Sickness is a recurring motif in Of Plymouth Plantation, in part because it was simply a fact of daily life in the 17th century; the Pilgrims suffer from scurvy both during and after the voyage to Plymouth, Native Americans repeatedly contract smallpox from European settlers, and the Pilgrims' business affairs in London are at one point thrown into chaos by an outbreak of the plague. The causes of most of these illnesses were poorly understood at the time Bradford was writing, so it is not surprising that he frequently attributes them to divine retribution. For instance, he apparently agrees with a letter claiming that epidemics in Boston and Charlestown are the result of residents' sinfulness. This supposed link between illness and morality, along with the contagiousness of many of the era's deadliest diseases, allows Bradford to use sickness as a metaphor for people and circumstances that threaten to "infect" (14) the Christian community at Plymouth. A letter from John Pierce warns Bradford that Plymouth may be "contaminated" (69) by the men Weston is sending over. Meanwhile, Bradford offers the Pilgrims' willingness to tend to various people suffering from disease as a sign of their Christian feeling.