A new variety of spirochaetes belonging to the genus Leptospira has been identified in the Peruvian Amazon region. The variety, reportedly pathogenic to man, has been associated to the genus Rattus.

Leptospirosis is a globally distributed zoonosis caused by spirochaetes belonging to the genus Leptospira. It is usually associated to catastrophic situations such as flooding, although rodents and dogs are also known as being their main reservoirs. The impact of leptospirosis on human health has increased considerably in recent years.

The genus Leptospira includes a wide variety of genospecies, also known as serovars. Some of them cause health problems in animals, man, and also in other organisms of less or no importance from a sanitary point of view. Recent studies performed by specialists from Peru, Argentina, USA and Canada have lead to the identification of a new pathogenic serovar in the Peruvian Amazon region. In this specific case, the variety has been associated to the genus Rattus.

The serovar described was isolated from men and rats from the species Rattus norvegicus and R. rattus, the latter being captured in urban, suburban and rural areas of the city of Iquitos. By means of molecular analysis and serological characterisation, the pathogen was genetically classified as belonging to a new group of pathogenic leptospiras.

Scientists involved in the study have agreed to classify the new entity as Leptospira licerasiae, serogroup Iquitos, serovar Varillal. The new serovar has also been incorporated in the current serological tests, thus allowing detection of the illness in patients believed to be affected by leptospirosis but without a proper biochemical diagnosis.

Knowing and identifying as many serovars as possible in a certain geographic region should allow their incorporation within the local antigenic pool and standard diagnosis procedures, and in this way diminish the number of cases suspected as lepospirosis from a clinical and epidemiological point of view, albeit without a concluding biochemical diagnosis.