Linear hoof defects in sheep infected with foot-and-mouth disease

During the epidemic of foot-and-mouth disease (FMD) in The Netherlands in 2001, a sheep farm was identified that had been subclinically infected with the disease. The FMD virus genome was detected in 12 of 16 probang samples collected from the sheep and the virus was isolated from four of these samples. Linear defects were observed, 1 to 3 cm from the coronary band, in the hooves of several of the sheep. The defects were thought to have been caused by the FMD infection. It was thought that the distance of the defects from the coronary band might be an indication of the time since the animals had been infected. To determine the growth rate of the claws of sheep, the growth of the hoof horn of uninfected lambs and ewes was measured; in the lambs the growth rate was 0.44 mm per day and in the ewes it was 0.29 mm per day.     

Comparison of the pathogenicity for pregnant sheep of Rift Valley fever virus and a live attenuated vaccine

A live attenuated mutant of Rift Valley fever virus, MV P12, was previously shown to be non-pathogenic in young lambs, but capable of producing protective immunity. The studies reported here show that the abortion in sheep caused by an infection with virulent virus is the result of necrosis of the maternal villi and cotyledons arising from an acute inflammation of the maternal caruncles. Pregnant ewes infected with the attenuated mutant virus MV P12 showed none of these lesions in the placenta and gave birth to healthy lambs. Colostrum from ewes infected with MV P12 virus was able to induce protective immunity in the offspring. These data along with previously published results suggest that the mutant virus MV P12 is an excellent candidate for use as a live attenuated veterinary vaccine.     

Use of serology and polymerase chain reaction for the rapid eradication of small ruminant lentivirus infections from a sheep flock: A case report

A SRLV-free sheep flock incurred infection which led to an SRLV infection rate of over 50% of the ewes (34/64) within a 30 months period, indicating that environmental conditions were favourable to transmission. An intensive regimen of sampling at short intervals and testing for SRLV antibodies and proviral DNA combined with strict management was implemented for the entire flock, lambs and yearlings included. This resulted in eradication of the infection within two testing and culling rounds with a 3 months interval. The additional value of the proviral DNA detection by PCR in identifying infected animals was clear in that nine infected animals were found that would have been missed if tested by serology alone. PCR also saved two lambs from being culled; they were sero-positive probably due to maternal antibodies, but not infected.     

Field evaluation of tracer sheep for the detection of early natural infection with Mycobacterium avium subsp paratuberculosis

OBJECTIVE: To determine whether tracer sheep could be used to detect S strain Mycobacterium avium subsp paratuberculosis on pasture, and to provide further insight into the early stages of infection. DESIGN: A field study on two farms in an endemic area for ovine Johne's disease in New South Wales. Procedure Lambs, weaners and adult ewes were introduced to pasture with varying amounts of M. a. paratuberculosis contamination and monitored using skin tests, gamma interferon assay, faecal culture and serial necropsy of small groups for up to 15 months after first exposure. RESULTS: Culture from tissues was the most sensitive method for detecting early infection in sheep after natural exposure to S strain M. a. paratuberculosis. The organism was detected in at least one introduced sheep from every exposed group, 6 to 12 months after first exposure. Histopathological lesions were detected in only 17% of culture-positive sheep, and only after at least 8 months of exposure. Similarly, antemortem diagnostic tests had low sensitivity during the early stages of naturally acquired infection. There was no evidence of any differences in infection rate between sheep first exposed as neonates, as weaners or as adults. A higher proportion of lambs born to ewes from an infected flock were infected than lambs suckling uninfected ewes introduced to the same infected environment, and infection was detected earlier in these 'resident' lambs. CONCLUSION: These findings indicate that groups of unexposed 'tracer' sheep, tested by culture of tissues at slaughter 6 to 12 months after first exposure, might be a useful way to assess pasture infectivity in control programs for ovine Johne's disease.     

Border disease without nervous signs or fleece changes

A natural infection with border disease virus occurred in a flock on low ground in Argyll in the spring of 1984. The outbreak was unusual in that the typical clinical signs of border disease, ie, tremor and, or, fleece changes were not present; manifestations of disease were restricted to abortion and the birth of small weak lambs. The disease was shown to have been introduced to the flock by four healthy ewes persistently infected with border disease virus among a group of 39 purchased in October 1983. Further investigations in late August 1984 detected viraemia in six of seven ill-thriven lambs and four of 24 apparently healthy lambs. Attempted 'natural vaccination' of susceptible sheep by mixing them at grass for three months with groups of ewes and lambs known to contain virus excretors was largely unsuccessful as only four of 22 'sentinel' sheep seroconverted. In October 1984 the persistently infected purchased animals and all that year's lamb crop were removed from the farm. No disease occurred in 1985 when the lambing percentage was 129 per cent compared with 100 per cent in 1984. Two of the four persistently infected purchased ewes were mated at Moredun Research Institute in December 1984 and both produced healthy but persistently infected lambs.     

The production and survival of lambs persistently infected with border disease virus.

From 1985 to 1989 lambs persistently infected with border disease virus (BDV) were produced for comparative immunological studies by infecting 57 susceptible pregnant ewes between 50 and 60 days' gestation with Moredun or Oban strains of BDV. Ewes were infected either by injection with virus grown in cell culture or by housing with lambs excreting BDV. There was no significant difference in the outcomes of these different methods of infection. There was a significant difference in the number of viable lambs born to ewes receiving the two viruses. Of 41 ewes infected with Moredun virus 21 produced 32 live lambs of which 17 were reared to 1 month old (53% viability). Of 16 ewes receiving Oban virus 10 gave birth to 17 live lambs of which 15 were reared to 1 month old (88% viability). All the lambs born to ewes infected with Moredun BDV had varying signs of tremor and increased hairiness ("hairy-shakers") while those born to ewes infected with the Oban virus had no obvious clinical signs. Survival of the lambs was poor. Up until February 1991, 14 Moredun and 10 Oban sheep between the ages of 4 months and 5.5 yr had died from a variety of causes. The two commonest causes were a chronic wasting syndrome and a mucosal disease-like syndrome which was associated with the recovery of cytopathic BDV. Mating of unrelated persistently infected sheep was largely unproductive although 2 lambs were reared.     

TRANSMISSION OF A MUCOSAL DISEASE VIRUS INFECTION BETWEEN SHEEP

The transmission of mucosal disease virus (MDV) from infected ewes and their lambs to susceptible sheep was investigated. MDV was recovered from the amniotic fluid of an infected pregnant ewe and from the blood, nasal swabs and urine of hairy lambs. MDV infection was transmitted either at lambing, from infective foetal fluids or lambs, or later as a result of contact with a surviving with a hairy lamb and either aborted or gave birth to an infected hairy lamb. Adult sheep and 12-months-old sheep were less readily infected than were newborn lambs. Pregnant ewes were infected by contact with a hairy lamb and either aborted or gave birth to an infected hairy lamb. A method to minimise spread of the infection in the field is suggested.     

Prevalence and molecular characterization of Cryptosporidium and Giardia species and genotypes in sheep in Maryland

In the United Kingdom and Australia sheep have been implicated as sources of Cryptosporidium and Giardia that infect humans, but no such studies have been conducted in North America. Therefore, a study was undertaken to investigate the prevalence of these parasites in sheep on a farm in Maryland. Feces were collected from 32 pregnant ewes 1, 2, and 3 days after parturition and from each of their lambs 7, 14, and 21 days after birth. The presence of Cryptosporidium oocysts and Giardia cysts was determined by both immunofluorescence microscopy and PCR/gene sequence analysis. PCR was consistently more sensitive than microscopy. The prevalence, by PCR, of Cryptosporidium in ewes and lambs was 25 and 77.4%, respectively. Three species/genotypes of Cryptosporidium were identified: C. parvum, a novel C. bovis-like genotype, and Cryptosporidium cervine genotype. Cryptosporidium parvum and the cervine genotype have been reported worldwide in human infections. The novel C. bovis-like genotype is reported here for the first time. The prevalence of Giardia in ewes and lambs was 12 and 4%, respectively. Most infections were Assemblage E which is not zoonotic; however, one ewe was infected with zoonotic Assemblage A. The identification of only two lambs infected with C. parvum and one ewe infected with G. duodenalis Assemblage A suggests a low prevalence of these zoonoses. However, the high prevalence of the zoonotic cervine genotype indicates that sheep should be considered a potential environmental source of this human pathogen.     

Maedi-visna control in sheep II. Half-yearly serological testing with culling of positive ewes and progeny

In 1979 a field trial was started to study the feasibility of maedi-visna control in sheep by half-yearly serological testing (by ELISA) with culling of sero-positive ewes and their progeny. In 13 commercial flocks, with a mean initial incidence of serological reactors of 17%, the sero-positive ewes and all their progeny, those of preceding years included, were culled after each half-yearly test. The percentage of sero-positive sheep decreased gradually and at the end of the second year, at the 5th test, all flocks were sero-negative. Also the 6th and 7th test did not yield sero-positive sheep. At the 8th test, however, 3 sero-positive ewes were detected in one of the flocks. A definite conclusion as to the source of infection could not be drawn. The following flock test was negative. In 2 other commercial flocks, which had a mean initial incidence of sero-positive sheep of 53%, those sero-positive and only their suckling lambs were culled. Here too, a gradual decrease in the incidence of sero-positive sheep was observed at the 2nd and 3rd test, but at the 4th test a sharp increase occurred. The programme was continued and a decrease followed until 0% was reached at the 7th test (end of third year). Age analysis of the sero-positive sheep which caused this peak revealed that the majority had been born before the start of the trial. This suggests that a 'second wave' of sero-positive sheep may be prevented and a quicker result obtained if progeny of preceding years are culled as well.(ABSTRACT TRUNCATED AT 250 WORDS)     

A MUCOSAL DISEASE VIRUS AS A CAUSE OF ABORTION, HAIRY BIRTH COAT AND UNTHRIFTINESS IN SHEEP

A condition in Australian sheep resembling border disease was transmitted by the inoculation of pregnant ewes with material from affected lambs. This material contained mucosal disease virus (MDV). Twenty-two lambs comprising 6 from uninoculated control ewes, together with 11 with hairy coats and 5 with normal coats from inoculated ewes, were observed from 7 to 182 days after birth. Nine of the lambs from inoculated ewes died during the experiment from a variety of causes. Glial cell abnormalities were observed in control and affected lambs, but only 4 of the 11 hairy lambs were judged to have abnormal glial cells. There were no consistent histopathological findings indicative of MDV infection. MDV was recovered from tissues of all 11 hairy lambs, but not from any of the lambs with normal coats. The hairy lambs appeared to be immunologically tolerant to the virus. Susceptible sheep in contact with the hairy lambs were infected with MDV. It is suggested that a condition in Australian lambs characterised by hairiness of the birth coat and poor viability is due to foetal infection with a mucosal disease virus.     

Risk factors associated with the prevalence of interdigital dermatitis in sheep from 1999 to 2000

As part of an investigation into improving the treatment and control of lameness in sheep flocks in England and Wales, a postal survey was conducted in November 2000. Farmers were asked to estimate the prevalence of footrot and interdigital dermatitis in their flocks. In the ewes the prevalence of interdigital dermatitis remained relatively stable throughout the year, but there was a large increase in lambs during late spring and early summer. Logistic regression models were used to assess statistically significant risk factors associated with prevalences of the condition of 5 per cent or more in ewes and 10 per cent or more in lambs. Factors that increased the risk in ewes were 'sometimes/never' catching lame sheep compared with 'always' farm land 100 m or less above sea level and renting-in winter grazing; factors that increased the risk in lambs were a prevalence of 5 per cent or more of footrot in ewes, 'sometimes/never' catching lame ewes compared with 'always', 'sometimes/never' treating ewes with footrot with parenteral antibiotics compared with 'always', showing sheep at agricultural events, farm land 100 m or less above sea level, and a prevalence of 5 per cent or more of interdigital dermatitis in ewes. Turning sheep on to a field which had been free from livestock for at least two weeks after footbathing decreased the risk of interdigital dermatitis in lambs. Footbathing without the use of a clean field compared with not footbathing did not significantly affect the prevalence of the interdigital dermatitis.     

Repetitive abortion in Neospora-infected ewes.

Pregnant ewes inoculated with cultured Neospora caninum tachyzoites in 1995, 1996, or 1995 and 1996 aborted or delivered weak or clinically normal lambs in 1996. Nine of 11 ewes in the study had previously produced infected lambs or fetuses after being experimentally infected in 1995. Fetuses and lambs produced in 1996 showed histologic lesions and zoites indicative of Neospora. Serologic responses and production of infected fetuses/lambs indicated systemic neosporosis in the ewes during gestation, although tachyzoites could not be cultured from maternal tissues. The repetitive infection of fetuses, and resulting clinical and histopathologic findings in the present study are similar to those reported in naturally infected cattle, adding to the already established similarities of neosporosis between sheep and cattle.     

Longitudinal studies of naturally acquired Brucella abortus infection in sheep.

Naturally acquired Brucella abortus infections were studied during consecutive pregnancies in eight sheep and in their lambs over a period of 40 months to evaluate epizootiologic aspects of natural infection in sheep. Brucella abortus was isolated from the ewes following 16 of 26 natural terminations of pregnancy: from 5 of 6 ewes in the first year, from six of eight ewes in the second year, from two of six ewes in the third year, and from three of six ewes in the fourth year. Vaginal swab samples and milk samples were the most consistent source of the brucella organisms. Brucella abortus was isolated from three ewes when standard tube test seroagglutination titers were less than 1:100. In contrast, results of supplemental tests (card, 2-mercaptoethanol, complement-fixation, and Rivanol) remained positive during the study. During the 40 months, B abortus was isolated from 4 of 4 aborted fetuses, 2 of 5 stillborn lambs, 10 of 37 living lambs, and as an indicator of continuing infection, from 6 of 12 lambs born during the fourth year. Although B abortus has a definite host preference for cattle, this study demonstrated that under appropriate management conditions, sheep may be naturally infected and may remain infected for more than 40 months. Epizootiologic evaluation of all factors, including husbandry practices and exposure potential, should be utilized in determining the need to test other species that may have been exposed to cattle infected with B abortus.     

Prevalence and analysis of potential risk factors for Cryptosporidium parvum infection in lambs in Zaragoza (northeastern Spain)

An epidemiologic study was carried out to investigate the prevalence of and to identify factors associated with the risk of Cryptosporidium infection in sheep in Zaragoza (northeastern Spain). Faecal samples from 583 lambs aged from 1 day to 3 months and 205 ewes older than 1 year were collected at 89 farms in the two regions of the province of Zaragoza with the highest sheep population (Zaragoza and Ejea de los Caballeros). In every sheep farm, data of the factors potentially associated with the likelihood of C. parvum infection were analysed: geographical location, season, size of herd, number of lambs in the herd at sampling time, lambing period, cleaning of lambing area and presence of diarrhoeic lambs in the farm. C. parvum oocysts were identified by using the Ziehl-Neelsen technique in 344 lambs (59%) from 75 farms (84.4%). Infected lambs ranged from less than 7 days to 90 days of age, although the percentage of animals shedding oocysts peaked at 8-14 days of age (76.2%). Statistical analysis showed that infection rates were significantly higher in lambs aged between 1 and 21 days (66.4%) than in those aged between 22 and 90 days (23%) (P<0.0001, chi(2)). Analysis of correlation between excretion of oocysts and diarrhoea revealed a relationship in all age groups and the probability of presenting diarrhoea was significantly higher for lambs shedding oocysts (86.3%) than for those which did not excrete the parasite (32.2%) (P<0.0001, chi(2)). Similarly, cryptosporidial infection rates were significantly higher in diarrhoeic (79.4%) than in non-diarrhoeic lambs (22.4%). Furthermore, infection intensity was correlated with the presence of clinical symptoms. Presence of diarrhoeic lambs in the farm was the only factor significantly associated with an increased risk of infection since the percentage of herds testing positive was significantly higher in farms with diarrhoeic lambs (91.3%) than in those without cases of neonatal diarrhoea (12.5%) (P<0.0001, chi(2)). Factors associated with a decreased risk of C. parvum infection in lambs included low numbers of lambs in the farm and cleaning of the lambing area. Additionally, lambs 8-14 days of age were less likely to be infected at the first lambing period and in spring/autumn. Cryptosporidial infection was also detected in 16 ewes (7.8%) which excreted few oocysts and without diarrhoea.     

Pilot project for eradicating maedi-visna in Walliser blacknose sheep

Maedi-Visna is a lentiviral disease of sheep with a worldwide distribution. The transmission of the virus occurs primarily via colostrum and milk from the infected ewe to its newborn lamb but also horizontally between sheep. The most obvious clinical symptoms are progressive dyspnea and emaciation. In this prospective study an eradication based on serological testing and removing of seropositive animals was performed in 24 flocks of sheep of the breed "Walliser Schwarznasenschafe" leading to a reduction of the seroprevalence from 36% to 1% within two years. The control group consisted of 21 flocks of sheep. Lambs of seropositive ewes had a 7.6 times higher risk to seroconvert within their first two years of life compared to those of seronegative ewes. The dynamics of the spread of the infection were studied in birth cohort groups. Cohort animals of seropositive ewes showed an obvious trend to seroconvert slowly. Seropositive ewes had a significantly lower reproduction rate and their lambs suffered from significantly higher death and lower growth rates, probably due to a reduced milk production, resulting in economic losses.     

The effects of maedi-visna virus infection on productivity in ewes

A total of five data sets obtained from four separate sheep flocks were used to evaluate the effects of subclinical maedi-visna virus infection (as determined by serological procedures) on productivity in ewes. In general, infection with maedi-visna virus had a detrimental effect on productivity. Infection resulted in a reduction in conception rates, with the odds of an infected ewe conceiving being only approximately 0.67 times those of a non-infected ewe. For ewes which did conceive, there was no detrimental effect of infection on the number of lambs born. The birth weights of lambs born to middle-aged (3–4 years) infected ewes were 3–6% lower than the weights of lambs born to non-infected ewes of the same age. There was very little apparent effect of infection in younger (1–2 years) and older (5 + years) ewes: some factors which may have biased these results are discussed. Lamb weights at 25–50 days of age appeared to be reduced by maedi-visna infection in the ewe but the results were not statistically significant.     

Seroreactivity of Peruvian sheep and goats to small ruminant lentivirus-ovine progressive pneumonia virus

Sera from 3,369 sheep and 1,394 goats in Peru were examined by agar-gel immunodiffusion for antibodies to ovine progressive pneumonia virus (OPPV). The point prevalence rates for antibodies to OPPV in sheep were 1.7% to 40.6% (mean, 19.02%) in the 7 flocks studied, whereas for goats, the point prevalence rates for antibodies that cross-reacted with OPPV in 12 herds were 0.0% to 45.1%. For sheep, a direct association between increasing age and increasing seroreactivity to OPPV was established, and there was evidence to indicate that lambs born to primiparous ewes and raised separated from all other sheep after they were weaned may have been less likely to become infected with OPPV than those lambs born to multiparous ewes and not separated from other sheep after they were weaned. For goats, antibodies to OPPV were detected in 7 of 12 herds studied, the highest infection rate being present within a herd in the Lima department (district).     

Maedi-visna control in sheep. I. Artificial rearing of colostrum-deprived lambs

A field trial to study the practicability and efficacy of maedi-visna control in sheep by artificial rearing of lambs was carried out during the lambing season of 1979. Lambs were immediately separated from the dams at birth, deprived of ovine colostrum, and reared isolated from the parent flock. Bovine colostrum was given instead of maternal colostrum. Eleven farms participated in the experiment. All flocks were severely infected with maedi-visna virus: 63-100% of the ewes were seropositive as demonstrated by ELISA. Artificially reared lambs were serologically tested and positives culled at the age of 6, 12, 18, 24, 30 and 36 months. Only very few positives were found: 1/389, 1/376, 0/337, 1/223, 1/192 and 0/144, respectively. The first two sero-positive lambs occurred in one flock, and it could be ascertained that both had mistakenly been given ovine colostrum probably containing maedi-visna virus. No explanation, other than sub-optimal hygiene and isolation, could be found for the two sero-positive sheep that turned up in another flock at 24 and 30 months of age although, transplacental infection cannot be entirely excluded. It is concluded that artificial rearing of ovine colostrum-deprived lambs is an effective and practicable method for the control of maedi-visna in sheep. The method appears particularly useful when valuable genetic material has to be salvaged.     

The dynamics, prevalence and impact of nematode infections in organically raised sheep in Sweden

A three-year survey (1997-99) was carried out on organically reared sheep flocks throughout Sweden. The aim was to determine the prevalence and intensity of nematode infections and to establish relationships between sheep management practices and parasite infections. Faecal samples from ewes and lambs were collected from 152 organic flocks around lambing-time and during the grazing-period for analysis. Results were compared with the different management practices that farmers use to prevent parasitism in their flocks. A high proportion of the flocks was infected with nematodes. The most prevalent species were Haemonchus contortus, Teladorsagia circumeincta, Trichostrongylus axei. T. colubriformis and Chabertia ovina and infections progressively increased during summer in lambs grazing on permanent pastures. Severity of parasitic infection in lambs was highly dependent on egg output from the ewes. H. contortus was found in 37% of the flocks, even at latitudes approximating the Polar Circle. Nematodirus battus was recorded for the first time in Sweden during the course of this study. Lambs turned out onto permanent pasture showed higher nematode faecal egg counts (epg) than lambs that had grazed on pastures, which had not carried sheep the previous year. This beneficial effect of lambs grazing non-infected pastures persisted if the ewes were treated with an anthelmintic before turn-out and if the lambs were kept on pastures of low infectivity after weaning. In lambs, the prevalence and the magnitude of their egg counts were higher during autumn in flocks where lambs were slaughtered after 8 months of age, compared with flocks where all lambs were slaughtered before this age. These results will be used in providing advice to farmers of ways to modify their flock management in order to minimise the use of anthelmintics, but at the same time efficiently produce prime lambs.     

Demonstration of lateral transmission of scrapie between sheep kept under natural conditions using lymphoid tissue biopsy

Scrapie free adult sheep were introduced to a sheep flock specifically maintained to maximise scrapie infection. Native born sheep of the highly susceptible VRQ/VRQ genotype in this flock show highly efficient transmission, evidenced by 100% infection, with an age at death of less than 2 years. Infection in introduced sheep was identified by biopsy of tonsilar and nictitating membrane lymphoid tissue. Progeny of these sheep were monitored and clinical disease confirmed by examination of the brain using routine diagnostic methods. Na?ve sheep of New Zealand origin introduced to the flock in adulthood became infected, demonstrating that lateral transmission had occurred. Lambs born to introduced ewes became infected and died at the same age as lambs born to native ewes, consistent with lateral transmission of scrapie to lambs. Although maternal transmission cannot be totally excluded for the lambs in this study, the data are consistent with lateral transmission being the most important means of spread leading to the high incidence of scrapie observed in this flock.