Monitoring of clinical signs in goats with transmissible spongiform encephalopathies

Abstract

BackgroundAs there is limited information about the clinical signs of BSE and scrapie in goats, studies were conducted to describe the clinical progression of scrapie and BSE in goats and to evaluate a short clinical protocol for its use in detecting scrapie-affected goats in two herds with previously confirmed scrapie cases. Clinical assessments were carried out in five goats intracerebrally infected with the BSE agent as well as five reported scrapie suspects and 346 goats subject to cull from the two herds, 24 of which were retained for further monitoring. The brain and selected lymphoid tissue were examined by postmortem tests for disease confirmation.ResultsThe sensitivity and specificity of the short clinical protocol in detecting a scrapie case in the scrapie-affected herds was 3.9% and 99.6%, respectively, based on the presence of tremor, positive scratch test, extensive hair loss, ataxia and absent menace response. All BSE- and scrapie-affected goats displayed abnormalities in sensation (over-reactivity to external stimuli, startle responses, pruritus, absent menace response) and movement (ataxia, tremor, postural deficits) at an advanced clinical stage but the first detectable sign associated with scrapie or BSE could vary between animals. Signs of pruritus were not always present despite similar prion protein genotypes. Clinical signs of scrapie were also displayed by two scrapie cases that presented with detectable disease-associated prion protein only in lymphoid tissues.ConclusionsBSE and scrapie may present as pruritic and non-pruritic forms in goats. Signs assessed for the clinical diagnosis of scrapie or BSE in goats should include postural and gait abnormalities, pruritus and visual impairment. However, many scrapie cases will be missed if detection is solely based on the display of clinical signs. PrPd accumulation in the brain appeared to be related to the severity of clinical disease but not to the display of individual neurological signs.

Clinical Examination Protocol to Detect Atypical and Classical Scrapie in Sheep

“…In addition, pruritus, usually evident as alopecia with or without excoriation, is often considered a characteristic sign of scrapie 13 . Thus, a neurologic disease without concomitant pruritus as observed in atypical scrapie 12 or the nonpruritic form of caprine scrapie 11 may not raise suspicion of scrapie.…”

“…Although a clinical examination is generally less sensitive in detecting TSE-affected animals than post mortem tests based on detection of prion protein 2,11 , particularly in an early stage of the incubation period, this is currently the only detection method in live animals and most relevant to those countries that do not have a targeted surveillance system in place to identify TSE-affected small ruminants.…”

“…Two major naturally occurring scrapie forms can be distinguished, which are epidemiologically, pathologically, and biochemically different: classical scrapie and atypical scrapie. In addition, a neurological disease with classical scrapie-like clinical signs can be induced in sheep and goats by experimental infection with the BSE agent 6,[10][11] . In fact, naturally occurring BSE has been diagnosed in goats 3,17 .…”

“…This protocol is a slight modification from the one used to monitor goats for signs of classical scrapie 11 and includes blindfolding of the animal, which may exacerbate clinical signs not normally associated with scrapie …”

Neurobehavioral Testing in Prion Disease Studies

“…This is most dramatically represented in subclinical prion disease (i.e., measurable CNS PrP Sc without clinical disease) and in prion-infected animals demonstrating significant clinical disease but lacking detectable PrP Sc [7,18,19]. This lack of correlation between patterns of brain PrP Sc deposition and clinical disease is well documented in many natural and experimentally infected TSE affected animals, including TSE-infected cattle, goats, and mice [18,[20][21][22]. In addition, a discordant relationship between neuronal loss and clinical signs is reported in BSE-infected cattle and between neuroinflammation and clinical signs in scrapie-infected sheep [23][24][25][26][27].…”