pest

(noun) a serious (sometimes fatal) infection of rodents caused by Yersinia pestis and accidentally transmitted to humans by the bite of a flea that has bitten an infected animal. Synonyms: plague, pestilence, pestis.

(noun) any epidemic disease with a high death rate. Synonyms: plague, pestilence.

(noun) a persistently annoying person. Synonyms: blighter, cuss, pesterer, gadfly.

(noun) any unwanted and destructive insect or other animal that attacks food or crops or livestock etc.. Examples: "He sprayed the garden to get rid of pests." "Many pests have developed resistance to the common pesticides."