Acute phase proteins have been used as tools for the diagnosis, monitoring, and prognosis of several diseases in domestic animals. However, the dynamics of these proteins in infection byTrypanosoma cruzi, the causative agent of Chagas disease in dogs, is still unknown. The aim of this study was to determine concentrations of acute phase proteins (C-reactive protein, haptoglobin, ferritin and paraoxonase-1) in dogs in a coastal town of Ecuador, with naturalTrypanosoma cruziinfection with or without seroreactivity ofEhrlichia canis,Ehrlichia ewingii,Anaplasma phagocytophilum,Anaplasma platys,Borrelia burgdorferiandDirofilaria immitis. For the detection ofTrypanosoma cruziserum antibodies, two different antigen-based enzyme-linked immunosorbent assay tests were implemented. For the detection of seroreactivity ofEhrlichia canis,Ehrlichia ewingii,Anaplasma phagocytophilum,Anaplasma platys,Borrelia burgdorferiandDirofilaria immitis, an IDEXX SNAP®4Dx®test was used. To determine the concentration of C-reactive protein and ferritin, an immunoturbidimetric assay was used; haptoglobin concentration was measured using a commercial colorimetric method validated in dogs; a spectrophotometric method was used to determine the serum concentration of paraoxonase-1. Results showed a reduction in the serum levels of paraoxonase-1 inTrypanosoma cruzi-seroreactive dogs, either with or without seroreactivity to other vector-borne diseases. A serum ferritin increment was observed inTrypanosoma cruzi-seroreactive dogs with seroreactivity to any other vector-borne diseases. Our findings suggest that paraoxonase-1 levels are reduced inTrypanosoma cruzi-seroreactive dogs without evident clinical signs of Chagas disease, despite their seroreactivity to the other vector-borne diseases studied. These findings could indicate an oxidative stress response inTrypanosoma cruzi-seroreactive dogs with no evident signs of inflammation.