virus is amplified. Another direct approach is the isolation of the virus and its growth in cell culture using blood plasma; this can take 1–4 weeks. Serologically, an enzyme-linked immunosorbent assay during the acute phase of the disease using specific IgM against yellow fever or an increase in specific IgG titer (compared to an earlier sample) can confirm yellow fever. Together with clinical symptoms, the detection of IgM or a four-fold increase in IgG titer is considered sufficient indication for yellow fever. As these tests can cross-react with other flaviviruses, such as dengue virus, these indirect methods cannot conclusively prove yellow fever infection. Liver biopsy can verify inflammation and necrosis of hepatocytes and detect viral antigens. Because of the bleeding tendency of yellow fever patients, a biopsy is only advisable post mortem to confirm the cause of death. In a differential diagnosis, infections with yellow fever must be distinguished from other feverish illnesses such as malaria. Other viral hemorrhagic fevers, such as Ebola virus, Lassa virus, Marburg virus, and Junin virus, must be excluded as the cause. Prevention Personal prevention of yellow fever includes vaccination and avoidance of mosquito bites in areas where yellow fever is endemic. Institutional measures for prevention of yellow fever include vaccination programmes and measures to control mosquitoes. Programmes for distribution of mosquito nets for use in homes produce reductions in cases of both malaria and yellow fever. Use of EPA-registered insect repellent is recommended when outdoors. Exposure for even a short time is enough for a potential mosquito bite. Long-sleeved clothing, long pants, and socks are useful for prevention. The application of larvicides to water-storage containers can help eliminate potential mosquito breeding sites. EPA-registered insecticide spray decreases the transmission of yellow fever. Use insect repellent when outdoors such as those containing DEET, picaridin, ethyl butylacetylaminopropionate (IR3535), or oil of lemon eucalyptus on exposed skin. Mosquitoes may bite through thin clothing, so spraying clothes with repellent containing permethrin or another EPA-registered repellent gives extra protection. Clothing treated with permethrin is commercially available. Mosquito repellents containing permethrin are not approved for application directly to the skin. The peak biting times for many mosquito species are dusk to dawn. However, A. aegypti, one of the mosquitoes that transmits yellow fever virus, feeds during the daytime. Staying in accommodations with screened or air-conditioned rooms, particularly during peak biting times, also reduces the risk of mosquito bites. Vaccination Vaccination is