Sequence analysis of measles virus hemagglutinin isolated in Argentina during the 1997–1998 outbreak

Abstract

Sequence analysis was performed on 50 measles viruses (MV) isolated in Argentina. Forty-six were obtained during the current outbreak (1997-1998), three from the previous outbreak (1991) and one sporadic case (1994). A 377-bp fragment of the hemagglutinin (H) gene was directly amplified by RT-PCR from nasopharyngeal secretions. Nucleotides 8152 to 8417 were sequenced and subjected to phylogenetic analysis. Multiple silent changes and point mutations were found in all MVs. In 1991, substitutions affected the third base in codons resulting in silent changes. In 1994 an A-->C substitution at position 8321 changed amino acids 351 (Leu-->Ile). In 1997-1998, an A-->G substitution at position 8339 changed amino acids 357 (Val-->Ile). In 3/46 viruses, guanine deletion at position 8205 changed the reading frame and insertion of an extra cytosine at nucleotide 8235 shifted it back to the original frame. Phylogenetic analysis revealed that viruses leading to the last two major outbreaks are clustered into two separate branches. MVs that prevailed until 1994 were related to genotype C1 and MVs of the current outbreak to D6. Random drift mutations rendered a 0.5 ratio of nonsilent over silent mutations in most of the MVs analyzed. However, in those showing a reading frame shift, the ratio was greater than 1, suggesting that it was driven by immune selection.

Genetic Analysis of Measles Viruses Isolated in the United States between 1989 and 2001: Absence of an Endemic Genotype since 1994

“…However, the widespread distribution of D3 viruses with a low level of nucleotide variability suggests that during the resurgence period, the epidemiological conditions favored rapid spread of virus along a limited number of chains of transmission. A similar pattern of spread was observed for a very large outbreak of measles that occurred in São Paulo, Brazil, during 1997 that subsequently led to smaller outbreaks in other areas of South America [22][23][24][25][26]. In this case, nearly identical genotype D6 sequences were obtained in São Paulo and from the other South American outbreaks.…”

Molecular epidemiology of measles virus in Japan

“…In the South American continent, the indigenous strain was C1 before 1994 and a new genotype, D6, was detected in Sao Paulo, Brazil, in 1997, which was the dominant circulating strain in Europe 27 . Genotype D6 spread further to Argentina during the 1997−1998 outbreak 28 , and to Uruguay in 1999 29 .…”

The Other Infectious Diseases of Concern

“…However, these cases do not occur in temporal or geographic clustering patterns that might suggest a chain of endemic transmission. Moreover, the diversity of measles virus genotypes observed in the United States since 1997 (3) reflects multiple imported sources of virus and indicates that no genotype of measles is endemic in the United States. …”