Efficacy of Intracerebral Immunization against Pseudorabies Virus in Mice

To evaluate the efficacy of intracerebral (IC) immunization, mice were immunized with formalin-inactivated pseudorabies virus (PRV) by either subcutaneous (SC) or IC injection, and then 10(6) plaque-forming units of PRV were introduced into the hindleg of the immunized or non-immunized mice by intramuscular injection. The antibody titer in serum was elevated and boosted by additional immunization via both the SC and IC routes, but was higher after IC immunization. Intracerebrally immunized mice were completely protected from mortality and neurological signs, whereas all the non-immunized and 80% of the subcutaneously immunized mice died after developing neurological signs. In mouse models, IC immunization is more effective at inducing a protective immune response against the transneural spread of PRV than SC immunization.

Epidemiological survey of viral diseases of pigs in the Mekong delta of Vietnam between 1999 and 2003

In the Mekong delta, backyard pig rearing plays an integral role in recycling nutrients in farming systems and generating valuable cash income. However, development has been hampered by fatal epizootics of piglets and reproductive failure of sows. Diseases are named by symptoms and blindly treated with antibiotics. As antibiotics are often ineffectual, involvement of viral diseases are suspected. To identify the causative agent, we first sero-surveyed porcine reproductive and respiratory syndrome (PRRS) and pseudorabies with 478 sera from non-vaccinated pigs collected from backyard farms, state farms and slaughterhouses in Can Tho province between 1999 and 2002. Antibodies for PRRS were first detected in 2002 in backyard farms and at high prevalence in state farms with increased piglet mortality. A few backyard breeder pigs had antibodies for pseudorabies in 2000 and 2002. With compulsory classical swine fever (CSF) vaccination, we examined the relationship between vaccination and antibodies in 70 serum samples. Seventy-nine percent of vaccinated breeders had CSF antibodies-higher than expected with irregular vaccination. Since circulation of CSF virus was suspected, isolation was attempted at 10 farms with fatal epizootics between 2002 and 2003. The viruses were detected at all farms and clustered within genogroup 2, despite vaccines corresponding to genogroup 1. This study demonstrated virologically/serologically the existence of PRRS, pseudorabies and CSF viruses in the Mekong delta of Vietnam. We also identified CSF as a cause of piglet mortality that disastrously affected backyard farming. Vaccine standardization and proper instructions are needed to simplify diagnosis and complement established simultaneous vaccination of sows with piglets.

Influence of tegument proteins of pseudorabies virus on neuroinvasion and transneuronal spread in the nervous system of adult mice after intranasal inoculation

Pseudorabies virus (PrV) is a neurotropic alphaherpesvirus that, after intranasal infection of adult mice, enters peripheral neurons and propagates to the central nervous system. In recent years we have analyzed the contribution of virus-encoded glycoproteins to neuroinvasion and transneuronal spread (reviewed in T. C. Mettenleiter, Virus Res. 92:197-206, 2003). We now extend our studies to analyze the role of tegument proteins in these processes. To this end, PrV mutants unable to express the UL11, UL37, UL46, UL47, and UL48 tegument proteins, as well as the corresponding rescued viruses, were intranasally instilled into 6- to 8-week-old CD1 strain mice. First, mean survival times were determined which showed that mice infected with the UL46 deletion mutant succumbed to the disease as early as wild-type PrV-infected animals. Survival times increased in the order: PrV-DeltaUL47-, PrV-DeltaUL11-, and PrV-DeltaUL48-infected animals, a finding which parallels the growth phenotype of these viruses in cell culture. In contrast, none of the PrV-DeltaUL37-infected animals died. Upon closer histological examination, all viruses except PrV-DeltaUL37 were able to infect the nasal cavity and propagate to first- and second-order neurons as shown by two-color immunofluorescence. However, neuroinvasion was delayed in PrV-DeltaUL47, PrV-DeltaUL11, and PrV-DeltaUL48, a finding that correlated with the extended survival times. Surprisingly, whereas PrV-DeltaUL48 and PrV-DeltaUL37 replicated to similar titers in cell culture which were approximately 500-fold lower than those of wild-type virus, after intranasal infection of mice PrV-DeltaUL48 was able to infect areas of the brain like wild-type PrV, although only after a considerably longer time period. In contrast, PrV-DeltaUL37 was not able to enter neurons and was restricted to the infection of single cells in the nasal respiratory epithelium. Thus, our data demonstrate the importance of herpesviral tegument proteins in neuronal infection and show a different contribution of tegument proteins to the neuroinvasion phenotype of a neurotropic alphaherpesvirus.

A study of the progress of the Aujeszky's disease control programme in Italy using survival analysis

A 3-year study (1997-2000) was performed on 294 swine herds from Italy, where a National Programme of Control of Aujeszky's Disease (AD) based on compulsory vaccination has been operative since 1997. Aim of the study was to evaluate the progress of this control programme using a survival approach applied to gE-seropositive herds at the beginning of the programme. The cumulative proportion of herds still gE-seropositive at the end of the study was 0.57. No significant difference in the probability of becoming gE-seronegative during the study period was found between herds of different type (breeding versus farrow-to-finish) whereas significant differences were seen between herds from different areas. The Cox's proportional hazards regression, performed on data from 79 herds, showed that the only risk factor significantly associated with a higher probability of becoming gE-seronegative is again the geographical location. Other risk factors considered in the analysis were: type of enterprise, type of replacement of animals, herd size, pig and pig herds densities around the farm, distance from the nearest pig herd and year of beginning of the vaccination with a gE-deleted vaccine.

Natural Aujeszky's disease in a Spanish wild boar population

We describe an outbreak of Aujeszky's disease (AD) in a wild boar (Sus scrofa) population from central Spain. Mortality was estimated to be at least 14% (14/100) in juveniles and 7.5% (3/40) in adults. Most of the affected animals (12/17) were between 4 and 8 months of age. Gross lesions mainly consisted of enlarged and congestive tonsils and lymph nodes, petechial hemorrhages on the small intestine, and engorged blood vessels in the brain and meninges. Histopathology revealed mild nonsuppurative meningoencephalitis. Positivity to the fluorescent antibody test was found in tissues from the affected animals. Seroprevalence of antibodies to AD virus (ADV) was 56% (9/16). To our knowledge, this is the first description of clinical cases in a wild suid population.

Vaccination of pigs with a recombinant porcine adenovirus expressing the gD gene from pseudorabies virus

Five week old, commercially available large white pigs were vaccinated with either a single dose or two doses of a recombinant porcine adenovirus expressing the glycoprotein D gene from pseudorabies virus (PRV). Pigs were monitored for the development of serum neutralizing antibodies to PRV and challenged 3 weeks after final vaccination. Prior to challenge, pigs given 2 doses of the vaccine demonstrated boosted levels of antibody compared with those given a single dose, and all surviving pigs had increased neutralization titres over pre-challenge levels. Following challenge, pigs were monitored for clinical signs of disease, with blood and nasal swabs collected for virus isolation. All control animals became sick with elevated temperatures for 6 days post challenge, whereas; vaccinated animals displayed an increase in body temperature for only 2-3 days. Control pigs and those given a single dose all lost condition, but the group given 2 doses remained healthy. At postmortem, gross lesions of pneumonia only occurred in control animals and those given a single dose of vaccine. Histology carried out on the brains of all animals demonstrated a difference in severity of infection and frequency of immunohistochemical antigen detection between test animals, with control and single dose groups being most severely affected and pigs given 2 doses the least. Virus isolation studies demonstrated that no viraemia could be detected, but virus was found in nasal swabs from some animals in both groups of vaccinates following challenge.

Aujeszky's disease in captive bears

Five of eight bears died during an outbreak of Aujeszky's disease in a travelling circus in the north of Spain. The bears had been fed on a diet which included raw pigs' heads. One of three Himalayan bears and a Kodiak bear died acutely with signs of the disease. One of four polar bears died acutely without signs, another died with signs of Aujeszky's disease while it was being treated, and a third died with enteritis and disseminated intestinal coagulation some time later without showing signs of the disease. A fourth polar bear recovered from the same gastrointestinal problem without showing signs of the disease. Although one of the two surviving Himalayan bears showed some signs referrable to Aujeszky's disease, the results of tests for neutralising antibodies were negative. Two of the polar bears, the Himalayan bear and the Kodiak bear were examined postmortem and three of them were examined histologically. No lesions referable to Aujeszky's disease were found. The tissues from one female polar bear were examined and shown to be positive for Aujeszky's disease virus by virus isolation, polymerase chain reaction, electron microscopy and fluorescent antibody tests. The DNA of the isolate was shown to be similar to that of the strains of the virus circulating in pigs in northern Spain some years earlier.

Isolation and characterisation of an Aujeszky's disease virus naturally infecting a wild boar (Sus scrofa)

Isolation of Aujeszky's disease virus (ADV) from an injured, female wild boar (Sus scrofa), shot dead by hunters, in an area adjacent to the Abruzzo National Park is reported. The brain was submitted for attempted virus isolation following episodes of mortality in several dogs and cats fed with meat from the wild boar. Virus was isolated on first passage from the brain of the wild boar. The restriction fragment length polymorphism profile of the isolate was assessed as a type I. The role of stress in reactivating latent ADV in wild boars, the possibility of transmitting infection to endangered species such as bears (Ursus arctos), wolves (Canis lupus), wild cats (Felis silvestris) and lynx (Lynx lynx), present in the Abruzzo National Park and the possible role of wild boars as reservoirs for ADV is discussed.

Comparison of the efficacy of replication-defective adenovirus and Nyvac poxvirus as vaccine vectors in mice

Adenovirus and poxvirus recombinant vectors are more and more used as live experimental vaccines. In order to compare the efficacy of these vectors to elicit serological response and protection against challenge, two recombinants carrying the same gene (pseudorabies virus gD) were used as experimental vaccines in mice, a permissive species to pseudorabies infection. Two routes were tested: intramuscular (i.m.) and intranasal (i.n.) in order to try to stimulate general and mucosal immune responses. Several doses ranging from 10(2.9) to 10(8.9) TCID50, depending on the vaccines were tested. The estimated log 10 (PD50) for the i.m. route were 7.1 +/- 0.2 for the adenovirus vector (Ad-gD), and 7.6 +/- 0.2 for the Nyvac vector (vP900). For the i.n. route, log 10 (PD50) of Ad-gD was 7.1 +/- 0.2, and was higher than 7.9 for vP900. While the adenovirus vector proved more efficient than the poxviral vector to elicit antibody response, only a slight difference was observed when comparing the survival times of animals after challenge. Adenovirus was found better only for the 10(7.9) TCID50 dose, when inoculated i.m. Intranasal vaccination appeared efficient only with the adenovirus vector for the TCID50 10(8.9) dose.

Productivity and profitability differences between pseudorabies-infected and pseudorabies-noninfected farrow-to-finish swine herds

Productivity and economic effects of pseudorabies were estimated for a mean-size, farrow-to-finish swine enterprise. A Delphi technique was used to elicit productivity effects from an expert panel. Enterprise budgets for pseudorabies-infected and noninfected herds were constructed by use of these productivity estimates, as well as by use of economic data from secondary sources. Data examined to determine effects on productivity included preweaning, nursery, and growing/finishing pig mortality; breeding hog mortality; feed conversion; labor; and veterinary services and medication expenses. Results indicated that profitability was lowered in infected herds by approximately $6/cwt of swine produced.

Economic impact of an epizootic of pseudorabies in a commercial swine herd in Ohio, achieving test negative status and quarantine release by use of vaccination and test and removal

The effect of pseudorabies in a commercial farrow-to-finish operation on selected production and economic values was estimated. Pseudorabies was first diagnosed in this herd by circle testing done in March 1988, as a required part of follow up from another herd that had been diagnosed with pseudorabies in the area. A pseudorabies virus vaccination program was initiated in the herd at that time. The mean litter size of pigs born alive varied from 9.26 to 10.02 pigs/litter throughout the study period; however, there was a twofold increase in suckling pig mortality and a 2.6-fold increase in nursery pig mortality when the months of the epizootic were compared with pre-epizootic months. In the 6-month period following the epizootic, suckling pig mortality was three-fold higher than that reported in the preepizootic months. Total net loss for this operation was estimated at $99,700 from when the epizootic started until eradication, when calculating losses directly. The major economic losses (76.5% of total loss) were related to suckling pig mortality, which was $16,240 during the epizootic or $24/inventoried sow/week; $19,395 in the 6 months following the epizootic or $3.8/inventoried sow/week; and $40,628 thereafter until eradication 26 months later or $0.37/inventoried sow/week. Nursery pig mortality losses were 12.6% of total net losses; $754 during the epizootic, $357 in the 6 months after the enzootic, and $11,444 thereafter until eradication 26 months later. Sow culling and deaths accounted for 9.4% of net losses that took place from 6 months after the epizootic until eradication.(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant interferon-gamma applied to the brain ventricular system protects rats against pseudorabies

We examined the prophylactic efficacy of recombinant rat interferon-gamma (IFN-gamma) administered directly into the brain ventricular system or via the intraperitoneal (i.p.) route against central and peripheral pseudorabies virus (PRV) infection. Intraperitoneally given IFN-gamma completely protected rats against a lethal i.p. PRV infection. The same regimen showed no protective effect against lethal intracerebroventricular (i.c.v.) PRV challenge even if IFN-gamma was given in high concentrations. When given via the i.c.v. route, IFN-gamma protected rats against lethal i.c.v. infection and also evoked partial protection with extended survival times of i.p. infected rats. Our results demonstrate an IFN-gamma-mediated antiviral effect in the central nervous system.

Economic assessment of a pseudorabies epizootic, breeding herd removal/repopulation, and downtime in a commercial swine herd

The effect of pseudorabies in a 150-sow farrow-to-finish operation on selected production and economic values was estimated. Mean litter size remained the same throughout the observation period; however, there was a 2-fold increase in suckling pig mortality and a 3.5-fold increase in stillbirths when the months of the epizootic were compared with pre-epizootic months. Following the epizootic, suckling pig mortality was 13.7% greater (P less than 0.05) than that observed in the months preceding the epizootic, whereas stillbirth rate was 71% higher (P less than 0.01) than that reported in the pre-epizootic months. Total net loss for this operation was estimated at +48,175. The major economic losses (approximately 88% of the total loss) were related to breeding herd removal/repopulation and production downtime.

Pseudorabies virus infection in raccoons: a review

Pseudorabies is a rarely reported disease of raccoons. Laboratory and field evidence of PRV infection suggests the raccoon is a "dead end" host with little opportunity for raccoon-to-raccoon spread of virus. All reported field cases have been associated closely with infected swine and swine have been considered the source of the raccoon infection. The clinical signs of PRV in raccoons closely resembles those of canine distemper and rabies virus infections. Infection with the latter viruses are considered more prevalent and likely to be mistaken for PRV infection. Both CD and rabies virus may be maintained in raccoon populations with raccoon-to-raccoon transfer while PRV may not. Differentiation of PRV, CD and rabies infections is best achieved by histopathologic analysis of lung and brain tissue, together with virus isolation. It is of utmost public health importance that wildlife authorities recognize the similarities between these diseases, together with the different epidemiologic behavior of the viruses and the means to differentiate clinical cases.

The pathogenesis of pseudorabies in mice: virus replication at the inoculation site and axonal uptake

Three-week-old mice were inoculated in the right ear pinna with pseuforabies virus. Ears were surgically removed at various times after inoculation and changes from the normal pathogenesis were observed. Virus replication in the ear tissue and cervical dorsal root ganglia was also monitored. Followed inoculation with a small dose of virus, local multiplication of the virus was necessary before the infection spread to the nerves. With larger infecting doses there was probably direct uptake of virus from the inoculum into the nerve endings. After these larger doses virus was first detected in the dorsal root ganglia 17 h agter infection, suggesting a retrograde axonal flow rate of at lease 1-7 mm/h.