PARASITES IN CATS AND DOGS: MANAGEMENT AND TREATMENT

Vet Times The website for the veterinary profession https://www.vettimes.co.uk PARASITES IN CATS AND DOGS: MANAGEMENT AND TREATMENT Author : HANY M ELSHEIKHA Categories : Vets Date : January 20, 2014 HANY M ELSHEIKHA highlights the importance of awareness of parasitic disease in companion animals, the effects parasites have on these pets, as well as control methods Summary Our understanding of the spectrum, aetiology, diagnosis and management of parasitic diseases in companion animals has changed dramatically throughout the past two decades. Parasitic diseases are an important challenge to the health and welfare of companion animals, as well as the public health worldwide. We cannot completely eliminate the exposure of pets to parasites because parasites have been evolved to co-exist within their host animals over millennia. However, we can reduce the incidence and spread of these parasites via understanding what factors increase parasitic disease risk and via utilising and promoting effective means for treatment and control. Management of any parasitic infection in pets relies on the sensible application of chemotherapeutic drugs to alleviate disease and maintain welfare, and sound hygienic measures to reduce the transmission of parasites. The role for integrated parasite control programmes has grown and will continue to grow as rates of antiparasitic resistance are likely to rise. Key words companion animals, parasites, parasite control, animal health and welfare, One Health, zoonosis COMPANION animals are exposed to infections by a wide range of endoparasites 1 / 16

(helminths and protozoa) and ectoparasites (ticks, mites, flies, fleas or lice; Figure 1). Endoparasites can affect every single organ of the animal body and induce clinical signs that range from general ill health with a dull coat, vomiting and intestinal obstruction to massive loss of blood with resulting anaemia, heart failure and death. Ectoparasites exert their deleterious effects by irritating the animal, interfering with growth and, most of the time, by acting as vectors of disease-causing pathogens. Some ectoparasitic species are associated with myiasis via invasion of the animal s tissue by fly larvae. Some companion animal parasites are significant sources of human disease as well. For these reasons, awareness of companion animal parasitic diseases in veterinary and human health communities is important for protecting pet health and preventing human disease. Over years, humans have developed a strong emotional bond with their companion animals (Figure 2 ). The role of pets as a source of emotional, therapeutic and psychological support to pet owners is well known (Raina et al, 1999; Friedmann and Son, 2009). As a result, pet owners seek ways to improve health and quality of life of their pets, including protecting them from parasites. Despite tremendous efforts, parasitic infections continue to be a significant health and welfare issue in companion animals. Additionally, the number of eradicated parasites is insignificant and the perspectives for future eradications would most likely be overbalanced by the emergence or reemergence of other parasites. Parasite strains resistant to antiparasitics arise as a response to challenges induced by the host animal immune system or to exposure to drug treatment. Parasites can even jump the species barrier from their natural host to a naïve one. These evolutionary changes could be a consequence of intrinsic parasite ability to evolve and/ or human-induced alterations in parasites ecosystems. Failure to control parasitic infections in companion animals is due, in part, to poor understanding of the biology and epidemiology of these infections. Implementation of any successful parasite control strategies will depend on educating and empowering both pet owners and practitioners to recognise the wide spectrum of factors that are important to consider before designing any parasite control programme. Some of these factors are discussed in this article. Challenges in parasite control Most types of parasite have a complex mode of transmission, which encompasses a wide range of domestic and wild definitive, intermediate and even paratenic/carrier host species, as well as humans. Also, the geographic distribution of many parasites is expanding as a consequence of human and animal movements, together with the effects of global warming. This means the control of these parasites is not straightforward. In fact, for many important parasitic diseases, no specific 2 / 16

control programmes have ever been implemented. Historically, parasite control in animals has been based on routine use of chemical compounds, often several times per year. Despite the vast importance of antiparasitic drugs in parasite control, approaches based solely on chemotherapy are not sustainable especially with the increasing problem of drug resistance. Integrated approach of parasite control The key to successfully controlling parasites in companion animals, without selecting parasite populations for drug resistance, is to rely on complementary approaches, such as targeted chemotherapeutic treatment and environmental management. This integrated parasite control approach must take into account the dynamic interactions between parasite, host and environment (Figure 3) and must consider interventions that are targeted at these three fronts. Chemotherapeutic treatment A large number of chemotherapeutic agents are available to treat parasite infections. Some are endectocides, produced either by having one active ingredient with a broad spectrum of activity or by combining active ingredients. Such products may be used to control both worms and ectoparasites; the precise spectrum of activity varies according to the active ingredients. Matching the spectrum of activity to the infection present or the risk for individual animals is an important part of managing parasite infection. The proper selection of drugs, active ingredients or dosages of medication for treatment or chemoprevention will not be discussed in this article, as this information was reported elsewhere. A review of the spectrum of activity of products in the NOAH Compendium is available on the European Scientific Counsel Companion Animal Parasites (ESCCAP) website (www.esccap.org). For endoparasites, an assessment must be made of the worms present or expected to be present, hence whether nematocidal treatment or cestocidal treatment or a combination is required. Additional factors to consider include drug activity against immature as well as adult stages of parasite and ease of administration. For ectoparasites, all dogs and cats in the household should be treated and the environment should be decontaminated. New animals should be quarantined and prevention of sharing of fomites will reduce the incidence of infestation. The appropriate frequency of worming is often debated and this is because there is no one answer that will fit all situations. Where it is critical to minimise risk of patent infection (for example, when 3 / 16

zoonotic infection control is essential) then re-treatment at a frequency close to the prepatent period (often monthly for convenience) will help to achieve this. However, this should not be viewed as a panacea as virtually no treatment can have absolute efficacy. In other situations, this frequency of treatment would be overkill particularly where other management measures are instigated to reduce the risk of parasite infection and there is no scientific evidence of what the frequency of treatment should be in these lower-risk situations. What is needed is a balance between minimising zoonotic and animal health risk, while managing environmental contamination and minimising the risk of selection for resistance. Fortunately, anthelmintic resistance has been very rarely reported for pet parasites, perhaps because of a decreased intensity of treatment compared to farm animals. However, evidence for resistance of cat fleas against some ectoparasiticides, cyclodienes, carbamates, organophosphates and pyrethroids has been reported (Lemke et al, 1989; Bossard et al, 1998; Bossard et al, 2002). The cost of treatment and the potential for resistance selection must be balanced against the health risks to achieve a management regimen that works well for an individual animal or group of animals. Practitioner s role in diagnosis and management of parasitic infection Evidence that the prevalence of parasitism may be increasing and early diagnosis and intervention are likely associated with better treatment outcome has made it imperative practitioners increase their account of knowledge regarding the diagnosis and management of parasitism. However, parasite infections in dogs and cats caused by helminth parasites present various challenges to practitioners, including: parasite identification where there is clinical disease caused by parasitism; and defining and imple- menting a rational and timely treatment plan to achieve the best outcome for the animal. In the first situation, it is important to reach a specific and early diagnosis, based on a combination of clinical history, physical examination, laboratory tests and imaging studies in some parasitic infections. For most infections, laboratory diagnosis depends on detection of eggs or larvae in the faeces, using flotation techniques such as the McMaster technique or the Baermann technique, respectively. Likelihood of diagnosis of some parasites, where daily excretion of eggs or larvae may be irregular, may be enhanced by sampling over two or three days where necessary. Occasionally, where there 4 / 16

is a prepatent infection or low level intermittent shedding, faecal examination may be negative. Thus, a negative result does not necessarily rule out the possibility of a helminth infection being present. Where true heartworm caused by adult Dirofilaria immitis is suspected normally associated with a history of travel then a blood sample for microfilaria, antigen or antibody detection is needed. Where a specific diagnosis is made then therapy can be instigated. The challenge for the practitioner does not end when the diagnosis of the parasitic infection has been made. More frequently, the situation is not one of evident clinical signs, rather the presentation is a healthy pet. Then, the question is what an appropriate management strategy is in order to prevent clinical signs, environmental contamination with eggs or larvae and zoonotic transmission. In this situation, assessment of the risk can be based on faecal examination, which will identify patent helminth infections present in sufficient numbers at the time of treatment and/or an assessment of the likelihood of infection based on a knowledge of the animal, the parasites it is likely to be exposed to and the risk those parasites pose either to the same animal, other animals or humans. Another consideration is the risk of zoonotic infection and its prevention. For instance, more consideration should be given to the prevention of worm infections in a puppy living in a household with small children. Theoretical assessment of the likely exposure is more useful than diagnostics for some parasite species such as cestodes where the diagnostic methods remain insufficiently sensitive and in situations where prevention of patent infection is highly desirable. Management and animal factors Knowledge of the animal and its management can be used to assess risk of parasitic infection and also, management can be manipulated to diminish the risk of infections. At-risk animals The age of the animal may be an important risk factor. For example, Toxocara infections are most common in puppies and kittens, and intensity of infection may be highest in these two populations. However, older dogs may repeatedly acquire patent Toxocara canis infections throughout life, apparently when they have not received large exposure as pups. Thus, it is a misconception to assume T canis is an infection of puppies only. However, prevalence in the adult dog population is generally low, with only about five per cent of adult dogs infected at 5 / 16

any one time. Feeding Canine and feline nutrition has contributed not only to improved longevity and well-being, but also to immunocompetence and resistance to pathogens. Good nutrition plays a big part in how well the animal s immune system mounts the proper defences and in the animal s overall ability to tolerate the presence of parasites. Healthy and well-nourished animals will be more able to endure a certain level of parasite burden. Access to uncooked meat, offal or prey (by hunting) may increase the risk of parasitic infection. Hence, feeding cooked, prepared food will decrease the risk of parasitism. Housing and management including poopascooping There may be more opportunity for introduction of parasites and accumulation of an environmental burden of immature stages or eggs (Figure 4) where there are groups of dogs or cats in kennel situations. Except for cestode eggs, worm eggs are not infective when passed and so if faeces are collected and disposed of hygienically then the risk of infective stages in the environment is reduced. Geographical location Some worms such as T canis are ubiquitous, while the distribution of others is more localised. In the UK, the tapeworm Echinococcus granulosus is largely confined to central Wales, the Welsh borders and the Hebrides. With evidence that the lungworm Angiostrongylus vasorum infection has spread out of its traditional hot spots, it is important to be alert to consistent clinical signs and to consider screening faecal samples for infection. Travel and risk of introductions The risk of parasitic diseases for travelling pets varies from region to region and depends on the intensity of transmission, the duration of the stay in the endemic area and the effectiveness of preventive measures before travel, while abroad and after coming back. With the latest changes in the Pet Travel Scheme (PETS), removal of obligatory tick treatment, the risk of introducing exotic tick species and tick-borne diseases into the UK is expected to increase. 6 / 16

Some of the ectoparasite prevention products need to be administered before potential exposure to the disease-causing agents. An assessment of the risks facing each pet is required, which will depend on which countries the pet will be visiting and the season of the year the travel will be scheduled. Even though the risk of introducing Echinococcus multilocularis infection into the UK is minimal, due to the obligatory treatment under the PETS, pets are still at risk while abroad especially in endemic areas in continental Europe. Hence, dogs (and cats) staying in this area especially if they have the opportunity to hunt for rodents should be treated monthly with praziquantel to decrease the risk of them carrying a patent infection. Maps showing the approximate distribution of this parasite and other species are shown in the ESCCAP worm control guidelines. Additional resources Further information on the topics raised in this article can be found in the BSAVA worm control guidelines, available on the BSAVA website (www.bsava.com). Additionally, ESCCAP UK has developed a website (www.esccapuk.org.uk) specifically for vets and other animal health care professionals. There is also a website for pet owners (www.petparasites.co.uk), which provides information and interactive maps for pet owners who are planning to travel to continental Europe with their pets. Conclusion Parasites remain a challenging and common infection affecting millions of people and their pets around the world. The goal of any parasite control programme is to minimise parasites load in animals, prevent contamination of environment and disrupt the parasite s life cycle. It is essential to develop more sustainable control strategies via strategic use of antiparasitics, which is a valuable tool in managing the adverse impact of parasitism on animals. The effectiveness of each parasite control programme should be reviewed regularly and any required amendments should be done whenever possible. Remember, prevention rather than cure is the philosophy used in developing control and prevention programmes against parasites. Raising awareness among pet owners is of utmost importance. Education of pet owners should focus on prevention and should include: personal hygiene and regular clearing up of pet faeces to reduce environmental pressure; and 7 / 16

minimising exposure of children and immunosuppressed individuals to potentially contaminated environments. Finally, collaboration between veterinary and health professionals in a One Health or One Medicine approach is essential. Disclosure The author declares he has no competing interest. References Bossard R L, Hinkle N C and Rust M K (1998). Review of insecticide resistance in cat fleas (Siphonaptera: Pulicidae), Journal of Medical Entomology 35(4): 415-422. Bossard R L, Dryden M W and Broce A B (2002). Insecticide susceptibility of cat fleas (Siphonaptera: Pulicidae) from several regions of the United States, Journal of Medical Entomology 39(5): 742-746. Friedmann E and Son H (2009). The human-companion animal bond: how humans benefit, Veterinary Clinics of North America: Small Animal Practice 39(2): 293-326. Lemke L A, Koehler P G and Patterson R S (1989). Susceptibility of the cat flea (Siphonaptera: Pulicidae) to pyrethroids, Journal of Economic Entomology 82(3): 839-841. Raina P, Waltner-Toews D, Bonnett B, Woodward C and Abernathy T (1999). Influence of companion animals on the physical and psychological health of older people: an analysis of a one-year longitudinal study, Journal of the American Geriatrics Society 47(3): 323-329. 8 / 16

Figure 1. Representatives of parasites affecting dogs and cats: (a) adult cat flea and (b) adult roundworms of the canine species Toxocara canis. 9 / 16

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Figure 1. Representatives of parasites affecting dogs and cats: (a) adult cat flea and (b) adult roundworms of the canine species Toxocara canis. 12 / 16

Figure 2. A bond can be normally established between people and their pets. IMAGE: Jackie Morrison. Figure 3. For a parasitic disease to occur, three critical factors must co-exist: a susceptible host 13 / 16

(animal or human), a parasite and the right environmental conditions, including the availability of the vector in some parasitic species, such as ticks act as a vector for Lyme disease. The relationship of these three elements is called the disease triangle. If any one of these elements is missing, parasitic disease will not occur. Better understanding of the disease cycle will help you find ways to reduce or eliminate parasite infections. 14 / 16

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Figure 4. Toxocara eggs are unembryonated and not infectious when excreted in the faeces of dogs or cats (egg size 90 75µm). 16 / 16 Powered by TCPDF (www.tcpdf.org)