A measles outbreak in Sindh, Pakistan caused by a genotype B3 virus

Measles continues to be a major public health issue causing substantial outbreaks worldwide, mostly affecting young children. Molecular analysis of measles viruses provides important information on outbreak linkages and transmission pathways that can be helpful towards implementation of appropriate control programs. In Pakistan, the control of measles is still tenuous, and progress towards elimination has been irregular and challenging. In the 2013 measles outbreak we received 4,682 sera collected from suspected patients in 23 districts across Sindh. A total of 3,283 samples were confirmed measles positive using IgM ELISA with the highest infection rate in children aged 1-12 months. Males were more affected than females and a visible peak was observed from January to April. Among the 3,283 cases, 59.1% were unvaccinated, 29.6% had received 1 dose and 10.3% had received 2 doses of measles vaccine while 0.85% had an unknown vaccination status. For genotype detection and phylogenetic analysis, 60 throat swab samples were collected from suspected patients below 15 years of age in eight districts of Sindh province. Forty four (73%; 44/60) throat swab samples were successfully genotyped using RT-PCR. Phylogenetic analyses based on partial sequences of the nucleocapsid protein gene revealed that all Pakistani measles virus strains belonged to genotype B3 and were closely related to those isolated from neighboring countries such as Iran, Afghanistan (99.1–100%) and India with 98.6 – 99.6% nucleotide homology. This is the first report on the phylogenetic analysis of measles B3 genotype strains from Pakistan and highlights the need for strengthening the surveillance systems and improving immunization coverage across the country.