Leptospirosis - Cats and Dogs

Description

Leptospirosis is an important zoonosis, affecing humans as well as animals. The disease can be caused by infection with a number of different serovars of the bacteria Leptospira interrogans. In general infection with a host adapted strain results in subclinical infection, intermittent shedding of the organism with the animal acting as a reservoir for infection. Infection with non host adapted strains results in clinical disease.

Transmission is via urine of affected animals; the organism gains entry at mucous membranes, broken skin, bite wounds and through ingestion of infected material. The organism can remain viable for weeks in damp conditions, rodents and other mammals act as a reservoir of infection. The incubation period is 2-12 days, after which dogs become lethargic, pyrexic and anorexic. The disease often progresses with renal and hepatic involvement. The host-adapted serovar canicolar causes acute renal failure in puppies; a chronic uraemic syndrome may follow. Incidental infections with serovar icterohaemorrhagica or copenhagenii cause renal failure, L. icterohaemorrhagiae may also cause hepatic jaundice. Serovar bratislava has been reported to casue abortion and infertility in dogs, which may be the maintenance host.

Vaccination against serovars canicola and icterohaemorrhagica has greatly reduced the prevalence and incidence of disease in the UK but in some areas the disease is re-emerging as owners decide not to vaccinate due to the reduced risk. Serovars pomona and grippotyphosa are becoming important.

Cats do not appear to be affected by clinical disease but can become subclinically infected acting as a resevoir with intermittent shedding.

Signalment

Leptospirosis can affect dogs of any age, breed or sex. Young male, adult working dogs are at greatest risk.

Diagnosis

Clinical Signs

• Pyrexia
• Lethargy
• Anorexia

Acute renal failure develops in 80-90% of cases, these dogs will show the typical signs of vomiting, dehydration, ureamic ulceration of the mouth and lumbar pain. In less severe renal cases polyuria and polydipsia may be the most obvious signs. Hepatic involvement results in icterus, bilirubinuria and elevations in liver enzymes.

Laboratory Tests

Dark field microscopy on fresh urine is best

Pathology

Grossly-

• widespread hameorrhages
• icterus
• pale foci in the liver (not always a constant finding)
• subcapsular and cortical renal haemorrhages

Microscopically-

• foci of necrosis
• dissociation of hepatocytes form each other (similar to post mortem change)
• substantial haemosiderin in the Kuppfer cells (from the haemolysis)
• need to use a silver stain or immunofluorescence to demonstrate the organisms in tissues

References

• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial
• Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier