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 leptospires 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).
Lipoproteins have been identified in many spirochetes including Treponema pallidum, T. denticola, T. phagedenis, Brachyspira hyodysenteriae, Borrelia burgdorferi, and the relapsing fever borreliae. Several surface-exposed lipoproteins from spirochetes are protective immunogens. We have shown that outer surface protein A (OspA), a lipoprotein from another spirochete (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.
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 without many of the disadvantages associated with conventional vaccines presently in use. Inoculation with plasmid DNA vectors encoding immunogenic proteins induces both antibody and cell-mediated immune responses that provide protective immunity. During our first year of study we have cloned and sequenced the 31 and 41 kDa outer membrane lipoprotein genes of L. interrogans serovar pomona type Kennewicki. In this study, we propose to use 31 and 41 kDa protein genes as DNA vaccine candidates in a hamster model. If the results of this study are promising, we will then propose to carry out a vaccination trial in horses next year.