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Journal of Clinical Microbiology, February 2005, p. 966-969, Vol. 43, No. 2
0095-1137/05/$08.00+0 doi:10.1128/JCM.43.2.966-969.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Indian Immunologicals Limited, Gachibowli, Hyderabad,1 Department of Biochemistry, Indian Institute of Sciences, Bangalore, India2
Received 12 August 2004/ Returned for modification 18 September 2004/ Accepted 30 September 2004
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The 1D region in the viral RNA codes for a major antigenic site consisting of the GH loop (140 to 160 amino acids) and a minor antigenic site (205 to 210 amino acids) at the C terminus of VP1 protein. These two sites are considered important for phylogenetic analysis, because genetic and antigenic variations in these sites are ascribed to differences among strains (9). Until recently two vaccine strains, C Bombay/64 and C IND/51/79, have been used in India; either of these strains was included in quadrivalent vaccines by different vaccine manufacturers. Hemadri et al. reported that the vaccine strain C Bombay/64 belonged to the European genotype (2); their study did not include the strain C IND/51/79. In the present study, the partial 1D sequences of various field isolates (1991 to 1994) and both the vaccine strains were studied to compare the relationship of these vaccine strains with the field isolates along with GenBank sequences available for type C viruses of European, South American, and Southeast Asian origin.
FMD viruses from independent outbreaks in different parts of India (Table 1) were obtained as tongue or foot epithelial tissue samples. A total of 11 isolates were included in this study, and all the isolates, except one (C MPH/12/92), were from nonvaccinated crossbred cattle. The virus isolates were passaged once in cells of the baby hamster kidney-21 (BHK-21) cell line, and antigenic comparison with the C IND/51/79 was performed using a Micro Neutralization test (MNT) as per the procedure of Rweyemamu and Hingley (7). The viruses were declared homologous when the r value was >0.23 and heterologous when the r value was <0.23.
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TABLE 1. Foot-and-mouth disease type C viruses isolated from convalescent cattle in different Indian states and used for partial 1D sequence comparisona
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TABLE 2. Foot-and-mouth disease virus type C isolates from Europe, South America, and Southeast Asia used for comparison of partial 1D sequences
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FIG. 1. Phylogenetic analysis of foot-and-mouth disease virus type C constructed using the neighbor-joining method. The bar represents the genetic distance. Numbers on the stems indicate bootstrap values.
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Amino acid comparisons made with those reported by Hemadri et al. (2) also revealed sequence similarity between the Indian serotype C isolates. However, C Bombay/64 strain has a deletion of one amino acid (R) in front of the RGD motif, in similarity to the European isolates. This may indicate that the C Bombay/64 strain is closer to the European isolates in the genetic makeup of the 1D region studied here than to the Indian isolates.
The GH loop near the C-terminal region and the BC loop near the N-terminal region of the VP1 region have been reported as the antigenic regions for the FMD viruses. Alignment of the deduced amino acid sequence revealed that there were 10 distinct substitutions in the field isolates compared to the results seen with the vaccine strain around the GH loop and in the C-terminal end of VP1. The substitutions were 131 T
S/N, 145 M
L, 149 A
V, 153 K
S, 188 V
I/H, 189 S
L, 190 F
P, 191 H
F/L/I, 198 Y
H, 202 I
L/S, and 203 I
V. Three substitutions were noticed in the GH loop (positions 138 to 156), and two were noticed in the carboxyl end (positions 195 to 200) of the 1D region. The residue H-147 in the RGD loop remained unchanged. Few isolates have shown distinct changes in their amino acid sequences. Changes in residues A-149 (A
T/V) and A-151 (A
T) have been noticed in few isolates. Residue T-194 of minor antigenic site C also remained unchanged except in one isolate. However, a change at the residue 203 is evident in four isolates. In spite of these changes the field isolates were found by use of the MNT to be homologous to the vaccine strain C IND/51/79.
Another interesting observation is that unlike other serotypes, classification of the C-type lineages is similar to the classification made on the basis of subtypes identified by Pereira (6). The phylogenetic analysis revealed seven distinct genotypes for the type C viruses (Fig. 1). The Southeast Asian and Indian isolates are grouped under two distinct genotypesgenotypes VI and VII, respectively. In the phylogenetic tree the C Bombay/64 strain is grouped with the European strains (genotype III). The C IND/51/79 is grouped with the Indian isolates but as a distinct lineage (genotype VII). The type C viruses in the subcontinent are not clearly descendants of the vaccine strains. The Indian type C viruses have a distinct evolution pattern and require further scrutiny to determine the origin of the type C viruses in India. The vaccine strain C IND/51/79 has a wide antigenic spectrum, as is evident from the MNT results, and is genetically related to the type C Indian isolates. This strain was characterized at the World Reference Laboratory, Pirbright, United Kingdom, after it was isolated from an outbreak in the state of Tamil Nadu, India. This vaccine strain was a part of the quadrivalent vaccine manufactured by Indian Immunologicals Ltd., Hyderabad, India, with technical support from the Wellcome Research Foundation, London, United Kingdom. Because of its homology to the Indian isolates, the C IND/51/79 may be considered a prototype strain of the type C viruses of Indian origin. Although type C outbreaks have been minimal, data presented in this study show that future type C FMD outbreaks in India and South Asia could be controlled by the use of C IND/51/79 vaccine strain.
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