Leptospirosis in Cattle
Posted: January 12, 2005
The causative agent is a motile, spiral-shaped bacterium (e.g., spirochete) that does not multiply outside of animal hosts, but survives for months in wet environments and stagnant water at moderate environmental temperatures. Worldwide, seven species of Leptospira are important pathogens. Over 200 different serovars of Leptospira are recognized based on antigenic variation on the organism's surface. Five serovars, hardjo-bovis, pomona, canicola, icterohaemorhagiae and grippotyphosa, are important leptospiral pathogens in North America.
Although leptospires can infect a wide variety of animals, outcome of an infection is not equal across animal species. Leptospira serovars are host adapted to specific species of wild or domesticated mammals (maintenance hosts) for the serovar. In maintenance hosts, leptospiral infections produce mild to unapparent infections, but produce a carrier state where the organism is shed in urine for weeks to months. Maintenance hosts serve as a reservoir for infection to other livestock, domestic animals and wildlife species (termed incidental hosts). Cattle are maintenance hosts for hardjo and pomona serovars. Important maintenance hosts for other leptospira serovars include dog (canicola), rat (icterohaemorrhagiae), skunks (pomona) and raccoons and opposums (grippotyphosa). Any other specie can be an incidental host and those being a maintenance host for one serovar can be an incidental host to other serovars. Incidental hosts for leptospiral infections experience more severe disease, generate high antibody titer, have large numbers of organisms in tissues and do not shed leptospires in urine for any period of time.
Transmission of leptospiral infection from maintenance hosts to other animals is very efficient. Disease transmission from incidental hosts is very limited. Leptospiral organisms are transmitted via direct contact with infected urine, milk or placental fluids. The disease can be transmitted from cow to fetus (transplacental) and from cow to bull or bull to cow during breeding (venereal).
Clinical signs associated with leptospirosis depend upon the infecting serovar and host species. Leptospiral infections in cattle where they are incidental hosts can induce clinical syndromes of abortion, typically between 4 and 7 months of gestation; birth of premature and weak calves; milk drop syndrome and severe kidney and liver disease. Chronic infections with serovars hardjo and pomona in cattle, where cattle are maintenance hosts, are the primary causes of leptospiral reproductive problems. Reproductive infertility is characterized by conception failure and early embryonic death resulting from chronic leptospiral colonization of the reproductive tract. Cows may not show any other clinical signs or even look sick with chronic leptospiral infections.
A number of leptospiral diagnostic tests have been and are under development, yet diagnosis of leptospirosis is difficult at best. Current methods either attempt to measure amount of antibody to specific Leptospira serovars or identify the presence of the organism. The organism is very difficult to grow in culture from collected specimens. No single test is sufficient in diagnosing a potential Leptospira infection. Diagnosis is especially difficult for Leptospira serovar infections of their maintenance hosts as antibody production is minimal.
The most commonly used antibody detection test is the microagglutination test (MAT). Paired serum samples 3 weeks apart from a potentially infected animal are used to detect amount of specific antibody concentration. A four-fold change in antibody titer to a specific serovar is highly suggestive of disease due to that serovar. Single serum samples can be used, but interpretation is more difficult. Currently it is suggested to screen herds for presence of chronic leptospiral infections by collecting serum and urine samples from 15 to 20 cows. Fluorescent antibody tests are used on urine samples to detect the presence of the organism. Cows identified as reproductive problems are the best candidates for diagnostic testing. Work with your veterinarian in determining your herd's need for undertaking screen testing. Special methods and collection containers are needed, so your veterinarian should be involved in the process and contact an appropriate diagnostic laboratory prior to sample collection. The Michigan State University Veterinary Diagnostic Laboratory (http://www.dcpah.msu.edu/) currently offers leptospiral diagnostic herd testing.
Treatment and Prevention
Leptospira organisms are sensitive to a number of antibiotics, although the primary antibiotic used to treat this infection, dihydrostreptomycin, is not available for use in the United States. Oxytetracyclines (LA-200®, Liquamycin®), ceftiofur (Naxcel®, Excenel®), tylosin (Tylan®) and tilmicosin (Micotil®) have all been shown to be effective in treating leptospira infections. A number of these antibiotics are not approved for lactating dairy cattle, therefore a veterinarian must be consulted for appropriate drug use and withdrawl times. Antibiotic use is only indicated for treating carrier state animals and should be used in conjunction with an appropriate vaccination protocol.
The primary method of controlling Leptospirosis is with a comprehensive vaccination program. Currently there are two vaccines approved in the U.S., the traditional 5-way Lepto and a newly approved single serovar, L. hardjo-bovis, bacterins. The five serovars contained within the multistrain vaccine include hardjo, pomona, icterohaemorrhagiae, grippotyphosa and canicola. For the 5-way vaccine, calves should initially be vaccinated around 6 months of age with 2 doses 3-to-4 weeks apart. Heifers should receive a booster prior to breeding and then annual or semiannual boosters. In the face of high disease challenge, some have advocated additional boosters throughout the year. The hardjo component of the 5-way vaccine does not necessarily prevent renal infection and urinary shedding or fetal infection with hardjo-bovis. Studies with the new single strain vaccine suggest its use can prevent renal and reproductive tract colonization and urinary shedding. Neither vaccine can clear infected carrier animals without antibiotic usage. Both vaccines can be used together for most complete leptospiral disease prevention. Work with your veterinarian to determine your herd's need and best vaccination strategy to prevent leptospiral disease problems.
Robert Van Saun, DVM, PhD