Terrestrial Animal Health Code
Terrestrial Animal Health Code |
Infection with Trypanosomaevansi (Surra)
General provisions
Surra is a disease caused by Trypanosoma evansi of the subgenus Trypanozoon and may manifest in acute, chronic or clinically inapparent forms.
T. evansi is a blood and tissue parasite that occasionally invades the nervous system. It can infect a large range of domestic and wild mammals. The disease has a significant socio-economic impact on animal production, especially in equids, camelids and bovines; it can also affect goats, sheep, deer, pigs, rodents and elephants. It has a serious clinical impact in dogs, cats and non-human primates, and may occasionally infect humans.
T. evansi is mainly transmitted mechanically by several biting flies such as tabanids and Stomoxys spp., but can also be transmitted vertically, iatrogenically and possibly venereally. Additionally, it is transmitted perorally (especially to carnivores) and it can be transmitted biologically by the bite of vampire bats (Desmodus spp.), which may act as host, reservoir or vector.
Co-infection of T. evansi with other Trypanosoma species (including T. vivax, T. brucei, T. congolense, T. simiae, T. equiperdum and T. cruzi) may occur although this may not always be detected using routine testing methods.
For the purposes of the Terrestrial Code, surra is defined as an infection of susceptible animals with T. evansi.
For the purposes of this chapter, 'susceptible animals' means domestic and wild animals from the families: Equidae, Camelidae, Bovidae, Suidae, Canidae, and Felidae; the orders Rodentia and Lagomorpha; and non-human primates.
The following defines the occurrence of infection with T. evansi:
trypanosomes with Trypanozoon morphology have been observed in a sample from a susceptible animal and identified as T. evansi by the detection of nucleic acid; or
trypanosomes with Trypanozoon morphology have been observed in a sample from a susceptible animal either epidemiologically linked to a confirmed case of infection with T. evansi or suspected of previous association or contact with T. evansi; or
nucleic acid specific to Trypanozoon has been detected in a sample from a susceptible animal either epidemiologically linked to a confirmed case of infection with T. evansi or suspected of previous association or contact with T. evansi; or
antibodies specific to Trypanosoma spp. have been detected in a sample from a susceptible animal epidemiologically linked to a confirmed case of infection with T. evansi.
For the purposes of the Terrestrial Code, the incubation period of infection with T. evansi shall be 90 days in all species of susceptible animals.
For the purposes of this chapter, a temporary importation of horses refers to the introduction of horses into a country or zone, for a defined period of time, not exceeding 90 days, during which the risk of transmission of the infection is mitigated through specific measures under the supervision of the Veterinary Authority. Temporarily imported horses are re-exported at the end of this period. The duration of the temporary importation period and the destination after this period, as well as the conditions required to leave the country or zone, should be defined in advance.
Standards for diagnosis and information on the epidemiology are described in the Terrestrial Manual.
Safe commodities
When authorising import or transit of the following commodities, Veterinary Authorities should not require any surra-related conditions regardless of the animal health status of the exporting country or zone:
pasteurised milk and pasteurised milk products;
hair, wool and fibre;
gelatine and collagen;
horns, hooves and claws;
meat from animals that have been slaughtered in a slaughterhouse/abattoir and have been subjected to ante- and post-mortem inspections with favourable results;
hides and skins (except raw);
embryos or oocytes collected, processed and stored in accordance with Chapters 4.8. to 4.10.
Country or zone free from surra
A country or zone may be considered free from surra when:
the infection is notifiable in the entire country for at least the past two years;
measures to prevent the introduction of infection have been in place; in particular, the importations or movements of susceptible animals and other commodities into the country or zone have been carried out in accordance with this chapter and other relevant chapters of the Terrestrial Code;
and either:
In order to maintain its status, a country or zone free from surra should:
comply with points 1 and 2 above;
if adjacent to an infected country or zone, include an area along the border, in which surveillance is conducted in accordance with Articles 8.23.12. to 8.23.15.
Compartment free from surra
The establishment of a compartment free from surra should follow the provisions laid down in this chapter and in Chapters 4.4. and 4.5.
Susceptible animals in the free compartment should be protected against the vectors by the application of an effective biosecurity management system.
Susceptible animals in the free compartment should be protected against both iatrogenic and venereal transmission.
Recovery of free status
Should a case of infection with T. evansi occur in a previously free country or zone, its status may be recovered after the following:
cases have been isolated and then immediately treated, killed or slaughtered and appropriately disposed of;
animals in contact with cases have been put immediately under protection from vector contact and tested;
appropriate biosecurity is in place, including vector control or protection from vector contacts in the affected area in accordance with Articles 1.5.2. and 1.5.3.;
surveillance in accordance with Articles 8.23.12. to 8.23.15. has been carried out with negative results;
for six consecutive months, either:
after the last case was killed or slaughtered, the animals in contact have undergone monthly repeated antibody detection and agent identification (microscope and molecular) tests with negative results in all tests; or
if appropriate trypanocide treatment is applied to the cases, after the last case was killed, slaughtered or treated, whichever occurred last, both treated and in contact animals have undergone monthly repeated agent identification tests (microscope and molecular) with negative results, and antibody detection tests with decreasing titres.
If points 1 to 5 are not applied, Article 8.23.3. applies.
Recommendations for importation of equids, camelids, bovids and suids from countries, zones or compartments free from surra
Veterinary Authorities of importing countries should require the presentation of an international veterinary certificate attesting that the animals:
showed no clinical sign of surra on the day of shipment;
were kept since birth or at least 90 days prior to shipment in a free country, zone or compartment;
did not transit through an infected zone during transportation to the place of shipment or were protected from vectors or any source of T. evansi by the application of effective biosecurity during transportation to the place of shipment.
Recommendations for importation of equids, bovids and suids from countries or zones infected with T. evansi
Veterinary Authorities of importing countries should require the presentation of an international veterinary certificate attesting that animals:
showed no clinical sign of surra during isolation and on the day of shipment;
were isolated in a quarantine station for at least 45 days prior to shipment, and all animals from the same group were subjected to antibody detection tests on samples taken on two occasions, with an interval of 30 days, with negative results.
Recommendations for importation of susceptible animals from countries or zones infected with T. evansi for direct slaughter
Veterinary Authorities of importing countries should require the presentation of an international veterinary certificate attesting that the animals:
showed no clinical sign of surra on the day of shipment;
were kept for the six months prior to shipment in an establishment in which surveillance in accordance with Articles 8.23.12., 8.23.13. and 8.23.14. demonstrates that no case had occurred during that period; or
were negative in an antibody detection test within 15 days prior to shipment;
were permanently identified and transported under the supervision of the Veterinary Services in a vector-protected vehicle, which underwent disinfection and disinsection before loading, directly from the establishment of origin to the place of shipment without coming into contact with other susceptible animals.
Recommendations for the temporary importation of horses
When importing on a temporary basis horses that do not comply with the recommendations in Article 8.23.6. or Article 8.23.7., Veterinary Authorities of importing countries should:
require:
the horses be accompanied by a passport in accordance with the model contained in Chapter 5.12. or be individually identified as belonging to a high health status subpopulation as defined in Chapter 4.17.;
the presentation of an international veterinary certificate attesting that the horses:
showed no clinical sign of surra on the day of shipment;
belong to a high health status subpopulation or were negative in an antibody detection test within 15 days prior to departure from the country of origin;
the duration of the temporary importation period and the destination after this period, and the conditions required to leave the country or zone be defined;
ensure that during their stay in the country or zone:
measures are taken to protect the horses from vectors or any source of T. evansi by the application of effective biosecurity;
the horses are not subjected to any practice that may represent a risk of iatrogenic transmission of surra;
the horses are kept and transported individually in stalls and vehicles/vessels which are subsequently cleaned and disinsected before re-use.
Recommendations for importation of semen of susceptible animals from countries, zones or compartments free from surra
Veterinary Authorities of importing countries should require the presentation of an international veterinary certificate attesting that:
the donor males:
showed no clinical sign of surra on the day of semen collection;
have been kept for at least 90 days prior to semen collection in a free country, zone or compartment; and
the semen was collected, processed and stored in a semen collection centre in accordance with Chapters 4.6. and 4.7.
Recommendations for importation of semen of susceptible animals from countries or zones infected with T. evansi
Veterinary Authorities of importing countries should require the presentation of an international veterinary certificate attesting that:
the donor males:
showed no clinical sign of surra on the day of semen collection;
AND
either
have been kept for at least 90 days prior to semen collection in an establishment in which surveillance in accordance with Articles 8.23.12., 8.23.13. and 8.23.14. demonstrates that no case had occurred during that period;
were subjected to an antibody detection test on a blood sample taken on two occasions, with an interval of 30 days, with negative results;
the semen was collected, processed and stored in a semen collection centre in accordance with Chapters 4.6. and 4.7.
Introduction to surveillance
Articles 8.23.12. to 8.23.14. define the principles and provide guidance on surveillance for surra, complementary to Chapter 1.4. and Chapter 1.5.
The purpose of surveillance could be the demonstration of the absence of infection, the early detection of cases, or the measurement and monitoring of the prevalence and distribution of the infection in a country, zone or compartment.
An important component of the epidemiology of surra is the capability of its vectors, which provides a measure of disease risk that incorporates vector competence, abundance, biting rates, survival rates, host affinity and in the case of biological vectors, the 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 surra should focus on transmission of T. evansi in susceptible animals.
The impact and epidemiology of surra widely differs between different regions of the world and therefore, it is not appropriate to provide specific recommendations for all situations. Member Countries should provide scientific data explaining the epidemiology of the disease in the country or zone concerned, such as host susceptibility and co-infections with other Trypanosoma spp., 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.
Although surveillance in susceptible wild animals presents challenges that may differ significantly from those in domestic animals, wildlife should be considered in the surveillance system as they are included in the definition of the occurrence and can serve as reservoirs of infection and as indicators of risk to domestic animals.
General conditions and methods of surveillance
The surveillance system for surra should be in accordance with Chapter 1.4. and be under the responsibility of the Veterinary Authority.
It should include:
formal and ongoing system for detecting and investigating outbreaks;
the collection and transport of samples from suspected cases to a laboratory for diagnosis or a procedure for the rapid diagnosis in the field;
appropriate tools, for collection, recording, managing and analysis of data; reporting and dissemination for decision making.
In addition, it should, at least:
in a free country or zone, have an early warning system capable of detecting T. evansi which obliges animal owners and keepers and other stakeholders who have regular contact with susceptible animals, as well as veterinarians or veterinary paraprofessionals, to report promptly any suspicion of surra to the Veterinary Services;
include representative or risk-based serological or parasitological surveys appropriate to the status of the country, zone or compartment.
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 T. evansi. The rate at which such suspected cases are likely to occur will differ between epidemiological situations and cannot therefore be reliably predicted. All suspected cases should be investigated immediately, and samples should be taken and submitted to a laboratory.
Surveillance strategies
The target population should include domestic and wild susceptible animals of epidemiological significance within the country, zone or compartment. Active and passive surveillance for surra should be ongoing as epidemiologically appropriate. Surveillance should be composed of representative or risk-based approaches using parasitological, serological, clinical and entomological methods appropriate for the status of the country, zone or compartment.
In a free country, zone or compartment, it is appropriate to focus surveillance in an area adjacent to an infected country, zone or compartment, considering relevant ecological or geographical features likely to interrupt the transmission of surra.
A Member Country should justify the surveillance strategy chosen as being adequate to detect the presence of infection with T. evansi in accordance with Chapter 1.4. and Chapter 1.5., and with the prevailing epidemiological situation.
If a Member Country wishes to declare freedom from surra in a specific zone, the design of the surveillance strategy should be targeted to the susceptible population within the zone.
For random surveys, the sample size selected for testing should be large enough to detect evidence of infection if it were to occur at a predetermined minimum expected prevalence. 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 the minimum expected prevalence and confidence level based on the objectives of surveillance and the epidemiological situation, in accordance with Chapter 1.4. 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 infection history and the different Trypanosoma species and other Kinetoplastid species (T. vivax, T. congolense, T. brucei, T. equiperdum, T. cruzi and Leishmania spp.) present in the target population.
Irrespective of the testing system employed, surveillance system design should anticipate the occurrence of cross reactions. There should be an effective procedure for following up cross reactions to determine, with a high level of confidence, whether they are indicative of infection with T. evansi 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 are technically well defined. The design of surveillance programmes to prove the absence of infection with T. evansi 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.
The results of random or targeted surveys are important in providing reliable evidence that no infection with T. evansi is present in a country, zone or compartment. It is, therefore, essential that the survey is thoroughly documented. It is critical to consider the movement history of the animals being sampled when interpreting the results.
An active programme of surveillance of susceptible populations to detect evidence of surra is essential to establish the animal health status of a country, zone or compartment.
Clinical surveillance
Clinical surveillance aims to detect clinical signs of surra in susceptible animals, particularly during a newly introduced infection. However, neither clinical nor post-mortem signs of surra are pathognomonic. Therefore, suspected cases of infection with T. evansi detected by clinical surveillance should always be confirmed by direct or indirect laboratory tests that confirm the presence of T. evansi.
Parasitological surveillance
Parasitological examination (or agent identification) can be conducted to:
Molecular techniques
Molecular techniques can be conducted to:
increase the sensitivity of the detection of active infections;
confirm clinically suspected cases;
identify parasites at the subgenus level (Trypanozoon), or at the species level (T. evansi); (in the host and/or the vector);
confirm active infection after positive serological results.
Serological surveillance
Serological testing of susceptible animals is one of the most effective methods for detecting exposure to T. evansi. The host species tested should reflect the epidemiology of the disease. Management variables that may influence likelihood of infection, such as animal treatment, should be considered.
Owing to cross reactions with other Kinetoplastid species, co-infections with these pathogenic agents should be considered when interpreting the results of the serological surveillance system.
Serological techniques can be used to:
Positive test results can have different possible causes:
Sentinel animals
Sentinel surveillance may provide evidence of freedom from infection or provide data on prevalence and incidence as well as the distribution of the infection. Sentinel surveillance may consist of:
the identification and regular testing of one or more of sentinel animal units of known health or immune status in a specified geographical location to detect the occurrence of infection with T. evansi;
the investigation of clinical suspect cases targeting highly susceptible animals such as dogs (hunting dogs and dogs living around slaughterhouses/abattoirs), camels, donkeys or horses.
Vector surveillance
This point should be read in conjunction with Chapter 1.5.
For the purposes of this chapter, vector surveillance aims at determining different levels of risk by identifying the presence and abundance of various vector species (biting flies and vampire bats) in an area.
The most effective way of gathering vectorsurveillance data should consider the biology and behavioural characteristics of the local vector species and include traps, net, sticky targets or other collection tools. The choice of the number and type of collecting tools to be used and the frequency of their use should be made by considering the size and ecological characteristics of the area to be surveyed. In the surveillance of wildlife species, molecular techniques may be applied to vectors.
When sentinel animals are used, vector surveillance should be conducted at the same locations.
Additional surveillance procedures for recovery of free status
In addition to the general conditions described in this chapter, a Member Country seeking recovery of country or zone free status, including a containment zone established in accordance with Article 4.4.7., should show evidence of an active surveillance programme to demonstrate absence of infection with T. evansi.
Populations under this surveillance programme should include:
establishments in the proximity of the outbreak;
establishments epidemiologically linked to the outbreak;
animals moved from previously affected establishments;
animals used to re-populate previously affected establishments.
nb: first adopted in 2024
2024 ©OIE - Terrestrial Animal Health Code |
