Prion infection relies on a continuous chain of PrPc -expressing tissues to spread from peripheral sites to the central nervous system (CNS). Direct neuroinvasion via peripheral nerves has long been considered likely. However, the speed of axonal flow is incompatible with the lengthy delay prior to the detection of PrP Sc in the brain. We hypothesized that Schwann cells could be the candidate implicated in this mechanism; for that, it has to express PrP c and to allow PrP

The aim of this work was to investigate whether an enzyme-linked immunosorbent assay (ELISA) was useful for early detection of maedi-visna virus (MVV) infection in sheep under field conditions. An ELISA based on p25 recombinant protein and a gp46 synthetic peptide was used. Sequentially obtained serum samples (n = 1,941) were studied for 4 years. ELISA results were compared with those of the agar gel immunodiffusion (AGID) test, and results of both tests were compared with a reference result established using consensus scores for at least 2 of 3 serologic techniques (AGID, ELISA, and western blotting, which was used to resolve result discrepancies between the other 2 techniques). A total of 247 discrepancies were observed between ELISA and AGID. Of these, 131 were due to an earlier detection of 120 sera by the ELISA and 11 sera by AGID. The remaining discrepancies (116) were due to the presence of false reactions in both tests. Fewer false-negative results were found by ELISA than with AGID (6 vs. 69 sera, respectively), whereas the number of false-positive results was virtually the same for ELISA and AGID (21 vs. 20, respectively). In relation to the reference result, ELISA sensitivity and specificity were 97.8% and 98.2%, respectively, whereas values for AGID were 76.3% and 98.3%, respectively. The agreement between ELISA and the reference result was higher than that between AGID and the reference result (K value: 0.96 and 0.77, respectively). A variation in the ELISA signal (based on optical density) was observed during the study period, suggesting different antibody levels throughout the animal's life. The ELISA was useful for detecting MVV-infected sheep in field conditions and has potential for use in control and eradication programs.

Reduced expression of synaptophysin p38, synaptic-associated protein of molecular weight 25,000 (SNAP-25), syntaxin-1, synapsin-1, and alpha- and beta-synuclein, matching the distribution of spongiform degeneration, was found in the neurological phase of scrapie-infected mice. In addition, synaptophysin and SNAP-25 were accumulated in isolated neurons, mainly in the thalamus, midbrain and pons, and granular deposits of alpha- and beta-synuclein were present in the neuropil of the same areas. No modifications in the steady state levels of Bcl-2, Bax, Fas and Fas ligand were observed following infection. Yet antibodies against the c-Jun N-terminal peptide, which cross-react with products emerging after caspase-mediate proteolysis, recognize coarse granular deposits in the cytoplasm of reactive microglia. In situ end-labeling of nuclear DNA fragmentation showed positive nuclei with extreme chromatin condensation in the thalamus, pons, hippocampus and, in particular, the granular layer of the cerebellum. More importantly, expression of cleaved caspase-3, a major executioner of apoptosis, was seen in a few cells in the same regions, thus indicating that cell death by apoptosis in scrapie-infected mice is associated with caspase-3 activation. The present findings support the concept that synaptic pathology is a major substrate of neurological impairment and that caspase-3 activation may play a pivotal role in apoptosis in experimental scrapie. However, there is no correlation between decreased synaptic protein expression and caspase-3-associated apoptosis, which suggests that in addition to abnormal prion protein deposition, there may be other factors that distinctively influence synaptic vulnerability and cell death in murine scrapie.

NASAL myiasis caused by the sheep bot fly, Oestrus ovis, is a common cause of disease in sheep in warm climates. In the Mediterranean, the disease occurs mainly in the spring and summer months when adult flies emerge, mate, and females deposit the first instar larvae on the nostrils of sheep. In the nasal cavity, larvae develop into the third instar which are recognised by the presence of two characteristic black oral hooks, two black posterior spiracles and dorsal transverse bands of pigment, measuring about 30 x 8 mm. After two to 10 months, mature larvae are sneezed into the external environment, where they complete the life cycle (Kimberling 1988). The present communication reports the diagnosis of an unusual infestation by 0 ovis in a dog.In May 1996, an eight-year-old intact male German shorthair pointer was presented at a private practice with frequent sneezing, moderate pyrexia (39.3'C) and slight weakness. No nasal discharge had been noted and, at general examination, the clinician only noted a rhinitic condition. The animal was correctly vaccinated against canine distemper, canine parvovirus, canine adenovirus hepatitis and leptospirosis. It was currently being treated with 6 pg/kg ivermectin orally (Cardotek, MSD AgVet) each month as a preventive measure against canine filariosis. The owner had kept the dog in a flat and it was rarely taken outside. Rhinitis was diagnosed and the animal was treated with a broad spectrum antibiotic (amoxycillin, 30 mg/kg per day for seven days) and anti-inflammatory therapy (a single dose of methylprednisolone, 10 mg/kg intramuscularly).After a week, the dog did not show any evidence of improvement, with frequent sneezing and slight pyrexia; it did, however, show apparently normal activity and a normal demeanour. The treatment was changed to an antihistamine (dexchlorpheniramine, 5 mg/kg twice a day) and broad spectrum antibiotic (doxycycline, 10 mg/kg per day for a week).Two weeks after the first visit to the clinician, the animal had not improved. Moreover, it started to show a serous unilateral (left) nasal discharge. Rhinoscopy was undertaken but no foreign bodies or masses were observed. Marked congestion and inflammation of the nasal mucosa was observed; the mucosa was prone to bleeding on contact with the rhinoscope making exploration difficult. Dorsal and lateral radiographs showed no abnormality.Over the following days the serous nasal discharge changed to a mucous discharge with frequent left unilateral epistaxis. An ELISA test to detect antibodies against Leishmania species was negative. Confirmation of this result was obtained a week later with a sec-FIG 1: Remnants of a third instar Oestrus ovis larvae located in the nasal cavity of a male German shorthair pointer. A hook is observed (arrow head) near a disrupted layer of chitin (arrows). The structure is surrounded by fungi. Periodic acid-Schiff, bar = 10 pm ond test against Leishmania species. Surgical exploration using a rhinotomy was declined by the owner, who requested that the dog be euthanased.At nec...