Academic journal article Iranian Journal of Public Health

Molecular Epidemiology of Measles Virus before and after the 2003 Mass Vaccination Campaign for Measles/Rubella in Iran

Academic journal article Iranian Journal of Public Health

Molecular Epidemiology of Measles Virus before and after the 2003 Mass Vaccination Campaign for Measles/Rubella in Iran

Article excerpt

Abstract

Background: Molecular epidemiology of measles virus (MV) is important, not only to measure the success of measles vaccination programs but also to monitor the circulation and elimination of the virus worldwide. In this study, we compared MV obtained from patients before the 2003 mass vaccination MR campaign and viruses detected after 2003 until 2008 in Iran.

Methods: The nucleoprotein (N) gene of 29 MV strains circulating in Iran between 2002 and 2008 were amplified by RT-PCR and subjected to sequence and phylogenetic analysis.

Results: Molecular characterization of MV studied here revealed that although the outbreaks in Iran were associated with MV genotype D4, the isolated viruses clearly belonged to several different lineages. Maximum and minimum homology within the 29 Iranian strains in our study was100% and 94.9% within the carboxyl terminus of the N gene, respectively. Using ClustalX program, the alignment of Iranian MV sequences showed nine lineages.

Conclusion: This study provides the usefulness of MV sequence analysis for the demonstration of local interruption of indigenous strain transmission as well as providing a valuable means for monitoring the elimination processes of MV control.

Keywords: Measles, Genotype, Mass campaign, Iran

Introduction

Measles virus (MV), an enveloped RNA virus classified in the family Paramyxoviridae, genus Morbillivirus (1), is the most transmissible virus known in humans (2). Despite the vaccination programs, MV remains a heavy public health burden worldwide, particularly in developing countries (3, 4). Because of the high infectivity of measles, 95%-98% vaccine coverage is required to prevent virus circulation (2, 5). Serologically MV is known as a monotypic virus (6), however sequence analysis of the complete H gene and the 450 C-terminal nucleotides of the N gene (7, 8) classifies MV strains into eight clades (A-H) dividing into 23 genotypes (9,10). The MV clades have been recognized in different parts of the world however five of them (B1, D1, E, F, and G1) considered inactive since they have not been detected in the past 15 yr (11). In the Eastern Mediterranean region with established measles elimination goals by 2010 the objective has been to achieve and maintain interruption of indigenous measles transmission (3). Molecular epidemiology of MV is important for either measuring the success of measles vaccination programs or monitoring circulation and elimination of the virus throughout the world (12). Hence, genetic characterization of wild type MV can help to measure transmission pathways and to clarify epidemiological links during outbreaks, especially in the countries with an advanced elimination program, where most cases are imported (12, 9).

Measles vaccination started in Iran in 1967. In 1970 and 2003 the incidence of measles has been reported 346/100,000 (13) and 18/100,000 (11644 measles cases) respectively (14). Despite the reduction in the incidence of disease and the high vaccination coverage with routine measles vaccination program, including a two-dose vaccination regimen at nine months and 15 yr of age, measles cases have been reported in different areas in Iran (15). In this context, on December 2003, Iran conducted a measles/rubella (MR) catch-up campaign for individuals 5 to 25 yr olds that reached more than 33 million people with measles vaccine (16). The measles vaccination coverage has increased to 98% and the number of measles cases has clearly reduced after vaccination program. A post campaign serum-survey conducted in 2004 revealed >97.4% of the population aged between 5 and 40 yr had immunity to measles (15). Case-based surveillance for measles identified three children with laboratory confirmed disease in 2004, 35 in 2005, and 42 in 2006. The interruption of indigenous virus circulation by mass vaccination campaigns could be demonstrated by comparing the variability of pre and post campaign viruses (5). …

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