A. Epstein-Barr virus → 1. Systemic lupus erythematosus (SLE) EBV is one of the most strongly associated infectious triggers for SLE. Molecular mimicry between EBV antigens (particularly EBNA-1) and host nuclear antigens drives autoimmunity in genetically susceptible individuals.

B. Mycoplasma pneumoniae → 3. Rheumatoid arthritis Mycoplasma pneumoniae has been implicated as a trigger for RA. It can induce immune activation and synovial inflammation through molecular mimicry with joint antigens.

C. Chlamydia → 2. Reactive arthritis Chlamydia trachomatis is a classic cause of reactive arthritis (formerly Reiter's syndrome). It is the most common sexually transmitted trigger of reactive arthritis, causing sterile joint inflammation after urogenital infection.

D. Parvovirus B19 → 4. Systemic sclerosis Parvovirus B19 has been linked to systemic sclerosis (scleroderma). The virus can infect endothelial cells and trigger the vasculopathy and fibrosis characteristic of SSc. It has also been linked to RA, but the best match here given the options is systemic sclerosis.