San Diego County physicians are heading into spring amid several early public health signals that may matter in practice: the county’s first West Nile virus detection of 2026, newly documented rat lungworm infections in local wildlife, and record-breaking March heat that could increase the risk of preventable illness among vulnerable patients.
The clearest vector-borne signal came on March 11, when San Diego County reported that a dead crow found in North Park tested positive for West Nile virus, the first local detection of the year. The County says that certain dead birds are collected and tested because they are good indicators of West Nile virus presence. County officials had reported no human West Nile infections in San Diego County at that point.
For frontline physicians, the practical significance is straightforward: avian detections can precede recognized human cases later in mosquito season. The North Park finding is an early reminder to keep West Nile virus in mind as temperatures rise and mosquito activity increases, particularly in patients presenting with unexplained fever, meningitis, encephalitis, or other neurologic symptoms during the warmer months. This clinical framing is an inference based on the County’s surveillance update and the known neurologic presentation of West Nile disease.
A second signal is less familiar, but potentially important. San Diego County’s Health Alerts page linked in February to a CDC Emerging Infectious Diseases report documenting locally acquired rat lungworm infections in a zoo-housed parma wallaby, free-ranging Virginia opossums, and roof rats in San Diego County. The CDC authors wrote that “angiostrongyliasis should be considered in central nervous system disease in humans and animals in this region,” and said the parasite could now be considered endemic in this part of Southern California.
Human infection with rat lungworm, Angiostrongylus cantonensis, remains rare, but it can cause eosinophilic meningitis. For physicians, the practical implication is exposure history: contaminated produce, ingestion of infected snails or slugs, and outdoor exposure may become useful clues in patients with unexplained meningitis-like illness or atypical neurologic presentations.
Heat is also becoming part of the clinical picture earlier than usual. NBC 7 reported that the average high temperature for March reached 75 degrees at San Diego International Airport, making it the hottest March on record there. KOGO similarly reported that nearly 10 local sites, including El Cajon, Escondido, Alpine, Ramona, and Oceanside Harbor, set or tied heat records.
San Diego County’s extreme-heat program warns that older adults, babies and young children, people with chronic conditions, outdoor workers and athletes, and people without air conditioning face elevated risk during heat events. For practicing physicians, that makes heat-related illness, dehydration, and exacerbations of chronic disease worth watching even before summer officially settles in.
State officials also placed a portion of San Diego County under quarantine after they detected Mexican fruit flies in La Mesa. The development does not pose a direct threat to human health, but it adds to a broader pattern of seasonal environmental surveillance already underway across the region.