Challenges of influenza A viruses in humans and animals and current animal vaccines as an effective control measure

Influenza A viruses (IAVs) are genetically diverse and variable pathogens that share various hosts including human, swine, and domestic poultry. Interspecies and intercontinental viral spreads make the ecology of IAV more complex. Beside endemic IAV infections, human has been exposed to pandemic and zoonotic threats from avian and swine influenza viruses. Animal health also has been threatened by high pathogenic avian influenza viruses (in domestic poultry) and reverse zoonosis (in swine). Considering its dynamic interplay between species, prevention and control against IAV should be conducted effectively in both humans and animal sectors. Vaccination is one of the most efficient tools against IAV. Numerous vaccines against animal IAVs have been developed by a variety of vaccine technologies and some of them are currently commercially available. We summarize several challenges in control of IAVs faced by human and animals and discuss IAV vaccines for animal use with those application in susceptible populations.

Genetic identification and serological evaluation of commercial inactivated foot-and-mouth disease virus vaccine in pigs

Vaccination is considered a frequently used tool to prevent and control foot-and-mouth disease (FMD). However, the effectiveness of conventional FMD virus (FMDV) vaccines in pigs has been controversial because the massive prophylactic vaccination could not elicit proper immune response nor prevent the broad spread of FMD outbreak, mainly in pig farms, in South Korea during outbreaks of 2014. In addition, there has been little information on the efficacy of inactivated, high potency, multivalent, oil-based FMDV vaccine in pigs, because an evaluation of FMDV vaccines had been mainly carried out using cattle. In this study, we evaluated the genetic identification of commercial inactivated FMDV vaccine and monitored the immune responses in pigs under the field condition. Results implied that it contained three different serotypes with a high level of antigen payload. However, serological results showed low mean percentage of inhibition, and positive rate reached its peak at 6-week post-vaccination, indicating current FMDV vaccine need to improve for a prophylactic vaccination policy in pigs. Therefore, there is an imperative need to develop FMDV vaccine that can provide rapid and long-lasting protective immunity in pigs.

Synergistic effect of ribavirin and vaccine for protection during early infection stage of foot-and-mouth disease

In many countries, vaccines are used for the prevention of foot-and-mouth disease (FMD). However, because there is no protection against FMD immediately after vaccination, research and development on antiviral agents is being conducted to induce protection until immunological competence is produced. This study tested whether well-known chemicals used as RNA virus treatment agents had inhibitory effects on FMD viruses (FMDVs) and demonstrated that ribavirin showed antiviral effects against FMDV in vitro/in vivo. In addition, it was observed that combining the administration of the antiviral agents orally and complementary therapy with vaccines synergistically enhanced antiviral activity and preserved the survival rate and body weight in the experimental animals. Antiviral agents mixed with an adjuvant were inoculated intramuscularly along with the vaccines, thereby inhibiting virus replication after injection and verifying that it was possible to induce early protection against viral infection prior to immunity being achieved through the vaccine. Finally, pigs treated with antiviral agents and vaccines showed no clinical signs and had low virus excretion. Based on these results, it is expected that this combined approach could be a therapeutic and preventive treatment for early protection against FMD.

Detection and genetic characterization of porcine circovirus 3 from aborted fetuses and pigs with respiratory disease in Korea

A novel porcine circovirus 3 (PCV3) was first detected in pigs showing porcine dermatitis and nephropathy syndrome, reproductive failure, and multisystemic inflammation in the USA. Herein, we report on PCV3 as a potential etiological agent of clinical signs, reproductive failure and respiratory distress on Korean pig farms, based on in situ hybridization, pathological, and molecular findings. Confirmation of the presence of PCV3 may increase co-infection with other causative agents of disease in Korean pig herds, indicating the need for further systemic investigation of pathogenicity and of multiple infections with PCV2 genotypes and bacteria, and the development of an effective PCV3 vaccine.

Acute porcine reproductive and respiratory syndrome outbreaksin immunized sow herds: from occurrence to stabilization under whole herd vaccination strategy / 대한수의학회지

Outbreaks of porcine reproductive and respiratory syndrome virus (PRRSV) in vaccinated sow herds from occurrence to stabilization were monitored and analyzed in terms of serology and reproductive performance. Three different conventional pig farms experienced severe reproductive failures with the introduction of a type 1 PRRSV. These farms had adopted mass vaccination of sows using a type 2 PRRSV modified live vaccine (MLV). Therefore, to control the type 1 PRRSV, an alternative vaccination program utilizing both type 1 and type 2 MLV was undertaken. Following whole herd vaccinations with both types of MLV, successful stabilization of PRRS outbreaks was identified based on serological data (no viremia and downward trends in ELISA antibody titers in both sows and suckling piglets) and recovery of reproductive performance. Additionally, through comparison of the reproductive parameters between outbreak and non-outbreak periods, it was identified that PRRSV significantly affected the farrowing rate and the number of suckling piglets per litter at all three pig farms. Comparison of reproductive parameters between periods when the different vaccination strategies were applied revealed that the number of piglets born in total and born dead per litter were significantly increased after the introduction of the type 1 PRRS MLV.

Acute porcine reproductive and respiratory syndrome outbreaksin immunized sow herds: from occurrence to stabilization under whole herd vaccination strategy

Outbreaks of porcine reproductive and respiratory syndrome virus (PRRSV) in vaccinated sow herds from occurrence to stabilization were monitored and analyzed in terms of serology and reproductive performance. Three different conventional pig farms experienced severe reproductive failures with the introduction of a type 1 PRRSV. These farms had adopted mass vaccination of sows using a type 2 PRRSV modified live vaccine (MLV). Therefore, to control the type 1 PRRSV, an alternative vaccination program utilizing both type 1 and type 2 MLV was undertaken. Following whole herd vaccinations with both types of MLV, successful stabilization of PRRS outbreaks was identified based on serological data (no viremia and downward trends in ELISA antibody titers in both sows and suckling piglets) and recovery of reproductive performance. Additionally, through comparison of the reproductive parameters between outbreak and non-outbreak periods, it was identified that PRRSV significantly affected the farrowing rate and the number of suckling piglets per litter at all three pig farms. Comparison of reproductive parameters between periods when the different vaccination strategies were applied revealed that the number of piglets born in total and born dead per litter were significantly increased after the introduction of the type 1 PRRS MLV.

Cross-Reactivity of Porcine Immunoglobulin A Antibodies with Fecal Immunoglobulins of Wild Boar (Sus scrofa) and Other Animal Species

Fecal samples obtained from wild boar habitats are useful for the surveillance of diseases in wild boar populations; however, it is difficult to determine the species of origin of feces collected in natural habitats. In this study, a fecal IgA ELISA was evaluated as a method for identifying the porcine species from fecal samples. Both domestic pigs (Sus scrofa domestica) and wild boars (Sus scrofa coreanus) showed significantly higher levels of fecal IgA than other animal species. Additionally, age dependent changes in the level of Ig A in wild boars and domestic pigs were identified; Titers of Ig A were highest in suckling period and lowest in weanling period.

Comparison of antibiotic resistance profiles for Escherichia coli isolated from wild boar and domestic pig fecal samples / 대한수의학회지

Increasing presence of wild boar around cities and suburban areas is a growing concern with respect to agronomy, environmental ecology, and public safety. In this study, antibiotic resistance profiles of Escherichia (E.) coli isolated from wild boar and domestic pig fecal samples were compared. Eighty E. coli samples were isolated from wild boars. Resistance of the bacteria to 14 common antimicrobial agents used in human and veterinary medicine was evaluated. Ninety-five E. coli isolates from domestic pig farms were used for comparison. Common and distinct antibiotic resistance patterns were observed when comparing wild boar and domestic pig isolates, indicating that wild boars may significantly influence environmental microbiology.

Porcine reproductive and respiratory syndrome virus vaccine does not fit in classical vaccinology

All vaccines are developed to elicit an effective immune response in vaccinated animals such as innate, humoral and cell mediated response to protect animal health. Quality and intensity of the immune responses are differing by characteristics of the vaccine formulation and nature of the infectious agent. Modified live virus vaccines showed advantages over killed vaccines in terms of rapid immune response, duration of the immunity and better cell mediated protection mechanism. The porcine reproductive and respiratory syndrome virus (PRRSV) is relatively newly emerging (1986 in United States, 1990 in Europe) viral pathogen in pigs and tremendous effort has been made to protect pigs from this economically devastating disease such as developing killed, modified live, recombinant protein based and DNA vaccines. However, only cell culture attenuated virus vaccine is practiced with arguably limited efficacy. The PRRSV vaccine did not clear virus from infected pigs nor prevent re-infection of the virus. The vaccine showed very limited innate immune response, low anamnestic immune response and negligible cell mediated immune response. Despite of the current developed scientific technology, there still remain many questions to solve a most important pig disease worldwide.

Aerobic bacteria from oral cavities and cloaca of snakes in a petting zoo / 대한수의학회지

It is important to identify the bacteria in snakes because they can cause disease; importantly, bacteria such as Stenotrophomonas maltophilia, Escherichia coli, Proteus vulgaris etc. could be pathogens especially in hospitalized, debilitated hosts, and immunocompromised patients. To analyze the distribution of snakes' bacteria in petting zoo, samples from 20 snakes were collected from 2002 to 2008. Nine bacteria species were isolated from both oral and cloaca while four and six species were identified only from oral and cloaca, respectively. Except for Actinobacter sp., all of the identified strains are opportunistic pathogens, and most of them can cause nosocomial infections in humans. Present results indicate that prevalence of various zoonotic bacterial strains in snakes could be involved in potential transfer of these bacteria into caretakers and other animals. Therefore, it needs to examine the antibiotic resistance of these pathogens to prevent outbreaks.

Serovars distribution and antimicrobial resistance patterns of Salmonella spp. isolated from the swine farms and slaughter houses / 대한수의학회지

Salmonella spp. is an important pathogen to both public and swine industry. The aim of this study was to investigate the distribution of Salmonella serovar and antibiotics susceptibility of the isolates from Korean swine producing systems. A total of 63 (5.28%) Salmonella spp. was isolated from 1,194 samples (977 fecal materials and 67 organ samples). The predominant Salmonella (S.) enterica serotype and serovar was group B (69.8%) and S. Typhimurium (47.6%), S. Derby (20.6%) and S. Heidelberg (1.6%). But S. Cholerasuis which is characterized host specific by septicemia and enteritis to pigs was not isolated. Antimicrobial susceptibility of the isolates varies as follows: Norfloxacine (75%), Ciprofloxacin (67.5%), Amikacin (60%), Colistin (60%), Enrofloxacin (55%). All of isolates were resistant to Erythromycin, Penicillin, Tetracycline and Lincomycin. The results of this study provided useful information regarding antimicrobial susceptibility and resistance patterns to treat salmonellosis and to prevent emergence of multidrug resistance Salmonella.

Characterization of the Recombinant Proteins of Porcine Circovirus Type2 Field Isolate Expressed in the Baculovirus System

Porcine circovirus (PCV) type2 was isolated using primary porcine kidney cells from lymph node of piglets with typical PMWS. The presence of the virus was identified by PCR using primers specific to PCV type2. The ORFs 1 and 2 were amplified by PCR using primers corresponding to the target genes of the PCV type 2. Cloned genes were inserted into the baculovirus expression vector and PCV recombinant proteins were expressed using baculovirus expression system. Recombinant protein expression was determined by indirect immunofluorescent assay (IFA) and immunoblotting using polyclonal antiserum to PCV. ORF1 gene expressed two proteins with approximately 17 kDa and 31 kDa proteins in the baculovirus system. Recombinant protein of the ORF2 was similar to that of the native virus except minor bands with different molecular weight were detected. Recombinant protein expressed in the baculovirus system showed at least two glycosylation sites based on the tunicamycin treatment. Recombinant protein of the ORF2 assembled virus-like particle in recombinant virus infected insect cells.

Genetic characterization of porcine circovirus-2 field isolates from PMWS pigs

PMWS is a new emerging disease in swine herds worldwide. Field isolates of PCV-2, a putative major causative agent of PMWS, were isolated and genetically characterized. Viral genome of two field isolates (PC201DJ and PC201SS) from pigs showing typical PMWS was sequenced. The nucleotide sequence homology with other PCV-2 isolates was ranging from 95% to 99% in complete viral genomic sequence. The highly conserved nonanucleotide motif of replication origin was identical to that of other PCV-2 isolates. To determine the genetic heterogeneity of PCV-2 isolates, the phylogenetic tree based on the complete genome of PCV-2 isolates were constructed. Two PCV-2 field isolates were closely related to Canadian isolates of PCV-2. PCV-2 isolated from field may have an origin of North America and is possibly originated from importation of breeding stocks. The result indicates that although the genome of PCV-2 is relatively stable in general, minor genetic variations exist among PCV-2 isolates from the different geographic locations. These differences of viral genome might have an important implication for genetic characteristics of PCV-2 infection. Three major immunorelevant epitopes of capsid protein showed variations in amino acid sequences. Also, the variance of amino acid sequence in antigenic epitope existed between two Korean PCV-2 isolates.