Excerpted from the thesis of Ta Hoang Long

1. Brief introduction

Title: “Generation of seed for food and mouth disease vaccine from the local isolate in Vietnam, field strain VP02 (subtype Ox)”.

– PhD candidate: Ta Hoang Long

– Scientific supervisors:

1. Ass. Prof. Dr. Nguyen Viet Khong
2. Ass. Prof. Dr.  Truong Van Dung

– Field of study: Microbiology     Code: 62 62 50 10

– Institution: National Institute of Veterinary Research

2. Dissertation contents

2.1 Aims and objects of the study

The study is aiming at the generation of seed for food and mouth disease vaccine from the local isolate in Vietnam. The objective of this study was the FMD virus strain VP02 isolated in Vietnam.

2.2 Research methods

The main methodologies included (i) Isolation and culture of virus; (ii) RT-PCR to detect FMD virus; (iii) sequencing and molecular genetic analyses (iv) Methods for viral Inactivation and adjuvant and antigen preparation; (v) Virus titration and neutralization test (vi) Infection of experimental animals and pigs.

2.3 Research’s results and conclusions

(1) We have demonstrated the VP02 isolate was a sub-lineage of serotype O, a new topotype, distinguishable from the conventional type O strains be genetic property of gene 1d (encoding for VP1 protein) and the VNT index remained only 36%. This new topotype Vit04, emerged since 2003, potentially re-emerged and expanded to other areas, which was threatening a high risk of co-infection and large outbreaks in futures.

(2) We have adapted the local isolate VP02 on BHK 21 cell culture, which was stable both in genetic property of VP1 encoding gene and virus amplification after 20 passages (7.19lg TCID₅₀), as well it showed the maintain of pathogenicity after 10 passages: ID₅₀ for pigs at 0.5 ml x 6.58lg TCID₅₀/ml; for mice: 10 µl 6.58lg TCID₅₀/ml and for guinea pigs at 100 µl 6.58lg TCID₅₀/ml.

(3) One dose of the inactivated antigens (1 ml of 1 x 7lg TCID₅₀ determined prior to inactivation) prepared from VP02 strain triggered the pig immune response of 1/64 titer and protected immunized pigs from challenges with 10 LD₅₀ of virulent original virus.

Scientific contributions:

(1) Molecular genetic analysis has provided scientific bases for the phylogenesis of a new Vit04 topotype, locally emerged, sharply marked a new complication of FMD situation in the region.

 (2) Establishments of pathogenesis and the infection protocol of VP02 strain for susceptible pigs, paving a new way for future study on animal model.

(3) Establishment of stepwise protocol for adaptation of a field isolate to select vaccine strain.

Practical relevance:

(1) Provided crucial information of a new emergence strain, which supported the disease control authority on the adaptation to have a better strategy.

(2) The cell-adaptive VP02 strain with the best antigen match to the circulating strains may be considered a supplementary candidate to the virus vaccine bank for controlling disease in Vietnam.

(3) Provide supplementary documents for Veterinary FMD courses.

New outputs:

1. We have determined, for the first time, a new FMDV topotype (Vit04, with the VP02 representative), a lineage of SEA-Mya98, harboring distinguishable genetic and antigenic and circulation currently only in Vietnam (and possibly surrounding areas)
2. This is the first time in Vietnam; we have experimentally succeeded and established method to re-produce FMD infection of susceptible pigs in laboratory conditions.
3. We have demonstrated, herein for the first time in Vietnam, a successful adaptation of FMD virus for a stable amplification in cell culture and satisfying the requirement of a vaccine seed, generating high protective potency in the immunized pigs from challenging, opening the possibility of generation seed and production of FMD vaccine locally.