Nasal carriage of Staphylococcus aureus in dairy sheep

The purpose of this study was to assess the prevalence of Staphylococcus aureus nasal carriage of dairy sheep in farms producing cheeses manufactured with raw ewe's milk. The study showed that 29% of ewes carried S. aureus in their nares. The genetic diversity of the 136 isolates recovered from the anterior nares of the ewes, from the ambient air of the milking parlour and from cheeses was investigated using pulsed-field gel electrophoresis (PFGE) of DNA SmaI digests. The genotyping results showed that 75 out of 106 isolates recovered from nasal carriage in dairy sheep belonged to a dominant pattern (previously named OV) and a genetically related pattern (named OV'). The same profile (OV or OV') was found in the ambient air and cheeses, suggesting a continuum between isolates within these different compartments.     

Comparison of milk-ELISA and serum-ELISA for the diagnosis of Brucella melitensis infection in sheep

Milk and blood samples from 704 lactating ewes were examined for the diagnosis of Brucella melitensis infection by milk-ELISA, serum-ELISA, RBPT, SAT and culture of milk. Of these ewes, 209 were from brucellosis free sheep flock, 443 from brucellosis infected sheep flock and 52 were from private sheep flocks of which status for brucellosis was not known. All the 209 ewes belonging to uninfected sheep flock were found negative in all the tests and of the remaining 495 ewes 105 were positive in serum-ELISA, 103 in milk-ELISA, 92 in RBPT, 85 in SAT, and B. melitensis biovar-1 was isolated from the milk of 29 ewes. Of the 105 serum-ELISA positive ewes, 99 were positive and 6 were negative in milk-ELISA, whereas of the 103 milk-ELISA positive ewes, 4 were negative in serum-ELISA. All together, 99 ewes were positive and 386 were negative in both the assays while 10 ewes yielded variable results. The specificity of milk-ELISA in brucellosis free flock was 100% and sensitivity and positive predictive value were 96.11% and 94.28%, respectively, in infected flocks. The Brucella antibody levels in milk and serum samples as determined by milk-ELISA and serum-ELISA were correlated significantly. The milk-ELISA for brucellosis appears to be an attractive alternative of serum-ELISA particularly in the lactating ewes.     

Evaluation by enzyme-linked immunosorbent assay of local and systemic production of milk immunoglobulins to surface exopolysaccharide antigen in cows with staphylococcal mastitis

An enzyme-linked immunosorbent assay (ELISA) was developed to evaluate milk immunoglobulin levels to surface exopolysaccharide antigen of Staphylococcus aureus in cows with staphylococcal mastitis. Quarter milk samples were obtained from 24 lactating dairy cows on two occasions, one month apart. Cows were classified as S. aureus-positive (S. aureus cultured from at least one quarter on both sample dates) or S. aureus-negative. Individual quarter samples were tested for IgA (representing local synthesis) and IgG1 (primarily of systemic origin) specific for staphylococcal surface exopolysaccharide antigen. No significant differences were found for specific IgA or IgG1 between S. aureus-positive and S. aureus-negative cows, nor between infected and non-infected quarters of S. aureus-positive cows. The data indicate that, in cows with staphylococcal mastitis, milk immunoglobulins specific for exopolysaccharide antigen are not significantly increased by either the systemic or the local immune response.     

Biofilm production by Staphylococcus aureus associated with intramammary infection

Biofilm production by 221 Staphylococcus aureus isolates from 45 dairy herds was evaluated. Isolates were from composite milk of 117 cows, from teat skin of 70 cows, and from 34 milking machine unit liners. Of S. aureus from milk samples, 41.4% were biofilm producers, as compared to 24.7 and 14.7% of the isolates collected from skin and liners. Pulsed field gel electrophoresis (PFGE) best categorized S. aureus biofilm producers as compared to phage typing and binary typing. PFGE types that were significantly associated with isolation from milk as opposed to teat skin or liners, had isolates that were more likely to produce biofilm than PFGE types that were isolated from milk, skin and liners at similar frequencies. By contrast, PFGE type A was significantly associated with isolation from teat skin and had few biofilm producers. PFGE type Q, which is exclusively a milk, isolate produced more biofilm as evidenced by absorbance values. Given S. aureus that are associated with milk are more likely to produce biofilm as compared to extramammary sources (teat skin and milking unit liners), suggests that biofilm production is a risk factor for infection.     

Genotyping of Staphylococcus aureus isolated from various sites on farms with dairy sheep using pulsed-field gel electrophoresis

We investigated the genetic diversity of 179 Staphylococcus aureus isolates recovered from various sites in 10 farms producing cheeses manufactured with raw ewe's milk. Isolates were collected from handcrafted cheeses, bulk tank milk, milk from half-udders, skin abscesses on the udder if present, hands and anterior nares of farmers, and air of the milking area. The isolates were typed using pulsed-field gel electrophoresis (PFGE) of DNA SmaI digests and compared to other isolates of S. aureus isolated in different hosts or in different locations. The results showed that nine farms were contaminated by S. aureus isolates with identical banding patterns (named OV) or by genetically related isolates (named OV'). These dominant banding patterns were found in a variable proportion of the samples from each farm (range: 11-100%). Most of the strains isolated from nasal carriage or strains isolated from other regions or from other animal species had different PFGE patterns to OV or OV', except for three strains. These results show that a single clone of S. aureus is widely distributed both in infected mammary glands and in cheese produced from raw milk. This study confirms that infected mammary glands are the main source of the contamination of dairy products in sheep.     

Epidemiological studies of clinical and subclinical ovine mastitis in Awassi sheep in northern Jordan

Forty-six Awassi sheep flocks selected by stratified random sampling were subjected to a cross-sectional study to determine the prevalence of intramammary infections, to assess the influence of flock size and parity on the prevalence of somatic cell count (SCC) and to identify major udder pathogens. Of the 3472 udder halves examined, 29.8% had over 10⁶ SCC/ml and 0.03% had dry teats due to chronic mastitis. Flocks with 30–49 milking ewes (small flock size) were much younger (P < 0.001) than flocks with 50–99 ewes (medium) and flocks with ≥ 100 ewes (large). Pairwise analysis of the InSCC of both halves of the udders revealed significant mean differences for small and large flock size (P < 0.05), and for medium and large flock size (P < 0.001). Mean InSCC was lower (P < 0.05) in samples obtained from the left half compared with samples of the right half of the udder. Multiparous ewes had higher (P < 0.001) mean InSCC than primiparous ewes. Also, ewes with twin lambs had higher (P < 0.001) mean InSCC in the right half of the udder compared with single-lamb ewes. Samples collected in January (winter) had lower (P < 0.05) mean InSCC compared with samples collected in June. The most common organisms isolated from subclinical mastitis cases were coagulase-negative Staphylococci (17.8%), E. coli (13.6%), Streptococcus agalactiae (6.8%) and Staphylococcus aureus (6.8%). Of the 46 flocks, 20 were monitored monthly for 9 consecutive months to determine the incidence of clinical mastitis diagnosed by shepherds or/and sheep farmers with major pathogens. The incidence of clinical mastitis (expressed as the number of clinical cases per 100 ewe-months) were 2.1 ± 1.9 (SD), 1.9 ± 1.1, and 1.2 + 2.1 for small, medium and large flocks size strata, respectively. The overall population estimate was 1.7 ± 0.02 cases per 100 ewe-months. The most-common clinical isolates were S. aureus (22% of all clinical isolates) and E. coli (14.2%).     

The seroprevalence of maedi-visna in Ontario sheep flocks and its relationship to flock demographics and management practices.

The objectives of this study were to describe the serological prevalence of maedi-visna in a sample of Ontario sheep flocks, and to identify management and demographic variables that were associated with seroprevalence for maedi-visna. A sample of 103 sheep flocks in Ontario was randomly selected from those flocks participating in the Red Meat Plan. The owners of these flocks were surveyed regarding management procedures on their farms, and blood samples were taken from a random sample of ewes in each flock. At least one ewe tested serologically positive, based on the agar gel immuno-diffusion test, in 69.9% of the farms. Positive serological reactions occurred in 20.9% of the 3880 sheep tested. Flock demographics and farm management variables were considered in a multiple regression model, and several factors were positively associated with higher maedi-visna seroprevalence rates. These included the average age of the flock, the number of years the owner had been sheep farming, the practice of using foster ewes, the practice of allowing lambs to have contact with other ewes that are lambing, and the average pasture acreage per ewe.     

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.     

Molecular and phenotypical characterization of Clostridium perfringens isolates from poultry flocks with different disease status

Due to the diminished use of growth-promoting antibiotics in the European Union, Clostridium perfringens induced necrotic enteritis and subclinical disease have become important threats to poultry health. A study was set up to genotypically and phenotypically characterise C. perfringens isolates from poultry flocks with different health status. Animals from healthy flocks were sampled by cloacal swabs, while intestinal and liver samples of animals suffering from necrotic enteritis were analysed. A total of 27 isolates was obtained from 23 broiler flocks without clinical problems and 36 isolates were obtained from 8 flocks with clinical problems. Using PFGE typing, high genetic diversity was detected between isolates from different flocks. Isolates derived from flocks where disease outbreaks occurred were clonal within each flock, but each flock harboured a different clone. All isolates were of toxin type A. Isolates from 5 out of 35 PFGE types carried the cpb2 gene, encoding the beta2 toxin, and isolates from 2 out of 35 PFGE types harboured the cpe gene, encoding the enterotoxin. In vitro alpha toxin production for all isolates was quantified by enzyme-linked immunosorbent assay. It was shown that in vitro alpha toxin production of C. perfringens isolates from diseased flocks was not higher than in vitro alpha toxin production from isolates derived from healthy flocks.     

Colonisation of the respiratory tract of lambs by strains of Mycoplasma ovipneumoniae

The age and time of year when colonisation of the nasal cavity of lambs by Mycoplasma ovipneumoniae occurs; the persistence of the organism, and its prevalence in the lungs at slaughter were examined in 2 flocks of sheep in New Zealand. No colonisation had occurred at the time of weaning at 6–7 weeks, but M. ovipneumoniae was recovered from most lambs on at least one occasion before they were slaughtered when about 8 months old. In most cases, colonisation of the nasal cavity by M. ovipneumoniae was a transient phenomenon. At slaughter M. ovipneumoniae was recovered from the lungs of 89% of the lambs of one flock and 80% of the other flock.

Bacterial restriction endonuclease DNA analysis (BRENDA) of 34 nasal isolates from one flock showed that it was possible to identify 7 “groups” each with markedly different BRENDA patterns. Lambs initially colonised by one strain, often lost that strain, and if recolonisation occurred it was with a different strain.

M. ovipneumoniae was recovered at slaughter from the lungs of most lambs, both normal and pneumonic. The isolates from one flock were examined by BRENDA, and approximately 90% of them gave similar or identical patterns. The predominant strain isolated from the lungs had been recovered from the nasal cavity of many of the lambs about 3 weeks earlier. This suggests that the nasal and lung isolates do not represent independent populations. However, nasal strains may differ in their ability to colonise the lungs.     

Isolation and characterisation of local strains of Chlamydophila abortus (Chlamydia psittaci serotype 1) from Tunisia

Chlamydiosis is one of the major diseases that can lead to abortion in ewes. Since 1997, in 5 regions of Tunisia, Chlamydia-related abortions have been reported in 15 sheep and goat flocks. One hundred and sixty-six sera and 50 vaginal swab samples were collected from adult ewes. Chlamydial antigens were detected in 29 (58%) of the vaginal swabs using Enzyme Linked Immunosorbent Assay (ELISA) while 9 (18%) were positive by cell culture. Five strains were recovered from 4 different sheep flocks. Monoclonal antibody profiles and restriction fragment length polymorphism (RFLP) analysis of the 16S-23S rRNA spacer region showed that these isolates were C. abortus. Using amplified fragment length polymorphism (AFLP), these Tunisian strains were shown to exhibit the same pattern as strains isolated in France.     

Genetic diversity and antimicrobial susceptibility profiles among mastitis-causing Staphylococcus aureus isolated from bovine milk samples

OBJECTIVE: To determine whether particular antimicrobial susceptibility profiles of bovine mastitis-causing Staphylococcus aureus isolates were associated with specific S aureus genotypes. SAMPLE POPULATION:357 S aureus isolates recovered from milk samples submitted for diagnostic bacteriologic testing from 24 dairy herds. PROCEDURES: Antimicrobial susceptibility of S aureus isolates was assessed by determining minimum inhibitory concentrations (MICs) to 14 antimicrobial agents. After digestion of S aureus genomic DNA by SmaI, electrophoretic patterns were obtained via pulsed-field gel electrophoresis (PFGE) and used to classify isolates into types. Gels were analyzed, and data were used to prepare dendrograms. RESULTS: 308 of 357 (86%) S aureus isolates were susceptible to all antimicrobials evaluated. Forty-nine S aureus isolates were resistant to 1 or more antimicrobials; of these isolates, 37 were resistant only to penicillin, 9 were resistant to penicillin and erythromycin, 2 were resistant to tetracycline, and 1 was resistant to erythromycin. Isolates were assigned to 7 PFGE types. An association was found between PFGE type and antimicrobial susceptibility profile. Organisms with resistance to at least one of the tested antimicrobial agents were identified in only 4 of the 7 types of S aureus. CONCLUSIONS AND CLINICAL RELEVANCE: Antimicrobial resistance was uncommon among the mastitis-causing S aureus isolates identified in the milk samples. A limited number of genotypes were associated with mastitis in these herds. Antimicrobial resistance phenotypes were associated with particular S aureus PFGE types; this association may have implications for future treatment and control of S aureus-associated mastitis in cattle.     

Field observations during the Bluetongue serotype 8 epidemic in 2006. II. Morbidity and mortality rate, case fatality and clinical recovery in sheep and cattle in the Netherlands

Data collected in the Netherlands during the Bluetongue serotype 8 (BTV-8) epidemic indicated that in outbreak cattle herds, predominantly dairy and nursing cows were clinically affected and not young stock, beef cattle, beef calves, or breeding animals. In outbreak sheep flocks, mainly ewes and - if present - rams, were clinically affected and not the lambs. Median morbidity rate in outbreak herds was 1.85 per 100 sheep-month at risk and 0.32 per 100 cattle-month at risk for sheep and cattle, respectively. The mean proportion of BT-affected animals in outbreak herds that recovered from clinical disease was approximately eight times higher for cattle compared to sheep in the Netherlands. Median mortality rate in outbreak herds was 0.5 per 100 sheep-month at risk of dying and 0 per 100 cattle-month at risk of dying for sheep and cattle, respectively. Median recovery time of both sheep and cattle that recovered from clinical disease in outbreak herds was 14 days. Median case fatality was 50% in sheep outbreak flocks and 0% in outbreak cattle herds. It is concluded that morbidity and mortality in outbreak cattle herds was very limited during the BTV-8 epidemic in the Netherlands in 2006. In outbreak sheep flocks, morbidity was limited, with exceptions for a few flocks. However, almost 50% of the clinically sick sheep died in outbreak sheep herds.     

Serotypes and analysis of distribution of Shiga toxin producing Escherichia coli from cattle and sheep in the lower North Island, New Zealand

AIMS: To serotype a subset of Shiga toxin-producing Escherichia coli (STEC) isolates from cattle and sheep to determine whether any corresponding serotypes have been implicated in human diarrhoeal disease, both in New Zealand and worldwide, and to examine the distribution of STEC and enteropathogenic Escherichia coli (EPEC) amongst cattle (calves, heifers and dairy) and sheep (lambs, rams and ewes), to assess whether carriage of identified bacterial genotypes may be associated with a particular age of animal. METHODS: Recto-anal mucosal swabs (RAMS) were taken from 91 calves, 24 heifers and 72 dairy cattle, and 46 lambs, 50 ewes and 36 rams, from four sites in the Manawatu and Rangitikei regions of New Zealand. Strains of E. coli selected from primary isolation plates were subjected to a multiplex polymerase chain reaction (PCR), to determine the presence of Shiga toxin genes (stx1 and stx2) and the E. coli attaching and effacing gene (eae). RESULTS: Overall, 186/319 (58.3%) animals sampled were positive for stx1, stx2, or eae isolates. More sheep (43.9%) were stx1-positive than cattle (2.7%; p = 0.036), and amongst sheep more lambs and ewes were stx1-positive than rams (p = 0.036). Amongst cattle, more calves and heifers were eae-positive than dairy cows (p = 0.030). Two or more different STEC were isolated from at least 28 (9%) animals (three cattle and 25 sheep), based on their stx/eae genotype. Enterohaemolysin genes were found in 39/51 (76%) isolates serotyped. Twenty-one different serotypes were detected, including O5:H-, O9:H51, O26:H11, O84:H-/H2 and O149:H8 from cattle, and O26:H11, O65:H-, O75:H8, O84:H-, O91:H-, O128:H2 and O174:H8 from sheep; O84:H-, O26:H11, O5:H-, O91:H- and O128:H2 serotypes have been associated with human disease. CONCLUSIONS: If nationally representative, this study confirms that cattle and sheep in New Zealand may be a major reservoir of STEC serotypes that have been recognised as causative agents of diarrhoeal disease in humans. Distribution of STEC and EPEC in cattle and sheep indicates that direct contact with, in particular, calves or their faeces, or exposure to environments cross contaminated with ruminant faeces, may represent an increased risk factor for human disease in New Zealand.     

Molecular typing of enterotoxigenic Staphylococcus aureus isolated from bovine mastitis in Korea

One hundred and sixty-six Staphylococcus aureus isolates from mastitic milk samples from different cows on 26 farms were investigated for staphylococcal enterotoxins(SEs) and toxic shock syndrome toxin-1(TSST-1) by polymerase chain reaction(PCR) and reverse passive latex agglutination assay(RPLA). SEs and the TSST-1 gene were detected in thirty-seven isolates based on a multiplex PCR; SEA was detected in 32 isolates, SEB in 3 isolates, SEC in 1 isolate, and SEA and the TSST-1 gene in 1 isolate. Of the 37 enterotoxigenic isolates, thirty-three isolates were enterotoxigenic according to RPLA, where 29 isolates produced SEA, 3 isolates produced SEB, and 1 isolate produced SEC. The enterotoxin-producing S. aureus isolates were further characterized by pulsed-field gel electrophoresis(PFGE). A macrorestriction analysis revealed 11 PFGE patterns. Among the 33 enterotoxigenic S. aureus isolates, 45.4% exhibited the same PFGE pattern I. Accordingly, although the enterotoxin-producing S. aureus isolates from bovine mastitis were genetically diverse, 1 common genotype prevailed on the farms, indicating that PFGE pattern I isolates may be the most disseminated in Korea.     

Listeriosis in sheep. Listeria monocytogenes excretion and immunological state in healthy sheep.

Listeriosis in sheep. Listeria monocytogenes excretion and immunological state in healthy sheep. Acta vet. scand. 1979, 20, 168–179. — The excretion of Listeria monocytogenes (Lm) in the faeces and milk, and humoral and cell mediated immunity against Lm, were examined in a sheep flock where no cases of listeriosis had occurred during the last 3 years. The investigation was carried out during the indoor season. During the first part of the season 2 of the 10 pregnant, 8 months old lambs excreted Lm in the faeces, but none of the 106 ewes, 2–10 years old. At lambing the organism was isolated from the faeces of 6 of the 10 1 year old lambs and from 64% of the ewes, and from the milk of 1 of the lambs and 41% of the ewes. Nearly all the isolates (98.5%) belonged to serotype 1.Antibody titres against Lm were found in sera and whey by an indirect haemagglutination method. The titres were higher for the ewes than for the hoggs and seemed to be influenced by the number of foetuses the animals carried.Cell mediated immunity was determined by a skin test where delayed hypersensitivity against an antigen prepared from Lm, was measured. Animals fed grass silage had a stronger reaction than animals fed hay, and a stronger reaction was found in animals with ≥ 3 foetuses than in the remainder.The investigation indicates that even in a healthy sheep flock all the animals may be exposed to Lm, and the majority may be latent carriers and excrete this organism in the faeces and milk during periods of stress.     

Evaluation of Ewe Performance in 795 Selected Sheep Flocks in South-Eastern Norway

A study of ewe performance was undertaken in 795 sheep flocks based on data from the Norwegian Sheep Recording System. Herd level data included in the annual report for 1998 were used as the basis for the study. Average flock size was 75.3 ewes. The material was considered as representative of the better and more motivated sheep farmers in the mountain valley regions in south-eastern Norway. The average number of lambs born per ewe, inclusive (and exclusive) of barren ewes, was 1.89 (2.02), and of autumn lambs (those surviving from birth in the spring to autumn) 1.60 (1.66). The average autumn weight of the lambs corrected to 145 days of age was 42.4 kg, giving an overall performance of 67.9 kg lambs live weight per ewe. When including artificially reared lambs, overall performance was 70.4 kg per ewe. Artificial rearing of lambs, mostly triplets which had been removed from the ewe, was practised on 395 of the farms. In the 74 flocks with a rate of artificial rearing of more than 10% of all lambs, overall performance per ewe was 13.3 kg higher than in flocks with no artificial rearing. Total lamb mortality from birth to autumn recording, including stillborn lambs, was 12.44%. Mortality had a skewed distribution, some flocks having very high mortality figures. The arithmetic means (and medians) for mortality were as follows: 2.75 (2.29)% stillbirths, 2.93 (2.30)% died during the indoor feeding period, 0.88 (0.00)% at spring pasture, and 6.16 (4.40)% at summer pasture. In regression models using Proc Genmod in SAS^®, it was found that average number of autumn lambs per ewe was negatively associated with the rate of barren ewes, late lambing date (flock average day in year when lambing took place), and total lamb mortality. The corrected autumn weight of the lambs was positively associated with the average number of lambs born per ewe and non-fertility rate, and negatively associated with flock size and total lamb mortality. The Dala breed had a positive effect on number of autumn lambs per ewe, and Spæl breed a negative effect on corrected autumn live weight of the lambs.     

Patterns of nonclinical intramammary infection in a ewe flock

Coagulase-negative staphylococci were the most frequent bacterial isolates from nonclinical intramammary infections (NIMI) in a ewe flock. The prevalence of NIMI was 22.9% of the udder halves at lambing and decreased to 12.5% or less between week 2 and week 6 of lactation. The decrease was due mainly to the elimination of infections involving coagulase-negative staphylococci. The frequency of new NIMI in the first 6 weeks of lactation was less than 1% of the noninfected udder halves per week. The prevalence of NIMI increased steadily from 16.1% of the udder halves at the time of weaning the lambs to 29% at postweaning week 3. The new infection rate averaged 9.7% per week during the postweaning 3 weeks. The principal bacterial isolate in the new NIMI was coagulase-negative staphylococcus. Nonclinical intramammary infection in a ewe flock was monitored by bacteriologic cultural examinations of milk samples obtained from both udder halves of 24 ewes during early lactation and of 31 ewes in the same flock during the early postweaning period. The patterns of NIMI were similar to the patterns reported in cattle.     

Production of malignant catarrhal fever virus-free sheep

The study was designed to better define the variables affecting the success of the establishment of ovine herpesvirus 2 (OHV-2)-free sheep flocks. A total of 38 lambs born to OHV-2-positive ewes was selected and divided into four groups. Three groups of 10 lambs each were separated from the positive ewes at 2, 2.5 and 3 months of age, respectively, and maintained in isolation facilities. One group of eight remained in the positive flock as controls. Peripheral blood samples from each lamb were examined regularly by PCR for OHV-2 DNA. All lambs (100%) that were weaned and maintained in isolation from the ages of 2, 2.5 and 3 months remained negative until the termination of the experiment at 1 year of age. One lamb was discovered to be PCR-positive on the day of isolation at 2.5 months of age, and was promptly removed from the isolation group. In contrast, all lambs (100%) that remained with the flock became PCR-positive by 6 months of age. The data confirmed that, with rare exceptions, separation of lambs from OHV-2 infected animals at around 2 months of age reliably yields OHV-2-free sheep. Appropriate PCR monitoring will enable the rare exceptions to be removed from the group, and is recommended as a safety measure.     

Comparison of blood polymerase chain reaction and enzyme-linked immunosorbent assay for detection of Mycobacterium avium subsp. paratuberculosis infection in cattle and sheep.

A study was carried out to compare the performance of enzyme-linked immunosorbent assay (ELISA) and blood polymerase chain reaction (PCR) for diagnosis of paratuberculosis in cattle and sheep. For cattle, a set of 278 samples from 1 paratuberculosis-affected Friesian farm was used; it included 80 ELISA-positive samples and 198 ELISA-negative samples from an age-matched group. Ninety-four samples were from heifers and 184 were from 2-5-year-old cows. The overall analysis showed a clear association (Fisher exact test [FET] P = 0.0049) but a weak negative agreement (45.3%, kappa = -0.1665 +/- 0.0994) between the 2 tests. It reflected a moderate agreement among heifers (87.7%, kappa = 0.4471 +/- 0.2435) and a moderate disagreement among cows (62.7%, kappa = -0.3670 +/- 0.1057). For sheep, 496 blood samples from 53 Latxa dairy flocks were used; 180 of the blood samples were from dam/offspring pairs. The overall association between the 2 tests on ovine samples was strong (FET, P = 0.0005), whereas the agreement was low (kappa = 0.1622 +/- 0.1188). There was slightly better agreement for ewes (kappa = 0.2135 +/- 0.1992) than for lambs (kappa = 0.1193 +/- 0.1301). There was also a highly unlikely proportion of dam/offspring positive results (FET, P < 0.0001, kappa = 0.6269 +/- 0.1854). Four of 6 lambs that were necropsied 1 year after testing had paratuberculosis microscopic lesions in the ileocecal valve (3 lambs) or a PCR-positive result (4 lambs). These results suggest that blood PCR testing might be a potentially useful new approach in paratuberculosis diagnosis, especially in young animals.