Validation of a bulk tank milk antibody ELISA to detect dairy herds likely infected with bovine viral diarrhoea virus in New Zealand

AIMS: To assess the sensitivity and specificity of a bulk tank milk (BTM) antibody enzyme-linked immunosorbent assay (ELISA) to detect likely infection of a dairy herd with bovine viral diarrhoea virus (BVDV). The ELISA was subsequently used to estimate the prevalence of likely infected herds in parts of the North Island of New Zealand. METHODS: BTM samples from 724 randomly selected dairy herds in the Waikato, Bay of Plenty and Northland regions of New Zealand were tested for BVDV antibodies. From this group, 20 herds were again randomly selected from each of the quartiles of the ELISA percentage inhibition (%INH) result. From each participant herd, serum from 15 randomly selected calves aged 6-18 months and 15 cows was collected and tested using an indirect blocking ELISA for BVDV antibodies. RESULTS: Among serum results from calves from 50 herds available for analysis, 34 (68%) herds were classified as likely non-infected (0-3 seropositive among 15 calves) and 16 (32%) as likely infected (5-15 seropositive among 15 calves). Receiver-operator characteristic (ROC) analysis identified an optimal cut-off for BTM of 80%INH associated with 81% sensitivity and 91% specificity for likely herd infection. The prevalence of BVDV antibodies in cows within herds and %INH for BVDV in bulk milk were positively correlated (p<0.01). The association between bulk milk %INH and the prevalence of BVDV antibodies in calves was stronger than the same association in cows. Based on the threshold of 80%INH, the 95% confidence interval (CI) for prevalence of likely infection in the 724 herds in the Waikato, Bay of Plenty and Northland regions of New Zealand was 12-17%. Vaccination against BVDV was not significantly associated with the likely infection status of the herd based on prevalence of BVDV antibodies among calves. CONCLUSION: An ELISA test result for BVDV antibodies in BTM >/=80%INH can be used as a threshold to indicate the presence of likely infection with BVDV in dairy herds in New Zealand, with 81% sensitivity and 91% specificity.     

Age distribution of animals persistently infected with bovine virus diarrhea virus in twenty-two Danish dairy herds.

The objectives of this study were to compare the age distribution of animals persistently infected (PI) with bovine virus diarrhea virus (BVDV) in 12 herds with clinical BVD compared to ten herds without clinical BVD and to examine the incidence of PI calves born after the oldest PI animal. Blood samples from all animals were tested for bovine virus diarrhea virus and antibodies. In five herds, blood samples were obtained from calves born after the whole herd had been tested. All calves born by PI dams were also blood tested. In herds with clinical BVD the median age of PI animals was 248 days and in herds without clinical BVD the median age was 144 days. There was no significant difference between the age of PI animals in herds with clinical BVD compared to herds without clinical BVD (p = 0.48) suggesting similar epidemiology of the occurrences of PI animals in the two herd categories. Thereafter, all herds were used to study the incidence of PI animals. A total of 129 PI animals were found. In ten herds with 72 PI animals the age range of PI animals was more than six months. In these herds 26.3% of the PI animals were born within the first two months after birth of the oldest PI animal, no PI animals were born 2- less than 6 months, 52.7% were born 6- less than 14 months, 6.9% were born 14- less than 22 months and 13.9% (all born by PI dams) were born later than 22 months after the oldest PI animal.(ABSTRACT TRUNCATED AT 250 WORDS)     

Validation of a bulk tank milk antibody ELISA to detect dairy herds likely infected with bovine viral diarrhoea virus in New Zealand

AIMS: To assess the sensitivity and specificity of a bulk tank milk (BTM) antibody enzyme-linked immunosorbent assay (ELISA) to detect likely infection of a dairy herd with bovine vi- ral diarrhoea virus (BVDV). The ELISA was subsequently used to estimate the prevalence of likely infected herds in parts of the North Island of New Zealand.

METHODS: BTM samples from 724 randomly selected dairy herds in the Waikato, Bay of Plenty and Northland regions of New Zealand were tested for BVDV antibodies. From this group, 20 herds were again randomly selected from each of the quartiles of the ELISA percentage inhibition (%INH) result. From each participant herd, serum from 15 randomly selected calves aged 6–18 months and 15 cows was collected and tested using an indirect blocking ELISA for BVDV antibodies.

RESULTS: Among serum results from calves from 50 herds available for analysis, 34 (68%) herds were classified as likely non-infected (0-3 seropositive among 15 calves) and 16 (32%) as likely infected (5–15 seropositive among 15 calves). Receiver- operator characteristic (ROC) analysis identified an optimal cut-off for BTM of 80%INH associated with 81% sensitivity and 91% specificity for likely herd infection. The prevalence of BVDV antibodies in cows within herds and %INH for BVDV in bulk milk were positively correlated (p<0.01). The association between bulk milk %INH and the prevalence of BVDV antibodies in calves was stronger than the same association in cows. Based on the threshold of 80%INH, the 95% confidence interval (CI) for prevalence of likely infection in the 724 herds in the Waikato, Bay of Plenty and Northland regions of New Zealand was 12–17%. Vaccination against BVDV was not significantly associated with the likely infection status of the herd based on prevalence of BVDV antibodies among calves.

CONCLUSION: An ELISA test result for BVDV antibodies in BTM ≥80%INH can be used as a threshold to indicate the presence of likely infection with BVDV in dairy herds in New Zealand, with 81% sensitivity and 91% specificity.     

Risk factors associated with Mycobacterium avium subspecies paratuberculosis seropositivity in Canadian dairy cows and herds

Our objective was to determine the risk factors associated with the seroprevalence of Mycobacterium avium subspecies paratuberculosis (MAP) in a large number of randomly selected Canadian dairy herds, controlling for important confounding variables and co-infections with bovine leukemia virus (BLV), bovine viral diarrhea virus (BVDV) and Neospora caninum (NC). Serum samples from 30 randomly selected cows, where available, in 315 herds from seven provinces were tested for antibodies against BLV, MAP and NC using commercially available enzyme-linked immunosorbant assay (ELISA) test kits, while five unvaccinated cattle >6 months old from each herd were tested for antibodies to BVDV. We used a zero-inflated negative-binomial (ZINB) multivariable model to determine simultaneously the risk factors associated with the count of MAP-seropositive cows in a herd, and the odds of herds having no MAP-seropositive cows as compared to having one or more MAP seropositive cows in a herd. The following factors were significantly positively associated with the count of MAP-seropositive cows: "more than one cow in the maternity pen", "group-housing for pre-weaned calves in winter", "open heifers purchased during the last 12 months", "beef cattle direct (nose-to-nose) contact", "BVDV-seropositive herds (> or = 1 animal with > or = 1:64 titer)" and "BVD vaccination not done properly in calves" (i.e. after 6 months old, animals were not boostered 2-4 weeks after their first killed vaccine, or not given modified live vaccine), with count ratios of 1.7, 2.0, 2.3, 1.9, 1.4 and 1.8, respectively. The variable "BVDV vaccination (modified live) done properly in calves" (i.e. received another modified live vaccination after 6 months as well) was associated with 0.4 times fewer MAP-seropositive cows.     

Detection of neutralizing antibodies in calves after single vaccination against foot-and-mouth disease virus type ASIA 1 in the field]

On June 20th 1984 appeared the first FMD-Type ASIA 1 outbreak in Greece. Around the outbreak all susceptible animals were vaccinated with ASIA 1 vaccine produced by IFFA Mereiux. Three weeks after this first vaccination blood samples have been collected and examined for neutralizing antibodies. From 101 examined calves 37 were younger than 6 months, 63 between 6-11 months and one was 12 months old. The titer of the first group was less than 1.2 in 14 and greater than 1.8 in 8 calves. By the second group (63 animals) the titer was less than 1.2 in 28 and greater than 1.8 in 11 calves. The 12 months old calf had a titer of 2.1. Generally the titer only of 59 out of the 101 examined calves was greater than or equal to 1.2 (59%). That means that the vaccine used had a weak immunogenicity.     

Serological diagnostic studies of the occurrence of coronavirus infections in cattle with respiratory diseases

Of paired serum samples of 196 cattle with respiratory disease from 37 herds which were tested for hemagglutination inhibiting antibodies against coronavirus (BCV) 185 of the first specimens and 190 of the second ones gave positive results. This difference was due to five animals of five different farms showing seroconversions between the time of the blood collections. A significant rise in antibody titer (no less than 4-fold) was evident in 28 cattle from 3 of the above mentioned and 12 other farms. Altogether serological indication of acute coronavirus infections were gained in 33 (16.8%) of animals with respiratory diseases which derived from 17 of 37 herds. Most of these infections (about 35%) occurred in animals older than 6 months while calves up to 3 or 6 months were only affected in a ratio of ca. 10%, respectively.     

Risk factors for calf mortality in large Swedish dairy herds

The aim of this study was to identify possible risk factors for 1-90 day calf mortality in large Swedish dairy herds. Sixty herds with a herd size of ≥160 cows were visited once between December 2005 and March 2006. Thirty herds were known to have low mortality (LM) and 30 were known high mortality herds (HM). Upon the visit, data about housing and management was collected from interviews with personnel responsible for the calves. The herd status regarding the calves' passive transfer (total protein), levels of α-tocopherol, β-carotene and retinol, and excretion of faecal pathogens (Cryptosporidium spp., Escherichia coli F5, rota and corona virus) was evaluated based on targeted sampling of high risk calf groups; in each herd, blood and faecal samples were collected from calves 1-7 and 1-14 days old, respectively. Similarly, the herd status regarding clinical respiratory disease in calves and history of respiratory virus exposure was evaluated based on lung auscultations and blood samplings of calves 60-90 days old. The median calf mortality risk (in calves 1-90 days of age) among HM herds was 9% (Range: 6-24%) and among LM herds 1% (Range: 0-2%). LM and HM herds were compared using five logistic regression models, covering potential risk factors within different areas: "Disease susceptibility", "Factors affecting the gastrointestinal tract", "Factors related to transmission of infectious disease", "Hygiene" and "Labour management". The percentage of calves, 1-7 days old, with inadequate serum concentrations of α-tocopherol and β-carotene were significantly higher in HM herds compared to LM herds and also associated with higher odds of being a HM herd (OR=1.02; p=0.023 and OR=1.05; p=0.0028, respectively). The variable "Average number of faecal pathogens in the sampled target group" was significantly associated with higher odds of being a HM herd (OR=4.65; p=0.015), with a higher average in HM herds. The percentage of calves with diarrhoea treated with antibiotics was significantly higher in HM herds and was associated with higher odds of being a HM herd (OR=1.08; p=0.021). The median age at death of calves in the age interval 1-90 days that died during a one-year period was significantly lower among HM herds (13 days) than in LM herds (24 days) (p=0.0013) The results indicate that gastrointestinal disorders may be an important cause of calf mortality in large Swedish dairy herds. Furthermore, our study provides additional indications that fat soluble vitamins might play an important role for calf health.     

The prevalence and level of colonisation by Mycoplasma dispar and other mycoplasmas on calf rearing farms

The prevalence and level of colonisation by respiratory mycoplasmas, especially by Mycoplasma dispar (M. dispar), in calves on 24 Finnish calf rearing farms were studied by using nasal swabs. A minimum of 5 calves from each farm was examined and 91.3 % of the 206 calves examined were 1 to 5 months old. Nine herds were selected on account a diagnosed respiratory disease problem, the others without anamnestic knowledge of their health condition.All 24 farms and 96.1 % of the calves examined were found to harbour one or more species of mycoplasma. M. dispar, M. bovirhinis and Acholeplasma laidlawii were isolated from 23, 19 and 3 farms or from 91.7, 51.9 and 3.4 % of the calves investigated, respectively.The prevalence for M. dispar was 97.8 % and the geometric mean titer 4.9 log₁₀ color changing units (ccu) among 1- to 5-month old calves belonging to the infected farms. The prevalence in the age-group of 6- to 12-month old calves was significantly lower (40 %). No significant difference was found in the level of colonisation by M. dispar among the one-month age-groups of the 1- to 5-month old calves. A high degree of colonisation among 1- to 2-month old calves was indicative of the high ability of M. dispar to spread and colonise the respiratory pathway of young calves in the conditions described. The same state still prevailing in calves aged 4 to 5 months supported the concept of a relatively long duration of a heavy colonisation by this mycoplasma. The prevalence of M. bovirhinis among 1-to 5-month old calves was lower than that of M. dispar. Any decrease in the level of colonisation of M. bovirhinis could not be demonstrated in older calves. The titer levels of both M. dispar and M. bovirhinis as well as the prevalence of M. bovirhinis were significantly higher in herds having a current respiratory disease problem than in healthy or mildly affected herds. The same relationship applied to the husbandry method of common pens as compared with individual pens. A causal relationship of increased colonisation level, either as cause or effect, to the respiratory disease is suggested, as well as a probably more indirect one to the common pen husbandry type.     

The significance of bredavirus as a diarrhea agent in calf herds in Lower Saxony]

The objective of this investigation was to determine the distribution of Bredavirus in cattle herds in Lower Saxony and to evaluate its significance as potential cause of diarrhea in calves. Fecal samples and paired blood samples of 119 diarrheic and 46 healthy calves up to two months of age were collected from herds where diarrhea of calves was a problem. Fecal samples were examined for Breda-, rota- and coronavirus by solid phase immune electron microscopy and by ELISA, for K99-positive E. coli and salmonella by microbiological methods, and for cryptosporidia in smears. Antibody titers against Bredavirus, total serum protein and serum gamma globulin content were evaluated in the blood samples. Bredavirus was found in fecal samples from 5% (n = 6) of diarrheic calves which came from four different herds, but not in healthy calves. Rotavirus (31.9%), coronavirus (18.5%) and cryptosporidia (29.9%) were detected more frequently in fecal samples than Bredavirus. In this investigation rotavirus, coronavirus and cryptosporidia were present in addition in all herds where Bredavirus was found. In contrast to the low percentage of fecal samples containing Bredavirus, antibody titers in 75% of calves confirmed the high prevalence of Bredavirus infection in the cattle population of Lower Saxony.     

Antibody titer against bovine respiratory syncytial virus in colostrum-fed dairy calves born in various seasons.

OBJECTIVE: To determine antibody titer against bovine respiratory syncytial virus (BRSV) in dairy calves on farms and to investigate whether passively acquired antibody titers differ in calves born in various seasons. SAMPLE POPULATION: Serum samples from 129 colostrum-fed replacement calves in 8 dairy herds. PROCEDURE: A standard ELISA was used to determine BRSV-specific antibodies in serum samples obtained monthly, and antibody titers for calves born in various seasons were compared. RESULTS: BRSV-specific antibody titer in colostrum-fed dairy calves decreased to undetectable values at 3 to 4 months old. Calves born in winter generally had lower titers, compared with those for calves born in other seasons (P < 0.05). Titers in calves born in seasons other than winter did not differ. CONCLUSIONS AND CLINICAL RELEVANCE: Calves born in winter generally have lower BRSV-specific antibody titers, which may be caused by generally lower antibody titers in colostrum or by factors influencing colostrum intake.     

High prevalence of Cryptosporidium bovis and the deer-like genotype in calves compared to mature cows in beef cow-calf operations

Recent studies have identified the novel, host adapted Cryptosporidium bovis and the deer-like genotype in dairy cattle from farms in the United States, China, India and Europe. This novel species and genotype appear to be more prevalent in older, post-weaned dairy cattle than previously thought. However, little information is available on their prevalence in beef cow-calf operations. In the present study, we determined the prevalence of Cryptosporidium species in 98 calves (6-8 months old) and 114 cows (>2 years old) in seven beef cow-calf herds in western North Dakota. DNA was extracted from fecal samples and Cryptosporidium spp. were identified by amplification of the 18S rRNA gene followed by sequencing or RFLP analysis. All seven herds tested positive for Cryptosporidium. Overall, 43/212 (20.3%) animals were positive. Only five of these positives were from cows. C. bovis, the deer-like genotype and C. andersoni were identified in 9.4, 6.6 and 1.4% of animals sampled, respectively. C. parvum was not identified in any of the positive samples. C. bovis, the deer-like genotype and C. andersoni were detected in 6/7, 5/7 and 2/7 herds, respectively. C. bovis and the deer-like genotype were primarily detected in calves, while C. andersoni was only detected in cows. Six isolates could not be typed. These results show a relatively high prevalence of C. bovis and the deer-like genotype in 6-8-month-old beef calves compared to cows older than 2 years in the seven herds studied.     

Antibody dynamics in BRSV-infected Danish dairy herds as determined by isotype-specific immunoglobulins

Using specific ELISAs, antibody levels of four different isotypes to bovine respiratory syncytial virus (BRSV) were determined in calves, following experimental BRSV infection.Most calves experienced an increase in the specific IgM and IgG1 titres about 6-10 days after infection with BRSV. The IgM titre was transient showing positive titres for only 5-10 days, while specific IgG1 was present for a longer time. IgA was detected concomitantly with IgM but at a lower level. Production of IgG2 anti-BRSV antibodies was detected from 3 weeks after infection.In two closed herds, repeated blood samplings were performed on young stock to analyse maternal immunity. The passively transferred antibodies were mainly of the IgG1 isotype and the half-life of IgG1 to BRSV was estimated to be 26.6 days. One of the herds had an outbreak of enzootic pneumonia, diagnosed to be caused by BRSV. Furthermore, another herd with acute BRSV was followed by weekly blood samples in six calves; in both herds IgM and IgG1 was detected shortly after the appearance of clinical signs. Serum samples from 50 Danish dairy herds (453 samples) were tested for immunoglobulins of the isotypes IgG1, IgG2 and IgM. The presence of antibodies to BRSV was widespread and more than 54% of the samples had BRSV antibodies of both the IgG1 and IgG2 isotypes indicating a high herd prevalence to BRSV. Test samples from two herds out of 50 were free from all isotypes to BRSV.     

Development and evaluation of an enzyme-linked immunosorbent assay for detection of bovine antibodies to epizootic hemorrhagic disease of deer viruses.

An indirect enzyme-linked immunosorbent assay (I.ELISA) is described for detection of bovine serum antibody to epizootic hemorrhagic diseases of deer virus (EHDV). Serum samples, at a dilution of 1:200, were incubated with group-specific EHDV antigens, pre-adsorbed to microtiter plates. Bound antibodies were detected by a murine monoclonal antibody to bovine immunoglobulin (Ig)G1 (heavy-chain specific) conjugated with horseradish peroxidase. The performance of the I.ELISA in detecting antibodies to EHDV in sequential serum samples from calves experimentally infected with serotypes 1,2,3 and 4 was evaluated. The I.ELISA detected EHDV antibodies from 14 days postinfection when seroconversion by the standard agar gel immunodiffusion (AGID) test was also evident. The group-specific antibodies to EHDV increased exponentially during the first two to four weeks postinfection and remained relatively stable for about 12 months in some calves. Unlike observations with the AGID test, no reaction was seen in the I.ELISA between blue-tongue virus (BTV) antigen and sera from calves given a single dose of EHDV. The performance of the I.ELISA and AGID were compared using 3,135 AGID negative bovine field sera from herds in Ontario, Alberta and British Columbia and 130 AGID positive samples collected from cattle in 1987 and 1988 during and after outbreaks of EHD in the Okanagan Valley, British Columbia. The specificity and sensitivity of the assay relative to the AGID test were 99.3% and 91.5% respectively, with an overall agreement of 99.0% between the tests.(ABSTRACT TRUNCATED AT 250 WORDS)     

Detection of calves persistently infected with bovine pestivirus in a sample of dairy calves in south-eastern Queensland

Objective To determine the proportion and incidence of calves persistently infected with bovine pestivirus in calves (n = 1521) supplied to the Tick Fever Research Centre and to assess the test regime to detect calves persistently infected with bovine pestivirus.
Design Calves, 1 to 6 weeks old, selected for use in the production of the tick fever vaccine were collected from 21 properties in 56 separate groups between October 1990 and December 1996. Each group was examined for the presence of calves persistently infected with bovine pestivirus.
Procedure All calves were routinely tested for antibody to bovine pestivirus and bovine pestivirus antigen using a serum neutralisation test and an antigen-capture ELISA, respectively. Pooled lymphocyte samples from calves were also monitored for bovine pestivirus by inoculation of sheep. Whole herd testing was carried out in eight herds, using a serum neutralisation test as a screen test followed by an antigen-capture ELISA of cattle with a serum neutralisation test titre of less than 32.
Results Fourteen of the 1521 calves tested (0.9%), were detected as persistently infected and the incidence ranged from 0.0 to 3.0 % per year over 6 years. Persistently infected calves were found in 13 of the 59 groups and originated from 7 of the 21 herds used. In whole herd testing on the properties of origin, cattle persistently infected with bovine pestivirus were detected in four of the eight herds tested
Conclusions The proportion of calves persistently infected with bovine pestivirus is similar to that in other countries and indicates that bovine pestivirus could be a significant cause of economic loss in Australian cattle herds. In detecting calves persistently infected with bovine pestivirus, the combination of sheep inoculation, paired antigen-capture ELISA and serum neutralisation tests appeared to be highly sensitive and specific.     

体细胞克隆牛0～12月龄生长的测定研究

通过对5头体细胞克隆母犊牛及其同期自然繁殖出生的荷斯坦母犊牛初生期、6月龄、12月龄的体重、体尺指标测定,初步分析了其生长发育速度的变化规律。结果表明:(1)克隆牛初生重53.67±7.00kg,明显高于自繁奶牛(P<0.01),6月龄体重141.00±16.49kg,明显低于自繁奶牛(P<0.01),12月龄体重302.80±32.17kg,与自繁奶牛基本相当;(2)克隆牛0～6月龄期间平均日增重0.70±0.11kg明显低于自繁奶牛(P<0.01),6～12月龄期间平均日增重0.90±0.12kg,与自繁奶牛基本相当(P>0.05),0～12月龄期间平均日增重0.70±0.11kg,与自繁奶牛基本相当(P>0.05);(3)克隆牛初生体尺指标明显大于自繁奶牛(P<0.01),6月龄体尺指标明显小于自繁奶牛(P<0.01),12月龄体尺指标与自繁奶牛相当(P>0.05);(4)克隆牛0～6月龄期间体尺平均增长明显低于自繁奶牛(P<0.01),6～12月龄期间体尺平均增长明显高于自繁奶牛(P<0.01),0～12月龄期间体尺平均增长明显低于自繁奶牛(P<0.01)。     

LABORATORY AND FIELD STUDIES WITH A BOVINE EPHEMERAL FEVER VACCINE

Bovine ephemeral fever (BEF) virus vaccines, prepared from the brains of suckling mice infected with strain 525 BEF virus, were evaluated in housed cattle and in the field. The virus in lyophilised preparations was stable for 6 months at -50 degrees C. Thirty-four calves, 5 to 18 months old, were used in laboratory vaccination trials. An increase in serum neutralising antibody was detected in 13 of 14 calves initially free of serum antibody, and all 13 failed to develop clinical illness following challenge with virulent BEF virus. Vaccination resulted in no detectable serum antibody increase in 4 calves, 5 months old, with pre-existing antibody of presumed maternal origin. Seven animals, 18 months of age with serum antibody presumed due to previous BEF infection, developed increased antibody titres following vaccination. In 3 animals vaccinated but not challenged, vaccine-induced antibodies decreased to low levels over 5 months. In contrast, the antibody titres following infection with virulent virus in 2 calves were maintained over 5 months. Field trials, involving 236 animals initially free of serum antibody, were conducted on 5 properties near Mackay and 4 properties near Brisbane. Most of 164 animals were vaccinated with a single dose of lyophilised vaccine containing aluminium hydroxide adjuvant. Only 4 animals failed to develop serum antibody and no adverse reactions to vaccination were reported. Natural infection with BEF occurred in 4 herds at Mackay and clinically mild BEF occurred in 3 of 109 vaccinated and 3 of 46 control animals. On the basis of measured serum antibody titres it was assumed that 8 of 53 animals receiving full vaccine volume, 20 of 40 animals receiving half vaccine volume and 18 of 40 control animals became infected with BEF virus. Two dairy herds in Brisbane became naturally infected with virulent BEF virus 7 months after vaccination. Clinical BEF was observed in 8 of 11 control animals and in 3 of 26 animals which received 2 doses of vaccine. Two strains of BEF virus were isolated from unvaccinated animals that developed clinically mild BEF in the field. These strains either failed to infect, or produced subclinical or very mild BEF, when inoculated intravenously into susceptible calves. The anitbody response to natural infection with apparently mild viruses was short-lived, similar to that produced by vaccination.     

Isospora orlovi infection in suckling dromedary camel calves (Camelus dromedarius) in Kenya

Outbreaks of isosporosis in young suckling dromedary camel calves (Camelus dromedarius) in Dubai, UAE and in Kenya were recently described. In the former outbreak the pathogen was shown to be Isospora orlovi by morphological features and was later characterized molecularly. In the present study, we have made a longitudinal investigation of 159 suckling dromedary calves < or =12 weeks of age belonging to 8 ranched camel herds (M1) in Northern Kenya. The study was carried out during 18 months. In three of the herds frequent samples were taken irregularly every 1-6 weeks. All calves < or =12 weeks of age present in the respective herds were sampled during the visits. In addition, 91 calves of the same age group but belonging to 42 pastoral herds (M2) in Northern Kenya were point sampled at convenience. Faecal samples from each calf were taken and the faeces were investigated for coccidia. Samples found with coccidian oocysts were suspended in a 2% potassium dichromate solution. Isospora sp. was identified and samples with relatively high numbers of Isospora sp. were analysed molecularly. The SSU rRNA gene and internal transcribed spacer 1 (ITS1) were amplified with primers complementary to conserved regions of the SSU rRNA gene in eukaryotes as well as a conserved part of the 5.8S rRNA gene of Eimeria. A relatively high number of the calves exhibited diarrhoea, 30.2% and 41.8% in the M1 and M2 herds, respectively. Isospora sp. was only found in diarrhoeic calves or in calves convalescent from recent scouring periods. No calf >8 weeks of age was found to be excreting Isospora sp. The parasite was only found in calves < or =4 weeks of age in the M1 herds and in the M2 herds in calves <8 weeks of age. Of the M1 and M2 calves exhibiting diarrhoea, 20.8% and 26.3% excreted Isospora sp., respectively. Morphologically the Isospora sp. was similar to I. orlovi and sequence analysis of the SSU rRNA gene from four Kenyan isolates (unfortunately only from the pastoral herds, M2) and ITS 1 segments from three of the isolates from Kenya and one from Dubai, confirmed that the Isospora isolates belonged to the species I. orlovi, and that the sequences were similar to the Dubai isolates.     

Influence of age,sex and herd characteristics on the occurrence of Verocytotoxin-producing Escherichia coli O157 in Danish dairy farms

Verocytotoxin-producing Escherichia coli (VTEC) O157 is an important emerging human pathogen. Cattle are considered to be the main reservoir for VTEC O157. The objectives of this study were to determine the prevalence of VTEC O157 in Danish dairy herds and to investigate the relationship between shedding of VTEC O157 and a number of animal and herd characteristics. Sixty dairy farms were visited once in August-October, and from each herd faecal samples from up to 50 animals were analysed for VTEC O157 by enrichment, immunomagnetic separation (IMS), and plating on selective agar. In total, 2419 animals were sampled, and 3.6% of these excreted VTEC O157. These animals were located on 10 farms (17%). On average, 21% of the sampled animals in the positive herds excreted VTEC O157. Register data, including age, sex, breed, housing conditions and herd composition, were extracted from a database. No influence of herd size or housing conditions was found. A strong effect of age was seen with 2-6-month-old calves as the high-risk age group (8.6% positive) in contrast to calves <2 months (0.7%) and cows (2.4%). There was a non-significant tendency of bull calves to have a higher prevalence than heifers within the age group of 2-6 months. Significantly, more of the herds characterised by having relatively many bull calves or many animals bought into the herd were positive for VTEC O157. Despite the low incidence of human VTEC O157 infections in Denmark, the prevalence in Danish dairy herds was found to be at a similar level as in many other countries.     

Actinobacillus pleuropneumoniae in Thai pig herds. Prevalence of serum antibodies and relation to performance

The aim of the study was to investigate the prevalence of Actinobacillus pleuropneumoniae infections in market weight pigs in Thailand. ELISA systems employing purified lipopolysaccharide antigens were used to detect antibodies in 549 serum samples collected from pigs of 22 herds. Relevant cut-off values were established from three herds defined seronegative. Serum antibodies were detected to all serotypes except serotype 10. Almost 60% of the samples were seropositive to at least one serotype and 45% of the pigs were seropositive to more than one serotype. Antibodies to the cross-reacting serotypes 1, 9 or 11 were found in 29% of the pigs. Other common serotypes included the cross-reacting serotypes 3, 6 or 8 (26% seropositive pigs) and serotype 5a (also 26%). Antibodies to serotypes 2, 5b and 12 were low in prevalence (<10%). Three herds were regarded to be seronegative and six to have a low pathogen load with respect to the prevalence of seropositive pigs. The remaining 13 herds had a high incidence of pigs with antibodies to A. pleuropneumoniae, dominated by serotypes 1-9-11 and 5a (n = 6), serotypes 3-6-8, and 5a (n = 4) or 1-9-11, 3-6-8, 5a and 4-7 (n = 3). A low pathogen load with respect to A. pleuropneumoniae, as well as small herd size and age-segregated rearing, tended to improve the performance of growers.