Tick-Borne Diseases Flashcards
Most hard ticks attach and feed for ______
Days
- immature and adult females have an incomplete scutum allowing them to completely engorge
- male ticks have complete scutum, imbibe less and more quickly
Soft ticks feed _______
Quickly and often
- go back to same host repeatedly, are rarely on host for 15-25 minutes
Competent host vector
Capable of transmitting and maintaining pathogen
Direct disease results
Tick bites
- paralysis (toxicosis)
- red meat allergy
Indirect disease
Transmission of pathogens
- viruses, bacteria
T/F: all ticks cause disease just by their bite
True, extent varies
Clinical presentation of tick bites
- pain and inflammation at site
- possible complications (anemia, secondary infections, tick worry)
______ can cause tissue reaction and make it difficult for tick to pull out of host
Cement
Tick paralysis
Caused by toxin in tick saliva
- often female hard ticks due to longer feeding time (could be larval, nymph, or adult)
- Argas persicus, Dermacentor variabilis, Amblyomma maculatum, A. americanum
- acute ascending flaccid paralysis
Red meat allergy
Allergic reaction to pork, beef, lamb
- delayed anaphylaxis in humans
- IgE antibodies to galactose-alpha-1,3-galactose
- -> oligosaccharide blood group found in non-primate species
Indirect disease - biological transmission
With reproduction or developmental changes in pathogen
- most vector borne diseases
Indirect disease - mechanical transmission
Without reproduction or developmental changes in pathogen
- vector is a fomite
What makes a tick a good vector?
- persistent blood-feeder
- wide host range
- few natural enemies
- long-lived (life cycle can take 2 years)
- high reproductive potential
- pathogen can be maintained in tick populations (transstadial, transovarial)
Transstadial transmission
If larvae is infected by first blood meal, then nymph is infected when it molts
- nymph can still be infected when it molts into an adult or it can transmit at next blood meal
Vector competency
Capable of acquiring, maintaining, and transmitting an infectious agen
Reservoir host
Capable of acquiring, maintaining, and transmitting infectious agent
- may be the vertebrate host or arthropod vector
- are not affected by the pathogen
What was the first described vector borne disease?
Texas cattle fever
- Babesia (protozoan)/Rhipicephalus
- 1893
Bacterial tick-borne diseases of importance
- lyme disease
- tularemia
- tropical canine pancytopenia
- canine granulocytic ehrlichiosis
- heartwater
- canine cyclic thrombocytopenia
- equine granulocytic anaplasmosis
- anaplasmosis
- rocky mountain spotted fever
Tick-borne encephalitis
Viral! Powassan encephalitis
- vector: Ixodes
- clinically affects humans, domestic animals
- midwestern, northeastern US, canada
Tick-borne hemorrhagic disease
Viral, Nairobi sheep disease
- vector: hard ticks
- hemorrhagic gastroenteritis in small ruminants
- Africa, Asia (FAD)
African swine fever
Ornithodoros
- systemic hemorrhagic disease
- domestic swine, wart hogs are asymptomatic reservoirs
- Africa (FAD)
Lyme disease - vector
- Ixodes scapularis (eastern US)
- Ixodes pacificus (western US)
Transmission requires >24 hr attachment
Lyme disease - agent
Borrelia burgdorferi
- mainly B. burgdorferi sensu stricto
- gram neg spirochete
Lyme disease - reservoir hosts
Rodents (white footed mouse)
- reservoir for bacteria
White tailed deer
- required host for tick only (maintains tick population)
Lyme disease is ______ transmitted
Transstadially
Distribution of Lyme disease
Northeastern, north-central US
Most dogs exposed to lyme disease are clinically ______
Normal
- requires combo of clinical signs, history, serology (antibodies to C6 peptide) to diagnose
Clinical signs of Lyme disease
Shifting leg lameness, fever, anorexia, lymphadenopathy
- polyarthritis, renal disease (glomerulonephritis)
Tularemia - vector
Dermacentor variabilis, D. andersoni, Amblyomma americanum
- also some tabanid flies (mechanical transmission)
Tularemia - agent
Francisella tularensis
- gram neg bacteria
Tularemia - clincial signs
Occurs in various domestic species (sheep, horses, cats)
- liver abscesses, spleen
- humans: ulcerated lesions, fever, headache
Rickettsial diseases
Obligate intracellular, gram neg
- Rickettsia, Ehrlichia, Anaplasma
- infection causes nonspecific signs
- Rickettsiae are transstadially and transovarially transmitted
- treatable with tetracyclines
Heartwater - vector
Amblyomma where endemic
- A. maculatum: experimentally (concern for migrating birds)
- FAD: sub-saharan africa, caribbean
- severe clinical signs in ruminants
Heartwater - causative agent
Ehrlichia ruminantium
- endothelial cells
Tropical canine pancytopenia - vector
Rhipicephalus sanguineus
Tropical canine pancytopenia - causative agent
Ehrlichia canis
- mononuclear cells
Tropical canine pancytopenia - clinical signs
- acute: fever, anorexia, lethargy
- subclinical: E. canis in blood (may resolve)
- chronic: ocular, neurologic abnormalities, scrotal/limb edema, hemorrhage, weight loss, death
- german shepards
Canine granulocytic ehrlichiosis - vector
Amblyomma americanum
- lone star tick
Canine granulocytic ehrlichiosis - causative agent
Ehrlichia ewingii
- granulocytes (neutrophils are typical cells)
- clinical signs are mild compared to E. canis
Canine cyclic thrombocytopenia - vector
Rhipicephalus sanguineus
Canine cyclic thrombocytopenia - causative agent
Anaplasma platys
- platelets
Canine cyclic thrombocytopenia - clinical signs
Usually asymptomatic
- acute: cyclic thrombocytopenia (10-14 days)
Granulocytic anaplasmosis - vector
Ixodes scapularis, Ixodes pacificus
- same vectors as Lyme disease!
Granulocytic anaplasmosis - causative agent
Anaplasma phagocytophilum
- granulocytes (HGA)
Granulocytic anaplasmosis clinical signs
Equine - mild, subclinical with fever, lethargy, stocking edema, petechiae Dogs and cats - asymptomatic, or nonspecific signs Ruminants (Europe) Humans
Bovine anaplasmosis - vector
Dermacentor andersoni (western US) Mechanical transmission: fomites, biting flies (eastern US)
Bovine anaplasmosis - causative agent
Anaplasma marginale
- RBCs (obligate intracellular)
Bovine anaplasmosis clinical signs in ruminants
Fever, hemolytic anemia
- severity increases with age: up to 50% mortality (adults)
Rocky Mountain spotted fever - vectors
D. variabilis, D. andersoni (western US)
- infection rates in tick vectors are low
RMSF - causative agent
Rickettsia rickettsii
- endothelial cells, vasculitis
RMSF - clinical signs in dogs
- fever
- lymphadenopathy
- polyarthritis
- edema
- petechiae
- ocular lesions
- also reported in cats*
Argasid tick-borne bacterial diseases
Epizootic bovine abortion - Ornithodoros coriaceus - agent: deltaproteobacterium Relapsing fever - Ornithodoros - agent: borrelia
