A Survey of Antibodies against Rickettsia rickettsii and Ehrlichia chafeensis in Domestic Animals from a Rural Area of Colombia

In a rural area of Colombia endemic for Rocky Mountain spotted fever, we performed indirect immunofluo- rescent antibody assays for Rickettsia spp. and Ehrlichia spp. using sera from randomly sampled dogs and horses to test the use of domestic animals as possible sentinels. Antibodies against Ehrlichia spp. were detected in 8 dogs (31.8%). Antibody titers against Rickettsia rickettsii antigen were positive in 4 dogs (18.2%) and 26 horses (16.3%). These values, albeit not directly comparable, are lower than those previously reported for humans in this region. A systemic approach to understand- ing dynamics of transmission is needed before implementing the use of domestic animals for disease surveillance activities. Spotted fever group (SFG) rickettsioses and ehrlichioses are tick-transmitted emerging human infections caused by obligate intracellular gram-negative bacteria belonging to the order Rickettsiales. 1 There is a current large re-emergence of Rocky Mountain spotted fever (RMSF) in the Americas; the highest number of RMSF cases reported in one year in the United States (1,514) occurred in 2004, 2 and new and large clusters of spotted-fever group rickettsioses have been recently reported from several Latin American countries including Argentina, 3,4 12 Therefore, we designed this study to test whether a similar concept could be applied to other areas of Latin America. The study area is particularly relevant because of the endemic- ity of SFG human rickettsioses. 11,13 We also wished to address the lack of data regarding the presence of Ehrlichia spp. or Rickettsia spp. in domestic mammals in this area of Colombia. Ehrlichiosis have been recognized as infectious diseases in animals for a long time, but they are now being recognized as important emerging zoonoses in humans and there is no data about their importance in Colombia. 2 The study area is located in Villeta, Cundinamarca, Colombia, (5°0¢53"N, 74°28¢29"W), which is 842 meters above sea level, and has an annual average temperature of 26°C and a relative humidity of 80-97%. The estimated horse popula- tion in the rural area is of 1,695 animals in 22 villages. The dog population could not be estimated because registration is not mandatory and because most dogs roam freely with access to pasture and forest areas. Horses graze on mixed overgrowth pastures in the study area. Three tick species have been doc- umented in the area: Amblyomma cajennense , Rhipicephalus sanguineus , and Anocentor nitens . Because of the high mobility of animals within the region, we applied a snowball sampling strategy. In the locations where horses were found, dogs where included for collection of serum samples. During March and April 2008, blood sam- ples were collected from 22 dogs, and 159 horses. An immu- nofluoresecent antibody assay was performed as previously described.