Q FEVER IN MARYLAND: PREVALENCE OF ANTIBODIES AGAINST COXIELLA BURNETII AMONG WILD MICE IN FREDERICK COUNTY

Abstract

Mice indigenous to the rural environment of Frederick County, Maryland, were surveyed for seropositive reactions to Coxiella burnetii, phase I and phase II. Three distinct ecological habitats (barns, wooded fencelines, and open fields) were sampled, and the proximity of the mice to the presence of large domestic animals, traditionally a major source of human infection, was ascertained. Seventy-four mice were trapped; 53 that were alive when removed from the traps were tested for antibodies against C. burnetii using an enzyme linked immunosorbent assay (ELISA). Three genera of mice were found within the habitats: Mus, Peromyscus, and Microtus. Initial testing by ELISA revealed the inability of Mus-derived conjugate to recognize immunoglobulins (IG) of Peromyscus or Microtus. To circumvent this problem, pools of sera from Peromyscus and Microtus were obtained; the IG portion was extracted from each pool, using ammonium sulfate precipitation followed by elution from a protein-A sepharose column. Each individual extract was used to immunize rabbits against either Peromyscus or Microtus IG. The species-specific antisera were then used in the ELISA to detect Peromyscus and Microtus IG which had bound to phase I or phase II C. burnetii antigens. Survey results showed a high proportion (65-84%, inclusive) of seropositives to Q fever among all three genera, regardless of habitat. These observations are analogous to those of other studies which showed a comparatively high incidence of antibodies against C. burnetii in both domestic ungulates and humans in central Maryland. However, in this study there appeared to be no relationship between proximity of mice to large domestic animals and prevalence of antibodies against C. burnetii. Results of this study strongly suggest the possibility of endemic foci of C. burnetii being maintained within wild animal communities in central Maryland.