Whole genome sequences of representative highly pathogenic avian influenza A(H5) viruses from Vie... more Whole genome sequences of representative highly pathogenic avian influenza A(H5) viruses from Vietnam were generated, comprising samples from poultry outbreaks and active market surveillance collected from January 2012 to August 2015. Six hemagglutinin gene clades were characterized. Clade 1.1.2 was predominant in southern Mekong provinces throughout 2012 and 2013, but gradually disappeared and was not detected after April 2014. Clade 2.3.2.1c viruses spread rapidly during 2012 and were detected in the south and center of the country. A number of clade 1.1.2 and 2.3.2.1c inter-clade reassortant viruses were detected with different combinations of internal genes derived from 2.3.2.1a and 2.3.2.1b viruses indicating extensive co-circulation. Although reassortment generated genetic diversity at the genotype level, there was relatively little genetic drift within the individual gene segments suggesting genetic stasis over recent years. Antigenically, clade 1.1.2, 2.3.2.1a, 2.3.2.1b, 2.3...
From the avian influenza virus (AIV) outbreaks and market surveillances in Vietnam during Novembe... more 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...
Newcastle disease virus (NDV) causes significant economic losses to the poultry industry in South... more Newcastle disease virus (NDV) causes significant economic losses to the poultry industry in Southeast Asia. In the present study, 12 field isolates of NDV were recovered from dead village chickens in Vietnam between 2007 and 2012, and were characterized. All the field isolates were classified as velogenic. Based on the sequence analysis of the F variable region, two distinct genetic groups (Vietnam genetic groups G1 and G2) were recognized. Phylogenetic analysis revealed that all the 12 field isolates fell into the class II genotype VII cluster. Ten of the field isolates, classified as Vietnam genetic group G1, were closely related to VIIh viruses that had been isolated from Indonesia, Malaysia, and Cambodia since the mid-2000s, while the other two field isolates, of Vietnam genetic group G2, clustered with VIId viruses, which were predominantly circulating in China and Far East Asia. Our results indicate that genotype VII viruses, especially VIIh viruses, are predominantly responsible for the recent epizootic of the disease in Vietnam.
In 2007, Vietnam experienced swine disease outbreaks causing clinical signs similar to the 'porci... more 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. Transboundary and Emerging Diseases
In spite of highly pathogenic avian influenza H5N1 vaccination campaigns for domestic poultry, H5... more In spite of highly pathogenic avian influenza H5N1 vaccination campaigns for domestic poultry, H5N1 viruses continue to circulate in Vietnam. To estimate the prevalence of avian influenza virus in Vietnam, surveillance was conducted between November 2011 and February 2013. Genetic analysis of 312 highly pathogenic avian influenza H5 viruses isolated from poultry in Vietnam was conducted and possible genetic relationships with strains from neighboring countries were investigated. As previously reported, phylogenetic analysis of the avian influenza virus revealed two H5N1 HPAI clades that were circulating in Vietnam. Clade 1.1, related to Cambodian strains, was predominant in the southern provinces, while clade 2.3.2.1 viruses were predominant in the northern and central provinces. Sequence analysis revealed evidence of active genetic evolution. In the gene constellation of clade 2.3.2.1, genotypes A, B, and B(II) existed during the 2011/2012 winter season. In June 2012, new genotype ...
Analysis of Asian H5N1 avian influenza (AI) virus hemagglutinin (HA) genes shows a common origin,... more Analysis of Asian H5N1 avian influenza (AI) virus hemagglutinin (HA) genes shows a common origin, but the virus has evolved into at least three major clades (clades 0, 1, and 2) over the last 13 years. Previous reports of Vietnam viruses have documented predominantly clade 1 viruses. Unexpectedly, 19 viruses from northern Vietnam isolated in December 2005 fell into clade 2. These viruses further clustered into two distinct sublineages. Representative viruses from each sublineage were chosen for antigenic and pathogenic evaluation. Two distinct antigenic groups correlating with the genetic information were present when comparing hemagglutination inhibition (HI) titers. All viruses were highly virulent not only in chickens, killing them within 2 days of experimental inoculation, but also in 2-and 5-week-old Pekin ducks, causing 100% mortality within 4 days of challenge. The information gained about these viruses provides insight with regards to implementing control programs, including vaccine seed strain selection.
There is increasing evidence that compounds in tick saliva and salivary gland extract (SGE) have ... more There is increasing evidence that compounds in tick saliva and salivary gland extract (SGE) have a suppressive effect on host immunity and that tick-borne pathogens exploit this situation to their benefit thus causing diseases. We have demonstrated that SGE derived from Rhipicephalus appendiculatus ticks has a suppressive effect on a macrophage like cell line, JA-4, in terms of secretion as well as mRNA transcription of three cytokines. Percent suppression of cytokine secretion by JA-4 cells cultured in the presence of lipopolysaccharide (LPS) and SGE in comparison to JA-4 cells cultured in the presence of LPS alone was 67.8, 89.1 and 82.0% for IL-1␣, TNF-␣ and IL-10, respectively (P < 0.05). A similar pattern of results was demonstrated in terms of mRNA transcription where SGE-induced suppression was 36.9% for IL-1␣, 25.0% for TNF-␣ and 31.5% for IL-10 (P < 0.05). In addition, we have demonstrated that SGE partially inhibited nitric oxide production by JA-4 activated with LPS. The results of the present study suggest that tick salivary gland compounds may exert their effect in vivo by blocking the functions of macrophages in the transcription of cytokines and production of nitric oxide. This SGE-induced immunomodulation may comprise a major gateway in the facilitation of tick feeding and transmission of pathogens in hosts.
Active surveillance for avian influenza (AI) viruses in poultry sold at live bird markets (LBMs) ... more Active surveillance for avian influenza (AI) viruses in poultry sold at live bird markets (LBMs) was conducted in 44 of 63 provinces throughout Vietnam over two periods from September 2011 to February 2012 and October 2012 to June 2013. The study objectives were to assess the prevalence of avian influenza type A, H5, and H5N1 subtype viruses and characterize the geographical and temporal distribution of H5N1 virus genetic variants across the country. Monthly sampling was conducted in 394 LBMs located in 372 communes. A total of 9790 oropharyngeal swabs from poultry were screened for influenza A virus by realtime reverse-transcriptase PCR. Virus isolation was attempted on all positive samples in embryonated chicken eggs, and the HA1 region of each H5 virus isolate was sequenced. Market prevalence of H5 subtype virus was 32.2% (127/394) over the cumulative 15 mo of surveillance. Phylogenetic analyses indicated that clade 1.1 viruses persisted in the south, whereas three genetically distinct subgroups of clade 2.3.2.1 were found simultaneously in northern, central, and southern Vietnam. Clade 2.3.2.1c viruses first appeared in July 2012 and spread rapidly to the center and south of Vietnam in late 2012, where they were predominant among clade 2.3.2.1 viruses and were detected in both active LBM surveillance and poultry outbreaks. Given the overlapping geographic distribution of clade variants and the antigenic divergence previously described for these clades, current AI poultry vaccines used in Vietnam may require bivalent formulations containing representatives of both clade 1.1 and clade 2.3.2.1 viruses.
Background Evaluation of two commercial lateral flow devices (LFDs) for avian influenza (AI) dete... more Background Evaluation of two commercial lateral flow devices (LFDs) for avian influenza (AI) detection in H5N1 highly pathogenic AI infected poultry in Vietnam.
Forty-six chickens and 48 ducks were sampled from four Vietnamese poultry premises in 2009 infect... more Forty-six chickens and 48 ducks were sampled from four Vietnamese poultry premises in 2009 infected with H5N1 highly pathogenic avian influenza (HPAI) clade 2.3.2 and 2.3.4 viruses, which also differed by cleavage site (CS) sequences in their haemagglutinin (HA) genes. All clinical specimens (n0282), namely tracheal and cloacal swabs plus feathers, were tested by five Eurasian reverse-transcriptase AI RealTime polymerase chain reaction (RRT-PCR) methods. Bayesian modelling showed similar high sensitivity for the validated H5 HA2 RRT-PCR and a new modified M-gene RRT-PCR that utilizes lyophilized reagents. Both were more sensitive than the validated ''wet'' M-gene RRT-PCR. Another RRT-PCR, which targeted the H5-gene CS region, was effective for clade 2.3.4 detection, but severely compromised for clade 2.3.2 viruses. Reduced sensitivity of the H5 CS and ''wet'' M-gene RRT-PCRs correlated with mismatches between the target and the primer and/or probe sequences. However, the H5 HA2 RRT-PCR sensitively detected both clade 2.3.2 and 2.3.4 viruses, and agreed with N1 RRT-PCR results. Feather testing from diseased chicken and duck flocks by AI RRT-PCRs resulted in the most sensitive identification of H5N1 HPAI-infected birds. Evolution of new H5N1 HPAI clades remains a concern for currently affected Asian countries, but also for more distant regions where it is important to be prepared for new incursions of H5N1 HPAI viruses. Genetic evidence for adamantane resistance and sensitivity was also observed in isolates from both clades.
Some publication in the name of To TL, searched by Medline
Email address: [email protected]
A... more Some publication in the name of To TL, searched by Medline Email address: [email protected] Actually, Dr. To Long Thanh is Director of the National Center for Veterinary Diagnosis of Vietnam.
Publication with the name of To LT. Email address: [email protected]
Actually, Dr. To Long Th... more Publication with the name of To LT. Email address: [email protected] Actually, Dr. To Long Thanh is Director of the National Center for Veterinary Diagnosis of Vietnam.
We characterized isolates from porcine respiratory and reproductive syndrome virus epidemics in V... more We characterized isolates from porcine respiratory and reproductive syndrome virus epidemics in Vietnam and China in 2007. These isolates showed ≈99% identity at the genomic level. Genetic analysis indicated that they share a discontinuous deletion of 30 aa in nonstructural protein 2, which indicates that identical variants emerged in Vietnam and China.
Background: Continuous outbreaks of the highly pathogenic H5N1 avian influenza A in Asia has resu... more 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.
Gnotobiotic pigs were orally inoculated with virulent Wa strain (G1P1A[8]) human rotavirus (group... more Gnotobiotic pigs were orally inoculated with virulent Wa strain (G1P1A[8]) human rotavirus (group 1), attenuated Wa rotavirus (group 2) or diluent (controls) and were challenged with virulent Wa rotavirus 21 days later. On various postinoculation or postchallenge days, virus-specific responses of systemic (blood and spleen) and intestinal (mesenteric lymph node and ileal lamina propria) mononuclear cells (MNC) were assessed by lymphoproliferative assays (LPA). After inoculation, 100% of group 1 pigs and 6% of group 2 pigs shed virus. Diarrhea occurred in 95, 12, and 13% of group 1, group 2, and control pigs, respectively. Only groups 1 and 2 developed virus-specific LPA responses prior to challenge. Group 1 developed significantly greater mean virus-specific LPA responses prior to challenge and showed no significant changes in tissue mean LPA responses postchallenge, and 100% were protected against virulent virus challenge. By comparison, both group 2 and controls had significantly lower LPA responses at challenge and both groups showed significant increases in mean LPA responses postchallenge. Eighty-one percent of group 2 and 100% of control pigs shed challenge virus, and both groups developed diarrhea that was similar in severity postchallenge. The virusspecific LPA responses of blood MNC mirrored those of intestinal MNC, albeit at a reduced level and only at early times postinoculation or postchallenge in all pigs. In a separate study evaluating antibody-secreting-cell responses of these pigs (L. Yuan, L. A. Ward, B. I. Rosen, T. L. To, and L. J. Saif, J. Virol. 70: , we found that the magnitude of a tissue's LPA response positively correlated with the numbers of virus-specific antibody-secreting cells for that tissue, supporting the hypothesis that the LPA assesses T-helper-cell function. The magnitude of LPA responses in systemic and intestinal tissues also strongly correlated with the degree of protective immunity elicited by the inoculum ( ؍ 0.81). We conclude that blood may provide a temporary ''window'' for monitoring intestinal T cells and that the LPA can be used to assess protective immunity to human rotaviruses.
Newborn gnotobiotic pigs were inoculated twice perorally (p.o.) (group 1) or intramuscularly (i.m... more 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.
Whole genome sequences of representative highly pathogenic avian influenza A(H5) viruses from Vie... more Whole genome sequences of representative highly pathogenic avian influenza A(H5) viruses from Vietnam were generated, comprising samples from poultry outbreaks and active market surveillance collected from January 2012 to August 2015. Six hemagglutinin gene clades were characterized. Clade 1.1.2 was predominant in southern Mekong provinces throughout 2012 and 2013, but gradually disappeared and was not detected after April 2014. Clade 2.3.2.1c viruses spread rapidly during 2012 and were detected in the south and center of the country. A number of clade 1.1.2 and 2.3.2.1c inter-clade reassortant viruses were detected with different combinations of internal genes derived from 2.3.2.1a and 2.3.2.1b viruses indicating extensive co-circulation. Although reassortment generated genetic diversity at the genotype level, there was relatively little genetic drift within the individual gene segments suggesting genetic stasis over recent years. Antigenically, clade 1.1.2, 2.3.2.1a, 2.3.2.1b, 2.3...
From the avian influenza virus (AIV) outbreaks and market surveillances in Vietnam during Novembe... more 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...
Newcastle disease virus (NDV) causes significant economic losses to the poultry industry in South... more Newcastle disease virus (NDV) causes significant economic losses to the poultry industry in Southeast Asia. In the present study, 12 field isolates of NDV were recovered from dead village chickens in Vietnam between 2007 and 2012, and were characterized. All the field isolates were classified as velogenic. Based on the sequence analysis of the F variable region, two distinct genetic groups (Vietnam genetic groups G1 and G2) were recognized. Phylogenetic analysis revealed that all the 12 field isolates fell into the class II genotype VII cluster. Ten of the field isolates, classified as Vietnam genetic group G1, were closely related to VIIh viruses that had been isolated from Indonesia, Malaysia, and Cambodia since the mid-2000s, while the other two field isolates, of Vietnam genetic group G2, clustered with VIId viruses, which were predominantly circulating in China and Far East Asia. Our results indicate that genotype VII viruses, especially VIIh viruses, are predominantly responsible for the recent epizootic of the disease in Vietnam.
In 2007, Vietnam experienced swine disease outbreaks causing clinical signs similar to the 'porci... more 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. Transboundary and Emerging Diseases
In spite of highly pathogenic avian influenza H5N1 vaccination campaigns for domestic poultry, H5... more In spite of highly pathogenic avian influenza H5N1 vaccination campaigns for domestic poultry, H5N1 viruses continue to circulate in Vietnam. To estimate the prevalence of avian influenza virus in Vietnam, surveillance was conducted between November 2011 and February 2013. Genetic analysis of 312 highly pathogenic avian influenza H5 viruses isolated from poultry in Vietnam was conducted and possible genetic relationships with strains from neighboring countries were investigated. As previously reported, phylogenetic analysis of the avian influenza virus revealed two H5N1 HPAI clades that were circulating in Vietnam. Clade 1.1, related to Cambodian strains, was predominant in the southern provinces, while clade 2.3.2.1 viruses were predominant in the northern and central provinces. Sequence analysis revealed evidence of active genetic evolution. In the gene constellation of clade 2.3.2.1, genotypes A, B, and B(II) existed during the 2011/2012 winter season. In June 2012, new genotype ...
Analysis of Asian H5N1 avian influenza (AI) virus hemagglutinin (HA) genes shows a common origin,... more Analysis of Asian H5N1 avian influenza (AI) virus hemagglutinin (HA) genes shows a common origin, but the virus has evolved into at least three major clades (clades 0, 1, and 2) over the last 13 years. Previous reports of Vietnam viruses have documented predominantly clade 1 viruses. Unexpectedly, 19 viruses from northern Vietnam isolated in December 2005 fell into clade 2. These viruses further clustered into two distinct sublineages. Representative viruses from each sublineage were chosen for antigenic and pathogenic evaluation. Two distinct antigenic groups correlating with the genetic information were present when comparing hemagglutination inhibition (HI) titers. All viruses were highly virulent not only in chickens, killing them within 2 days of experimental inoculation, but also in 2-and 5-week-old Pekin ducks, causing 100% mortality within 4 days of challenge. The information gained about these viruses provides insight with regards to implementing control programs, including vaccine seed strain selection.
There is increasing evidence that compounds in tick saliva and salivary gland extract (SGE) have ... more There is increasing evidence that compounds in tick saliva and salivary gland extract (SGE) have a suppressive effect on host immunity and that tick-borne pathogens exploit this situation to their benefit thus causing diseases. We have demonstrated that SGE derived from Rhipicephalus appendiculatus ticks has a suppressive effect on a macrophage like cell line, JA-4, in terms of secretion as well as mRNA transcription of three cytokines. Percent suppression of cytokine secretion by JA-4 cells cultured in the presence of lipopolysaccharide (LPS) and SGE in comparison to JA-4 cells cultured in the presence of LPS alone was 67.8, 89.1 and 82.0% for IL-1␣, TNF-␣ and IL-10, respectively (P < 0.05). A similar pattern of results was demonstrated in terms of mRNA transcription where SGE-induced suppression was 36.9% for IL-1␣, 25.0% for TNF-␣ and 31.5% for IL-10 (P < 0.05). In addition, we have demonstrated that SGE partially inhibited nitric oxide production by JA-4 activated with LPS. The results of the present study suggest that tick salivary gland compounds may exert their effect in vivo by blocking the functions of macrophages in the transcription of cytokines and production of nitric oxide. This SGE-induced immunomodulation may comprise a major gateway in the facilitation of tick feeding and transmission of pathogens in hosts.
Active surveillance for avian influenza (AI) viruses in poultry sold at live bird markets (LBMs) ... more Active surveillance for avian influenza (AI) viruses in poultry sold at live bird markets (LBMs) was conducted in 44 of 63 provinces throughout Vietnam over two periods from September 2011 to February 2012 and October 2012 to June 2013. The study objectives were to assess the prevalence of avian influenza type A, H5, and H5N1 subtype viruses and characterize the geographical and temporal distribution of H5N1 virus genetic variants across the country. Monthly sampling was conducted in 394 LBMs located in 372 communes. A total of 9790 oropharyngeal swabs from poultry were screened for influenza A virus by realtime reverse-transcriptase PCR. Virus isolation was attempted on all positive samples in embryonated chicken eggs, and the HA1 region of each H5 virus isolate was sequenced. Market prevalence of H5 subtype virus was 32.2% (127/394) over the cumulative 15 mo of surveillance. Phylogenetic analyses indicated that clade 1.1 viruses persisted in the south, whereas three genetically distinct subgroups of clade 2.3.2.1 were found simultaneously in northern, central, and southern Vietnam. Clade 2.3.2.1c viruses first appeared in July 2012 and spread rapidly to the center and south of Vietnam in late 2012, where they were predominant among clade 2.3.2.1 viruses and were detected in both active LBM surveillance and poultry outbreaks. Given the overlapping geographic distribution of clade variants and the antigenic divergence previously described for these clades, current AI poultry vaccines used in Vietnam may require bivalent formulations containing representatives of both clade 1.1 and clade 2.3.2.1 viruses.
Background Evaluation of two commercial lateral flow devices (LFDs) for avian influenza (AI) dete... more Background Evaluation of two commercial lateral flow devices (LFDs) for avian influenza (AI) detection in H5N1 highly pathogenic AI infected poultry in Vietnam.
Forty-six chickens and 48 ducks were sampled from four Vietnamese poultry premises in 2009 infect... more Forty-six chickens and 48 ducks were sampled from four Vietnamese poultry premises in 2009 infected with H5N1 highly pathogenic avian influenza (HPAI) clade 2.3.2 and 2.3.4 viruses, which also differed by cleavage site (CS) sequences in their haemagglutinin (HA) genes. All clinical specimens (n0282), namely tracheal and cloacal swabs plus feathers, were tested by five Eurasian reverse-transcriptase AI RealTime polymerase chain reaction (RRT-PCR) methods. Bayesian modelling showed similar high sensitivity for the validated H5 HA2 RRT-PCR and a new modified M-gene RRT-PCR that utilizes lyophilized reagents. Both were more sensitive than the validated ''wet'' M-gene RRT-PCR. Another RRT-PCR, which targeted the H5-gene CS region, was effective for clade 2.3.4 detection, but severely compromised for clade 2.3.2 viruses. Reduced sensitivity of the H5 CS and ''wet'' M-gene RRT-PCRs correlated with mismatches between the target and the primer and/or probe sequences. However, the H5 HA2 RRT-PCR sensitively detected both clade 2.3.2 and 2.3.4 viruses, and agreed with N1 RRT-PCR results. Feather testing from diseased chicken and duck flocks by AI RRT-PCRs resulted in the most sensitive identification of H5N1 HPAI-infected birds. Evolution of new H5N1 HPAI clades remains a concern for currently affected Asian countries, but also for more distant regions where it is important to be prepared for new incursions of H5N1 HPAI viruses. Genetic evidence for adamantane resistance and sensitivity was also observed in isolates from both clades.
Some publication in the name of To TL, searched by Medline
Email address: [email protected]
A... more Some publication in the name of To TL, searched by Medline Email address: [email protected] Actually, Dr. To Long Thanh is Director of the National Center for Veterinary Diagnosis of Vietnam.
Publication with the name of To LT. Email address: [email protected]
Actually, Dr. To Long Th... more Publication with the name of To LT. Email address: [email protected] Actually, Dr. To Long Thanh is Director of the National Center for Veterinary Diagnosis of Vietnam.
We characterized isolates from porcine respiratory and reproductive syndrome virus epidemics in V... more We characterized isolates from porcine respiratory and reproductive syndrome virus epidemics in Vietnam and China in 2007. These isolates showed ≈99% identity at the genomic level. Genetic analysis indicated that they share a discontinuous deletion of 30 aa in nonstructural protein 2, which indicates that identical variants emerged in Vietnam and China.
Background: Continuous outbreaks of the highly pathogenic H5N1 avian influenza A in Asia has resu... more 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.
Gnotobiotic pigs were orally inoculated with virulent Wa strain (G1P1A[8]) human rotavirus (group... more Gnotobiotic pigs were orally inoculated with virulent Wa strain (G1P1A[8]) human rotavirus (group 1), attenuated Wa rotavirus (group 2) or diluent (controls) and were challenged with virulent Wa rotavirus 21 days later. On various postinoculation or postchallenge days, virus-specific responses of systemic (blood and spleen) and intestinal (mesenteric lymph node and ileal lamina propria) mononuclear cells (MNC) were assessed by lymphoproliferative assays (LPA). After inoculation, 100% of group 1 pigs and 6% of group 2 pigs shed virus. Diarrhea occurred in 95, 12, and 13% of group 1, group 2, and control pigs, respectively. Only groups 1 and 2 developed virus-specific LPA responses prior to challenge. Group 1 developed significantly greater mean virus-specific LPA responses prior to challenge and showed no significant changes in tissue mean LPA responses postchallenge, and 100% were protected against virulent virus challenge. By comparison, both group 2 and controls had significantly lower LPA responses at challenge and both groups showed significant increases in mean LPA responses postchallenge. Eighty-one percent of group 2 and 100% of control pigs shed challenge virus, and both groups developed diarrhea that was similar in severity postchallenge. The virusspecific LPA responses of blood MNC mirrored those of intestinal MNC, albeit at a reduced level and only at early times postinoculation or postchallenge in all pigs. In a separate study evaluating antibody-secreting-cell responses of these pigs (L. Yuan, L. A. Ward, B. I. Rosen, T. L. To, and L. J. Saif, J. Virol. 70: , we found that the magnitude of a tissue's LPA response positively correlated with the numbers of virus-specific antibody-secreting cells for that tissue, supporting the hypothesis that the LPA assesses T-helper-cell function. The magnitude of LPA responses in systemic and intestinal tissues also strongly correlated with the degree of protective immunity elicited by the inoculum ( ؍ 0.81). We conclude that blood may provide a temporary ''window'' for monitoring intestinal T cells and that the LPA can be used to assess protective immunity to human rotaviruses.
Newborn gnotobiotic pigs were inoculated twice perorally (p.o.) (group 1) or intramuscularly (i.m... more 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.
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Papers by Thanh L To
44 of 63 provinces throughout Vietnam over two periods from September 2011 to February 2012 and October 2012 to June 2013.
The study objectives were to assess the prevalence of avian influenza type A, H5, and H5N1 subtype viruses and characterize the
geographical and temporal distribution of H5N1 virus genetic variants across the country. Monthly sampling was conducted in 394
LBMs located in 372 communes. A total of 9790 oropharyngeal swabs from poultry were screened for influenza A virus by realtime reverse-transcriptase PCR. Virus isolation was attempted on all positive samples in embryonated chicken eggs, and the HA1
region of each H5 virus isolate was sequenced. Market prevalence of H5 subtype virus was 32.2% (127/394) over the cumulative
15 mo of surveillance. Phylogenetic analyses indicated that clade 1.1 viruses persisted in the south, whereas three genetically distinct
subgroups of clade 2.3.2.1 were found simultaneously in northern, central, and southern Vietnam. Clade 2.3.2.1c viruses first
appeared in July 2012 and spread rapidly to the center and south of Vietnam in late 2012, where they were predominant among
clade 2.3.2.1 viruses and were detected in both active LBM surveillance and poultry outbreaks. Given the overlapping geographic
distribution of clade variants and the antigenic divergence previously described for these clades, current AI poultry vaccines used in
Vietnam may require bivalent formulations containing representatives of both clade 1.1 and clade 2.3.2.1 viruses.
Email address: [email protected]
Actually, Dr. To Long Thanh is Director of the National Center for Veterinary Diagnosis of Vietnam.
Actually, Dr. To Long Thanh is Director of the National Center for Veterinary Diagnosis of Vietnam.
44 of 63 provinces throughout Vietnam over two periods from September 2011 to February 2012 and October 2012 to June 2013.
The study objectives were to assess the prevalence of avian influenza type A, H5, and H5N1 subtype viruses and characterize the
geographical and temporal distribution of H5N1 virus genetic variants across the country. Monthly sampling was conducted in 394
LBMs located in 372 communes. A total of 9790 oropharyngeal swabs from poultry were screened for influenza A virus by realtime reverse-transcriptase PCR. Virus isolation was attempted on all positive samples in embryonated chicken eggs, and the HA1
region of each H5 virus isolate was sequenced. Market prevalence of H5 subtype virus was 32.2% (127/394) over the cumulative
15 mo of surveillance. Phylogenetic analyses indicated that clade 1.1 viruses persisted in the south, whereas three genetically distinct
subgroups of clade 2.3.2.1 were found simultaneously in northern, central, and southern Vietnam. Clade 2.3.2.1c viruses first
appeared in July 2012 and spread rapidly to the center and south of Vietnam in late 2012, where they were predominant among
clade 2.3.2.1 viruses and were detected in both active LBM surveillance and poultry outbreaks. Given the overlapping geographic
distribution of clade variants and the antigenic divergence previously described for these clades, current AI poultry vaccines used in
Vietnam may require bivalent formulations containing representatives of both clade 1.1 and clade 2.3.2.1 viruses.
Email address: [email protected]
Actually, Dr. To Long Thanh is Director of the National Center for Veterinary Diagnosis of Vietnam.
Actually, Dr. To Long Thanh is Director of the National Center for Veterinary Diagnosis of Vietnam.