Leptospirosis - Cats and Dogs

Description

Leptospirosis is an important zoonosis, affecting 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.

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

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 cause 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.

Signalment

Leptospirosis can affect dogs of any age, breed or sex. Young male, adult working dogs are at greatest risk. There are usually more cases in years with higher rainfall.

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

Diagnosis can be confirmed by culture of the organism from urine, blood or tissues. The organism can also be identified through dark field microscopy of urine or PCR carried out on blood, urine or tissues. A rising antibody titre in conjunction with suggestive clinical signs is also sufficient for diagnosis.

The tests may reveal false negatives due to the intermittent shedding of the organism.

Pathology

Grossly-

• Widespread haemorrhages
• Icterus
• Pale foci in the liver (not always a constant finding)
• Subcapsular and cortical renal haemorrhages

Microscopically-

• Foci of necrosis
• Dissociation of hepatocytes
• Substantial haemosiderin in the Kuppfer cells
• A silver stain or immunofluorescence will demonstrate the organisms in tissues

Treatment

Supportive treatment should be given in cases of renal failure and hepatic disease.

Doxycycline is the antibiotic of choice for treating leptospirosis as it also targets the renal carrier phase, preventing transmission of the disease.

Appropriate protective measures should be taken by those treating cases of leptospirosis due to the zoonotic potential.

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