Coronavirus infections in the laboratory rat: degree of cross protection following immunization with a heterologous strain.

One hundred and twenty-one specific pathogen-free male Wistar rats eight to ten weeks of age were used to evaluate the efficacy of Parker's rat coronavirus (PRC) in affording cross protection on subsequent challenge with virulent sialodacryoadenitis (SDA) virus. Sixty-two animals were inoculated intranasally on day 0 and 21 days later with approximately 10(2) median tissue culture infective doses (TCID50) of the tenth passage of PRC replicated in L-2 cells. Animals were selected at random postvaccination to evaluate the safety and efficacy of PRC by histopathology, immunohistochemistry and serology. At three and six months postvaccination (PV), vaccinated and seronegative control rats were inoculated intranasally with approximately 10(3) TCID50 doses of virulent SDA virus. Challenged rats were then killed at 6, 10 and 14 days postchallenge and necropsied. Evaluations were based on lesion indices in lacrimal and salivary glands and respiratory tract, the presence of viral antigen by immunohistochemistry, and antibody response. Lesions were observed in rats killed PV, but in general, they were significantly reduced compared with those present in seronegative animals post-exposure to virulent SDA virus (p < or = 0.05). However, they were still considered to be an unacceptable level for a routine vaccination procedure. Potvaccination antibody titers to rat coronavirus were evident in all animals tested at three or six months prior to challenge with SDA virus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sialodacryoadenitis virus-associated lesions in the lower respiratory tract of rats

Eight- to 10-week-old outbred Wistar rats were inoculated intranasally with 10(2.9) medium mouse lethal infective doses of sialodacryoadenitis (SDA) virus. Sham inoculated control rats and challenged rats were killed at 1 day intervals for the first 8 days, then on days 10, 12, 14, and 20. Typical lesions associated with SDA were seen microscopically in the salivary and lacrimal glands of inoculated rats. In addition, laryngitis, tracheitis, bronchitis, bronchiolitis, and multifocal alveolitis were present during the acute stages of the disease. Viral antigen was demonstrated in epithelial cells lining airways by immunofluorescence microscopy. SDA virus was recovered from the lower respiratory tract from days 2 to 6 post-inoculation (PI). Serum antibodies to SDA virus, but not to Sendai virus or Mycoplasma pulmonis were present in rats tested at day 20 PI. These findings demonstrate that during the acute stages of the disease, significant lesions do occur in the lower respiratory tract of SDA virus-infected rats.     

Sialodacryoadenitis in the rat: effects of immunosuppression on the course of the disease

Eight-week-old outbred male and female Crl:CD(SD)BR rats were treated with prednisolone (PR) or cyclophosphamide (CY) and were inoculated intranasally with sialodacryoadenitis (SDA) virus. The course of the disease was compared with nonimmunosuppressed, SDA virus-inoculated rats of the same stock. Criteria used to compare SDA in the 3 groups, included histologic changes in salivary and lacrimal glands, immunofluorescent microscopy of paraffin-embedded tissues, serum amylase levels, and antibody response. Based on these criteria, there was little detectable difference in the course and intensity of SDA in PR-treated and nonimmunosuppressed rats. In CY-treated rats, there was a delay in the onset of SDA, in the appearance of inflammatory cells in affected glands, and in the reparative process in the salivary and lacrimal glands. Viral antigen persisted longer in CY-treated rats than in PR-treated and nonimmunosuppressed rats. Antibody to SDA virus was not detected in CY-treated rats. The efficacy of immunosuppression by PR and CY was confirmed by the sheep erythrocyte agglutination procedure performed in selected rats. Male and female rats of the same strain were immunosuppressed beginning 4 weeks after inoculation with SDA virus to produce recrudescence of the disease. Histologic examination of salivary and lacrimal glands, immunofluorescent microscopy, serum amylase values, and viral isolation studies did not reveal evidence of reactivation of a persistent viral infection or viral shedding. Based on these studies, there is no evidence that SDA virus may persist as an inapparent infection after recovery from the disease.     

Sequential changes in the harderian and exorbital lacrimal glands in Wistar rats infected with sialodacryoadenitis virus

A sequential light and electron microscopic study of the exorbital and Harderian lacrimal glands was done on 2.5- to 15-month-old Wistar rats exposed to sialodacryoadenitis (SDA) virus. Typical coronaviral particles were readily demonstrated in cytoplasmic vesicles of Harderian and exorbital glands examined at 6 days post-inoculation. Lesions were seen in a relatively high percentage of lacrimal glands in infected animals of all ages, with no obvious age-related variations in the incidence and extent of changes. Lesions frequently persisted for a longer interval post-exposure in lacrimal glands than in salivary glands. The persistence of lesions commonly seen in Harderian glands was attributed, at least in part, to the cytotoxic effects of porphyrin-containing secretions released during the acute necrotizing stages of the disease. The persistence of lesions in some lacrimal glands indicates that they are useful tissues for microscopic examination for the retrospective provisional diagnosis of SDA. Persistent lesions also indicate that normal functions of these glands may be compromised for up to several weeks following outbreaks of SDA.     

Effects of an orally administered live Escherichia coli pilus vaccine on duration of lacteal immunity to enterotoxigenic Escherichia coli in swine

Primigravid swine were vaccinated orally with a live enterotoxigenic Escherichia coli (ETEC) strain that produces pilus antigen K99. The titers of K99 antibody in colostrum and milk of vaccinates remained higher than those of nonvaccinated controls through the first lactation after vaccination (4 weeks). Some control swine had low titers of K99 antibody in colostrum or developed low titers of K99 antibody in milk during lactation. Lacteal K99 antibody titers of vaccinates dropped to control levels during the second lactation, 6 months after vaccination. Pigs suckling vaccinates and controls were equally susceptible to challenge exposure to K99+ ETEC during the second lactation. Orally vaccinated swine given a parenteral booster vaccination (with killed K99+ ETEC) during their second gestation had K99 antibody in milk through their second lactation. During the second lactation, these orally vaccinated parenterally revaccinated swine had higher titers of K99 antibody in postcolostral milk than did nonvaccinated controls, controls given only the parenteral booster injection, or controls vaccinated parenterally during both gestations.     

Interaction of a combined feline viral rhinotracheitis-feline calicivirus vaccine and the FVR carrier state.

The effect of field feline viral rhinotracheitis (FVR) virus challenge on cats previously vaccinated with a combined FVR/feline calicivirus intramuscular vaccine was studied in relation to the development of an FVR carrier state. There was no virus shedding of either of the two vaccine viruses following vaccination. Treatment with corticosteroid 60 days after vaccination and before challenge with FVR virus did not induce virus re-excretion in vaccinates or controls; neither did similar treatment induce shedding 63 days after challenge of both vaccinates and controls with virulent field virus. After a further 55 days however, FVR virus shedding was elicited in one of four previously vaccinated and challenged cats compared with two of four unvaccinated and challenged controls. Two sentinel cats remained virologically and serologically free of FVR throughout. The vaccine was shown to be effective in controlling the disease; 12 weeks after initial vaccination no clinical signs were seen in three of four cats following intranasal challenge with 10(5)CCID50 of virulent field FVR virus, and a mild transient unilateral ocular and nasal discharge was seen in the remaining cat for one day only. Severe clinical signs of approximately 10 days' duration were seen in all four unvaccinated challenged controls. The virological and serological responses of the cats were also recorded.     

Efficacy of an inactivated respiratory syncytial virus vaccine in calves.

OBJECTIVE: To determine whether an inactivated bovine respiratory syncytial virus (BRSV) vaccine would protect calves from infection with virulent BRSV. DESIGN: Randomized controlled trial. ANIMALS: 27 nine-week-old calves seronegative for BRSV exposure. PROCEDURE: Group-1 calves (n = 9) were not vaccinated. Group-2 calves (n = 9) were vaccinated on days 0 and 21 with an inactivated BRSV vaccine containing a minimum immunizing dose of antigen. Group-3 calves (n = 9) were vaccinated on days 0 and 21 with an inactivated BRSV vaccine containing an amount of antigen similar to that in a commercial vaccine. All calves were challenged with virulent BRSV on day 42. Clinical signs and immune responses were monitored for 8 days after challenge. Calves were euthanatized on day 50, and lungs were examined for lesions. RESULTS: Vaccination elicited increases in BRSV-specific IgG and virus neutralizing antibody titers and in production of interferon-gamma. Virus neutralizing antibody titers were consistently less than IgG titers. Challenge with BRSV resulted in severe respiratory tract disease and extensive pulmonary lesions in control calves, whereas vaccinated calves had less severe signs of clinical disease and less extensive pulmonary lesions. The percentage of vaccinated calves that shed virus in nasal secretions was significantly lower than the percentage of control calves that did, and peak viral titer was lower for vaccinated than for control calves. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the inactivated BRSV vaccine provided clinical protection from experimental infection with virulent virus and decreased the severity of pulmonary lesions. Efficacy was similar to that reported for modified-live BRSV vaccines.     

Immune response of pigs inoculated with virulent pseudorabies virus and pigs inoculated with attenuated or inactivated pseudorabies virus vaccine before and after challenge exposure

Pseudorabies virus (PRV) antibodies, detectable by indirect radioimmunoassay (IRIA), serum-virus neutralization test (NT), or microimmunodiffusion test (MIDT) were developed within 8 days after pigs were inoculated with virulent PRV or attenuated PRV vaccine. Indirect radioimmunoassay and NT titers in pigs inoculated with virulent PRV were developed at the same rate, with IRIA titers being higher than NT titers. Pigs inoculated with attenuated or inactivated PRV vaccine developed peak mean prechallenge NT antibody titers of 4 and 1 (reciprocals of serum dilutions), respectively. Pigs inoculated with attenuated PRV vaccine had peak mean prechallenge IRIA antibody titers of 6, whereas pigs inoculated with inactivated PRV vaccine had mean IRIA antibody titers of 64. Challenge exposure of swine inoculated with attenuated or inactivated PRV vaccine elicited quantitatively equivalent responses, as measured by IRIA or NT, which were higher than prechallenge titers. There were no false-positive IRIA, NT, or MIDT results obtained when sera from nonvaccinated, nonchallenge-exposed pigs were tested. It appears that the PRV infection status of a seropositive swine herd could be ascertained by serologically monitoring several representative animals from a herd, using the NT. If 2 or more tests of representative animals at 14-day intervals were done and the mean NT titer was 4 or less, it could be concluded that the herd was vaccinated against, but not infected with, virulent virus.     

Immune response of cattle to antigens obtained from bovine herpesvirus 1-infected tissue culture.

The ability of two antigens, termed EV and CM, derived from bovine herpesvirus 1 infected cultures to produce serum-virus neutralizing antibodies has been studied in cattle. Both EV and CM when inoculated with adjuvant induced significant increases in serum-virus neutralizing antibody titers. Control groups inoculated in a similar manner failed to induce significant increases in serum-virus neutralizing antibody. Some of the animals were vaccinated, then were bred, challenged with a virulent strain of bovine herpesvirus 1 and held until calving was completed. During this 18-month period titers declined slowly in the vaccinated animals. Proportionally there were fewer live calves born to the control cattle than to the CM vaccinated group but reduction was not large enough to conclude that this vaccine had protected the cattle against the abortigenic activity of bovine herpesvirus 1. Further challenge studies should be made to determine whether the administration of these antigens can prevent the subsequent onset of the clinical signs associated with bovine herpesvirus 1.     

3种非猪瘟病毒单独或混合感染对猪瘟弱毒疫苗免疫效力的影响

将 2 0头 9月龄左右猪瘟、伪狂犬、猪繁殖与呼吸障碍综合征抗原、抗体阴性猪分成 6组 ,分别利用猪细小病毒(PPV)、猪伪狂犬病毒 (PRV)和猪繁殖与呼吸障碍综合征病毒 (PRRSV)单独或混合感染。 7d后连同对照猪 4头 ,免疫接种猪瘟兔化弱毒疫苗 (HCL V) ,13d后连同 4头阴性对照猪一起攻击猪瘟石门强毒。整个试验期间分别每天测温 ,观察临床症状 ,每周采集扁桃体和血样做各种病毒抗原及抗体检测。结果表明 ,非猪瘟病毒感染 7d后 ,所有各组猪均从体内检测到了相应感染的病原 ,表明 3种非猪瘟病毒感染成功。在攻击猪瘟石门强毒后 2周 ,感染了非猪瘟病毒后接种 HCL V疫苗的 4个免疫组 12头猪除 1头外 ,11头全为猪瘟病毒 (HCV)抗原检测阳性 ,且多呈强阳性 ;而单一 HCL V疫苗免疫组在猪瘟强毒攻击后检测不到 HCV;所有 HCL V疫苗免疫猪均存活 ,而非免疫对照组 4头猪全部在攻毒 16 d内死亡。     

Duration of immunity in foxes vaccinated orally with ERA vaccine in a bait.

Red foxes (Vulpes vulpes) vaccinated orally with the ERA strain of rabies vaccine in a bait were challenged after 83 mo. Ten of 11 foxes that had seroconverted following vaccination resisted challenge with a virulent rabies virus which produced clinical signs of rabies in 6 of 6 unvaccinated foxes. Five of 11 vaccinated animals retained titers of rabies virus neutralizing antibody throughout the period. Although 6 of 11 had no detectable antibody at the time of challenge, 5 of these 6 resisted challenge and had an anamnestic response, as indicated by elevated titers of antibody when measured at day 77 postchallenge. These results show that foxes can be immunized successfully with a single oral dose of ERA vaccine, probably with protection against a lethal rabies challenge, for at least 7 y.     

Studies on the efficacy of intranasal vaccination for the prevention of experimentally induced parainfluenza type 3 virus pneumonia in calves.

The efficacy of intranasal vaccination in preventing or limiting disease of the lower respiratory tract induced by parainfluenza 3 (PI3) virus was evaluated under experimental conditions, using a commercially available live vaccine containing a temperature-sensitive strain of PI3 virus. In a preliminary study four colostrum-deprived calves were vaccinated intranasally at one week and again at two months of age, and two similar calves were given an intranasal placebo. After the second vaccination serum antibodies to PI3 virus were detected in all four vaccinated calves, but not in the control animals. Seventeen days after the second vaccination all six calves were challenged with virulent PI3 virus, and they were killed six days later. The clinical scores and the extent of pulmonary consolidation were reduced in the vaccinated animals; PI3 virus was detected in the upper and lower respiratory tract of the control calves but in none of the vaccinated calves. In a larger scale study with 14 colostrum-fed calves, seven were vaccinated at one week and again at five weeks of age, and seven were given an intranasal placebo. Two weeks after the second vaccination all 14 calves were challenged with virulent PI3 virus. The clinical scores and lung consolidation were significantly reduced in the vaccinated calves in comparison with the controls. Six days after infection, 10 of the 14 calves were killed; PI3 virus was detectable in the nasal secretions of all seven control calves but in only one of the vaccinated animals, and PI3 viral antigen was detected in the lungs of the control calves but not in those of the vaccinated animals. One of the vaccinated calves had developed a severe clinical response after the challenge, but it had only minor lung consolidation when killed.     

LABORATORY AND FIELD STUDIES WITH A BOVINE EPHEMERAL FEVER VACCINE

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

Fowl cholera immunity in broiler breeder chickens determined by the enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) was developed to detect antibodies in broiler breeders vaccinated (wing web) with the CU fowl cholera vaccine. Birds were bled weekly from 9 to 26 weeks, every other week from 26 to 40 weeks, and every 4 weeks from 40 to 56 weeks of age. Overall mean ELISA antibody titers (9 to 56 weeks) reported as log10 values and survivability of the vaccinates after virulent challenge were as follows: unvaccinated--5.75, 48%; birds vaccinated once at 8 weeks--5.91, 78%; birds vaccinated twice at 8 and 14 weeks--6.11, 100%; birds vaccinated thrice at 8, 14, and 20 weeks--6.23, 100%; birds vaccinated twice at 8 and 20 weeks--6.12, 100%; and birds vaccinated twice at 8 and 20 weeks (plus fowl pox at 8 weeks)--6.08, 95%. Survivability in the vaccinates after virulent challenge with strain X-73 Pasteurella multocida was 100% in birds with ELISA antibody titers (log10) greater than 6.02. Under the conditions of this experiment, birds vaccinated two or three times between 8 and 20 weeks proved to be sufficiently immune at 56 weeks of age to withstand a virulent fowl cholera challenge. Birds not vaccinated or vaccinated only once at 8 weeks were not sufficiently immunized to withstand virulent challenge.     

Immune response of sows and their offspring to pseudorabies virus: serum neutralization response to vaccination and field virus challenge.

One month prior to breeding, sows were vaccinated with an attenuated pseudorabies virus vaccine or challenged with a field strain of pseudorabies virus. A third group of sows were not vaccinated or challenged before breeding. Pigs from these sows were vaccinated at 3, 6, or 12 weeks of age and challenged with virulent virus three weeks later. One pig from each litter served as an unvaccinated, unchallenged control. Serum neutralization titers of these pigs were monitored from birth until 22 weeks of age. Titers of the sows were monitored through breeding, gestation and farrowing. The maximum prefarrowing anti-pseudorabies virus titer in the field virus challenged sows occurred four weeks following challenge. A significant decline in titers occurred at farrowing. Titers rose from one week postfarrowing and then declined. Titers in the field virus infected sows were consistently two to threefold greater than those of the vaccinated sows. The maximum prefarrowing anti-pseudorabies virus titer in the vaccinated sows occurred six weeks following vaccination. The geometric mean titer in these sow's then decreased and increased for two weeks after farrowing. The results in the pigs can be summarized as follows: Pigs from control sows had a greater serological response following field virus challenge than following vaccination with a modified live virus. Pigs from control sows responded serologically to vaccination at 3, 6 and 12 weeks of age. Pigs from control sows which were challenged at 6, 9 and 15 weeks of age had similar antibody responses. Pigs from vaccinated sows had no increase in titer following vaccination at three and six weeks of age. Titers increased when these pigs were vaccinated at 12 weeks of age. There was no significant increase in mean titers of pigs from challenged sows following vaccination at 3, 6 and 12 weeks of age. Vaccinated pigs from control and vaccinated sows had a secondary response following challenge three weeks after vaccination.(ABSTRACT TRUNCATED AT 250 WORDS)     

Depletion of salivary gland epidermal growth factor by sialodacryoadenitis virus infection in the Wistar rat

Male and female Wistar rats 2 to 15 months of age were inoculated intranasally with sialoda-cryoadenitis (SDA) virus and killed at 8 to 21 days post-inoculation (PI). Submandibular glands were evaluated by light and electron microscopy, and levels of salivary gland epidermal growth factor (EGF) were quantitated by cytochemistry and competitive radioreceptor assay. Apical granules in the epithelial cells of the granular convoluted tubules (GCT) were selectively depleted during the acute and convalescent stages of the disease. In addition, levels of immunoreactive EGF were reduced in affected submandibular glands, especially at 8 to 14 days PI with SDA virus, but some evidence of EGF depletion was seen at up to 3 weeks PI. A corresponding transient depletion of EGF receptor reactive salivary EGF was seen between 1 and 3 weeks after experimental SDA infection. These studies suggest that a clinical (or subclinical) infection with SDA virus could have significant effects on experimental studies on EGF-dependent functions, including reproductive physiology and carcinogenesis.     

Experimental rabies in skunks: Immune response and salivary gland infection

Groups of striped skunks (Mephitis mephitis) were inoculated intramuscularly with graded doses of street rabies virus. At various intervals after inoculation, saliva and sera were tested for rabies virus and neutralizing antibodies, respectively. Skunks that developed rabies were killed in terminal stages of the disease and the following examinations were made: titers of virus and antibody in submandibular salivary glands and brain, extent of immunofluorescence in submandibular salivary glands, and histologic examination of various tissues.

Skunks that received inocula containing 4 × 10⁴ to 4 × 10⁵ mouse intracerebral lethal dose₅₀ (MICLD₅₀) had detectable serum neutralizing antibodies by 7–12 days postinoculation; however, most of the skunks that received lower doses (40 to 4 × 10³ MICLD₅₀) did not have detectable serum neutralizing antibodies until clinical signs began. In the salivary glands, slight and extensive immunofluorescence corresponded to high and low titers of tissue neutralizing antibody. Also low viral titers were associated with high tissue neutralizing antibody titers. There was a close correlation between viral titers in right and left submandibular salivary glands.

The results suggest that the immune response can impede the process of infection of the salivary glands resulting in lack of antigen or low amounts of antigen in this tissue. This could occur through interference with centrifugal neural transport of virus and/or neutralization of virus during transfer from neural elements to epithelial cells. Lack of infectious virus or low viral titers in salivary glands containing antigen and high levels of tissue neutralizing antibodies can be caused partly by postmortem virus neutralization (during viral titration).     

Protective immunity induced by a recombinant pseudorabies virus expressing the GP5 of porcine reproductive and respiratory syndrome virus in piglets

Pseudorabies virus (PRV) has been developed as a vaccine vector for expressing foreign immunogens. Porcine reproductive and respiratory syndrome (PRRS), caused by porcine reproductive and respiratory syndrome virus (PRRSV), continues to be a major problem to the pork industry worldwide. Many vaccine strategies have been developed to control the disease but most of them turn out to be unsuccessful. The objective of this research was to explore the feasibility of PRV-based vector vaccine in protection against PRRSV. A live attenuated vaccine-based PRV recombinant expressing the envelope protein GP5 of PRRSV was generated using recombinant DNA techniques. The Bartha-K61-derived recombinant virus, named rPRV-GP5, was shown to express PRRSV GP5 efficiently. Sixteen healthy piglets were assigned to one of four groups (one to four, four pigs per group). Animals in Groups 1 and 2 were each inoculated intramuscularly and intranasally with 10(7.0) PFU of rPRV-GP5 and its parent Bartha-K61, respectively; Group 3 were vaccinated intramuscularly with one-dose of PRRS inactivated vaccine; Group 4 was served as non-vaccinated control. One month later, all animals were all challenged with 10(6.5) TCID(50) of virulent PRRSV CH-1a. All animals in Groups 1 and 3 remained clinically healthy before and after challenge, with only a short period of fever (no more than 41 degrees C and 3 days), mild and gradually improving lung and kidney lesions, and short-term viremia (2 and 3 week, respectively) in spite of no detectable anti-PRRSV antibody before challenge. On the other hand, all animals in the other two groups showed evident clinical signs with higher temperatures (more than 41 degrees C) after challenge, and severe lung, kidney and spleen lesions and extended viremia (4 weeks). The results indicate that the rPRV-GP5 is safe for vaccinates and able to confer significant protection against clinical disease and reduce pathogenic lesions induced by PRRSV challenge in vaccinated pigs.     

牛病毒性腹泻病毒弱毒活疫苗免疫持续期的研究

为检测牛病毒性腹泻病毒(BVDV)弱毒活疫苗在免疫牛体内抗体产生及其消长规律,评价弱毒疫苗的保护效力,并确定免疫持续期,本试验对免疫试验牛每头颈部肌肉接种BVDV SM株弱毒疫苗104.5TCID50,监测血清抗体效价,进行免疫持续期的确定。在疫苗免疫后的6个月、9个月和12个月,分别抽取5头免疫组和5头对照组牛,采用BVDV-JL强毒株进行攻毒试验,每头牛攻毒剂量为6×107.0TCID50/mL。结果显示疫苗免疫后12个月时血清中和抗体效价仍维持在1∶1048以上。攻毒结果显示,在3个不同时间点进行强毒攻击后,免疫组所有动物白细胞数量都没有下降也没有分离到病毒,而对照组动物白细胞数下降均超过30%,6个月和9个月时动物血清中均能分离到病毒,而12个月对照组动物由于年龄大,没有分离到病毒,因此暂定此疫苗的免疫持续期为9个月。     

牛病毒性腹泻弱毒活疫苗免疫持续期的研究

为检测牛病毒性腹泻病毒(BVDV)弱毒活疫苗在免疫牛体内抗体产生及其消长规律,评价弱毒疫苗的保护效力,并确定免疫持续期,本试验对免疫试验牛每头颈部肌肉接种BVDV SM株弱毒疫苗10^4.5TCID₅₀/头,监测血清抗体效价,进行免疫持续期的确定。在疫苗免疫后的6、9和12个月分别抽取5头免疫组和5头对照组牛采用BVDV-JL强毒株进行攻毒试验,每头牛攻毒剂量为6×10^7.0 TCID₅₀/mL。结果显示疫苗免疫后12个月时血清中和抗体效价仍维持在1∶1048以上,攻毒结果显示3个时间点强毒攻击后,免疫组所有动物白细胞数量都没有下降也没有分离到病毒,而对照组动物白细胞数下降均超过30%,6和9个月动物均分离到病毒,而12个月对照组动物由于年龄大,没有分离到病毒,因此暂定此疫苗的免疫持续期为9个月。