The Shasta Mosquito & Vector Control District (SMVCD) has been receiving increased reports of aggressive day-biting mosquitoes, primarily in response to Aedes Aegypti mosquitoes (the yellow fever mosquitoes), a very aggressive mosquito that we find in Summer months and into the early Fall season. Mosquitoes in California are responsible for transmitting serious viruses such as West Nile virus (WNV) and Dengue virus (DENV), which can cause debilitating cases of illness and even death. Some species of mosquitoes can lay their eggs in very small sources of water, like a bottle cap. 2025 Shasta County West Nile virus activity: 0 dead birds, 0 sentinel chickens, 2 mosquito samples, and 0 humans tested positive for West Nile virus. 2025 California West Nile virus activity: 138 dead birds, 49 sentinel chickens, 2500 mosquito samples, and 47 humans tested positive for West Nile virus.