Leptospirosis

Introduction

There are over 200 serovars of lepospirae that are found world-wide. Although the bacteria are maintained in specific hosts, they can cause disease in other accidental host including humans. The bacteria are transmitted by contact with contaminated urine, water sources or feed. L.pomona may also be transmitted venereally via semen of infected bulls. Because of the widespread infection of wild animals and the difficulty in diagnosing sub-clinical cases, Leptospirosis must be controlled by sanitation and vaccination.

Cause

Leptospirosis is caused by a small filamentous bacteria, or spirochete, that can survive in a variety of wet environments (waste water, moist soil). The bacteria typically had a diameter of 0.1 µm and a length of 6-30 µm. The bacteria are motile by means of two flagella, one extending from each end of the cell. After infection, the bacteria multiply in the blood and colonize the kidney and the fetus of pregnant animals. Organisms can survive in the kidney for up to two years and be chronically shed in the urine.

Below is a table of the most common serovars.

Serovar Maintenance Host Accidental Host
L pomona Pig, skunk, raccoon, opossum sheep, cattle, horse, human
L. hardjo-bovis cattle sheep, human
L. bratislava pig, horse
L. grippotyphos Raccoon, opossum, squirrels sheep, cattle,dogs?
L. icterohaemorrhagiae brown rat cattle, pig, dog, human(Weil’s disease)

Diagnosis

The disease can take four forms:

Disease Type Species Symptoms
Acute All Species fever, anorexia, hemolytic anemia (blood in urine)
cattle Abortion (7-10 days after fever), decreased milk production, blood or blood clots in milk
sows Abortion (last 3 weeks of gestation), piglets born mummified or weak
horses Abortion?
Subacute cattle, horses less severe clinical symptoms
Occult All species increased antibody titer
Chronic All species multiple late term abortions, mild clinical symptoms
Horse Recurrent uveitis (moon blindness), develops 12 months after infection,
may lead to blindness

Human infections with Leptospira are classified as icteric or anicteric. The icteric form (Weil’s disease) is the classic hepatic and renal form most often due to infection with L. Icterohaemorrhagiae. Symptoms include: fever headache, conjunctivitis, rash, myalgia, diarrhea, petechiae, hepatomegaly and jaundice, renal tubular damage and meningitis. The less severe, anicteric disease presents as flu-like symptoms followed by a second phase of severe headaches, myalgia and possibly aseptic meningitis. Laboratory procedures to isolate the organism from urine and serological tests on milk and serum are necessary to diagnose leptospirosis.

Treatment and Control

The primary aim of treatment is to control the infection before irreparable damage is caused in the liver and kidneys. Antibiotics such as streptomycin or tetracyclines are the most effective. Annual vaccinations against leptospirosis in cattle, swine and dogs is now in general use to control the disease.

Other Links:

AVMA brochure on Leptospirosis in Dogs and Cats.

CDC Site on Leptosipirosis in humans: https://www.cdc.gov/leptospirosis/index.html

Merck Manual of Veterinary Medicine (on-line) - Leptospirosis with general information and specifics on dogs, horses, ruminants and swine.