Euthyroid Sick Syndrome and Changes in Thyroid Hormones in Dogs with Hemoparasitosis

Abstract

Background: Hemoparasitoses are extremely important in the clinical routine because they affect a large number of dogs. In spite of the abundance of studies on this topic, hormonal alterations caused by infection with these agents are still poorly known. Therefore, the goal of this work was to assess the serum levels of thyroid hormones of dogs infected with Ehrlichia canis (E. canis) alone, and dogs infected with E. canis and Babesia canis vogeli (B. vogeli) and/or Anaplasma platys (A. platys) before and after treatment with doxycycline chlorohydrate. This study also aimed at checking for presence of euthyroid sick syndrome (ESS) in these animals.Materials, Methods & Results: The concentrations of the thyroid hormones total triiodothyronine (TT3), total tetraiodothyronine (TT4), free tetraiodothyronine (FT4), and canine thyroid-stimulating hormone (cTSH) were assessed by chemiluminescence in 12 dogs. Nested polymerase chain reaction (nPCR) was used to confirm diagnoses. The dogs were divided into 2 groups: G1, which comprised animals infected by E. canis alone, and G2, which included animals simultaneously infected by E. canis and B. vogeli and/or A. platys. The serum concentrations of the thyroid hormones were measured at two time points: before (D1) and after (D2) the 28-day treatment with generic doxycycline chlorohydrate (DC) at a dose of 10 mg/kg SID. On D2, another nPCR was carried out to check the efficacy of the treatment. On D2, in both groups, all dogs became negative for E. canis; however, 8 animals remained infected or were reinfected by other hemoparasites. On D1, 4 dogs in G1 exhibited low TT3 in conjunction with low TT4; one of the dogs had increased TT3 alone, and another dog had an increased TT3 accompanied by decreased TT4. In G2, on D1, one dog exhibited high TT3 accompanied by a decreased concentration of TT4; 2 dogs had decreased TT4; 2 dogs had increased TT3; and one dog had both TT3 and TT4 decreased. On D2, with only one exception, the animals in G1 that became negative for all hemoparasites under study exhibited normal serum levels of TT3 and TT4. Three dogs in G1, which were reinfected on D2, sustained decreased TT4 serum concentrations. Whereas, in G1 on D2, only one dog remained with a reduced serum TT4 concentration.Discussion: DC was effective at eliminating infection by E. canis in all dogs on D2. Even though this drug was unable to prevent reinfection of the animals by other hemoparasites, and in spite of divergent results on its efficacy at eliminating babesiosis and anaplasmosis, a clinical improvement was observed in all patients. A decrease in the serum concentrations of thyroid hormones (ESS) may occur in dogs with severe non-thyroid related diseases. Different authors have demonstrated the presence of ESS in dogs with hemoparasitoses; however, this is the first study to provide evidence on the existence of this syndrome in dogs with hemoparasitoses in Brazil, including dogs simultaneously infected by E. canis and B. vogeli and/or A. platys.We observed a reduction in TT3 and/or TT4 in dogs infected by E. canis, B. vogeli, and A. platys. We believe these results may help assessment of prognosis and patient follow-up, as TT4 concentrations returned to normal levels in all dogs that became negative for all hemoparasites after treatment; and only one dog in G1 sustained increased TT3, albeit lower than observed on D1. In animals of G1 that were reinfected after treatment started, TT3 returned to normal, even though TT4 levels remained decreased. In sum, all dogs in G1 and G2 exhibited TT3 and/or TT4 concentrations outside of the reference value ranges on D1, which indicates that alterations in the levels of thyroid hormones were due to infection by the hemoparasites. The animals infected by E. canis alone or simultaneously infected by B. vogeli and/or A. platys exhibited ESS.