Lepto: A New Vaccine, A New Disease?

Livestock Update, February 2005

Dr. W. Dee Whittier Extension Veterinarian, Cattle VA-MD Regional College of Veterinary Medicine, VA Tech

Lepto, short for Leptospirosis, is not a new word to cattle producers. Lepto has been considered one of the "critical use" vaccines. As such it has been included in many vaccination programs prescribed by veterinarians and employed by Virginia beef cattle producers. New discoveries about the disease and the introduction of a new vaccine for Lepto has resulted in the asking of a number of questions about the proper approach to dealing with this disease in beef cattle herd in Virginia.

Although Lepto can cause sickness and bloody urine in calves or mastitis in cows, these forms of the disease are seen only rarely in beef cattle in this country. The evidence for the role of Lepto as a cause of disease losses in cattle has been the large number of cows that have titers (antibodies to the disease in their blood) and the finding of the organism in aborted fetuses. For this reason abortion has been the major disease loss attributed to Lepto.

A number of strains of Lepto have been shown to cause disease in cattle. The vaccine used against Lepto for many years in the US contains five stains (technically serovars). The strains that have been included in the 5-way are generally strains that are carried by other domestic or wildlife animal species and then spread to livestock where they result in disease. This table shows the important strains, their source animals and the animals to which they are shed.

Strain	Source Animal	Final Target
Pomona	Cattle, Pigs, Skunks	Cattle, Sheep
Canicola	Dogs	Cattle, Pigs
Icterohaemorrhagiae	Rats	Cattle, Pigs
Grippotyphosa	Raccoons, Opossums	Cattle, Pigs

Throughout the world there are other strains of Lepto which have important effects. In Australia, there is a strain of Lepto which commonly affects cattle but is also spread to humans in milking parlors such that human Leptospirosis is a problem. In Great Britain, there is a strain of Lepto accepted to cause significant disease in their cattle which has never been detected in the US.

Recently, it has been discovered that there is a strain of Lepto not previously recognized in the US but which has probably been present for along period of time. This Lepto is being called "Lepto hardjo-bovis". It should not be confused with the Lepto hardjo which is present in the 5-way vaccine. This strain of Lepto is called "host adapted" in cattle, meaning that it is able to set up infections in cattle that last for years, even the lifetime of the animal. It has essentially figured out how to avoid the immune systems of cattle and thus persist, especially in the kidney where it is shed in the urine, without causing much damage to the animals. Research suggests that the main problem that comes with Lepto hardjo-bovis infections is with fetuses which are not resistant to the effects of the bacteria. Fetuses that are infected may be killed or survive and be born as carriers.

Through the years, there has been continual suspicion that Lepto is resulting in decreasing pregnancy rates in cattle, in addition to the abortions that it causes. This has been difficult to prove, however, since the fetuses that might be killed by the infection are tiny and are either reabsorbed or lost environment. However, in a study done in a large California dairy, unvaccinated cows with titers to Lepto hardjo (4.3% of the cows) took over a month longer to get pregnant on the average.

The diagnosis of Lepto hardjo-bovis is quite difficult. Because the organism is host adapted looking for titers by simply taking a blood sample is not thought to be a reliable way to tell if a herd is infected. The currently recommended way for diagnosing the disease is to take both blood and urine samples from at least 15 mature animals in the herd. The urine samples must be taken following administration of medication to greatly increase the flow of urine so that Lepto organisms are washed from the kidney. The isolation of organisms is then interpreted in light of blood sample results to be sure those organisms that are found are not from infections of other strains of Lepto. This procedure is time consuming and involves cost of hundreds of dollars for each her tested.

How likely are beef cattle in Virginia to be experiencing losses from Lepto hardjo-bovis? The answer is clearly that we don't know. Most work on the disease has been done in dairy herds where, because of their greater confinement, it is suspected that much greater rates of infection exist. In a recent survey, 57% of herds tested (probably tested because of a suspicion of disease) were infected with Lepto hardjo-bovis. The map below shows that there were considerable differences in infection rates across the country.

Lepto hardjo-bovis can be controlled in two basic ways. One approach is to eliminate carriers with antibiotic treatment. Both long acting tetracyclines and ceftiofur have been shown to cure infected animals. The new vaccine, Spirovac® from Pfizer, is directed specifically at Lepto hardjo-bovis. Initial vaccination requires one 2-mL dose, followed by a second 2-mL dose four to six weeks later. Annual revaccination maintains protective immunity. Spirovac® is labeled for the prevention of infection by Leptospira hardjo-bovis, including reproductive and renal tract colonization and urinary shedding for up to 12 months. Vaccination with Spirovac also aids in the prevention of fetal infection caused by hardjo-bovis.

The decision of whether to include Spirovac in a beef herd vaccination program is not an easy one. It must be based on the severity of losses that are occurring and the likelihood that these losses are coming from Lepto hardjo-bovis. Since this infection involves long-term carrier states it would be a long-term problem. A single year of reproductive failure is probably not good evidence for this condition. Of course, testing for the disease is an option but its cost and complexity does not make it a procedure that is widely performed currently.

The vaccine is relatively expensive and implementing Lepto hardjo-bovis vaccination may cost more than the entirety of "critical use" vaccination programs that most Virginia beef producers are using. Certainly Virginia beef cattle producers contemplating use of this new vaccine should be sure that other causes of reproductive failure are addressed in addition to the addition of a new vaccination.

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