The rise in mosquito-borne diseases poses significant health risks to California residents. West Nile virus, for example, can cause severe neuroinvasive diseases such as meningitis and encephalitis in about 1% of cases. Dengue fever, also on the rise, is a painful and potentially fatal disease. Flea-borne typhus, which has seen an increase in Southern California, is another concern, particularly in areas where human activity overlaps with wildlife habitats. The spread of these diseases is exacerbated by climate change, which extends the active seasons of disease-carrying insects, and by human encroachment into previously undisturbed ecosystems.