Genotyping of measles viruses to monitor the elimination process of the disease
Abstract number: s410
Santibanez S., Wolbert A., Mankertz A., Siedler A., Burki D., Tischer A.
WHO has set the goal for elimination of measles in the European Region by the year 2010. A very low incidence of measles (< 1 case per 1 Mio population and year) and an absence of endemic transmission have to be achieved. This implies that the transmission of indigenous measles virus (MV) has been interrupted and that an imported MV can not establish long-term circulation. Therefore, the level of measles susceptibility in the population has to be kept as low as possible by maintaining very high immunization coverage (> 95%) with two doses of measles vaccine. Genetic data of the detected MVs are essential to trace the pathway of the virus transmission. This information is required to discriminate whether local appearance of measles is due to virus importation or if it reflects a still ongoing circulation of an indigenous virus. The standardized nomenclature for genotyping of MVs, introduced by the WHO in 1998, enables description of MV circulation in a global context. At present, 23 distinct MV genotypes are recognized by the WHO. Experience shows that in countries with an area-wide and continuous monitoring of measles, the level of incidence correlates with the pattern of MV genotypes. This can be demonstrated for Germany where a laboratory supported nation-wide measles sentinel was established in 1999. Genotyping data over a period of > 6 years revealed that the few sporadic cases observed recently in the eastern part were mainly caused by imported MVs (genotypes B3, D4, D5, G2, H1, B2). In contrast, in the western part, endemic transmission has been observed until 2002. It was associated with the MV genotypes C2, D6 and the newly emerged D7. In 2003, endemic transmission was tapering off and in 2004, measles occurred only sporadically. The nation-wide incidence of measles decreased from 7.3 in 2001 to 0.2 in 2004. However, in 2005, local outbreaks occurred in the federal states of Hesse and Bavaria. The Hesse outbreak was due to importation of a D4 MV from Romania where an epidemic has been observed since the last quarter of 2004. The origin of the D6 MV that caused the Bavarian outbreak, however, remains unknown. The observation of two independent outbreaks demonstrates that despite the decline of measles incidence in recent years, the potential for a limited circulation of MV is still present in Germany. A study performed in Switzerland from 2003 onwards also indicates absence of endemic transmission. Imported MVs (genotypes D5, D8, D4) were predominantly detected and some could even establish limited circulation in 2003. This corresponds with the incidence of measles that remarkably increased from 0.8 in the years 2001/2002 to 10.2 in 2003 and decreased again to 0.8 in 2004/ 2005. Our studies demonstrate that for assessment of the level achieved in the process of measles elimination, it is essential to combine both MV genotype information and epidemiological data, even in the WHO European Region where the circulation of the former widespread MV genotypes may be interrupted in many countries, but nonetheless continues in some other countries.
|Session name:||XXIst ISTH Congress|
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