Raja, D (2009) Molecular Characterization of Indigenous Measles Virus Clades in Tamilnadu, Identification of Transmission Pathways and Its Implications on Measles Control Programme. Doctoral thesis, The Tamilnadu Dr. M.G.R. Medical University, Chennai.
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Abstract
In Tamil Nadu, measles outbreaks were reported from almost all the districts of the state, despite the maintenance of high level immunization coverage in the last decade. • 85.6% of the suspected outbreaks were confirmed as measles, 2.6% rubella, 10.5% mixed and 1.3% negative. • Highest number of suspected and confirmed outbreaks was in 2005. This is probably because effective surveillance with laboratory support was established in Tamil Nadu in 2005. • Highest number of measles outbreaks was reported during winter season (January – February). In case of rubella, during the Premonsoon season (March – May). Measles and rubella viruses were found to be co circulating. • Age shift was observed; maximum number of cases was reported between 5 and 10 years. This is in concurrence with other countries with good routine measles immunization coverage. • Since 2005, the percentage of measles outbreaks / cases decreased gradually and simultaneously the percentage of rubella and mixed outbreaks increased, which was statistically significant. This suggests the incidence of measles in the state is decreased possibly, as a result of high level of immunization coverage being maintained in the state. This surveillance also indirectly indicates the burden of rubella in the state. • It is concluded that blood samples collected between 4 and 10 days after the onset of rash proved to be more sensitive for laboratory confirmation and attempts should be made to optimize sample collection to between 4 to 10 days, This will become more critical for confirming individual cases for case based investigation in the measles elimination phase. • Success rate for virus isolation was better if samples were collected with in 2 days after the onset of rash. The success rate of virus isolation from throat swabs was higher than the success rate of virus isolation from urine samples. • Vero/hSLAM cell line found most sensitive for virus isolation. • Measles genotype D4, D7 and D8 were found to be co circulating in the state and multiple genotypes (D4 and D8) were in circulation in two districts (Vellore and Krishnagiri). This is the first isolation of genotype D7 in India. The genotype D7 detected in Tamil Nadu is unrelated to D7 in India but related to strains detected in European countries, than strains detected from SEAR countries. Probably the primary source of the strains that was circulating in Europe may have been from India, as prior to 1999 D7 was not detected in Europe. • The genotype D8 strains detected in Tamil Nadu was indigenous, multiple lineages were in circulation and disseminated through out the state during 2003 – 2007 and it has been associated with importation into USA and UK for at least 10 instances. • The study emphasis the importance of molecular surveillance to document the indigenous genotypes of measles. This would be invaluable to trace importation and confirm control and elimination status in the state in future and it should be continued. • Approximately 30% of the children who had received single dose of monovalent measles vaccine were susceptible to measles. This explains why the measles outbreaks have been reported from all the districts of the state. The susceptibility reduced to less than 20% if the children had received two dose vaccines. • It is also observed that antibodies were not detected in 8.6% of the children who had received single dose of measles vaccine and 3.3% of the children who had received two doses of vaccines. Probably these are vaccine failures. • The study has achieved its objective by confirming measles and Rubella outbreaks, providing data on measles and rubella incidences in the state and baseline molecular data about circulating measles viruses in the state of Tamil Nadu. This will help the health authorities to initiate and implement control strategies, monitor the efficacy of immunization and trend of the disease and monitor importation of virus when control is achieved.
| Item Type: | Thesis (Doctoral) |
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| Uncontrolled Keywords: | Indigenous measles virus clades, transmission pathways, measles control programme. |
| Subjects: | Respiratory Medicine > Community Medicine > Respiratory Medicine > Community Medicine |
| Depositing User: | Devi S |
| Date Deposited: | 20 Jun 2017 09:59 |
| Last Modified: | 11 Sep 2022 09:48 |
| URI: | http://repository-tnmgrmu.ac.in/id/eprint/134 |
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