30 min), hypochlorites - 2.3% chlorine (30 min), 3/1,000 formalin (30 min), 3% ortho-phenylphenol (30 min) and iodine compounds. For animal housing and equipment, soaps and detergents, oxidising agents and alkalis are recommended.

            Soaps, detergents and Alkalis are useful to disinfect machinery, clothing, and vehicles, human housing etc and also Vircon is also recommended to be employed in aircraft.

            The procedure to be employed in feed, effluents, and manure, include bury or burn, or in the latter also by Acids and Alkalis.

            Insecticides (organophosphates and synthetic pyrethroids) for tick eradication,

            Survival: Remains viable for long periods in blood, faeces and tissues. Can multiply in vectors.

          • Species involved

          • Animal infected/carrier/disease

            Swine are the only animal species naturally infected by ASFV. The disease occurs through complex transmission cycles involving domestic pigs, wild boars, warthogs and bush pigs (African wild pigs).

            Domestic pigs, wild boars and feral/American pigs are susceptible to ASFV infection showing a range of clinical signs and mortality rates. ASFV usually induces an asymptomatic infection in wild African pigs.

            GAPS:

              -        Assessment of the survival pigs in virus transmission, maintenance and dissemination of the disease.

               

              -        Geographical distribution of wild boar.

              • Human infected/disease

                None.

              • Vector cyclical/non-cyclical

                Soft ticks (Ornithodoros spp), including O. moubata and O. erraticus also act as reservoirs and vectors for virus transmission. Transovarial, and sexual transmission can occur. In Africa, ASFV is thought to cycle between newborn warthogs and the soft ticks (Ornithodoros moubata) that live in their burrows. Individual ticks can apparently remain infected for life, and infected soft tick colonies can maintain this virus for years. All the Ornithodoros spp experimentally infected until now were susceptible to ASFV infection.

                GAPS:

                - Geographical distribution in Europe and worldwide.

                - The potential role in the actual ASF European Situation

              • Reservoir (animal, environment)

                Wild African pigs, most importantly warthogs (Phacochoerus aethiopicus), bush pigs (Potamochoerus porcus) and giant forest hogs (Hylochoerus meinertzhageni) are also infected but usually do not exhibit clinical signs, acting as reservoir hosts in Africa usually showing  an asymptomatic infection. These species of wild pigs act as reservoir hosts of ASFV in Africa. Soft ticks of the Ornithodoros genus have been shown to be both reservoirs and transmission vectors of ASFV (ASFV)

                GAPS:

                -     Host-virus interaction in wild African pigs, determining asymptomatic infection.

              • Description of infection & disease in natural hosts

              • Transmissibility

                Direct and indirect contact between infected and susceptible pigs/wild boar and wild African pigs. See Route of Transmission.

                GAPS:

                -          Studies on Neighbourhood transmission in densely population areas.

                -          Studies on pig to pig , wildboar-pig, wild and indigenous  suids in Africa – domestic pigs .

                -          Role of carrier state in the transmission of ASFV

              • Pathogenic life cycle stages

                Survivors of infection can be virus carriers for life. Around a 10% of survivors of infection are virus carriers.

                GAPS:

                -          Long-term persistence studies in recovered animals

              • Signs/Morbidity

                ASF viruses produce a range of syndromes varying from peracute, acute to chronic disease and apparently healthy virus carriers. At present chronic forms is not observed in the actual infection areas.

                GAPS:

                  -          Host factors determining the clinical outcome of infection.

                  -          Studies on recovered animals as potential carriers status in affected regions and potential changes in virulence characteristics of the circulating isolates.

                  • Incubation period

                    Incubation period is 3-15 days.

                  • Mortality

                    Depending on the ASFV isolate virulence.

                    -          Acute form (highly virulent virus) -90-100%

                    -          Subacute form (moderately virulent virus) 30-80% varies

                    -      Chronic form –low mortality.

                  • Shedding kinetic patterns

                    Unknown.

                    GAP:

                    -      Shedding  Kinetic Patterns

                  • Mechanism of pathogenicity

                    ASF is generally spread via oral and nasal routes, but also by tick bite, cutaneous scarification, and intramuscular, subcutaneous, intraperitoneal or intravenous injection.  The incubation period varies widely (4-19 days), depending on the ASFV isolate and the route of exposure.

                    By oral route, monocytes and macrophages of the tonsils and mandibular lymph nodes are the first involved. From these sites, the virus spreads through the blood and/or lymphatic system to the main sites of secondary replication – i.e., lymph nodes, bone marrow, spleen, lung, liver, and kidney. Viremia usually begins 1-8 days post infection depending of ASFV virulence and persists for weeks or months. ASFV is associated with red blood cell membranes

                    GAP:

                    • Pathogenesis mechanism of infection by ASFV of different virulence are not well understood.

                     

                  • Zoonotic potential

                  • Reported incidence in humans

                    ASFV has never been shown to infect humans and is not considered to be a zoonotic pathogen.

                  • Risk of occurence in humans, populations at risk, specific risk factors

                    None.

                  • Symptoms described in humans

                    None.

                  • Estimated level of under-reporting in humans

                    None.

                  • Likelihood of spread in humans

                    None.

                  • Impact on animal welfare and biodiversity

                  • Both disease and prevention/control measures related

                    ASF outbreaks have an impact both due to the severity of the disease and with the introduction of control measures especially movement controls.

                    GAP:

                    • No vaccine available to date

                  • Endangered wild species affected or not (estimation for Europe / worldwide)

                    European species of wild pigs are affected but this is not the case for African wild pigs in which no clinical signed are observed.

                  • Slaughter necessity according to EU rules or other regions

                    Slaughter of infected and in contact pigs.

                  • Geographical distribution and spread

                  • Current occurence/distribution

                    African swine fever was first recorded in Kenya in 1921 and is present as endemic in most sub-Saharan African countries. It spread to southern Europe in 1957 (genotype I) affecting different countries in Europe and central and south America. In Europe, ASF is still endemic in Sardinia (Italy). Since the introduction of ASF in Georgia in 2007 from East Africa (genotype II) the disease is affecting East Europe. The situation in Russia in wild boar and domestic pigs, with two endemic regions recently described has originated a sporadic spill-over of ASF to the adjacent countries such Ukraine and Belarus. In earlier 2014, ASF cases in wild boar were reported in Lithuania and Poland in bordering regions with Belarus. Since then ASF cases or outbreaks in wild boar and domestic pigs have been detected in the EU countries Estonia, Latvia, Lithuania, and Poland.  The events have proved that the threat of ASF spreading to other regions remains and it is potentially devastating to the global pig industry. Source of information: www.oie.int and EU: Animal disease notification system (ADNS)

                    GAPS:

                    • Education, awareness and preparedness of veterinary staff and producers.

                  • Epizootic/endemic- if epidemic frequency of outbreaks

                    -          Become endemic mainly in developing countries, due to presence of complex transmission cycles which could involve a sylvatic cycle, a domestic cycle and a pig-tick cycle.

                    -     Greatly influenced by presence – and subsequent infection- of wild boar and         vectors (wild African pigs and soft ticks acting as reservoirs) GAPS:
                      •  Appropriate control measures adapted to the different scenarios
                      • The role of wildboar and soft ticks in the virus transmission, maintenance and dissemination of the disease in Europe.
                      • Vectorial capacity in Europe and biting habits.
                      •  Evolution of the circulating strains in Europe and Africa, from the molecular and biological point of view, and what is the mechanism involve in virus maintenance.
                      • Seasonality

                        None.

                        GAP:

                        • Assessment of seasonality
                      • Speed of spatial spread during an outbreak

                        Can be high mainly due to transport and movements of affected animals (domestic and wild board) and products as well as the pig density and farms biosecurity.

                        GAP:

                        • The role of wild boars in spreading the disease under different conditions.
                      • Transboundary potential of the disease

                        Potentially high and wide spreading, dependant on the movement of infected pigs/wild boars/ African wild pigs or infected meat or other pig products, and illegal movements.

                      • Seasonal cycle linked to climate

                        Few information available.

                        GAP:

                        • More information about seasonal cycle linked to climate.
                      • Distribution of disease or vector linked to climate

                        Not known.

                        GAP:

                        • More information about disease distribution linked to climate
                      • Outbreaks linked to extreme weather

                        No.

                      • Sensitivity of disease or vectors to the effects of global climate change (climate/environment/land use)

                        Not known.

                        GAP:

                        • More information about seasonal cycle linked to climate
                      • Route of Transmission

                      • Usual mode of transmission (introduction, means of spread)

                        Direct transmission: contact between sick (domestic and wildboar) and healthy animals; contact with asymptomatic infected African wild reservoirs (carriers) and soft ticks.

                        Indirect transmission:

                        • feeding with garbage containing infected meat
                        • fomites: premises, vehicles, implements, clothes, …
                      • Occasional mode of transmission

                        Ornithodoros ticks, where present, can act as transmission vector of the ASF virus.

                      • Conditions that favour spread

                        -          The virus can survive outside the pig for a long time, so the movement of contaminated vehicles, clothing, footwear and equipment can also spread disease.

                        -          Unspecific clinical symptoms could easily be confused with other diseases such as CSF, Salmonellosis, Erysipela or any other septicaemia condition. It might delay diagnosis.

                        -          Density of wild boar population.

                        -          The use of swill feeding.

                        -          Presence of carrier animals and soft ticks.

                        -          Socio-cultural way of life.

                        GAP:

                        • The role of reservoirs in the transmission of the disease under different conditions.
                        • Intensive communication campaigns are required to raise awareness between vets, keepers and producers.
                      • Detection and Immune response to infection

                      • Mechanism of host response

                        -          Pigs often die before the development of a humoral response when infected with a virulent strain. Pigs which do not die will mount an antibody response and have significant levels of ASF specific cytotoxic T lymphocytes. Pigs will demonstrate a solid immunity to challenge from homologous strains but not heterologous strains. However there is an absence of neutralizing antibodies against ASFV. 

                        -          The ASFV replicates in porcine macrophages.

                        -     The essential effectors immune mechanisms involved in protection against         ASF are poorly understood. All attempts to develop an effective vaccine have         been unsuccessful to date.

                        GAPS:

                          • The role of MGF and its manipulation to induce a protective immune response.
                          • Identification and role of viral genes interfering with host gene host defences and immune response .
                          • Deeper characterization of viral interactions with pig macrophages and with the host (domestic pigs) , in ASFV infection with isolates exhibiting different virulence, and well characterised at genome level, may open new insights for the manipulation of pig immune responses, towards the  stimulation of protective immune response.
                          • Deeper effectors immune mechanisms characterization, involved in protection in surviving pigs.
                          • Characterization of the immune response in wild African suids.

                           

                          • Immunological basis of diagnosis

                            Detection of antibodies and evidence of the virus genome or virus antigen. ASFV infection produces a long-term viremia from early stages of infection. Specific IgG antibodies are detectable in blood from the first week and for a long period of time, months even year, in the surviving pigs. The early appearance and subsequent persistence of antibodies is the reason they are so useful in studying subacute and chronic forms of the disease. For the same reason, they play an important role in testing strategies implemented as part of eradication programmes.  

                          • Main means of prevention, detection and control

                          • Sanitary measures

                            -          Control of live animals and swine product imports, control of waste food. Movement controls can all be successful. Quarantine.  Once established in an area tick control becomes important using acaricides.

                            -          Strict sanitary measures on infected farms, stamping out of animals, cleansing, disinfection, sentinels, serological control of sentinels after a month.

                            -     Identification of carrier pigs. Stamping out.

                            GAP:

                            • New control strategies and eradication models depending on the epidemiological situation, taking into account the complex transmission cycles, involving domestic pigs and the presence of wild boar and/or soft ticks and /or wild African pigs.
                          • Mechanical and biological control

                              -          Avoid contact between pigs, wild boar and soft tick vectors, including warthogs in Africa - i.e. prevent pigs from wandering.

                              -     Performing good tracing sources of infection and sources of spreading. 
                              • Diagnostic tools

                                Since no vaccine is available, ASF diagnosis by virus detection and serological tests are critical for disease containment.

                                Virus detection and isolation :

                                • Virus isolation/Haemadsorption test(CPE/HAD) (HAD) in primary cell cultures.
                                • PCR techniques: Real-time, Conventional gel based PCR and Multiplex conventional and rt-PCR. Most of the PCR systems show good to high sensitivity and specificity.  
                                • Direct Immunofluorescence (DIF). Low sensitivity, in case of specific antibody presence.
                                • Ag-ELISAs. Low sensitivity. Not recommended for screening of          individuals.

                                ASF antibody detection: 

                                •  ELISAs: A number of commercial and "in-house" ELISAs, based on different detection systems.
                                • Confirmatory tests
                                            - Immunoblotting test (IB) based on the use of ASFV semipurified antigen                strips.            - Indirect Immunofluorescence test (IIF).            - Immunoperoxidase test (IPT)
                                • Penside test for antibody detection.

                                ASFV genotyping: i) sequencing of the C- terminal end of VP72 gene,which differentiates up to 22 distinct genotypes; ii) full genome sequence of the p54-gene and iii) analysis of the central variable region (CVR) to distinguish between closely related isolates and identify virus subgroups within the 22 p72 genotypes.

                                GAPS:

                                  • Virus isolation techniques need to find cell lines that replace primary cultures.
                                  •  Assessment of diagnostic techniques taking into account the epidemiological situation with special regards to the new circulating isolates. 
                                  •  Appropriate validation of newly developed diagnostic tests prior to implementation its routine diagnosis. 
                                  •  New large scale diagnostic techniques adapted to scenarios.
                                  • Penside tests for antigen detection
                                  •  Evaluation of current diagnostic tests for diagnosing ASF in new source of samples (oral fluids, meat juice, support for transporting samples, etc…)
                                  • To improve detection it is necessary wider knowledge of clinical presentations.
                                  • To define new genetic markers related to virulence.
                                • Vaccines

                                  None available at present.

                                  GAPS:

                                    • More research based on virus-host interaction and immunity against infection is need.
                                    • A deep evaluation of the mechanisms involved in attenuation  of  the  potential  vaccine candidates  is need.
                                    • New strategies to develop an effective vaccine using non-conventional approaches.
                                    • Therapeutics

                                      No effective treatment at present.

                                      GAP:

                                      • Potential of antivirals. It may be of interest in ASF control.
                                    • Biosecurity measures effective as a preventive measure

                                      Rapid slaughtering of all pigs and proper disposal of cadavers and litter is essential. Thorough cleaning and disinfection.  Movement controls.

                                    • Border/trade/movement control sufficient for control

                                      • Careful import policy for animals and animal products.
                                      • Proper disposal of waste food from aircraft or ships coming from infected countries.

                                      GAP: Not always fully enforced.

                                    • Prevention tools

                                      Efficient sterilisation of garbage.

                                      GAP:

                                      • The prohibition of swill feeding is not fully enforced in certain countries.
                                    • Surveillance

                                      Through regular clinical monitoring of animals (wild and domestics), in parallel with appropriate sampling collection and laboratory diagnosis.

                                      Pigs recovered from acute and subacute or chronic infections usually exhibit a viremia for several weeks making the PCR test a very useful tool for the detection of ASFV in pigs infected with low or moderately virulent strains. In addition, Antibody detection techniques are very useful in detecting surviving infected animals.GAPS:
                                      • Appropriate surveillance adapted to the risk.
                                      • Lack of appropriate surveillance programs in developing countries.
                                    • Past experiences on success (and failures) of prevention, control, eradication in regions outside Europe

                                      Recovered ASFV carrier pigs and persistently infected wild pigs constitute the biggest problems in controlling the disease. Eradication was successful in the Iberian Peninsula and in the Caribbean.

                                      Some common failures have been identified:

                                      -          Late detection.

                                      -          Low/insufficient resources or political instability.

                                      -           Scavenging pig husbandry or free-roaming pigs.

                                      -          Uncooked swill feed.

                                      -          Presence of wild pigs and ticks as reservoirs.

                                      -          Co-circulation of several isolates and or genotypes with different characteristics.

                                      -          Failure to identify risk factors.

                                      Invert in prevention is the best measure to avoid the significant socio-economic consequences of this disease.

                                      GAPS:

                                        • Disease modelling taking into account the different scenarios, /specific epidemiological conditions, for  best control options
                                        • To develop Risk mapping to support a targeted surveillance/control programme.
                                        • Costs of above measures

                                          Costs can be high. Outbreaks in Europe were controlled by animal quarantine and slaughter, frequently at a very high cost.
                                        • Disease information from the OIE

                                        • Disease notifiable to the OIE

                                          Yes.

                                        • Socio-economic impact

                                        • Zoonosis: impact on affected individuals and/or aggregated DALY figures

                                          None.

                                        • Zoonosis: cost of treatment and control of the disease in humans

                                          None.

                                        • Direct impact (a) on production

                                          Variable depending on the strains involved. With 100% mortality can have a very high cost. This disease produces huge economic and social loses in many African countries, and impairs the development of the porcine industry.

                                        • Direct impact (b) cost of private and public control measures

                                          Disease outbreaks have occurred in Europe, South America, and the Caribbean; the cost of eradication has been significant. During outbreaks in Malta and the Dominican Re-public, the swine herds of these countries were completely depopulated. In Spain and Portugal, ASFV became endemic in the 1960s and complete eradication took more than 30 years.

                                        • Indirect impact

                                          Main indirect impact is on the constraints on livestock production and the trade in pigs and their products. Loss of export markets.

                                        • Trade implications

                                        • Impact on international trade/exports from the EU

                                          Controls on the movement, of pigs and products from infected countries. Likely ban on imports from affected countries. Quarantine measures.

                                        • Impact on EU intra-community trade

                                          Movement controls on live pigs and their products from infected areas.

                                        • Impact on national trade

                                          Restrictions and controls on internal movements form the protection and surveillance zones.

                                        • Main perceived obstacles for effective prevention and control

                                          -          Lack of vaccines, carrier recovered pigs, reservoirs in ticks and wild pigs in Africa.

                                          -          Improvement of sanitary infrastructures at animal holdings and Biosecurity in some countries. . 

                                          -          Individual identification of every animal.

                                          -          Census update, in some countries.

                                          GAPS:

                                            • Lack of awareness by farmers, and veterinary staff.
                                            • Improvement of control strategic
                                            • Improvement of control measures  by means of :

                                            o   improvement of sanitary infrastructures at animal holdings and Biosecurity in some countries. . 

                                            o   Individual identification of every animal. Census up date in some countries.

                                            o   epidemiological surveys.

                                            o   promoting associations

                                            • Main perceived facilitators for effective prevention and control

                                              -          Ability to identify carriers, control of ticks.

                                              -          Improvement of sanitary infrastructures at animal holdings and Biosecurity in some countries. . 

                                              -          Individual identification of every animal.

                                              -          Census up date, in some countries.

                                              GAP:- appropriate vaccines

                                            Risk

                                            • Changes in production practices and increased globalization have in-creased the risk of African swine fever being introduced into free areas.

                                              The main risk of ASF introduction into Europe is via infected pig meat or pig meat products, for example illegally imported pig meat or bush meat from infected countries or legally imported meat from areas with undetected infection

                                              GAPS:

                                              • Control movements.
                                              • Improve awareness of field staff, veterinary and producers.
                                              • Biosecurity
                                              • Type of holdings: free ranging of back-yards.
                                              • The role of soft ticks in the potential ASF transmission and their distribution in European countries requires further investigation.

                                            Main critical gaps

                                            Conclusion

                                            • ASF has the potential to enter free countries if sanitary and border controls are ineffective. The development of effective vaccines for contingency use in Europe and for routine use in endemic countries would be advantageous.

                                            Sources of information

                                            • Expert group composition

                                              Names included are included where permission has been given

                                              José Manuel Sánchez-Vizcaíno - Director del Laboratorio de Referencia de la OIE, Universidad Complutense de Madrid (Leader)

                                              Marisa Arias/ INIA-CISA, Madrid, Spain

                                              Yolanda Revilla/ CSIC, Spain

                                              Carmina Gallardo/ INIA-CISA, Madrid, Spain

                                              Cristina Jurado/ Universidad Complutense de Madrid, Spain

                                            • Reviewed by

                                              Project Management Board.

                                            • Date of submission by expert group

                                              9th of April 2015.

                                            STAR-IDAZ Research Road Maps