Dengue fever is a self-limiting, acute febrile disease which may aggravate to haemorrhage, plasma leakage and organ impairment in small number of cases. An outbreak of dengue fever occurred in Delhi, India after rainy season in the year 2013. Dengue virus specific RT-PCR was carried out on 378 suspected blood samples that were collected during the outbreak. Dengue virus was detected in 71% samples with highest number of patients infected by DENV-2 (86%) followed by DENV-1 (19 %) and DENV-3 (8%). Co-infection with more than one DENV serotype was detected in 14% samples. Twenty nine DENV strains (10 DENV-1, 12 DENV-2 and 7 DENV-3) were sequenced for partial envelope protein gene. Phylogenetic analysis grouped DENV-1 strains in the American African genotype, DENV-2 strains in the Cosmopolitan genotype and DENV-3 in Genotype III. We report the serotype distribution, circulating genotypes and partial envelope protein gene sequence of 29 DENV strains detected during 2013 outbreak in Delhi, India.
Funding StatementThe study was funded by University Grants Commission, Government of India. The URL of the funder’s website is http://www.ugc.ac.in. The grant number is 41-1287/2012 (SR).The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Delhi, the capital of India, is a large metropolitan city which attracts thousands of people from all over India for better business and career opportunities. Many housing areas have cropped up to meet the demands of its ever growing population but the infrastructure and drainage facilities are poor causing favorable conditions for mosquito breeding. As a result, Dengue fever, a mosquito borne disease, is common in Delhi reaching epidemic proportions after every 3-4 years. Dengue fever outbreaks have been reported in Delhi in 19671 , 19702 , 19823 , 19884 , 19965 , 20036 , 20067 and 20108. Dengue fever is characterized by fever, aches and pain, rash, nausea, vomiting, weakness and prostration while in some cases it aggravates to haemorrhage, plasma leakage and organ impairment9. A vaccine for dengue is not available yet as the virus exists as 4 serotypes which do not cross-protect and enhance the risk of severe disease by antibody dependent enhancement of infection10. There was an increase in the number of cases of dengue fever reported from Delhi and all over India in the year 201311. The present study was undertaken to characterize dengue viruses detected during the outbreak in Delhi in 2013.
Materials and Methods
The study was granted approval by Institutional Ethics Committee, Jamia Millia Islamia and was done in accordance with the World Medical Association Declaration of Helsinki. Acute phase blood samples were collected from suspected dengue patients from Dr. M. A. Ansari Health Centre, Jamia Millia Islamia, New Delhi. Dr. M. A. Ansari Health Centre is a small health centre situated in the University campus which provides basic medical facilities to approximately 40,000 university students, employees and their dependents. Patients showing symptoms of fever accompanied by any two of the following; nausea, vomiting, rash, aches and pains, positive tourniquet test, leukopenia, were enrolled in the study. Written informed consent in English and Hindi was obtained from all adult subjects or a parent or guardian in case of minors. The age/sex, clinical symptoms and duration of fever of the patients were recorded in proformas. Serum was separated from the blood samples and stored at-80°C in aliquots. Dengue viruses were detected in the serum samples by semi nested RT-PCR for C-prM region as described previously12. RNA was extracted from the serum samples using QIAamp Viral RNA Mini kit (Qiagen, Germany) according to the manufacturer’s instructions. Extracted RNA was aliquoted and stored at -80°C. RNA was reverse transcribed into complimentary DNA (cDNA) copy in a 25µL reverse transcription (RT) reaction mixture using 20ng of random primers (Promega, USA), 1mM dNTPs (Promega, USA), 8U of rRNAsin (Promega, USA) and 10U of Avian M