Coloured transmission electron micrograph (TEM) of chikungunya viruses particles. This alphavirus is composed of an RNA (ribonucleic acid) genome (dark brown) enclosed in a protein coat, or nucleocapsid, which is itself surrounded by a lipoprotein envelope. The virus, which is transmitted by mosquitoes, causes a rare form of viral fever. Symptoms include a high fever, rash and arthritic joint pain. There is no vaccine or treatment for the disease, which although often severe is rarely fatal. Magnification: x 98,000 when printed at 10 centimetres wide.