Enteric viral infections of calves and passive immunity

Bovine Immunology: Implications for Dairy Cattle

The growing world population (7.8 billion) exerts an increased pressure on the cattle industry amongst others. Intensification and expansion of milk and beef production inevitably leads to increased risk of infectious disease spread and exacerbation. This indicates that improved understanding of cattle immune function is needed to provide optimal tools to combat the existing and future pathogens and improve food security. While dairy and beef cattle production is easily the world's most important agricultural industry, there are few current comprehensive reviews of bovine immunobiology. High-yielding dairy cattle and their calves are more vulnerable to various diseases leading to shorter life expectancy and reduced environmental fitness. In this manuscript, we seek to fill this paucity of knowledge and provide an up-to-date overview of immune function in cattle emphasizing the unresolved challenges and most urgent needs in rearing dairy calves. We will also discuss how the combination of available preventative and treatment strategies and herd management practices can maintain optimal health in dairy cows during the transition (periparturient) period and in neonatal calves.

Microbial colonization of the gastrointestinal tract of dairy calves - a review of its importance and relationship to health and performance

This review aims to explain how microbial colonization of the gastrointestinal tract (GIT) in young dairy calves is related to health and, consequently, to the performance of these animals. The review addresses everything from the fundamental aspects of microbial colonization to the current understanding about the microbiota manipulation to improve performance in adult animals. The ruminal microbiota is the most studied, mainly due to the high interest in the fermentative aspects, the production of short-chain fatty acids, and microbial proteins, and its effects on animal production. However, in recent years, the intestinal microbiota has gained space between studies, mainly due to the relationship to the host health and how it affects performance. Understanding how the GIT's microbiota looks like and how it is colonized may allow future studies to predict the best timing for dietary interventions as a way to manipulate it and, consequently, improve the health and performance of young ruminants.

Phylogenetic Analyses of Rotavirus A from Cattle in Uruguay Reveal the Circulation of Common and Uncommon Genotypes and Suggest Interspecies Transmission

Uruguay is one of the main exporters of beef and dairy products, and cattle production is one of the main economic sectors in this country. Rotavirus A (RVA) is the main pathogen associated with neonatal calf diarrhea (NCD), a syndrome that leads to significant economic losses to the livestock industry. The aims of this study are to determine the frequency of RVA infections, and to analyze the genetic diversity of RVA strains in calves in Uruguay. A total of 833 samples from dairy and beef calves were analyzed through RT-qPCR and sequencing. RVA was detected in 57.0% of the samples. The frequency of detection was significantly higher in dairy (59.5%) than beef (28.4%) calves (p < 0.001), while it did not differ significantly among calves born in herds that were vaccinated (64.0%) or not vaccinated (66.7%) against NCD. The frequency of RVA detection and the viral load were significantly higher in samples from diarrheic (72.1%, 7.99 log₁₀ genome copies/mL of feces) than non-diarrheic (59.9%, 7.35 log₁₀ genome copies/mL of feces) calves (p < 0.005 and p = 0.007, respectively). The observed G-types (VP7) were G6 (77.6%), G10 (20.7%), and G24 (1.7%), while the P-types were P[5] (28.4%), P[11] (70.7%), and P[33] (0.9%). The G-type and P-type combinations were G6P[11] (40.4%), G6P[5] (38.6%), G10P[11] (19.3%), and the uncommon genotype G24P[33] (1.8%). VP6 and NSP1-5 genotyping were performed to better characterize some strains. The phylogenetic analyses suggested interspecies transmission, including transmission between animals and humans.

Effects of Bovine Immunoglobulins on Immune Function, Allergy, and Infection

This review aims to provide an in depth overview of the current knowledge of the effects of bovine immunoglobulins on the human immune system. The stability and functional effects of orally ingested bovine immunoglobulins in milk products are described and potential mechanisms of action are discussed. Orally ingested bovine IgG (bovine IgG) can be recovered from feces, ranging from very low levels up to 50% of the ingested IgG that has passed through the gastrointestinal tract. In infants the recovered levels are higher than in adults most likely due to differences in stomach and intestinal conditions such as pH. This indicates that bovine IgG can be functionally active throughout the gastrointestinal tract. Indeed, a large number of studies in infants and adults have shown that bovine IgG (or colostrum as a rich source thereof) can prevent gastrointestinal tract infections, upper respiratory tract infections, and LPS-induced inflammation. These studies vary considerably in target group, design, source of bovine IgG, dosage, and endpoints measured making it hard to draw general conclusions on effectiveness of bovine immunoglobulin rich preparations. Typical sources of bovine IgG used in human studies are serum-derived IgG, colostrum, colostrum-derived IgG, or milk-derived immunoglobulins. In addition, many studies have used IgG from vaccinated cows, but studies using IgG from nonimmunized animals have also been reported to be effective. Mechanistically, bovine IgG binds to many human pathogens and allergens, can neutralize experimental infection of human cells, and limits gastrointestinal inflammation. Furthermore, bovine IgG binds to human Fc receptors which, enhances phagocytosis, killing of bacteria and antigen presentation and bovine IgG supports gastrointestinal barrier function in in vitro models. These mechanisms are becoming more and more established and explain why bovine IgG can have immunological effects in vivo. The inclusion of oral bovine immunoglobulins in specialized dairy products and infant nutrition may therefore be a promising approach to support immune function in vulnerable groups such as infants, children, elderly and immunocompromised patients.

Probiotic-Induced Priming of Innate Immunity to Protect Against Rotaviral Infection

Understanding of probiotic-induced regulatory gene expression and networking is critical to further explore their roles in controlling infection. Transcriptional profile of selected innate immune genes in primary bovine intestinal epithelial cells was assessed over a time course of incubation with the probiotic Lactobacillus plantarum 299v. Based on gene expression results, a time point was chosen to prime epithelial cells with the probiotic prior to infection with rotavirus. Plaque assays and genomic analysis provided the basis for establishing the efficacy of probiotics in preventing a rotaviral infection. Plaque assays revealed that the probiotic is capable of decreasing (at least by 100-fold) the levels of live virus when the cells were primed with the probiotic. Results from gene expression studies (a) suggested that homeostasis in the gut is maintained in probiotic-primed cells despite infection with rotavirus and (b) revealed preliminary mechanisms for understanding the pathway of pathogen protection by using probiotics.

Egg yolk IgY antibodies: A therapeutic intervention against group A rotavirus in calves

Bovine group A rotavirus (RVA) is considered the major cause of diarrhea in intensively reared neonatal calves. Chicken egg yolk antibodies (IgY) are efficient in protecting neonatal calves from RVA diarrhea; however, the value of this intervention in calves once diarrhea has appeared is unclear. The aim of the present study was to evaluate the application of RVA-specific IgY as a passive treatment in those cases. The experimental groups were: G1 = RVA-specific IgY treatment; G2 = no Ab treatment; and G3 = colostrum deprived + no Ab treatment. IgY treatment significantly reduced virus shedding, diarrhea duration and severity compared to G2 and G3 calves. However, it caused a partial suppression of systemic Ab responses to RVA that could be associated with less severe diarrhea. The oral treatment with IgY for 7 days was associated with significantly higher antibody secreting cell responses in the calves compared with other groups of animals.

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Neonatal calf diarrhea is a critical problem and passive therapy with IgY Abs is a way to control it.

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There are no solid studies using rotavirus specific IgY Abs once calves suffer from diarrhea.

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We provide here scientific information regarding the effects of IgY-based products.

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This information is critical considering that IgY Abs are being sold in several countries.

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We prove the therapeutic value of IgY-based treatment and the industrialization of this product.

Effects of dietary vitamin A content on antibody responses of feedlot calves inoculated intramuscularly with an inactivated bovine coronavirus vaccine

OBJECTIVE

To investigate effects of low dietary vitamin A content on antibody responses in feedlot calves inoculated with an inactivated bovine coronavirus (BCoV) vaccine.

ANIMALS

40 feedlot calves.

PROCEDURES

Calves were fed diets containing high (3,300 U/kg) or low (1,100 U/kg) amounts of vitamin A beginning on the day of arrival at a feedlot (day 0) and continuing daily until the end of the study (day 140). Serum retinol concentrations were evaluated in blood samples obtained throughout the study. Calves were inoculated IM with an inactivated BCoV vaccine on days 112 and 126. Blood samples obtained on days 112 and 140 were used for assessment of BCoV-specific serum IgG1, IgG2, IgM, and IgA titers via an ELISA.

RESULTS

The low vitamin A diet reduced serum retinol concentrations between days 112 and 140. After the BCoV inoculation and booster injections, predominantly serum IgG1 antibodies were induced in calves fed the high vitamin A diet; however, IgG1 titers were compromised at day 140 in calves fed the low vitamin A diet. Other isotype antibodies specific for BCoV were not affected by the low vitamin A diet.

CONCLUSIONS AND CLINICAL RELEVANCE

Dietary vitamin A restriction increases marbling in feedlot cattle; however, its effect on antibody responses to vaccines is unknown. A low vitamin A diet compromised the serum IgG1 responses against inactivated BCoV vaccine, which suggested suppressed T-helper 2-associated antibody (IgG1) responses. Thus, low vitamin A diets may compromise the effectiveness of viral vaccines and render calves more susceptible to infectious disease.

Heat treatment of colostrum increases immunoglobulin G absorption efficiency in high-, medium-, and low-quality colostrum

Previous studies with heat-treated colostrum fed to neonatal calves have consistently used average-quality colostrum. Studies have not compared colostrum across a range of immunoglobulin levels. This study was conducted to investigate IgG absorption in neonatal dairy calves using colostrum of various qualities. Colostrum from the Pennsylvania State University dairy was collected over 2 yr and sorted into high, medium, and low quality based on colostrometer measurement. Colostrum within each category was pooled to create 3 unique, uniform batches. Half of each batch was frozen to be fed without heat treatment. The second half of each batch was heat treated at 60°C for 30min. This process was conducted in September 2011, and repeated in June 2012. Colostrum treatments were analyzed for standard plate count, coliforms, noncoliform gram-negative bacteria, and total IgG concentration. Plasma samples were collected from 145 calves 48h after birth and analyzed for IgG1, IgG2, total protein, and hematocrit. Colostrum quality (high, medium, or low), treatment (unheated or heat treated), and their interactions were analyzed as fixed effects, with year included as a random effect. Heat treatment significantly reduced all types of bacteria and IgG concentration. Plasma IgG concentration at 48h increased linearly with the concentration of IgG in the colostrum that was consumed. Heat treatment of colostrum increased plasma IgG concentration by 18.4% and apparent efficiency of absorption by 21.0%. Results of this study suggest that heat treatment of colostrum containing approximately 50 to 100mg IgG/mL increases absorption of IgG from colostrum.

Case-control study of microbiological etiology associated with calf diarrhea

Calf diarrhea is a major economic burden for the US cattle industry. A variety of infectious agents are implicated in calf diarrhea and co-infection of multiple pathogens is not uncommon in diarrheic calves. A case–control study was conducted to assess infectious etiologies associated with calf diarrhea in Midwest cattle farms. A total of 199 and 245 fecal samples were obtained from diarrheic and healthy calves, respectively, from 165 cattle farms. Samples were tested by a panel of multiplex PCR assays for 11 enteric pathogens: bovine rotavirus group A (BRV-A), bovine coronavirus (BCoV), bovine viral diarrhea virus (BVDV), bovine enterovirus (BEV), bovine norovirus (BNoV), Nebovirus, bovine torovirus (BToV) Salmonella spp. (Salmonella), Escherichia coli (E. coli) K99⁺, Clostridium perfringens with β toxin gene and Cryptosporidium parvum (C. parvum). The association between diarrhea and detection of each pathogen was analyzed using a multivariate logistic regression model. More than a half of the fecal samples from the diarrheic calves had multiple pathogens. Statistically, BRV-A, BCoV, BNoV, Nebovirus, Salmonella, E. coli K99⁺, and C. parvum were significantly associated with calf diarrhea (p < 0.05). Among them, C. parvum and BRV-A were considered to be the most common enteric pathogens for calf diarrhea with high detection frequency (33.7% and 27.1%) and strong odds ratio (173 and 79.9). Unexpectedly BNoV (OR = 2.0) and Nebovirus (OR = 16.7) were identified with high frequency in diarrheic calves, suggesting these viruses may have a significant contribution to calf diarrhea.

Effect of air temperature on the abomasal and small intestinal digestion of a milk substitute diet given to young calves

Twelve Friesian calves were each fitted with an abomasal cannula. The calves were placed in a controlled environment chamber and given a milk substitute diet in buckets at 12-h intervals. The calves were exposed to air temperatures of 25°C from 4 to 10 days of age, 5°C from 11 to 14 days of age, and 25°C at 15 days of age. At 9, 10, 11, 14 and 15 days of age, the abomasal contents of the calves were sampled at 2-h intervals and the temperature and pH of the abomasal contents were recorded at 40-min intervals for a period of 12 h. The rectal and abomasal temperatures of the calves were lower at 11 days of age than at 10 days of age, and were greater at 15 days of age than at 14 days of age (P < 0·05).

In a similar experiment four Friesian calves were each fitted with an ileal re-entrant cannula. The calves were exposed to air temperatures of 25°C from 5 to 19 days of age, 5°C from 20 to 26 days of age, and 25CC at 27 days of age. At 18, 19, 20, 26 and 27 days of age the ileal contents of the calves were collected and sampled for a period of 12 h.

No significant effects of the air temperatures of 25° and 5°C on the abomasal digestion (acidity and proteolytic activity of the abomasal contents) and ileal apparent digestibility of the diet were found.

Development of a panel of multiplex real-time polymerase chain reaction assays for simultaneous detection of major agents causing calf diarrhea in feces

Calf diarrhea is a major economic burden to the bovine industry. Since multiple infectious agents can be involved in calf diarrhea, and the detection of each of the causative agents by traditional methods is laborious and expensive, a panel of 2 multiplex real-time polymerase chain reaction (PCR) assays was developed for rapid and simultaneous detection of the 5 major bovine enteric pathogens (i.e., Bovine coronavirus [BCoV; formally known as Betacoronavirus 1], group A Bovine rotavirus [BRV], Salmonella spp., Escherichia coli K99(+), and Cryptosporidium parvum). The estimated detection limit (i.e., analytic sensitivity) of the panel was 0.1 TCID(50) (50% tissue culture infective dose) for BCoV and group A BRV; 5 and 0.5 colony-forming units for E. coli K99(+) and Salmonella, respectively; and 50 oocysts for Cryptosporidium per reaction. In testing 243 fecal samples obtained from submissions to the Iowa State University Veterinary Diagnostic Laboratory or from experimental animals with known infection status, the newly developed multiplex real-time PCR panel simultaneously detected all 5 pathogens directly from fecal samples and was more rapid and sensitive than the traditional diagnostic tests. The PCR panel showed 89%-97% agreement with those conventional diagnostic tests, demonstrating diagnostic sensitivity equal to or better than that of the conventional tests. In conclusion, the multiplex real-time PCR panel can be a tool for a timely and accurate diagnosis of calf diarrhea associated with BCoV, group A BRV, E. coli K99(+), Salmonella, and/or Cryptosporidium.

Bovine coronavirus associated syndromes

Bovine coronaviruses, like other animal coronaviruses, have a predilection for intestinal and respiratory tracts. The viruses responsible for enteric and respiratory symptoms are closely related antigenically and genetically. Only 4 bovine coronavirus isolates have been completely sequenced and thus, the information about the genetics of the virus is still limited. This article reviews the clinical syndromes associated with bovine coronavirus, including pneumonia in calves and adult cattle, calf diarrhea, and winter dysentery; diagnostic methods; prevention using vaccination; and treatment, with adjunctive immunotherapy.

Feeding heat-treated colostrum to neonatal dairy heifers: effects on growth characteristics and blood parameters

Newborn Holstein heifer calves were studied to compare absorption of immunoglobulin G (IgG(1) and IgG(2)), total serum protein concentration, lymphocyte counts, health scores, growth, and starter intake after receiving unheated or heat-treated colostrum. First-milking colostrum was collected from Holstein cows and frozen at -20 degrees C to accumulate a large batch. After thawing and mixing, half of the colostrum was transferred into 1.89-L plastic containers and frozen at -20 degrees C until needed for feeding. The remaining half was heated at 60 degrees C for 30 min, transferred into 1.89-L plastic containers, and then frozen at -20 degrees C until needed for feeding. Forty heifer calves weighing > or =32 kg at birth were enrolled into 1 of 2 treatment groups before suckling occurred. For the first feeding, 3.8 L of colostrum was bottle fed by 1.5 to 2 h of age. For the second and third feedings, pasteurized whole milk at 5% of birth body weight (BW) was fed. Subsequently, calves received milk replacer containing 20% crude protein and 20% fat at 10% of birth BW/d until wk 5. Milk replacer was reduced to 1 feeding of 5% birth BW until weaning at 6 wk of age. Blood samples and growth data were collected through wk 8. Batch heat-treatment of colostrum at 60 degrees C for 30 min lowered colostrum bacteria concentration while maintaining colostral IgG concentration and viscosity. Calves fed heat-treated colostrum had significantly greater IgG concentrations at 24 h and greater apparent efficiency of IgG absorption (IgG = 23.4 g/L; apparent efficiency of absorption = 33.2%) compared with calves fed unheated colostrum (IgG = 19.6 g/L; apparent efficiency of absorption = 27.7%). There was no difference between treatment groups in growth measurements, calf starter intake, lymphocyte counts, or health scores.

Pathophysiology of diarrhea in calves

Infectious diarrhea in calves is most commonly associated with enterotoxigenic Escherichia coli, Cryptosporidium parvum, rotavirus, coronavirus, or some combination of these pathogens. Each of these agents leads to diarrhea through either secretion or malabsorption/maldigestion, though the specific mechanisms and pathways may differ. Specific pharmacologic control and treatment are dependent on gaining a greater understanding of the pathophysiology of these organisms.

Prevalence of four enteropathogens in the faeces of young diarrhoeic dairy calves in Switzerland

The prevalences of Cryptosporidium parvum, rotavirus, bovine coronavirus (BCV), and enterotoxigenic Escherichia coli (E coli K99) were determined in diarrhoeic dairy calves aged one to 21 days on 71 dairy farms in western Switzerland during the winter of 2005 to 2006. Faecal samples from 147 untreated calves suffering from acute diarrhoea were analysed by standardised diagnostic methods, and the immunoglobulin status of each calf was evaluated. The prevalences of C parvum, rotavirus, BCV and E coli k99 were 55.0 per cent, 58.7 per cent, 7.8 per cent and 5.5 per cent, respectively. The proportions of herds positive for the respective pathogens among the herds with diarrhoeic calves were 41.7 per cent, 52.1 per cent, 2.1 per cent and 2.1 per cent. The immunoglobulin concentration in the serum of 90.5 per cent of the diarrhoeic calves was below 8 g/l.

Establishment of fetal bovine intestinal epithelial cell cultures susceptible to bovine rotavirus infection

Mucosal epithelial cells are infected by a wide variety of pathogens and determining their response to infection is critical for understanding disease pathogenesis. A protocol was developed for culturing primary epithelial cells from fetal bovine intestine and the cultured cells were evaluated for susceptibility to an enteric viral infection. Immunohistochemical staining for cytokeratin confirmed that 60-75% of cultured cells were epithelial cells. Furthermore, following infection with bovine rotavirus (BRV) over 80% of cells in the ileal and jejunal cultures contained viral protein at 16 h post-infection. The intestinal epithelial cell cultures also contained fibroblasts so a jejunal fibroblast culture was established and infected with BRV. Viral protein was detected in jejunal fibroblasts but viral-induced cytopathology was delayed in fibroblast cultures when compared to epithelial cell cultures. This study describes an effective protocol for culturing bovine epithelial cells from fetal intestine and confirmed that the epithelial cells were susceptible to BRV infection. Ileal and jejunal cultures displayed limited growth following continuous passage but early passage epithelial cells provide competent target cells for studying host cell responses to an enteric viral pathogen.

Comparative analysis of innate immune responses following infection of newborn calves with bovine rotavirus and bovine coronavirus

Bovine rotavirus (BRV) and bovine coronavirus (BCV) are important causes of diarrhoea and death in newborn calves. Although these viruses belong to distinct viral classes, they both infect intestinal epithelial cells and induce similar clinical symptoms. Rotavirus usually causes an acute infection, but coronavirus infection can persist and reoccur in adults. Differences in viral structure and clinical outcome prompted us to postulate that innate mucosal immune responses would be markedly different following rotavirus and coronavirus infections. To address this hypothesis, gene expression following BRV and BCV infection was analysed in surgically prepared intestinal loops from 1-day-old colostrum-deprived calves. Gene expression was profiled at 18 h post-infection using bovine cDNA microarrays; the majority of differentially expressed significant genes were associated with the cell cycle and innate immune responses. A select group of these genes was validated by quantitative real-time PCR (qRT-PCR). The expression of genes associated with interferons (IFNs), cytokines and Toll-like receptors, which were not present on the microarray, was analysed further by qRT-PCR. Strong activation of TLR3, IL-6 and p65 was observed in BRV-infected host tissues, but not in tissues infected with BCV. Both viruses also downregulated IFN- and pro-inflammatory cytokine-associated pathways. In vitro studies confirmed that IFN inhibited viral replication. All of these results together suggested either that very early events of host responses at 18 h post-infection were being observed, or that both viruses have unique effective strategies to evade host immune responses.

Comparative pathology of infection by novel diarrhoea viruses

Examination of diarrhoeic faeces in the electron microscope often reveals viruses that are presumed to be enteropathogenic. Lesions caused by novel rotaviruses were similar to those of group A rotaviruses, but enterocyte syncytia were seen which are probably pathognomonic for novel rotaviruses. In adenovirus infection in piglets, mature enterocytes were infected and destroyed; intranuclear inclusion bodies were seen in infected enterocytes. Calici-like viruses infected mature enterocytes in calves and the lesions were similar to those described in humans infected with calici-like viruses; in both host species it was impossible to demonstrate virus particles in enterocytes examined in the electron microscope. The Breda virus infected villi and crypts in the lower small intestine and the surface and crypts in the large intestine; it was the only enteropathogenic virus to show this distribution of infection and lesions. Astrovirus infection in lambs was comparable to a mild rotavirus infection, but in calves the epithelium of the dome villi of Peyer's patches was infected. Parvovirus in cats and dogs infected and destroyed small intestinal crypt cells, causing dilated crypts and stunted villi; intranuclear inclusion bodies were prominent.

Transmission of bovine coronavirus and serologic responses in feedlot calves under field conditions

OBJECTIVE

To compare shedding patterns and serologic responses to bovine coronavirus (BCV) in feedlot calves shipped from a single ranch in New Mexico (NM calves) versus calves assembled from local sale barns in Arkansas (AR calves) and to evaluate the role of BCV on disease and performance.

ANIMALS

103 feedlot calves from New Mexico and 100 from Arkansas.

PROCEDURES

Calves were studied from before shipping to 35 days after arrival at the feedlot. Nasal swab specimens, fecal samples, and serum samples were obtained before shipping, at arrival, and periodically thereafter. Bovine coronavirus antigen and antibodies were detected by use of an ELISA.

RESULTS

NM calves had a high geometric mean titer for BCV antibody at arrival (GMT, 1,928); only 2% shed BCV in nasal secretions and 1% in feces. In contrast, AR calves had low antibody titers against BCV at arrival (GMT, 102) and 64% shed BCV in nasal secretions and 65% in feces. Detection of BCV in nasal secretions preceded detection in feces before shipping AR calves, but at arrival, 73% of AR calves were shedding BCV in nasal secretions and feces. Bovine coronavirus infection was significantly associated with respiratory tract disease and decreased growth performance in AR calves.

CONCLUSIONS AND CLINICAL RELEVANCE

Replication and shedding of BCV may start in the upper respiratory tract and spread to the gastrointestinal tract. Vaccination of calves against BCV before shipping to feedlots may provide protection against BCV infection and its effects with other pathogens in the induction of respiratory tract disease.

Growth performance and health of dairy calves bedded with different types of materials

Granite fines, sand, rice hulls, long wheat straw, and wood shavings were compared as bedding for 60 female dairy calves. Growth, health, stress indices, and behavior of newly born calves, along with physical characteristics and bacterial counts of bedding, were evaluated for 42 d during August to October, 2002. Overall average daily gain and dry matter intake of calves did not differ due to bedding type, although during wk 2 calves housed on rice hulls had the greatest dry matter intake and those housed on wood shavings had the lowest. During wk 2, calves housed on granite fines and sand were treated more often for scours, and calves housed on long wheat straw received the fewest antibiotic treatments (week by bedding material interaction). Granite fines formed a harder surface than other bedding, and calves housed on granite fines scored the dirtiest. When bedding materials were evaluated, sand was scored to be the dirtiest, while pens bedded with rice hulls, long wheat straw, and wood shavings scored cleaner. Long wheat straw had the warmest surface temperature, and rice hulls and wood shavings were warmer than granite fines and sand. Serum cortisol, alpha(1)-acid glycoprotein, immunoglobulin G concentrations, and the neutrophil:lymphocyte ratio were not affected by bedding type. On d 0, coliform counts were greatest in rice hulls. After use, coliform counts were greatest in long wheat straw (week by bedding material interaction). On d 42, the concentration of ammonia at 10 cm above the bedding was lowest for long wheat straw. Growth performance of calves bedded for 42 d with 5 bedding types did not differ; however, the number of antibiotic treatments given for scours was greatest on granite fines and sand; coliform counts in the bedding were highest in rice hulls before use and in long wheat straw after 42 d of use.

Modulation by colostrum-acquired maternal antibodies of systemic and mucosal antibody responses to rotavirus in calves experimentally challenged with bovine rotavirus

The effect of colostral maternal antibodies (Abs), acquired via colostrum, on passive protection and development of systemic and mucosal immune responses against rotavirus was evaluated in neonatal calves. Colostrum-deprived (CD) calves, or calves receiving one dose of pooled control colostrum (CC) or immune colostrum (IC), containing an IgG1 titer to bovine rotavirus (BRV) of 1:16,384 or 1:262,144, respectively, were orally inoculated with 10^5.5 FFU of IND (P[5]G6) BRV at 2 days of age. Calves were monitored daily for diarrhea, virus shedding and anti-BRV Abs in feces by ELISA. Anti-rotavirus Ab titers in serum were evaluated weekly by isotype-specific ELISA and virus neutralization (VN). At 21 days post-inoculation (dpi), all animals were euthanized and the number of anti-BRV antibody secreting cells (ASC) in intestinal and systemic lymphoid tissues were evaluated by ELISPOT. After colostrum intake, IC calves had significantly higher IgG1 serum titers (GMT=28,526) than CC (GMT=1195) or CD calves (GMT<4). After BRV inoculation, all animals became infected with a mean duration of virus shedding between 6 and 10 days. However, IC calves had significantly fewer days of diarrhea (0.8 days) compared to CD and CC calves (11 and 7 days, respectively). In both groups receiving colostrum there was a delay in the onset of diarrhea and virus shedding associated with IgG1 in feces. In serum and feces, CD and CC calves had peak anti-BRV IgM titers at 7 dpi, but IgA and IgG1 responses were significantly lower in CC calves. Antibody titers detected in serum and feces were associated with circulation of ASC of the same isotype in blood. The IC calves had only an IgM response in feces. At 21 dpi, anti-BRV ASC responses were observed in all analyzed tissues of the three groups, except bone marrow. The intestine was the main site of ASC response against BRV and highest IgA ASC numbers. There was an inverse relationship between passive IgG1 titers and magnitude of ASC responses, with fewer IgG1 ASC in CC calves and significantly lower ASC numbers of all isotypes in IC calves. Thus, passive anti-BRV IgG1 negatively affects active immune responses in a dose-dependent manner. In ileal Peyer’s patches, IgM ASC predominated in calves receiving colostrum; IgG1 ASC predominated in CD calves. The presence in IC calves of IgG1 in feces in the absence of an IgG1 ASC response is consistent with the transfer of serum IgG1 back into the gut contributing to the protection of the intestinal mucosa.

Factors involved in the early pathogenesis of bovine Staphylococcus aureus mastitis with emphasis on bacterial adhesion and invasion. A review

Staphylococcus aureus is the most important and prevalent contagious mammary pathogen; it causes clinical and subclinical intramammary infection with serious economic loss and herd management problems in dairy cows. In vitro studies have shown that Staphylococcus aureus adheres to mammary epithelial cells and extracellular matrix components and invades into mammary epithelial as well as other mammary cells. Staphylococcus aureus strains from intramammary infection produce several cell surface-associated and extracellular secretory products. The exact pathogenic roles of most of the products and their effects on adhesion and invasion are not well evaluated. It is also known that mammary epithelial cell-associated molecules and extracellular matrix components interact with S. aureus during the pathogenesis of mastitis, but their roles on adhesion and invasion have not been characterized. The adhesion of S. aureus to epithelial cells may involve non-specific physicochemical interactions and/or specific interactions between bacterial cell-associated ligands and host cell surface receptors. In vitro adhesion depends on the S. aureus strain, the growth phase of the bacteria, the growth medium and the origin of the epithelial cells. Adhesion is hypothesized to be a prerequisite and crucial early step for mammary gland infection. Staphylococcus aureus invades mammary epithelial cells. It also invades other cells such as endothelial cells and fibroblasts. Bacteria are found enclosed in membrane bound vacuoles in the cytoplasm of mammary epithelial cells. Recent observations indicate that S. aureus escapes from the phagosome into the cytoplasm and induces apoptosis. The invasion into mammary epithelial cells may occur through an endocytic process that requires involvement of elements of the cytoskeleton or by direct binding of bacteria to epithelial cells through a process mediated by specific receptors that needs de novo protein synthesis by both cells. Thus, the recurrent subclinical infection may result from this intracellular existence of bacteria that are protected from host defenses and effects of antibiotics. This review emphasizes on recent findings on S. aureus adhesion to mammary epithelial cells and extracellular matrix components and invasion into mammary epithelial cells.

Influence of diet on the shedding of Candida glabrata by experimentally infected preweaned calves

The influence of three diets, comprising dam's milk (DM) from the same farm, commercial milk replacer with (CMRL) or without 3.2% lactose (CMR), on the duration and intensity of Candida glabrata shedding in the faeces of preweaned calves following experimental oral infection was examined. Shedding of other potential enteric pathogens was also monitored. The duration and intensity of C. glabrata shedding in DM-fed calves were reduced significantly compared with the calves fed the two diets based on milk replacers. Consequently, feeding calves with DM might disrupt the infective cycle, resulting in the yeast's elimination from a farm. In the CMR and CMRL groups, the periods of intensive shedding of C. glabrata and rotavirus overlapped but no diarrhoea was associated with the shedding of either microorganism. There was no evidence that lactose diminished colonization in vivo.

Production of hybrid double- or triple-layered virus-like particles of group A and C rotaviruses using a baculovirus expression system

Dual infections by group A and group C rotaviruses have been reported, but no reassortants between group A and group C rotaviruses have been described. The VP6 major inner capsid protein of group A and C rotaviruses shares common antigens detected by monoclonal antibodies and also shares 40-43% amino acid identity. Coinfection of Spodoptera frugiperda (Sf9) insect cells with different combinations of the recombinant baculoviruses encoding either group A [RF VP2 (A-VP2), IND VP6 (A-VP6), and VP7 (A-VP7[IND]), 2292B VP7 (A-VP7[2292B])] or C [Shintoku VP6 (C-VP6) and VP7 (C-VP7)] bovine rotavirus proteins produced hybrid group A/C triple-layered VP2/6/7 virus-like particles (TLPs) composed of A-VP2/C-VP6/C-VP7, A-VP2/C-VP6/A-VP7(IND), A-VP2/C-VP6/A-VP7(2292B), and A-VP2/A-VP6/C-VP7. To our knowledge, this is the first report that the inner capsid VP6 of group A or group C rotavirus can support attachment of the heterologous, antigenically distinct group A (G6, IND or G10, 2292B) or group C rotavirus outer capsid VP7 to produce hybrid TLPs in vitro.

Lactogenic antibody responses in cows vaccinated with recombinant bovine rotavirus-like particles (VLPs) of two serotypes or inactivated bovine rotavirus vaccines

Triple-layered virus-like particles (VLPs) were produced in a baculovirus expression system from the two prevalent bovine rotavirus (BRV) serotypes, IND (P[5]G6) and 2292B (P[11]G10). Five groups of pregnant cows were inoculated intramuscularly and intramammarily with IND VLPs [BRV RF VP2, and IND VP4, 6, and 7, 250 microg per dose], 2292B VLPs [RF VP2, Cr VP4 (P[11]), and 2292B VP6 and 7, 250 microg per dose], combined IND/2292B VLPs (125 microg each VLP per dose), inactivated IND BRV (5x10(7)PFU per dose, pre-inactivation), or cell supernatant (mock-controls) in incomplete Freund's adjuvant. Serum, colostrum and milk were collected and tested for isotype-specific antibodies, and homologous and heterologous neutralizing antibodies (VN) to BRV by ELISA and VN tests, respectively. After vaccination, the IgG1 and homologous VN geometric mean antibody titers (GMTs) to BRV in serum of vaccinated groups were significantly (P<0.05) higher than in the mock-controls through postpartum day (PPD) 30. In colostrum, the IgG1 and IgA, and the homologous and heterologous VN GMTs of the IND VLP, 2292B VLP, combined IND/2292B VLP and the inactivated IND groups were significantly enhanced compared to the mock-controls, except for the heterologous VN GMTs in the inactivated IND group. However, the VLP vaccine groups had significantly higher homologous and heterologous VN GMTs than the inactivated IND group. The VN GMTs of the IND/2292B VLP group were statistically similar to the homologous VN GMTs of the IND or 2292B VLP groups, although the IgG1 GMT was lower. In milk, the IgG1 and homologous VN GMTs of the VLP groups were significantly higher than the inactivated IND or the mock-control groups through PPD30. However, the heterologous and homologous VN GMTs of inactivated IND group were statistically similar to the mock-control group at PPD0 and 30, respectively. These results demonstrate that the BRV antibody titers in serum, colostrum and milk are significantly enhanced by the use of triple-layered VLPs and inactivated IND vaccines, but significantly higher antibody responses were observed in the VLP vaccinated cows. The combined IND/2292B VLP vaccine induced comparable VN responses to BRV in serum, colostrum and milk compared to those induced by the individual IND or 2292B VLP vaccines, suggesting that at least two different serotypes can be mixed to confer maximum antibody responses to the incorporated serotypes.

Experimental reproduction of winter dysentery in lactating cows using BCV -- comparison with BCV infection in milk-fed calves

Infection models were developed for adult cows and for young calves using the same strain of bovine coronavirus (BCV), which for the first time allows experimental reproduction of winter dysentery (WD) in seronegative lactating cows. The cattle were infected through direct contact with an experimentally inoculated calf. All experimental cattle shed faecal BCV with development of diarrhoea, being profusely watery with small amounts of blood in the most severely affected animals, including both cows and calves. The cows, in contrast to the calves, showed depressed general condition and appetite leading to a marked decrease in milk yield. Further age-associated differences were a shorter incubation period in the two youngest calves, but with milder fever and milder decrease in white blood cell counts. These findings shed light on the apparent epidemiological differences between WD and calf BCV diarrhoea suggesting that, (1) the same strains of BCV cause natural outbreaks of calf diarrhoea and WD, (2) seronegative cows are more severely affected by the infection than seronegative conventionally reared calves, and (3) unaffected general condition in diarrhoeic calves may lead to underestimation of the occurrence of calf diarrhoea in WD outbreaks.

In response to infection, all cattle produced early interferon type 1 in serum and, except for one calf, in nasal secretions. A finding not previously reported is the detection of interferon type 1 responses in bovine milk. All cattle developed high IgM antibody responses and long-lasting IgA antibody responses both systemically and locally. The serum IgM antibody responses came earlier in most of the calves than in the cows. Prolonged IgM antibody responses were detected in serum and milk, while those in nasal secretions were much shorter. BCV-specific IgA was present in nasal secretions from all cattle throughout the 6 months follow-up. The IgA antibody response in serum was detected up to 17 months post-infection and the duration showed an age-related variation indicating a more prominent IgA memory in the adult cattle and in the older calves than in the younger ones. BCV-specific IgG was detected in all cattle during the experimental period of up to 22 months.

In conclusion, WD was reproduced in seronegative lactating cows. The cows showed a more severe general diseases than seronegative calves infected concurrently. Very long-lasting IgA antibody responses were detected both systemically and locally.

Bovine milk antibodies for health

The immunoglobulins of bovine colostrum provide the major antimicrobial protection against microbial infections and confer a passive immunity to the newborn calf until its own immune system matures. The concentration in colostrum of specific antibodies against pathogens can be raised by immunising cows with these pathogens or their antigens. Immune milk products are preparations made of such hyperimmune colostrum or antibodies enriched from it. These preparations can be used to give effective specific protection against different enteric diseases in calves and suckling pigs. Colostral immunoglobulin supplements designed for farm animals are commercially available in many countries. Also, some immune milk products containing specific antibodies against certain pathogens have been launched on the market. A number of clinical studies are currently in progress to evaluate the efficacy of immune milks in the prevention and treatment of various human infections, including those caused by antibiotic resistant bacteria. Bovine colostrum-based immune milk products have proven effective in prophylaxis against various infectious diseases in humans. Good results have been obtained with products targeted against rotavirus, Shigella flexneri, Escherichia coli, Clostridium difficile, Streptococcus mutans, Cryptosporidium parvum and Helicobacter pylori. Some successful attempts have been made to use immune milk in balancing gastrointestinal microbial flora. Immune milk products are promising examples of health-promoting functional foods, or nutraceuticals. This review summarises the recent progress in the development of these products and evaluates their potential as dietary supplements and in clinical nutrition.

Correlation between maternal serum antibodies and protection against bovine rotavirus diarrhea in calves

The correlation between maternal serum antibodies in beef calves at 2 days old and protection against diarrhea induced by natural bovine rotavirus (BRV) infection was examined. Virus neutralizing (VN) antibody titers against BRV in sera from calves that developed diarrhea by BRV infection within 14 days of age (BRV-diarrheal calves) were significantly lower than those from calves that had no diarrhea. In the BRV-diarrheal calves, a positive correlation was found between the VN antibody titers and age of the onset of diarrhea. There were negative correlations between the VN antibody titers and duration of the diarrhea, VN antibody titers and cumulative diarrhea scores, and the VN antibody titers and duration of virus shedding. These results suggest that the VN antibody titers against BRV in newborn calf serum could be an indicator of protection against BRV-induced diarrhea.

Prospects for vaccines against rotaviruses

Candidate vaccines against rotavirus-caused diarrhoea have been under development for more than ten years. Recent research has helped to identify virological and immunological parameters which are most likely to be correlates of protection from rotavirus infection and disease. Large double-blind, placebo-controlled trials in the United States and Venezuela have resulted in successful protection from severe disease and dehydration after immunisation with live-attenuated rhesus rotavirus-based monovalent and tetravalent vaccine candidates. The tetravalent vaccine is now submitted for regulatory approval in the United States. The anticipated widespread use of such a vaccine will need careful safety and effectiveness surveillance as the enormous diversity of rotavirus antigenicity may affect efficacy in different geographical regions. To proceed from licensure to reduction of disease a series of goals must be achieved: the vaccine must be recommended by major immunisation advisory committees, be financed in both the public and private sectors, be integrated into existing vaccination schedules, be promoted, find parental acceptance and achieve a high level of coverage. Copyright 1998 John Wiley & Sons, Ltd.

Enhancement of passive immunity with maternal vaccine against newborn calf diarrhea

The effects of a maternal vaccine against newborn calf diarrhea associated with group A bovine rotavirus (BRV), bovine coronavirus (BCV), bovine parvovirus and K99 Escherichia coli (E. coli) were examined on a beef cow-calf herd. After vaccination, serum or colostrum antibody titers to BRV, BCV and E. coli K99 in the vaccinated cows were significantly higher than those in unvaccinated control cows. Serum antibody titers to BRV, BCV and E. coli K99 in calves from the vaccinated cows were also significantly higher than those in calves from the control cows for 3-4 weeks after birth. These results suggested that the immunization of cows with the maternal vaccine enhanced the passive immunity levels in calves against BRV, BCV and K99 E. coli.

Influence of injectable immunoglobulin on serum immunoglobulin concentrations in dairy calves

The influence of a purified Ig preparation on morbidity, mortality, and performance of purchased calves was evaluated. Calves (n = 187) were 3 to 8 d of age and were infused i.v. (blocks 1 and 2) or s.c. (blocks 3 and 4) with a purified Ig preparation derived from bovine blood that was obtained from an abattoir (n = 88) or were infused with 0.9% NaCl saline (n = 99). The Ig solution was purified by column chromatography and (NH4)2SO4 precipitation (blocks 1 and 2) or by column chromatography only (blocks 3 and 4). Calves were infused with 504 g of Ig solution containing a mean of 47 g of IgG. Serum IgG concentrations at 24 h postinfusion increased 2.9 g/L when calves in blocks 1 and 2 were infused with Ig, but concentrations declined when calves in blocks 3 and 4 were infused with Ig or when calves were infused with NaCl saline. Total protein in serum increased with infusion of Ig in blocks 1 and 2 also. Serum urea N increased when calves in blocks 3 and 4 were infused with Ig. Mean BW at 28 d after arrival, BW gain, DMI, mortality, and scour scores were unaffected by treatment. Infusion of Ig increased the concentration of serum IgG but was dependent on the method of processing. Increased serum Ig did not markedly influence incidence or severity of disease in young dairy calves.

Effects of housing and colostrum feeding on the prevalence of selected infectious organisms in feces of Jersey calves

Neonatal Jersey calves (n = 96) were used to evaluate effects of housing (individual hutches or wooden pens in a barn) and colostrum feeding (calves were separated from the dam and fed 2 L of colostrum in nipple-bottles or allowed to nurse the dam for 3 d) on the prevalence of selected organisms in feces. Prevalence of Cryptosporidium and Eimeria were reduced, and prevalence of rotavirus tended to be reduced, when calves were housed in hutches. Prevalence of coronavirus was unaffected by treatment. Weekly prevalence of Giardia was increased when calves were left to nurse the dam for 3 d. Mean prevalence of Cryptosporidia (wk 1 to 4), Eimeria (wk 4 to 5), Giardia, rotavirus, and coronavirus (wk 1 to 5) were 34.7, 20.6, 27.1, 15.8, and 4.9%, respectively. Escherichia coli (K99 positive) were observed in 3 of 174 samples cultured. Methods of housing and colostrum feeding affected acquisition of enteropathogens in this study.

A study on neonatal calf diarrhea induced by rotavirus

This review summarizes the results of a study on rotaviruses isolated from calves affected by neonatal diarrhea. The results indicated that rotavirus infection is widespread and supported the evidence for an etiologic role of these viruses in neonatal diarrhea. Differences in virulence among bovine rotaviruses appeared also to be confirmed. Conventionally reared calves were fully susceptible to the experimental infection induced by rotaviruses originating from heterologous hosts, i.e. monkeys, pigs and rabbits. When rotavirus strains of bovine, simian and rabbit origin were compared by cross neutralization tests, it was found the simian and porcine strains were indistinguishable and both appeared to relate antigenically to the bovine strain. Finally, it was proven that feeding newborn calves with colostrum and first milk of their dams, previously vaccinated with an inactivated adjuvanted rotavirus vaccine, could prevent the neonatal diarrhea from occurring.

Toroviruses of animals and humans: a review

Toroviruses are a group of enveloped positive-stranded RNA viruses that cause enteric, respiratory, and perhaps generalized infections in animals and humans. Their name refers to their unique morphological features: an elongated bacilliform core with two rounded ends is surrounded by a membrane that may either tightly adhere to or “shrink-wrap” it, without respecting the capsid's rod shape; in the first instance, straight or curved rhabdovirus-like particles are formed, whereas in the latter a biconcave disk results. Torovirus history is brief: the first representative, Berne virus (BEV), was isolated in Berne, Switzerland, in 1972 from a rectal swab taken from a horse with diarrhea 1 week before it died. BEV is the only equine torovirus isolate that replicates in cell culture; since most molecular data have been obtained with this isolate, BEV has been acknowledged as the torovirus prototype. Recognition of toroviruses as a new group of potentially pathogenic viruses came seven years after the discovery of BEV, when morphologically similar particles were discovered by electron microscopy (EM) in stool specimens from calves with severe diarrhea in a dairy herd in Breda, Iowa. Despite repeated attempts, BRV has not been adapted to the growth in cell or tissue culture, a problem which has hampered its biochemical, bio-physical, and molecular characterization. However, its pathogenesis and pathology have been studied in the experimentally infected gnotobiotic calves, showing that BRV infections may cause gastroenteritis. Recently, Vanopdenbosch et al. reported the isolation of a torovirus-like virus from the respiratory tract of calves with pneumonia, suggesting that both enterotropic and pneumotropic bovine toroviruses exist. Besides the established toroviruses of horses and cattle, torovirus-like particles (TVLPs) have been found by EM in different animal species; torovirus antibodies appear to be widespread in higher vertebrates, indicating that these viruses infect a broad range of animal hosts. The possibility of a torovirus infecting humans was first reported in 1984 and has become more likely in view of the recent data. This chapter is intended to update the information about toroviruses, and to describe the similarities and differences with the related coronaviruses.

Concentrations of passively acquired IgG1 antibodies in the intestinal lumen of the neonatal calf

Passively acquired specific antibodies in the intestinal lumen are thought to provide protective immunity against infections with rotaviruses and other enteropathogens. In this study, concentrations of functional antibody in the intestinal lumen derived from diet and circulation were measured using 2,4-dinitrophenol (DNP) specific antibody of the IgG1 isotype, radiolabelled with 125I. The labelled IgG1 antibody was administered to neonatal calves either orally in the daily milk diet for three consecutive days (Group 1), or by a single intravenous injection (Group 2). After equilibration, the concentrations of protein-bound 125I and the specific DNP binding activities of the labelled protein in the intestinal lumen were measured, and intestinal concentrations of functional IgG1 were estimated. In Group 1 calves, protein bound 125I concentrations in the pooled small intestinal contents at 2 and 12 h after a milk meal were 50.8 +/- 20.5% and 7.9 +/- 3.4%, respectively, of the milk concentration. Protein bound 125I concentrations in the small intestinal contents were 0.7 +/- 0.4% (mean +/- SD) of serum concentrations of Group 2 calves, and were similar at 2 and 12 h after a milk meal. For a calf with average serum passive IgG1 concentrations drinking milk with normal IgG1 content, these results predict IgG1 concentrations in the small intestinal contents of milk fed calves at 2 h after a milk meal to be 0.6 mg ml-1, half of which originates from the milk and half from the circulation. At 12 h after a milk meal, intestinal IgG1 concentrations fall to approximately 0.3 mg ml-1, most of which originates from the circulation. Antibody in the intestinal lumen originating from serum retained more antigen (DNP) binding affinity than that ingested in the milk diet. Therefore, both dietary and circulating IgG1 contribute significantly to passive IgG1 antibody concentrations in the small intestinal lumen of neonatal calves, but milk derived IgG1 antibody concentrations in the small intestinal lumen were not maintained between twice daily feedings.

Active protection against rotavirus infection of mice following intraperitoneal immunization

Active immunity to rotavirus has been demonstrated following oral inoculation with live virus but little is known about the effects of parenteral immunization. In this study, adult mice were immunized by intraperitoneal (ip) inoculation with live rotaviruses and later orally challenged with murine rotavirus (EDIM) to measure active immunity against infection. Three doses of EDIM (8 micrograms/dose) given intraperitoneally (ip) provided full protection against EDIM infection, whether administered with or without Freund's adjuvant. Only partial protection was found when the quantity of immunogen was reduced to < 2 micrograms/dose. Reduction of the number of doses from three to one (8 micrograms/dose), however, still resulted in protection of all mice. Significant protection was also observed after inoculation with one or three doses (2 micrograms/dose) of heterologous rotaviruses. Protection provided by the heterologous strains did not correlate with neutralizing antibody to EDIM, which indicated that neutralizing antibody to the challenge virus was not required for protection. uv-Inactivated EDIM also provided significant protection against EDIM, thus demonstrating that viral replication was not required for protection. These results suggest that parenteral immunization may be an effective method to vaccinate against rotavirus disease.

A lactogenic-immune-deficiency-syndrome in cows: unexplained phenomenon

The majority of adult cows in a certain dairy herd, were found to have very low levels of immunoglobulins (Igs) in their colostrum. This phenomenon was defined by us as Lactogenic-Immune-Deficiency-Syndrome (LIDS). The mean IgG levels were 44.5 and 57.2 mg ml-1 respectively (on two different occasions) as compared to that of a control group which was 103.4 mg ml-1. The levels of Igs in the colostra of heifers from the same herd were found to be higher than those of adult cows. The degree of LIDS was found to be closely related to the age of cows in the herd. The low levels of Igs in the colostra were not directly linked to their concentrations in the sera of the affected cows. The relatively low amount of IgA in the affected colostra suggests that the local production in the lymph tissue associated with the mammary glands is impaired as well. In order to investigate the etiology of the phenomenon, tests were carried out to reveal whether bovine leucosis virus (BLV) infection or immune complexes were involved in the pathogenesis of LIDS. The results were negative. The etiology of LIDS remains for the time being unknown.

Murine intestinal antibody response to heterologous rotavirus infection

Rotavirus is the most important worldwide cause of severe gastroenteritis. Extensive efforts have been devoted to the design of a vaccine that will prevent disease, but development of a more effective vaccine strategy may require progress in the understanding of the mucosal immune response to replicating viral antigens. In this article, we report the characterization of the intestinal antibody response of a murine model to heterologous infection with the rhesus rotavirus vaccine strain. We have adapted the enzyme-linked immunospot assay to measure this response without the difficulties associated with measurement of antibodies in intestinal contents or the artifacts associated with culturing of lymphocytes. The predominant response in terms of antibody-secreting cells (ASC) is seen in the small intestine lamina propria, which can be measured within 4 days of infection, peaks 3 weeks after infection, and remains near that level for longer than 8 weeks. The magnitude of the immunoglobulin A (IgA) cell response is approximately 10 times greater than the intestinal IgG cell response, and IgM cells are rare. Virus-specific ASC constitute approximately 50% of all ASC in the gut at the peak of the virus-specific response. This response is considerably greater than responses to nonreplicating mucosal antigens measured by similar techniques. Enteral infection engenders minimal virus-specific ASC response in the spleen. Rhesus rotavirus-specific enzyme-linked immunosorbent assay and neutralization assays of serum and intestinal contents did not correlate with virus-specific ASC response.

cDNA probes for the diagnosis of bovine torovirus (Breda virus) infection

A genomic cDNA library of RNA from Breda virus (BRV), a bovine torovirus, was prepared. The nucleotide sequence of the 3' end of the genome was found to be highly conserved (93% identical) between BRV and Berne virus, the torovirus prototype. Cross-hybridization experiments were performed to select Berne virus cDNA clones for use as probes in a dot hybridization assay; the objective was to detect heterologous torovirus RNA in fecal material. A rapid RNA extraction method was employed to make the test applicable for routine diagnosis. Samples from calves after experimental and natural infection with BRV were assayed to establish the sensitivity and specificity of the test and to compare the test with the enzyme-linked immunosorbent assay (ELISA) for antigen detection. For this purpose, 53 samples from seven infected calves were tested with both methods. In the ELISA, BRV was detected in six fecal samples from three inoculated calves. By use of the hybridization test, 16 samples from seven calves reacted positively. With one exception, only postinoculation samples were found positive in hybridization. No signal was seen in feces from uninoculated calves or from calves infected with rotavirus or coronavirus.

Some infectious causes of diarrhea in young farm animals

Escherichia coli, rotaviruses, and Cryptosporidium parvum are discussed in this review as they relate to enteric disease in calves, lambs, and pigs. These microorganisms are frequently incriminated as causative agents in diarrheas among neonatal food animals, and in some cases different strains or serotypes of the same organism cause diarrhea in humans. E. coli causes diarrhea by mechanisms that include production of heat-labile or heat-stable enterotoxins and synthesis of potent cytotoxins, and some strains cause diarrhea by yet undetermined mechanisms. Rotaviruses and C. parvum induce various degrees of villous atrophy. Rotaviruses infect and replicate within the cytoplasm of enterocytes, whereas C. parvum resides in an intracellular, extracytoplasmic location. E. coli, rotavirus, and C. parvum infections are of concern to producers, veterinarians, and public health officials. These agents are a major cause of economic loss to the producer because of costs associated with therapy, reduced performance, and high morbidity and mortality rates. Moreover, diarrheic animals may harbor, incubate, and act as a source to healthy animals and humans of some of these agents.

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.