Re-emergence of Chikungunya virus in India

smaller joints), low back pain, and rash. The symptoms are most often clinically indistinguishable form those observed in dengue fever. Indeed, simultaneous isolation of both dengue and chikungunya from the sera of the same patients has been reported earlier indicating the presence of dual infections. 9 Therefore it is very important to clinically distinguish dengue from chikungunya virus infection. Unlike dengue, hemorrhagic manifestations are relatively rare and as a rule shock is not observed in chikungunya virus infection. Most often chikungunya is a self limiting febrile illness. However, neurological complications such as meningoencephalitis have been reported in a small proportion of patients during the first Indian outbreak as well as the recent French Reunion islands outbreaks. 10-11 Mother to child transmission of chikungunya virus was a new observation recorded during the recent French Reunion islands outbreak. 11 The precise reasons for the re-emergence of chikungunya in the Indian subcontinent as well as the other small countries in the southern Indian Ocean are an enigma. Although, it is well recognized that re-emergence of viral infections are due to a variety of social, environmental, behavioural and biological changes, which of these contributed to the re-emergence of chikungunya virus would be interesting to unravel. Genetic analysis of chiungunya viruses have revealed that two distinct lineages were delineated, 12 one containing all isolates from western Africa and the second comprising all southern and East African strains, as well as isolates from Asia. Phylogenetic trees corroborated historical evidence that the virus originated in Africa and subsequently was introduced into Asia. 13 Such studies need to be conducted on virus isolates obtained during the current outbreak in order to understand if any mutation has occurred in the virus that has facilitated the large scale spread of this virus in the region. Alternatively, one could take the simplistic view that the lack of herd immunity within the country probably lead to its rapid spread across several states. A serosurvey conducted at Calcutta a decade ago did reveal that only 4.37% of the sera tested were positive for chikungunya antibodies with the highest seropositivity rates observed in the age group of 51-55 years and no chikungunya antibodies detected in the young and young adults. These findings probably suggest that there is indeed lack of herd immunity to chikungunya virus. Yet another challenge faced during this large outbreak in the country has been the lack of rapid diagnostic facilities. Although, the National Institute of Virology at Pune, has been of great help in determining the etiology of the outbreak relying on one institute in the country to render diagnostic help for case