Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SHEEP”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31Linked to original sources
PubMed2001

Copper-associated liver disease in North Ronaldsay sheep: a possible animal model for non-Wilsonian hepatic copper toxicosis of infancy and childhood.

Indian childhood cirrhosis (ICC), endemic Tyrolean infantile cirrhosis (ETIC) and idiopathic copper toxicosis (ICT), are clinically and pathologically indistinguishable liver disorders of infants and young children linked with exogenous copper and with increasing evidence for a genetic predisposition. North Ronaldsay sheep are a primitive breed which have adapted to a copper impoverished environment (<5 ppm) and display an abnormal sensitivity to copper poisoning when transferred to a copper replete (11 ppm) habitat. The aetiological parallels prompted a study of copper-associated liver disease in North Ronaldsay sheep (RCT) to see if the pathology could contribute to the understanding of the childhood disorder. A retrospective study was performed in which the livers of 22 mainland-bred North Ronaldsay sheep were compared with three island-bred sheep and categorized for liver copper content and pathomorphology. It was found that all the mainland sheep had accumulated liver copper (>300 microg/g), in contrast to the island sheep, although 10 sheep with increased liver copper (mean 600 SD 270 microg/g) showed no evidence of liver damage. A further 10 sheep with liver copper (mean 1276 SD 508 microg/g) exhibited periportal to panlobular histochemical copper retention, a periportal and/or panlobular pericellular fibrosis, a mixed inflammatory infiltrate and cholangioplasia. Steatosis was absent and regeneration was in abeyance. Finally, two sheep (liver copper >2000 microg/g) had a more active hepatitis with a florid pericellular, panlobular fibrosis and cirrhosis. Electron microscopy identified large numbers of collagen-producing hepatic stellate (Ito) cells in periportal regions. The pathological findings were sufficiently reminiscent of ICC, ETIC and ICT to warrant further exploration of RCT as a putative animal model. The North Ronaldsay sheep liver may be a useful tool for the investigation of copper-induced fibrogenesis.

Animals↗
PubMed1984

Control of ovine brucellosis in Najdi sheep in Saudi Arabia.

A practical programme for control of ovine brucellosis in a Najdi sheep flock at Haradh and protection of sheep handlers from infection was implemented. Haradh sheep were serologically tested three times at six-month intervals. Of 2,721 sheep subjected to the first tests, 387 (14.2%) were positive reactors. At the second test 2,072 sheep were tested and 31 (1.5%) were positive. The third test was performed on 2,963 sheep and only nine (0.3%) positive reactors were found. Of eight sheep handlers six had Malta fever. Positive reactor sheep were slaughtered and buried after each test. Following the third test all negative sheep were vaccinated with inactivated Brucella melitensis vaccine. Infected sheep handlers were treated at the Haradh clinic. One year after completion of the programme abortions and infertility problems had disappeared and the lambing percentage had increased from 0.8 to 1.3 lambs per ewe. In addition all young lambs born to vaccinated ewes were found to be serologically negative. We suggest expansion of the present programme into a national brucellosis control campaign in the kingdom.

Abortion, Veterinary↗
PubMed1996

Efficacy of ivermectin and moxidectin injection against larvae of Wohlfahrtia magnifica (Diptera: Sarcophagidae) in sheep.

The therapeutic efficacies of ivermectin (Ivomec injection, Merck Sharp & Dohme B.V.) and moxidectin (Cydectin 1% injection, American Cyanamid Company) were evaluated in sheep naturally infested with larvae of Wohlfahrtia magnifica. Sheep were randomly allocated to one of the 2 groups, each consisting of 19 animals. Sheep in one group received ivermectin and those in the other, moxidectin by subcutaneous injection at a dose of 0.2 mg/kg body weight. Evaluation was performed at 19, 24, 28, 39, 43, 48, 52, 63, 67, 72, 87, 96, 120, 144 and 168 h after treatment. At 144 and 168 h post-treatment, late third-instar larvae were collected from wounds of four sheep in both groups and from untreated, infested sheep. These larvae were reared in the laboratory to assess adult emergence. Neither ivermectin nor moxidectin was effective as a rapid acting treatment or as a long-term, or even short-term, prophylactic. Despite the treatment, 30-40% of sheep had live larvae at every evaluation. Although larvae disappeared from the wounds of some sheep in both groups after the treatment, the wounds in these animals failed to recover and were reinfested by larvae of W. magnifica. On day 7 post-treatment the trial had to be finished because the majority of treated sheep were severely infested by Wohlfahrtia maggots. The average number of infested sheep in the two groups and the number of adults that were produced from larvae collected from treated sheep indicate that ivermectin and moxidectin did not differ significantly in efficacy.

Animals↗
PubMed1989

The relationship between ovine lymphocyte antigens and parasitological and production parameters in Romney sheep.

The occurrence of ovine lymphocyte antigen (OLA) types in two flocks of New Zealand Romney sheep was examined in relation to resistance to nematode parasites [as judged by faecal egg counts (FEC)], plasma pepsinogen levels, liveweight and weight gains. A panel of OLA-typing antisera (SY 1-16) which determine class 1 MHC antigens of the sheep was used. The OLA combination SY 1a + 1b was found exclusively in Romney sheep of both flocks having below average FEC, but was present in low frequency (5%). In one flock, sheep possessing this antigen combination had consistently lower FEC from weaning to 1 year of age than sheep without this combination. SY 6 occurred significantly more frequently in above average FEC sheep and was associated with significantly higher FEC during secondary challenge infection. Plasma pepsinogen levels were significantly lower in those sheep possessing SY 2 or SY 3 but these OLA types were not associated with lower than average FEC. No OLA type was associated with above average weight gain but in one flock sheep with SY 1b and SY 1a + 1b had significantly lower weight gains between weaning and 6 months of age than sheep without these OLA types. A similar association was not found in the other flock. Sheep in one flock with SY 16 were significantly heavier than those without this antigen. No other associations between OLA types and liveweight were found.

Animals↗
PubMed1988

Relationship of nematode cholinesterase activity and nematode burdens to the development of resistance to trichostrongyle infections in sheep.

The changes in nematode cholinesterase (ChE) activities were examined in relation to the development of resistance in (1) a flock of young grazing sheep, (2) grazing and penned sheep treated with dexamethasone and (3) penned sheep receiving a single mixed infection. Nematodes from grazing sheep with high faecal egg counts (FECs) had higher ChE activities than those from sheep with low FECs. Female nematodes tended to have higher ChE activities than males, and ChE activities in both tended to decline with increasing age of the sheep. The decline in female Trichostrongylus colubriformis ChE activity was associated with a decline in both worm length and in utero egg count. No decline in nematode ChE activity was observed when grazing sheep were treated with dexamethasone. ChE activity of T. colubriformis established in immunosuppressed penned sheep declined 10-20 fold 8 weeks after cessation of treatment. Nematode burdens in the small intestine and abomasum of grazing sheep were significantly correlated, and in individual species they were also correlated with ChE activities. The development of resistance in sheep and the elimination of adult nematode burdens is discussed in relation to gastrointestinal mucosal globule leucocyte numbers, mucus antiparasite activity and the impairment of nematode metabolic function.

Animals↗
PubMed1995

Identification of sero-reactive Brucella melitensis cytosoluble proteins which discriminate between antibodies elicited by infection and Rev.1 vaccination in sheep.

Distinction between Brucella melitensis infected and vaccinated sheep is needed to fully achieve ovine brucellosis eradication in several countries. For this purpose, we probed immunoblots of cytosoluble protein extract (CPE) of the rough (R) B. melitensis strain B115 with sera of Brucella-free, naturally infected, B. melitensis H38 experimentally infected and B. melitensis Rev.1 vaccinated sheep to identify immunogenic Brucella cytosoluble proteins which may lead to the development of more useful diagnostic tests and which may eventually differentiate vaccinated sheep from infected sheep. Brucella-free sheep sera showed IgM antibody reactivity to protein bands between 19 and 92 kDa. The use of conjugate specific for sheep IgG avoided non specific reactivity to all these bands except to the 39 and 50 kDa bands which were still detected in some Brucella-free sheep sera. In sera of B. melitensis H38 experimentally infected sheep, a specific IgG antibody response was observed against proteins of molecular masses of 19, 24, 28, 32, 39, 50 and 54 kDa. These proteins were also variably detected by IgG of sera from naturally infected sheep. Other proteins of 10, 12, 23, 36, 38, 42, 46, 68, 80 and 92 kDa were also detected by the latter sera. In sera from B. melitensis Rev.1 vaccinated sheep, an IgG antibody response was only observed against proteins with molecular masses of 39 and 50 kDa. These results suggest that the 19, 24, 28, 32 and 54 kDa proteins (the first recognized after experimental infection and that provoked a consistent humoral response during natural infection) could be interesting to develop serological tests for differentiating B. melitensis infection from B. melitensis Rev.1 vaccination.

Animals↗
PubMed2006

Phylogenetic diversity of Pasteurellaceae and horizontal gene transfer of leukotoxin in wild and domestic sheep.

Wild and domestic animal populations are known to be sources and reservoirs of emerging diseases. There is also a growing recognition that horizontal genetic transfer (HGT) plays an important role in bacterial pathogenesis. We used molecular phylogenetic methods to assess diversity and cross-transmission rates of Pasteurellaceae bacteria in populations of bighorn sheep, Dall's sheep, domestic sheep and domestic goats. Members of the Pasteurellaceae cause an array of deadly illnesses including bacterial pneumonia known as "pasteurellosis", a particularly devastating disease for bighorn sheep. A phylogenetic analysis of a combined dataset of two RNA genes (16S ribosomal RNA and RNAse P RNA) revealed remarkable evolutionary diversity among Pasteurella trehalosi and Mannheimia (Pasteurella) haemolytica bacteria isolated from sheep and goats. Several phylotypes appeared to associate with particular host species, though we found numerous instances of apparent cross-transmission among species and populations. Statistical analyses revealed that host species, geographic locale and biovariant classification, but not virulence, correlated strongly with Pasteurellaceae phylogeny. Sheep host species correlated with P. trehalosi isolates phylogeny (PTP test; P=0.002), but not with the phylogeny of M. haemolytica isolates, suggesting that P. trehalosi bacteria may be more host specific. With regards to populations within species, we also discovered a strong correlation between geographic locale and isolate phylogeny in the Rocky Mountain bighorn sheep (PTP test; P=0.001). We also investigated the potential for HGT of the leukotoxin A (lktA) gene, which produces a toxin that plays an integral role in causing disease. Comparative analysis of the combined RNA gene phylogeny and the lktA phylogenies revealed considerable incongruence between the phylogenies, suggestive of HGT. Furthermore, we found identical lktA alleles in unrelated bacterial species, some of which had been isolated from sheep in distantly removed populations. For example, lktA sequences from P. trehalosi isolated from remote Alaskan Dall's sheep were 100% identical over a 900-nucleotide stretch to sequences determined from M. haemolytica isolated from domestic sheep in the UK. This extremely high degree of sequence similarity of lktA sequences among distinct bacterial species suggests that HGT has played a role in the evolution of lktA in wild hosts.

Alleles↗
PubMed2004

Immunohistochemical studies of scrapie archival material from Irish ARQ/ARQ sheep for evidence of bovine spongiform encephalopathy-derived disease.

Since scrapie and bovine spongiform encephalopathy (BSE) in sheep are clinicopathologically indistinguishable, BSE in sheep may have been misdiagnosed as scrapie. Disease-specific prion protein (PrP(d)) patterns in archival tissues of 38 Irish ARQ/ARQ sheep diagnosed as scrapie-affected were compared to those in four Dutch BSE-challenged sheep. When medulla oblongata was immunolabelled with an antibody directed against amino acids 93-99 of ovine prion protein (ovPrP), intraneuronal PrP(d) was apparent in all 38 Irish sheep but was absent in BSE-challenged sheep. When lymphoid follicles were immunolabelled with antibodies directed against amino acids 93-106 of ovPrP, granule clusters of PrP(d) were seen in 34 of the 38 Irish sheep. Follicles of the remaining four archive sheep contained either no PrP(d) or single PrP(d) granules, similar to follicles from BSE-challenged sheep. Based on the medulla results, none of the archival cases had BSE-derived disease. The identification of some scrapie sheep with little or no intrafollicular PrP(d) suggests that this technique may be limited in discriminating between the two diseases.

Animals↗
PubMed2006

Pulsed-field gel electrophoresis of Campylobacter jejuni sheep abortion isolates.

Campylobacter species are a significant cause of sheep abortion in most sheep-raising countries. In New Zealand, Campylobacter fetus subsp. fetus is the leading cause of diagnosed sheep abortion and the species C. jejuni and C. coli have also been implicated. To date, strain typing information of C. jejuni sheep abortion isolates is limited. The objective of the present study was to genotype C. jejuni isolates cultured from sheep abortions submitted to diagnostic laboratories in New Zealand during the 2000 breeding season, using pulsed-field gel electrophoresis (PFGE). In this study, C. jejuni isolates were cultured from approximately 10% of farms from which Campylobacter species were isolated from sheep abortions in the year 2000. This equated to 25 C. jejuni isolates from 21 farms. These isolates were obtained from the veterinary diagnostic laboratories and strain typed using the molecular typing technique PFGE. Ten distinct PFGE types were identified amongst the isolates. No particular PFGE type was found most frequently amongst these C. jejuni sheep abortion isolates. However, indistinguishable or similar C. jejuni PFGE types were identified from different aborted foetuses from the same flock, consistent with the role of C. jejuni as an infectious cause of abortion in sheep. These strain types were similar or indistinguishable from C. jejuni sheep abortion isolates obtained in 1999 in a smaller study (Mannering, S.A., Marchant, R.M., Middelberg, A., Perkins, N.R., West, D.M., Fenwick, S.G., 2003. Pulsed-field gel electrophoresis typing of C. fetus subsp. fetus from sheep abortions in the Hawke's Bay region of New Zealand. NZ Vet. J. 51, 33-37).

Abortion, Veterinary↗
PubMed2005

Haemonchus contortus and Trichostrongylus colubriformis in pen-trials with Javanese thin tail sheep and Kacang cross Etawah goats.

Weight gain costs due to infection were higher in sheep than goats, 28 and 17.5%, respectively, for Trichostrongylus colubriformis and 48.7 and 32.2%, respectively, for Haemonchus contortus. The extent of bodyweight cost attributed to anorexia in sheep infected with H. contortus was higher (13.5 g/day) than in sheep infected with T. colubriformis (2.3 g/day). On the other hand, bodyweight cost due to the other pathogenic effects in sheep infected with T. colubriformis were higher (35.6 g/day) compared to sheep infected with H. contortus (10.9 g/day). A strong relationship between faecal egg count and worm count (r=0.79, P=0.006) was shown only in sheep infected with T. colubriformis. About half of the infected sheep and goats had low or zero faecal egg counts throughout the study. In about 40% the egg count rose initially but became low by weeks 10-16, whereas in about 10% counts increased progressively throughout the period of observation and these animals also had the highest numbers of worms at slaughter. Packed cell volume was reduced in sheep and goats infected with H. contortus but serum protein and haemoglobin levels were unaffected. Sheep infected with T. colubriformis had a higher level of eosinophilia after 8 weeks (18.4%) than sheep infected with H. contortus (11.4%), whereas this pattern was reversed in goats and levels were also lower (4.1 and 8.9%, respectively). There was no apparent relationship between eosinophilia and resistance to infection with H. contortus or T. colubriformis.

Animals↗
PubMed2006

Serum antibody isotype responses of Fasciola-infected sheep and cattle to excretory and secretory products of Fasciola species.

This study investigated the immunoglobulin isotype responses of sheep and cattle chronically infected with Fasciola hepatica and Fasciola gigantica to adult F. hepatica excretory/secretory products (Fh-ES) or F. gigantica excretory/secretory products (Fg-ES), respectively. An antibody enzyme-linked immunosorbent assay (Ab-ELISA) was used to determine serum antibody (total Ig, IgG(1), IgM, IgG(2) and IgA) responses. At necropsy, the mean number of flukes recovered was lower in cattle than in sheep. All F. hepatica and F. gigantica infected sheep and cattle showed an increased total Ig levels from 3 to 4 weeks post-infection (wpi). Among isotypes IgG(1) was most dominant while IgM was the earliest (2 wpi) to be detected in both sheep and cattle infected with both F. hepatica and F. gigantica animals. IgG(2) response was early (2 wpi) in sheep infected by F. hepatica but there was no response in sheep infected with F. gigantica. There was a late and strong IgG(2) response in cattle infected with both flukes. The IgA isotype showed an early and a clear biphasic response in sheep with F. hepatica but was less pronounced in F. gigantica infected sheep. While IgA response to Fh-ES was noticed 5 wpi in F. hepatica infected cattle, it appeared much later (21 wpi) in those infected with F. gigantica. The dominance of IgG(1) isotype in infected sheep and cattle suggest an associated Th2 response. This early response to adult Fasciola spp. ES antigen suggests an early exposure to the antigen presumably through the cross-reacting ES products of juvenile flukes. There is clearly difference in IgG(2) isotype response in cattle (resistant) compared to sheep (susceptible). The late IgG(2) response in cattle may suggest late Th1 involvement in bovine cellular responses to adult Fh-ES/Fg-ES.

Animals↗
PubMed1999

The effects of urea supplementation on production and parasitological responses of sheep infected with Haemonchus contortus and Trichostrongylus colubriformis.

Merino wether lambs were individually confined and fed a basal diet of oaten chaff containing essential minerals which was untreated or contained 3% urea. Within each dietary group animals were orally infected with either 200 H. contortus (H), 1000 T. colubriformis (T) or both species (H + T) thrice weekly or remained uninfected (C). Weight gain, wool production, and parasite burden were measured over a 19-week period. Sheep on the diet containing urea gained more weight, consumed more feed and grew more wool of higher fibre diameter than their counterparts given no urea. On both diets uninfected sheep consumed more feed than infected sheep and the sheep given no urea and infected with both H and T worm species consumed the least feed. Parasitised sheep gained less weight than uninfected control sheep. Sheep with urea in their diet had lower faecal egg counts when infected with H alone or with H and T but there was no effect of urea on egg count of sheep infected with T alone. In contrast, T numbers after slaughter were reduced in sheep fed diets containing urea whereas H numbers were not affected by diet. It was concluded that supplementation with urea can increase resilience to parasitism thereby improving production and also enhance resistance mechanisms against worms in young sheep on low quality roughage diets. These responses can be partly attributed to stimulation of feed intake, presumably due to enhanced ruminal digestion, but also to elevated rumen NH3-N levels which would be expected to have increased rumen microbial protein synthesis and availability to the intestines.

Abomasum↗
PubMed2002

An interferon-gamma assay for diagnosis of Corynebacterium pseudotuberculosis infection in adult sheep from a research flock.

The optimal method of control of caseous lymphadenitis of sheep caused by Corynebacterium pseudotuberculosis is eradication of infection by identification and removal of infected carrier animals. Current serological approaches to identification of infected sheep are generally hampered by low sensitivity and specificity of available tests. The objective of this study was to develop a whole blood assay for detection of C. pseudotuberculosis-infected sheep, based on detection of IFN-gamma response to whole cell C. pseudotuberculosis antigens, and to determine the reliability of the assay. A commercially available bovine interferon-gamma assay enzyme-linked immunosorbent assay was used and the test optimised using experimentally infected sheep. The assay was also tested on known CLA-negative sheep. Setting a IFN-gamma optical density cut-off at 0.100 as positive under the conditions used, the test detected C. pseudotuberculosis experimentally infected sheep over a 450-day period with a reliability of 95.7%. It identified known non-infected sheep with a reliability of 95.5%. Repeated vaccination of three uninfected sheep with a commercially available bacterin-toxoid vaccine did not interfere with the assay. The IFN-gamma response of sheep whole blood to C. pseudotuberculosis antigens offers promise for use in a test-and-removal approach to eradication of CLA in sheep.

Animals↗
PubMed2002

Natural Ehrlichia phagocytophila transmission coefficients from sheep 'carriers' to Ixodes ricinus ticks vary with the numbers of feeding ticks.

In a longitudinal study in a UK upland site, 38% of adult sheep were detected as infected with the tick-borne bacterium Ehrlichia phagocytophila by PCR of blood samples. Infection prevalence declined significantly with sheep age but varied significantly and non-linearly with the number of adult Ixodes ricinus ticks feeding per sheep. These findings suggested that under conditions of natural repeated tick-borne challenge sheep remain partially susceptible to re-infections, but the likelihood of re-infection depended on the numbers of feeding ticks. Transmission efficiency from sheep to immature ticks also varied significantly and non-linearly with the number of adult ticks feeding per sheep: transmission efficiency was almost zero in sheep with low adult tick infestations rising to 30% at certain levels of adult tick infestation. Infection intensity in infected engorged immature ticks also varied with the number of adult ticks feeding per sheep, but neither prevalence nor intensity of infection in engorged ticks were related to sheep blood PCR result. These findings suggest that variation in the numbers of ticks feeding per sheep may influence E. phagocytophila transmission by direct effects on transmission at the tick-host interface.

Animals↗
PubMed2002

Field evidence for density-dependent facilitation amongst Ixodes ricinus ticks feeding on sheep.

Engorged Ixodes ricinus nymphs collected from sheep resident in an upland UK field site were significantly lighter than nymphs that engorged on previously tick-naïve sheep, indicating that site-resident sheep continually exposed to ticks acquired anti-tick resistance. The weights of engorged nymphs that fed on naturally tick-resistant sheep increased significantly, however, when increasingly high numbers of adult female ticks fed on the sheep during seasonal peaks of tick activity. This relationship was unaffected by variations in nymph weight amongst individual sheep, between seasons and years, and potential effects of sheep infection with Ehrlichia phagocytophila; this suggests that high adult tick infestations may directly inhibit the expression of acquired anti-tick resistance by sheep. The length, width and weight of adult ticks and the scutum length of adult females were linearly related to their weight as an engorged nymph. The mean scutum length of adult female ticks feeding on sheep in the field site was greater than that of adult females obtained from engorged nymphs collected from sheep of the same site. This suggests that larger ticks have a survival advantage and that I. ricinus ticks exhibit density-dependent intraspecific facilitation at high infestation levels with potential consequences for the transmission of tick-borne diseases.

Animals↗
PubMed1998

The eosinophil leucocyte, a phenotypic marker of resistance to nematode parasites, is associated with calm behaviour in sheep.

The hypothesis that behaviour in sheep is influenced by resistance to infections with Trichostrongylus colubriformis and Haemonchus contortus was explored. Sheep were assessed phenotypically as resistant and susceptible in four ways and thereafter, the effect of resistance on several behavioural traits was measured in an arena test. The behavioural parameters recorded for each sheep were: approach/avoidance distance; travel; number of moves; and spread. Four phenotypic groups of sheep were set up each with two subgroups: ovine lymphocyte antigen (OLA) type (subgroups SY1a type vs other types); blood eosinophil leucocyte counts (high vs low); T. colubriformis and H. contortus serum antibodies (high vs low titres) and faecal egg count (FEC) (high vs low). Only the behavioural comparison between sheep with high versus low eosinophil leucocyte count showed consistent differences that were statistically significant, although other comparisons favoured associations between OLA type SY1a, low FEC and reduced approach/avoidance distance and/or locomotor behaviour. The eosinophil leucocyte association was established on two non-overlapping test populations of sheep, with mean eosinophil leucocyte counts of 3.19 x 10(5)/mL blood for high and 0.83 x 10(5)/mL blood for low subgroups; results were reproduced on five separate occasions over 6 weeks to detect differences as approach/avoidance distance (P < 0.01), travel (P < 0.01), number of moves (P < 0.01), and spread (P < 0.05). High eosinophilia correlated with low FEC for the infected sheep, which identified sheep that were resistant to parasites. We concluded, therefore, that the resistant sheep were more at ease with the environment of the test than were the sheep with low eosinophil leucocyte counts. The strong association between high eosinophil leucocyte counts and behaviour is consistent with other reports which suggest that retention of normal levels of circulating eosinophil leucocytes is associated with resistance to stress.

Age Factors↗
PubMed2001

Oral inoculation of sheep with the agent of bovine spongiform encephalopathy (BSE). 1. Onset and distribution of disease-specific PrP accumulation in brain and viscera.

Sixty-three Romney sheep aged 6 months, consisting of three groups (PrP(ARQ/ARQ), PrP(ARQ/ARR), and PrP(ARR/ARR)genotypes) of 21 animals, were infected orally with brain tissue from BSE-infected cattle. Sub-groups of the 21 PrP(ARQ/ARQ) animals were killed, together with uninfected controls 4, 10, 16, 22 or 24-28 (after the development of full clinical disease) months post-inoculation (mpi). One sheep from each of the two groups of four killed at 4 or 10 mpi were shown by immunohistochemical examination to possess disease-specific PrP accumulations in single lymph nodes. At 16 mpi, such accumulations were detected in two of four infected sheep in some viscera and in the spinal cord and brain. At 22 mpi, three of five infected sheep had widespread disease-specific PrP accumulations in all tissues examined, but the remaining two animals gave positive results only in the central nervous system. Clinical disease appeared at 20-28 mpi. Three sheep killed with advanced clinical signs showed widespread PrP accumulation in brain, spinal cord and peripheral tissues. These results confirmed that PrP(ARQ/ARQ) Romney sheep are susceptible to experimental infection with the BSE agent. The different sites at which initial PrP accumulations were detected suggested that the point of entry of infection varied. Once established, however, infection appeared to spread rapidly throughout the lymphoreticular system. The results suggested that in some BSE-infected sheep neuroinvasion occurred in the absence of detectable PrP accumulations in the viscera or peripheral nervous system. In contrast to cattle with BSE, however, most sheep showed disease-specific PrP accumulations in the lymphoreticular system. In this respect, BSE-infected resembled scrapie-infected sheep; it is possible, however, that future research will reveal differences in respect of targeting of cell types within the lymphoreticular and peripheral nervous systems. The PrP(ARQ/ARR)and PrP(ARR/ARR)sheep were also killed in sub-groups at intervals after inoculation. Up to 24 mpi, however, none of these animals showed disease-specific PrP accumulations. Further results will be reported later.

Administration, Oral↗
PubMed2003

Epidemiological implications of the susceptibility to BSE of putatively resistant sheep.

The experimental infection of sheep with bovine spongiform encephalopathy (BSE) by the oral route and the likelihood that sheep were fed BSE-infected meat and bone meal has led to extensive speculation as to whether or not sheep are naturally infected with BSE. In response, the UK government has initiated the National Scrapie Plan (NSP), an ambitious pound 120 million per year project to create a BSE- and scrapie-resistant national sheep flock, by selectively breeding for a genotype of sheep believed to be resistant to both diseases. This genotype has recently been shown to be susceptible to BSE by intracerebral (i.c.) inoculation. Should these sheep be sufficiently susceptible to BSE via natural transmission, the NSP might fail. Here we estimate the susceptibility of this genotype to horizontal (sheep-to-sheep) transmission of BSE by comparison with more extensive oral and i.c. exposure data for other sheep genotypes. We show that a previous estimate of the risk of BSE transmission to sheep via the feedborne route remains robust. However, using a mathematical model for the within-flock transmission of BSE, we show that, while the best estimate indicates that the NSP should be successful, current data cannot exclude the failure of the NSP.

Animals↗