Zoonosis: An infectious disease in animals that can be transmitted to people. The natural reservoir for the infectious agent is a animal.
When your dog receives his or her "distemper-parvo" combination vaccine, there is usually a list of letters that you'll see on your receipt or medical record. If there is an "L" in the list, this stands for "leptospirosis". Commonly shortened to just "lepto" when talking about it, this part of the vaccine protocols is actually controversial. There is a belief among some in the veterinary community and many breeders that the leptospirosis vaccine has a high risk of causing an allergic reaction, potentially leading to serious consequences for the dog. Since it's not the focus of my topic today, I won't get into all of the specifics of this discussion, but for now I will just state that the controversy is unfounded. Studies have shown that there is no statistical difference in reaction rates between vaccines with lepto and those without it. Those who believe that lepto vaccines are highly reactive are using outdated information and merely passing on what was told to them.
Leptospirosis is a bacterial organism that can infect many wild animals and is passed through their urine. If a dog (or even human) drinks water contaminated with this urine, or licks ground or grass also contaminated, they can become infected. Transmission can also occur through broken skin or open wound, as well as through mucous membranes in the mouth, nose, genitals, and so on. The more rain and wet ground in an area, the greater the risk of transmission as it survives in these wet conditions. How many pet owners have been urinated on by their dogs, or had to clean up urine from the floor? If your dog is infected, you have just been exposed to lepto.
In dogs, liver and/or kidney failure is the most common consequence. In humans this disease may begin with flu-like symptoms and go undiagnosed until it is far advanced. Meningitis can also be a consequence of advanced disease. As you can imagine from this list, leptospirosis is a serious disease with the potential to be fatal.
Once diagnosed, the disease is potentially treatable with several kinds of antibiotics, but some of the damage done may be permanent. The best option is prevention. That means for humans to be careful when being exposed to water sources that wild animals have been around, and washing hands carefully after being in these situations. For dogs this means being vaccinated against lepto. Talk to your veterinarian about this vaccine, and realize that there are several opinions on it and no consensus across the profession.