French Blood Donor Screening Detected WNV Ahead of Equine, Symptomatic Cases

Preemptive nucleic acid testing (NAT) for West Nile virus (WNV) in French regions with a history of WNV served as the earliest indicator of virus circulation, according to a research letter published July 31 in JAMA Network Open.

Investigators from the French Blood Service conducted WNV NAT on approximately 56,000 donations from four southern French departments (Bouches-du-Rhône, Gard, Hérault and Var) during an enhanced surveillance period surrounding the 2024 Summer Olympic Games. In the Var department, the first human WNV case was detected two weeks before detection in equines and mosquitos, and three weeks before the first symptomatic case. In the Gard department, NAT detected the first WNV case two weeks before the first symptomatic human case.

The researchers noted that existing surveillance strategies in France, which rely primarily on detection of symptomatic cases, may not fully capture early or asymptomatic circulation.

“To improve our national WNV human surveillance system and enable early preventive measures to avoid transmissions by substances of human origin, a strategy that combines systematic WNV screening in symptomatic cases with nucleic acid testing in blood donors in high-risk areas may be relevant,” they concluded.