| Direct | Direct contact (skin, mucosa, sexual) | STIs, scabies, leprosy (prolonged close contact), Ebola (body fluids) |
| Droplet (short‑range, larger particles) | Diphtheria, pertussis, meningococcus, influenza |
| Contact with soil | Tetanus, hookworm |
| Inoculation into skin/mucosa | Rabies (bite) |
| Transplacental (vertical) | Syphilis, HIV, rubella (TORCH), hepatitis B, Zika |
| Indirect | Vehicle‑borne (water, food, milk, blood, tissues) | Cholera, typhoid, hepatitis A/E, brucellosis (milk), HBV/HCV/HIV (blood) |
| Vector‑borne: mechanical (housefly) or biological (propagative, cyclo‑developmental, cyclo‑propagative) | Malaria (cyclo‑propagative), filaria (cyclo‑developmental), dengue/plague (propagative) |
| Airborne (droplet nuclei, dust) | TB, measles, varicella |
| Fomite‑borne | Diphtheria, trachoma, hepatitis A (contaminated objects) |
| Unclean hands and fingers | Faeco‑oral infections |