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WSVA7-0399
PARASITOLOGY (ESCCAP)
THE RISE OF TICK-BORNE DISEASE IN NORTHERN EUROPE
I. Wright1
1ESCCAP, UK & Ireland, Malvern, United Kingdom
RISK OF TICK-BORNE DISEASE IN NORTHERN EUROPE
Ian Wright BVMS.Bsc. Msc. MRCVS
The Mews Studio, Portland Road, Malvern, Worcs, WR14 2TA, UK
Contact e mail – hammondia@hotmail.com
Introduction
Tick-borne disease represents an ongoing and growing risk to pets and their owners in Northern Europe. This comes from both increasing numbers of endemic ticks, and the increasing distribution of tick species and tick-borne diseases. This is driven by a combination of factors including habitat and climate change, increased wildlife reservoirs, pet travel and human migration. Ixodes spp ticks and Dermacentor reticulatus as vectors of Lyme disease and Babesia canis respectively, remain the most significant tick-borne disease threats in Northern Europe but pets travelling to, and being imported from, Rhipicephalus sanguineus endemic countries is leading to Ehrlichia canis being seen in Northern Europe. Tick- Borne encephalitis is also spreading North and West through Europe, presenting a significant zoonotic risk.
Lyme disease
Lyme disease is caused by spirochete bacteria of the Borrelia burgdorferi complex and transmitted by Ixodes spp ticks. The sheep tick Ixodes ricinus is the most important vector throughout Europe and although I.hexagonus and I.canisuga are also implicated in Lyme disease transmission, they are not thought to be as significant vectors.
Where Lyme disease is endemic it is maintained by reservoir hosts that act as sub clinical carriers of infection and reproductive hosts that do not carry infection but maintain populations of infected ticks. Small rodents and birds are the most significant reservoir hosts of Lyme disease but deer act as epidemiologically important reproductive hosts, carrying Lyme disease to new geographic areas.
Ticks mostly become infected as larvae and then remain infected as nymphs and adults. When these life-cycle stages of the tick feed, Borrelia spp multiply in the gut and, over a period of several days, penetrate the gut epithelium and migrate to the salivary glands where they
may then be potentially delivered to a new mammalian host. As a result, a tick has to feed for several hours and often 24-48 hours before transmission occurs. Nymphs are thought to be more significant in terms of overall transmission than adults as they are more abundant than adults and due to their size, less likely to be groomed off pets and missed when looking for attached ticks.
Although transovarian transmission of Borrelia spp in ticks can occur, it is currently not thought to be epidemiologically significant.
Countries in Western Europe have a highly variable
but increasing incidence of Lyme disease. The highest reported incidences have reported in southern Sweden with 464 cases per 100 000 people per year and the lowest in Italy of 0.001 per 100 000. The unweighted mean for the included data provided an incidence of 56.3 per 100 000 persons per year, equating to approximately 232 125 cases in one year throughout the region (Sykes, 2014). Data of the incidence of disease in cats and dogs is lacking but prevalence in ticks was found to be 2.37% in the UK (Abdullah et al, 2016).
Most infections with B. burgdorferi are sub clinical with 5-10% of infected dogs going on to develop clinical signs. When Lyme disease does develop, this is often due to re exposure to infection with an incubation period of 2-5 months. Dogs present primarily with acute or sub-acute arthritis in one or more joints with associated lameness, joint swelling and heat. Other acute signs may then follow including fever, anorexia, lethargy and lymphadenopathy. The acute form is often transient
with relapses occurring. The common primary human clinical presentation of a circular skin rash known as erythema migrans is not recognised in dogs. Chronic disease is often described in human infection but is
less commonly seen in canines. When it does occur
in dogs it tends to occur when acute cases have not been treated and consists of a non-erosive polyarthritis. Protein losing nephropathy can be a sign of renal disease in chronic Lyme disease patients. This should not be confused with the syndrome Lyme nephritis. This occurs in 1-2% of dogs diagnosed with Lyme disease in the US with an average onset at 5-6 years. Labrador and Golden Retrievers are over represented and prior
or concurrent lameness is described in 9-28% cases. Typically, these dogs present with an acute progressive protein-losing nephropathy with membranoproliferative glomerulonephritis, tubular necrosis and interstitial nephritis, but possibly milder forms exist (Littman, 2013). Fortunately, this syndrome is rare in Europe for reasons that are not understood.
Lyme disease should be considered as a differential in pets presenting with any of these clinical signs described
An Urban Experience
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