Borrelia are bacteria which belong to the spirochaete family. Spirochaetes are characterised by contractile axial filaments which are located under a multi-layered outer membrane and that give the spirochaetes their typical spiral shape as well as their motility. Borrelia species which are discussed in connection with Lyme borreliosis in dogs are included in the group Borrelia burgdorferi sensu lato, which currently comprises more than 20 different Borrelia species.
Borrelia are transmitted by vectors (ticks or lice) and except for B. recurrens and B. dutonii they all have a reservoir among wild animals.
The main mode of transmission is a bite of the tick Ixodes ricinus (European castor bean tick). The bacteria are located in the intestine of the tick, are activated by the blood meal and migrate to the salivary glands. It then takes up to 24 hours until transmission via the saliva takes place. If the tick is properly removed within this period, the risk of infection can be greatly reduced.
In contrast to humans, the clinical signs of Lyme borreliosis (Lyme disease) in dogs are rather non-specific and can easily be overlooked. In dogs, there is rarely an erythema migrans. Fatigue, loss of performance, possibly fever and, after a symptom-free phase of several weeks, reluctance to move, alternating lameness, emaciation, vomiting and oedema occur. Occasionally, neurological deficits are also observed. A serious complication is the development of glomerulonephritis with subsequent kidney failure due to the deposition of immune complexes.
The main vector, Ixodes ricinus, occurs throughout Germany but can be found more frequently in certain areas. In such areas, it is therefore recommended to regularly check for any infestation of the dog with ticks and to have a Lyme disease test carried out if the symptoms mentioned above occur.
Infections and diseases in cats and cattle are reported more and more often. Furthermore, Lyme disease is classified as an emerging bacterial zoonosis.
Grazing animals are often used for blood meals by borrelia-infected ticks. Clinical diseases appear as well as seropositive animals without any clinical signs, with the evaluation often being difficult.
In horses, a variety of signs are associated with borrelia: reduced performance, lameness, changes in the skin, eyes or heart up to neurological deficits and abortions. However, there is still controversy as to whether the infection in horses leads to any clinical signs at all.
Lyme disease in cattle is associated with lameness, weight loss and abortion. Pathogen isolation from clinical material is sometimes successful (Borrelia burgdorferi sensu stricto, Borrelia afzelii). Seroconversions have been shown as well as the response to tetracycline therapy.