How did yellow fever weaken the French army in Saint-Domingue?

During the French expedition to Saint-Domingue in 1802, the army led by Gen. Charles Leclerc was severely weakened by a devastating yellow fever epidemic.1

This outbreak decimated the French forces, significantly reducing their military capacity at a critical juncture when they were facing renewed resistance from Black rebels led by Jean-Jacques Dessalines and Henry Christophe. The disease was so widespread that it claimed the life of General Leclerc himself in November 1802. The loss of manpower and leadership caused by the epidemic left the French military unable to maintain control, ultimately leading to their surrender in November 1803.12