Attenuation of porcine circovirus 2 in SPF piglets by abrogation of ORF3 function

Porcine circovirus 2 (PCV2), open reading frame 3 (ORF3) codes a 105 amino acid protein that causes apoptosis of PCV2 infected cells. In infected cells, the ORF3 causes the accumulation of p53 by interacting with pPirh2 and possibly by disrupting the association of p53 and pPirh2 (J.Virol.81(2007)9560). Mutant PCV2 lacking the expression of ORF3 are infectious and replicate in cells in vitro, but do not cause apoptosis of the infected cells. The ORF3 of PCV2 has been shown to be involved in pathogenesis of the virus in mice model (J. Virol. 80(2006)5065). Here we report the experimental inoculation of ORF3 deficient PCV2 in its natural host, the piglets. The pathogenicity of the ORF3 deficient virus is attenuated in the piglets. The mutant virus did not cause any observable disease or perturbation of the lymphocyte count in the inoculated piglets and elicited an efficient immune response. When compared with the wildtype virus infection, the mutant virus infection was characterized by mild viremia and absence of pathological lesions. The findings highlight the role of ORF3 in the pathogenesis of PCV2 infection in its host.

Immune responses to foot-and-mouth disease virus in pig farms after the 1997 outbreak in Taiwan

This paper reports on a retrospective study of the antibody responses to structural and non-structural proteins of FMD virus O Taiwan 97 in six pig herds in Taiwan in the year after the 1997 Taiwanese FMD outbreak. All herds were vaccinated against FMD after the outbreak as part of the countrywide control program. Three of the herds had confirmed FMD infections (herds N, O and P) and three herds remained non-infected (herds K, L and M). The serum neutralizing antibody titers and the non-structural protein ELISA (NSP) antibody responses in sows and 1-month-old pigs in the infected herds were higher than in the non-infected herds, but over time a number of positive NSP reactors were detected. From the serological studies and the herd monitoring and investigations it was considered that the FMD NSP positive reactors may not have constituted a true reservoir of FMD virus infection especially in herds where susceptible pigs were no longer present post-exposure or post-vaccination. Pigs vaccinated with an unpurified FMD type O vaccines being used at that time also showed false positive responses for NSP antibodies.

Immune responses of pigs to commercialized emulsion FMD vaccines and live virus challenge

The immune response to structural and non-structural proteins (NSPs) was studied on sequential serum samples in swine from O/Taiwan/97 FMDV challenge studies, outbreaks and after vaccination. The results showed that pigs vaccinated with a commercial vaccine prior to or after infection maintained high neutralizing antibody titers with gradual decline from peak titers over the duration of this study. However, neutralizing antibody titers in non-vaccinated pigs only reached moderate levels 2-4 weeks post infection and remained low thereafter. For the 3B and 3ABC NSP antibody ELISA responses, there were gradually decreasing levels of NSP antibody over time. In multiple vaccinations, all pigs showed significant increases in neutralizing antibodies after booster vaccination. For the 3B NSP antibody ELISA after vaccination, the mean S/P ratios for pigs vaccinated with all three FMD vaccines were all below the 0.23 cut-off value set by the manufacture, but some sera from individual vaccinated pigs gave results above this cut-off after primary or secondary vaccination. However, with the 3ABC NSP antibody ELISA, all sera from vaccinated pigs had negative results for NSP antibody for all time points.

Comparison of sensitivity and specificity in three commercial foot-and-mouth disease virus non-structural protein ELISA kits with swine sera in Taiwan

Three commercialized ELISA kits for the detection of antibodies to the non-structural proteins (NSPs) of FMD virus were compared, using sera from uninfected, vaccinated, challenged and naturally infected pigs. The kinetics of the antibody response to NSPs was compared on sequential serum samples in swine from challenge studies and outbreaks. The results showed that ELISA A (UBI) and ELISA B (CEDI) had better sensitivity than that of the 3ABC recombinant protein-based ELISA C (Chekit). The peak for detection of antibodies to NSPs in ELISA C was significantly delayed in sera from natural infection and challenged swine as compared to the ELISA A and B. The sensitivity of the three ELISAs gradually declined during the 6-month post-infection as antibodies to NSP decline. ELISA kits A and B detected NSP antibody in 50% of challenged pigs by the 9-10th-day and 7-8th-day post-challenge, respectively. ELISA B and C had better specificity than ELISA A on sequential serum samples obtained from swine immunized with a type O FMD vaccine commercially available in Taiwan. Antibody to NSPs before vaccination was not detected in swine not exposed to FMD virus, however, antibody to NSPs was found in sera of some pigs after vaccination. All assays had significantly lower specificity when testing sera from repeatedly vaccinated sows and finishers in 1997 that were tested after the 1997 FMD outbreak. However, when testing sera from repeatedly vaccinated sows or finishers in 2003-2004, the specificity for ELISAs A, B and C were significantly better than those in 1997. This effect was less marked for ELISA A. The ELISA B was the best test in terms of the highest sensitivity and specificity and the lowest reactivity with residual NSP in vaccinates.

Phylogenetic analysis of classical swine fever virus in Taiwan

Two envelope glycoprotein (Erns and E2) regions of the classical swine fever virus (CSFV) were amplified by RT-PCR and sequenced directly from 158 specimens collected between 1989 and 2003 in Taiwan. Phylogenetic analysis of the two regions revealed a similar tree topology and the Erns region provided better discrimination than the E2 region. One hundred and fifteen isolates out of the 158 isolates were clustered within subgroup 2.1 (further classified as 2.1a and 2.1b) and 2.2, which were considered to be likely of the introduced strains, whereas the remaining 43 isolates were clustered within subgroup 3.4 and were considered to be of the endemic strains. The subgroup 2.1a viruses were first detected in 1994 and predominated from 1995 onwards. However, subgroup 3.4 viruses were prevalent in the early years, not being isolated after 1996. We have observed a dramatic switch in genotype from subgroup 3.4 to 2.1a. The subgroup 2.1a isolates are closely related to the Paderborn and Lao isolates, whereas 2.1b isolates have a close relationship to the Chinese Guangxi isolates. The phylogenetic tree of 27 CSFV sequences based on the complete envelope glycoprotein gene (Erns-E2) displayed better resolution than that based on the complete open reading frame.

Efficacy of foot-and-mouth disease vaccine in pigs with single dose immunization

Two experiments were conducted to demonstrate the efficacy of a commercial foot-and-mouth disease (FMD) vaccine in pigs born to well-vaccinated sows at various ages with a single injection under field conditions. The first experiment showed that single dose vaccination of pigs could be conducted at an age younger than 10 weeks. Second experiment demonstrated that pigs vaccinated once at the age of 8 weeks had mean serum neutralization (SN) titer of 1.89+/-0.95 log(10)SN(50) with full protection by challenge test at the age of 24 weeks. Results indicate that the most appropriate age for single dose FMD vaccination in pigs born to well-vaccinated sows would be at 8 weeks.

Optimization of foot-and-mouth disease vaccination protocols by surveillance of neutralization antibodies

An appropriate immunization program for pigs in a foot-and-mouth disease (FMD) endemic area was proposed based on data analysis obtained from serological surveillance in Taiwan, after an intensive vaccination program. To provide an adequate passive immunity for piglets, gilts that have completed two basic vaccinations must be boosted once before breeding. To achieve an efficient response to the FMD vaccine for piglets born to well vaccinated sows, vaccination need to be delayed until 10-12 weeks of ages for the first immunization, followed by a boost 4 weeks later.

Effective synthetic peptide vaccine for foot-and-mouth disease in swine

We have designed a peptide-based vaccine for foot-and-mouth disease (FMD) effective in swine. The peptide immunogen has a G-H loop domain from the VP1 capsid protein of foot-and-mouth disease virus (FMDV) and a novel promiscuous T helper (Th) site for broad immunogenicity in multiple species. The G-H loop VP1 site was optimised for cross-reactivity to FMDV by the inclusion into the peptide of cyclic constraint and adjoining sequences. The incorporation of consensus residues into the hypervariable positions of the VP1 site provided for broad immunogenicity. The vaccine protected 20 out of 21 immunised pigs from infectious challenge by FMDV O1 Taiwan using peptide doses as low as 12.5 microg, and a mild adjuvant that caused no lesions. A safe chemically-defined product would have considerable advantages for vaccination against FMD.

Synthetic peptide-based vaccine and diagnostic system for effective control of FMD

We have designed synthetic peptides corresponding to two different regions of the genome of foot-and-mouth disease virus (FMDV) that are effective as (a) a vaccine or (b) a diagnostic reagent which differentiates convalescent from vaccinated animals, respectively. The peptide vaccine is based on a sequence from the prominent G-H loop of VP1, one of the four capsid proteins. The sequence was optimized by the inclusion of a cyclic constraint and adjoining sequences, and broader immunogenicity was obtained by the incorporation of consensus residues at hypervariable positions. The peptide also included a promiscuous T-helper epitope for effective immunogenicity in outbred populations of large animals.The diagnostic reagent, a peptide based on non-structural (NS) protein 3B, is used in immuno-assays for the detection of antibodies. Antibodies to this NS protein are present in the sera of infected animals but not in the sera of vaccinated animals. The VP1 peptide can be used in complementary immuno-assays for confirmation of NS test results and to monitor for vaccination. This system for differential diagnosis is important to establish the disease-free status of a country.

Molecular characterization of foot-and-mouth disease virus isolated from ruminants in Taiwan in 1999-2000

In 1999, 10 sporadic outbreaks of cattle foot-and-mouth disease (FMD) occurred in Taiwan. By the time, infection was limited to the Chinese yellow cattle (a native species of beef cattle in Mainland China), which did not develop vesicular lesions under field conditions. Five viruses isolates obtained from individual farms were confirmed to be the serotype O FMD virus (O/Taiwan/1999). During January-February 2000, however, this virus has spread to dairy cattle and goat herds, causing severe mortality in goat kids and vesicular lesions in dairy cattle. Partial nucleotide sequence of the capsid coding gene 1D (VP1) was determined for the virus isolates obtained in this study. Phylogenetic analysis of the VP1 sequences indicated that the O/Taiwan/1999 viruses shared 95-97% similarities to the virus strains isolated from the Middle East and India. The species susceptibility of the O/Taiwan/1999 virus was experimentally studied in several species of susceptible animals, showing that the virus did cause generalized lesions in dairy cattle and pigs, however, it would not cause vesicular lesions on the Chinese yellow cattle and the adult goats. These studies suggested that the O/Taiwan/1999 virus was a novel FMD virus of Taiwan and it presented various levels of susceptibility in cattle species.

Enhancement of the immunity to foot-and-mouth disease virus by DNA priming and protein boosting immunization

Subunit vaccination is effective in eliciting humoral responses to a variety of viral antigens, however, it has not generated persistent protective immunity to foot-and-mouth disease virus (FMDV). In this study, we observed that priming mice with a DNA plasmid encoding VP1 of the FMDV O/Taiwan/97 capsid protein followed by boosting with a VP1 peptide conjugate (P29-KLH) resulted in production of not only high titers of antibodies but also antibodies with FMDV neutralizing activities. Moreover, the mice immunized in this manner cleared the virus from their sera in FMDV challenge experiments. Mice subjected to DNA plasmid priming and P29-KLH protein boosting had relatively higher ratio of IgG2a/IgG1 than those primed and boosted with P29-KLH conjugate. Addition of an oligodeoxynucleotide (ODN) containing immunostimulatory cytosine-phosphate-guanosine (CpG) motifs to P29-KLH conjugate also induced a higher ratio of IgG2a/IgG1 and significantly higher titer of neutralizing antibodies. These results indicate that treating animals with DNA plasmids priming and FMDV antigen(s) boosting may elicit immunity to FMD and this immune response may be augmented by CpG ODN.

Characteristics of foot and mouth disease virus in Taiwan

Since March 1997 two strains of foot and mouth disease (FMD) virus have found their way into Taiwan, causing severe outbreaks in pigs and in Chinese yellow cattle. Outbreaks occurred in March 1997 were caused by a pig-adapted virus strain (O/Taiwan/97) which did not infect other species of cloven-hoofed animals by natural route. The epidemic spread over the whole region of Taiwan within two months and the aftermath was 6,147 pig farms infected and 3,850,746 pigs destroyed. In June 1999, the second strain of FMD virus (O/Taiwan/99) was isolated from the Chinese yellow cattle in the Kinmen Prefecture and in the western part of Taiwan. By the end of 1999, Chinese yellow cattle were the only species infected and those infected cattle did not develop pathological lesions. Seroconversions of serum neutralization antibody and on non-structural protein (NSP) antibodies were the best indicators for infection in non-vaccinated herds. The infected animals, however, excreted infectious levels of virus to infect new hosts. Based on the detection of the specific antibody to FMD virus, and virus isolation from oesophageal-pharyngeal (OP) fluid samples, ten herds of Chinese yellow cattle located in Kinmen and Taiwan were declared to have been infected. During the period of January to March 2000, however, five outbreaks caused by FMD virus similar to the O/Taiwan/99 virus occurred in four prefectures of Taiwan. The infected species included goats, Chinese yellow cattle and dairy cattle. Those outbreaks have caused high mortality in goat kids under two weeks old and also developed typical clinical signs of infection in dairy cattle.

Molecular epidemiological studies on foot-and-mouth disease type O Taiwan viruses from the 1997 epidemic

Sequence diversity was assessed of the complete VP1 gene directly amplified from 49 clinical specimens during an explosive foot-and-mouth disease (FMD) outbreak in Taiwan. Type O Taiwan FMD viruses are genetically highly homogenous, as seen by the minute divergence of 0.2-0.9% revealed in 20 variants. The O/HCP-0314/TW/97 and O/TCP-022/TW/97 viral variants dominated FMD outbreaks and were prevalent in most affected pig-raising areas. Comparison of deduced amino acid sequences around the main neutralizable antigenic sites on the VP1 polypeptide showed no significant antigenic variation. However, the O/CHP-158/TW/97 variant had an alternative critical residue at position 43 in antigenic site 3, which may be due to selective pressure in the field. Two vaccine production strains (O1/Manisa/Turkey/69 and O1/Campos/Brazil/71) probably provide partial heterologous protection of swine against O Taiwan viruses. The type O Taiwan variants clustered in sublineage A1 of four main lineages in the phylogenetic tree. The O/Hong Kong/9/94 and O/1685/Moscow/Russia/95 viruses in sublineage A2 are closely related to the O Taiwan variants. The causative agent for the 1997 epidemic presumably originated from a single common source of type O FMD viruses prevalent in neighboring areas.

A paravaccinia virus isolated from cattle

Isolation of viruses from calves with acute respiratory tract disease were attempted on bovine embryonic lung cell cultures. An isolate obtained from one calf with oral lesions and respiratory disease, designated 44-M-E482, was characterized as a paravaccinia virus on the basis of biological and physical properties. The calf from which the paravaccinia virus 44-M-E482 was isolated did not possess serum neutralizing antibody in its convalescent sera; neither did experimentally inoculated calves possess serum neutralizing antibody to the isolate. However, a low titer of serum neutralizing antibody was produced in one calf after several intravenous injections of the virus. Inoculation of calves with 44-M-E482 into the oral mucosa, skin, nasal cavity and pharynx did not cause any noticeable illness or lesions. The relation of 44-M-E482 to the viruses which cause bovine papular stomatitis and pseudocowpox is discussed.