Which organism is a spirochete transmitted by contaminated water and can cause severe illness?

• A. Leptospira interrogans
• B. Borrelia burgdorferi
• C. Treponema pallidum
• D. Leptospira bifida

Answer: (A)

Transmitted by water contaminated with animal urine points to leptospirosis, caused by Leptospira interrogans. This pathogenic spirochete is shed in the urine of infected animals (like rats) and can enter humans through breaks in the skin or mucous membranes when people swim or wade in contaminated water. The illness can be mild, but in severe cases it progresses to Weil disease, with jaundice, kidney failure, and bleeding. The other organisms are spirochetes as well, but they have different transmission routes or disease patterns: Borrelia burgdorferi is tick-borne and causes Lyme disease; Treponema pallidum causes syphilis and is typically sexually transmitted; Leptospira biflexa is nonpathogenic.