Canine tick-borne diseases are transmitted by Rhipicephalus sanguineus (brown dog tick), which is common in Thailand  and is distributed worldwide . Ticks not only feed on blood cells but also transmit different types of pathogen, for example, protozoa, virus, rickettsia and bacteria , causing both morbidity and mortality. Ehrlichia canis, Babesia canis vogeli and Hepatozoon canis are commonly found in Thailand [4, 5]. Ehrlichiosis and babesiosis can develop when a dog is bitten by an infected tick, but hepatozoonosis is caused by its ingestion. B. canis subspecies vogeli is the main species causing canine babesiosis in Thailand . B. canis is the large form of Babesia spp., and Babesia organisms enter and multiply in erythrocytes of the host. Clinical manifestations are anorexia, lethargy, pale mucous membranes, fever, jaundice, and renal disease . The severity of infection depends on the subspecies of canine babesiosis. B. canis causes a sub-clinical-to-mild degree of infection [6, 7]. E. canis is a gram-negative intracellular rickettsia that can infect monocytes and lymphocytes in dogs . Canine ehrlichiosis can be classified into three stages according to clinical signs: acute, sub-clinical and chronic. In the acute stage, clinical signs appear around 1–3 weeks after infection and include fever, weakness, lethargy, depression, lack of appetite and limb oedema. In the sub-clinical stage, the organism may be present for months to years without clinical symptoms. In the chronic stage, the infected dog has abnormal bleeding due to thromocytopenia, severe weight loss, fever, difficulty in breathing due to lung inflammation, joint pain, seizures in some cases, a lack of coordination, anaemia and kidney failure . H. canis is an apicomplexan parasite that belongs to the family Hepatozoidae and clinical signs of H. canis infection can vary from sub-clinical to severe and life-threatening. The most frequently observed clinical signs are anaemia, extreme lethargy, intermittent fever and emaciation .
SPEPs show the fractions of two major types of protein: albumin and globulin. Albumin is a crucial protein component in the serum and is produced by the liver. Globulins account for a smaller fraction of total serum content. In dogs, globulin fractions can be separated into five fractions: α1-globulin, α2-globulin, β1-globulin, β2-globulin and γ-globulin. The measurement of serum protein may be key in the detection, diagnosis and monitoring of various diseases and pathological processes. SPEPs can be used as a diagnostic tool in a wide spectrum of diseases, including infectious and inflammatory disease, renal disorders, hepatic disorders, gastrointestinal disorders, immunodeficiency status and paraproteinemia caused by plasma cell neoplasia .
The acute-phase response is considered part of the innate host defence system and systemic effects include leukocytosis, fever and increased blood cortisol. C-reactive protein (CRP) is one of the acute-phase proteins and is synthesised by hepatocytes, smooth muscle cells, macrophages, endothelial cells, lymphocytes and adipocytes. It is a major acute-phase protein in dogs and is part of the γ-globulin fraction. Its concentration increases dramatically in response to inflammation, infection from pathogens (including bacteria and parasites), and injury, and it has been used as a predictive marker for risk of disease and to monitor the response to treatment . The aim of this study was to investigate the SPEPs and CRP concentrations associated with single infections of E. canis, B. canis and H. canis and in canine blood parasite co-infection.