|Source of the outbreak(s) or origin of infection
||Official Veterinary Services (SVO) has identified contemporary animals with the detected case which shared the same holding where the case was identified. These were cows aged around 15 years, also raised for breeding purposes and which were found clinically normal. The animals were raised on a grass-fed basis, which is the system used for over 95% of Brazilian bovine population. These animals were humanely destroyed, and their carcasses buried on site. Samples were collected for BSE diagnosis, which resulted negative on both histopathology and immunohistochemistry (IHC) tests performed by the National Reference Laboratory, LANAGRO/PE.
Tracing back allowed the identification of other animals from the farm of origin of the affected cow. They were placed under direct official supervision, being individually identified with ear tags and having their movements restricted.
It is important to mention that the case was suspected of having the BSE prion only in June 2012, when IHC test for identification of the prion was performed by the National Reference Laboratory.
The case showed no characteristic clinical signs of a typical BSE case, as it presented hyper acute clinical course (approximately in 24 hours), was about 13 years old and grass-fed, without receiving supplemental feed. Its brain was submitted to test for rabies, as this disease is endemic in the region, resulting negative. The laboratory of the TSE surveillance network did not find any histopathological lesions in April 2011. Due to an incident in one of the regional BSE accredited laboratories, which brought an overload to the network of laboratories, there was a delay (already corrected) in the further processing of this sample, being the IHC test conducted only in mid-2012, when the marker of prion protein was finally found. This result was confirmed on 6 December 2012, by the OIE Reference Laboratory, Weybridge (United Kingdom).
Due to the unusual characteristics of the case, the OIE Reference Laboratory proposed to proceed with further investigations aiming to identify the nature of the agent (classic or atypical) through the western blotting technique. Results came out as inconclusive on 14 December 2012. According to the laboratory, the quality of the blot is not good enough to enable an unequivocal classification of the sample by this method. Even though, the laboratory report states that “Although the poor quality and the indeterminate fixation history of the sample compromises interpretation, even so we note that the sample appears to have some characteristics of H-Type rather than L or C-Type of BSE”, in other words, atypical BSE.
Bearing in mind the aforementioned results, as well as the results of the exhaustive epidemiological investigation conducted by Brazilian veterinary services, it can be stated that this is highly probable a case of atypical BSE (rare and spontaneous) that should have no impact neither on animal nor on public health. Furthermore, it is important to highlight that this animal did not enter the meat-processing chain, having been buried on the farm where it died.