Parasites 101

Vector-Borne Diseases in Pets: The Stealth Health Threat

Michael W. Dryden, DVM, MS, PhDa Kansas State University

Elizabeth Hodgkins, DVM, JD Summit VetPharm Rutherford, New Jersey

n 1975, in the small coastal town of Lyme, Connecticut, the bite of the deer (Ixodes scapularis) and was asso- a group of mothers brought a unique, remarkable clus- ciated with neurologic symptoms in some patients. Today, Itering of cases to the attention of local health authori- human Lyme borreliosis is the most commonly diagnosed ties: all had children with diagnosed rheumatoid arthritis. infectious VBD, with more than 20,000 cases reported each Unfortunately, this malady was not immediately recognized year in the alone.1 as a bacterial vector-borne disease (VBD). Not until 1985 The history of the recognition of the insidious and often was “Lyme arthritis” associated with infection by the spiro- debilitating signs of illustrates how easily infec- chete , by Dr. Willy Burgdorfer. tious agents can enter the human population and, unsus- Throughout the 1980s, many skeptics denounced the pected and undetected, wreak medical havoc for decades existence of Lyme disease, as it came to be known, as a or longer. The prevalence of clinical and subclinical Lyme discrete infectious disease of humans or . The mat- borreliosis in pets is poorly understood at present, much as ter was not settled until the 1990s, when the genome of the the prevalence of its human counterpart was decades ago. causative agent was sequenced and the pathogenesis of the This issue is complicated by a lack of agreement about how human disease was fully understood. to detect infection with the causative agent and controversy In fact, the first recorded case of Lyme disease had about when and whether to immunize pets in endemic been described more than a century earlier by Dr. Alfred areas against B. burgdorferi.2–4 Buchwald, who noted a degenerative human skin condi- Recent studies suggest that the US prevalence of B. burg- tion known as acrodermatitis chronica atrophicans (ACA). dorferi infection in dogs may be highest (more than 6%) in In 1921, Dr. Arvid Afzelius published research about the the upper Midwest and northeastern areas of the country, expanding ring skin lesion (erythema migrans) that is now where prevalence of the infection in humans is also high- well associated with Lyme disease in people. Dr. Afzelius est.5 Studies of this infection in cats are sparse; however, it speculated that this skin condition was somehow caused by is clear that cats, while not clinically affected, do become infected.6 What is most clear is that scientific understanding aDr. Dryden discloses that he has received financial benefits from Bayer Health, Elanco, Merial, Novartis Animal Health, Pfizer of the importance of this VBD is incomplete and awaits a Animal Health, and Summit VetPharm. great deal more research. As this research unfolds, we may

Contributed by the Companion Animal Parasite Council

The Companion Animal Parasite Council (CAPC) is an independent association of veterinarians and other animal health care professionals established to create guidelines for the optimal control of internal and external parasites that threaten the health of pets and people. It brings together broad expertise in parasitology, internal medicine, public health, veterinary law, private practice, and association leadership. Initially convened in 2002, the CAPC was formed with the expressed purpose of chang- ing the way veterinary professionals and pet owners approach parasite management. The CAPC advocates best practices for protecting pets from parasitic infections and reducing the risk for zoonotic parasite transmission. For more information, visit www.capcvet.org.

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Parasites 101: Vector-Borne Diseases in Pets discover that we have seriously underestimated the impor- • I. scapularis and Ixodes pacificus (black-legged ), tance, prevalence, and severity of borreliosis in companion vector for B. burgdorferi in the eastern and western animals. United States, respectively, as well as for Anaplasma and Unfortunately, B. burgdorferi is only one of a myriad of Bartonella spp VBD agents known to infect and cause mild to severe clini- • Rhipicephalus sanguineus (the brown dog tick, which cal signs in pets. Most of these agents, including Ehrlichia, lives in homes and kennels), vector for Babesia spp, Anaplasma, , Bartonella, Mycoplasma, Babesia, Ehrlichia canis, and the Rocky Mountain spotted fever and Cytauxzoon spp, are incompletely characterized. In , Rickettsia rickettsii 2008, Dr. Susan Little, of the University of Oklahoma, speak- • Dermacentor andersoni, vector for R. rickettsii and the ing at the North American Veterinary Conference, discussed pathogen, Francisella tularensis the disturbing findings that tick populations are expand- • Dermacentor variabilis, vector for Cytauxzoon felis, R. ing geographically and appear to be carrying an increasing rickettsii, and F. tularensis array of pathogenic organisms. Her data showed that at least • Amblyomma americanum, vector for Ehrlichia spp, C. one VBD agent exists in each of the 50 US states and that felis, and F. tularensis several disease agents are present in the tick populations of • Amblyomma maculatum, vector for Hepatozoon many states.7 americanum All of these have at least one thing in com- mon: they are transmitted to companion animals by arthro- Mosquitoes are also important disease vectors for pets, pod vectors worldwide. Only for Lyme disease does a notably as carriers of infective heartworm (Dirofilaria immi- preventive vaccine exist, and the widespread use of this tis) larvae. The species most commonly implicated vaccine is controversial among veterinary experts. However, in heartworm transmission to dogs and cats in the United there is hope for control of these vectors and the diseases States are Aedes (including the Asian tiger mosquito), Culex, they transmit to household pets. Regular, appropriate use of Anopheles, and Ochlerotatus. Mosquitoes also carry West arthropod-effective ectoparasiticides in the home environ- Nile , which can infect humans and many species of ment and, more importantly, on pets, is the most effective animals, but the importance of this disease in cats and dogs preventive measure available against VBD transmission in is thought to be small.10 companion animals. Although these products cannot guar- antee prevention of tick-transmitted diseases, regular and Can We Afford to Ignore Vector-Borne Diseases Any correct application can reduce the likelihood that pets will Longer? become infected. Public health authorities warn that VBDs are spreading from narrow historical ranges well into new areas of the United The Vectors and Their Diseasesb States. The vectors appear to be moving into new areas and , ticks, and mosquitoes are major arthropod carriers increasing in other areas due to the following factors11–13: of many potentially serious diseases of humans and pets in the United States. The cat , Ctenocephalides felis, is the • Natural climate fluctuations that favor the development most important flea species infesting dogs and cats in most of fleas, ticks, and mosquitoes areas of the world.8 In addition to causing serious skin irrita- • Mobility of people and pets and residential and recre- tion, flea bites can lead to the important clinical condition ational encroachment on highly populated wildlife areas flea allergy dermatitis, caused by injection of flea-specific • Population increases among critical reservoir wildlife spe- antigens.8,9 Occasionally, severe, even life-threatening, ane- cies, especially deer and wild turkeys, across the country mia can occur in young or debilitated pets with severe flea infestations. Adding to the complexity of VBD expansion is the under- Infectious agents transmitted by cat fleas include diagnosis of VBDs in pets and humans in regions where Bartonella henselae (the cause of cat-scratch disease in these diseases are already well established.7,14,15 The years humans), Rickettsia typhi (murine or endemic typhus), and ahead will almost certainly show physicians and veterinar- Rickettsia felis (murine typhus–like disease). Fleas are also ians that VBDs are far more important causes of serious the intermediate hosts for a clinically important tapeworm infectious disease in the United States than previously sus- of dogs and cats (Dipylidium caninum). pected. Improved understanding of the importance of VBDs Several tick species are responsible for transmitting dis- in humans may well come, in large part, from efforts to bet- eases of companion animals in North America. Some of the ter understand and diagnose these diseases in pets.16 most important are: Although veterinarians play an important role in the bFor more information on vector species and the infectious agents identification and prevention of zoonotic infections that they carry, visit www.capcvet.org. affect humans, the profession’s central focus is the success-

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Parasites 101: Vector-Borne Diseases in Pets

ful diagnosis, treatment, and elimination of animal diseases insecticide (permethrin) is considered an effective means when possible. When it comes to the many important VBDs of controlling malaria, a widespread and deadly VBD, in that affect companion animals, however, veterinarians need Africa,17–20 available insecticides and repellents are important to take a step back and also consider measures to prevent weapons against VBDs in pets around the world. transmission of the infectious agent. For example, efforts Compare the sometimes extraordinary cost of treating directed at managing heartworm disease depend on pre- clinically apparent VBDs in pets with the relatively low cost vention of disease development in animals that have been of preventive insecticide administration. The modest expen- bitten by an infected mosquito. Although this is a critical diture required for a year-round, veterinary-recommended, aspect of preventing heartworm disease, effective mosquito topical ectoparasiticide can help reduce the potential trans- control should also play a role. mission of VBDs to treated pets.21,22 Use of such a product Other important VBDs in dogs and cats remain almost also decreases the environmental parasite load capable of entirely unaddressed. While vaccines exist for preventing spreading zoonotic disease to other family members. Lyme disease in dogs, their use is mired in debate. Lyme dis- Unfortunately, many veterinarians recommend environ- ease and other potentially serious infections are not always mental and topical insecticide treatment only when their cli- included in the differential diagnosis of pets that present ents mention seeing arthropods on their pets during warmer with fever, lethargy, hematopoietic disturbances (anemia, months. Except for flea allergy dermatitis and heartworm thrombocytopenia, generalized granulocytopenia), lame- disease, the profession has a low sense of alarm about vec- ness, neurologic disease, kidney failure, and shock, even in tor-mediated medical conditions. As a result, the urgency to areas endemic for VBDs known to cause these signs. prevent, rather than treat, the infestation of pets with fleas, The cost of treating an animal with a VBD, regardless of ticks, and mosquitoes is low for most practitioners. whether the condition is correctly diagnosed at presentation, The growing threat to the health of companion animals can be substantial. Although many infected pets do not suc- posed by these vectors and the potentially considerable cumb to clinical illness, we do not have a clear understand- costs of treating VBDs make it essential for veterinarians to ing of which factors influence the development of overt use all available means to prevent fleas, ticks, and mosqui- clinical pathology or what percentage of the population of toes from transmitting infectious agents to pets and causing infected companion animals eventually requires treatment. disease. The tools to make a significant difference in the What we do know is that some infected pets present to epidemiology of VBDs are readily available, and ongoing their veterinarians with mild, moderate, or severe debilita- research is providing the veterinary profession with a pipe- tion and that extreme cases require expensive, even heroic, line of new products for combating VBDs. medical care to save their lives. Sadly, delayed treatment or Today’s veterinarians recognize the importance of rou- complicating organ failure can lead to lifelong disability or tine preventive measures in the prevention of infections death. like canine distemper, canine and feline parvovirus, upper Today, the financial cost of treatment for clinically appar- respiratory diseases, and rabies. However, except for Lyme ent VBDs can reach thousands of dollars. With early diag- disease, no vaccines exist for the prevention of VBDs. nosis, most of these diseases can be treated effectively with Clinicians must, therefore, understand the crucial role of antibiotics and simple supportive care at home. Disease routine and continuous ectoparasiticide administration in that progresses to advanced, multisystemic pathology may preventing these relatively new and dangerous infectious require extended hospitalization with intensive care, includ- diseases. Only lack of knowledge about the importance and ing repeated laboratory evaluation, constant nursing care, prevalence of VBDs in companion animals prevents the vet- and expensive pharmacologic support. A seriously ill pet erinary profession from arming itself and its patients against may remain debilitated for weeks, exhausting the budget the emerging threat of an alarming array of arthropod-trans- and emotional resources of its family. Worse, the most seri- mitted infectious disease agents. ously ill pets do not survive, exacting an enormous emo- For their part, pet owners need to follow their veterinar- tional toll on not only the family but also the attending ians’ directions by using recommended products. Clinicians veterinarian and staff members. understand the geography of their region as well as the spectrum of parasites targeted by available products and “An Ounce of Prevention Is Worth a Pound of Cure” can make informed, educated recommendations on the The situation is far from hopeless, despite our primitive proper product for each pet based on the pet’s size and risk understanding of VBDs in veterinary medicine. Although factors. widespread availability and use of effective vaccines against common arthropod-borne diseases are years away, we References 1. Little S. Vector-borne diseases. In: Bowman DD, ed. Georgi’s Parasitology for Vet- already have the means to reduce the gathering momentum erinarians. 9th ed. St. Louis: Saunders Elsevier; 2009:247. of these infections in pets. Just as bed netting treated with 2. Littman MP, Goldstein RE, Labato MA, et al. ACVIM small animal consensus state-

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Parasites 101: Vector-Borne Diseases in Pets

ment on Lyme disease in dogs: diagnosis, treatment and prevention. J Vet Intern Med 13. Bradley CA, Altizer S. Urbanization and the ecology of wildlife diseases. Trends 2006;20(2):422-434. Ecol Evol 2007;22(2):95-102. 3. Littman MP. Canine borreliosis. Vet Clin North Am Small Anim Pract 2003;33(4):827- 14. Harrus S, Baneth G. Drivers for the emergence and re-emergence of vector-borne 862. protozoal and bacterial diseases. Int J Parasitol 2005;35:1309-1318. 4. Skotarczak B. Canine borreliosis–epidemiology and diagnostics. Ann Agric Envi- 15. Molyneux H. Common themes in changing vector-borne disease scenarios. Trans ron Med 2002;9(2):137-140. Royal Soc Trop Med Hyg 2003;97(2):129-132. 5. Bowman D, Little SE, Lorentzen L, et al. Prevelance and geographic distribution of 16. Schmidt PL. Companion animals as sentinels for public health. Vet Clin North Am Dirofilaria immitis, Borrelia burgdorferi, Ehrlichia canis,and Anaplasma phagocytophi- Small Anim Pract 2009;39(2):241-250. lum in dogs in the United States: results of a national clinic-based serologic survey. Vet 17. Curtis CF, Jana-Kara B, Maxwell CA. Insecticide treated nets: impact on vector Parasitol 2009;160(1-2):138-148. populations and relevance of initial intensity of transmission and pyrethroid resistance. 6. Magnarelli LA, Bushmich SL, Ijdo JW, et al. Seroprevalence of antibodies J Vector Borne Dis 2003;40(1-2):1-8. against Borrelia burgdorferi and Anaplasma phagocytophilum in cats. Am J Vet Res 18. Curtis CF, Maxwell CA, Magesa SM, et al. Insecticide-treated bed-nets for malaria 2005;66(11):1895-1899. mosquito control. J Am Mosq Control Assoc 2006;22(3):501-506. 7. Rosenthal M. Tick-borne diseases reported in most states, expert says. Vet Forum 19. Dabire RK, Diabate A, Baldet T, et al. Personal protection of long-lasting insecti- 2008;25(4):22-24. cide-treated nets in areas of Anopheles gambiae s.s. resistance to pyrethroids. Malar 8. Rust MK, Dryden MW. The biology, ecology, and management of the cat flea.Ann J 2006;5:12. Rev Entomol 1997;34(2):173-178. 20. Fettene M, Balkew M, Gimblet C. Utilization, retention and bio-efficacy studies 9. Lam A, Yu A. Applied dermatology: overview of flea allergy dermatitis. Compend of PermaNet in selected villages in Buie and Fentalie districts of Ethiopia. Malar J Contin Educ Pract Vet 2009;31(5):220-225. 2009;8:114. 10. Greene CE, Baldwin CA. Mosquito and gnat-borne infections. In: Greene CE, ed. In- 21. Spencer JA, Butler JM, Stafford KC, et al. Evaluation of permethrin and imida- fectious Diseases of the Dog and Cat. 3rd ed. St. Louis: Saunders Elsevier; 2006:192- cloprid for prevention of Borrelia burgdorferi transmission from black-legged ticks 193. (Ixodes scapularis) to Borrelia burgdorferi-free dogs. Parasitol Res 2003;90(3 suppl): 11. Otranto D, Dantes-Torres F, Breitschwerdt EB. Managing canine vector-borne dis- 106-107. eases of zoonotic concern: part one. Trends Parasitol 2009;25(4):157-163. 22. Blagburn BL, Spencer JA, Billeter SA, et al. Use of imidacloprid-permethrin to 12. Otranto D, Dantes-Torres F, Breitschwerdt EB. Managing canine vector-borne dis- prevent transmission of Anaplasma phagocytophilum from naturally infected Ixodes eases of zoonotic concern: part two. Trends Parasitol 2009;25(5):228-235. scapularis ticks to dogs. Vet Ther 2004;5:212-217.

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