Download Vector-Borne Diseases in Pets: The Stealth Health Threat

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
I
n 1975, in the small coastal town of Lyme, Connecticut,
a group of mothers brought a unique, remarkable clustering of cases to the attention of local health authorities: all had children with diagnosed rheumatoid arthritis.
Unfortunately, this malady was not immediately recognized
as a bacterial vector-borne disease (VBD). Not until 1985
was “Lyme arthritis” associated with infection by the spirochete Borrelia burgdorferi, by Dr. Willy Burgdorfer.
Throughout the 1980s, many skeptics denounced the
existence of Lyme disease, as it came to be known, as a
discrete infectious disease of humans or animals. The matter was not settled until the 1990s, when the genome of the
causative agent was sequenced and the pathogenesis of the
human disease was fully understood.
In fact, the first recorded case of Lyme disease had
been described more than a century earlier by Dr. Alfred
Buchwald, who noted a degenerative human skin condition known as acrodermatitis chronica atrophicans (ACA).
In 1921, Dr. Arvid Afzelius published research about the
expanding ring skin lesion (erythema migrans) that is now
well associated with Lyme disease in people. Dr. Afzelius
speculated that this skin condition was somehow caused by
a
Dr. Dryden discloses that he has received financial benefits from
Bayer Animal Health, Elanco, Merial, Novartis Animal Health, Pfizer
Animal Health, and Summit VetPharm.
the bite of the deer tick (Ixodes scapularis) and was associated with neurologic symptoms in some patients. Today,
human Lyme borreliosis is the most commonly diagnosed
infectious VBD, with more than 20,000 cases reported each
year in the United States alone.1
The history of the recognition of the insidious and often
debilitating signs of Lyme disease illustrates how easily infectious agents can enter the human population and, unsuspected and undetected, wreak medical havoc for decades
or longer. The prevalence of clinical and subclinical Lyme
borreliosis in pets is poorly understood at present, much as
the prevalence of its human counterpart was decades ago.
This issue is complicated by a lack of agreement about how
to detect infection with the causative agent and controversy
about when and whether to immunize pets in endemic
areas against B. burgdorferi.2–4
Recent studies suggest that the US prevalence of B. burgdorferi infection in dogs may be highest (more than 6%) in
the upper Midwest and northeastern areas of the country,
where prevalence of the infection in humans is also highest.5 Studies of this infection in cats are sparse; however, it
is clear that cats, while not clinically affected, do become
infected.6 What is most clear is that scientific understanding
of the importance of this VBD is incomplete and awaits a
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 changing 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 ticks),
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, Rickettsia, Bartonella, Mycoplasma, Babesia,
Ehrlichia canis, and the Rocky Mountain spotted fever
and Cytauxzoon spp, are incompletely characterized. In
pathogen, 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
tularemia 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 pathogens have at least one thing in common: 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 immipreventive vaccine exist, and the widespread use of this tis) larvae. The mosquito 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 virus, 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 guarantee 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?
Public health authorities warn that VBDs are spreading from
become infected.
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
Fleas, 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 flea, 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 recretion, 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 speantigens.8,9 Occasionally, severe, even life-threatening, anecies, 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 veterinarRickettsia 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 suspected. Improved understanding of the importance of VBDs
of dogs and cats (Dipylidium caninum).
Several tick species are responsible for transmitting dis- in humans may well come, in large part, from efforts to beteases of companion animals in North America. Some of the ter understand and diagnose these diseases in pets.16
Although veterinarians play an important role in the
most important are:
b
identification and prevention of zoonotic infections that
For more information on vector species and the infectious agents
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 expenbitten 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 transmission of VBDs to treated pets.21,22 Use of such a product
control should also play a role.
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 environease and other potentially serious infections are not always mental and topical insecticide treatment only when their cliincluded 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 vecness, neurologic disease, kidney failure, and shock, even in tor-mediated medical conditions. As a result, the urgency to
prevent, rather than treat, the infestation of pets with fleas,
areas endemic for VBDs known to cause these signs.
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 mosquiclinical 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 pipetion 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 roucomplicating organ failure can lead to lifelong disability or tine preventive measures in the prevention of infections
like canine distemper, canine and feline parvovirus, upper
death.
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 vetand 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-transand 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 veterinartional toll on not only the family but also the attending ians’ directions by using recommended products. Clinicians
understand the geography of their region as well as the
veterinarian and staff members.
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 Vetalready 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 stateVetlearn.com | June 2010 | Compendium: Continuing Education for Veterinarians®
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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
2006;20(2):422-434.
3. Littman MP. Canine borreliosis. Vet Clin North Am Small Anim Pract 2003;33(4):827862.
4. Skotarczak B. Canine borreliosis–epidemiology and diagnostics. Ann Agric Environ Med 2002;9(2):137-140.
5. Bowman D, Little SE, Lorentzen L, et al. Prevelance and geographic distribution of
Dirofilaria immitis, Borrelia burgdorferi, Ehrlichia canis, and Anaplasma phagocytophilum in dogs in the United States: results of a national clinic-based serologic survey. Vet
Parasitol 2009;160(1-2):138-148.
6. Magnarelli LA, Bushmich SL, Ijdo JW, et al. Seroprevalence of antibodies
against Borrelia burgdorferi and Anaplasma phagocytophilum in cats. Am J Vet Res
2005;66(11):1895-1899.
7. Rosenthal M. Tick-borne diseases reported in most states, expert says. Vet Forum
2008;25(4):22-24.
8. Rust MK, Dryden MW. The biology, ecology, and management of the cat flea. Ann
Rev Entomol 1997;34(2):173-178.
9. Lam A, Yu A. Applied dermatology: overview of flea allergy dermatitis. Compend
Contin Educ Pract Vet 2009;31(5):220-225.
10.Greene CE, Baldwin CA. Mosquito and gnat-borne infections. In: Greene CE, ed. Infectious Diseases of the Dog and Cat. 3rd ed. St. Louis: Saunders Elsevier; 2006:192193.
11.Otranto D, Dantes-Torres F, Breitschwerdt EB. Managing canine vector-borne diseases of zoonotic concern: part one. Trends Parasitol 2009;25(4):157-163.
12.Otranto D, Dantes-Torres F, Breitschwerdt EB. Managing canine vector-borne diseases of zoonotic concern: part two. Trends Parasitol 2009;25(5):228-235.
E4
13.Bradley CA, Altizer S. Urbanization and the ecology of wildlife diseases. Trends
Ecol Evol 2007;22(2):95-102.
14.Harrus S, Baneth G. Drivers for the emergence and re-emergence of vector-borne
protozoal and bacterial diseases. Int J Parasitol 2005;35:1309-1318.
15.Molyneux H. Common themes in changing vector-borne disease scenarios. Trans
Royal Soc Trop Med Hyg 2003;97(2):129-132.
16.Schmidt PL. Companion animals as sentinels for public health. Vet Clin North Am
Small Anim Pract 2009;39(2):241-250.
17.Curtis CF, Jana-Kara B, Maxwell CA. Insecticide treated nets: impact on vector
populations and relevance of initial intensity of transmission and pyrethroid resistance.
J Vector Borne Dis 2003;40(1-2):1-8.
18.Curtis CF, Maxwell CA, Magesa SM, et al. Insecticide-treated bed-nets for malaria
mosquito control. J Am Mosq Control Assoc 2006;22(3):501-506.
19.Dabire RK, Diabate A, Baldet T, et al. Personal protection of long-lasting insecticide-treated nets in areas of Anopheles gambiae s.s. resistance to pyrethroids. Malar
J 2006;5:12.
20.Fettene M, Balkew M, Gimblet C. Utilization, retention and bio-efficacy studies
of PermaNet in selected villages in Buie and Fentalie districts of Ethiopia. Malar J
2009;8:114.
21.Spencer JA, Butler JM, Stafford KC, et al. Evaluation of permethrin and imidacloprid for prevention of Borrelia burgdorferi transmission from black-legged ticks
(Ixodes scapularis) to Borrelia burgdorferi-free dogs. Parasitol Res 2003;90(3 suppl):
106-107.
22.Blagburn BL, Spencer JA, Billeter SA, et al. Use of imidacloprid-permethrin to
prevent transmission of Anaplasma phagocytophilum from naturally infected Ixodes
scapularis ticks to dogs. Vet Ther 2004;5:212-217.
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©Copyright 2010 MediMedia Animal Health. This document is for internal purposes only. Reprinting or posting on an external website without written permission from MMAH is a violation of copyright laws.