4. SURVEILLANCE FOR SCRAPIE
4.1 Awareness of clinical signs
SENASA, recognises the importance of identifying suspect clinical cases of scrapie, and has established a continuous AWARENESS PROGRAMME whereby the clinical signs of scrapie are demonstrated visually in talks and literature to veterinary students and veterinary surgeons, farmers and animal health staff such us vaccinators and animal technicians. There is a widespread knowledge of scrapie in the veterinary and farming community despite the absence of the clinical disease in Argentina.
4.2 Awareness programme for BSE and Scrapie
Argentina regards the AWARENESS PROGRAMME as very important in establishing and maintaining the country as BSE and scrapie-free. The following is a resume of the essential components.
By whom conducted
Total staff involved:
by Jan. 1999 TOTAL
Staff training and updating
How (Number in 1997/9)
Further details of the Animal Health Services in Argentina are given in APPENDIX B.
Other than by repeated and continuous clinical surveillance since the establishment of the animal health service in 1900, there has been little specific pathological surveillance for scrapie until recently. Currently surveillance takes the form of passive and active surveillance. By passive surveillance is meant examination of sheep at the initiation of anyone e.g. farmers or veterinarians who have some concern about an animal or group of animals. Active surveillance is initiated by SENASA staff and might include clinical examination of sheep at markets, gatherings or at abattoirs, imported sheep and goats and pathological examination of brains of targeted slaughtered animals. Pathological study of brains, including the use of immunoblotting, has only been initiated on a formal basis since May 1997 though some brains have always been examined mostly by microscopic examination. Scrapie is a notifiable disease in Argentina (RESOLUTION 685/96, APPENDIX B). Failure to report suspect cases is an offence under the federal law.
4.3.1 Passive surveillance
All sheep reported or seen to have neurological signs suspicious of scrapie are investigated. Suspected animals are compulsorily slaughtered and brains are examined for evidence of scrapie by histopathology and by immunoblotting for PrP in SENASA-controlled laboratories. Compensation can be paid if a financial loss is established. A balance is kept between compensation for economic losses and punishment for not reporting.
4.3.2 Active surveillance
Active surveillance is done in SENASA-controlled abattoirs by examination of live adult sheep and goats. Brains for pathological study are selected on a basis of risk and age e.g. imported animals, animals with suspect clinical signs or non-specific illness. This type of surveillance will be developed.
The aim of the surveillance programme is to:
Once a tissue is received at a veterinary centre controlled by SENASA or INTA the diagnostic procedures are secure and no case of scrapie will be missed. This is because pathologists, virologists and immunologists responsible for diagnosis are fully trained and continuously professionally developed to meet internationally agreed standards. SENASA and INTA staff have visited and been trained at centres of excellence in the UK, USA and Sweden. Furthermore, the protocols used are those currently recommended for use by the OIE, European Commission (EC) and World Association of Veterinary Laboratory Diagnosticians (WAVLD). Argentina has a continuously progressive system of surveillance and diagnosis in place and keeps abreast of all the relevant new developments around the world.
4.4 Surveillance for Scrapie in Argentina - Results
For more detailed information on surveillance and how it is conducted by SENASA, please see APPENDIX B.
4.4.1 Clinical surveillance – indigenous sheep
Since 1990 when the FMD programme was commenced all ruminants (including the majority of sheep, goats and moufflon) have been clinically examined by staff trained by SENASA to recognise scrapie during their twice a year visits to all cattle herds to perform FMD vaccination and for other activities related to the FMD programme (e.g. blood sampling). Furthermore sheep are additionally inspected visually as part of the programme to control sheep scab. Since 1928, all sheep and goats destined for commercial human consumption have been examined ante-mortem by federal veterinary staff.
No case of scrapie has been detected.
4.4.2 Surveillance of imported sheep and genetic materials
All imports of sheep and goats are quarantined and clinically inspected along with any progeny until death. The same applies to offspring from imported sheep and to recipients of semen, ova or embryos and the offspring derived therefrom.
Since 1990 no sheep have been imported from a country that had declared to the OIE that it had scrapie at the time of the importation. However five sheep of the Manchega breed and 8 of the Churra breed have been imported in 1989 from Spain which later declared cases of scrapie to the OIE - but not in this breed, nor on the farm, nor in the area where the Manchega sheep originated. These breeds have never to our knowledge been affected with scrapie.
In any case the imported sheep, as all other imports, are inspected on arrival and found to be clinically healthy and are quarantined on the destination farm. There, they are regularly inspected and cannot be moved except under licence from SENASA (RESOLUTION 471/95). Their brains will be examined after death. Progeny from these sheep or any genetic material from then will be movement restricted and followed in precisely the same way.
The risk of scrapie occurring and spreading from this source is low. This same procedure is followed with all imports of ruminant species including goats, recipients of imported semen, embryos and the offspring of these. The protocols for surveillance of imported animals will be extended in the future by the introduction of a marking system so SENASA has a unique, easily recognisable identification of all imported animals, and recipients of semen, ova, embryos and the offspring derived from them.
4.4.3 Pathological examination of brains
Five veterinary or scientific specialists have been trained in centres of excellence round the world in the UK, USA and Sweden in the latest diagnostic methods including, light microscopy, immunocytochemistry and immunoblotting for PrPSc. These skilled veterinarians and scientists conduct most of the diagnostic work for active surveillance but they give specialist advice, guidance and training to staff in provincial laboratories who may be the first point of contact with suspect cases (passive surveillance).
22.214.171.124 Records and origin of cases
Records of pathological diagnosis of neurological illness in sheep exist since at least 1970. It is intended that all records will be kept for at least seven years. The origin of cases is country-wide and the diagnoses fit the general pattern seen in other countries without scrapie (TABLE 2). The origin of these cases was mainly stimulated by sheep farmers and private veterinarians i.e., it is a continuous form of passive surveillance.
Since May 1997 a formal active surveillance system has been initiated. The origin of the brains were from selected animals over 4 years old (confirmed mainly by study of the dentition) from abattoir kills, from farms and from imported sheep and goats. A small proportion of the donor animals showed neurological signs though none was characteristic for scrapie.
126.96.36.199 Laboratory examinations
All brains are examined by conventional light microscopy and several brains areas are examined from each sheep including the medulla oblongata at the obex. A proportion of brains is examined by internationally-validated methods for the detection of PrPSc by immunoblotting. The results are shown in TABLE 1.
Sheep and goat surveillance. Number of brains collected and examined in 1997/98/99*
Examined by light microscopy
Examined by immunoblotting for PrPSc
* till April 1999.
** 17 sheep and 24 goats brains were from animals which showed neurological clinical signs though none was characteristic for scrapie
No brains showed evidence of a scrapie-like TSE by either method.
Argentina has the intention to expand this surveillance and to use any other methods recommended by the OIE if that is appropriate (please see CHAPTER 5, Future Aims).
Table 2 shows the differential diagnoses of neurological disease in sheep in the last twenty seven years.
4.4.4 PrP genotypes
The study of PrP genotypes of Argentinean sheep was started using blood samples, mostly from sheep of the Corriedale, Hampshire Down, Texel and Friesian breeds. The animals belonged to sheep ranches from different provinces, as well as to breeding farms. The analyses are carried out using the method employed at the Veterinary Laboratories Agency (VLA), New Haw, UK. So far, susceptible and resistant genotypes have been found. The presence of susceptible genotype animals, which may be considered as sentinels for detection of the disease, supports the consideration of a scrapie-free status for Argentina.
4.5 Argentine goats, moufflon and Scrapie surveillance
By comparison with sheep the population of goats is small (2,916,000). Because goats are kept in close association with sheep, what applies to the latter species with respect to animal health matters applies also to goats but the depth of investigation has been less. Goats are less likely to be clinically examined by federal agencies than by provincial veterinary authorities as many never leave the farm and rarely are slaughtered in federal abattoirs. If they are slaughtered for commercial use, like sheep, they will be examined ante-mortem by federal veterinarians.
Because goats are usually regarded as susceptible to scrapie and in Argentina are run closely with sheep in local areas mainly of subsistence farming, would potentially act as sentinels for the detection of scrapie, as they do in other countries. Goats are kept only in small family enterprises, kids are killed usually on farm and any parts not consumed are buried on site. Adults often die in old age or are killed for welfare or production reasons. Carcases are buried. No goat materials, whether from slaughtered animals or fallen stock, are rendered.
Those rare cases of neurological disease in goats that have shown signs, have brains examined unless recovery is complete. It is intended that, beyond the normal clinical inspections of goats as part of the FMD programme (which equate with those for sheep), brains from targeted populations will be collected and examined. These will include the brains of imported animals.
A number of goat brains are included in the active surveillance programme (TABLE 1) and it is intended to extend surveillance for scrapie in goats in the future both at the clinical and pathological level.
The pathological methods used to examine goat brains are the same as for sheep.
No case of scrapie has been found in goats in Argentina either by clinical or pathological examination.
There is only a small number of moufflon in zoos in Argentina and none are free living. Dead moufflon in zoos or tissues from them are not rendered. If there is no perceived animal health risk carcases may be fed to carnivores. Waste is otherwise buried or incinerated. Scrapie has never been seen in moufflon in Argentina but it is intended that zoo owners will be made aware that this particular species of ruminant has succumbed to scrapie, albeit rarely, in the UK, the only country to have reported cases.
4.6 Enforcement of the ban on feeding ruminant protein to ruminant animals
Argentine-produced MBM can be fed to poultry, pigs and pets but not to ruminants (RESOLUTIONS 252/95 and 611/1996). Sheep are never fed concentrate rations and therefore would never consume MBM even accidentally. In the few instances where cattle are fed concentrate rations, samples have been collected and subjected to microscopic examination for mammalian bone and ELISA to detect species-specific protein. None has been found which suggests the ban is secure.
No MBM has been imported into Argentina from any country since 1990 and there is now a law to prevent it (RESOLUTIONS 429/90, 382/95, 203/96, 252/95 and 611/96, APPENDIX B). Port inspection by SENASA and customs and Excise staff ensures this law is vigorously enforced.
4.7 Surveillance for Creutzfeldt-Jakob disease (including v-CJD) in Argentina
Surveillance is conducted for the occurrence of human transmissible spongiform encephalopathies of all types in Argentina. Sporadic CJD occurs at an incidence that is within the norm for the incidence of this form of CJD in the rest of the world. Monitoring and surveillance is closely co-ordinated with the form of surveillance and monitoring carried out in western Europe. The physicians, neurologists, psychiatrists and health officials in Argentina are familiar with the clinical and pathological signs of the new variant form of CJD known as v-CJD. No cases of this form of CJD have been found in Argentina. If, as some believe, BSE-infected cattle tissues could be responsible for the occurrence of v-CJD it is not surprising that the disease has not been reported in Argentinian citizens domiciled in Argentina since BSE does not occur in Argentina either. For further information on this subject see the sister volumes to this one that are related to the risk assessment for the occurrence of BSE in Argentina (SENASA/INTA, 1991; SENASA, 1997, IICA,1999, in preparation).