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Leptospirosis

Pathogenic Agent

Rodents are the most important transmitter of leptospira spp.

Serovars of the species Leptospira interrogans: Leptospira hardjo, pomona, icterohaemorrhagiae, canicola, grippotyphosa

Etiology

Leptospirosis infection is a common cause of economic losses due to abortions, reduced milk yield, mortality in calves, and decreased daily gains in dairy and also in beef production. Rodents, swine, sheep, horses, goats, dogs and man are also susceptible.

Recovered animals and maintenance hosts that act as long-term shedders may pass leptospires in the urine for long periods. Pasture, drinking water and feed are contaminated by infected urine, aborted fetuses or uterine discharges of affected cattle.

The organisms have the capacity to survive in the environment for weeks. Favorable conditions are muddy feedlots, marshy fields, moist areas around ponds, streams and water troughs in combination with temperatures from 45 to 97°F (7 to 36°C). Leptospires penetrate broken skin and mucous membranes of the mouth, nose and eye.
Replication takes place in the liver and kidney.

Clinical signs

Abortions occur commonly in the last trimester of gestation, 3 to 10 weeks subsequent to systemic invasion and infection of the fetus. The initial infection may have been accompanied by decreasing yields of milk, blood tinged or yellowish, thick milk. Usually the udder is flaccid and there are no signs of inflammation. Several cows may not develop clinical signs at all but abort after a few weeks.

Calves up to one month are most susceptible to systemic infection. They develop icterus, hemoglobinuria, depression, tachycardia, petechial hemorrhages, and pallor of mucous membranes due to anemia. Body temperatures rise to 104 - 105,8°F (40 - 41°C). Hemoglobinuria lasts 3 to 4 days. Death may occur within 4 to 5 days. The mortality rate is 5 to 15%. Recovered animals often fall behind in development and have poor daily gains.

Diagnosis

Abortions occur commonly in the last trimester of gestation

Leptospirosis infection may be suspected as a cause in the following: abortions during the last trimester of gestation; a reduced milk yield that persists for several weeks; and bloodstained or yellowish, thick milk in conjunction with cases of hemoglobinuria and jaundice.

To confirm your diagnosis, submit paired serum samples.

Increased antibody titers indicate leptospiral abortion. The organism can be identified in the urine two weeks after infection. Centrifuged samples are examined by dark field illumination at specialized laboratories. Aborted fetuses are autolysed, edematous and icteric. Fetal kidney, liver and fetal fluid should be submitted for demonstration of leptospires. It is also possible to identify leptospires in blood samples of acutely infected animals by immunofluorescence.

Differential Diagnosis

Regarding hemoglobinuria and/ or anemia:

babesiosis, anaplasmosis, rape and kale poisoning, postparturient hemoglobinuria, bacillary hemoglobinuria, cold water hemolytic anemia of calves

Regarding abortion

IBR, BVD, campylobacteriosis, brucellosis, listeriosis, salmonellosis, Q-fever, chlamydial abortions, mycotic abortions

Prevention

  • vaccinate all cattle of 6 months and older
  • revaccinate after 4 weeks
  • booster annually at mid-pregnancy or at drying off...or according to recommendations by your vaccine manufacturer
  • isolate aborting cows
  • remove aborted tissue from the premises (wear gloves!)
  • avoid mechanical transmission
  • rodent control
  • fly control
  • disinfection
  • separate cattle from pigs in case you run a mixed dairy-pig farm
  • fence your herd from wild pigs
  • prevent access to streams and ponds
  • dry up muddy areas around water troughs
  • dairy farmers should undergo blood test

Treatment

Treatment includes antibiotic therapy. Administration of streptomycin, chlortetracycline or oxytetracycline in early stages of infection reduces the number of leptospires in the tissues and the amount of excreted organisms. Pregnant cows should be vaccinated promptly with killed vaccine.

Farmers should be advised to isolate aborting cows and remove contaminated tissues.

Literature

  • Blood D.C., Radostis, O.M., Veterinary Medicine, 1989
  • Fraser, C.M. et al., The Merck Veterinary Manual, 1991
  • Jensen, R. et al Diseases of Feedlot Cattle, 1979
  • Larson, B.L., Immunization to Decrease Pregnancy Wastage in Beef Cattle. Part II. Available Vaccines, Compendium on Continuing Education, Vol. 18, No 5, May 1996
  • Roenfeldt, S., 5 diseases you can't ignore, Dairy Herd Management, May 1997
  • Smith, B. P., Large Animal Internal Medicine, 1990

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