You cannot tell by looking, because the rodent is not ill

Rat-bite fever is an infectious disease people get from contact with
rodents — rats, mice, gerbils, guinea pigs and squirrels.

Why a healthy-looking pet is no reassurance

**The bacteria that cause RBF are part of the natural germs in these
rodents' bodies. Rodents carrying the bacteria do not show signs of illness,
so it is not possible to tell if a rodent carries the bacteria just by
looking at it.**

The organism is normal flora for the animal. There is no sick rodent to avoid,
no symptom to check for at the pet shop, and no way to inspect your way to
safety.

Who is at risk

Anyone with contact with infected rodents, and particularly:

• People with pet rodents — several of the carriers are popular pets
• People who work in pet stores
• People who work in laboratories with rodents

RBF is rare in the United States — but rare is not the same as unlikely if
you handle rodents daily.

The part that makes it dangerous

**The infection is resistant to many commonly used antibiotics. Getting
treatment with the right antibiotics is important to keep the disease from
progressing.**

And:

**RBF must be treated quickly, or it can cause severe illness and possibly
death.**

Those two together are why the advice is so insistent about speed. An
empirical antibiotic chosen for a generic infection may simply not work here —
so the diagnosis has to be made, not guessed around.

**If you were bitten or scratched by a rodent and develop symptoms consistent
with RBF, seek medical care immediately** — and say that you handle rodents.
That sentence is what gets the right antibiotic prescribed.

Source: Centers for Disease Control and Prevention.