Joseph Vinetz, M.D., professor of medicine in UC San Diego’s Division of Infectious Diseases – working in collaboration with colleagues from Universidad Peruana Cayetano Heredia in Lima, Peru, and others – headed the study that led to discovery of the new species in the family of pathogens, Leptospira, which is spread from animals to humans.
Leptospirosis is a severe, water-borne disease transmitted from animals to humans, with tens of millions of human cases worldwide each year. Fatality rates can range as high as 20 to 25 percent in some regions, and it is particularly prevalent in tropical countries where poor people live under highly crowded condition, or in rural areas where people are exposed to water contaminated by the urine of Leptospira-infected animals such as rats.
The new species reflects Amazonian biodiversity, according to Vinetz, and the pathogen has apparently evolved to become an important cause of leptospirosis in the Peruvian Amazon region of Iquitos. There, Vinetz leads an international team of physicians from the U.S. and Peru in an NIH-funded training program studying malaria, leptospirosis and other infectious diseases that impact disadvantaged populations in developing countries.
The researchers found that the new species, Leptospira licerasiae – cultured from a very small number of patients, as well as eight rats – is significantly different from other forms of the bacteria at a genomic level and has novel biological features.
“This strain has fundamentally different characteristics,” said Vinetz, adding that the next step is to sequence its genome. “We think that hundreds of patients are infected with this pathogen, which is so unique that antibodies for the disease don’t react to the regular tests for leptospirosis.”
In testing 881 patients in a prospective clinical study of fever, the researchers found that 41 percent of them had antibodies that reacted only to this new strain of the bacteria, showing a much higher incidence of leptospirosis than previously suspected.
“This observation is relevant to other regions of the world where leptospirosis is likely to be common, because it’s necessary to identify the right strain of the Lepstospira in order to make the correct diagnosis,” Vinetz said.
Since isolation of the new Leptospira in people was rare despite the high prevalence of antibodies to this strain of the bacteria in the Amazonian population, Vinetz theorizes that the individuals with positive cultures may have a previously undiscovered immune system defect, making them more susceptible to the disease.
Journal reference: Matthias MA, Ricaldi JN, Cespedes M, Diaz MM, Galloway RL, et al. (2008) Human Leptospirosis Caused by a New, Antigenically Unique Leptospira Associated with a Rattus Species Reservoir in the Peruvian Amazon. PLoS Negl Trop Dis 2(4): e213. doi:10.1371/journal.pntd.0000213
Additional contributors to the paper include Michael A. Matthias, Jessica N. Ricaldi, Kailash Patra, and Mayuko Saito of UCSD, Manuel Cespedes of the National Institute of Health in Lima, Peru, M. Monica Diaz of the University of Tucuman, Argentina, Renee Paul N. Levett, ReneeL. Galloway and Arnold G. Steigerwalt of the Centers for Disease Control and Prevention, Atlanta , Carlos Vidal Ore of the Peruvian Ministry of Health, Loreto, Peru, Eduardo Gotuzzo of Universidad Peruana Cayetano Heredia, Lima, Peru, and Robert H. Gilman of Johns Hopkins School of Public Health. The study was supported by U.S. Public Health Service grants from the National Institutes of Health.