West Nile virus is a zoonose, or a disease which is transmitted from animals to humans. In the case of West Nile virus, mosquitoes are the agent of transmission; humans can become ill when bit by a mosquito carrying the virus. Symptoms usually appear within two weeks of infection, and include a headache which progresses into fever and flu-like symptoms. Complicated cases of West Nile virus may result in meningitis, changes in heartbeat, hepatitis, inflammation of the pancreas, encephalitis and partial paralysis. As a viral disease, West Nile virus has no cure; treatment is palliative, and aimed at relieving acute symptoms. Prognosis for patients is usually positive, but doctors warn that it can take up to three months to fully recover.