These are notes I have compiled from a Veterinary Entomology class, and summarized as a quick overview on our favorite parasitic arachnid:
Ticking you off:
By Joe.
some biology
Ticks have no distinct head
-adults and nymphs have 4 pairs of legs, larvae have 3.
some have a plate like scutum (the hard thing on the back)
Family: Ixodidae. In males, the entire dorsum may be covered, females and nymphs, only the anterior part of the dorsum is covered. (that means the females and nymphs don't have that hard plate covering their back entirely, their ass is hanging out.)
Ixodidae are your hard ticks-attach for extended periods of time, sometimes days for a single engorgement. ONLY the female becomes tremendously distended by engorgement (she becomes one big fatty)
Argasidae are the soft ticks- live in lairs, dens, burrows, Not as important as vectors of disease as the hard ticks. (They think is because of the sedentary nature of the soft ticks)
Ticks have 4 stages in their life cycle:
eggs, deposited on the ground. Its the only stage that isn't able to over winter. The females can lay anywhere from 100-18,000
Larvae-6 legged
Nymphs-8 legs
Adults- 8 legs
tidbits about species, illnesses they can transfer:
Three host ticks:
Dermacentor andersoni- Rocky mountain wood tick-
vector of Rocky mountain spotted fever (RMSF) (actually rickettsia) and Colorado tick fever (virus)
-western US and Canada in areas where suitable host is found-ie. small mammals for larvae and nymphs, larger hosts for adults
-all stages feed on intermediate-sized hosts such as porcupines and jack rabbits
-nymphs are noticed in the spring time
-unfed can live long time
larvae 317 days
nymphs ca. 1yr
adults 413 days
RMSF-
Rocky mountain tick research lab was established in Hamilton, Montana to study the disease.
H.T. Ricketts was assigned to the lab (remember rickettsia?)
he discovered an unnamed bacteria in 1911
he died of the disease in Montana
Dermacentor variablis
AMERICAN DOG TICK
East of the 100th meridian
3 host tick.........Larvae prefers small mammals, adults prefer dogs, but will feed on livestock and humans
RMSF- vaccine started in the west during 30's
severe reactions were common including hearing loss.
1176 cases in the us in 1980 (709 South Atlantic states, 321 in NC)
365 Cases in 1998 ...148 in South Atlantic states, 71 in NC)
The pathogen!: Rickettsia rickettsi
Invades and multiplies within cells that line small blood vessels, causes damage to cell nucleus. Causes blood to leak through tiny holes in vessel walls to adjacent tissues, causes the rash. Rash occurs in 20% of cases.
Rash appears within first week. Starts and the wrists and ankles, then it expands to the trunk.
Incubation period 2-14 days.
Can be fatal: 11.7% in 30-39 year old age class
-fatalities occur when there is lack of known tick exposure, no rash, and gastrointestinal involvement.
THE BAD GUYS:
Vectors of RMSF
Dermacentor andersoni Rky. Mt wood Tick
Dermacentor variablis (Am dog tick)
Amblyomma americanum (Lone star tick)
Haemaphysalis leporispalustris (rabbit tick)
-Rhipecephalus sanguines (Brown dog tick)
ok- THE NO MUMBO JUMBO on RKSF
Infection greatly reduced if the feeding tick is removed within 10 hrs of attaching
-many individuals become infected by de-ticking their dogs (dogs can become infected)
-crushing the ticks with their fingers and pathogen enters through abraded skin.
-need for early diagnosis and treatment is important
of 94 patients infected in NC
-death rates were significantly lower
- when treated within five days of onset of illness versus those that received delayed treatment
Ehrlichioses:
Recognized in '86
2 forms: human monocytic ehrlichiosis, and human granulocytic ehrlichiosis-clinically almost indistinguishable.
aggregates in white blood cells.
Clinical characterization:
-generally a mild disease.
-fever, headache, myalgia, thrombocytopenia, leukopenia, and elevated liver enzyme levels.
-A rash occurs in 1/3 of patients
Severe cases
adult respiratory distress syndrome, renal failure, neurology disorders, intravascular coagulation (disseminated)
- 5% for HME, 10% for HGE
some report less than 5% for these diseases.
Diagnosis
-clinical indications
-lab confirmation by indirect amino assay.
treatment:
good ol' tetracycline
Lone Star tick
Amblyomma americanum
vector OF HME
three host tick; larvae and nymphs-indiscriminant feeders, adults readily feed on deer, livestock, humans.
-severe reaction to feeding
Black legged tick
Ixodes scapularis
3 host tick- 2 year lifecycle
importance:
Ehrlichioses isn't well recognized
non-specific symptoms may interfere with a timely diagnosis
could be life threatening
there is risk for blood transfusion transmission
there is no ehrlichiosis surveillance program
incidence rates haven't really been determined
many states lack lab equipment for proper testing.
A tick's thermal minimum is around 50F. Any warmer than that, and you may want to check yourself.
Black Legged Ticks (deer ticks) have no white markings, they can carry Lymes disease.
Brown Dog Ticks
A. Engorged Female
D. Larvae
B. Female
Black-Legged Ticks (Deer Ticks)
E. Nymphs
C. Male
F. Males
G. Females
H. Engorged Female
Source:
http://www.health.state.ri.us/disease/communicable/lyme/facts.htm