Longitudinal study of bovine rotavirus group A in newborn calves from vaccinated and unvaccinated dairy herds

Reports of rotavirus excretion in calves usually result from cross-sectional studies, and in face of the conflicting results regarding protection of calves born to vaccinated dams against diarrhea, the aim of the present study was to evaluate rotavirus excretion in dairy calves born to vaccinated or unvaccinated dams, to identify the genotypes of bovine rotavirus group A (RVA) strains isolated from these animals as well as to investigate characteristics of the disease in naturally occurring circumstances throughout the first month of life. Five hundred fifty-two fecal samples were taken from 56 calves, 28 from each farm and, in the vaccinated herd, 11/281 samples (3.91%) taken from six different calves tested positive for RVA while in the unvaccinated herd, 3/271 samples (1.11%) taken from 3 different calves tested positive. The genotyping of the VP7 genes showed 91.2% nucleotide sequence identity to G6 genotype (NCDV strain), and for the VP4 gene, strains from the vaccinated herd were 96.6% related to B223 strain, while strains from the unvaccinated herd were 88% related to P[5] genotype (UK strain). Genotypes found in this study were G6P[11] in the vaccinated herd and G6P[5] in the unvaccinated herd. All calves infected with rotavirus presented an episode of diarrhea in the first month of life, and the discrepancy between the genotypes found in the commercial vaccine (G6P[1] and G10P[11]) and the rotavirus strains circulating in both vaccinated and unvaccinated herds show the importance of keeping constant surveillance in order to avoid potential causes of vaccination failure.     

A longitudinal study of bovine coronavirus enteric and respiratory infections in dairy calves in two herds in Ohio

This prospective longitudinal study examined the epidemiology and disease syndrome associated with bovine coronavirus (BCV) infections in a cohort of 8 conventional calves from 0 to 120 days of age, in two dairy herds in Ohio. The periods of respiratory shedding of BCV were determined by direct immunofluorescent (DIF) staining of nasal epithelial cells and ELISA of nasal swab supernatant fluids. The periods of fecal shedding of BCV were determined by ELISA and immunoelectron microscopy (IEM). The isotype-specific antibody titers to BCV in serum (at selected intervals between 0 and 120 days of age) and the post-suckling (24 to 48 h after birth) total immunoglobulin levels were examined by ELISA and zinc sulfate turbidity tests, respectively. Of the 8 calves studied, 4 had evidence of BCV respiratory (by DIF or ELISA) or enteric infections (by IEM or ELISA) in association with diarrhea or rhinitis, even though 7 of 8 calves showed increases in one or more serum antibody isotypes to BCV and 6 of 8 calves showed BCV respiratory or enteric antigen shedding by ELISA. Serological antibody titer increases occurred in 3 calves before 30 days of age and in 4 calves after 30 days of age; two of the latter calves had a second rise in serum antibody titers to BCV after the initial rise. A serological antibody titer increase was not observed in one calf. This suggests that BCV infections may be very common in a closed herd and may occur in older calves, although many may be subclinical and some may be recurrent. There were no statistically significant correlations between total serum immunoglobulin levels or BCV antibody isotype titers in serum (24-48 h after birth) and clinical disease or infection by BCV; however, calves with low levels of IgA BCV antibodies in serum (24-48 h after birth) had a significantly greater average number of days with diarrhea than those calves having high levels of IgA BCV-specific antibodies in serum.     

Prevalence of serotypes G6 and G10 group A rotaviruses in dairy calves in Quebec.

Fecal samples from diarrheic and nondiarrheic dairy calves (1 to 3 weeks old) from 12 regions of Quebec, collected between 1992 and 1994, were screened for group A bovine rotavirus (BRV) using a combination of 2 VP6-specific monoclonal antibodies (MAbs) in an enzyme-linked immunosorbent assay (ELISA). The overall prevalence of BRV infection was 26.4% (107/405). In diarrheic calves, BRV infection reached 74.3% (55/74), but only 15.7% (52/331) in nondiarrheic calves. BRV-positive samples were serotyped by enzyme-linked immunosorbent assay (ELISA) using G6 and G10 specific MAbs. The analysis of 107 field samples revealed that, in diarrheic calves, 34.5% (19/55) were G6, 27.2% (15/55) were G10, 9% (5/55) were G6 and G10 positive, and 29.9% (16/55) were G6 and G10 negative. In nondiarrheic calves, 19.2% (10/52) were G6, 19.2% (10/52) were G10, 7.6% (4/52) were G6 and G10 positive, and 53.6% (28/52) were G6 and G10 negative. Rotavirus dsRNA was extracted from BRV-positive samples and examined by polyacrilamide gel electrophoresis (PAGE). Of 107 samples tested, 74 (69.1%) were positive, and all the samples demonstrated a typical group A rotavirus migration pattern.     

兰州地区犊牛轮状病毒性腹泻的流行病学调查

为明确甘肃省兰州地区犊牛轮状病毒性腹泻的流行动态,从该区的3个大型奶牛场采集1月龄以内的犊牛粪便样品19份,利用轮状病毒酶标诊断试剂盒检测技术对粪便进行检测,并对粪便特征和防治药物进行调查分析.结果表明:该地区犊牛轮状病毒性腹泻的发病率为36.84%;腹泻犊牛粪便颜色多为黄白或浅黄绿色水泻样;防治药物以抗生素为主(占60%),辅助治疗药物占24%,中药制剂占16%.     

Molecular characterization of a novel bovine group A rotavirus

In this study, by partial sequence analysis of the genome segments encoding VP5* and VP7, we characterized a novel bovine group A rotavirus, namely, Tak2, that was detected from adult cattle diarrhea in Tochigi Prefecture, Japan. The nucleotide (nt) and deduced amino acid (aa) sequences of the genome segments encoding VP5* and half of the amino terminal portion of VP7 of Tak2 revealed a low identity with those of group A rotaviruses carrying previously published P and G type specificities (VP5*: nt identity, 61.6%-67.6% and aa identity, 58.0%-71.4%; half of the amino terminal portion of VP7: nt identity, 57.8%-73.5% and aa identity, 61.2%-70.9%). Additionally, phylogenetic analysis of the nt sequences of the genome segments encoding VP5* and half of the amino terminal portion of VP7 revealed that Tak2 formed a branch separate from the established P and G types. These results suggested that Tak2 could possess novel P and G types yet not reported among group A rotaviruses.     

Prevalence of fecal shedding of Salmonella spp in dairy herds

OBJECTIVE: To estimate prevalence of Salmonella spp in Ohio dairy farms and to identify potential risk factors for fecal shedding of salmonellae. DESIGN: Cross-sectional study. SAMPLE POPULATION: 105 Ohio dairy farms. PROCEDURE: Individual fecal samples from all mature cows in study herds were tested for Salmonella spp by use of standard bacteriologic culture procedures. Herds were identified as infected if at least 1 cow was shedding Salmonella spp. Information regarding herd characteristics, management practices, and health history were collected. Potential risk factors for herd-level Salmonella infection were identified. RESULTS: In 31% of the study herds (95% confidence interval, 22 to 40%), at least 1 cow was shedding Salmonella spp. Six percent of 7,776 fecal samples contained Salmonella organisms; prevalence within infected herds ranged from < 1 to 97%. Herd size, use of free stalls for lactating and nonlactating cows, and use of straw bedding in nonlactating cows were significantly associated with fecal shedding of Salmonella spp, as determined by use of univariate analysis. By use of multivariate analysis, large herds were more likely to be infected than smaller herds; however, no other factors were associated with Salmonella infection after adjustment for herd size. CONCLUSIONS AND CLINICAL RELEVANCE: Subclinical shedding of Salmonella spp is common in Ohio dairy herds, although we could not identify specific interventions that may influence the prevalence of Salmonella spp on dairy farms. It appears that large herd size and intensive management may provide an environment conducive to Salmonella shedding and chronic dairy herd infection.     

Pulmonary hypertension in a group of dairy calves

An episode of pulmonary arteritis and sclerosis in twenty 5- to 6-month-old dairy calves was investigated. Sixteen of the calves died acutely, without marked premonitory signs of disease. Four calves evaluated clinically had lethargy, pallor, weakness, tachycardia, tachypnea, and jugular venous distention. Cardiac catheterization performed in 3 of the calves revealed pulmonary hypertension; 1 of these calves survived. Necropsy findings in 19 calves included pale lungs and excess free fluid in the pleural and abdominal cavities. In addition, 13 of 19 calves had a dilated and thin-walled right ventricle; 4 of the calves had right-sided cardiac hypertrophy, and 2 had dilatation of the pulmonary artery. Microscopically, pulmonary arteritis and sclerosis of the small to medium-sized arteries were evident in all calves submitted for necropsy. A lung biopsy specimen from a surviving calf had similar lesions. Centrilobular hepatic necrosis was found in 17 of 19 calves. Investigation of the disease episode, including feed analysis for toxins and serologic and microbiological studies of clinically affected calves and clinically normal in-contact penmates, failed to reveal any associated risk factor. The pulmonary arterial changes in the calves were similar to lung lesions in rats fed monocrotaline.     

Prevalence of bovine parvovirus infection in Ontario dairy cattle.

Studies were conducted to determine prevalence and dynamics of bovine parvovirus (BPV) infection. Dairy cows from 29 randomly selected herds in southwestern Ontario were tested twice, one year apart, for the presence of hemagglutination inhibition (HI) antibodies against BPV. Fifty-one percent of 1141 cows tested had BPV-HI titers > 1:32. One year later, the seroprevalence was 83% in 1131 cows from the same farms. The herd mean seroprevalence was 49% and 86% for the year-1 and year-2 samples, respectively. Evidence of BPV infection was found in 96% (27/28) of herds in year-1 and 100% of herds in year-2. A comparison of titers from 716 cows tested twice showed evidence of frequent BPV infection. Sixty-two percent of 326 animals selected in a systematic manner from 40 Guelph area dairy farms had BPV-HI titers > 1:32. The herd mean seroprevalence was 64% Two herds had no animals with titers above the critical titer (1:32) while in one-quarter of the herds all animals exceeded the critical titer.     

The shedding of group A rotavirus antigen in a newly established closed specific pathogen-free swine herd.

A longitudinal study was undertaken in a newly established specific pathogen-free (SPF) swine herd to determine the dynamics of rotavirus antigen shedding in a closed swine facility. Pregnant SPF gilts which populated the herd, and their offspring, were monitored weekly for three consecutive lactations. Fecal samples were assayed for the presence of group-specific viral antigen by a solid phase immunoassay (ELISA). Results indicate that in the week prior to farrow, 35% of samples from gilts/sows contained rotavirus antigen. During nursing, 37% of the gilts'/sows' fecal samples also contained virus antigen. Over the course of three farrowings, every gilt/sow in the herd excreted virus antigen. Virus antigen was present in 25% of the samples tested from nursing pigs and in 70% of the samples tested from pigs in the postnursing period; 95% of the litters excreted virus antigen either while nursing or postweaning. Seasonal incidence in virus antigen excretion was noted with proportionally more suckling pigs virus antigen-positive in summer and proportionally more sows/gilts positive during winter. Diarrhea occurred only rarely in the sampled population. Although piglets shed rotavirus subclinically, ELISA positive feces from piglets of each lactation caused severe disease when fed to neonatal gnotobiotic pigs. Electropherotyping of these passaged viruses indicated minor variation in RNA banding patterns over time.     

我国A群牛轮状病毒感染的血清流行病学调查

为调查A群牛轮状病毒(BRV)在我国不同地区牛群中的感染和流行情况,本研究采用间接ELISA检测2005年～2006年期间在我国12个不同地区收集的1760份牛血清中抗A群BRV抗体。结果显示,其强阳性血清225份(12.8%);中等阳性血清1240份(70.4%);弱阳性血清279份(15.9%);阴性血清16份(1%)。总抗体阳性率高达99%。不同地区强阳性、中等阳性及弱阳性血清所占比例有所不同。结果表明,A群BRV在我国牛群中的感染和流行不但非常广泛,而且极为严重。本研究对我国BRV感染进行了较大规模的血清流行病学调查,其结果可为我国犊BRV腹泻疾病的防制提供重要的依据。     

Prevalence of Giardia duodenalis genotypes in pre-weaned dairy calves

To determine the prevalence of Giardia genotypes in pre-weaned dairy calves, fecal samples were collected from a minimum of 18, 1-7-week-old dairy calves per farm on two farms each in the states of Vermont, New York, Pennsylvania, Maryland, Virginia, North Carolina, and Florida. Samples cleaned of fecal debris and concentrated using CsCl density gradient centrifugation were stained and examined by immunofluorescence microscopy and also subjected to PCR and gene sequence analysis. Prevalence by PCR ranged from 9% on a farm in Pennsylvania to 93% on a farm in Vermont, with an average prevalence for 407 calves on 14 farms of 40%. Gene sequence analysis of the TPI, beta-giardin and 16S rRNA genes revealed 85% of the positive samples to be Assemblage E, while 15% were Assemblage A, although the percentages of these genotypes varied greatly from farm to farm. Some farms had no Assemblage A Giardia. Thus, while a majority of the calves were infected with a genotype that is not known to be infectious for humans, calves on 7 of 14 farms did harbor Assemblage A Giardia. Calves should be considered as a potential source of human infectious cysts in the environment.     

Natural transmission of bovine leukemia virus in dairy calves by dehorning.

Gouge dehorning was evaluated as a mode of transmitting bovine leukemia virus in Holstein calves at a commercial dairy. Significantly (p less than 0.05) more calves dehorned by the gouge method developed antibodies to bovine leukemia virus, as measured by agar-gel immunodiffusion, three months after dehorning, than calves not dehorned. The field use of a blood-contaminated dehorning device resulted in transmission of bovine leukemia virus.     

Detection of group a rotavirus strains circulating in calves in Tunisia

Faecal samples were collected from 89 dairy calves to determine the prevalence of rotavirus infection in Tunisia and the genomic diversity of bovine rotavirus strains. After screening of all faecal samples by enzyme-linked immunosorbent assay, rotavirus strains were analysed by RNA polyacrylamide gel electrophoresis and characterized antigenically by monoclonal antibodies to the VP6 subgroup. The VP7 genotype was determined by nested RT-PCR. Of the 89 calves tested, 27 (30%) were positive for rotavirus antigen. Four different long electrophoretypes were identified. All VP6 typeable strains carried the subgroup I specificity. G8 genotype was the most prevalent, but G6 and mixed strains G(6 + 8) were also detected.     

Prevalence of Cryptosporidium infection in dairy calves in western Washington

The prevalence and intensity of Cryptosporidium infection were examined in 445 Holstein calves at 10 dairy farms in western Washington, near Seattle. Fifty-one percent (176) of calves in the 7- to 21-day-old age group (n = 342) were positive for oocysts in the feces by carbolfuchsin staining. Prevalence and intensity of infection were highest in calves 8 to 14 days old; prevalence was 60% in this group, and 48% of the Cryptosporidium-positive calves had oocyst shedding at a 4+ level. A seasonal pattern in prevalence was not evident.     

Prevalence and genotypes of Giardia duodenalis in post-weaned dairy calves

To determine the prevalence of Giardia genotypes in post-weaned dairy calves, fecal specimens were collected from 3 to 11-month-old dairy calves per farm on two farms in Vermont, New York, Pennsylvania, Maryland, Virginia, North Carolina, and Florida. Specimens cleaned of fecal debris and concentrated using CsCl density gradient centrifugation were stained and examined by immunofluorescence microscopy and also subjected to PCR and DNA sequence analysis. Overall, PCR provided more sensitive detection than IFA. Prevalence of Giardia infection, as detected by PCR ranged from 20% on NC-2 to 81% on VT-2, with an overall prevalence of 52% (237 positive samples out of 456 total). DNA sequence analysis of the 16S rRNA gene revealed 87% of the 237 Giardia isolates were Assemblage E, and 13% were Assemblage A although the prevalence of these genotypes varied greatly from farm to farm, with five farms having no Assemblage A Giardia. Therefore, Assemblage E was present in 45% of all animals tested and Assemblage A was present in 7% of the animals. Thus, while many of the calves were infected with a genotype that is not known to be infectious for humans, post-weaned calves on nine of 14 farms did harbor Assemblage A Giardia. Therefore calves should be considered as a potential source of human infectious cysts in the environment, with some farms representing a much higher risk than others.