Chikungunya Outbreaks Caused by African Genotype, India

Chikungunya fever is reported in India after 32 years. Immunoglobulin M antibodies and virus isolation confirmed the cause. Phylogenic analysis based on partial sequences of NS4 and E1 genes showed that all earlier isolates (1963–1973) were Asian genotype, whereas the current and Yawat (2000) isolates were African genotype.

source of antibodies (9). Dengue/CHIKV IgM antibodies and negative control human sera were included for respective tests. Approval for use of mice for antigen preparation was obtained from the institutional ethical committee according to national guidelines.
Immunofluorescence assay (IFA) was used to detect the virus in cell culture and in crushed heads of adult mosquitoes (10). A patient with the following was confirmed as having CHIKV infection: acute onset of moderate-to-high fever with joint pain of varying severity; negative test results for malaria, typhoid, and tuberculosis; and positive results for IgM anti-CHIKV antibodies, seroconversion, or CHIKV isolation. We used χ 2 test to compare proportions of cases in different age groups.
Using ClustalX, version 1.83, multiple alignments of nucleotide sequences were performed. The phylogenic status of the CHIKV isolates was assessed with the software MEGA 3.1 (13), Kimura 2-parameter distance, and neighbor-joining algorithm. The reliability of different phylogenic groupings was evaluated with the bootstrap test (1,000 bootstrap replications) available in MEGA.
Acute onset of moderate-to-high fever in association with body ache, backache, and headache was recorded. Joint pain of varying severity occurred within 2 days of onset of fever and, in decreasing order of affliction, involved knees, ankles, wrists, hands, and feet. Joint pain was severe and incapacitating and lasted for weeks to months. Inflammation of joints and transient macular rash on earlobes, neck, trunk, and upper extremities were reported for a few patients. Hemorrhage did not occur. The cases were reported predominantly from rural areas; distribution was focal. Multiple cases were recorded in families. All ages and both sexes were affected; significantly more cases occurred in persons aged >15 years (299 [89.8%] of 333, p<0.001). Cases were reported from 11 of 23 districts in Andhra Pradesh, 15 of 27 in Karnataka, and 16 of 35 in Maharashtra ( Figure 1). Results of serologic testing and virus isolation are shown in Table 2.
State governments of Andhra Pradesh, Karnataka, and Maharashtra have declared outbreaks of CHIKV. By mid-April, the declared numbers of fever cases associated with this outbreak were >25,000 in Andhra Pradesh, >65,000 in Maharashtra, and >36,000 in Karnataka. In absence of active surveillance for this disease, these numbers may be underestimates.
The predominant mosquito species in the affected areas was Ae. aegypti. Ae. albopictus was either absent or present in negligible numbers. The population of Ae. aegypti was reasonably high in most of the localities; adult household indexes and Breteau indexes, respectively, were 10-60 and 13-75 in Andhra Pradesh, 20-70 and 40-200 in Karnataka, and 10-30 and 30-50 in Maharashtra. High density of Ae. aegypti populations in affected areas and 23 isolations or detections of CHIKV from adult mosquitoes indicates that this species is the main vector in India. Earlier outbreaks in India were mainly restricted to large cities; in contrast, the current outbreak is predominantly rural.
Anti-CHIKV IgM was detected in 33.5% to 41.9% of patients tested. The finding of antibodies to dengue virus in 0.9% to 9.9% of patients and to CHIKV and dengue virus in 0.4% to 4.3% of patients indicates that these viruses cocirculate in the area. Nine patients whose acute-phase serum sample was negative had anti-CHIKV IgM in the early convalescent-phase sample, collected during the second week of illness.

Conclusions
This report confirms CHIKV as the causative agent for large outbreaks of fever with arthralgia and arthritis in 3 Indian states. Thus, chikungunya fever has emerged in outbreak form after 32 years.
The current epidemic is caused by central/East African genotype of CHIKV. That the Yawat isolate is grouped with central/East African genotype suggests that this genotype had been introduced >5 years before the current outbreaks. In this context, determining the genotype of currently circulating strains in Southeast Asia and understanding the modes of transportation of this strain in India and the conditions favoring such large outbreaks would be worthwhile.