Differential susceptibility & replication potential of Vero E6, BHK-21, RD, A-549, C6/36 cells & Aedes aegypti mosquitoes to three strains of chikungunya virus.

Background & objectives: Chikungunya virus (CHIKV), a mosquito-borne arthritogenic virus causes infections ranging from febrile illness to debilitating polyarthralgia in humans. Re-emergence of the virus has affected millions of people in Africa and Asia since 2004. During the outbreak, a new lineage of the virus has evolved as an adaptation for enhanced replication and transmission by Aedes albopictus mosquito. A study was designed to compare the susceptibility of four vertebrate cell lines, namely Vero E6 (African green monkey kidney), BHK-21 (Baby hamster kidney), RD (human rhabdomyosarcoma), A-549 (human alveolar basal epithelial cell) and C6/36 (Ae. albopictus) to Asian genotype and two lineages of East, Central and South African (E1:A226 and E1:A226V) of CHIKV. Methods: One-step growth kinetics of different CHIKV strains was carried out in the above five cell lines to determine the growth kinetics and virus yield. Virus titre was determined by 50 per cent tissue culture infectious dose assay and titres were calculated by the Reed and Muench formula. Growth and virus yield of the three strains in Ae. aegypti mosquitoes was studied by intrathoracic inoculation and virus titration in Vero E6 cell line. Results: Virus titration showed Vero E6, C6/36 and BHK-21 cell lines are high virus yielding with all the three lineages while RD and A-549 yielded low virus titres. C6/36 cell line was the most sensitive and yielded the maximum titre. Ae. aegypti mosquitoes, when inoculated with high titre virus, yielded an almost equal growth with the three strains while rapid growth of E1:A226V and Asian strain was observed with 1 log virus. Interpretation & conclusions: C6/36 cell line was found to be the most sensitive and high yielding for CHIKV irrespective of lineages while Vero E6 and BHK-21 cell lines yielded high titres and may find application for vaccine/diagnostic development. Infection of Ae. aegypti mosquitoes with the three CHIKV strains gave almost identical pattern of growth.

Clinical progression of chikungunya fever during acute and chronic arthritic stages and the changes in joint morphology as revealed by imaging.

This longitudinal follow-up study of 203 patients with serologically confirmed chikungunya (CHIK) virus infection describes the clinical features of CHIK fever during the first and tenth months of illness. During the acute stage CHIK fever presents with a wide array of symptoms. The foremost chronic symptoms at the end of a month were rheumatism (75%) and fatigue (30%). During the tenth month of follow-up the symptoms/signs observed were joint pain/swelling (46%), fatigue (13%) and neuritis (6%). The cure rate at the end of 9 months was 51%. Among the patients who had joint pain, 36% (34/94) met the American College of Rheumatology criteria to classify them as having rheumatoid arthritis. A subpopulation of the patients with joint pain (20/94) was tested for rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibody, and the joints were imaged by X-ray and magnetic resonance imaging (MRI). All tested negative for RF and one tested positive for anti-CCP. A radiolucent lesion in the X-ray was seen in the bones of five patients. The MRI findings were joint effusion, bony erosion, marrow oedema, synovial thickening, tendinitis and tenosynovitis. The study proves with relative certainty that CHIK arthritis is chronic inflammatory erosive arthritis, which has implications for management of the infection.