I know there's always talk of bioweapons, but warzones are also a melting pot for diseases, especially in a modern war where soldiers are more likely to survive wounds that would've once killed you outright - Those same wounds are the perfect breeding ground for all kinds of disease.

Pair that with our lax intl' response to antibiotic resistance (which is probably even less of a concern to doctors in warzones) you have a powder keg of pandemic proportions ready to blow.