Leptospirosis - Horses

Description

Leptospirosis is a disease caused by the bacteria Leptospira interrogans. It affects domestic species, wildlife and has zoonotic potential. There are several different serovars which vary in pathogenesis and their host specificity. Most infections result in in a self limiting pyrexia and anorexia, however occasionally the condition is more serious causing recurrent uveitis, abortion, or renal and hepatic disease.

Signalment

Exposure to the disease is worldwide, with the predominent serovar varying with location. Serological studies show that exposure is high but clinical disease is low.

Diagnosis

Clinical signs

Infection with pathogenic Leptospira spp cause a bacteraemia with the following clinical signs

• Pyrexia
• Depression
• Lethargy
• Anorexia

The disease can then invade a specific organ system resulting in associated clinical signs:

Opthalmic: The initial signs are blephrospasm, increased lacrimation, photophobia and corneal oedema, with progression to retinal detachment, synechia formation, and cataracts. Chronic leptospirosis causes recurrent uvietis, typically signs develop 2-8 months after initial infection. Up to 67% of .

Reproductive: Leptospirosis can cause abortion, still birth or neonatal disease depending on the serovar and the stage of gestation when infected. Abortions are most frequently late term.

Renal: leptospirosis rarely causes urologic signs including polyuria/polydipsia, azotaemia, pyuria and haematuria.

Hepatic: Horses with the hepatic form of the disease will bei icteric, pyrexic and lethargic.

Horses with subclinical infections or those in the carrier state are asymptomatic.

=Laboratory Tests

Culture of Leptospira is challenging but can be attempted from urine, blood and aqueous humour in antemortem diagnosis, or from liver, kidney, fetus or placenta in post mortem diagnosis.

A MAT or ELISA opn serum is a more sensitive diagnostic method. Paired titres 4 weeks apart are optimal.

References

• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial