Green’s Dictionary of Slang

scrud n.

[ext. of crud n. (1c)]

1. (US, orig. milit.) a painful disease, esp. a venereal disease.

[US]Wentworth & Flexner DAS 454/1: scrud n. 1. A mythical disease alleged to be very serious, painful, and socially objectionable. 2. Any venereal disease [...] since ca. 1935.
[US]Trimble 5000 Adult Sex Words and Phrases.

2. (UK juv.) the junior members of a school.

OnLine Dict. of Playground Sl. [Internet] scruds n. new pupils at school. Used particularly of new first formers (year 7) in secondary school.