In the natural resorvoir hosts, leptospira does not produce any manifestations. When humans come into contact with water polluted with the urine of resorvoir hosts, leptospira enter the body through abrasions in skin or through intact mucous membranes of nose, mouth or conjunctiva.
The incubation period is about 10 days (range – 2-26 days). Manifestations can range from mild fever to severe illness with hepatorenal damage (Weils disease). Symptoms include rigors, vomiting, headache and intense congesion of eyes. Jaundice may be present in 10-20% cases by second or third day. Fever usually subsides in 10 days. Aseptic meningitis and abdominal symptoms may be present. Purpuric hemorrhages may be present in skin or mucous membranes. Albuminuria is always present.
Leptospires can be found in the blood in the acute phase and are difficult to demonstrate after 8-10 days. They persist in internal organs, especially the kidney. So leptospires can be demonstrated in urine in later stages.
Serotype icterohaemorrhagiae is the one usually producing severe disease. Aseptic meningitis is found with canicola and abdominal symptoms with grippotyphosa infections.