VETcpd - Parasitology Peer Reviewed The changing face of canine tick borne diseases
Tick borne diseases remain a significant risk to UK dogs. This predominantly comes from Lyme disease endemic in the UK but also from other tick borne diseases encountered when travelling abroad. As both the incidence of Lyme disease in the UK and the frequency of pet travel increases, so will the risks of tick borne diseases. This article focuses primarily on Lyme disease and its epidemiology, clinical signs, treatment and prevention but also considers some of the infections harbored by ticks that dogs may be exposed to during European travel.
Key words: ticks, Lyme disease, zoonosis, tick borne disease, pet travel Ian Wright BVMS BSc MSc MRCVS Introduction Endemic tick borne disease Ian is a practising Veterinary surgeon Tick borne diseases in the UK – Lyme disease at the Withy Grove Veterinary represent a potential Surgery and Co-owner of the Mount risk to dogs living Epidemiology – background Veterinary Practice in Fleetwood. He in the UK. This risk Lyme disease was first identified as a has a Master’s degree in Veterinary comes from endemic Parasitology and is a member of distinct medical condition in a case tick borne diseases the European Scientific Counsel of originating in the town of Lyme in Companion Animal Parasites (ESCCAP and from infections Connecticut, USA, from where it gains UK). Ian is regularly published in harboured by ticks its name. Lyme disease is now recognised peer reviewed journals and is a peer in mainland Europe as a disease complex which is widespread reviewer for the Veterinary Parasitology where pet travel is now increasing. The in humans and dogs living in temperate and Companion Animal journal. primary tick borne pathogen in UK dogs regions of the Northern hemisphere Ian continues to carry out parasite is Borrelia burgdorferi, the cause of Lyme (Bennett CE, 1995). prevalence research in practice. disease. While there are some UK diseases Withy Grove Veterinary Surgery, with zoonotic potential that remain under Lyme disease is caused by spirochete 39 Station Road., Bamber Bridge, the public radar, there are some that have bacteria of the Borrelia burgdorferi complex Preston PR5 6QR gained greater recognition and Lyme and is transmitted by Ixodes spp ticks (Fig 1). Although it has been reported Tel: 01772 330103 or 07816337293 disease fits very much into the latter category with the incidence of disease in a wide variety of mammals, dogs and E-mail: [email protected] in the UK human population appearing people seem relatively more susceptible to to be increasing. It is unclear whether disease. The sheep tick Ixodes ricinus is the this is the case in dogs but canine most important vector throughout Europe exposure to the vector of Lyme disease and although in the UK I.hexagonus and is commonplace. Ixodes spp ticks which I.canisuga are also implicated in Lyme carry Borrelia spp are endemic in the UK disease transmission, they are not thought and have a seasonal peak in numbers in to be as significant vectors as I.ricinus. spring and autumn months. While these Various other Ixodes spp ticks may also peaks still occur, ticks are now commonly be involved in maintaining transmission seen all year round in most parts of the cycles of Borrelia spp in small mammals, UK (Smith F., Ballantyne R., Morgan but because most of these species do not E, 2011) providing potential exposure commonly bite humans or dogs, they are of dogs to the parasite throughout an not thought to be significant vectors of extended tick season. This has led to the disease transmission.
risk of a dog encountering an infected ® Plus , dants, probiotics viding antioxi plement, pro ents tritional sup ytonutri The best nu amins, minerals, ph enzymes, vit re intended Where Lyme disease is endemic it is prebiotics, and so much more, as natu 16th Edition
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Page 42 - VETcpd - Vol 1 - Issue 3 VETcpd - Parasitology particularly true of Wales where Roe using polymerase chain reaction (PCR). Of deer have facilitated spread of the disease these, 2.3% of the ticks tested were positive though the Wye valley and Wales. giving an overall prevalence of infected ticks on all studied dogs of 0.5%. This Ticks largely become infected as larvae suggests that the prevalence of Borrelia spp and then remain infected as nymphs and in the UK tick population is considerably adults. When these life-cycle stages of higher than previous estimates indicate. the tick feed, Borrelia spp multiply in the gut and, over a period of several days, Clinical presentation in dogs penetrate the gut epithelium and migrate to the salivary glands where they may Most infections with B. burgdorferi are then be potentially delivered to a new sub clinical with 5-10% of dogs that are mammalian host. As a result a tick has to exposed to infection going on to develop clinical signs. Where clinical signs do feed for several hours and often 24-48 Figure 1: Ixodes spp tick in situ hours before transmission occurs. Nymphs develop, this is often after reinfection are thought to be more significant in with an incubation period of 2-5 months. terms of overall transmission than adults (Wlodarek J., Zuraw A., Walczak R., et as they are more abundant than adults and al, 2013). The long incubation period due to their size, less likely to be groomed means there may not be a recent history off pets and missed when looking for of tick bites before signs develop. Dogs attached ticks. present primarily with acute or sub- acute arthritis in one or more joints with Although transmission can occur from associated lameness, joint swelling and adult ticks to eggs and subsequently to the heat. Other acute signs may then develop next generation of ticks, the significance including fever, anorexia, lethargy and of this route of transmission has yet to be lymphadenopathy. The acute form may quantified (Nefedova VV, Korenberg EI, be transient and relapses may occur. The Gorelova NB et al., 2004). circular skin rash, erythema migrans, often seen in human infection, is rarely Epidemiology – Distribution of Figure 2: Scanning electronmicrograph of observed in dogs. Chronic disease is also human Lyme disease in UK Dermacentor spp adult (courtesy Bayer) less commonly seen in dogs than people The reported incidence of Lyme disease in but may develop, especially in the absence people is increasing. There were 0.5 cases work will be vital if accurate information of treatment. Chronic disease typically per 100,000 people in England and Wales is to be given to the public and disease consists of a non-erosive polyarthritis and in 2001. This had risen to 1.73 cases per transmission slowed. glomerular nephritis, rarely progressing 100, 000 in 2011. In 2010 there were 953 to kidney and heart failure. Another reported cases in England and Wales, but Epidemiology – Distribution of uncommon complication of chronic disease is neurological disease with seizures with considerable under-reporting likely, canine Lyme disease in UK the number of cases was probably nearer and behavioural changes (Dambach DM., The current incidence of Lyme disease to 3,000 (Health Protection Agency, 2011). Smith CA., Lewis RM., et al., 1997). in dogs is unknown but the distribution The growing number of reported cases is and prevalence of ticks infesting domestic likely to be a combination of a genuine Diagnosis dogs was recently examined (Smith F., increase in disease transmission, heightened With the exception of erythema migrans Ballantyne R., Morgan E, 2011) as well awareness among the general public and in human infection, none of the clinical as the prevalence of B. burgdorferi in these increased surveillance. A real increase signs associated with Lyme disease are ticks (Smith F., Ballantyne R., Morgan E, in transmission may be due to changes pathognomonic. It should be considered 2012). Between March and October 2009, in human activity, increase in wild host as a differential in pets presenting with any 173 veterinary practices were recruited to reservoir and tick numbers. The arrival of of the clinical signs described, that have monitor tick attachment to dogs. A total infected migrants to the UK from Eastern had potential exposure to Ixodes spp ticks of 3,534 dogs were examined and 810 Europe, where the prevalence of Lyme or visited highly endemic regions for ticks dogs were found to be carrying at least disease is considerably higher may also be and/or Lyme disease. Table 1 summarises one tick. Ixodes ricinus was identified in a factor (O’Connell S., Grantrom M., Gray the diagnostic methods available for 72.1% cases, Ixodes hexagonus in 21.7% JS. et al, 1998). It has been suggested that detection of Borrelia spp. Results must be and Ixodes canisuga in 5.6%. Five samples dog owners might be at greater risk of interpreted in the light of clinical signs and of Dermacentor reticulatus (Fig 2.) were also infection from Lyme disease than people other ongoing conditions when deciding identified in the South of England and without dogs, but studies have found no if the results indicate active clinical disease, Wales, suggesting that endemic foci of correlation between dog ownership and previous exposure or sub clinical infection. Dermacentor reticulatus exist in these areas. risk of infection. (Goosens HAT., Van Treatment may often be started with an The estimated incidence of tick attachment Den Bogaard AE and Nohlmans MKE, index of suspicion rather than a definitive was 0.013 per day in March (lowest) and 2001). It is difficult to distinguish between diagnosis, and this is justified where 0.096 per day in June (highest). all of these factors without widespread diagnostic test results, clinical history and randomised surveys of the UK population The prevalence of B. burgdorferi was signs support but do not prove Lyme and these have yet to be carried out. This examined in 739 of the ticks collected disease. Early treatment intervention will
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