Survival of pseudorabies virus in aerosol

The survival of pseudorabies virus in an aerosol was studied under different environmental conditions of temperature and relative humidity. Pseudorabies virus decayed logarithmically with mean half-lives of 17.4 (85% relative humidity, 22 C), 18.8 (25% relative humidity, 22 C), 27.3 (85% relative humidity, 4 C), 36.1 (55% relative humidity, 22 C), and 43.6 (55% relative humidity, 4 C) minutes. Virus survival was significantly improved in environments at 55% relative humidity, compared with those at 85% relative humidity (P = 0.017). Rates of survival were improved in environment at 4 C in comparison with those at 22 C. Results suggest that, under the best conditions of this study, the infectivity of pseudorabies virus in an aerosol decreases by 50% in less than 1 hour.     

Survival of Corynebacterium pseudotuberculosis in axenic purulent exudate on common barnyard fomites

Several inanimate surfaces (eg, plastic, wood, and steel) and particulate fomites (eg, wood shavings, hay, straw, and feces), common to the environment of confined small ruminants, were inoculated with Corynebacterium pseudotuberculosis in axenic purulent exudate that had been surgically removed from a naturally occurring case of caprine caseous lymphadenitis. Each inoculated fomite was incubated at 37, 22, and 4 C, and the length of time that C pseudotuberculosis survived was determined by isolation of bacteria from the fomite. The organism remained viable longer when caseous lymphadenitis abscess contents were mixed with particulate fomites than when spread on surfaces. Incubation at lower temperatures generally extended the survival potential of C pseudotuberculosis. Depending on the particulate fomite and the incubation temperature, viable C pseudotuberculosis organisms were isolated for mean periods ranging from 7 to 55 days, whereas recovery of bacteria from surfaces varied from 1 to 8 days.     

Physicochemical properties of pseudorabies virus hemagglutinin.

Pseudorabies virus hemagglutinin was readily adsorbed on mouse erythrocytes at 4, 22, or 37 degrees C, but not on cattle erythrocytes. The adsorbed hemagglutinin could not be eluted from the cells by resuspending in phosphate-buffered saline (PBS), by incubating at 37 or 50 degrees C, or by incubating in the presence of neuraminidase. The receptor on mouse erythrocytes for the hemagglutinin was inactivated by trypsin, but not by neuraminidase, sodium deoxycholate (DOC), potassium periodate (KIO4), dithiothreitol (DTT), 2-mercaptoethanol (2-ME) and formalin. The hemagglutinin was inactivated by trypsin, alpha-amylase, pepsin, DOC, KIO4, and ethylendiamine-tetraacetic acid (EDTA), but not by papain, beta-glucosidase, phospholipase C, neuraminidase, DTT, 2-ME, Tween-80, ethylether, chloroform, trichloro-trifluoroethane, beta-propiolactone and formalin, suggesting that the hemagglutinin active component involved glycoproteins. The hemagglutinin was stable at 37 degrees C for lower temperatures but not at 60 degrees C or higher. The hemagglutinin activity was resistant to ultraviolet irradiation, while the infectivity was very susceptible. The hemagglutinin and the infectivity were readily sedimented by ultracentrifugation at 48,000 x g for 3 hr. In rate zonal centrifugation of the preparation on a sucrose density gradient, the hemagglutination (HA) activity showed a sharp peak at 1.22 g/ml coinciding with the peak of infectivity. The HA activity in the peak fraction seemed to be structually associated with virus particles. After fractionation of the virus by Nonidet P-40, the HA activity was found only in the fraction of the envelope material, indicating that the hemagglutinin is situated in the viral envelop.     

Laboratory evaluation of selected disinfectants as virucidal agents against porcine parvovirus, pseudorabies virus, and transmissible gastroenteritis virus

Of a variety of disinfectants evaluated, only sodium hypochlorite and sodium hydroxide inactivated porcine parvovirus (PPV) after a 5-minute incubation period. After the same incubation time, pseudorabies and transmissible gastroenteritis viruses were inactivated by all of the disinfectants tested. When the incubation time was increased to 20 minutes, 2% glutaraldehyde and a double-strength concentration of a commercial formaldehyde preparation also inactivated PPV. Formaldehyde vapor and ultraviolet radiations inactivated PPV also, but relatively long exposure times were required.     

Immunoperoxidase plaque staining for the detection of pseudorabies virus.

A quantitative indirect immunoperoxidase plaque staining method was developed for the detection of pseudorabies virus infection in a pig kidney cell line (PK-15). The method is rapid and specific and foci of infection, represented by stained plaques, are easily counted by the unaided eye. Possible modification of this technique in a plaque reduction assay for the detection of antipseudorabies virus antibody is also discussed.     

Survival and immunization of raccoons after exposure to pseudorabies (Aujeszky's disease) virus gene-deleted vaccines

In a controlled experiment, 16 wild-trapped raccoons were exposed to 1 of 2 genetically modified live pseudorabies virus (PRV) vaccines used in swine. One vaccine had genes deleted for thymidine kinase (TK(-)) and glycoprotein G (gG(-)); the other had an additional deletion for glycoprotein E (gE(-)). These vaccines were administered orally and intranasally at four dose levels: 10(3), 10(4), 10(5), and 10(6) TCID(50). The 21 days survival rate was 37.5% for the gG(-)TK(-) vaccine; all of the survivors developed antibodies to PRV. All animals receiving the gG(-)gE(-)TK(-) vaccine survived; 75% (all except the lowest dose) developed anti-PRV antibodies. Survivors were challenged intranasally with a 3.2x10(3) TCID(50) dose of the virulent wildtype PRV Shope strain. Two of the remaining three gG(-)TK(-) vaccinated raccoons survived the challenge; for the gG(-)gE(-)TK(-) vaccine, the survival rate was 50% (4/8). The raccoons with higher vaccine-induced antibody titers were more likely to survive the challenge with the virulent PRV; there was a 100% mortality rate for raccoons lacking detectable anti-PRV antibodies. This experiment indicates that exposure of raccoons to modified live gene-deleted PRV vaccines may result in an immune response, and that this immunity provides some protection against exposure to virulent virus.     

Pathologic changes in ferrets exposed to pseudorabies virus.

Ferrets experimentally infected by various routes with pseudorabies virus were examined for gross and microscopic lesions. Nonsuppurative meningoencephalomyelitis, as well as visceral lesions, occurred. The incubation period seemed related to the viral dose and to the distance between the inoculation site and the central nervous system. The distribution of the lesions in the central nervous system appeared to be closely related to the peripheral nerve pathways from the inoculation sites. Other findings indicated that the lymphohematogenous route could have a role in the dissemination of the virus in infected ferrets.     

Latent infection and subsequent reactivation of pseudorabies virus in swine exposed to pseudorabies virus while nursing immune dams

The ability of pseudorabies virus (PRV) to infect and establish latency in pigs with passively acquired (maternal) antibody for PRV was tested by exposing such pigs to the virus and subsequently attempting to reactivate latent virus by administering large doses of dexamethasone. Pigs of each of 4 litters that had nursed gilts with relatively high (512, gilts 1 and 2), moderate (32, gilt 3), and no (less than 2, gilt 4) serum titers of virus-neutralizing (VN) antibodies for PRV were allotted to 3 treatment groups (A, B, C) when they were 2 weeks old. Group-A pigs were separated from littermates and dam and thereafter kept in isolation; group-B pigs were experimentally exposed oronasally to PRV and 1 hour later returned to their dam; group-C pigs were kept with their dam and potentially exposed to PRV by contact with littermates of group B. Sera obtained from pigs at selected intervals until they were 17 weeks old were tested for VN activity and for precipitating activity for radiolabeled viral proteins. All group-A pigs remained clinically normal throughout the experiment. Depending on the initial amount of passively acquired antibody, little or no serum VN or precipitating activity remained by the time these pigs were 17 weeks old. Group-B and -C pigs, with relatively high amounts of passively acquired antibody when exposed to PRV, also remained clinically normal. However, most became latently infected as subsequently evidenced by either dexamethasone-induced or noninduced virus reactivation. Noninduced reactivation may have been initiated by weaning the pigs when they were about 8 weeks old.(ABSTRACT TRUNCATED AT 250 WORDS)     

Horizontal transmission of pseudorabies virus in cattle

Pseudorabies virus (PRV) was not transmitted horizontally from 3 PRV-infected calves to 2 contact control calves during 4 days of comingling in experiment 1. Although these contact control calves developed clinical signs of pseudorabies when infected intranasally with PRV in experiment 2, they did not transmit PRV to a second pair of contact control calves. However, 1 of 2 pigs comingled with these 4 calves seroconverted. During both experiments, moderate amounts (10(2) to 10(5) TCID50) of PRV were present in the nasal secretions of the infected calves during the contact periods. All infected calves traumatized their nares or periorbital tissue. Infected calves developed a nonsuppurative meningoencephalitis mainly involving the brain stem. Four of the 5 infected calves had nonsuppurative ganglioneuritis and acute lymphoid necrosis of germinal centers. Virus could not be recovered from nasal and tonsillar swab samples from contact-control calves and pigs.     

Study of the potential involvement of pseudorabies virus in swine respiratory disease.

In order to investigate the potential involvement of pseudorabies virus (PRV) in swine respiratory disease, nine week old pigs were intranasally inoculated with the PRV strain 4892. Two doses of infection were used: 10(4.5) median tissue culture infectious doses (TCID50)/pig and 10(3.5) TCID50/pig, with ten pigs per group. In the group of pigs inoculated with 10(4.5) TCID50, seven out of ten pigs died within six days after inoculation. The mortality rate in the group of pigs inoculated with the lower dose was only two out of ten and, there were several pigs in this group that showed signs of respiratory distress besides some mild nervous signs. Pseudorabies virus was isolated from various tissues collected postmortem, including alveolar macrophages. Virus localization in tissues was also detected by in situ hybridization. The histopathological examination of the respiratory tract tissues revealed a pathological process that was progressing from mild pneumonia to severe suppurative bronchopneumonia. The isolation of virus from alveolar macrophages provides support to the hypothesis that replication of PRV during the course of infection produces an impairment of the defense mechanisms in the respiratory tract.     

Abortion induced by cell-associated pseudorabies virus in vaccinated sows.

Pregnant sows, immune against pseudorabies after vaccination, were inoculated at 70 days of gestation either with autologous blood mononuclear cells that had been infected in vitro with pseudorabies virus (PRV) or with cell-free PRV. The infected cells or cell-free PRV were inoculated surgically into the arteria uterina. Eight sows (A to H) had been vaccinated with an inactivated vaccine. The titer of seroneutralizing antibodies in their serum varied between 12 and 48. Five sows (A to E) were inoculated with autologous mononuclear cells, infected either with a Belgian PRV field strain or with the Northern Ireland PRV strain NIA3. These 5 sows aborted their fetuses: 2 of them (B and C) 3 days after inoculation, and the other 3 (A, D, and E) 10, 11, and 12 days after inoculation, respectively. Sows F, G, and H were inoculated with a cell-free PRV field strain. They farrowed healthy litters after normal gestation. Neutralizing antibodies were absent against PRV in the sera of the newborn pigs, which were obtained prior to the uptake of colostrum. The 23 fetuses that were aborted in sows B and C 3 days after the inoculation were homogeneous in appearance and size. Foci of necrosis were not detected in the liver. Viral antigens were located by immunofluorescence in individual cells in lungs, liver, and spleen of 15 fetuses. Virus was isolated from the liver, lungs, or body fluids of 12 fetuses. The 39 fetuses that were aborted in sows A, D, and E between 10 and 12 days after inoculation were of 2 types: 17 were mummified and 22 were normal-appearing.(ABSTRACT TRUNCATED AT 250 WORDS)     

A skin test for pseudorabies virus infection in swine.

Heat-inactivated pseudorabies virus caused cutaneous delayed-type hypersensitive reactions when injected intradermally on the dorsolateral aspect of the thorax and tips of the ears of pigs previously exposed to the homologous virus. The reaction induced by subcutaneous injection in the lower eyelid was more easily administered and evaluated. Nonexposed control pigs did not react to the antigen and exposed and control pigs did not react when injected with a cell control antigen prepared in a similar manner. A positive response was detectable as early as seven days after exposure, reached near maximal levels by 28 days, and remained at similar levels for at least 90 days.     

猪伪狂犬病病毒的分离和鉴定

从病猪脑部分离到1株病毒.该病毒接种Balb/c小鼠出现神经症状,病死率为60% ,接种PK-15细胞出现拉网病变.伪狂犬病阳性血清能特异性的中和该分离毒.根据基因库(GenBank)的PRV gE基因设计的引物能扩增出特异性片段,证实该病毒为伪狂犬病病毒.     

重组伪狂犬病病毒(rPRV-GP5)对绵羊的安全和效力试验

为了验证表达猪繁殖与呼吸综合征病毒(PRRSV)GP5蛋白的重组伪狂犬病病毒(rPRV-GP5)的安全性和免疫原性,将10只5～6月龄健康绵羊分成三组,安检组(3只)肌注108.0PFU/只、效检组(4只)肌注106.0 PFU/只,3只作为不接种对照组.接种后14 d,效检组与对照组每只臀部肌注伪狂犬病病毒"双城系"猪源强毒S株103 LD50,结果效检组全部保护,对照组全部死亡,安检组未见异常.结果表明,重组病毒完全符合伪狂大病活疫苗制造及检验规程中对疫苗的安全和效力检验标准.     

Spread of pseudorabies virus among breeding swine in quarantined herds.

In theory, pseudorabies virus (PRV) may be eliminated from any size of breeding herd by phased test and removal if replacement gilts are not infected with PRV, culling decisions are partially based on PRV status, and the cull rate is higher than the incidence rate of PRV. Annual cull rates are commonly at least 50%, but little information exists on the incidence of PRV within enzootically infected swine herds. The purpose of this study was to develop a method by which spread of PRV could be detected among breeding swine within enzootically infected herds and to determine the incidence of PRV infection in these herds. Data were collected from 17 herds that were quarantined for PRV and ranged in size from 120 to 1,100 sows. At each herd, within the first 5 days of introduction, a group of approximately 30 replacement gilts was identified, vaccinated with a glycoprotein X-deleted PRV vaccine, and blood sample was collected. The owner of 1 herd had a nonvaccinated breeding herd and elected to leave incoming gilts nonvaccinated. After vaccination, blood samples were collected every 1 to 2 months for an average of 13.6 months. Serum samples from vaccinated gilts were tested for antiglycoprotein X antibodies by a specific differential ELISA. Samples from nonvaccinated gilts were evaluated by serum neutralization test. Product-limit method was used to estimate the probability of not becoming infected with PRV. Spread was detected in 7 of 8 herds that had more than 400 sows and in 2 of 9 herds that had less than 400 sows.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular biology of pseudorabies (Aujeszky's disease) virus.

In this review, some of the aspects concerning the molecular biology of pseudorabies virus (PrV), the causative agent of Aujeszky's disease, will be discussed. It will mainly focus on new findings concerning viral glycoproteins, factors determining PrV virulence, the problem of PrV latency and the development regarding genetically engineered vaccines.     

Efficacy of a killed gpX deleted pseudorabies virus vaccine.

Ten inactivated vaccines containing one of four adjuvants and varying concentrations of pseudorabies virus (PRV) antigens were compared in order to select a vaccine suitable for commercial production. A genetically engineered strain of PRV lacking the gene coding for glycoprotein X (gpX) was used in these vaccines. Vaccinated pigs were challenged intranasally with virulent PRV to determine the efficacy of vaccines. Vaccination of pigs with one dose of experimental vaccines adjuvanted with 50% Montanide ISA 50 or 20% Syntrogen induced a protective immunity at least equal to that induced by two commercially available killed PRV vaccines also evaluated. An experimental vaccine containing 20% Syntrogen was selected and further evaluated according to United States Department of Agriculture licensing requirements. None of the pigs vaccinated with this vaccine produced gpX antibodies detectable by the HerdChek: Anti-PRV-gpX assay. Therefore, this assay could differentiate PRV vaccine induced antibodies from antibodies induced by natural exposure when used in conjunction with this killed gpX deleted PRV vaccine.     

一例猪伪狂犬病病毒的诊断

2015年11月,当地某养殖户15日龄仔猪出现角弓反张、精神沉郁等疑似猪伪狂犬病病毒感染的典型神经症状,但查看免疫程序,已免疫猪伪狂犬病疫苗（Bartha-k61株）。经gE基因血清学调查和针对gE基因的PCR诊断,证实该病例为猪伪狂犬病病毒感染所致。