| Measles has been an important global health issue recently, particularly in developing countries, due to high incidence and the mortality in children. The post-1990's epidemiological characteristics of measles have changed comparatively with the 70-80's, and have become a focused issue. Therefore, it opens the question about the gene variation of the wild-measles strains and the efficiency of vaccine protection. In this study, we conducted epidemiological surveillance of wild-measles strains and the serum antibody of the population in Shanghai in 2005．The measles virus (MV) was isolated from throat swab specimens collected from suspected measles cases. The Antigen variation of MV and vaccine immuno protective efficiency was determined using molecular epidemiological approaches. The influence parameters of the measles epidemiological characteristics were evaluated according to the level of the measles antibody and antibody positive rate in different age groups and special populations. This study provided useful information in regards to the prevention and control of measles in China.Part one: epidemiological characteristics study of measles in Shanghai districts.During the 1990's, the incidence of measles decreased gradually to under 0．5/ 100,000 in local citizens, and started to try out elimination measles. However that number rapidly increased starting from 2001 because of the influence of migrants. In 1999-2004, the incidence of measles increased to above 1/100,000．Many changes took place in the age ranges of measles patients, which were mostly infants of younger than 8 months and adult of more than 20 years. In 2005, the number of measles cases increased rapidly once more. The incidence in local citizens was 8．12/100,000 during the period of January to June, which was 6．66 times the average incidence from 1999 to 2004．The incidence in infants of less than 8 months was the highest at 186．33/100,000．The incidence in adults of 30 to 39 years old was 30．85/100,000．These numbers were 2．48 and 12．28 times of the average incidence of the same age group during 1999-2004, respectively. The incidence in 15-19 years old was 4．24/100,000, which was 22．58 times of the average incidence from 1999 to 2004．2．The epidemiological characteristics in migrants from 1994 to 2004, the incidence in migrants was 2．14-13,63/100000 (higher than that in local citizens in all age groups), the cases was mostly children under 10 years old and adult of 15-29 years old, the incidence in infants < 8 months was the highest to 121．29/10万。In 2005, The incidence in migrants was 26．28/100000, which was 2．47 times of the average incidence during 1999-2004．The case number in 15-39 years old was 46．45%。Part two: the genotype Analysis and antigen variation of measles virus isolated in Shanghai in 20051．To ascertain the genetic characterization and genotype, the 450bp fragment of C terminus of the nucleprotein(N) gene and the complete H genes was amplified by RT-PCR and sequenced. The sequence analysis shows that the isolated wild-measles virus strain belonged to the H1 genotype, H1a sub-genotype, which was the native epidemic virus in china and was the same genotype with the other measles virus strain isolated in China. The vaccine strain (S191) belonged to the A genotype.2．H gene sequence analysis shows that there is a difference of about 91-97 nucleotides and 27-28 amino acids from vaccine strain S191 . The719th nucleotide was changed from G to A results in amino acid mutation from Ser (S) to Asn (N). Furthermore, one N-glycosylation site in 240th amino acids was lost because of the mutation. The 1441th nucleotide was changed f rom T to A, results in amino acid mutation from Tyr(Y) to Asn (N) , hemadsorption (HAD) from positive to negative. The most of the major neutralization sites have not apparent difference by comparing with vacccine strain s1913．A Cross-neutralization test was preformed against MV and s191 in the sera of measles cases and health population. The result indicated: The vaccine strains s191 enable to effectively protect from circulating wild-measles virus, but the neutralization antibody titer against MV and s191 were significantly different in the serum of naturally infected individuals and the initial vaccinated individuals. The high titer of vaccine strains antibody may neutralize the wild-measles virus. It is obvious that the measles outbreak in 2005 is related with the lower level of measles antibody.Part three: The level of measles antibody surveillance in difference population.1．The surveillance results in different age groups showed that The level of measles antibody distributing was significant difference in people of different age(<8 months, 1-19, 20-39 and >40 years old). In infant under 8 months, there were no antibody positive, the titer of neutralization antibody (NT) was all under 1: 8, the positive rate of neutralization antibody in 15-19 and 30-39 age groups was lower than other groups. It was 66．3%-70%. The highest titer of NT was in 1-age groups and 60-age groups, the positive rate was 96．7%-100%.which was vaccinated and naturally infected, respectively. The lower of transplacental antibodies may lead to the result of low antibody titers in infant.2．The surveillance results in matched mother and infant showed that the level of measles antibody of infants has closely relation with the level of mother's. The correlation coefficient of neutralization antibody (NT) was 0．889(p<0．001) , the titer of neutralization antibody was identical in mother and in infant, it indicated that improving the antibody level of mother was important to prevent the infant measles. 3．The surveillance results about the immunoprotection time show that the level of measles antibody was decreased with the growth up. After the fist vaccinated, in 1-2 years old, the vaccine neutralization antibody and wild-measles neutralization antibody was highest, which were 1:163．72 and1: 107．12．After about 10 years, the level of measles antibody became lower, the vaccine neutralization antibody and wild-measles neutralization decreased gradually to 41．20 and 28．11．Most of that has no protection to wild-measles strains, compared with the naturally infected, the immunoprotection time after the vaccination was shorter than that of 70-80's.4．The surveillance results in the other region showed that the positive rates of measles antibody in pregnant women in Zhejiang province and newborn in Heilongjiang province is not high, this indicated that the prevalence of pregnant women and infant was a focus issue in mostly region of china.Part four: the prevention strategy analysisThe results in this study indicated that the measles antibody distribution in different age groups was closely correlated with the infection status of measles in historical periods. With the vaccine coverage increasing, the measles has been successfully controlled at a low incidence in the 1990's.Giving that there are almost no naturally infection after the initiation of immunization program and the level of measles antibody in the first generation of vaccinated population and their infants was significantly decreased, the epidemiological characteristics was observably changed, which grouped the majority of the cases as adults and infants. It is suggested that the immunization program should be adjusted accordingly. It has been proved that a valid strategy to control and eliminate measles is to maintain high titers of the measles antibody in developed countries. It is necessary to carry out catch-up measles vaccinations, follow-up vaccinations and special population vaccinations in order to boost up the level of the measles antibody in the population. It is also important to develop epidemiological surveillance for the wild-measles strains, and attend to its antigen difference from the vaccine. It is critical to modify the current strategy in controlling and eliminating measles in the vaccine's age.
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