It is always out there, but makes an appearance when social upheaval leave people cold, filthy and hungry. Typhus is a disease of crowding and dirt, particularly likely to occur in conditions where people are crowded together and lacking means of ensuring bodily cleanliness. This disease clearly illustrates the importance of public health and social justice in the eradication of disease. Transmission is by the bite of the louse. Typhus is always there among lice, ready to recur whenever public health measures are lax.
Vaccination provides an effective, long-lasting immunity and is necessary for military personnel.
Prevention also requires cleanliness and louse killing measures. This is a recent disease, with its history largely confined to the last two hundred years. The causative organism is a Spirillaceae bacterium. Cholera was originally confined to India early in the nineteenth century. Humans are the only known host for the cholera vibrio .