Egon Erwin Kisch was a writer and journalist who developed a style of writing called reportage in the early 1900s. This combination of prose and literature is not journalism or fiction but is based on fact. Reportage books have more detail than a newspaper report but a style more similar to a novel than a reference guide. Egon was inspired by social authors such as Charles Dickens, Emile Zola and Maxim Gorki.
Whats all this got to do with flea circuses you ask?
In 1920 Kisch published a book called "Die Abenteuer in Prag" - "The adventures in Prague" which contains a chapter The dramaturgy of the Flea Theatres. It is possible that he read the reference to flea circuses in Dicken's "Boz".
I have recently aquired a copy of this book and will keep you updated as I translate the relavent pages.