The immune system is known to be involved in the early phase of scrapie pathogenesis. However, the infection route of naturally occurring scrapie and its spread within the host are not entirely known. In this study, the pathogenesis of scrapie was investigated in sheep of three PrP genotypes, from 2 to 9 months of age, which were born and raised together in a naturally scrapie-affected Romanov flock. The kinetics of PrP Sc accumulation in sheep organs were determined by immunohistochemistry. PrP Sc was detected only in susceptible VRQ/VRQ sheep, from 2 months of age, with an apparent entry site at the ileal Peyer's patch as well as its draining mesenteric lymph node. At the cellular level, PrP Sc deposits were associated with CD68-positive cells of the dome area and B follicles before being detected in follicular dendritic cells. In 3-to 6-month-old sheep, PrP Sc was detected in most of the gut-associated lymphoid tissues (GALT) and to a lesser extent in more systemic lymphoid formations such as the spleen or the mediastinal lymph node. All secondary lymphoid organs showed a similar intensity of PrP Sc -immunolabelling at 9 months of age. At this time-point, PrPSc was also detected in the autonomic myenteric nervous plexus and in the nucleus parasympathicus nervi X of the brain stem. These data suggest that natural scrapie infection occurs by the oral route via infection of the Peyer's patches followed by replication in the GALT. It may then spread to the central nervous system through the autonomic nervous fibres innervating the digestive tract.

Information from a scrapie epidemic in a closed INRA Romanov flock is presented. Performances, pedigree, histopathological diagnoses and PrP genotypes were recorded from the beginning of the outbreak (in 1993). Between 1st of April, 1993 and 1st of May, 1997, 1015 animals were exposed to scrapie, and 304 died from this disease. A major influence of the polymorphisms at codons 136, 154 and 171 is shown, A136H154Q171 allele carriers proving to be nearly as resistant as A136R154R171 carriers. A possible relationship between gastrointestinal parasitism and scrapie is discussed. There is evidence of maternal transmission, with a risk ratio for artificially fed lambs of 67 percent of the risk of lambs fed by their mother. Our results strongly suggest that resistant animals were not healthy carriers or at least were less infectious when comparing risk for lambs born to healthy dams either of resistant (risk = 0.431) or of susceptible (risk = 1.000) genotype.

Until now, the analysis of the genetic diversity of bovine respiratory syncytial virus (BRSV) has been based on small numbers of field isolates. In this report, we determined the nucleotide and deduced amino acid sequences of regions of the nucleoprotein (N protein), fusion protein (F protein), and glycoprotein (G protein) of 54 European and North American isolates and compared them with the sequences of 33 isolates of BRSV obtained from the databases, together with those of 2 human respiratory syncytial viruses and 1 ovine respiratory syncytial virus. A clustering of BRSV sequences according to geographical origin was observed. We also set out to show that a continuous evolution of the sequences of the N, G, and F proteins of BRSV has been occurring in isolates since 1967 in countries where vaccination was widely used. The exertion of a strong positive selective pressure on the mucin-like region of the G protein and on particular sites of the N and F proteins is also demonstrated. Furthermore, mutations which are located in the conserved central hydrophobic part of the ectodomain of the G protein and which result in the loss of four Cys residues and in the suppression of two disulfide bridges and an ␣ helix critical to the three-dimensional structure of the G protein have been detected in some recent French BRSV isolates. This conserved central region, which is immunodominant in BRSV G protein, thus has been modified in recent isolates. This work demonstrates that the evolution of BRSV should be taken into account in the rational development of future vaccines. (38,39,40,49). These two related viruses share common epidemiological, clinical, and pathological characteristics. The respiratory syncytial viruses (RSV) are the most common and important cause of lower respiratory tract illness in cattle and young infants (71). More than 70% of calves exhibit a positive serological response against BRSV by the age of 12 months. Bovine respiratory syncytial virus (BRSV) and human respiratory syncytial virus (HRSV) are members of the genus Pneumovirus, subfamily Pneumovirinae, and family ParamyxoviridaeNeutralization tests (9) and reaction patterns with specific monoclonal antibodies (2, 48) have revealed that HRSV contains two major groups, A and B. The main differences between these two groups are located in the glycoprotein (G protein), while others are located in the fusion protein (F protein) and nucleoprotein (N protein) (48, 51). Subgroups within the G and F proteins of BRSV have been characterized more recently by serological analysis of a limited number of isolates and confirmed by phylogenetic analysis (20,54,60). Further studies of BRSV variability have focused on the G protein, which was shown to be the most variable protein and, with the F protein, one of the targets for neutralizing antibodies. A low percentage of sequence divergence between and within the G proteins of BRSV subgroups has been reported, suggesting that BRSV has the same extent of diversity as HRSV (15,21,36,44,66).The G protein is responsib...

In sheep, susceptibility to scrapie is mainly influenced by polymorphisms of the PrP gene. In goats, there are to date few data related to scrapie susceptibility association with PrP gene polymorphisms. In this study, we first investigated PrP gene polymorphisms of the French Alpine and Saanen breeds. Based on PrP gene open reading frame sequencing of artificial insemination bucks (n=404), six encoding mutations were identified at codons 127, 142, 154, 211, 222 and 240. However, only seven haplotypes could be detected: four (GIH154RQS, GIRQ211QS, GIRRK222S and GIRRQP240) derived from the wild-type allele (G127I142R154R211Q222S240) by a single-codon mutation, and two (S127IRRQP240 and GM142RRQP240) by a double-codon mutation. A case–control study was then implemented in a highly affected Alpine and Saanen breed herd (90 cases/164 controls). Mutations at codon 142 (I/M), 154 (R/H), 211 (R/Q) and 222 (Q/K) were found to induce a significant degree of protection towards natural scrapie infection. Compared with the baseline homozygote wild-type genotype I142R154R211Q222/IRRQ goats, the odds of scrapie cases in IRQ211Q/IRRQ and IRRK222/IRRQ heterozygous animals were significantly lower [odds ratio (OR)=0.133, P<0.0001; and OR=0.048, P<0.0001, respectively]. The heterozygote M142RRQ/IRRQ genotype was only protective (OR=0.243, P=0.0186) in goats also PP240 homozygous at codon 240. However, mutated allele frequencies in French Alpine and Saanen breeds were low (0.5–18.5 %), which prevent us from assessing the influence of all the possible genotypes in natural exposure conditions.

Acid-base abnormalities are frequently present in sick calves. The mechanism for an acid-base disturbance can be characterized using the strong ion approach, which requires accurate values for the total concentration of plasma nonvolatile buffers (A tot ) and the effective dissociation constant for plasma weak acids (K a ). The aims of this study were to experimentally determine A tot , K a , and net protein charge values for calf plasma and to apply these values quantitatively to data from sick calves to determine underlying mechanisms for the observed acid-base disturbance. Plasma was harvested from 9 healthy Holstein-Friesian calves and concentrations of quantitatively important strong ions (Na ϩ , K ϩ , Ca 2ϩ , Mg 2ϩ , Cl Ϫ , L-lactate) and nonvolatile buffer ions (total protein, albumin, phosphate) were determined. Plasma was tonometered with CO 2 at 37ЊC, and plasma PCO 2 and pH measured over a range of 15-159 mm Hg and 6.93-7.79, respectively. Strong ion difference (SID) was calculated from the measured strong ion concentrations, and nonlinear regression was used to estimate values for A tot and K a from the measured pH and PCO 2 and calculated SID. The estimated A tot and K a values were then validated using data from 2 in vivo studies. Mean (Ϯ SD) values for calf plasma were A tot ϭ 0.343 mmol/g of total protein or 0.622 mmol/g of albumin; K a ϭ (0.84 Ϯ 0.41) ϫ 10 Ϫ7 ; pK a ϭ 7.08. The net protein charge of calf plasma was 10.5 mEq/L, equivalent to 0.19 mEq/g of total protein or 0.34 mEq/g of albumin. Application of the strong ion approach to acid-base disturbances in 231 sick calves with or without diarrhea indicated that acidemia was due predominantly to a strong ion acidosis in response to hyponatremia accompanied by normochloremia or hyperchloremia and the presence of unidentified strong anions. These results confirm current recommendations that treatment of acidemia in sick calves with or without diarrhea should focus on intravenous or PO administration of a fluid containing sodium and a high effective SID.Key words: Calf diarrhea; D-lactic acidosis; Hyponatremia; Metabolic acidosis.A cidemia and metabolic acidosis occur commonly in sick calves with or without diarrhea. Metabolic acidosis in diarrheic calves was originally attributed to fecal bonate loss as well as the presence of unidentified organic acids in plasma and a decrease in glomerular filtration rate in response to severe dehydration.1-4 These proposed mechanisms for development of metabolic acidosis were based, in part, on the presence of hyper-L-lactatemia in diarrheic calves, 1,2,5,6 hyper-L-lactatemia and extensive loss of bicarbonate in the watery stool of humans with cholera, 7 and from (personal communication) of a high fecal bicarbonate concentration (40 mEq/L) in 4 calves with experimentally induced enterotoxigenic Escherichia coli diarrhea.c However, metabolic acidosis in diarrheic calves is probably predominantly due to causes other than fecal bicarbonate loss because diarrheic calves have measured mean daily fecal losses of s...