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1.
Unsuckled specific pathogen free calves were inoculated at 3-4 weeks of age, either intranasally (IN) or orally (O) with bovine coronavirus or O plus IN (O/IN) or O with bovine rotavirus. Shedding of virus in nasal or fecal samples, and virus-infected nasal epithelial cells were detected using immunofluorescent staining (IF), ELISA or immune electron microscopy (IEM). Isotype-specific antibody titers in sera, nasal and fecal samples were determined by ELISA. Calves inoculated with coronavirus shed virus in feces and virus was detected in nasal epithelial cells. Nasal shedding persisted longer in IN-inoculated calves than in O-inoculated calves and longer than fecal shedding in both IN and O-inoculated calves. Diarrhea occurred in all calves, but there were no signs of respiratory disease. Calves inoculated with rotavirus had similar patterns of diarrhea and fecal shedding, but generally of shorter duration than in coronavirus-inoculated calves. No nasal shedding of rotavirus was detected. Peak IgM antibody responses, in most calves, were detected in fecal and nasal speciments at 7-10 days post-exposure (DPE), preceeding peak IgA responses which occurred at 10-14 DPE. The nasal antibody responses occurred in all virus-inoculated calves even in the absence of nasal shedding of virus in rotavirus-inoculated calves. Calves inoculated with coronavirus had higher titers of IgM and IgA antibodies in fecal and nasal samples than rotavirus-inoculated calves. In most inoculated calves, maximal titers of IgM or IgA antibodies correlated with the cessation of fecal or nasal virus shedding. A similar sequence of appearance of IgM and IgA antibodies occurred in serum, but IgA antibodies persisted for a shorter period than in fecal or nasal samples. Serum IgG1 antibody responses generally preceeded IgG2 responses and were predominant in most calves after 14-21 DPE.  相似文献   

2.
OBJECTIVE: To correlate tissue distribution with development of lesions after experimental infection with a virulent strain of noncytopathic bovine viral diarrhea virus (BVDV) type 2 in calves. ANIMALS: Ten 14-day-old and two 2-month-old colostrum-deprived calves. PROCEDURE: Calves were intranasally inoculated with BVDV type-2 strain 1373 from an outbreak of clinically severe bovine viral diarrhea (BVD).Two 14-day-old calves served as noninfected controls. Two calves each were euthanatized on postinoculation days 3, 6, and 12, and 1 each on days 8, 9, 13, and 14. Tissues were collected for immunohistologic and histologic examination. RESULTS: Inoculated calves developed nonspecific clinical signs characterized by high fever and decreased numbers of leukocytes and thrombocytes. Viral antigen was detected focally in lymphoid tissues on day 3. On days 6, 8, 9, 12, and 14, viral antigen became increasingly widespread throughout organs and tissues. Viral antigen in lymphoid tissues was associated with severe depletion of all compartments. Lesions in other tissues were not well correlated with distribution of viral antigen. Depletion of lymphoid tissues was observed in a calf on day 13, but viral antigen had been cleared from most tissues and was detected in vascular walls only. CONCLUSIONS AND CLINICAL RELEVANCE: Infection with a virulent BVDV strain resulted in wide dissemination of viral antigen in host tissues. Severe lymphoid depletion developed in lymphoid tissues, whereas viral antigen was generally not associated with lesions in other tissues. Findings suggest that development of lesions in acute BVD is not solely a function of viral replication and is also attributable to host reaction to infection.  相似文献   

3.
Over a period of 3 summers, 21 colostrum-fed Holstein bull calves, 1 to 3 days old, were assigned to 7 replicates, each consisting of 3 calves. Within each replicate of 3 calves, 2 were selected at random, to be given 100,000 to 146,000 sporulated coccidia oocysts (principally Eimeria bovis) orally 60 hours after arrival at the college research farm. On the thirteenth day after coccidia inoculation, 1 of the 2 calves that had been given coccidia and the third calf that had not been inoculated, were given coronavirus by intranasal and oral routes. Calves were observed daily, and consistency of feces was scored visually. Nasal swab specimens for indirect immunofluorescent antibody testing for coronavirus and fecal samples for oocyst determination were obtained approximately every third day. Of 7 calves that were given only coronavirus, 3 developed diarrhea of short duration. Of 7 calves that were given only coccidia oocysts, 6 developed diarrhea. All 7 calves inoculated initially with coccidia and subsequently with coronavirus developed diarrhea. For 5 of 7 replicates, calves that were given coccidia and coronavirus developed diarrhea first. When overall severity, measured by fecal score and by blood in the feces, was compared, calves inoculated with coccidia followed by coronavirus were more severely affected (P less than 0.05) than were calves that were given only coronavirus. Calves that were given only coccidia oocysts appeared more severely affected than calves that were given only coronavirus, but differences were not significant.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

4.
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.  相似文献   

5.
OBJECTIVE: To evaluate therapeutic efficacy of a high extralabel dose of ceftiofur for treatment of experimental salmonellosis in neonatal calves. ANIMALS: Forty-two 1- to 4-day-old Holstein bull calves. PROCEDURE: 36 calves were orally challenged with Salmonella enteritica serovar Typhimurium (6.5 x 10(8) colony-forming units). Six additional calves were retained as nonmedicated nonchallenged control calves. Four days following Salmonella challenge, surviving calves were randomly allocated to ceftiofur-treated (5 mg/kg, IM, q 24 h) or nonmedicated control groups. Calves assigned to the treated group were medicated daily for 5 days starting on day 4 after challenge. Calves were monitored for 18 days following Salmonella challenge. Outcome assessments included clinical parameters (attitude, appetite, fecal characteristics, and rectal temperature), mortality rate, and quantitative Salmonella culture of fecal samples, mesenteric lymph nodes, and cecal contents. RESULTS: Ceftiofur treatment was associated with a significant decrease in rectal temperature and diarrhea. Three of 15 medicated calves and 4 of 14 non-medicated calves died or were euthanatized between days 4 and 18. A significant decrease in fecal shedding of Salmonella organisms was observed in treated calves, compared with nonmedicated calves. Salmonella organisms were isolated from all 10 non-medicated calves at necropsy, whereas no Salmonella organisms were isolated from 5 of 12 medicated calves. CONCLUSIONS AND CLINICAL RELEVANCE: Treatment of salmonellosis in neonatal calves with a high extralabel dose of ceftiofur (5 mg/kg, IM, q 24 h) promotes animal welfare, reduces fecal shedding of Salmonella organisms, and may promote clearance of Salmonella infections when plasma ceftiofur concentrations are maintained above minimal inhibitory concentrations.  相似文献   

6.
OBJECTIVE: To determine effects of the selectin inhibitor TBC1269 on neutrophil-mediated pulmonary damage during acute Mannheimia haemolytica-induced pneumonia in newborn calves. ANIMALS: Eighteen 1- to 3-day-old colostrum-deprived calves. PROCEDURE: Mannheimia haemolytica or saline (0.9% NaCl) solution was inoculated in both cranial lung lobes of 12 and 6 calves, respectively. Calves were euthanatized 2 (saline, n = 3; M haemolytica, n = 4) or 6 hours (saline, n = 3; M haemolytica, n = 8) after inoculation. Four M haemolytica-inoculated calves euthanatized at 6 hours also received TBC1269 (25 mg/kg, IV) 30 minutes before and 2 hours after inoculation. Conjugated diene (CD) concentrations, inducible nitric oxide synthase (iNOS) expression, and apoptotic cell counts were determined in lung specimens collected during necropsy. RESULTS: Conjugated diene concentrations were significantly increased in all M haemolytica-inoculated groups, compared with saline-inoculated groups. Calves treated with TBC1269 had decreased concentrations of CD, compared with untreated calves, although the difference was not significant. Number of apoptotic neutrophils and macrophages increased significantly inTBC1269-treated calves, compared with untreated calves. Inducible nitric oxide synthase was expressed by epithelial cells and leukocytes. However, iNOS was less abundant in airway epithelial cells associated with inflammatory exudates. Degree of iNOS expression was similar between TBC1269-treated and untreated calves. CONCLUSIONS: Mannheimia haemolytica infection in neonatal calves resulted in pulmonary tissue damage and decreased epithelial cell iNOS expression. The selectin inhibitor TCB1269 altered, but did not completely inhibit, neutrophil-mediated pulmonary damage.  相似文献   

7.
Recrudescence of bovine herpesvirus-5 in experimentally infected calves   总被引：2，自引：0，他引：2  
A latent infection of bovine herpesvirus-5 (BHV-5) was established in 4 calves. These calves, plus 2 controls, were given dexamethasone (DM) to reactivate the latent virus. The 4 principal calves developed antibodies to BHV-5 by postinoculation day (PID) 21. Antibody titers increased until PID 42 before decreasing to low levels of PID 75. After the first DM treatment (started on PID 76), an anamnestic antibody response was demonstrated in the 4 principal calves. Calves, 2, 3, and 4 were euthanatized and necropsied at PID 121, and their antibody titers were again decreasing. The virus BHV-5 was not isolated from the tissues by conventional techniques of viral isolation but was isolated from the trigeminal ganglion and spinal cord of calf 3 by explantation techniques. The BHV-5 was isolated, using conventional viral isolation techniques, from a nasal swab sample of calf 1 on PID 91 (15 days after the first DM treatment) and from the thoracic lymph node 6 days after the start of a 2nd DM treatment. Seemingly, BHV-5 may be latently harbored in the nerve tissues or calves and this virus may be reactivated from the upper respiratory tract following subsequent DM treatment.  相似文献   

8.
Sixteen 7-week-old Holstein male calves were inoculated with sporulated oocysts of Eimeria zuernii. Four calves (controls) were euthanatized and necropsied at 14 and 20 days after inoculation (DAI). Two calves were treated with 20 mg of dexamethasone (IM) on 13, 14, and 15 DAI and euthanatized and necropsied 17 DAI and 2 calves were given similar treatments and necropsied 20 DAI. The 8 other calves were euthanatized and necropsied 20 DAI. Two were started on the anticoccidial drug decoquinate in feed 13 DAI; 2 others were given decoquinate on the same schedule plus dexamethasone on 13,14, and 15 DAI. Two calves were given the antibiotic narasin in feed beginning 13 DAI and 2 calves were given parasin on the same schedule plus dexamethasone on 13,14, and 15 DAI. All calves, except 2 controls necropsied 14 DAI and 4 calves given decoquinate, discharged moderate-to-large numbers of oocysts in feces and had moderate-to-serve changes in fecal consistency. Histologic examinations revealed large numbers of endogenous stages in tissues of calves treated or not treated with dexamethasone. Few endogenous stages were observed in tissues from calves that were given decoquinate or decoquinate plus dexamethasone. Calves given narasin or narasin plus dexamethasone had moderate-to-large numbers of endogenous stages in the tissues.  相似文献   

9.
OBJECTIVE: To measure antibody titers against bovine coronavirus (BCV), determine frequency of BCV in nasal swab specimens, and compare calves treated for bovine respiratory tract disease (BRD) between those given an intranasally administered vaccine and control calves. DESIGN: Randomized clinical trial. ANIMALS: 414 heifer calves. PROCEDURE: Intranasal BCV antigen concentration and antibody titer against BCV were measured on entry to a feedlot. Calves were randomly assigned to receive 3.0 mL of a modified-live virus vaccine against bovine enteric coronavirus and rotavirus or 3.0 mL of saline (0.9% NaCl) solution. Calves were confined to 1 of 2 pens, depending on vaccination status, for a minimum of 17 days of observation (range, 17 to 99). Selection of calves for treatment of BRD and scoring for severity of disease were done by veterinarians unaware of treatment status. RESULTS: Intranasal BCV (125/407 [31%]) and serum antibody titers > or = 20 against BCV (246/396 [62%]) were identified in calves entering the feedlot. Vaccination was associated with significant decrease in risk of treatment for BRD; intranasal BCV on entry to the feedlot was associated with increased risk of treatment. Univariate analysis revealed that control calves with intranasal BRD on entry to the feedlot and those with antibody titer < 20 were significantly more likely to be treated for BRD. CONCLUSIONS AND CLINICAL RELEVANCE: These data provide further evidence of an association between BCV and respiratory tract disease in feedlot calves. An intranasally administered vaccine appeared to reduce risk of treatment for BRD.  相似文献   

10.
OBJECTIVE: To determine whether a single intranasal dose of modified-live bovine respiratory syncytial virus (BRSV) vaccine protects calves from BRSV challenge and characterize cell-mediated immune response in calves following BRSV challenge. ANIMALS: 13 conventionally reared 4- to 6-week-old Holstein calves. PROCEDURES: Calves received intranasal vaccination with modified live BRSV vaccine (VC-group calves; n = 4) or mock vaccine (MC-group calves; 6) 1 month before BRSV challenge; unvaccinated control-group calves (n = 3) underwent mock challenge. Serum virus neutralizing (VN) antibodies were measured on days -30, -14, 0, and 7 relative to BRSV challenge nasal swab specimens were collected for virus isolation on days 0 to 7. At necropsy examination on day 7, tissue specimens were collected for measurement of BRSV-specific interferon gamma (IFN-gamma) production. Tissue distribution of CD3+ T and BLA.36+ B cells was evaluated by use of immunohistochemistry. RESULTS: The MC-group calves had significantly higher rectal temperatures, respiratory rates, and clinical scores on days 5 to 7 after BRSV challenge than VC-group calves. No difference was seen between distributions of BRSV in lung tissue of VC- and MC-group calves. Production of BRSV-specific IFN-gamma was increased in tissue specimens from VC-group calves, compared with MC- and control-group calves. Virus-specific IFN-gamma production was highest in the mediastinal lymph node of VC-group calves. Increased numbers of T cells were found in expanded bronchial-associated lymphoid tissue and airway epithelium of VC-group calves. CONCLUSIONS AND CLINICAL RELEVANCE: An intranasal dose of modified-live BRSV vaccine can protect calves against virulent BRSV challenge 1 month later.  相似文献   

11.
A protein A-colloidal gold immunoelectron microscopy (PAG-IEM) technique was developed for the detection of bovine coronavirus (BCV) in the feces and nasal secretions of infected calves. Feces or nasal swab fluids were incubated sequentially with hyperimmune bovine anti-bovine coronavirus serum and protein A-gold, negatively stained, applied to formvar-coated copper grids and viewed using an electron microscope. The PAG-IEM method specifically identified BCV particles and possible subviral particles in feces and nasal-swab fluids from infected calves. The PAG-IEM method did not label other enveloped enteric viruses or morphologically similar fringed particles commonly found in feces. Detection of BCV using PAG-IEM was compared with ELISA and direct immunofluorescence (IF) of nasal epithelial cells by monitoring fecal and respiratory tract shedding of BCV from two experimentally infected and two naturally infected calves from birth to 3 weeks of age. PAG-IEM and ELISA detected shedding of BCV in fecal (4/4 animals) and nasal (3/4 animals) samples for an average of 5.25 days each. The observed agreement of BCV detection by PAG-IEM and ELISA was 85%. PAG-IEM may be a more sensitive immunoassay for the detection of BCV in diagnostic specimens from infected neonatal calves than ELISA. BCV infection of nasal epithelial cells was detected by immunofluorescence in 4/4 calves, persisted for the duration of the study in 2/4 calves and was sporadic in the other two animals. The observed agreement of BCV detection by PAG-IEM and IF was 57%.  相似文献   

12.
Hysterectomy-produced colostrum-deprived 5- and 27-day-old pigs were inoculated intramuscularly (IM) or intranasally (IN) with the temperature-sensitive and thymidine kinase-deficient ZHtsTK- strain of Aujeszky's disease virus (ADV), and the nasal swabs and organs of the pigs were periodically collected for virus isolation. No abnormal clinical signs were observed in these pigs, except for a mild febrile response. Viral shedding in the nasal swabs with low titers was detected in the pigs inoculated IN between postinoculation day (PID) 1 and 5, but not in those of the pigs inoculated IM. No contact infection, however, occurred in the cohabiting pigs. Viruses with low titers were isolated only from the muscles and lymph nodes at the site of inoculation in the pigs inoculated IM on PID 2 and 4, but not from any organs of the pigs inoculated IN. To investigate the ability of the ZHtsTK- strain to establish a latent infection in pigs, the pigs inoculated IM or IN with the ZHtsTK- strain were treated with prednisolone. No virus was detected in the trigeminal ganglia or the nasal swabs collected after prednisolone treatment by the cocultivation method. The immunological evaluation demonstrated that immunization of pigs with this strain was effective in preventing clinical signs caused by ADV infection. The duration of virus shedding was markedly shortened in immunized pigs, particularly in those immunized twice and the total quantity of virus recovered from immunized pigs was reduced in comparison with unimmunized pigs.  相似文献   

13.
Clinical signs of a winter dysentery-like syndrome in 6- to 9-month-old cattle in 3 feedlots included acute onset of diarrhea with high morbidity and low mortality, respiratory tract problems that included dyspnea, coughing, and nasal discharge, and high rectal temperatures. Bovine coronavirus was detected by use of an ELISA and immune electron microscopy in fecal and nasal swab samples and by immunohistochemical analysis of intestinal sections collected from calves during necropsy. Bovine coronavirus should be considered in the differential diagnoses for diseases that cause acute onset of bloody diarrhea in feedlot cattle.  相似文献   

14.
Fecal and nasal samples were collected from 180 calves with diarrhea and 36 clinically normal co-habitants, and tested for virus using HRT-18 cell cultures derived from human rectal adenocarcinoma. A cytopathic virus was isolated from 5 fecal and 56 nasal samples obtained from diarrheic calves. All calves in which the virus was isolated from diarrheic feces were positive for virus isolation from nasal swabs. The virus was also isolated from the nasal swabs of 10 clinically normal calves that were co-habitants with diarrheic calves. Because they were morphologically similar to coronavirus, agglutinated mouse erythrocytes and serologically identical with the Nebraska calf diarrhea coronavirus, new isolates were identified as bovine coronavirus. The demonstration of viral antigens in nasal epithelial cells by a direct immunofluorescence was in close agreement with the virus isolation in HRT-18 cell cultures. This is the first report on the isolation of bovine coronavirus from newborn calves with diarrhea in Japan. The evidence that the virus was frequently isolated from nasal swabs is of great interest for understanding the pathogenesis of bovine coronavirus infection.  相似文献   

15.
Blood, feces, and nasal swabs specimens were collected 12 to 24 hours after birth and then 3 times/week (blood only once per week) from one group of 10 calves until they were 10 weeks old and from a second group of 10 calves until they were 10 to 20 weeks old. Colostrum was collected from all calves' dams and tears from 5 randomly selected calves in the first group. All fecal and nasal specimens were assayed for bovine coronavirus (BCV) antigens by ELISA. Nasal epithelial cells were examined for BCV antigens by direct immunofluorescence. Isotype antibody titers to BCV in all samples from 5 calves in group 1 were evaluated by ELISA. Zinc sulfate turbidity (ZST) values were determined on the first serum samples taken from all calves in group 1. To determine whether any correlation existed between ZST values, isotype antibody titers to BCV (12 to 24 hours after birth), number of respiratory sick days, number of enteric sick days, or days to first shedding of virus, a Spearman rank order correlation coefficient was done. Bovine coronavirus respiratory tract and enteric tract infections were common on this farm. Most initial infections developed when calves were 1 to 3 weeks old; however, there were also multiple incidences of shedding of viral antigens or seroconversions at later times during the study. Persistence of infection or reinfection of the upper respiratory tract with BCV was common. Colostral antibody titers to BCV (IgG1) were in all cows at moderate amounts; however, calf serum antibody titers and ZST values (12 to 24 hours after birth) were highly variable.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

16.
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.  相似文献   

17.
Intestinal lesions caused by a virus serologically unrelated to the calf diarrheal rotavirus or coronavirus were studied in gnotobiotic calves. The virion purified from feces from infected calves was a fringed particle with a diameter of about 100 nm. The incubation period from time of inoculation per orum to onset of diarrhea in calves was as short as 8 hours. The viral infection in bacteria-free calves or calves not contaminated with pathogenic bacteria caused severe illness for only 24 hours. When bacteria such as the K99 antigen Escherichia coli were present, the combined infection caused mortality. Lesions occurred only in the small intestinal villous epithelium. Calves euthanatized shortly before or after the onset of diarrhea had developed villous epithelial cell syncytia that contained numberous virions in the cytoplasm. Within 2 to 3 hours after onset of diarrhea, the infected cells were shed and the villi had denuded tips or had cuboidal to squamous epithelial cells.  相似文献   

18.
Nine young calves given respiratory syncytial virus by a combined intranasal and intratracheal route developed a severe respiratory tract disease in which coughing, tachypnea, and hyperpnea were prominent clinical features. Calves were euthanatized on postinoculation (initial) days (PID) 1 to 13. At necropsy, large areas of consolidation were present in the cranial, middle, accessory, and cranial parts of the caudal lung lobes of calves killed between PID 4 and 13. Histopathologic examination revealed widespread and severe lesions in small bronchi, bronchioli, and alveoli. Multinucleate epithelial syncytia on bronchiolar and alveolar walls, many containing eosinophilic intracytoplasmic inclusion bodies, were present in the lungs of calves killed on PID 4, 5, and 6. Necrosis and epithelial loss, hyperplasia, and metaplasia were also observed in the epithelium of small bronchi and bronchioli. The lumina of these airways were occluded to varying degrees with exudate. Exudate was present within alveoli, and interalveolar septa were markedly thickened. Collapse of the thickened septa produced large areas where alveolar air spaces were totally obliterated. Repair was evident in the lungs of calves killed at PID 10 and 13 with reepithelialization of damaged bronchiolar mucosa, organization of bronchiolar exudate leading to bronchiolitis obliterans, and peribronchial and peribronchiolar fibrosis. Inoculation of 3 calves by an intranasal route alone produced a less severe clinical disease with only minimal lesions present at necropsy.  相似文献   

19.
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20.
OBJECTIVE: To determine the effect of intranasal exposure to live leukotoxin (LktA)-deficient Mannheimia haemolytica (MH) at the time of feedyard arrival on nasopharyngeal colonization by wild-type MH in calves. ANIMALS: 200 calves. PROCEDURE: Calves from Arkansas (AR calves; n = 100; mean body weight, 205 kg) were purchased from an order buyer barn. Calves from New Mexico (NM calves; n = 100; mean body weight, 188 kg) were obtained from a single ranch. Calves were transported to a feedyard, where half of each group was exposed intranasally with LktA-deficient MH at the time of arrival. Calves were observed daily for respiratory tract disease (RTD), and nasal swab specimens were collected periodically to determine nasopharyngeal colonization status with MH. Serum samples were assayed for antibodies to MH. RESULTS: 15 AR calves had nasopharyngeal colonization by wild-type MH at the order buyer barn, whereas none of the NM calves had nasopharyngeal colonization. Intranasal exposure to LktA-deficient MH elicited an increase in serum antibody titers against MH in NM calves, but titers were less in NM calves treated for RTD. Exposure of NM calves to LktA-deficient MH offered protection from nasopharyngeal colonization by wild-type MH. CONCLUSIONS AND CLINICAL RELEVANCE: Exposure of calves to LktA-deficient MH elicited an increase in serum antibody titers against MH and decreased colonization of the nasopharynx by wild-type MH. Earlier exposure would likely allow an immune response to develop before transportation and offer protection from nasopharyngeal colonization and pneumonia caused by wild-type MH.  相似文献   

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