according to my med. dict.

The Salmonella typhi bacterium is carried only by humans and no other animal carrier has been found. The Salmonella paratyphi bacterium is carried by humans and, rarely, domestic animals.
https://www.betterhealth.vic.gov.au/health/healthyliving/typ...

The primary source of leptospires is the surface of the renal tubes in the kidney of an excreting carrier animal. Carrier animals pass urine containing leptospires into the surrounding environment.
http://www.who.int/water_sanitation_health/bathing/recreadis...

A large number of people who drink contaminated water can become carriers with little or no symptoms at all. People who are carriers can continue to excrete the bacteria for a period of up to a few weeks.
http://www.waterwise.co.za/site/water/diseases/waterborne.ht...

Not all individuals are symptomatic - that is, a number of carriers excrete cysts or oocysts for months or years without knowing they have a disease.
http://www.elibrary.dep.state.pa.us/dsweb/Get/Document-11166...

Humans are another significant carrier. Giardia is the most commonly reported intestinal parasite in the world.
The mobile form propels itself with eight whip-like tails or flagella. The parasite is tiny. More than 15,000 can fit on the head of a pin. There’s also an active amoeba-like form of giardia called a trophozoite. It will attach to the walls of the intestine and feed off the host.
Once it makes its way further down the digestive track, it encases itself in a cyst to ensure survival upon being passed from the body. During bad cases of infection, the human body might excrete hundreds of millions of cysts per day.
http://www.ontariofishing.net/news2009/feb2009-2.html