During December 2005, twelve leptospirosis cases were diagnosed in dogs from Vashon and Maury Islands . The majority of cases had the highest titers to L. autumnalis, a serovar that is most closely associated with raccoons. Rodents and opossums are other possible reservoirs of this serovar. Typically, Public Health receives fewer than three dog case reports each month, and a cluster like this is very unusual. A seroprevalence survey of raccoons conducted in Western Washington in 2005 found that 13 of 47 (27%) had antibodies to leptospirosis with the most common serovars being L. autumnalis, however, L. pomona, L. harjo, and L. bratislava were also present. Human cases are uncommon in Washington but may be underdiagnosed and underreported. Only twelve cases were reported  between 1990 and 2005, and, of these, seven were exposed in Washington , including three in 2005. The last confirmed case reported in King County was in 2003.

Leptospirosis is a bacterial disease of worldwide distribution that affects humans and numerous animal species. While it is a zoonotic disease worldwide, only 100-200 cases are reported annually in the US , and half of these are from Hawaii . It is caused by infection with bacteria of the genus Leptospira, specifically the species L. interrogans which has over 200 serovars. Serovars vary by region and are associated with different domestic or wild animal hosts which can be chronic carriers. The most commonly identified serovars in the U.S. are L. icterohaemorrhagiae, L. canicola, L. autumnalis, L. hepdomadis, L. australis and L. pomona . Transmission from a mammalian host happens most often through contact of skin (especially if abraded) or mucous membranes with water contaminated by urine from infected animals. Drinking contaminated water can also cause infection. Leptospirosis is an occupational hazard for rice and sugarcane field workers, farmers, miners, veterinarians, dairy, slaughterhouse, sewer workers, and military troops. Recent outbreaks have been associated with exposure to contaminated water during outdoor events such as triathlons or adventure racing. Leptospirosis appears to be increasing in some urban areas especially during heavy rains when flooding occurs.

The incubation time is about ten days, with a range of two to twenty days. Infection in humans can cause a range of symptoms from subclinical to serious disease that tends to depend on the infecting serovar. The common features are fever with sudden onset, severe headache, myalgia, and conjunctival suffusion. Other manifestations include diphasic fever, meningitis, rash, hemolytic anemia, hepatorenal failure, jaundice, mental confusion and depression, myocarditis and pulmonary involvement with or without hemorrhage or hemoptysis. Weil’s disease, characterized by impaired hepatic and renal function, may develop after the acute phase.

Diagnosis is confirmed by seroconversion or 4-fold or greater increase in leptospiraemic titers using the microscopic agglutination test (MAT), and by isolation of leptospires from blood (first 7 days) or CSF (days 4-10) during acute illness, and from urine after the 10^th day. Because of regional variations in serovars, the MAT should use locally occurring serovars. Treatment with antibiotics should be initiated promptly and preferably before the 5^th day of illness to reduce severity and duration of illness. Penicillin is probably the drug of choice. Doxycycline or erythromycin can be used in patients who are allergic to penicillin. 

Leptospirosis is a notifiable disease, and health care providers must report cases to Public Health at (206) 296-4774. For suspect human cases, Public Health will arrange for laboratory testing at the Centers for Disease Control and Prevention (CDC) to confirm the diagnosis. Leptospirosis in animals is also a notifiable disease and veterinarians should report cases to Public Health at (206) 296-4880.

For more information see the CDC’s Website at: www.cdc.gov/ncidod/diseases/submenus/sub_lepto.htm

For information about pets and leptospirosis, see: www.cdc.gov/ncidod/dbmd/diseaseinfo/leptospirosis_g_pet.htm