Novel formulation with essential oils as a potential agent to minimize African swine fever virus transmission in an in vivo trial in swine

BACKGROUND AND AIM

African swine fever (ASF) is currently the most prevalent disease in swine. The disease is spreading throughout primary swine-producing countries with heavy losses in population and revenue. To date, no successful vaccines or medications have been reported. This study aimed to design and develop a blend of natural essential oils and test its efficacy against the ASF virus (ASFV) in swine.

MATERIALS AND METHODS

We attempted to develop a natural oil blend formulation (NOBF) and determine its efficacy against the ASFV. This study follows on from a previously published in vitro study that reported that the NOBF has anti-ASFV properties. A study was designed using 21 healthy piglets of triple-cross (Landrace + Yorkshire + Durok) crossbred pathogen-free pigs with an average weight of 15 kg. The study consisted of NOBF-incubated, NOBF, positive control, and negative control groups. The NOBF groups were administered NOBF (80 mL/ton mixed in drinking water) beginning 10 days before the challenge and continuing throughout the experiment. The positive and negative control pigs consumed regular drinking water. The pigs were challenged by a sublethal dose of pure isolate ASFV strain Vietnam National University of Agriculture-ASFV-L01/HN/04/19 inoculation with 103.5 HAD50/dose through the intramuscular route. There were sic pigs in each group, three pigs directly IM challenged, and three pigs were considered cohoused pigs.

RESULTS

Both challenged (three) and cohoused (three) pigs in the positive control showed clinical signs of ASFV infection, as detected by real-time polymerase chain reaction (RT-PCR) in blood samples, oral swabs, and feces. There was 100% cumulative mortality, that is, both challenged and contact pigs died in the positive control group on day 20 of infection. No signs of infection or mortality were observed in the NOBF-incubated group. The challenged pigs in the NOBF-direct challenge group showed clinical signs and mortality, whereas no clinical signs or symptoms occurred in the cohoused pigs. The immunoglobulin G (IgG) level of the contact pigs was the highest in the treatment group and the lowest in the positive control group. The IgM level of the contact pigs in the treatment groups was the lowest, whereas that of the positive control was the highest. The RT-PCR test showed that the ASFV was deactivated in the NOBF-incubated group. The challenged and contact pigs of the positive control group had high Ct values. The challenged pigs of the NOBF group had high Ct values, whereas the contact pigs from the same group and those of the negative control were negative for the ASFV, determined by PCR, in all samples. The comparison of the challenged groups showed that the appearance of the virus was delayed by at least 2 days in the NOBF group compared to the positive control group.

CONCLUSION

The results showed that NOBF can prevent the spread of the ASFV in a population. Moreover, NOBF can enhance the pig humoral immune system by enhancing IgG levels and reducing IgM levels. This study successfully demonstrated that NOBF is an anti-ASFV agent, which prevents horizontal transmission and enhances pig humoral immunity.

Natural oil blend formulation as an anti-African swine fever virus agent in in vitro primary porcine alveolar macrophage culture

BACKGROUND AND AIM

African swine fever is one of the severe pathogens of swine. It has a significant impact on production and economics. So far, there are no known remedies, such as vaccines or drugs, reported working successfully. In the present study, the natural oil blend formulation's (NOBF) efficacy was evaluated against ASFV in vitro using porcine alveolar macrophages (PAMs) cells of swine.

MATERIALS AND METHODS

The capacity of NOBF against the ASFV was tested in vitro. The NOBF combines Eucalyptus globulus, Pinus sylvestris, and Lavandula latifolia. We used a 2-fold serial dilution to test the NOBF formulation dose, that is, 105 HAD50/mL, against purified lethal dose of African swine in primary PAMs cells of swine. The PAM cells survival, real-time polymerase chain reaction (PCR) test, and hemadsorption (HAD) observation were performed to check the NOBF efficacy against ASFV.

RESULTS

The in vitro trial results demonstrated that NOBF up to dilution 13 or 0.000625 mL deactivates the lethal dose 105 HAD50 of ASFV. There was no HAD (Rosetta formation) up to dilution 12 or 0.00125 mL of NOBF. The Ct value obtained by running real-time PCR of the NOBF group at 96 h post-infection was the same as the initial value or lower (25), whereas the Ct value of positive controls increased several folds (17.84).

CONCLUSION

The in vitro trial demonstrated that NOBF could deactivate the ASFV. The NOBF has the potential to act as anti-ASFV agent in the field. The next step is to conduct in vivo level trial to determine its efficacy.

Protective efficacy of vaccines of the Korea national antigen bank against the homologous H5Nx clade 2.3.2.1 and clade 2.3.4.4 highly pathogenic avian influenza viruses

The occurrence of severe outbreaks of highly pathogenic avian influenza in Korea led to establishment of a national antigen bank for emergency preparedness. Here, we developed five vaccines for this bank (clade 2.3.2.1C, clade 2.3.4.4A, B, C, and D) by reverse genetics, inactivated them with formalin, and evaluated the protective efficacy and potency of serial dilutions against lethal homologous challenge in specific-pathogen-free chickens. After vaccination with one dose, each vaccine resulted in 100% survival, with no clinical symptoms, or lack of detectable virus shedding, and high levels of pre-challenge protective immunity (8.4-10.2 log₂). After vaccination with one-tenth of the full dose, protection was similar to that with the full dose. After vaccination with one-hundredth of the initial dose, survival was 20-80%, and all vaccines showed virus shedding. Four vaccines (excluding clade 2.3.2.1C) had satisfactory potency. In antibody-persistence tests, all vaccines maintained long-lasting protective immunity. Our results suggest that inactivated reverse-genetics vaccines genetically matched to outbreak viruses provide adequate protection after a single vaccination.

Antigenic characterization of highly pathogenic avian influenza A(H5N1) viruses with chicken and ferret antisera reveals clade-dependent variation in hemagglutination inhibition profiles

Highly pathogenic avian influenza (HPAI) A(H5N1) viruses pose a significant economic burden to the poultry industry worldwide and have pandemic potential. Poultry vaccination against HPAI A(H5N1) viruses has been an important component of HPAI control measures and has been performed in Vietnam since 2005. To systematically assess antigenic matching of current vaccines to circulating field variants, we produced a panel of chicken and ferret antisera raised against historical and contemporary Vietnamese reference viruses representing clade variants that were detected between 2001 and 2014. The antisera were used for hemagglutination inhibition (HI) assays to generate data sets for analysis by antigenic cartography, allowing for a direct comparison of results from chicken or ferret antisera. HI antigenic maps, developed with antisera from both hosts, revealed varying patterns of antigenic relationships and clustering of viruses that were dependent on the clade of viruses analyzed. Antigenic relationships between existing poultry vaccines and circulating field viruses were also aligned with in vivo protection profiles determined by previously reported vaccine challenge studies. Our results establish the feasibility and utility of HPAI A(H5N1) antigenic characterization using chicken antisera and support further experimental and modeling studies to investigate quantitative relationships between genetic variation, antigenic drift and correlates of poultry vaccine protection in vivo.

Appearance of reassortant European avian-origin H1 influenza A viruses of swine in Vietnam

Three subtypes-H1N1, H1N2 and H3N2-of influenza A viruses of swine (IAVs-S) are currently endemic in swine worldwide, but there is considerable genotypic diversity among each subtype and limited geographical distribution. Through IAVs-S monitoring in Vietnam, two H1N2 influenza A viruses were isolated from healthy pigs in Ba Ria-Vung Tau Province, Southern Vietnam, on 2 December 2016. BLAST and phylogenetic analyses revealed that their HA and NA genes were derived from those of European avian-like H1N2 IAVs-S that contained avian-origin H1 and human-like N2 genes, and were particularly closely related to those of IAVs-S circulating in the Netherlands, Germany or Denmark. In addition, the internal genes of these Vietnamese isolates were derived from human A(H1N1)pdm09 viruses, suggesting that the Vietnamese H1N2 IAVs-S are reassortants between European H1N2 IAVs-S and human A(H1N1)pdm09v. The appearance of European avian-like H1N2 IAVs-S in Vietnam marks their first transmission outside Europe. Our results and statistical analyses of the number of live pigs imported into Vietnam suggest that the European avian-like H1N2 IAVs-S may have been introduced into Vietnam with their hosts through international trade. These findings highlight the importance of quarantining imported pigs to impede the introduction of new IAVs-S.

Effect of herd size on subclinical infection of swine in Vietnam with influenza A viruses

Background

Influenza A viruses of swine (IAV-S) cause acute and subclinical respiratory disease. To increase our understanding of the etiology of the subclinical form and thus help prevent the persistence of IAV-S in pig populations, we conducted active virologic surveillance in Vietnam, the second-largest pig-producing country in Asia, from February 2010 to December 2013.

Results

From a total of 7034 nasal swabs collected from clinically healthy pigs at 250 farms and 10 slaughterhouses, we isolated 172 IAV-S from swine at the weaning and early-fattening stages. The isolation rate of IAV-S was significantly higher among pigs aged 3 weeks to 4.5 months than in older and younger animals. IAV-S were isolated from 16 large, corporate farms and 6 family-operated farms from among the 250 farms evaluated. Multivariate logistic regression analysis revealed that “having more than 1,000 pigs” was the most influential risk factor for IAV-S positivity. Farms affected by reassortant IAV-S had significantly larger pig populations than did those where A(H1N1)pdm09 viruses were isolated, thus suggesting that large, corporate farms serve as sites of reassortment events.

Conclusions

We demonstrate the asymptomatic circulation of IAV-S in the Vietnamese pig population. Raising a large number of pigs on a farm has the strongest impact on the incidence of subclinical IAV-S infection. Given that only some of the corporate farms surveyed were IAV-S positive, further active monitoring is necessary to identify additional risk factors important in subclinical infection of pigs with IAV-S in Vietnam.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0844-z) contains supplementary material, which is available to authorized users.

Prevalence and diversity of H9N2 avian influenza in chickens of Northern Vietnam, 2014

Despite their classification as low pathogenicity avian influenza viruses (LPAIV), A/H9N2 viruses cause significant losses in poultry in many countries throughout Asia, the Middle East and North Africa. To date, poultry surveillance in Vietnam has focused on detection of influenza H5 viruses, and there is limited understanding of influenza H9 epidemiology and transmission dynamics. We determined prevalence and diversity of influenza A viruses in chickens from live bird markets (LBM) of 7 northern Vietnamese provinces, using pooled oropharyngeal swabs collected from October to December 2014. Screening by real time RT-PCR revealed 1207/4900 (24.6%) of pooled swabs to be influenza A virus positive; overall prevalence estimates after accounting for pooling (5 swabs/pools) were 5.8% (CI 5.4–6.0). Subtyping was performed on 468 pooled swabs with M gene Ct < 26. No influenza H7 was detected; 422 (90.1%) were H9 positive; and 22 (4.7%) were H5 positive. There was no evidence was of interaction between H9 and H5 virus detection rates. We sequenced 17 whole genomes of A/H9N2, 2 of A/H5N6, and 11 partial genomes. All H9N2 viruses had internal genes that clustered with genotype 57 and were closely related to Chinese human isolates of A/H7N9 and A/H10N8. Using a nucleotide divergence cutoff of 98%, we identified 9 distinct H9 genotypes. Phylogenetic analysis suggested multiple introductions of H9 viruses to northern Vietnam rather than in-situ transmission. Further investigations of H9 prevalence and diversity in other regions of Vietnam are warranted to assess H9 endemicity elsewhere in the country.

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We report detection of highly pathogenic avian influenza (HPAI) from healthy chickens in Live Bird Markets of Vietnam. Because all breeds of domestic chickens are extremely susceptible to HPAI, we speculate that HPAI detections from market chickens may reflect infections that occur after arrival in the market. Alternatively, shedding of HPAI from healthy birds may reflect vaccine-induced protective immunity that mitigates disease but does not block viral infection.

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As many as 49% of all pooled surveillance swabs were positive for influenza A virus, corresponding to an overall Influenza A prevalence of 5.45% (95% Confidence Interval 5.4-6.0%).

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Low pathogenicity avian influenza (LPAI) H9N2 accounted for the vast majority of all influenza A detections in market chickens sampled from 9 northern provinces.

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To date there is no evidence to suggest an interaction effect between circulation of H5 and H9 viruses; however sampling strategies that involve pooling of surveillance swabs from multiple birds greatly complicates the assessment of co-infection rates or evaluation of epidemiological associations.

Geographical distribution of low pathogenic avian influenza viruses of domestic poultry in Vietnam and their genetic relevance with Asian isolates

From the avian influenza virus (AIV) outbreaks and market surveillances in Vietnam during November 2011 and March 2012, a total of 196 AIV were isolated. Although H5N1 highly pathogenic avian influenza (HPAI) was the most prevalent subtype in Vietnam, 57 low pathogenic avian influenza (LPAI) viruses were identified from mainly domestic ducks and some chickens. Of note, various subtypes of LPAI viruses were isolated from domestic ducks in Vietnam: H3 (n = 16), H4 (n = 4), H6 (n = 24), H7 (n = 1), and H9 (n = 10). Geographically, the LPAI viruses were identified in different regions of Vietnam. Phylogenetic analysis of HA and NA genes in LPAIV in Vietnam showed that some H3 (group I) and H4 subtypes AIV clustered with the viruses of several Asian isolates from domestic poultry and wild birds. However, the H6, H9, and some H3 (group II and III) subtypes AIV were closely related to isolates from domestic poultry in Southern China. In addition, whereas the N2 and N6 subtypes AIV belonged to the Eurasian lineage, the N8 subtype AIV was classified to be both of Eurasian and American lineage. These findings revealed that the regional trade and wild birds play a key role transmission of LPAIV in domestic ducks in Vietnam. Further surveillance at the intercountry level is needed to understand the epidemiology of these viruses and to cope with emergence of novel AIV types.

Pathogenicity and molecular characterization of emerging porcine reproductive and respiratory syndrome virus in Vietnam in 2007

In 2007, Vietnam experienced swine disease outbreaks causing clinical signs similar to the 'porcine high fever disease' that occurred in China during 2006. Analysis of diagnostic samples from the disease outbreaks in Vietnam identified porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV-2). Additionally, Escherichia coli and Streptococcus equi subspecies zooepidemicus were cultured from lung and spleen, and Streptococcus suis from one spleen sample. Genetic characterization of the Vietnamese PRRSV isolates revealed that this virus belongs to the North American genotype (type 2) with a high nucleotide identity to the recently reported Chinese strains. Amino acid sequence in the nsp2 region revealed 95.7-99.4% identity to Chinese strain HUN4, 68-69% identity to strain VR-2332 and 58-59% identity to strain MN184. A partial deletion in the nsp2 gene was detected; however, this deletion did not appear to enhance the virus pathogenicity in the inoculated pigs. Animal inoculation studies were conducted to determine the pathogenicity of PRRSV and to identify other possible agents present in the original specimens. Pigs inoculated with PRRSV alone and their contacts showed persistent fever, and two of five pigs developed cough, neurological signs and swollen joints. Necropsy examination showed mild to moderate bronchopneumonia, enlarged lymph nodes, fibrinous pericarditis and polyarthritis. PRRSV was re-isolated from blood and tissues of the inoculated and contact pigs. Pigs inoculated with lung and spleen tissue homogenates from sick pigs from Vietnam developed high fever, septicaemia, and died acutely within 72 h, while their contact pigs showed no clinical signs throughout the experiment. Streptococcus equi subspecies zooepidemicus was cultured, and PRRSV was re-isolated only from the inoculated pigs. Results suggest that the cause of the swine deaths in Vietnam is a multifactorial syndrome with PRRSV as a major factor.

Specific detection of H5N1 avian influenza A virus in field specimens by a one-step RT-PCR assay

Background

Continuous outbreaks of the highly pathogenic H5N1 avian influenza A in Asia has resulted in an urgent effort to improve current diagnostics to aid containment of the virus and lower the threat of a influenza pandemic. We report here the development of a PCR-based assay that is highly specific for the H5N1 avian influenza A virus.

Methods

A one-step reverse-transcription PCR assay was developed to detect the H5N1 avian influenza A virus. The specificity of the assay was shown by testing sub-types of influenza A virus and other viral and bacterial pathogens; and on field samples.

Results

Validation on 145 field specimens from Vietnam and Malaysia showed that the assay was specific without cross reactivity to a number of other infuenza strains as well as human respiratory related pathogens. Detection was 100% from allantoic fluid in H5N1 positive samples, suggesting it to be a reliable sampling source for accurate detection.

Conclusion

The assay developed from this study indicates that the primers are specific for the H5N1 influenza virus. As shown by the field tested results, this assay would be highly useful as a diagnostic tool to help identify and control influenza epidemics.

Antibody-secreting cell responses and protective immunity assessed in gnotobiotic pigs inoculated orally or intramuscularly with inactivated human rotavirus

Newborn gnotobiotic pigs were inoculated twice perorally (p.o.) (group 1) or intramuscularly (i.m.) (group 2) or three times i.m. (group 3) with inactivated Wa strain human rotavirus and challenged with virulent Wa human rotavirus 20 to 24 days later. To assess correlates of protection, antibody-secreting cells (ASC) were enumerated in intestinal and systemic lymphoid tissues from pigs in each group at selected postinoculation days (PID) or postchallenge days. Few virus-specific ASC were detected in any tissues of group 1 pigs prior to challenge. By comparison, groups 2 and 3 had significantly greater numbers of virus-specific immunoglobulin M (IgM) ASC in intestinal and splenic tissues at PID 8 and significantly greater numbers of virus-specific IgG ASC and IgG memory B cells in spleen and blood at challenge. However, as for group 1, few virus-specific IgA ASC or IgA memory B cells were detected in any tissues of group 2 and 3 pigs. Neither p.o. nor i.m. inoculation conferred significant protection against virulent Wa rotavirus challenge (0 to 6% protection rate), and all groups showed significant anamnestic virus-specific IgG and IgA ASC responses. Hence, high numbers of IgG ASC or memory IgG ASC in the systemic lymphoid tissues at the time of challenge did not correlate with protection. Further, our findings suggest that inactivated Wa human rotavirus administered either p.o. or parenterally is significantly less effective in inducing intestinal IgA ASC responses and conferring protective immunity than live Wa human rotavirus inoculated orally, as reported earlier (L. Yuan, L. A. Ward, B. I. Rosen, T. L. To, and L. J. Saif, J. Virol. 70:3075-3083, 1996). Thus, more efficient mucosal delivery systems and rotavirus vaccination strategies are needed to induce intestinal IgA ASC responses, identified previously as a correlate of protective immunity to rotavirus.

Systematic and intestinal antibody-secreting cell responses and correlates of protective immunity to human rotavirus in a gnotobiotic pig model of disease

Neonatal gnotobiotic pigs orally inoculated with virulent (intestinal-suspension) Wa strain human rotavirus (which mimics human natural infection) developed diarrhea, and most pigs which recovered (87% protection rate) were immune to disease upon homologous virulent virus challenge at postinoculation day (PID) 21. Pigs inoculated with cell culture-attenuated Wa rotavirus (which mimics live oral vaccines) developed subclinical infections and seroconverted but were only partially protected against challenge (33% protection rate). Isotype-specific antibody-secreting cells (ASC were enumerated at selected PID in intestinal (duodenal and ileal lamina propria and mesenteric lymph node [MLN]) and systemic (spleen and blood) lymphoid tissues by using enzyme-linked immunospot assays. At challenge (PID 21), the numbers of virus-specific immunoglobulin A (IgA) ASC, but not IgG ASC, in intestines and blood were significantly greater in virulent-Wa rotavirus-inoculated pigs than in attenuated-Wa rotavirus-inoculated pigs and were correlated (correlation coefficients: for duodenum and ileum, 0.9; for MLN, 0.8; for blood, 0.6) with the degree of protection induced. After challenge, the numbers of IgA and IgG virus-specific ASC and serum-neutralizing antibodies increased significantly in the attenuated-Wa rotavirus-inoculated pigs but not in the virulent-Wa rotavirus-inoculated pigs (except in the spleen and except for IgA ASC in the duodenum). The transient appearance of IgA ASC in the blood mirrored the IgA ASC responses in the gut, albeit at a lower level, suggesting that IgA ASC in the blood of humans could serve as an indicator for IgA ASC responses in the intestine after rotavirus infection. To our knowledge, this is the first report to study and identify intestinal IgA ASC as a correlate of protective active immunity in an animal model of human-rotavirus-induced disease.

The gnotobiotic piglet as a model for studies of disease pathogenesis and immunity to human rotaviruses

Gnotobiotic piglets serve as a useful animal model for studies of human rotavirus infections, including disease pathogenesis and immunity. An advantage of piglets over laboratory animal models is their prolonged susceptibility to human rotavirus-induced disease, permitting cross-protection studies and an analysis of active immunity. Major advances in rotavirus research resulting from gnotobiotic piglet studies include: 1) the adaptation of the first human rotavirus to cell culture after passage and amplification in piglets; 2) delineation of the independent roles of the two rotavirus outer capsid proteins (VP4 and VP7) in induction of neutralizing antibodies and cross-protection; and 3) recognition of a potential role for a nonstructural protein (NSP4) in addition to VP4 and VP7, in rotavirus virulence. Current studies of the pathogenesis of group A human rotavirus infections in gnotobiotic piglets in our laboratory have confirmed that villous atrophy is induced in piglets given virulent but not cell culture attenuated human rotavirus (G1, P1A, Wa strain) and have revealed that factors other than villous atrophy may contribute to the early diarrhea induced. A comprehensive examination of these factors, including a proposed role for NSP4 in viral-induced cytopathology, may reveal new mechanisms for induction of viral diarrhea. Finally, to facilitate and improve rotavirus vaccination strategies, our current emphasis is on the identification of correlates of protective active immunity in the piglet model of human rotavirus-induced diarrhea. Comparison of cell-mediated and antibody immune responses induced by infection with a virulent human rotavirus (to mimic host response to natural infection) with those induced by a live attenuated human rotavirus (to mimic attenuated oral vaccines) in the context of homotypic protection has permitted an analysis of correlates of protective immunity. Results of these studies have indicated that the magnitude of the immune response is greatest in lymphoid tissues adjacent to the local site of viral replication (small intestine). Secondly, there was a direct correlation between the degree of protection induced and the level of the intestinal immune response, with significantly higher local immune responses and complete protection induced only after primary exposure to virulent human rotavirus. These studies thus have established basic parameters related to immune protection in the piglet model of human rotavirus-induced disease, verifying the usefulness of this model to examine new strategies for the design and improvement of human rotavirus vaccines.