A focus of dogs and Rickettsia massiliae-infected Rhipicephalus sanguineus in California

Abstract

A recurrent focus of Rhipicephalus sanguineus infestation was investigated in a suburban area of southern California after reports of suspected Rocky Mountain spotted fever in two dogs on the same property. Abundant quantities of Rh. sanguineus were collected on the property and repeatedly from each dog, and Rickettsia massiliae DNA was detected by polymerase chain reaction (PCR). Whole blood and serum samples from four dogs were tested by using PCR and microimmunofluorescent assay for antibodies against spotted fever group rickettsiae. Serum samples from all four dogs contained antibodies reactive with R. massiliae, R. rhipicephali, R. rickettsii, and 364D Rickettsia but no rickettsial DNA was detected by PCR of blood samples. Serum cross-absorption and Western blot assays implicated R. massiliae as the most likely spotted fever group rickettsiae responsible for seropositivity. To our knowledge, this is the first detection of R. massiliae in ticks in California.

Figure 1.

Western blotting assay and cross-absorption studies on serum from dog B, California. Western blotting was performed with serum collected on 4/20/2009 and 15 μg of rickettsial protein per lane (A). Treatment of serum with antigen diluents (A), and Rickettsia massiliae (B), R. rhipicephali (C), 364D Rickettsia (D) and R. rickettsii (E) antigens, followed by Western blotting on the resulting treated serum samples, was performed according to the procedure described in the Materials and Methods. Antigens were loaded on the gel in the following order: lane1, R. massiliae AZT-80; lane 2, R. rhipicephali CA871; lane 3, 364D Rickettsia; lane 4, R. rickettsii Bitterroot. Positions of prestained broad range sodium dodecyl sulfate-polyacrylamide gel electrophoresis standards (Bio-Rad, Hercules, CA) are indicated on the sides of the blots. All serum samples were tested by Western blotting at a final dilution of 1:5,000.