Concentrations of cortisol, thyroid hormones and thyrotropin in Beagle dogs experimentally infected with Babesia rossi

Abstract

Experimental protozoal infections can provide novel insights into the host’s response before presentation to the veterinarian. The aim of this study was to track endocrine variables longitudinally in an experimental Babesia (B.) rossi infection in beagle dogs and to assess changes in endocrine variables between dogs infected with a high (108 parasites) and a low dose (104 parasites) of parasite inoculum.

Six purpose bred castrated male beagle dogs were included in this prospective longitudinal observational study. The infectious inoculum was raised in a splenectomised dog. The remaining five dogs were randomly divided into two groups. Two dogs were infected with the low dose of parasite inoculum and three were infected with the high dose. Basal serum cortisol, thyroxine (T4), triiodothyronine (T3), and thyrotropin (TSH) concentrations were measured every second day, until the predetermined end points of infection. Samples were analysed using a solid- phase, competitive chemiluminescent enzyme immunoassay (Immulyte® 2000, Siemens). Once the end points were reached, the dogs were drug cured with diminazene aceturate (3.5 mg/kg subcutaneously).

In both groups, the median cortisol concentration increased and the median T4 and T3 concentrations decreased after infection with a return towards baseline concentration post treatment. The high dose group showed a rapid and more pronounced increase in cortisol concentration, whilst the low dose group demonstrated a slower and milder increase. One dog from the high dose group died during the study. This dog showed the highest recorded cortisol concentration of 610 nmol/L at 96 hours after infection, shortly before death. The high dose group showed a rapid and greater decline in T4 concentration whilst the low dose group showed a more gradual and milder decrease. The T3 concentration also decreased post infection and was significantly lower in the high dose group when compared to the low dose group, at certain timepoints. The TSH concentration remained within the reference interval throughout the study period.

This study illustrated the temporal changes in endocrine parameters during experimental B. rossi infection and demonstrated that cortisol rose, whilst T4 and T3 declined proportionate to the severity of disease which is associated with the dosage of the parasite inoculum.