This from a thread in the World-Building Alliance, specifically, some ideas I had for diseases that can effect changelings (one being exclusive to them).

Loveblight: a disease caused by a thaumavorous(magic-eating) amoeba. It invades the digestive tract of changelings, multiplies, and forms a semi-permeable barrier over the lining of the small intestine. Nutrients from solid food and fluids are allowed to pass through, but the amoeba colony devours almost all empathic energy, like love, that would normally pass. Over time this causes the changeling to starve to death no matter how often it feeds. In some cases, the changeling can even die from gorging itself, since the Loveblight colony allows the empathic energy to enter the body, but simply absorbs it before the body can. Loveblight can be treated easily if caught before any serious symptoms appear, but it's high rate of reproduction makes death an almost complete certainty once it has become symptomatic.

Horn Warts: an extremely rare disease that can afflict anything that channels its magic through a horn. Horn Warts are caused by a normally harmless virus that is found naturally in the section of hardened brain tissue found in unicorn, alicorn, and changeling horns. The virus typically acts as the first line of defense against bacterial infections, as it can enter the bodies of bacteria, but not of other types of cells. However, in rare cases, the viruses produced from infecting those bacteria will have errors encoded in their RNA. Normally, those viruses are merely rendered incapable of infecting anything. But if a specific set of errors occurs, the viruses will begin to infect the bone marrow cells surrounding the inner horn. However, instead of forcing the cells to just produce more viruses, they force the cells to produce more of themselves, creating threadlike tumors that spread through the horn's air pockets (which act as a cushion during collisions) until they reach the outer horn, where they then form bulbous, wartlike protuberances on the surface of the horn.

Horn Warts are exceedingly rare, but incredibly dangerous. Treatment of them is difficult, since the only way to truly kill the tumors is to kill the infected cells at their heart, which lies extremely close to the inner horn's brain tissue. However, if they are left untreated, the tumors will eventually pierce the walls of the inner horn and begin spreading through the brain, leading to almost certain death.

Perhaps the most alarming part about Horn Warts is that they are one of the few diseases that alicorns are not immune to, though it is as rare for them as it is for unicorns and changelings. The only instance of an alicorn contracting Horn Warts in the last fifteen hundred years was when Princess Cadance had them when she was a teenager. Luckily, the tumors' core had been located further from the inner horn than usual, and they were caught early, so they were easily treated.

2163944 Changeling Flu: a simple disease that causes a changeling to change shape with every sneeze.

Emotion Sickness: caused by feeding on only one positive emotion, as opposed to a mixture. This disease causes symptoms similar to Megalomania, Superiority Complex, and partial insanity. thankfully, it is easily cured by cutting off the flow of said emotion.

Form Lock: when a changeling cannot turn back to normal for some reason. cured by plenty of bedrest.

Shift Fever: a disease which causes the changeling affected to undergo a strange and nonsensical transformation, with certain individuals sprouting purple feathers, and others changing shape every time they sneezed. It is fatal unless cured within forty-eight hours by means of a potion consisting of Black Morrigan, Golden Joke (a very rare poison joke relative that changes the species of those who touch it and is cured by eating the flower of the same plant that affected them), cockatrice scales, timberwolf bark, and manticore venom.

Why would a changeling have an intestine? If they eat love, they probably don't poop. I propose that they merely possess a small blind gut that basically ends at the stomach, and the stomach is mostly used to secrete mucuses and venoms.

guile blight: a contagious disease that causes those infected to be unable to disguise properly(wrong parts, wrong colors, wrong sex, voice, etc.), or not at all in severe cases. those who contract the disease are either exiled or quarantined to protect the others.

2169602

The idea is that they can eat normal food, though reasons why could vary depending on the writer (keeping up appearances, or it being a source of secondary nutrition that can mitigate their hunger for emotions).

2185911 In my headcanon, one of the larval forms of the changeling is the parasprite, so the adult changelings farm the love the parasprites give off while feeding the parasprites normal food. The parasprites are also scouts that go out of the hive to look for new sources of love.