Port miasma from nyano (#8926)

Co-authored-by: Kara <lunarautomaton6@gmail.com>

Content.Server/Chemistry/ReagentEffects/ChemCauseRandomDisease.cs

@@ -0,0 +1,32 @@
+using Content.Shared.Chemistry.Reagent;
+using Content.Server.Disease;
+using Content.Shared.Disease.Components;
+using Robust.Shared.Random;
+using JetBrains.Annotations;
+
+namespace Content.Server.Chemistry.ReagentEffects
+{
+    /// <summary>
+    /// Default metabolism for medicine reagents.
+    /// </summary>
+    [UsedImplicitly]
+    public sealed class ChemCauseRandomDisease : ReagentEffect
+    {
+        /// <summary>
+        /// A disease to choose from.
+        /// </summary>
+        [DataField("diseases", required: true)]
+        [ViewVariables(VVAccess.ReadWrite)]
+        public List<string> Diseases = default!;
+
+        public override void Effect(ReagentEffectArgs args)
+        {
+            if (args.EntityManager.TryGetComponent<DiseasedComponent>(args.SolutionEntity, out var diseased))
+                return;
+
+            var random = IoCManager.Resolve<IRobustRandom>();
+
+            EntitySystem.Get<DiseaseSystem>().TryAddDisease(args.SolutionEntity, random.Pick(Diseases));
+        }
+    }
+}