A Brief Review of Ticks
and Tick-Borne Diseases
...with a little radiology
Billy 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 fever
rodents
Dermacentor
human
Tick-borne Viral Diseases
• Colorado tick fever
rodents
Dermacentor
• tick-borne encephalitis
humans, cattle, horses, dogs
human
Tick-borne Viral Diseases
• Colorado tick fever
rodents
Dermacentor
human
• tick-borne encephalitis
humans, cattle, horses, dogs
• African swine fever
wild suids
Ornithodorus
pig
Tick-borne Rickettsial Diseases
• Rickettsia rickettsii
RMSF
rabbits, rodents
Dermacentor
dogs, humans
Tick-borne Rickettsial Diseases
• Rickettsia rickettsii
• Anaplasma sp.
bovine anaplasmosis: cattle
Dermacentor
canine anaplasmosis: rodents, ruminants, dogs
Ixodes
Tick-borne Rickettsial Diseases
• Rickettsia rickettsii
• Anaplasma sp.
• Ehrlichia sp.
canine ehrlichiosis
dogs, 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.
obligate intracellular parasites
• Coxiella burnetti...no longer grouped with Rickettsia
– Q fever
Tick-borne Bacterial Diseases
• Borrelia sp.
Lyme disease
bovine borreliosis
avian spirochetosis
Tick-borne Bacterial Diseases
• Borrelia sp.
• Mycoplasma haemocanis
canine hemoplasmosis
dogs
Rhipicephalus
Tick-borne Bacterial Diseases
• Borrelia sp.
• Mycoplasma haemocanis
• Francisella tularensis
tularemia
rabbits
various ticks
humans, dogs
Tick-borne Protozoal Diseases
• Hepatozoon canis
Rhipicephalus
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
Lyme Disease...a closer look
Ixodes pacificus
Ixodes scapularis
Lyme Disease...a closer look
etiologic agent: Borrelia burgdorferi
white-footed deer mouse
Ixodes sp.
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
treatment
• antibiotic therapy
– for arthritis: doxycycline, amoxicillin, azithromycin
– for neurological manifestations: cefotaxime,
chloramphenicol
• vaccines
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
dog ingests tick
sporozoites in GI tract
circulation
“onion skin” cyst in skeletal muscle
striated muscle
dog ingests tick
sporozoites in GI tract
circulation
“onion skin” cyst in skeletal muscle
asexual reprod. (merogony)
merozoites released into
surrounding tissues
severe inflamm. reaction
neutrophilic granuloma formation
~ 4 weeks...parasite infected neutrophils
(gamonts) present in peripheral blood
striated muscle
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 and
lumbar vertebrae of a dog infected with H. canis
Hepatozoonosis via radiology?
Periosteal proliferation on the femur, tibia, pelvis and
lumbar vertebrae of a dog infected with H. canis
...lesions resemble HO
Hepatozoonosis via radiology?
Periosteal proliferation on the femur
of a dog infected with H. canis
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.
Questions??