Lyme disease - Borrelia burgdorferi sensu lato complex
Lyme disease is a tick-borne zoonosis caused by bacteria of the Borrelia burgdoferi sensu lato (s.l.) complex. This complex comprises 21 different species, of which B. burgdoferi sensu stricto (s.s.), B. afzelii, B. garinii and B. bavariensis have been described as human pathogens. The species B. bissettiae, B. lusitaniae, B. spielmanii and B. valaisiana have been detected in humans, but their pathogenicity is unknown.
Vector-borne bacterial infection
Borrelia is transmitted by the native tick species Ixodes ricinus and is closely linked to the vector development cycle. I. ricinus undergoes four developmental stages: egg, larvae, nymph, and adult female/male ticks. Larvae, nymphs and adult ticks take a blood meal to reach the next developmental stage or to lay eggs. The pathogen is transmitted transstadial and (rarely) transovarial. A transmission from B. burgdorferi s.l. takes place after approx. 16h to 24h after attachment, but time of transmission depends on the vector, the host and the Borrelia species. Ticks are active from March to October, depending on the weather. The prevalence of B. burgdorferi s.l. in I. ricinus varies regionally and may be higher than 20%.
Lyme disease is a zoonosis
Lyme disease is one of the "emerging vector-borne bacterial zoonoses". This is related to warmer winters, living in rural areas close to nature, introduction of ticks by migratory birds, natural design of green spaces or renaturation, as well as reduced use of insecticides. The pathogen circulates between ticks and free-living vertebrates (reservoir) and susceptible hosts. Mice, hedgehogs, rabbits and birds are known as reservoirs. During outdoor activities in the forest or meadows, susceptible pets and humans can become infected by a B. burgdorferi s.l. carrying tick.
Lyme disease in humans
Human Lyme disease is a multisystemic disease. The most characteristic sign is the formation of an erythema migrans, a circularly enlarging red rash around the bite site, which occurs after 3-30 days in 70-90% of all cases. Fever, exhaustion, headache, a stiff neck, localized swelling, discoloration of the skin (Lyme lymphocytoma), joint pain and muscle pain can occur (stage I, initial manifestation). In the course of the infection, multiple erythemata migratia and/or acrodermatitis atrophicans on the extremities may appear. The pathogen can spread to the central nervous system (Lyme neuroborreliosis), the heart and joints (Lyme arthritis) (stage II, dissemination). In the late infection stage, irreversible damage to the joints, the nervous system and skin can occur (stage III, chronification).
Diagnosis is based on serological evidence. Lyme disease is treated with antibiotics.
Lyme disease in animals
The knowledge on clinical symptoms and diagnostics in the field of veterinary medicine is low and is based on individual case descriptions. Animals with clinical symptoms as well as seropositive animals without clinical signs occur. The diagnosis of lyme borreliosis is often difficult due to unspecific symptoms. Therefore, the number of cases in animals is probably underrepresented.
Serologically positive dogs display usually no symptoms, but may experience lameness, lethargy, painful and swollen joints, swollen lymph nodes, and loss of appetite. During the course of infection, the lameness can be intermittent and affecting different legs (shifting leg lameness). Lyme arthritis is rare. Lyme nephritis is often fatal and occurs more frequently in some dog breeds. Dermatological, neurological, or cardiac symptoms, as described for humans, are not well documented for dogs.
Serologically positive cats display usually no symptoms, but may experience lameness, fever, lethargy, loss of appetite, and respiratory problems. Lyme carditis has been described.
In horses, symptoms such as lameness, fever, lethargy, loss of appetite and respiratory problems have been described. Neuroborreliosis, inflammation of the eye and pseudolymphoma of the skin have also been associated with Borrelia infection.
Cattle can be serologically positive. Clinical symptoms affecting the limbs (lameness, joint swelling, arthritis, claw inflammation, lying down), loss of appetite, fever, weight loss, enlargement of the lymph nodes, as well as the occurrence of erythema on the udder and reduction in milk yield have been described in connection with a Borrelia infection. The relevance of B. burgdorferi s.l. in milk is unknown and milk from infected cattle is probably not infectious.
The situation in sheep and zoo animals is unclear or has not been sufficiently investigated. Antibodies were found in goats, but no clinical signs have been observed so far. Wild boars were also found serologically positive without any pathophysiological indications. Like other birds, pheasants are reservoir hosts probably without clinical signs.
For a case definition of lyme borreliosis in animals, current knowledge about clinical symptoms, availability and interpretation of laboratory diagnostic parameters and therapy options, are not sufficient.
Transmission of B. burgdorferi s.l. from animals to humans is not known.
The diagnosis of Lyme disease in human medicine relies on clinical data and subsequent laboratory diagnostics; this should be practiced in a similar way in veterinary medicine. Given the incomplete clinical experience to date, this is certainly not yet possible. Thus, laboratory diagnostics in veterinary medicine is currently more important, although the results often do not provide any pathophysiological information. Nevertheless, both the clinical picture and the tick infestation should be included in the diagnosis.
Tasks of the reference laboratory:
- Support in diagnostic questions (PCR, sequencing, serology)
- Providing non-commercially available diagnostic reagents to testing facilities