Klinische Relevanz der Lyme-Borreliose und der Equinen Granulozytären Anaplasmose bei Pferden in Deutschland

"Clinical relevance of Lyme Disease and Equine Granulocytic Anaplasmosis in horses in Germany"

Unspecific clinical changes with often chronic courses of the disease, desperate horse owners and lack of knowledge about a disease that could not be reproduced experimentally so far, lead to uncertainty in in the diagnosis of Lyme Disease (LD) in horses. The lack of a uniform clinical picture or pathognomonic clinical changes as in human medicine, and the lack of standardization of examination methods contribute to the uncertainty.
The objectives of this study were to gain insight into the seroprevalence of Borrelia burgdorferi sensu lato (Bbsl) and Anaplasma phagocytophilum (Ap) infections in horses in Germany, and to identify risk factors for infection, to better delineate the clinical picture of equine LD, and to better assess the clinical relevance of both equine LD and equine granulocytic anaplasmosis. For this purpose, a sick case group with clinical suspicion of LD was to be compared with a healthy control animal group, whereby a control animal from the same stable was a prerequisite for the examination of each suspect animal.
In this study, blood samples from horses all over Germany were tested for Bbsl-antibodies by ELISA and immunoblot and for Ap-antibodies by a validated snap test (SNAP® 4Dx Plus® ELISA). Extensive questionnaires for the owners(own) of the affected equine patients and the treating veterinarians(vet) were used to collect accompanying data on signaling, clinical picture, medical history, and risk factors for pathogen exposure.
A total of 236 horses were included in the study, of which 123 were sick case animals and 113 healthy control animals. Sample collection took place from May 2017 to August 2018.
Regional differences in seroprevalence could be detected: Southern Germany (27.3 %) had more frequent detections of Bbsl-antibodies than Northern Germany (17.5 %) (p=0.022). The chance for detection of antibodies suggestive of coinfection with Ap was also higher in Southern Germany (OR=3.1 (1.195-7.848)). Clinical changes characteristic for equine LD have not been found with the data material obtained.
The veterinary community was divided in their assessment of the clinical relevance of LD in horses in general: 51.4 % of veterinarians reported having seen clinically manifest LD in horses in practice, while the remainder (48.6 %) ruled out its existence or had not seen any cases themselves.
Serologic detection of infection-specific antibodies using a two-step test and supplemental rapid C6 peptide test provides an important clue to Bbsl- and Ap-infections but cannot and should not replace a thorough diagnostic workup. Serological findings must always be interpreted in the context of the observed clinical changes as well as pre-reported tick exposure. Furthermore, the diagnosis should only be made after exclusion of other differential diagnoses and can be supported by the improvement of clinical manifestations within one week at the latest after the initiation of pathogen-specific antibiosis. Without concrete suspicion, non-specific testing for antibodies against Bbsl or Ap must currently be discouraged. Existing prophylactic measures should be used judiciously after risk assessment.