The use of non structural protein of FMDV to differentiate between vaccinated and infected animals 
in Thailand
The use of various non structural protein kits to differentiate between vaccinated and infected animals with foot and mouth disease virus
Antigenic variation of foot and mouth disease virus field outbreak in Thailand  and South East Asia region
during 2004-2005
Antigenic evolution of foot and mouth disease virus strains in Thailand
Molecular Epidemiology Analysis of Foot and Mouth Disease Virus Type O Field Outbreaks in Thailand
during 2005-2007
Development of competitive enzyme linked immunosorbent assay (C-ELISA) for detection of antibody to Foot and Mouth disease virus
Study on serological correlation of foot and mouth disease virus isolated from Thailand, Cambodia, Laos PDR and Vietnam during 2006-2007
Detection of foot and mouth disease virus from infected tissue specimens using rapid pen-side test
The use of molecular biology techniques for the diagnosis and epidemiological study of foot and mouth disease virus in Thailand
Antigenic relationship of foot and mouth disease viruses from field outbreaks in Thailand
Comparison of Various Types of Blocked Diluent in Seromonitoring of FMDV by Liquid Phase Blocking ELISA
Study of protective antibody titer in cattle and pigs after vaccination with foot and mouth disease vaccine by liquid phase blocking ELISA
Development of ELISA technique for detection of antibody to 3ABC non structure protein of foot and mouth disease virus to differentiate vaccinated from infected animals
Recent Characteristic of FMD virus in Thailand
Serological Correlation between Field Isolates and Vaccine Strain of Foot-and-mouth Disease Virus Type O in Thailand by Liquid Phase Neutralizing ELISA Test
การศึกษาด้านระบาดวิทยาระดับโมเลกุลของไวรัสโรคปากและเท้าเปื่อย ไทป์ เอ ที่ระบาดในประเทศไทย ระหว่างปี พ.ศ.2547-2548
การหาค่าความสัมพันธ์ทางซีรัมวิทยาของไวรัสโรคปากและเท้าเปื่อยไทป์ A ที่แยกได้ในประเทศไทยระหว่างปี 2546-2548

 The use of non structural protein of FMDV to differentiate between vaccinated and infected animals  in Thailand
Authors : Wilai Linchongsubongkoch,  Dilok Ounpomma and Panithan Thongtha
Publication : Proceedings of a final Research Co-ordination meeting. IAEA TECDOC-1154.  165-184
Abstract      
The detection of antibody to non-structure protein (NS) of foot and mouth disease virus (FMDV) using various type of NS kits which were produced from World Reference Laboratory (WRL) , United Biomedical Inc.(UBI), Bommeli/Intervet , CEDI and other research institutes have been studied.   The LP ELISA for measurement of antibody to FMDV type O, A and Asia1 have been carried out in parallel with the NS test in order to study the specificity and sensitivity of each NS test kit.  Three thousand nine hundred and twenty two serum samples from cattle, buffaloes and pigs which were grouped into non vaccination, single vaccination,  multiple vaccination and field infected animals have been examined.  The NS test using kit from WRL, UBI, Bommeli/Intervet, and CEDI were shown negative results in non vaccination cattle = 100%, 100%, 99% and 100% respectively , in pigs = 100% by both WRL and UBI.  While in the single vaccination were shown NS negative from WRL = 99.5% and UBI = 97.8%.   The NS test in multiple vaccination cattle and buffaloes were shown negative results by WRL= 97.73%, and UBI = 100%.   In the FMD field outbreak area,  the infected cattle were distinguished show highly positive result by NS test from WRL , UBI , Bommeli/Intervet, CEDI, Inoue/Japan , USDA and Pen Side/Korea were 98.3 %, 88.9 %,      84.6 %, 90.1%,  93.8% ,  88.3% and  84.6 % respectively as well as the infected pigs, a highly positive by the NS test from WRL = 73.33%  and UBI 80%.   This study indicated that the NS kit from WRL, UBI, Bommeli/ Intervet, and CEDI giving a high specificity assay in both cattle and pigs from 99-100 % and giving a high sensitivity assay from 84.6- 93.8 % in cattle and  73.33 - 80 % in pigs.    In addition, the NS test have been applied to be used in FMD sero-surveillance in animals being quarantined at the international quarantine station in multilateral Malaysia Thailand Myanmar (MTM) project and there has been applied to be used in sero-monitoring in field animals in the national plan of FMD vaccination campaign program in the country.   Hence, the use of NS test to differentiate between vaccinated and infected animals would be used as a standard diagnostic test for the control and eradication of FMD in the region. 
 
The use of various non structural protein kits to differentiate between vaccinated and infected animals with foot and mouth disease virus
Authors : Wilai Linchongsubongkoch,  Dilok Ounpomma and Panithan Thongtha
Publication : Journal of the Thai Veterinary Medical Association. 55(2):21-29.
Abstract:
The detection of antibody to non structural protein (NS) of foot and mouth disease virus (FMDV) using various types of NS kits which were produced from World Reference Laboratory (WRL),   United Biomedical Inc.(UBI), Bommeli/Intervet (Bomm) and CEDI Diagnostic B.V. (CEDI), was studied.   The conventional method of VIA test was also carried out in parallel with the NS test in order to study the specificity and sensitivity of each NS test kit.     One thousand one hundred and ninety seven serum samples (cattle = 918, buffaloes = 40, pigs = 239) from non vaccinated, single vaccinated,  multiple vaccinated and field infected animals were examined.   The NS test using kits from WRL, UBI, Bomm, CEDI and VIA test were shown high negative results in non vaccinated cattle were 100%, 99.74%, 99%, 100% and 100%, respectively, in pigs were shown all 100% negative results by  WRL, UBI and VIA test.   While in the single vaccinated cattle and pigs were shown NS negative results by WRL, UBI and VIA test were 99.03%, 98.4% and 97.7%, respectively.    The NS test in multiple vaccinated cattle and buffaloes were shown negative results by WRL, UBI and VIA test were 97.73%, 100% and 65.45%, respectively.  In the FMD field outbreak area,  the infected cattle were distinguished giving the highly positive results by NS test from WRL, UBI, Bomm, CEDI and VIA test were 98.3%, 88.9%, 84.6%, 90.1% and 100%, respectively, while in the infected pigs gave the highly positive by the NS test from  WRL, UBI and VIA test were found 73.33%, 80%, and 100%, respectively. This study indicated that the NS kit from WRL, UBI, Bomm, and CEDI giving the high specificity assay in both non vaccinated cattle and pigs from 99-100% and giving the high sensitivity assay from 84.6–98.3 % in cattle and 73.33-80% in pigs.  In addition,the false positive results from VIA test were found in multiple vaccinated animals.  Thus, the NS test could be used to replace VIA test to differentiate the vaccinated from naturally infected animals in serological assay for FMD diagnosis with increasing efficiency and accuracy.

Antigenic variation of foot and mouth disease virus field outbreak in Thailand  and South East Asia region during 2004-2005
Authors :  Romphruke Udon  and Wilai Linchongsubongkoch     
Publication : Journal of the Thai Veterinary Medical Association. 57(1): 15-23.
Abstract:
Antigenic variation of foot and mouth disease virus (FMDV) type O and Asia1 field outbreak in Thailand and South East Asia region during 2004 - 2005 were studied by liquid phase blocking ELISA (LP ELISA) method.   Totally 32 samples which were type O from Thailand = 20, Myanmar = 4, Vietnam = 7 and 1 sample of type Asia1 from Myanmar were submitted to the Regional Reference Laboratory for FMD in South East Asia for confirming the FMD diagnosis and further investigation of antigenic variation of FMDV field outbreak in the region.   The serological relationship (r-value) to the Thailand current vaccine strain of O/Udornthani/87 and Asia1/Petchburi/85 were determined.     The result found that   FMDV type O from Thailand gave r-value greater then 0.40 = 100% (20/20 )  as well as  the r-value both from Myanmar and Vietnam were greater than 0.40 = 100% (4/4 and 7/7 respectively).    This indicating no antigenic variation was found in FMDV type O in the region and trust that vaccine O/Udornthani/87 could give protection to field outbreak strain in Thailand,  Myanmar and Vietnam.   In addition one sample of type Asia1 from Myanmar was given r-value greater than 0.40 , this indicating no antigenic variation to Asia1/Petchburi/85 vaccine strain.    In conclusion, FMDV type O and Asia1 field outbreak in the region were belonged to the same Thailand vaccine strain. Hence, the current seed vaccine of O/Udornthani/87 and Asia1/Petchburi/85 could protect all field outbreak type O and Asia1 in Myanmar and Vietnam.

Antigenic evolution of foot and mouth disease virus strains in Thailand
Authors : Wilai Linchongsubongkoch,   Romphruke Udon  and Janya Samanit  
Publication: Submission to Journal of the Thai Veterinary Medical Association. 59 (1)
Abstract:                   
Type identification of foot and mouth disease virus (FMDV) in Thailand was carried out using standard ELISA typing test.    The samples collected during the past 11  years were used for evolution study of antigenic variation of FMDV type O, A and Asia1 by liquid phase blocking ELISA (LP ELISA).  The results were expressed as the serological relationship (r-value) between the ratio of serum titer against heterologous field strain and homologous vaccine strain.  R-values of type O and Asia1  showed close antigenic relationship to vaccine strains (O/189/87 and Asia1/85) respectively. It is therefore suggested that the existing seed vaccine strains for these serotypes  need not to be changed.   In contrast, the r-value of type A demonstrated antigenic variation compared to that of vaccine strain. Therefore, a new vaccine strain selected and changed to A/Sakolnakorn/97 in late 1997 and then to A118/ 87 in the beginning of year 2002 up to the present.  As a consequence, new strains were then selected for vaccine production.  This study demonstrated that continued monitoring of the evolution FMDV in Thailand is warranted as there may be discrepancy between the field and the vaccine strains.  This study would be useful in supporting the selection of appropriate virus vaccine strain for production of high efficacy vaccine and also supporting the control of FMD in Thailand.

Molecular Epidemiology Analysis of Foot and Mouth Disease Virus Type O Field Outbreaks in Thailand during 2005-2007
Authors : Panithan Thongtha, Wilai Linchongsubongkoch, Rattanee  Thongtha
Publication : Thai-NIAH eJournal. 3(1): 18-27.
Abstract :
Fifteen samples of foot and mouth disease virus field outbreaks in Thailand during 2005-2007 were tested by polymerase chain reaction (PCR) and nucleotide sequencing. All samples were detected by ELISA typing and amplified of cDNA by PCR technique using specific primer 1C-609/NK61. The PCR product (816 bp) which is specific to FMDV was shown clearly in each sample. The PCR products were then sequenced at VP1 genomic region in order to study on molecular epidemiological analysis. The complete sequence of 639 bp VP1 genome from each virus isolate was compared and analyzed as phylogenetic tree. It was found that all of type O viruses belonged to Cathay topotype and SEA topotype. The molecular epidemiological information in this study is useful for tracing back to the original virus causing outbreak in the field and can be used to support the seed vaccine virus selection to enhance the efficacy of vaccine production.

Development of competitive enzyme linked immunosorbent assay (C-ELISA) for detection of antibody to Foot and Mouth disease virus
Authors : Dilok Ounpomma and Wilai Linchongsubongkoch
Publication : Thai-NIAH eJournal. 3(1): 40-51.
Abstract :
A competitive enzyme linked immunosorbent assay (C-ELISA) for the detection of antibody against foot and mouth disease virus in 358 cattle sera was developed. Reagents used were polyclonal antisera and inactivated antigen developed in the country. Samples from non-vaccinated and uninfected, vaccinated, and infected animals were used and validated by comparing with liquid phase blocking ELISA (LP ELISA) and Cedi? FMDV type O test. Animal sample sera were diluted 1:5 and phosphate buffer saline 5% skim milk and 10% normal rabbit serum was used as a blocking diluent, and the inhibition reaction was cut off at 40%. The results showed a high specificity for non-vaccinated and uninfected animal serum samples (100%) and a high relative sensitivity with LP-ELISA and Cedi?  FMDV type O test for vaccinated and infected animal serum samples. In conclusion, C-ELISA can be used to differentiate naive animals from immunized animals.

Study on serological correlation of foot and mouth disease virus isolated from Thailand, Cambodia, Laos PDR and Vietnam during 2006-2007
Authors : Romphruke Udon, Dilok Ounpomma and Panithan Thongtha
Publication : Thai-NIAH eJournal. 3(1): 52-60.
Abstract :
A study on serological correlation (r-value) of foot and mouth disease virus (FMDV) types O, A and Asia1 from Thailand, Cambodia, Laos PDR and Vietnam during 2006-2007 to compare with the Thai current vaccine strains by liquid phase blocking ELISA (LP ELISA) was performed. Total 69 samples, type O=19 samples (5 from Thailand, 4 from Cambodia, 4 from Laos PDR and 6 from Vietnam ), type A=46 samples (27 from Thailand, 2 from Cambodia and 17 from Laos PDR) and 4 samples of type Asia1 from Vietnam were tested. In comparison with vaccine strain type O (strain O/Udornthani/87), type A (strain A/Saraburi/87) and type Asia1 (strain Asia1/Petchburi/85), it was found that all samples of FMDV types O and Asia1 gave r-value greater than 0.40, and 96.65% of samples of FMDV type A gave r-value greater than 0.40 and 4.35% gave r-value between 0.20-0.39. The result indicated that most of the isolates showed no antigenic variation with vaccine strains types O, A and Asia1 used in Thailand. In conclusion, field samples of FMDV types O, A and Asia1 collected from Thailand, Cambodia, Laos PDR and Vietnam during 2006-2007 belong to the same group of vaccine strains.

Detection of foot and mouth disease virus from infected tissue specimens using rapid pen-side test
Authors : Dilok  Ounpomma,  Romphruke  Udon  and  Wilai  Linchongsubongkoch    
Publication : Journal of Animal Science Gazette 5. 8(1): 37-46.
Abstract :
The rapid pen-side test kit (BioSign TM) for detection of foot and mouth disease virus (FMDV) antigen in samples  both from 10% tissue suspension (10%TS) and virus isolation fluid (VICF)  have been studied.  Totally 81 of known FMD positive and 9 of not type samples  by  ELISA were tested by using FB 4F11 kit which detected the structural protein of FMDV type O, A, Asia1, C and 3ABC non structural protein (3ABC NSP). While 51 of known FMD positive and 6 of not type samples by ELISA were test by using FB 4E11 kit which detected the structural protein of only FMDV type O and 3ABC NSP. It was founded that the average sensitivity of FB 4F11 kit was 81.48% (66/81) and 100% specificity (9/9), while  FB 4E11 kit gave 73.33% sensitivity (22/30) for type O samples and 100% spectivity (6/6 of the not type sample) while 21/21 of type A samples were negative.  In conclusion the test kits were simple and convenience in use and rapid in reading the results without using ELISA equipment. However the application of using FB 4F11 kit in the field should be further studied of its sensitivity and specificity with FMDV type Asia 1 and C. While the FB 4E11 kit is not suitable for the use in Thailand where several types of FMDV outbreaks.

The use of molecular biology techniques for the diagnosis and epidemiological study of foot and mouth disease virus in Thailand
Authors : Wilai Linchongsubongkoch, Thanarat Janukit, Sunan Romlumdoan, and Anuroj Phusirimongkol
Publication : Proceedings of a final Research Co-ordination meeting. IAEA TECDOC-1150. 105-112
Abstract
The detection of foot and mouth disease (FMD) virus from various kinds of field samples (tissue extract and cell culture isolate) was studied using polymerase chain reaction (PCR) technique. The gene selected for diagnosis was the polymerase gene and an amplification target product of 454 bp in length was produced using AP5/AP6 primer sets. The PCR product was further examined by NcoI endonuclease digestion. The presence of the internal restriction site was confirmed by demonstration of two small fragments of 330 bp and 124 bp in length. Forty-nine samples that gave positive and negative results by ELISA typing and were positive by the PCR test were tested by NcoI digestion to confirm the results. About 10% of PCR products could not be confirmed by the method. Furthermore the FMD RNA polymerase gene could be detected by the PCR method in samples negative in both ELISA typing and the virus isolation test. A total of 23 these samples were examined and compared after each stage of the testing process. At the end of the extraction for ELISA the amplification product band at 454 bp was detected in 73.91% of negative tissue extract samples, and from 47.82% at the end of the virus isolation procedure. The PCR technique was shown to rapidly and sensitively detect FMD viral genome, when compared with virus titration by tissue culture infectious dose 50% (TCID50) method. The PCR was about 10 times more sensitive than the virus titration technique in detection of virus. Therefore the PCR technique can be used in conjunction with current procedures for FMD diagnosis, to support the routine standard ELISA typing and virus isolation test in clinical samples. The nucleotide sequencing technique was introduced with a view to study genetic relationship of FMD outbreak viruses. The appropriate and specific primer sets used to detect the PCR products from field isolate viruses. The PCR products of FMDV type O, A and Asia1 showed a clear band at 720 bp, 814 bp and 914 bp respectively This work showed the technique could be introduced to perform the nucleotide sequencing to support epidemiological investigations. A small number of field isolate viruses type O were investigated, the result of dendrogram indicated that most of field isolate viruses were shown the close relationship to the virus vaccine strain.

Antigenic relationship of foot and mouth disease viruses from field outbreaks in Thailand
Authors : Wilai Linchongsubongkoch, Sunan Romlumdoan, Somjai Kamolsiripichaiporn, and Thanarat Janukit
Publication : Proceedings of a final Research Co-ordination meeting. IAEA TECDOC-1150. 113-118.
Abstract
The antibody titre against FMD type O, A and Asia1 was measured in 125 serum samples submitted to the laboratory. The antibody titre was estimated by a duplicate well two-fold dilution series using the liquid phase (LP) ELISA systems from the World Reference Laboratory (WRL), Pirbright, United Kingdom (supplied by FAO/IAEA) and Pakchong, FMD Center, Thailand. The titres expressed as log two base compared by linear regression. The linear regression equation coefficient (R) between the antibody titre from IAEA and Pakchong systems were R= 0.80 for type O, R= 0.73 for type A and R= 0.80 for type Asia 1 respectively. In addition the antigenic relationship to the current vaccine strains of type O, A and Asia1 FMD field viruses isolated during 1994-1998 was investigated by duplicate well two-fold dilution series LP ELISA method using Pakchong reagents. The serological relationship (r-value) of 122 field isolate viruses, type O = 74 samples, type A = 13 samples and type Asia1 = 35 samples have been studied and described. Most of field isolates type O showed the r-value greater 0.40 = 97.30%, r-value range 0.2-0.39 = 2.70%, and r-value < 0.19 = 0 %, indicating that vaccine strain O/Udornthani/87 should be protected the field virus strains as well as the r- value of type Asia1 field isolates were greater 0.40 = 97.14% and r-value range 0.20 - 0.39 = 2.86 which indicating that the recent vaccine strains Asia1/Petchburi/85 could be protected all field strains. While the r-value of type A field isolate virus in 1997 showed the antigenic diverge from A/Nakornpatom/87 recent vaccine strain, r-value <0.19 = 76.92%, r-value range 0.20-0.39 = 23.08% and r-value >0.40 = 0%

Comparison of Various Types of Blocked Diluent in Seromonitoring of FMDV by Liquid Phase Blocking ELISA
Authors : Anuroj Phusirimongkol, Dilok Aunpromma, Panithan Thongtha, Wilai Linchongsubongkoch
Publication : The Journal of Veterinary Biologics. Vol.11 no. 1-2. 45-55.
Abstract
The comparison among several type of blocked diluents containing of 0.5% gelatin, 5% Anlene skimmed milk and 5% Marvel skimmed milk were studied. One hundred and fifty eight of field serum samples were used to determine the antibody titer to foot and mouth disease virus (FMDV) type O, A and Asia1 by liquid phase blocking ELISA (LP ELISA). The result of antibody titer to FMDV type O, A and Asia1 using those blocked diluents were compared and expressed as a correlation coefficient (r) . For type O, r = 0.79, 0.90 and 0.81 respectively, type A, r = 0.73, 0.80 and 0.66 respectively and type Asia1, r = 0.84, 0.84 and 0.78 respectively. The conclusion in this study was proved that all blocked diluents gave a very high correlation among each serotype and could be replaced or used as a blocked diluent for reducing the non specific binding reaction in enzyme immunoassay process.

Study of protective antibody titer in cattle and pigs after vaccination with foot and mouth disease vaccine by liquid phase blocking ELISA
Authors : Wilai Linchongsubongkoch, Anuroj Phusirimongkol, Somkiat Petchwanichkul, Romphruke Udon
Publication : The Journal of Veterinary Biologics. Vol.10 no. 1-2. 41-49.
Abstract
The antibody titer against foot and mouth disease virus (FMDV) type O, A and Asia1 in sera of 130 cattle and 125 pigs at 3 weeks post vaccination in vaccine potency test were studied by liquid phase blocking ELISA (LP ELISA). These animals were protected after direct challenge with 10,000 ID50 of FMD homologous virus in cattle and 100 ID50 in pig. The protective level were defined as no presenting of clinical sign and localized lesion at the mouth and feet in experimental challenge animals. In cattle, the mean of protective antibody titer to FMDV type O, A and Asia1 were 1.982+ 0.611 (1:96) , 2.332+ 0.464 (1:214) and 2.00 + 0.514 (1:100) respectively. In pig, the mean of protective antibody titer to FMDV type O, A and Asia1 were 1.925+0.545 (1:84), 1.950+0.491 (1:90) and 1.861+ 0.588 (1:72) respectively.

Development of ELISA technique for detection of antibody to 3ABC non structure protein of foot and mouth disease virus to differentiate vaccinated from infected animals
Authors : Wilai Linchongsubongkoch, Anuroj Phusirimongkol, Nopporn Patanaprasith, Dilok Aunpromma, Panithan Thongtha
Publication : Proceedings on the 17th Annual Livestock Seminar. 27-42.
Abstract
The ELISA technique was developed to detect antibody to the 3ABC nonstructure protein (NS) of foot and mouth disease virus (FMDV) parallel with the VIA test and LP ELISA test. The assay indicated the satisfactory result to differentiate vaccinated from infected animals . Eight hundred and twenty five serum samples (cattle = 561, pigs = 264 ) from native, single vaccination, multiple time vaccination , experimentally challenged and field infected animals have been studied. The NS and VIA test in native animals were shown all negative in both assays and the mean of antibody titer to FMDV type O, A and Asia1 in cattle sera were 1.275+0.299, 1.603+0.315 and 1.215+0.330 respectively while in pig sera were 1.123+0.231, 1.115+0.245 and 1.06+0.192 respectively. The cattle sera which have been once vaccinated with FMDV trivalent vaccine were shown positive to NS and VIA test 5/272 (1.84%) and 9/272 (3.31%) whereas in pig sera were 4/90 (4.44%) and 0/90 (0%). The mean of antibody titer to FMDV type O, A and Asia1 in cattle sera were 2.063+0.440, 2.184+0.444 and 2.096+0.499 respectively while in pig sera were 1.610+0.479, 1.540+0.519 and 1.58+0.603 respectively. The sera from cattle which have been received multivaccination (2-7 times) were shown positive to NS and VIA test 3/80 (3.75%) and 28/80 (35%). The mean of antibody titer to FMDV type O, A and Asia1 were 2.509+0.532, 2.403+0.560 and 2.489+0.582 respectively. The result of sera from cattle after experimental challenge with FMD virus were shown positive to NS 4/44(9.09%) and VIA test 16/44 (36.36%) and the mean of antibody titer to FMDV type O,A and Asia1 in cattle sera were 2.875+0.593, 2.80+0.586 and 2.943+0.615 respectively. While in pig sera were shown positive to NS 35/66 (53.03%) and VIA test 5/66 (7.58%) and the mean of antibody titer to FMDV type O, A and Asia1 were 2.437+0.574, 2.473+0.610 and 2.594+0.648 respectively. In natural infected pig, the sera were shown high positive to NS 11/25 (44%) and VIA test 15/25 (60%). The mean of antibody titer to FMDV type O, A and Asia1 were 3.13+0.728, 2.88+0.672 and 2.985+0.691 respectively. Furthermore, the duration of NS antibody and VIA antibody in experimentally challenged animals could be detected from the first week to 16 weeks or more after infection. This study indicated that the NS test gave result in agreement with the VIA test . Therefore, the NS test could be helpful in reducing the false positive results in multivaccination serum samples. In addition, the NS test could be used as a serological assay for FMD diagnosis to distinguish or differentiate the vaccination from infection of FMDV in animal herd.

Recent Characteristic of FMD virus in Thailand
Authors : Wilai Linchongsubongkoch
Publication : Proceedings the 11th international Symposium of the World Association of Veterinary
Laboratory Diagnosticians and OIE Seminar on Biotechnology, page S9-15
Abstract
The laboratory diagnosis of foot and mouth disease in Thailand has been carried out by standard ELISA typing test and virus isolation on field samples from infected animals submitted for type identification. Those samples were used for further investigation of antigenic variation by liquid phase blocking ELISA (LP ELISA). The results were expressed as the serological relationship (r-value) between the ratio of serum titer against heterologous field strain and homologous vaccine strain. During the past 10 years, the antigenic variation of FMD type O, A and Asia1 have been studied. The r-value of type O and Asia1 demonstrated that there had been no recent antigenic change from the vaccine strain, and therefore it was not necessary to change the existing seed vaccine strain. In contrast the r-value of type A has varied antigenically from the vaccine strain from time to time. Therefore, a new vaccine strain has been necessary and the seed strain was changed to A/Sakolnakorn/97 in late 1997 and then to A/118/ 87 in the beginning of year 2002. In addition, the nucleotide sequencing of FMD field isolate and reference vaccine virus of type O, A and Asia1 was done and these strains were compared by sequencing at nucleotide 469-639 of VP1(1D) region. Sequences were analysed using dendrogram or phylogenetic tree. Type O field isolate belonged to the South East Asia (SEA) group. Isolate from recent type A outbreak were classified as belonging to Asia group while type Asia1 isolates were defined as topotype South Asia.

Serological Correlation between Field Isolates and Vaccine Strain of Foot-and-mouth Disease Virus Type O in Thailand by Liquid Phase Neutralizing ELISA Test
Authors : Romphruke Udon and Somjai Kamolsiripichaiporn
Publication : Animal Science Gazette 6(2), 46-55, June 2002
Abstract
Antigenic variation of foot-and-mouth disease virus type O field isolates from 1999 - 2001 in Thailand were studied. The liquid phase neutralizing ELISA (LP ELISA) was used to determine r-value of 80 field viruses and the vaccine strain (O/Udornthani/87). The range of r-value was 0.25 - 1 which 93.75% gave r-value greater than 0.4 while 6.25% gave r-value between 0.2 - 0.39. The results indicated that these field vuruses type O belonged to the same group of O/Udornthani/87. Therefore, O/Udornthani/87 still can be use as a seed vaccine in production line.