Opinion on SVD and VS

SCOFCAH, 07/05/ 2012

Mandate

Request for a scientific opinion on Swine Vesicular disease (SVD) and Vesicular Stomatitis (VS)

• Differential diagnostic with FMD• Epidemiological situation/impact for AH• Proportionality of current measures• Notifiable diseases (swine)

– SVD – OIE list A – swine diseases• Enterovirus, Picornaviridae

– VS – OIE list A – multi species diseases• Vesiculoviruses, Rhabdoviridae

– 2 immunological groups: New Jersey and Indiana» No cross-protection among the 2 groups

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ToR SVD

1. The significance of the presence, origin and occurrence of SVD and its actual impact on livestock as a disease, separated from its impact related to trade, in particular in terms of the current EU epidemiological situation;

2. An assessment of the risk of the spread of SVD within EU and the risk of new introductions of SVD into the EU specially by animals and animal products?

3. The availability and suitability of different laboratory diagnostic tests (and analytical cut-off when appropriate) for SVD that together with clinical diagnosis can be used for the differential diagnosis with other major vesicular diseases like FMD; 3

ToR SVD

4. The identification of possible control measures, the suitability, proportionality and sustainability of current measures compared with other possible measures to control and eradicate SVD including surveillance, in particular targeted surveillance, restrictions on movements of animals and animal products, control measures and other elements; taking into account advantages and disadvantages;

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ToR VS

1. The significance of the presence and occurrence of VS in susceptible species (specially livestock animals) outside EU and the significance of a potentialintroduction of VS in the EU and its potential impact on EU livestock, including equidae, in the context of the current epidemiological situation

2. An assessment of the risk of introduction and spread of VS in the EU, especially by animals, animal products and vectors and an assessment of the risk of an epizootic or virus persistence being maintained in he EU, considering livestock which includes equidae, epidemiology, vectors and climatic situation;

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ToR VS

3. The availability and suitability of different laboratory diagnostic tests (and analytical cut-off when appropriate) for VS under different epidemiological circumstances that together with clinical diagnosis can be used for differential diagnosis with other major vesicular diseases like FMD;

4. The identification of possible control measures, the suitability, proportionality and sustainability of the possible measures to avoid introduction, or to control and eradicate VS, including surveillance, in particular targeted surveillance, restrictions on movements of animals and animal products, testing regimes on herds and animals, control measures and other elements; taking into account advantages and disadvantages; 6

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Amendments of ToRs

• During the kick off meeting the above request was focused on: – the significance of the presence, origin and occurrence of SVD,

VS – their actual impact on livestock as a disease, separated from

their impact related to trade, in particular in the context of the current EU epidemiological situation

– assessment of the risk of spread and of (new) introductions • Impact was defined as morbidity, mortality and production losses• It was clearly stated that if a suspicion of a vesicular disease was

observed a diagnosis for FMD is always required.• It was decided that depending on the results of the assessment of

those ToRs, the ToRs on availability and suitability of laboratory diagnostic tests and on possible control measures will or will not need to be assessed

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ToRs SVD

• the significance of the presence, origin and occurrence of SVD and its actual impact on livestock as a disease, separated from its impact related to trade, in particular in the context of the current EU epidemiological situation;

• an assessment of the risk of spread of SVD within the EU and of the risk of new introductions of SVD into the EU specially by animals and animal products.

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ToRs VS

• the significance of the presence and occurrence of VS in susceptible species (specially livestock animals) outside the EU and the significance of a potential introduction of VS in the EU and its potential impact on EU livestock, including equidae, in the context of the current epidemiological situation;

• an assessment of the risk of introduction and spread of VS into the EU, especially by animals, animal products and vectors and an assessment of the risk of an epizootic or virus persistence being maintained in the EU, considering livestock which includes equidae, epidemiology, vectors and climatic situation;

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Occurrence and the significance of the presence of the disease

• National surveillance programmes:– questionnaire was developed and information on SVD was

gathered through the EFSA focal points from EU MS– for VS also to researchers and national veterinary authority staff in

the Americas

• Annual reports of EU CRL in Pirbright were consulted concerning the actual surveillance activities

Methodological approach

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Impact on livestock as a disease and the spread of the disease within the EU

A. Observations of impact and spread when control measures are implemented after detection of infection:

•Peer-reviewed studies (Systematic Literature Review)•Details from unpublished field observations and clinical trials

Since the current stamping out policy does not permit a long-term evaluation of the final impact and spread of any SVD or VS outbreak, a spatially-explicit structured model was used to evaluate the disease impact and spread without intervention. Since SVD often has a subclinical course seroprevalence was considered as an indication of the infection.

Methodological approach

Methodological approach

B. Estimation of impact and spread without implementation of any control measures:

• spatially-explicit mechanistic Model for risk of impact and spread of SVD and VS

– Using data from „Occurrence and the significance of the presence of the disease” and from A

– Modelled impact and spread of SVD and VS were compared to those of CSF in a stochastic structured model.

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Methodological approach

Assessment of the risk of introduction of VS to EU

National surveillance programmes (questionnaire was developed and information on VS was gathered from researchers and national veterinary authority staff in the Americas

Probabilistic approach to estimate the likelihood of introduction of VSV in Europe through the importation of live animals from third countries

The idea

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Import (N)

Free

Likelihood of Introduction of VSV

Equidea Non Equidea

General responses SVD

• affects pigs • in Europe, during the last 10 years only Italy and Portugal

have reported SVD outbreaks; reports have been persistent in Italy.

• all provisions in the EU directives related to SVD are based on the threat of FMD and biological properties of FMDV

• suitable diagnostics tools are available and described in the OIE manual and annual proficiency testing is carried in the EU, demonstrating an adequate diagnostic capacity within the EU

The significance of the presence, origin and occurrence of SVD and its actual impact on livestock as a disease, separated from its impact related to trade, in particular in terms of the current EU epidemiological situation

• The significance and the impact of SVD on animal health and production are considered low :– Case-fatality is negligible and the morbidity is low:

• Italy (2004-2010) below 1% on farm level; 0,64% on animal level in affected farms

• Portugal (2003,2004 and 2007) between 0 and 1%– Production losses reported in the field are negligible– In a natural setting, the infection is often subclinical and is

frequently limited to some pens only. – In experimental studies, the majority of SVDV-infected animals

have developed clinical signs, although these were mild, with no deaths, and fever only persisting for 2 days.

An assessment of the risk of the spread of SVD within the EU and the risk of new introductions of SVD into the EU especially by animals and animal products

• The modeled spread within farms was limited (When applying SVD estimates of transmission).– The viraemic period is two to three days, transmission occurs mainly in the first week after infection. – SVDV is extremely resistant to normal disinfectants and is noted for its persistence in the environment.– spread of SVD is limited, mostly limited to a few pens. – When SVD has been introduced into a farm, good biosecurity practice has been shown to slow down the spread

within the farm, minimising the risk of further transmission.

• The observed spread of SVD between farms – The between-farm spread of SVD is mainly related to movements of infected animals and/or contaminated lorries. – It has also been demonstrated that between farm spread of SVD can be linked to introduction of contaminated

material, as well as visit of contaminated personnel such as veterinarians, inseminators or farm workers.

• The modeled spread of SVD between farms is at least similar to CSFIf all transportation procedures of CSF contribute to transmission of SVD in the model,

– Assuming that between-farm transmission of SVD is as low as the detected between-animal SVD transmission when comparing SVDV and CSFV, the resulting spread was reduced to about 1/100 of infected farms or infectious farm days.

– Even when assuming that only animal transportation causes between farm transmission, the modeled SVDV is spreading.

• It is unlikely that animal products will contribute to the risk of introduction of SVDV.

– In old outbreaks it was found feeding of waste food was an important source of infection through the ingestion of contaminated meat (15%) the role of swill feeding is not clear.

– In recent outbreaks in Italy swill feeding was not found to be among the causes of between-farm transmission – Since SVDV can only be detected in muscles and organs during the 2-3 days viraemic period and since infected

animals (field and experimentally infected) do not always develop viraemia, it is unlikely that animal products will contribute to the risk of introduction of SVDV.

SVD

• The main reason for the low impact observed in an outbreak is the pen disease characteristic.Therefore:– larger farms will suffer a lower relative impact on health and production

because of the small number of pens becoming infected on a givenfarm.

– the impact of SVD outbreaks has to be assessed at the level of infected farms and not at the level of the spread within livestock populations.

• Biosecurity plays a major role to control the disease.

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The significance of the presence and occurrence of VS in susceptible species (livestock animals) outside EU and the significance of a potential introduction of VS in the EU and its potential impact on EU livestock, including equidae, in the context of the current epidemiological situation

• The clinical manifestations and pathology do not differ broadly between susceptible species

– The estimated proportion of clinically-affected animals observed in experimental VSV studies was 0.24 in pigs, 0.60 in cattle and 0.54 in equidae.

• Observational studies on VS outbreaks indicated several subclinical infections with limited observed clinical signs, both in equidae and cattle.

• The mean incubation period observed in experimental VSV studies was three days and the mean duration of virus shedding was three days.

• The overall significance and impact of VS is difficult to estimate, but higher than for SVD.

– The case-fatality and mortality is negligible. – The within-herd prevalence can vary widely between affected herds (5-70%). – In the 1995 VS outbreak in the USA the overall reported prevalence was 0.35 in equidae and

0.29 in cattle, with no sheep and goats being affected, but the infection was limited to selected geographical areas.

– The reported prevalence in Colorado, the state most affected by the 2004-2005 outbreak, was 0.81.

– In VSV-endemic countries (e.g. South and Central Americas), the mean seroprevalenceobserved in cattle was 0.40 and 0.08 for the New Jersey and Indiana virus respectively.

– In VSV-endemic countries, the mean seroprevalence observed in equidae was 0.64 and 0.25 for the New Jersey and Indiana virus respectively.

– Data on production losses are limited, but they seem to be variable

An assessment of the risk of introduction and spread of VS in the EU, especially by animals, animal products and vectors and an assessment of the risk of an epizootic or virus persistence being maintained in the EU, considering livestock which includes equidae, epidemiology, vectors and climatic situation

• In comparison to CSFV, the modeled spread of VSV was less predictable but with the potential for increased spread. Including insect vectors in the model resulted in a spread worse than CSFV.

– The mean incubation period observed in experimental VSV studies was three days. VS has a short-lived and distinct disease period and does not lead to a carrier state.

– VSV can be easily inactivated and the virus can survive in the environment for up to four days.– Insects are suggested to play a role in the transmission of VSV, but the mechanism is not clear. Experimental studies have shown

that the virus can replicate in insects. – Humans can become infected mainly through direct contact with infected animals or the virus, but the disease is considered mild

and self-limiting. Data on the prevalence of infection in humans are contradictory.– In both observational and experimental studies, when VS is introduced into a naïve population, the infection can lead to a wide

range of clinical signs but they can be mild to severe.• Transmission of VSV by meat is not likely. The potential for VSV transmission by other animal

products has not been addressed in literature.– Although in cattle, horses, and swine, high titers of VSV are found at the margins of lesions and in vesicular fluids for a short period

after infection, viraemia is undetectable in other tissues including muscle, brain, liver, spleen, mesenteric lymph nodes, kidneys and spinal cord.

• Risk of introduction:– Depending on the testing system and the VSV prevalence in the subpopulation destined for export and considering that 4000

susceptible animals are imported per year, it is likely to take 50 years (testing system sensitivity 0.98, prevalence 0.00025), 14 years (testing system sensitivity 0.98, prevalence 0.0009), 100 years (testing system sensitivity 0.99, prevalence 0.00025) or 27 years (testing system sensitivity 0.99, prevalence 0.0009) before an infected animal is introduced to the EU.

Conclusions for SVD

• The significance and the impact of SVD on animal health and production are considered low

• The modeled spread within farms was limited• The modeled spread of SVD between farms is

similar or lower compared to CSF • The main reason for the low impact observed in

an outbreak is the pen disease characteristic.• It is unlikely that animal products will contribute

to the risk of introduction of SVDV.

Conclusions VSV

• The overall significance and impact of VS is difficult to estimate, but higher than for SVD.

• The modeled spread of VSV was less predictable but with the potential for increased spread. Including insect vectors in the model resulted in a spread worse than CSFV.

• Transmission of VSV by meat is not likely. The potential for VSV transmission by other animal products has not been addressed in literature.

• Risk of introduction variable between 14 and 100 years

Recommendations

• SVD– Knowledge about and implementation of biosecurity principles – Diagnostic tools should be maintained up to date and annual proficiency testing

organised – Because clinical signs in infected animals are rare and mild, in situations where

the level of spread of SVDV needs to be assessed, surveillance should be done at the level of pig holdings.

– SVD should be considered as one of the differential diagnostic panels for vesicular diseases in swine populations.

• VS– Quarantine and prior testing for animals imported from VSV endemic countries

should be maintained.– Laboratory capacity for diagnosis should be improved and annual proficiency

testing organised in the EU,– Because the clinical signs are rare and mild, in situations where the level of

spread of VSV needs to be assessed, it is recommended to carry out active surveillance in susceptible species using appropriate tests.

– VS should be considered as one of the differential diagnostic panels for vesicular diseases in susceptible species.

– More information concerning the role of vectors in the spread of VSV should be gathered.

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Likelihood of Introduction of VSV