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A Brief Review of Ticksand Tick-Borne Diseases
...with a little radiologyBilly MacDonald
Ticks
• Class Arachnida– closely related to mites
Ticks
• Class Arachnida– closely related to mites
• obligate blood-feeding ectoparasites– vectors
Ticks of Veterinary Importance
Ixodidae• sclerotized dorsal shield
– “hard ticks”
Argasidae• unsclerotized
– “soft ticks”
Ticks of Veterinary Importance
Ixodidae• sclerotized dorsal shield
– “hard ticks”
• sexually dimorphic– females larger– male scutum covers dorsum
Argasidae• unsclerotized
– “soft ticks”
• little sexual dimorphism
Ticks of Veterinary Importance
Ixodidae• primarily off host
– “sit-and-wait”
• mate on host• require days to complete
engorgement• live outdoors
Argasidae• live in close proximity to
host• mate off host• require mins - hrs to feed
and feed repeatedly• live in dwelling/sleeping
places of hosts
Tick Pathogenesis
• anemia– heavy infestations
Tick Pathogenesis
• anemia• dermatosis
– inflammation, swelling, itching, ulceration from tick’s saliva and mouthparts
Tick Pathogenesis
• anemia• dermatosis• paralysis
– neurotoxin present in saliva of some species
Dermacentor sp.
Tick Pathogenesis
• anemia• dermatosis• paralysis• vector-borne diseases
– viral, bacterial, and protozoal
Tick-borne Viral Diseases
• Colorado tick feverrodents Dermacentor human
Tick-borne Viral Diseases
• Colorado tick feverrodents Dermacentor human
• tick-borne encephalitishumans, cattle, horses, dogs
Tick-borne Viral Diseases
• Colorado tick feverrodents Dermacentor human
• tick-borne encephalitishumans, cattle, horses, dogs
• African swine fever wild suids Ornithodorus pig
Tick-borne Rickettsial Diseases• Rickettsia rickettsii
RMSFrabbits, rodents Dermacentor dogs, humans
Tick-borne Rickettsial Diseases• Rickettsia rickettsii• Anaplasma sp.
bovine anaplasmosis: cattle Dermacentorcanine anaplasmosis: rodents, ruminants, dogs Ixodes
Tick-borne Rickettsial Diseases• Rickettsia rickettsii• Anaplasma sp.• Ehrlichia sp.
canine ehrlichiosisdogs, white-tail deer Rhipicephalus
Tick-borne Rickettsial Diseases• Rickettsia rickettsii• Anaplasma sp.• Ehrlichia sp.
obligate intracellular parasites
Tick-borne Rickettsial Diseases• Rickettsia rickettsii • Anaplasma sp.• Ehrlichia sp.
• Coxiella burnetti...no longer grouped with Rickettsia– Q fever
obligate intracellular parasites
• Borrelia sp. Lyme diseasebovine borreliosisavian spirochetosis
Tick-borne Bacterial Diseases
• Borrelia sp. • Mycoplasma haemocanis
canine hemoplasmosis dogs Rhipicephalus
Tick-borne Bacterial Diseases
• Borrelia sp. • Mycoplasma haemocanis• Francisella tularensis
tularemiarabbits various ticks humans, dogs
Tick-borne Bacterial Diseases
• Hepatozoon canisRhipicephalus dog
Tick-borne Protozoal Diseases
• Hepatozoon canis• Babesia sp.
bovine, canine, feline babesiosis, equine piroplasmosis
Rhipicephalus
Tick-borne Protozoal Diseases
• Hepatozoon canis• Babesia sp.• Cytauxzoon felis
wild felids Dermacentor cats
Tick-borne Protozoal Diseases
Lyme Disease...a closer look
Ixodes pacificus Ixodes scapularis
Lyme Disease...a closer look
Ixodes sp.
white-footed deer mouse
etiologic agent: Borrelia burgdorferi
humans, dogs, cattle, horses
clinical signs...in dogs
• fever, anorexia, malaise• lymphadenomegaly• shifting leg lameness
– sudden onset• painful articular swelling• *nonerosive polyarthritis
– pathologic changes in the joints are progressive• rarely: renal disease (glomerulonephritis),
neurological disease
diagnosis
• clinical lab findings– inflammatory changes in synovial fluid
• serology– ELISA detects antibodies to B. burgdorferi
• Isolation– culture is most definitive...but also most difficult
due to limited number of organisms present– PCR
• antibiotic therapy– for arthritis: doxycycline, amoxicillin, azithromycin– for neurological manifestations: cefotaxime,
chloramphenicol
• vaccines
treatment
Hepatozoonosis...a closer look• etiologic agent:
– Hepatozoon canis...an intracellular parasite in various tissues
– transmitted via ingestion of infected tick (Rhipicephalus sanguineous)
dog ingests tick
dog ingests tick
sporozoites in GI tract circulation striated muscle
“onion skin” cyst in skeletal muscle
dog ingests tick
sporozoites in GI tract circulation striated muscle
“onion skin” cyst in skeletal muscle
~ 4 weeks...parasite infected neutrophils (gamonts) present in peripheral blood
dog ingests tick
sporozoites in GI tract circulation striated muscle
asexual reprod. (merogony)
merozoites released into surrounding tissues
severe inflamm. reaction
neutrophilic granuloma formation
Hepatozoonosis...a closer look• etiologic agent:
– Hepatozoon canis...an intracellular parasite in various tissues
– transmitted via ingestion of infected tick (Rhipicephalus sanguineous)
• clinical signs:– fever, anorexia, weight loss, diarrhea...wax and wane
• diagnosis:– CBC, Biochem.: non-specific inflammation– UA: +/- proteinuria– muscle biopsy for definitive diagnosis
• treatment:– symptomatic: NSAIDs
Hepatozoonosis via radiology?
Periosteal proliferation on the femur, tibia, pelvis andlumbar vertebrae of a dog infected with H. canis
Hepatozoonosis via radiology?
Periosteal proliferation on the femur, tibia, pelvis andlumbar vertebrae of a dog infected with H. canis ...lesions resemble HO
Periosteal proliferation on the femur of a dog infected with H. canis
Hepatozoonosis via radiology?
Hepatozoonosis via Bone Scan
Skeletal lesions in a dog infected with H. canis (americanum)
References• Craig, T.M. 1998. Hepatozoonosis, pp 458-465, In: Infectious Diseases of
the Dog and Cat, 2nd Edition; Craig E. Greene (Ed), W.B. Saunders, Pennsylvania.
• Greiner, E.C. 2006. Diagnosis of arthropod parasites, pp 185-263, In: Veterinary Clinical Parasitology, 7th Edition; Anne M. Zajak and Gary A. Conboy (Eds), Blackwell Publishing, Iowa.
• Holman, P.J., and K.F. Snowden. 2009. Canine hepatozoonosis and babesiosis, and feline cytauxzoonosis. Vet Clin Small Anim 39: 1035-53.
• Little, S.E. 2009. Vector-borne diseases, pp 240-253, In: Georgis’ Parasitology for Veterinarians, 9th Edition; Dwight D. Bowman (Ed), Saunders Publishing, Missouri.
• Panciera, R.J., Mathew, J.S., Ewing, S.A., Cummings, C.A., Drost, W.T., and A.A. Kocan. 2000. Skeletal lesions of canine hepatozoonosis caused by Hepatozoon americanum. Vet Pathol 37: 225-230.
• Shaw, D. and S. Ihle. 2006. Joint diseases, pp 439-450, In: Small Animal Internal Medicine; Shaw, D. and S. Ihle (Eds), Blackwell Publishing, Iowa.
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