Chikungunya, an alpha virus of the Togaviridae family, is transmitted to humans by the bite of an Aedes aegypti mosquito and causes fever, headache, rash, and severe arthralgia. Although the Chikungunya virus is not neurotropic, incidences of meningoencephalitis have been observed during epidemics. Neurological complications are more common in children than in adults; the most frequent manifestation is a nonprogressive encephalitis that may lead to long-term disability. Gram-negative bacilli include both gram-positive and negative organisms. While gram positive bacteria such as staphylococci can cause infection, most often it is gram-negative bacteria that cause disease. Examples of gram-negative bacteria include Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Enterobacter spp. , Serratia marcescens, and Haemophilus influenzae. The virulence factors responsible for bacterial pathogenesis include enzymes, toxins, and other proteins capable of killing host cells or inhibiting their function. Some bacteria produce enzymes that degrade tissue components, allowing the bacteria to spread through the body. Other enzymes can break down drugs so they cannot kill the bacteria or inhibit their growth. Finally, some bacteria produce toxins that cause disease by themselves or by triggering immune responses that result in inflammation. Bacteria infect humans with antibiotics frequently used to treat them.