Specifically, in the case of cholera, the breakdown of water/sanitation systems and significant decrease in hygeine standards can cause diarrheal diseases.
Crowding in shelters/camps, increasing contact between people
Mixing of different regional populations with different levels of vaccination or endemic disease
Contamination of drinking water
Spread of infectious mud or soils (leptospirosis)
Disruption or delay of vaccination programs
Death or disappearance of key medical and administrative staff
Destruction of key facilities (laboratories, hospitals, clinics, etc.)