Molecular characterization of measles virus circulating in the Indian Ocean Islands during 2005-2006 and in France in 2006.

Despite the availability of safe and immunogenic vaccines, measles still causes significant morbidity and mortality especially in Africa. In this study, two measles outbreaks in the Indian Ocean Islands; Mayotte in 2005-2006 and Seychelles in 2006 were studied. Nasopharyngeal swabs, urine and/or blood samples were collected from patients with clinically diagnosed measles. Measles viruses were isolated in four cases from patients in Mayotte. Measles strains circulating in both outbreaks were determined to be genotype D4 when compared to the WHO reference strains. During this time, measles virus was isolated from patients in France and they were also found to belong to the same genotype. The viruses clustered into two distinct D4 subgroups; The Indian Ocean strains were similar to the Montreal-subgroup, whereas the French strains associated with the Johannesburg-subgroup. The Indian Ocean strains formed a homogeneous group. They shared four specific amino acids in the 3' region of the N gene and two amino acids in the H gene, which differed from other genotype D4 viruses. This suggests that the same measles lineage circulated in Mayotte and Seychelles. Sequence comparison of the French isolates with other measles strains showed that they were more closely related to strains circulating in Germany in 2005, which had their origin in Romania. This study provides the baseline for molecular epidemiology of measles virus in Mayotte and Seychelles. The knowledge of circulating measles virus will help in documenting measles elimination program. This report also highlights the fact that progress of measles elimination is blighted continually by the phenomenon of measles importation.