You have several labs in Texas.
Texas A&M Veterinary Medical Diagnostic Laboratory (Main) 483 Agronomy Road College Station, Texas 77843-4471 Phone: 979-845-3414
Texas A&M Veterinary Medical Diagnostic Laboratory – Gonzales (Branch) 1162 East Sarah DeWitt Drive Gonzales, Texas 78629 Phone: 830-672-2834
Texas Animal Health Commission State-Federal Laboratory 8200 Cameron Road, Suite A186 Austin, Texas 78754-3832 Phone: 512-832-6580
Texas A&M Veterinary Medical Diagnostic Laboratory - Center (Branch) 635 Malone Dr Center, Texas 75935-3530 Phone: 936-598-4451
Texas A&M Veterinary Medical Diagnostic Laboratory - Amarillo (Branch) 6610 Amarillo Blvd West Amarillo, Texas 79106-1706 Phone: 806-353-7478
You are probably right. Chances are the new birds brought something your birds weren't resistant to.