A simple protein change in the chikungunya virus enables it to adapt to new mosquito hosts and spread to more regions, new research shows.
Studies at the US-based University of Texas Medical Branch have found that a single amino acid change in the protein of the virus's outer shell helps it adapt to a new mosquito host, Aedes albopictus. The findings were published last week (7 December) in PLoS Pathogens.
Chikungunya virus is emerging as a problem in South-East Asia and the Pacific, and caused major outbreaks on the island of Reunion in the Indian Ocean in 2006, and in India in 2006–2007. Typical symptoms include fever, headache, severe joint pain and nausea.
The virus is transmitted to humans by Aedes mosquitoes, mainly Aedes aegypti. The Reunion outbreak puzzled scientists as A. aegypti is not present in the area — the virus was instead transmitted by A. albopictus.
This study found that the mutation allows the virus to infect and replicate in A. albopictus more efficiently. It says the findings provide an explanation of how the virus caused an epidemic in an area lacking the typical host, and has important implications for how viruses can be transmitted when introduced in new areas.
Scientists in India — which has both species of Aedes mosquito — have presented varying reports on the presence or absence of the mutation in chikungunya virus samples from India.
The country witnessed an outbreak in 2005–06, after a gap of 32 years, with 1.3 million cases in 13 states. Cases continued to be reported in 2007 too, largely in the southern state of Kerala.
Scientists from the National Institute of Virology (NIV) in Pune, reported at a meeting of the Indian Academy of Sciences (IAS) last month (November) that they did not find the Reunion mutation in Indian isolates.
NIV scientist Vidya Arankalle said she and her colleagues found several other mutations, though no specific pattern could be identified. The detailed genetic analysis of samples isolated from India was reported in the July edition of Journal of General Virology.
However, random checking of five samples from Kerala state by the Rajiv Gandhi Centre for Biotechnology (RGCB) in Thiruvananthapuram has showed the presence of the Reunion mutation.
RGCB scientist Easwaran Sreekumar told the IAS meeting that more studies are needed to confirm the trend.
Reference: PLoS Pathogens 3, e201 doi 10.1371/journal.ppat.0030201 (2007)