The Harry M. Zweig Memorial Fund for Equine Research

Equine Leptospirosis: Part I. Vaccination Against Equine
Equine Leptospirosis in a Hamster Model

Dr. Yung-Fu Chang

Leptospirosis is caused by a group of highly invasive spiral bacteria (spirochetes) that are capable of infecting people and animals, including horses. Transmission occurs either through direct contact with an infected animal or through indirect contact with soil or water contaminated with urine from infected animals. Infection of horses with leptospira interrogans serovar pomona type Kennewicki causes Uveitis (periodic ophthalmia), corneal opacity, abortion, and fever and icterus.

Currently, there is no vaccine against equine leptospirosis. Most veterinarians use commercially available vaccines for cattle. these vaccines contain heat- or formalin-killed leptospira and produce only incomplete, short-term immunity. Further, the need for an equine vaccine against leptospirosis is exemplified by recent outbreaks of the disease in New York and other states (Pennsylvania and Kentucky).

Several surface-exposed lipoproteins from spirochetes like Treponema pallidum, T. denticola, T. phagedenis, Brachyspira hyodysenteriae, and Borrelia burgdorferi are protective immunogens. We have shown that outer surface protein A (OspA), a lipoprotein from B. burgdorferi, can protect dogs and horses against Lyme infection and disease. Thus, it is logical that surface-exposed lipoproteins of Leptospira spp.would also be immunogenic and therefore, potential candidates for vaccine development.

To date, only a few leptospiral outer membrane proteins have been characterized and relatively little work has been done on DNA vaccine development for equine leptospirosis. During our first year of study we have cloned and sequenced the 32 and 41 kDa outer membrane lipoprotein genes of L. interrogans serovar pomona type Kennewicki and the 31kDa protein from various serovars like L. interrogans serovar pomona type Kennewicki, L. grippotyphosa, L. wolfi, L. copenhageni, L. hardjo, L. icterrohemorrhagiae and L. pyrogenes serovar.

Our long-term goal is to develop a genetic (DNA) vaccine or a recombinant vaccine against equine leptospirosis. This novel class of vaccines, based on immunization with plasmid DNA, has the potential of protecting against disease wthout many of the disadvantages associated with vaccines presently used. Inoculation with plasmid DNA vectors encoding immunogenic proteins induces both antibody and cell-mediated immune responses that provide protective immunity. In this study, we propose to use the 32 and 41 kDa lipoprotein genes as DNA vaccine candidates in a hamster model of leptospirosis. If the results of this study are promising, we will then propose to carry out the vaccination experiment in horses next year.