Leptospirosis Study Rodent Transmission


Leptospirosis is a potential threat to people and to dogs. Leptospirosis is caused by a bacterial organism spread by urine of infected rodents and other animals, and found in water (most commonly standing water).

Since people in the U.S. don’t typically drink directly from ponds, streams or puddles, the impact to people – compared to other nations in the world – is rather low. However, dogs do get sick (sometimes very sick) commonly.

For dogs, the good news is the prevention is possible with a vaccine to prevent leptospirosis.

Still, leptospirosis is responsible for death in America of people, and also dogs that are unvaccinated. And relatively little is known about how rapidly it is spread. Hawaii is actually the state with the most incidents (likely because of all the water, and the tropical climate).

In an effort to learn more, according to Science Daily, researchers used remote sensing and Geographic Information Systems (GIS) to expand knowledge on rodents’ habitats. These studies allow a better understanding of their behavior, depending on land use changes, and infection risks caused by human activities.

Rodents are major reservoirs of human pathogens such asLeptospira spp., the bacteria responsible for leptospirosis. This bacteria is transmitted to humans via the animals’ urine, mainly through skin lesion in contact with contaminated water. The disease occurs in most parts of the world. The number of cases, which is estimated at 500,000 a year, is constantly growing. The rate is especially high in Southeast Asia, where Lepto is considered as endemic.

So, taking a sample of nearly 3,000 rats and mice from about twenty different species in Lao P.D.R., Cambodia and Thailand, researchers have made a unique collection of tissues and parasites. This sampling allowed them to cover and compare different environments, regarding a gradient of anthropogenic disturbances, from forests to villages. For instance in the two study sites in Cambodia, most of the species carried Leptospira, with an average of 11% of the rodents identified as positive. This proved that the bacteria were present in various environments. Rice fields, secondary forests and their neighbouring fields had the highest prevalence among rodents, implying that such areas could present the highest risk of infection for people staying there. The data also demonstrated the impact of seasons on the risk of infection. As bacteria survive longer in a wet environment, they are spreading more efficiently during the rainy season.

The study used of Geographic Information Systems or GIS, remote sensing and geo-statistics. The GPS allowed to georeference each animal to their sampling location. Various kinds of information, such as the characteristics of its environment, were integrated into the GIS. Historical comparisons were made, based on archive and recent images from the SPOT observation satellites in the late 1980s. This study measured changes in the Thai, Cambodian and Laotian landscapes, and how it may have impacted the rodent and pathogens population dynamics.

How does this research translate to the U.S? Not completely clear, at least not yet. We do know leptospirosis is on the rise here too, though. And it even occurs in big cities (not just rural areas). If your veterinarian is seeing lepto, ask about the vaccine. And, though you may be tempted, don’t drink from puddles or retention ponds.