Slang in an early Wodehouse story

I've moved house recently, and one of the things I had to deal with was getting rid of a number of books I've had for a long time. This took place over the last two or three years, with the result that I've now got less than half the books I used to have. 

That's still quite a few books, but now they fit on two bookcases instead of four or five. And we'd already culled our books a couple of times before the most recent slashing and burning. The house must have been straining under the weight of all those books for nearly forty years.

Anyway, looking at these books in the first week or so of being in our new home, I made the possibly rash decision to read them all again, to prove to myself perhaps that I'd actually kept the cream of the crop. I also discovered that there were still a few among them that I'd never read, even though in some cases I'd had them since I was a young man. 

The very dull cover of
my copy of the book

One of these is A Gentleman of Leisure, originally published in the USA under the oddly awkward title of The Intrusion of Jimmy. The English version was serialised under this US title in the magazine Tit-Bits, and then published in book form a few months later in November 1910 under the title I have, though my edition is probably the reprint from 1921.

The book zips along at a good pace, though in the early parts of the book, the typical Wodehouse style doesn't seem fully formed yet. As the book progresses, however, there's more of the Wodehouse flavour in the prose, the wit and mangled quotes, as though he was finding his feet. 

It's common for period slang to appear in Wodehouse's books. You can usually gauge from the context what the words mean - except when he's being purposely obscure for the fun of it. But on page 94 of A Gentleman of Leisure we have this bit of dialogue between the main character, Jimmy Pitt, and the girl he fell in love with a year before, called Molly. They've just met out of the blue on an English country road. The conversation goes like this:

"You must be a very restless sort of person," she said. "You seem to do a great deal of moving about."

"I do," said Jimmy. "I can't keep still. I've got the go-fever, like the man in Kipling's book."

"But he was in love."

"Yes," said Jimmy; "he was. That's the bacillus, you know." 

'Go-fever' is presumably some sort of play on something written by Rudyard Kipling, possibly in one of the Just So Stories, and can be worked out easily enough. But "that's the bacillus" is a different kettle of fish. In general usage, a bacillus is a bacteria, so how did it get to be used in what seems like a slang phrase at this point? Maybe it's a fancy word for 'bug' as in 'travel-bug', but it doesn't seem quite to fit to the conversation. Molly obviously understands it as she makes no comment. Whether it was commonly used or not I don't know: Google only finds it in the online versions of this book, and nowhere else, and no dictionary seems aware of it. 

Perhaps some other reader can help me...?

A modern cover of an ebook version
in which the artist seems to mistake
the period in which the book is set -
making it look more like a Russian novel.