Infections in horses: diagnosis and therapy

Borna Disease Virus (BDV) is a unique RNA virus, whose organs of manifestation are the brain and blood of animals as well as humans. The infection disrupts certain cell functions, but does not damage the cell structure. The infection with BDV can exist without associated clinical symptoms. Furthermore the majority of natural BDV-infections occur unnoticed without causing symptoms particularly those in connection with only a slight BDV-infection. BDV-infected horses can be detected by an extremely practicable ELISA based on blood samples and developed by the Berlin Working Group under guidance of Ludwig and Bode. All three serological Borna-Disease (BD) parameters antigen-, immune complex- and antibody-titer can be measured with this ELISA. However a single testing can not lead to a final evaluation of the infection so that progressive investigations are unavoidable. Blood tests in intervals of 4-6 weeks show the course of infection and help to adjust the specific treatment. After an infection an examination of the antigen- and immune complex-titer will show whether this occurrence is acute and activated or not. Therefore we examined 3481 blood samples of different horses by ELISA. 1841 (50%) were BDV-infected. Approximately 40% of the infected horses were clinically healthy and approximately 43% were clinically ill. The relatively high infection rate could be justified by the fact that these subjects had more or less direct contact with clinically ill horses. Furthermore, it is possible that the highly Borna positive, but not clinically ill horses were tested shortly before the symptoms of disease would appear. Moreover there were also horses that have had a high BDV-titer without showing any sign of the BDV-disease. These animals were thus able to live with the infection. Our investigations focused on highly seropositive BDV-infected horses (1) (Fig. 1). The results can not be linked to BD typical endemic regions due to the fact of today's far more sophisticated testing methods. Horses are more than ever used for leisure activity and become subjects to a worldwide marketing and movement. Any stress situation, especially in competitions as shown in long-term monitoring of sick horses, leads to worsening of symptoms. In this context it should be noted that a test for activated BDV-infection is still not common. EU-wide regulations should therefore be considered.