An official website of the United States government
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS
A lock (
LockA locked padlock
) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
Image Number D1730-1
Veterinary microbiologist Hong Li selects MCF virus-free sheep for a viral replication study.
Photo by Peggy Greb.
640 pixels wide: (d1730-1.jpg)