During 2008-2009, fifteen field infectious bronchitis viruses (IBVs) were isolated from commercial chicken farms in Thailand. After sequencing of the complete S1 gene, phylogenetic analysis was performed and this found that the Thai IBV isolates were divided into three distinct groups, unique to Thailand (group I), QX-like IBV (group II), and Massachusetts type (group III). This finding indicated that the recent Thai IBVs evolved separately and that at least three groups of viruses are circulating in Thailand. The recombination analysis of the S1 gene demonstrated that the 5'-terminus of the group I was similar to isolate THA001 which was unique to Thailand, isolated in 1998 whereas the 3'-terminus was similar to the group II. Moreover, the analysis of the S1 gene of the group II showed that the 5'-terminus was similar to QXIBV, isolated in China whereas the remaining region at the 3'-terminus was similar to the Chinese strain JX/99/01. The results indicated that the recombination events occurred in the S1 gene between the field strains. Based on these facts, the field IBV in Thailand has undergone genetic recombination.

Thirteen field isolates of infectious bronchitis virus (IBV) were isolated from broiler flocks in Thailand between January and June 2008. The 878-bp of the S1 gene covering a hypervariable region was amplified and sequenced. Phylogenetic analysis based on that region revealed that these viruses were separated into two groups (I and II). IBV isolates in group I were not related to other IBV strains published in the GenBank database. Group 1 nucleotide sequence identities were less than 85% and amino acid sequence identities less than 84% in common with IBVs published in the GenBank database. This group likely represents the strains indigenous to Thailand. The isolates in group II showed a close relationship with Chinese IBVs. They had nucleotide sequence identities of 97-98% and amino acid sequence identities 96-98% in common with Chinese IBVs (strain A2, SH and QXIBV). This finding indicated that the recent Thai IBVs evolved separately and at least two groups of viruses are circulating in Thailand.

The development of acquired resistance in opisthorchiasis was studied in hamsters experimentally infected with Opisthorchis viverrini. The induction of protective immunity was attempted by first exposing adult female golden Syrian hamsters to 1, 2 or 3 doses of infective metacercariae obtained from naturally infected cyprinoid fishes and then reinfecting them with 80 metacercariae. In other experiments, animals that were infected with 50 metacercariae were treated with praziquantel prior to being rechallenged in order to eliminate the flukes that had developed from the first infection. The effect of long-term chronic infections was also studied. Faecal egg counts were determined at weekly intervals from 4-5 weeks onwards. The animals were killed 2-3 months after the last infection for worm recovery, and terminal faecal egg output/g faeces/worm was calculated. The data showed that prior infection of animals with O. viverrini did not induce significant protective immunity against reinfection by the same parasite. Lack of protection was also noted in animals reinfected several times with small doses of metacercariae. However, under certain circumstances, prior infection could result in a significant reduction in the faecal egg output due to subsequent infection.