Leptospirosis is caused by a bacterial agent. This bacteria can live for months in the soil or in water, just waiting to be ingested. Many wild animals can carry Leptospirosis, including rats, mice, raccoons, voles, skunks, and opossums. 

Leptospirosis causes very vague clinical signs, varying from just not doing right to fever, pain, vomiting, diarrhea, bleeding issues, swollen joints, and anorexia. It can cause serious kidney and liver issues. If the disease is caught early, most dogs receiving intensive supportive care will survive, but Leptospirosis can be fatal.

Leptospirosis is transmissible to humans, usually through infected urine. Not all animals show signs of infection, so even an apparently healthy animal could be shedding Leptospirosis.

The good news is that we have a vaccine! Annual vaccination with the Leptospirosis vaccination is recommended. The initial vaccine will require a booster in 2-4 weeks, then subsequent boosters once a year. 

https://www.avma.org/public/PetCare/Pages/Leptospirosis.aspx