Isolation and diagnosis of Chikungunya virus causing outbreaks in Andhra Pradesh, India

Background: Chikungunya fever has recently re-emerged in India with a high morbidity. However, the prevalence of chikungunya fever in India has been underreported due to non-availability of specialized kits to confirm the disease in most of the laboratories. Methods: Nine hundred and fifty six serum samples were collected from subjects presenting with a short febrile illness from various places in Chittoor district, Andhra Pradesh, between January to October 2009 and were screened for Chikungunya Virus (CHIKV) infection. Virus isolation, reverse transcriptase - polymerase chain reaction (RT-PCR) and immunoglobulin M (IgM) rapid strip method were employed for the identification of the causative agent. Results: Chikungunya Virus (CHIKV) infection was confirmed in 520 (68.1%) patients by RT-PCR. Seventy seven (40.1%) patients showed the presence of anti-CHIKV IgM antibodies while 12 (6.3%) patients showed the presence of both anti-CHIKV IgM and immunoglobulin G (IgG) antibodies respectively. The isolation of CHIKV was successful from five patients. Conclusions: The re-emergence and persistence of CHIKV in Andhra Pradesh suggests the need for continuous monitoring and identification of the pathogen and thereby prevention of the spread of the virus to other parts of the country.