Borreliosis (Lyme disease)

Background
Borreliosis [bore-El-ee-Oh-sis] (also known as Lyme disease) is caused by a spirochaetal bacterium of the Borrelia genus. Several species of this organism exist in Europe, most of which can cause disease if transmitted to humans. Clinical disease can also occur in dogs but is less commonly reported in cats and horses. It is possible that this lack of reported cases could be attributed to undiagnosed / misdiagnosed disease, due to limitations of laboratory testing techniques and lack of awareness amongst owners and veterinarians.

Borrelia bacteria infect many forms of wildlife, but generally no symptoms occur, unless the animal is immune-compromised by old age or disease. However, various species of wildlife can act as reservoirs for the bacteria and can transmit the pathogens to a tick when it feeds on the animal’s blood. If the infected tick then goes on to bite a human or a pet animal, symptomatic infection can result.

It is generally Ixodid ticks (a family of hard ticks) that transmit Borreliosis. The sheep tick (Ixodes ricinus) and the hedgehog tick (Ixodes hexagonus) are both carriers of Borrelia bacteria, and both unfortunately often attach to people and domestic pets. I. hexagonus is most likely to be encountered by urban populations of dogs and cats. One species of Argasid (a soft tick), called Argas reflexus, and known as the pigeon tick, also carries Borreliosis.

Borrelia spirochaetes migrate in connective tissues, disseminate, and eventually establish long-term infection in peripheral sites including the heart, joints, and neural tissue. Resident bacteria incite inflammation with tissue damage. The spirochaetes evade the host’s immune response and persist in tissues.

In animals, the characteristic rash (which can be the first indicator of infection) is not usually observed. Instead, the first sign of illness is when the animal appears to be generally “off-colour”. Lethargy and loss of appetite can often be accompanied by lameness.