Terrestrial Animal Health Code
Terrestrial Animal Health Code |
Infection with bluetongue virus
General provisions
For the purposes of the Terrestrial Code, bluetongue is defined as an infection of ruminants and camelids with bluetongue virus (BTV), that is transmitted by Culicoidesvectors.
The following defines the occurrence of infection with BTV:
BTV has been isolated from a sample from a ruminant or camelid or a product derived from that ruminant or camelid; or
antigen or ribonucleic acid specific to BTV has been identified in a sample from a ruminant or camelid showing clinical signs consistent with bluetongue, or epidemiologically linked to a suspected or confirmed case; or
antigen or ribonucleic acid specific to a BTV live vaccine strain has been identified in a sample from a ruminant or camelid that is unvaccinated, or has been vaccinated with an inactivated vaccine, or with a different live vaccine strain, showing clinical signs consistent with bluetongue, or epidemiologically linked to a suspected or confirmed case, or
antibodies to structural or nonstructural proteins of BTV that are not a consequence of vaccination have been identified in a sample from a ruminant or camelid that either shows clinical signs consistent with bluetongue, or is epidemiologically linked to a suspected or confirmed case.
For the purposes of the Terrestrial Code, the infective period for bluetongue shall be 60 days.
Standards for diagnostic tests and vaccines are described in the Terrestrial Manual.
When authorising import or transit of the commodities covered in the chapter, with the exception of those listed in Article 8.3.2., Veterinary Authorities should require the conditions prescribed in this chapter relevant to the BTV status of the ruminant and camelid populations of the exporting country or zone.
Safe commodities
When authorising import or transit of the following commodities, Veterinary Authorities should not require any bluetongue-related conditions regardless of the bluetongue status of the exporting country:
milk and milk products;
meat and meat products;
hides and skins;
wool and fibre;
in vivo derived bovine embryos collected, processed and stored in accordance with Chapter 4.7.
Country or zone free from bluetongue
Historical freedom as described in Chapter 1.4. does not apply to bluetongue.
A country or a zone may be considered free from bluetongue when infection with BTV is notifiable in the entire country and either:
a surveillance programme in accordance with Articles 8.3.14. to 8.3.17. has demonstrated no evidence of infection with BTV in the country or zone during the past two years; or
an ongoing surveillance programme has found no Culicoides for at least two years in the country or zone.
A country or zone free from bluetongue in which ongoing vectorsurveillance, performed in accordance with point 5) of Article 8.3.16., has found no Culicoides will not lose its free status through the introduction of vaccinated, seropositive or infective ruminants or camelids, or their semen or embryos from infected countries or zones.
A country or zone free from bluetongue in which surveillance has found evidence that Culicoides are present will not lose its free status through the introduction of seropositive or vaccinated ruminants or camelids, or semen or embryos from infected countries or zones, provided:
an ongoing surveillance programme focused on transmission of BTV and a consideration of the epidemiology of infection with BTV, in accordance with Articles 8.3.14. to 8.3.17. and Chapter 4.3., has demonstrated no evidence of transmission of BTV in the country or zone; or
the ruminants or camelids, their semen and embryos were introduced in accordance with this chapter.
A country or zone free from bluetongue adjacent to an infected country or zone should include a zone in which surveillance is conducted in accordance with Articles 8.3.14. to 8.3.17.
Country or zone seasonally free from bluetongue
A country or zone seasonally free from bluetongue is, respectively, an infected country or a part of an infected country or zone, for which surveillance conducted in accordance with Articles 8.3.14. to 8.3.17. demonstrates no evidence either of transmission of BTV or of adult Culicoides for part of a year.
For the application of Articles 8.3.7., 8.3.9. and 8.3.11., the free season is taken to commence the day following the last evidence of transmission of BTV (as demonstrated by the surveillance programme), and of the cessation of activity of adult Culicoides.
For the application of Articles 8.3.7., 8.3.9. and 8.3.11., the free season is taken to conclude either:
at least 28 days before the earliest date that historical data show transmission of BTV may recommence; or
immediately if current climatic data or data from a surveillance programme indicate transmission of BTV or an earlier resurgence of activity of adult Culicoides.
A seasonally free zone in which ongoing surveillance has found no evidence that Culicoides are present will not lose its free status through the introduction of vaccinated, seropositive or infective ruminants or camelids, or semen or embryos from infected countries or zones.
Country or zone infected with BTV
For the purposes of this chapter, a country or zone infected with BTV is one that does not fulfil the requirements to qualify as either free or seasonally free from bluetongue.
Recommendations for importation from countries or zones free from bluetongue
For ruminants and camelids
Veterinary Authorities should require the presentation of an international veterinary certificate attesting that:
the animals showed no clinical sign of bluetongue on the day of shipment;
AND
the animals were kept in a country or zone free from bluetongue since birth or for at least 60 days prior to shipment; or
the animals were kept in a country or zone free from bluetongue for at least 28 days, then were subjected, with negative results, to a serological test to detect antibodies to the BTV group and remained in the free country or zone until shipment; or
the animals were kept in a country or zone free from bluetongue for at least 14 days, then were subjected, with negative results, to an agent identification test, and remained in the free country or zone until shipment; or
the animals:
were vaccinated, at least 60 days before the introduction into the free country or zone, from which they are to be exported, against all serotypes demonstrated to be present in the source population through a surveillance programme as described in Articles 8.3.14. to 8.3.17.;
were identified as having been vaccinated;
remained in the free country or zone for at least seven days until shipment;
AND
if the animals were exported from a free zone within an infected country, either:
did not transit through an infected zone during transportation to the place of shipment; or
were protected from attacks from Culicoides in accordance with point 2 of Article 8.3.13. at all times when transiting through an infected zone; or
had been vaccinated in accordance with point 5) above.
Recommendations for importation from countries or zones seasonally free from bluetongue
For ruminants and camelids
Veterinary Authorities should require the presentation of an international veterinary certificate attesting that the animals:
showed no clinical sign of bluetongue on the day of shipment;
AND
were kept during the free season in a seasonally free country or zone since birth or for at least 60 days prior to shipment; or
were kept during the free season in a seasonally free country or zone for at least 28 days prior to shipment, and were subjected during that residence period to a serological test to detect antibodies to the BTV group, with negative results, carried out at least 28 days after the commencement of the residence period; or
were kept during the free season in a seasonally free country or zone for at least 14 days prior to shipment, and were subjected during that residence period to an agent identification test, with negative results, carried out at least 14 days after the commencement of the residence period; or
were:
vaccinated, at least 60 days before shipment, against all serotypes demonstrated to be present in the source population through a surveillance programme in accordance with Articles 8.3.14. to 8.3.17.;
identified as having been vaccinated;
kept during the free season in the seasonally free country or zone for at least seven days, and until shipment;
AND
either:
did not transit through an infected zone during transportation to the place of shipment; or
were protected from attacks from Culicoides in accordance with point 2 of Article 8.3.13. at all times when transiting through an infected zone; or
were vaccinated in accordance with point 5) above.
Recommendations for importation from countries or zones infected with BTV
For ruminants and camelids
Veterinary Authorities should require the presentation of an international veterinary certificate attesting that the animals:
showed no clinical sign of bluetongue on the day of shipment;
AND
were protected from attacks from Culicoides in accordance with Article 8.3.13. in a vector-protected establishment for at least 60 days prior to shipment and during transportation to the place of shipment; or
were protected from attacks from Culicoides in accordance with Article 8.3.13. in a vector-protected establishment for at least 28 days prior to shipment and during transportation to the place of shipment, and were subjected during that period to a serological test to detect antibodies to the BTV group, with negative results, carried out at least 28 days after introduction into the vector-protected establishment; or
were protected from attacks from Culicoides in accordance with Article 8.3.13. in a vector-protected establishment for at least 14 days prior to shipment and during transportation to the place of shipment, and were subjected during that period to an agent identification test, with negative results, carried out at least 14 days after introduction into the vector-protected establishment; or
were:
vaccinated, at least 60 days before shipment, against all serotypes demonstrated to be present in the source population through a surveillance programme in accordance with Articles 8.3.14. to 8.3.17.;
identified as having been vaccinated; or
were demonstrated to have antibodies for at least 60 days prior to shipment against all serotypes demonstrated to be present in the source population through a surveillance programme in accordance with Articles 8.3.14. to 8.3.17.
Recommendations for importation from countries or zones free or seasonally free from bluetongue
For semen of ruminants and camelids
Veterinary Authorities should require the presentation of an international veterinary certificate attesting that:
the donor males:
showed no clinical sign of bluetongue on the day of collection and were kept in a country or zone free from bluetongue or in a seasonally free country or zone during the free season for at least 60 days before commencement of, and during, collection of the semen; or
comply with point 1 of Article 8.3.10.;
the semen was collected, processed and stored in accordance with Chapters 4.5. and 4.6.
Recommendations for importation from countries or zones infected with BTV
For semen of ruminants and camelids
Veterinary Authorities should require the presentation of an international veterinary certificate attesting that:
the donor males:
showed no clinical sign of bluetongue on the day of collection;
AND
were kept in a vector-protected establishment in accordance with point 1 of Article 8.3.13. for at least 60 days before commencement of, and during, collection of the semen; or
were subjected to a serological test to detect antibodies to the BTV group, with negative results, between 28 and 60 days after each collection for this consignment; or
were subjected to an agent identification test on blood samples collected at commencement and conclusion of, and at least every 7 days (virus isolation test) or at least every 28 days (PCR test) during, semen collection for this consignment, with negative results;
the semen was collected, processed and stored in accordance with Chapters 4.5. and 4.6.
Recommendations for importation from countries or zones free or seasonally free from bluetongue
For in vivo derived embryos of ruminants (other than bovine embryos) and other BTV susceptible herbivores and for in vitro produced bovine embryos
Veterinary Authorities should require the presentation of an international veterinary certificate attesting that:
the donor females:
showed no clinical sign of bluetongue on the day of collection and were kept in a country or zone free from bluetongue or in a seasonally free country or zone during the free season for at least the 60 days prior to, and at the time of, collection of the embryos; or
comply with point 1 of Article 8.3.12.;
the embryos were collected, processed and stored in accordance with Chapters 4.7., 4.8. and 4.9., as relevant;
the semen used to fertilise the oocytes complied with Article 8.3.9. or Article 8.3.10.
Recommendations for importation from countries or zones infected with BTV
For in vivo derived embryos of ruminants (other than bovine embryos) and other BTV susceptible animals and for in vitro produced bovine embryos
Veterinary Authorities should require the presentation of an international veterinary certificate attesting that:
the donor females:
showed no clinical sign of bluetongue on the day of collection;
AND
were kept in a vector-protected establishment in accordance with point 1 of Article 8.3.13. for at least 60 days before commencement of, and during, collection of the embryos; or
were subjected to a serological test to detect antibodies to the BTV group, between 28 and 60 days after collection, with negative results; or
were subjected to an agent identification test on a blood sample taken on the day of collection, with negative results;
the embryos were collected, processed and stored in accordance with Chapters 4.7., 4.8. and 4.9., as relevant;
the semen used to fertilise the oocytes complied with Article 8.3.9. or Article 8.3.10.
Protecting animals from Culicoides attacks
Vector-protected establishment or facility
The establishment or facility should be approved by the Veterinary Authority and the means of protection should at least comprise the following:
appropriate physical barriers at entry and exit points, such as double-door entry-exit system;
openings of the building are vector screened with mesh of appropriate gauge impregnated regularly with an approved insecticide in accordance with manufacturers' instructions;
vectorsurveillance and control within and around the building;
measures to limit or eliminate breeding sites for vectors in the vicinity of the establishment or facility;
standard operating procedures, including description of back-up and alarm systems, for operation of the establishment or facility and transport of animals to the place of loading.
During transportation
When transporting animals through infected countries or zones, Veterinary Authorities should require strategies to protect animals from attacks from Culicoides during transport, taking into account the local ecology of the vector.
Transport by road
Risk management strategies may include:
treating animals with insect repellents prior to and during transportation;
loading, transporting and unloading animals at times of low vector activity (i.e. bright sunshine, low temperature);
ensuring vehicles do not stop en route during dawn or dusk, or overnight, unless the animals are held behind insect-proof netting;
darkening the interior of the vehicle, for example by covering the roof or sides of vehicles with shade cloth;
surveillance for vectors at common stopping and unloading points to gain information on seasonal variations;
using historical information or information from appropriately verified and validated bluetongue epidemiological models to identify low risk ports and transport routes.
Transport by air
Prior to loading the animals, the crates, containers or jet stalls should be sprayed with an insecticide approved in the country of dispatch.
Crates, containers or jet stalls in which animals are being transported and the cargo hold of the aircraft should be sprayed with an approved insecticide when the doors have been closed and prior to take-off. All possible insect harbourage should be treated. The spray containers should be retained for inspection on arrival.
In addition, during any stopover in countries or zones not free from bluetongue prior to the opening of any aircraft door and until all doors are closed, netting of appropriate gauge impregnated with an approved insecticide should be placed over crates, containers or jet stalls.
Introduction to surveillance
Articles 8.3.14. to 8.3.17. define the principles and provide guidance on surveillance for infection with BTV, complementary to Chapter 1.4. and for vectors complementary to Chapter 1.5.
Bluetongue is a vector-borne infection transmitted by various species of Culicoides in a range of ecosystems.
The purpose of surveillance is the detection of transmission of BTV in a country or zone and not determination of the status of an individual animal or herds or flocks. Surveillance deals with the evidence of infection with BTV in the presence or absence of clinical signs.
An important component of the epidemiology of bluetongue is the capacity of its vector, which provides a measure of disease risk that incorporates vector competence, abundance, biting rates, survival rates and extrinsic incubation period. However, methods and tools for measuring some of these vector factors remain to be developed, particularly in a field context. Therefore, surveillance for bluetongue should focus on transmission of BTV in domestic ruminants and camelids.
The impact and epidemiology of bluetongue widely differ in different regions of the world and therefore it is not appropriate to provide specific recommendations for all situations. Member Countries should provide scientific data that explain the epidemiology of bluetongue in the country or zone concerned and adapt the surveillance strategies for defining their status to the local conditions. There is considerable latitude available to Member Countries to justify their status at an acceptable level of confidence.
Surveillance for bluetongue should be in the form of a continuing programme.
General conditions and methods for surveillance
A surveillance system in accordance with Chapter 1.4. should be under the responsibility of the Veterinary Authority. In particular:
a formal and ongoing system for detecting and investigatingoutbreaks of disease should be in place;
a procedure should be in place for the rapid collection and transport of samples from suspected cases of infection with BTV to a laboratory for diagnosis;
a system for recording, managing and analysing diagnostic and surveillance data should be in place.
The bluetongue surveillance programme should:
in a free country or zone or seasonally free zone, have an early warning system which obliges farmers and workers, who have regular contact with domestic ruminants, as well as diagnosticians, to report promptly any suspicion of bluetongue to the Veterinary Authority.
An effective surveillance system will periodically identify suspected cases that require follow-up and investigation to confirm or exclude whether the cause of the condition is bluetongue. The rate at which such suspected cases are likely to occur will differ between epidemiological situations and cannot therefore be predicted reliably. All suspected cases of bluetongue should be investigated immediately and samples should be taken and submitted to a laboratory. This requires that sampling kits and other equipment be available for those responsible for surveillance;
AND
conduct random or targeted serological and virological surveillance appropriate to the status of the country or zone.
Surveillance strategies
The target population for surveillance aimed at identification of disease or infection should cover susceptible domestic ruminants and camelids, and other susceptible herbivores of epidemiological significance within the country or zone. Active and passive surveillance for bluetongue should be ongoing as epidemiologically appropriate. Surveillance should be composed of random or targeted approaches using virological, serological and clinical methods appropriate for the status of the country or zone.
It may be appropriate to focus surveillance in an area adjacent to a border of an infected country or zone for up to 100 kilometres, taking into account relevant ecological or geographical features likely to interrupt the transmission of BTV or the presence in the bordering infected country or zone of a bluetongue surveillance programme (in accordance with Articles 8.3.14. to 8.3.17.) that supports a lesser distance.
A Member Country should justify the surveillance strategy chosen as being adequate to detect the presence of infection with BTV in accordance with Chapter 1.4. and the prevailing epidemiological situation. It may, for example, be appropriate to target clinical surveillance at particular species likely to exhibit clinical signs (e.g. sheep).
Similarly, virological and serological testing may be targeted to species that rarely show clinical signs (e.g. bovines).
In vaccinated populations, serological and virological surveillance is necessary to detect the BTV serotypes circulating to ensure that all circulating serotypes are included in the vaccination programme.
If a Member Country wishes to declare freedom from bluetongue in a specific zone, the design of the surveillance strategy should be aimed at the population within the zone.
For random surveys, the design of the sampling strategy should incorporate epidemiologically appropriate design prevalence. The sample size selected for testing should be large enough to detect evidence of infection if it were to occur at a predetermined minimum rate. The sample size and expected prevalence determine the level of confidence in the results of the survey. The Member Country should justify the choice of design prevalence and confidence level based on the objectives of surveillance and the epidemiological situation, in accordance with Chapter 1.4. Selection of the design prevalence in particular should be based on the prevailing or historical epidemiological situation.
Irrespective of the survey approach selected, the sensitivity and specificity of the diagnostic tests employed are key factors in the design, sample size determination and interpretation of the results obtained. Ideally, the sensitivity and specificity of the tests used should be validated for the vaccination and infection history and the different species in the target population.
Irrespective of the testing system employed, surveillance system design should anticipate the occurrence of false positive reactions. If the characteristics of the testing system are known, the rate at which these false positives are likely to occur can be calculated in advance. There should be an effective procedure for following up positive reactions to ultimately determine with a high level of confidence, whether they are indicative of infection or not. This should involve both supplementary tests and follow-up investigation to collect diagnostic material from the original sampling unit as well as those which may be epidemiologically linked to it.
The principles involved in surveillance for disease or infection are technically well defined. The design of surveillance programmes to prove the absence of infection with, and transmission of, BTV should be carefully followed to avoid producing results that are either insufficiently reliable to be accepted by international trading partners, or excessively costly and logistically complicated.
Clinical surveillance
Clinical surveillance aims to detect clinical signs of bluetongue at the herd or flock level, particularly during a newly introduced infection. In sheep and occasionally goats, clinical signs may include oedema, hyperaemia of mucosal membranes, coronitis and cyanotic tongue.
Suspected cases of bluetongue detected by clinical surveillance should always be confirmed by laboratory testing.
Serological surveillance
An active programme of surveillance of host populations to detect evidence of transmission of BTV is essential to establish the bluetongue status of a country or zone. Serological testing of ruminants is one of the most effective methods of detecting the presence of BTV. The species tested should reflect the epidemiology of bluetongue. Bovines are usually the most sensitive indicator species. Management variables that may influence likelihood of infection, such as the use of insecticides and animal housing, should be considered.
Samples should be examined for antibodies against BTV. Positive test results can have four possible causes:
natural infection,
maternal antibodies,
the lack of specificity of the test.
It may be possible to use sera collected for other survey purposes for bluetongue surveillance. However, the principles of survey design described in these recommendations and the requirements for a statistically valid survey for the presence of infection with BTV should not be compromised.
The results of random or targeted serological surveys are important in providing reliable evidence that no infection with BTV is present in a country or zone. It is, therefore, essential that the survey is thoroughly documented. It is critical to interpret the results in light of the movement history of the animals being sampled.
Serological surveillance in a free zone should target those areas that are at highest risk of transmission of BTV, based on the results of previous surveillance and other information. This will usually be towards the boundaries of the free zone. In view of the epidemiology of bluetongue, either random or targeted sampling is suitable to select herds, flocks or animals for testing.
Serological surveillance in infected zones will identify changes in the boundary of the zone, and can also be used to identify the BTV types circulating. In view of the epidemiology of bluetongue, either random or targeted sampling is suitable.
Virological surveillance
Isolation and genetic analysis of BTV from a
proportion of infected animals provides information on serotype
and genetic characteristics of the viruses concerned.
Virological surveillance can
be conducted:
Sentinel animals
Sentinel animals are a form of targeted surveillance with a prospective study design. They are the preferred strategy for bluetongue surveillance. They comprise groups of unexposed animals that have not been vaccinated and are managed at fixed locations and sampled regularly to detect new infections with BTV.
The primary purpose of a sentinel animal programme is to detect infections with BTV occurring at a particular place, for instance sentinel groups may be located on the usual boundaries of infected zones to detect changes in distribution of BTV. In addition, sentinel animal programmes allow the timing and dynamics of infections to be observed.
A sentinel animal programme should use animals of known source and history of exposure, control management variables such as use of insecticides and animal housing (depending on the epidemiology of bluetongue in the area under consideration), and be flexible in its design in terms of sampling frequency and choice of tests.
Care is necessary in choosing the sites for the sentinel groups. The aim is to maximise the chance of detecting transmission of BTV at the geographical location for which the sentinel site acts as a sampling point. The effect of secondary factors that may influence events at each location, such as climate, may also be analysed. To avoid bias, sentinel groups should comprise animals selected to be of similar age and susceptibility to infection with BTV. Bovines are the most appropriate sentinels but other domestic ruminant species may be used. The only feature distinguishing groups of sentinels should be their geographical location.
Sera from sentinel animal programmes should be stored methodically in a serum bank to allow retrospective studies to be conducted in the event of new serotypes being isolated.
The frequency of sampling will depend on the reason for choosing the sampling site. In endemic areas, virus isolation will allow monitoring of the serotypes and genotypes of BTV circulating during each time period. The borders between infected and uninfected areas can be defined by serological detection of infective period. Monthly sampling intervals are frequently used. Sentinels in declared free zones add to confidence that infection with BTV is not occurring unobserved. In such cases, sampling prior to and after the possible period of transmission is sufficient.
Definitive information on the presence of BTV in a country or zone is provided by isolation and identification of the viruses. If virus isolation is required, sentinels should be sampled at sufficiently frequent intervals to ensure that samples are collected during the period of viraemia.
Vector surveillance
BTV is transmitted between ruminant hosts by species of Culicoides which vary around the world. It is therefore important to be able to identify potential vector species accurately although many such species are closely related and difficult to differentiate with certainty.
Vectorsurveillance aims to demonstrate the absence of vectors or to determine areas of different levels of risk and local details of seasonality by determining the various vector species present in an area, their respective seasonal occurrence, and abundance. Vectorsurveillance has particular relevance to potential areas of spread.
Long term surveillance can also be used to assess vector abatement measures or to confirm continued absence of vectors.
The most effective way of gathering this information should take account of the biology and behavioural characteristics of the local vector species of Culicoides and may include the use of Onderstepoort-type light traps or similar, operated from dusk to dawn in locations adjacent to domestic ruminants, or the use of drop traps over ruminants.
Vectorsurveillance should be based on scientific sampling techniques. The choice of the number and type of traps to be used and the frequency of their use should take into account the size and ecological characteristics of the area to be surveyed.
The operation of vectorsurveillance sites at the same locations as sentinel animals is advisable.
The use of a vectorsurveillance system to detect the presence of circulating virus is not recommended as a routine procedure as the typically low vectorinfection rates mean that such detections can be rare.
Animal-based surveillance strategies are preferred to detect virus transmission.
Documentation of bluetongue free status
Additional surveillance requirements for Member Countries declaring freedom from bluetongue
In addition to the general requirements described above, a Member Country declaring freedom from bluetongue for the entire country or a zone should provide evidence for the existence of an effective surveillance programme. The strategy and design of the surveillance programme will depend on the prevailing epidemiological circumstances and should be planned and implemented in accordance with general conditions and methods described in this chapter, to demonstrate absence of infection with BTV during the preceding 24 months in susceptible domestic ruminant populations. This requires the support of a laboratory able to undertake identification of infection with BTV through virus detection and antibody tests. This surveillance should be targeted to unvaccinated animals. Clinical surveillance may be effective in sheep while serological surveillance is more appropriate in bovines.
Additional requirements for countries or zones that practise vaccination
Vaccination to prevent the transmission of BTV may be part of a disease control programme. The level of flock or herd immunity required to prevent transmission will depend on the flock or herd size, composition (e.g. species) and density of the susceptible population. It is therefore impossible to be prescriptive. The vaccine should also comply with the provisions stipulated for BTV vaccines in the Terrestrial Manual. Based on the epidemiology of bluetongue in the country or zone, it may be decided to vaccinate only certain species or other subpopulations.
In countries or zones that practise vaccination, virological and serological tests should be carried out to ensure the absence of virus transmission. These tests should be performed on unvaccinated subpopulations or on sentinels. The tests should be repeated at appropriate intervals in accordance with the purpose of the surveillance programme. For example, longer intervals may be adequate to confirm endemicity, while shorter intervals may allow on-going demonstration of absence of transmission.
nb: first adopted in 1968; most recent update adopted in 2018.
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