What is leptospirosis primarily caused by?

Leptospirosis is primarily caused by contact with water contaminated by the urine of infected animals, particularly rodents, livestock, and wildlife. This bacterium can thrive in various environmental conditions, and when water sources are contaminated, humans can become infected through skin abrasions or mucous membranes, such as those in the eyes, nose, or mouth.

The other choices, while associated with other diseases or modes of transmission, do not accurately reflect how leptospirosis is spread. For instance, mosquito bites primarily transmit diseases like West Nile virus or Zika virus, and contaminated food can lead to various foodborne illnesses, but not leptospirosis specifically. Furthermore, airborne transmission is not relevant in the context of leptospirosis, as the pathogen requires direct contact with contaminated water or surfaces. Thus, understanding the specific route of transmission is critical for effective prevention and control of leptospirosis.