Measly

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late 16th century (describing a pig or pork infected with measles): from measles + -y1. The current sense dates from the mid 19th century.

wiktionary

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measle(“ singular of  measles”) +‎  -y; the word measle is either from Middle Dutch masel(“a  blister filled with  blood; a  pustule, a  skin blemish”), or Middle Low German masel(“a  red skin blemish”), from Proto-Germanic *masuraz(“a  knot or  scar in  wood; a  knarl”), from  *mas-,  *mēs-(“a  spot; a  sore; a  scar”), from Proto-Indo-European *mos-(“a skin  sore”). 

etymonline

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measly (adj.)

"infected with measles," 1680s, from measle (see measles) + -y (2). The Middle English word for "infected with measles" was maseled. Sense of "meager and contemptible, good for nothing" is attested by 1864 in British slang.