Read the Spanish translation: Asociación Entre las Serovariedades de Leptospira en Roedores Nativos y Exóticos de la Isla de Cozumel, México

Abstract

Oceanic island ecosystems are used as models for ecological studies because they are sensitive to human activities and especially vulnerable to exotic species and pathogen introductions.^1-3 Leptospira was selected as a model to identify possible host-pathogen interactions based on the recognized serovars-host relationships, specifically by looking at the relationships among native fieldmouse (Oryzomys couesi cozumelae) and introduced (Mus musculus and Rattus rattus) rodent populations, and the seroprevalence (SP) of six Leptospira serovars (Australis, Ballum, Canicola, Autumnalis, Icterohaemorrhagiae, and Hardjoprajitno) in the Mexican Island of Cozumel. Sera samples (Oryzomys n=66, Mus n=156, and Rattus n=57) were analyzed by the microagglutination test (MAT). The most seroprevalent (all species together) with average MAT titers ≥1:100, were Australis (73%), Canicola (66.5%), and Ballum (42%). Icterohaemorrhagiae and Autumnalis had SP<26% with average MAT titers <1:50 and were assumed to be nonspecific reactions. All tests were negative for Hardjoprajitno. Australis SP ranged from 67–75% among the three species and were not significantly different by chi-square test (p>0.05). Significant differences were observed for Canicola, where Oryzomys and Mus (mice species) had SP>71% while Rattus had 14% (p≤0.05). Similarly, for mice species Ballum SP ranged from 39–49%, while the Rattus had a SP of 23% (p≤0.05). Simple logistic regression was used to explore associations between SP and rodent characteristics (species, capture area, age, and sex). The observed seroprevalences suggest rodents, introduced or native, serve as reservoirs for pathogenic Leptospira spp. Results for serovars Australis and Ballum indicate a host-adapted serovar relationship (SP>50% and average titer >1:100), the former serovar with the three species, whereas for Ballum only with mice. Canicola SP was mostly found in both mice species and illustrate a host-accidental serovar (SP>60% and the highest average titer), and these serovar SP could be the consequence of each rodent species behavior and its interaction with dogs and raccoons on the Island. The SP was greater in urban areas, and lowest in the natural areas. In Cozumel, rodents could play a role in risk for infection to other native and domestic mammals, or humans. Surveillance, isolation, and molecular characterization of Leptospira spp. should be performed to increase understanding of the serovar and host relationships, and related risk in Cozumel Island.

Acknowledgments

We thank the project “Ecology and conservation of a critically endangered island endemic biota” (SEMARNAT-2002.COI-0571), in Cozumel Island directed by Dr. Alfredo D. Cuarón, and the Laboratory of Vaccinology and Leptospirosis, Faculty of Veterinary Medicine, National Autonomous University of México.

Literature Cited

1.  Courchamp F., J.L. Chapuis, and M. Pascal. 2003. Mammal invaders on islands: impact, control and control impact. Biol Rev Cam Philos Soc. 78:347–383.

2.  Crump J.A., D.R. Murdoch, and M.G. Baker. 2001. Emerging infectious diseases in an island ecosystem: the New Zealand perspective. Emerg Infect Dis. 7:767–772.

3.  Cuarón A.D. 2009. Cozumel. In: Gillespie R., and D. Clague, (eds.). Encyclopedia of Islands. Berkeley, CA: University of California Press. 203–206.