Terrestrial Animal Health Code
Terrestrial Animal Health Code |
Infection with African horse sickness virus
General provisions
For the purposes of the Terrestrial Code, African horse sickness (AHS) is defined as an infection of equids with African horse sickness virus (AHSV).
The following defines an infection with AHSV:
AHSV has been isolated and identified from an equid or a product derived from that equid; or
antigen or ribonucleic acid specific to AHSV has been identified in samples from an equid showing clinical signs consistent with AHS, or epidemiologically linked to a suspected or confirmed case; or
serological evidence of active infection with AHSV by detection of seroconversion with production of antibodies against structural or nonstructural proteins of AHSV that are not a consequence of vaccination have been identified in an equid that either shows clinical signs consistent with AHS, or is epidemiologically linked to a suspected or confirmed case.
For the purposes of the Terrestrial Code, the infective period for AHS is 40 days for domestic horses. Although critical information is lacking for some species, this chapter applies to all equidae.
All countries or zones adjacent to a country or zone not having free status should determine their AHSV status from an ongoing surveillance programme. Throughout the chapter, surveillance is in all cases understood as being conducted as described in Articles 12.1.11. to 12.1.13.
Standards for diagnostic tests and vaccines are described in the Terrestrial Manual.
AHS free country or zone
A country or zone may be considered free from AHS when infection with AHSV is notifiable in the whole country, systematic vaccination is prohibited, importation of equids and their semen, oocytes or embryos are carried out in accordance with this chapter, and either:
historical freedom as described in Chapter 1.4. has demonstrated no evidence of AHSV in the country or zone; or
the country or zone has not reported any case of AHS for at least two years and is not adjacent to an infected country or zone; or
a surveillance programme has demonstrated no evidence of AHSV in the country or zone for at least two years; or
the country or zone has not reported any case of AHS for at least 40 days and a surveillance programme has demonstrated no evidence of Culicoides for at least two years in the country or zone.
An AHS free country or zone which is adjacent to an infected country or zone should include a zone in which surveillance is conducted in accordance with Articles 12.1.11. to 12.1.13., as relevant.
An AHS free country or zone will not lose its free status through the importation of seropositive or vaccinated equids and their semen, oocytes or embryos from infected countries or zones, provided these imports are carried out in accordance with this chapter.
To qualify for inclusion in the list of AHS free countries or zones, a Member Country should:
have a record of regular and prompt animal disease reporting;
send a declaration to the OIE stating:
the section under point 1) on which the application is based;
no routine vaccination against AHS has been carried out during the past year in the country or zone;
equids are imported in accordance with this chapter;
supply documented evidence that:
surveillance in accordance with Articles 12.1.11. to 12.1.13. is applied, unless historically free in accordance with Article 1.4.6.;
regulatory measures for the early detection, prevention and control of infection with AHSV have been implemented.
The Member Country will be included in the list only after the submitted evidence has been accepted by the OIE. Retention on the list requires that the information in points 4 b) ii) and iii) and 4 c) above be annually re-submitted and changes in the epidemiological situation or other significant events be reported to the OIE in accordance with the requirements in Chapter 1.1., and in particular, formally state that:
AHS infected country or zone
For the purposes of this chapter, an AHS infected country or zone is one that does not fulfil the requirements to qualify as AHS free.
Establishment of a containment zone within an AHS free country or zone
In the event of limited outbreaks within an AHS free country or zone, a single containment zone can be established for the purpose of minimising the impact on the entire country or zone. Such a zone should include all cases and can be established within a protection zone. For this to be achieved, the Veterinary Authority should provide documented evidence that:
the outbreaks are limited based on the following factors:
immediately on suspicion, a rapid response including notification has been made;
standstill of movements of equids has been imposed, and effective controls on the movement of equids and their products specified in this chapter are in place;
epidemiological investigation (trace-back, trace-forward) has been completed;
the infection has been confirmed;
investigations on the likely source of the outbreak have been carried out;
all cases have been shown to be epidemiologically linked;
no new cases have been found in the containment zone within a minimum of two infective periods as defined in Article 12.1.1.;
the equids within the containment zone are clearly identifiable as belonging to the containment zone;
increased passive and targeted surveillance in accordance with Articles 12.1.11. to 12.1.13. in the rest of the country or zone has not detected any evidence of infection;
animal health measures are in place to effectively prevent the spread of AHSV infection to the rest of the country or zone, taking into consideration the establishment of a protection zone within the containment zone, the seasonal vector conditions and existing physical, geographical and ecological barriers;
ongoing surveillance in accordance with Articles 12.1.11. to 12.1.13. is in place in the containment zone.
The free status of the areas outside the containment zone is suspended while the containment zone is being established in accordance with points 1) to 5) above. The free status of the areas outside the containment zone may be reinstated irrespective of Article 12.1.5. once the is recognised by the OIE.
In the event of the recurrence of AHSV infection in the containment zone, the approval of the containment zone is withdrawn.
The recovery of the AHS free status of the containment zone should follow Article 12.1.5.
Recovery of free status
To regain free status when an AHS outbreak occurs in a country or zone previously free, Article 12.1.2. applies, irrespective of whether emergency vaccination has been applied or not.
Recommendations for importation from AHS free countries or zones
For equids
Veterinary Authorities should require the presentation of an international veterinary certificate attesting that the animals:
showed no clinical sign of AHS on the day of shipment;
have not been vaccinated against AHS within the last 40 days;
were kept in an AHS free country or zone since birth or for at least 40 days prior to shipment;
either:
did not transit through an infected zone during transportation to the place of shipment; or
were protected from Culicoides attacks at all times when transiting through an infected zone.
Recommendations for importation from AHS infected countries or zones
For equids
Veterinary Authorities should require the presentation of an international veterinary certificate attesting that the animals:
showed no clinical sign of AHS on the day of shipment;
have not been vaccinated against AHS within the last 40 days;
were held in isolation in a vector-protected establishment:
for a period of at least 28 days and a serological test to detect antibodies against the AHSV group, was carried out with a negative result on a blood sample collected at least 28 days after introduction into the vector-protected establishment; or
for a period of at least 40 days and serological tests to detect antibodies against AHSV were carried out with no significant increase in antibody titre on blood samples collected on two occasions, with an interval of not less than 21 days, the first sample being collected at least 7 days after introduction into the vector-protected establishment; or
for a period of at least 14 days and an agent identification test was carried out with a negative result on a blood sample collected not less than 14 days after introduction into the vector-protected establishment; or
for a period of at least 40 days and were vaccinated, at least 40 days before shipment, against all serotypes whose presence in the source population has been demonstrated through a surveillance programme in accordance with Articles 12.1.12. and 12.1.13., and were identified in the accompanying certification as having been vaccinated;
were protected from Culicoides attacks at all times during transportation (including transportation to and at the place of shipment).
Recommendations for the importation of equine semen
Veterinary Authorities of importing countries should
require the presentation of an international veterinary certificate attesting
that the donor animals:
showed no clinical sign of AHS on the day of collection of the semen and for the following 40 days;
had not been immunised against AHS with a live attenuated vaccine within 40 days prior to the day of collection;
were either:
kept in an AHS free country or zone for at least 40 days before commencement of, and during collection of the semen; or
kept in an AHS free vector-protected artificial insemination centre throughout the collection period, and subjected to either:
a serological test to detect antibodies against the AHSV group, carried out with a negative result on a blood sample collected at least 28 days and not more than 90 days after the last collection of semen; or
agent identification tests carried out with negative results on blood samples collected at commencement and conclusion of, and at least every seven days, during semen collection for this consignment.
Recommendations for the importation of in vivo derived equine oocytes or embryos
Veterinary Authorities of importing countries should require the presentation of an international veterinary certificate attesting that:
the donor animals:
showed no clinical sign of AHS on the day of collection of the oocytes or embryos and for the following 40 days;
had not been immunised against AHS with a live attenuated vaccine within 40 days prior to the day of collection;
were either:
kept in an AHS free country or zone for at least 40 days before commencement of, and during collection of the oocytes or embryos, or
kept in an AHS free vector-protected collection centre throughout the collection period, and subjected to either:
a serological test to detect antibodies against the AHSV group carried out with a negative result on a blood sample collected at least 28 days and not more than 90 days after the last collection of oocytes or embryos; or
agent identification tests carried out with negative results on blood samples collected at commencement and conclusion of, and at least every seven days during oocytes or embryos collection for this consignment;
the embryos were collected, processed and stored in accordance with Chapters 4.7. and 4.9., as relevant;
the semen used to fertilise the oocytes complies at least with the requirements in Article 12.1.8.
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, for example 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 the instructions of the manufacturer;
vectorsurveillance and control within and around the building;
measures to limit or eliminate breeding sites for vectors in vicinity of the establishment or facility;
Standard Operating Procedure, including description of back-up and alarm systems, for operation of the establishment or facility and transport of equids to the place of loading.
During transportation
When transporting equids through AHS infected countries or zones, Veterinary Authorities should require strategies to protect animals from Culicoides attacks during transport, taking into account the local ecology of the vector.
Transport by road
Potential risk management strategies include a combination of:
treating animals with chemical repellents prior to and during transportation, in sanitized vehicles treated with appropriate residual contact insecticide;
loading, transporting and unloading animals at times of low vector activity (i.e. bright sunshine and 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 offloading points to gain information on seasonal variations;
using historical, ongoing or modelling information on AHS to identify low risk ports and transport routes.
Transport by air
Prior to loading the equids, the crates, containers or jet stalls are sprayed with an insecticide approved in the country of dispatch.
Crates, containers or jet stalls in which equids 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 AHS, 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 all crates, containers or jet stalls.
Introduction to surveillance
Articles 12.1.11. to 12.1.13. define the principles and provide guidance on surveillance for AHS, complementary to Chapter 1.4. and, for vectors, complementary to Chapter 1.5.
AHS is a vector-borne infection transmitted by a limited number of species of Culicoides insects. Unlike the related bluetongue virus, AHSV is so far geographically restricted to sub Saharan Africa with periodic excursions into North Africa, southwest Europe, the Middle East and adjacent regions of Asia. An important component of AHSV epidemiology is vectorial capacity which provides a measure of disease risk that incorporates vector competence, abundance, seasonal incidence, biting rates, survival rates and the extrinsic incubation period. However, methods and tools for measuring some of these vector factors remain to be developed, particularly in a field context.
According to this chapter, a Member Country demonstrating freedom from infection with AHSV 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. This requires the support of a laboratory able to undertake identification of infection with AHSV through the virus detection and antibody tests.
Susceptible captive wild, feral and wild equine populations should be included in the surveillance programme.
The purpose of surveillance is to determine if a country or zone is free from AHS. Surveillance deals not only with the occurrence of clinical signs caused by AHSV, but also with evidence of infection with AHSV in the absence of clinical signs.
General conditions and methods for surveillance
A surveillance system should be under the responsibility of the Veterinary Authority. In particular the following should be in place:
a formal and ongoing system for detecting and investigating outbreaks of disease;
a procedure for the rapid collection and transport of samples from suspected cases of AHS to a laboratory for diagnosis;
a system for recording, managing and analysing diagnostic, epidemiological and surveillance data.
In a free country or zone, the surveillance programme for AHS should include an early warning system for reporting suspected cases. Persons who have regular contact with equids, as well as diagnosticians, should report promptly any suspicion of AHS to the Veterinary Authority. An effective surveillance system will periodically identify suspected cases that require follow-up and investigation to confirm or exclude that the cause of the condition is AHS. 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 AHS should be investigated immediately and samples should be taken and submitted to a laboratory. This requires that sampling kits and other equipment be available to those responsible for surveillance.
In an AHS infected country or zone, random or targeted serological and virological surveillance, appropriate to the epidemiological situation, should be conducted in accordance with Chapter 1.4.
Surveillance strategies
The target population for surveillance aimed at identification of disease or infection should cover susceptible equids within the country or zone. Active and passive surveillance for infection with AHSV should be ongoing. Surveillance should be composed of random or targeted approaches using virological, serological and clinical methods appropriate to the epidemiological situation.
A Member Country should justify the surveillance strategy chosen as appropriate to detect the presence of infection with AHSV 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. horses). Similarly, virological and serological testing may be targeted to species that rarely show clinical signs (e.g. donkeys).
In vaccinated populations serological and virological surveillance is necessary to detect the AHSV types circulating to ensure that all circulating types are included in the vaccination programme.
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 infection if it were to occur at a predetermined minimum rate. The sample size, expected prevalence and diagnostic sensitivity of the tests 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 or 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 positives 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 for surveillance for disease or infection are technically well defined. Surveillance programmes to prove the absence of AHSV infection or transmission, should be carefully designed to avoid producing results that are insufficiently reliable to be accepted by the OIE for official recognition of status. The design of any surveillance programme, therefore, requires inputs from professionals competent and experienced in this field.
Clinical surveillance
Clinical surveillance aims at the detection of clinical signs of AHS in equids particularly during a newly introduced infection. In horses, clinical signs may include pyrexia, oedema, hyperaemia of mucous membranes and dyspnoea.
Suspected cases detected by clinical surveillance should always be confirmed by laboratory testing.
Serological surveillance
Serological surveillance of equine populations is an important tool to confirm absence of AHSV transmission in a country or zone. The species tested should reflect the local epidemiology of infection with AHSV, and the equine species available. Management variables that may reduce the likelihood of infection, such as the use of insecticides and animal housing, should be taken into account when selecting equids to be included in the surveillance system.
Samples should be examined for antibodies against AHSV. Positive AHSV antibody tests results can have four possible causes:
natural infection with AHSV;
vaccination against AHS;
maternal antibodies;
lack of specificity of the test.
Sera collected for other purposes may be used
for AHSV 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
AHSV should not be compromised.
The results of random or targeted serological
surveys are important in providing reliable evidence that no infection with
AHSV 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 AHSV transmission, 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 AHSV, either random or targeted sampling
is suitable to select herds or animals
for testing.
Serological surveillance in
a free country or zone should
be carried out over an appropriate distance from the border with
an infected country or zone, based
upon geography, climate, history of infection and
other relevant factors. The surveillance should
be carried out over a distance of at least 100 kilometres from the
border with that country or zone, but
a lesser distance could be acceptable if there are relevant ecological
or geographical features likely to interrupt the transmission of
AHSV. An AHS free country or zone may
be protected from an adjacent infected country or zone by
a protection zone.
Serological surveillance in infected zones will identify changes in the boundary of the zone, and can also be used to identify the AHSV types circulating. In view of the epidemiology of infection with AHSV, either random or targeted sampling is suitable.
Virological surveillance
Isolation and genetic analysis of AHSV from a
proportion of infected animals is beneficial in terms of providing information
on serotype and genetic characteristics of the viruses concerned.
Virological surveillance can
be conducted:
to identify virus transmission
in at risk populations;
to confirm clinically suspected cases;
to follow up positive serological results;
to better characterise the genotype of circulating
virus in a country or zone.
Sentinel animals
Sentinel animals are a form of targeted surveillance with
a prospective study design. They comprise groups of unexposed equids
that have not been vaccinated and are managed at fixed locations
and observed and tested regularly to detect new infections with
AHSV.
The primary purpose of a sentinel equid programme
is to detect infections with
AHSV occurring at a particular place, for instance sentinel groups
may be located on the boundaries of infected zones to
detect changes in distribution of AHSV. In addition, sentinel equid
programmes allow the timing and dynamics of infections to
be observed.
A sentinel equid 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 AHSV 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 AHSV
activity 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 confounding factors sentinel groups should comprise
animals selected to be of similar age and susceptibility to infection with
AHSV. 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 should reflect the
equine species used and the reason for choosing the sampling site. In
endemic areas virus isolation will allow monitoring of the serotypes
and genotypes of AHSV circulating during each time period. The borders
between infected and non-infected areas can be defined by serological
detection of infection. Monthly
sampling intervals are frequently used. Sentinels in declared free zones add
to confidence that infections with
AHSV are not occurring unobserved. Here sampling prior to and after
the possible period of transmission is sufficient.
Definitive information on AHSV circulating 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 some samples are collected during the period of viraemia.
Vector surveillance
AHSV is transmitted between equine hosts by species of Culicoides which vary across 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 is aimed at demonstrating the absence of vectors or defining high, medium and low-risk areas and local details of seasonality by determining the various 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 equids.
Vectorsurveillance should be based on scientific sampling techniques. The choice of the number and types of traps to be used in vectorsurveillance 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 viruses 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.
nb: first adopted in 1968; most recent update adopted in 2014.
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