Vector-borne diseases and their implications for cats and dogs

Vet Times The website for the veterinary profession https://www.vettimes.co.uk Vector-borne diseases and their implications for cats and dogs Author : Jenny Helm Categories : RVNs Date : April 1, 2013 Jenny Helm BVMS, CertSAM, Dip-ECVIM(CA), MRCVS, looks at diseases indigenous to the UK and those that may be picked up by pets abroad Summary VECTOR-borne infectious disease covers a wide range of parasitic, bacterial or viral diseases affecting dogs and cats, which are transmitted by the bite of haematophagous arthropods (mainly ticks and mosquitoes/sand flies). This article focuses on parasitic and bacterial diseases. Borreliosis (Lyme disease) and ehrlichiosis/ anaplasmosis are discussed, and both may affect pets that have not travelled outside the United Kingdom. There is also discussion of vector-borne diseases indigenous to the UK, uncommon in dogs and cats, but that may affect travelling pets or those in contact with travelling animals (for example babesiosis and leishmaniosis). Some diseases not seen in the UK may become more common with increased pet movement and if we see temperature increases due to climate change, with a subsequent change in vector habitats. Tick and mosquito prevention is clearly very important and this is summarised at the end of the article. Key words vector-borne disease, Lyme disease, tick, pet travel IN YEARS to come it is likely vector-borne disease will be more of a concern for UK veterinary practices. The reasons include the fact that the geographical distribution of 1 / 8

vector-borne diseases has expanded and some diseases are now found in previously unaffected areas. Babesiosis, for example, has been described in Germany and The Netherlands, Anaplasma platys in France and A phagocytophilum throughout northern Europe (Beugnet and Marié, 2009). Increasing transportation of pets is likely to contribute heavily to this increased incidence and wider spread of vector-borne diseases (Beugnet and Marié, 2009). A 2003 study showed 32 per cent of pets entering the UK under the Pet Travel Scheme (PETS) had at least one pathogen, including babesiosis, ehrlichiosis or leishmaniosis (Shaw et al, 2003). Additionally, climate change may increase the density of vectors in an area or cause them to drift northwards into areas previously considered uninhabitable (Beugnet and Marié, 2009). PETS was introduced by the Government in 2001 to replace the quarantine system. Its main aim is to keep the UK free of rabies. As of January 1, 2012 it is no longer a requirement to treat pets for ticks before travel into the UK and there is no longer a requirement to document an adequate rabies titre after vaccination. Tapeworm treatment given one to five days before reentry to the UK is still required for dogs. Despite this change in legislation, in the author s opinion it is sensible to recommend owners take adequate precautions to prevent ticks and mosquitoes biting their pets if they do travel abroad, in light of the risk of acquiring vector-borne diseases. Anti-tick treatment should be started at least one week, but preferably 10 to 14 days prior to leaving the UK and continued regularly (as per the manufacturer s guidelines) until the animal returns. Details of PETS can be found at www.defra.gov.uk/wildlife-pets/pets/travel/pets/ Borreliosis Borrelia burgdorferi is the cause of borreliosis, also called Lyme disease. B burgdorferi is a corkscrew-shaped bacterium that can move through connective tissue using its motile flagellae (long, thread-like appendages). Borreliosis is transmitted via ixodid ticks. The sheep tick (Ixodes ricinus) and the hedgehog tick (I hexagonus) are known carriers of Borrelia and both can attach to humans and domestic animals. The pigeon tick (Argas reflexus), is also thought to carry Borrelia. Rarely, other insects, such as mosquitoes and fleas, may transmit this disease. Borrelia organisms do not survive in the environment so direct transmission of disease (without a tick vector) is very unlikely. Lyme disease is important as it can occur in pets that have not travelled outside the UK, given the ticks that carry borreliosis can be found in the UK (May et al, 1991; Shaw et al, 2005). Despite this, Lyme disease appears to have been under-recognised as a cause of disease in people and pets, but awareness is increasing and it appears to be a particular problem in the west of Scotland. In Scotland, lyme borreliosis is a reportable disease, and 605 human cases were notified to Health 2 / 8

Protection Scotland in 2009, which represents a 55-fold increase in cases since 1998 (James et al, 2011). Borrelia may affect various species of wildlife, but generally clinical signs do not develop unless the animal is immunocompromised (by old age, pregnancy or another co-morbid disease); however, these wild animals may serve as a reservoir of disease. Borrelia species are known to cause clinical disease in humans, dogs and, less commonly, cats and horses. Clinical signs Sub-clinical (or undetectable) disease is common in dogs. When borreliosis disease does occur it may be vague and clinical signs may overlap with many other disease processes. Clinical disease in cats is rare, but signs are similar to those listed in Table 1. The exact incubation period for borreliosis in dogs is unknown, but the time taken to develop joint disease in experimentally infected dogs can be as long as two to five months, and clinical signs often develop first in the limb closest to the tick bite. Diagnosis Making a diagnosis of borreliosis is extremely challenging. Firstly, the vague clinical signs lead to a lengthy list of differential diagnoses. Secondly, there is no agreement of what constitutes a definitive diagnostic test result. Thirdly, serology (for anti-borrelia antibodies) may be falsely positive in asymptomatic dogs that have been previously exposed, or falsely negative in clinically affected dogs, because it can take some time for adequate antibodies to be produced. Performing bacterial culture to grow Borrelia organisms is difficult and insensitive, and PCR will only provide a definitive diagnosis if the sample obtained contains live Borrelia organisms, which may not always be the case. A history of tick exposure and/or attachment, compatible clinical signs, a positive test or rising titre for antibodies, and a response to appropriate antibiotics are considered useful clinical criteria. Treatment Standard treatment for disease in dogs is doxycycline PO 10mg/ kg q24h for 30 days; however, longer courses may be necessary, especially in dogs with neurological signs. Given that clinical disease is rare in cats there is less information about treatment, but general recommendations are amoxicillin, tetracycline and doxycycline. Prevention 3 / 8

There is no vaccine against borreliosis for dogs or cats in the UK. Preventing tick exposure is paramount. Ehrlichiosis Ehrlichia are members of the Rickettsiaeceae family ( Figure 2 ) and are small intracellular bacteria (coccobacilli). Like Borellia, they rely on transmission by ticks. The species of Ehrlichia that affect dogs, the ticks that transmit them, and the cells they go on to parasitise are listed in Table 2. Like borreliosis, clinical disease can occur in cats but is rare. Clinical signs Again, clinical signs can be frustratingly vague. In the acute phases presenting signs may include: depression; lethargy; fever; lymphadenopathy; splenomegaly; and ocular or nasal discharge (including nose bleeds). After two to four weeks these signs may resolve, leading to chronic infection, which may cause a decrease in platelets and signs associated with bleeding. Numbers of other blood cell lines (red blood cells and neutrophils) may also decrease. Diagnosis In some cases identification of morulae (Latin for mulberry) within cells may be possible. Blood serology or PCR is used to confirm disease. Treatment Standard treatment for disease in dogs is doxycycline. Enrofloxacin and other fluroquinolones are not recommended as Ehrlichia may have inherent resistance to fluroquinolone antibiotics (Maurin et al, 2001). 4 / 8

Anaplasmosis Anaplasma phagocytophilum is the cause of canine granulocytic anaplasmosis. It is transmitted by ixodid ticks, thus, co-infection with Borrelia is relatively common. Clinical signs are similar to those listed for ehrlichiosis, and a fall in platelet numbers is common, but quite often the disease is self-limiting in dogs. It was first described as a cause of tick fever in Scottish sheep and DNA from A phagocytophilum has been detected in Scottish ticks. It is therefore possible to see A phagocytophilum in animals that have not travelled outside the UK (Bexfield et al, 2005; Shaw et al, 2005). A clinical case of feline granulocytic anaplasmosis has been described in Sweden (Bjoersdorff et al, 1999), but although it is possible for cats to be antibody-positive for anaplasma, clinical disease is rare. A platys is the cause of canine thrombocytic anaplasmosis, and morulae may be visualised within platelets. It is a cause of cyclical decreases in platelet numbers (every one to two weeks). Leishmaniosis Leishmaniosis is a disease caused in dogs by Leishmania infantum. It can be acquired by pets travelling outside the UK, especially to areas of southern Europe (such as southern Spain or Italy). It can be transmitted from dog to dog via blood transfusions or during congenital transfer. However, it is mainly transmitted by biting sand flies. The incubation period is often lengthy; ranging from one month to several years. Leishmania infection causes a variety of clinical signs and may be found in two forms (visceral or cutaneous). Signs associated with visceral leishmaniosis include weight loss, polyuria/ polydipsia, depression, coughing, vomiting, diarrhoea, fever, painful joints, and ocular disease. The cutaneous form of disease causes skin lesions (such as ulceration or crusting and alopecia). Diagnosis is commonly confirmed (in non-endemic areas) either by identifying organisms in the dog s macrophages ( figure 3 ), by PCR or a positive antibody titre. Treatment of leishmaniosis can improve the clinical signs; however, successful elimination of disease is rare. Treatment includes antimony (meglumine antimonite), allopurinol, and miltefosine/allopurinol combination. A vaccine is available in some countries. Owners should be made aware of the risk of leishmaniosis if they are travelling with their pets, and they should take steps to prevent mosquito or sand fly bites (see below). Owners should be aware that leishmaniosis has zoonotic potential. Babesiosis 5 / 8

Babesia is a protozoal parasite transmitted by ticks. It infects red blood cells and is a potential cause of haemolytic anaemia. Babesia canis and B gibsoni are the most common species that affect dogs, but other species are described. Although tick bites remain the major route of transmission for babesiosis, dog bites and blood transfusion may also spread the disease. Cats may be affected by infection with B felis and B cati. Clinical signs are associated with haemolytic anemia and include: fever, lethargy, weakness, discoloured/red urine and collapse. With time, severe anaemia, jaundice and multiple organ failure can occur. It is possible for dogs to become carriers of disease if they overcome the initial clinical signs. Diagnosis can be made if organisms are detected in red blood cells; blood serology and PCR may also be used. Despite babesiosis treatments being effective in reducing the burden of parasitaemia and/or eliminating clinical signs, it may not be possible to eradicate the organism completely. Therefore, any dog infected with Babesia should be considered a possible life-long carrier of disease. In an anaemic patient supportive care, such as blood transfusion medicine, other fluid therapy, nursing and ICU care, is of vital importance. There is no vaccine available against babesiosis, so tick prevention is paramount. Medications may include: imidocarb dipropionate; diminazene aceturate; pentamidine isethionate; atovaquone; and azithromycin. Dirofilariasis Discussion of dirofilariasis is outside the scope of this article. Tick prevention 6 / 8

Tick prevention starts with careful grooming and monitoring of pets. Owners should be encouraged to do this on a regular basis, especially during March and November when tick numbers increase. Tick removal should be done using a proprietary removal tool where available ( Figure 4 ). Fine tweezers or forceps may serve as an alternative. If removal is not done correctly there is increased risk of disease transmission due to stress/injury to the tick, rupturing its abdomen or leaving the mouthparts behind. For these reasons it is important to avoid using what I consider outdated techniques, such as Vaseline, alcohol or burning (Roupakias et al, 2011). A variety of veterinary tick prevention products are available. Each has pros and cons that are outside the scope of this article. ( Figure 3 ). Previously it was thought that ticks needed to attach to the host for more than 48 hours to transmit diseases such as borreliosis; however, recent reports suggest this may not be the case. The author recommends, where feasible, ticks are removed as soon as they are seen, ideally within 24 hours. Owners should be encouraged to use veterinaryrecommended tick repellant products on their pets. Mosquito prevention Preventing mosquitoes is most relevant to pets that are travelling abroad. The author s general advice is to keep pets indoors when mosquitoes are most active, such as dusk, dawn and early evening, encourage use of a mosquito repellent, remove or avoid of areas of standing water and change water bowls frequently to remove any mosquito eggs. Avoid applying any products that contain N,N-Diethyl-meta-toluamide (DEET), as this may be harmful if ingested by the pet. References and further reading Beugnet F and Marie J-L (2009). Emerging arthropod-borne diseases of companion animals in Europe. Veterinary Parasitology, 163: 298-305. Bexfield N H, Villiers E J and Herrtage M E (2005). Immune-mediated haemolytic anaemia and thrombocytopenia associated with Anaplasma phagocytophilum in a dog. Journal of Small Animal Practice, 46(11): 543-548. Bjoersdorff A, Svendenius L, Owens J H and Massung R F (1999). Feline granulocytic ehrlichiosis: a report of a new clinical entity and characterisation of the infectious agent, Journal of Small Animal Practice 40: 20-24. James M C, Furness R W, Bowman A S et al (2011).The importance of passerine birds as tick hosts and in the transmission of Borrelia burgdorferi, the agent of Lyme disease: a case study from Scotland, Ibis 153: 293-302. Maurin M, Abergel C and Raoult D (2001). Gyrase-mediated natural resistance to fluroquinolones in Ehrlichia spp, Antimicrob Agents Chemother 45(7): 2,098-2,105. May S D, Cartert A, Barnes S, et al (1991). Sero-diagnosis of Lyme disease in UK dogs, Journal of Small Animal Practice 32: 170-174. Roupakias S, Mitsakou P and Al Nimer A (2011). Tick removal. Short communication J 7 / 8

Powered by TCPDF (www.tcpdf.org) Prev Med Hyg 52: 40-44. Shaw S E, Binns S H, Birtles et al (2005). Molecular evidence of ticktransmitted infections in dogs and cats in the United Kingdom, Veterinary Record 157: 645-648. Shaw S E, Lerga A I, Williams S et al (2003). Review of exotic infectious diseases in small animals entering the United Kingdom from abroad diagnosed by PCR, Veterinary Record 152(6): 176-177. www.bada-uk.org/ www.defra.gov.uk/wildlife-pets/pets/travel/pets www.langfordvets.co.uk/acarus/vet.htm 8 / 8