Aphasia virus: A virus genetically engineered by Dekon Elig and spread by an "aphasia device". Those afflicted spoke and perceived all language as gibberish; if not cured, they would eventually have died. The majority of those on DS9 at the time fell victim, including most of the senior staff; the only ones immune were the Ferengi and Odo. Kira was able to force Surmak Ren to find a cure. [Babel]

Blight, the: The name given by the natives of the Teplan system to the disease that they were infected with by the Jem'Hadar as an example to all who defied the Dominion. Everyone there is born with it. In the asymptomatic stage, the victim has blue lesions on the face and body, which turn red with the onset of the terminal stage, known as Quickening; death soon follows. Bashir was able to isolate the virus and develop an antigen--however, the virus was found to mutate after Quickening when exposed to EM fields like those from Starfleet medical instruments. It was discovered, however, that the antigen did cure babies in utero. When Bashir left, plans were underway to vaccinate all pregnant women.
[The Quickening]

Cartalian fever: Bashir mentions this deadly virus while Jake was thinking that an outbreak of this virus would be just the thing to liven up his article on the doctor.
[Nor the Battle to the Strong]

Cygnian Respiratory Diseases: Dax caught Bashir boning up on them in preparation for Dr. Elizabeth Lense's visit. [Explorers]

Dorek Syndrome: A rare, incurable, fatal disease which strikes one out of every five million Ferengi. Quark was diagnosed with it while on Ferenginar; but the diagnosis turned out to be false. [Body Parts]

Kalla-Nohra Syndrome: A chronic pulmonary disease unique to individuals, both Bajoran and Cardassian, who survived a particular mining accident at Gallitep. [Duet]

Larosian Virus: When the Dax of his dreams started behaving amorously toward him, Bashir wondered if she had contracted it. [If Wishes Were Horses]

Morphogenic Virus: A virus engineered by Section 31 and planted in Odo with the intent of killing the Founders who link with him. In 2372, when Odo was at Starfleet Medical for an examination, he was unknowingly given the virus, but it did not manifest itself until three years later. The main symptom is a decreasing ability to shapeshift, accompanied by pain and peeling skin; the progress is accelerated by frequent shapeshifting and in the final stage of the disease, the Changeling cannot revert back to liquid state at all and die in a solid form. The cure for the disease contains a nucleotide marking sequence consisting of adanine, asporadine, lytastolanine, and radanine. [When It Rains]

Mutagenic Retrovirus: A biological weapon which the Regent of Palamar wanted to use against General Nassuc's native city. He dealt with Hagath to obtain some; Quark claimed their supplier had already sold all he had. [Business As Usual]

Orket's Disease: A childhood virus that swept through Bajoran work camps during the Occupation. It killed thousands of Bajoran children. [State of Flux, a Voyager episode]

Pottrik Syndrome: A disease similar to Kalla-Nohra syndrome, which Marritza at first claimed to have. [Duet]

Quickening: The terminal stage of the Blight. Symptoms include the turning of the blue skin lesions to red; toward the end, the victim is weak and prone to muscle spasms, all accompanied by extreme pain. [The Quickening]

Redellian Brain Fever: When Keiko returned from Bajor, saying she was not Keiko but was holding his wife's body hostage, O'Brien wondered at first if there had been another outbreak of this on Bajor. [The Assignment]

Rudellian Plague: Pentath III was stricken by an outbreak of it, for which the Cardassians requested humanitarian aid from the Federation. [Rules of Engagement]

TE Virus: A virus Bashir had been studying for months, which had mutated on him. Sarina provided the solution: he hadn't accounted for the L2 codon. [Chrysalis]

Temeklian Virus: Odo claimed to Kasidy Yates that there had been an outbreak of it on Bajor and he had to make a health inspection of the Xhosa, a pretext in order to search the ship for evidence of smuggling. [For the Cause]

Rugelan Fever: A disease which causes a deep coma in Trills; Dax recalled Audrid sitting by her daughter Nema's bedside when Nema contracted it. [Nor the Battle to the Strong]

Tuvan Syndrome: A degenerative, incurable neurological disease which affects mainly Vulcans, Romulans, and Rigellians. In the very early stages, the patient's eyelids are slightly displaced, facial muscles are weakened, and respiration is irregular. Loss of motor skills occurs in 10-15 years; life expectancy is 20-25 years. In less than 5% of cases, the disease can accelerate without warning. [Inter Arma Enim Silent Leges]

Yarim-Fel Syndrome: A terminal illness affecting Cardassians; it attacks the digestive tract, circulatory and respiratory systems, and cartilaginous tissues. It can be treated with hexagen therapy or neuro-regeneration procedures, but there is apparently no cure. Ghemor eventually died of Yarim-Fel. [Ties of Blood and Water]

Zanthi Fever: A virus affecting the empathic abilities of "mature" Betazoids. It causes brief, intense headaches, during which the sufferer unconsciously projects his or her emotions onto others nearby, provided those emotions already exist in those others subconsciously. Lwaxana Troi unknowingly had it when she came to DS9 for the 2371 Gratitude Festival; since she is in love with Odo, others began acting on their own various latent romantic attractions. Fortunately, the sufferer is easily cured with a simple wide-spectrum antibiotic, and the effects on other people wear off in a day or two. [Fascination]

The above material comes from Deep Space Nine Encyclopedia & Lexicon
MEDICAL DISEASES