Darragh Kenny, the top-ranked Irishman in the world at #9, produced his winning round on a horse he had only been riding for two weeks.
Hopes that the virus had not spread south from Valencia have been dashed with news of positives related to second jumping venue in Spain.
HITS Saugerties has upped its FEI rating to fill the void for grand prix riders left by the cancellation of the Spruce Meadows Summer Series.
Calgary's Darrin Dlin was top Canadian aboard Buddy Bounce in 6th place as week 6 at the Desert International Horse Park concluded.
The FEI has issued a detailed timeline of events amid widespread criticism over the handling of the neurological form of EHV-1 in Spain.
Sunday's feature class at WEF 8 saw another big win for the German rider; Mario Deslauriers' former mount Amsterdam is 3rd with new rider.
The US rider took the $50,000 CaptiveOne Advisors 1.50m National Grand Prix; top Canadian was Tiffany Foster and Windsor Grey, 4th.
Peder Fredricson and Marcus Ehning logged flawless rounds to seal the deal, while Eric Lamaze and the Cascais Charms finish 9th overall.
Lamaze was one of seven to qualify for the jump-off at Al Shaqab; Niels Bruynseels (BEL) won while Lorenzo de Luca (ITA) was second.
Amy Millar delivers a double clear with Truman for the Canadian Team as the United States claims victory, followed by Ireland and Brazil.