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parasit
10/16/97
dr lok

ticks, cont. new handout given.


yesterday we discussed ticks, and now dr lok is repeating himself again. 
I'm going to start with the new stuff, when he's done the old stuff.


yada yada hard ticks more susceptible to stress, yada yada soft ticks 
more resistant...

Ok. new stuff.

metamorphosis in ticks. 
the 
generalized life cycle: 

adult female in environment - leaf litter, 
cracks/crevices, etc ---> egg --> hatches into larval form (6 legged). 
--->feeds on blood -->molts to 8 legged nymphal stage ---> blood feeding 
on same or different host--->molt to 8 legged adult stage (male or 
female). males also blood feed. blood engorgement in females stimulates 
egg development. female will die after laying the eggs. males after 
mating are going to also leave host and die. 

if looking at soft ticks, 
you could see one or more nymphal stages - 4 or more can occur. each 
nymphal stage is punctuated by a blood meal and a molt. this fits in well 
with the fact that soft ticks are lair ectoparasites, feeding quickly and 
frequently. 

as discussed, the different blood feeding stages can all 
occur on the same host during a life cycle, or may occur on two, three, 
or more differnt host individuals.

ixodids can have up to three hosts - 
larva, nymph and adult can each be on different host. soft ticks can have 
as many as there are stages (since they can have many nymphal stages). 
this should raise some flags about vector competency. if they use more 
hosts, they can transfer pathogens from host to host. when you have 
different numbers of hosts - can be of same or diff species. in some 
ticks, always use dogs. in others, some use rats, and others use dogs or 
deer or whatever. progression -> small host to large host.

how can 
generalized life cycle be further broken down?

one host tick life cycle: 
boophilus, the cattle tick. in a one host life cycle, adult females lay 
eggs, larvae hatch, and climb onto host. larvae feed on host, molt to 
nymphs, nymphs stay there, feed, and molt to adult, which feed,then drop 
off. this is a fairly straightforward life cycle to bring under control. 


two host life cycle: in this case, eggs hatch in environment where the 
female lays them. climb on to host one, larvae feed on host one and molt 
to nymph, nymph stays and feeds, then falls off and molts to adult in 
environment. adult seeks host 2, and feeds on host 2. this happens to be 
a hyalomma example he's showing us which uses cattle as both hosts. in 
another tick, the host one is a rabbit, and host 2 is a cow. here,small 
tick stages feed on small animal, and adult stage on larger animal. this 
is pretty common in multiple host ticks. 

3 host life cycle. larvae 
hatch and climb onto host one, feed, drop off, molt to nymph, nymphs 
climb onto host 2, feed, fall off, molt to adult, get on host 3 feed, 
drop off, lay eggs. each stage occurs on a different host individual (of 
same or different species). eg, host one can be a mouse, host two can be 
a rabbit, dog, host three can be a cow. just an example.

ticks of 
veterinary importance - starting with soft ticks. (non scutate ticks). 
have leathery integument, recessed capitulum, capable of enduring 
starvation and heat and dryness. lair ectoparasites for the most part. 


argas persicus (sp?) is a true lair ectoparasite. classic looking soft 
tick. an important pest of domestic fowl, chickens, turkeys, etc. adults 
tend to hide in protected areas of nest or bedding, and come out and feed 
on the host when nesting. also dangerous to nestlings - can exsanguinate. 
larvae stay on for about 5 days, but nymphs and adults feed quickly in 
less than an hour and then hiding again. can endure months of starvation 
and are vectors of borrelia ancerina.

otobius magnini (sp?)- spinous ear 
tick. not a lair ectoparasite. the larvae and nymphs attach to ear of 
host and stay for 120 days or so. has spines around circumference.  dark 
brown/bluish w/light colored legs. this tick has environmental component 
to life cycle - eggs laid in crevices. larvae/nymphs attach to ear, 
adults are nonparasitic. engorged nymphs drop off, adults live in host 
environment. fairly large ticks. we'll see them in lab. fully engorged 
ticks in ear cause irritation, copious oily/waxy exudate. tick bites are 
also subject to secondary infxn/myiasis. 

ornothodorus (sp?)- probably 
most important for blood loss is o.coriaceus(???) which occurs in mexico 
and west coast of US. important in cattle. vicious biters, also bite 
humans! are found in environment between feedings - typical lair 
ectoparasites. they do have a painful bite,and saliva has potent toxins. 


other ornithodorus spp act as vectors of important pathogens. one is 
vector of african swine fever, and another vecotrs a number of 
spirochetes which cause relapsing fevers - a bunch of borellia spp. 

end 
soft ticks.
start hard ticks.

the hard ticks have the scutum. note that 
the engorged female tick has her engorged abdomen extending WAY past the 
scutum - she can engorge a lot more than the male can, because her scutum 
isn't in the way. you can't really use size with much confidence as a 
character to ID ticks, b/c there is a whole range of stages of 
engorgement between newly molted adult and fully engorged female. size 
can vary a lot.

in life cycle each stage may be on same or different 
host/sp of host.

first sp: deer tick, ixodes scapularis. probalby the 
only tick ever on the cover of Newsweek! this tick is the classic vector 
of the agent of Lyme dz, in the eastern US. it's a brown/chestnut colored 
tick. scutum is brown with no markings. mouthparts in female and nymphal 
stages are quite elongate. "two toned" ticks. scutum is dark brown, rest 
of body kinda light brown. in the unengorged state, these ticks are very 
small, compared to say the common american dog tick. the nymphal stage 
feeds commonly on humans and is about the size of the head of a pin when 
fully engorged. this is the stage that transmits borrellia burgdorferi, 
usually. this is a three host tick. larval stages feed almost always on 
rodents, esp white footed mice, paramiscus luposis, which are reservoir 
host for the agent of lyme dz. also meadow voles. these larvae are fairly 
host specific. nymphal stages are more catholic, more cosmopolitan - feed 
on birds, squirrels, chipmunks, occasionally rodents - this is how they 
infect new rodent populations - and also will feed on dogs, horses, and 
people. this is the main way lyme is transferred from reservoir into the 
incidental host population (dog, horse, man). the preferred host of the 
adult is the white tailed deer, but the adult will also feed on dogs, 
horses, and humans, and fairly commonly on cats. this is another 
potential route of lyme dz out of enzootic cycle into domestic animal and 
human populations. white footed deer are not that reservoir competent. 
they do not have high enough levels of spirochete in them to act as 
donors of infection to the tick. they are more there to provide 
maintenance. probably upsurge in deer population has contributed to 
upsurge of lyme, esp with people/animals living so close to deer habitat, 
or IN deer habitat.

these ticks like typical woodland pathway habitat. 
think like a mouse - they hang out on the margins of woodland paths. 
ticks seeking a host will climb up vegetation, host will brush against 
it, tick will latch onto the host. pathways, cutover area between woods 
and pastures, ecological transition zones.

population dynamics: really a 
sort of weird progression of life cycles. first we see in april/may a 
peak in adult activity. then in may/june you see a peak of nymphs, then 
in aug/sep you see a peak of larvae. why is that? why aren't larvae 
before nymphs? well, we think this encompasses two or three years - eggs 
hatch in summer, larvae peak late summer/early fall, spending first 
winter as nymphs, which exit dormancy in spring and cause that peak we 
see. then they pass second winter as adults. so these are long lived 
ticks, that persist for a long time in environment. 

these ticks also 
are vectors for other pathogens, using similar enzootic reservoir. 
babesia microti (human babesiosis) is also enzootic in white footed mice. 
can cause serious blood dz in humans. HGE  (human granulocytic 
ehrlichiosis) is also transmitted by these ticks, using white footed 
mouse reservoir. they talk about this sort of functional association of 
pathogens - they call it a "guild". 
distribution is - heavy on east 
coast, hot focus in upper midwest. highly enzootic on long island, 
nantucket, other island areas, all along S. Jersey coast, Montgomery 
County PA in PA has very high incidence. 

on the west coast, ixodes 
pacificus has a similar life cycle to i.scapularis, and is the vector for 
b. burgdorferi out there. this tick also causes tick paralysis in its 
hosts. a neurotoxin is secreted in teh saliva. toxin from one tick alone 
can cause ascending flaccid paralysis and can cause respiratory failure. 
usually removal of tick quickly resolves the clinical signs. 

another 
tick, with two host life cycle, that we aren't that concerned with, is 
hemophysalis - larvae and nymphs on rabbits, adults on humans/lg animals. 
transmits rocky mt spotted fever and tularemia (rabbit fever). 


amblyomma: the lone star tick. three host type of life cycle. this tick a 
distinct white spot on the scutum, and the male has white markings around 
the posterior of the scutum. we call this "ornateness". this is an ornate 
tick, whereas i.scapularis is "inornate" 
this tick bites humans, 
livestock. has been incriminated as secondary vector of borrellia 
burgdorferi. this may have been somewhat hasty. it may be the tick is 
transmitting something similar to b. burgdorferi that causes a rash as 
well. it was associated with lyme because we have occasionally seen lyme 
dz outside the range of principle vector, this tick is there, and the 
agent has been seen there.

gulf coast tick: a. maculatum. ornate scutum- 
variegated white markings. pest of cattle.

ticks in dogs: 
american dog 
tick: dermacentor variabilis. common pest of dogs. an ornate tick with 
white markings on scutum. has variegated white markings. all spp of this 
genus are ornate in the US. from veterinary standpoint - primary vector 
in eastern US of rickettsial agent of RMSF which is enzootic in 
chipmunks, squirrels. we see transovarial transmission between female 
ticks and offspring. hangs out in same habitat as i.scapularis. another 
three host tick. larvae feed on rodents. nymphs feed on rodents, 
lagomorphs, etc (not large animals)., adults highly opportunistic - 
feeding on horses, dogs, humans, a number of animals. so adult is the 
stage that transfers pathogeens from enzootic reservoir. where are 
american dog ticks found? on woodland paths, cutoffs between field and 
woods, etc and of course, on american dogs.

peaks of adults in early 
spring/late summer.
numbers of ticks we see on individual host is 
moderate to small. 1-5 on one host, usually. 

Western counterpart ot 
that is dermacenter andersoni. similar life cycle. uses ground squirrels, 
prairie dogs. also a vector of RMSF in western us. incidence of RMSF now 
higher east of mississippi than in rocky mountain area. we have seen 
cases here in Philadelphia, etc.

skip d. albipictus the winter tick of 
horses.

the other important pest in dogs is the Brown Dog Tick - 
rhipicephalus sanguineus. plain brown inornate tick. when engorged, 
female looks greyish or greenish. the American Dog Tick is an outside 
tick, using rodents etc as hosts. this tick is also a  three host tick, 
*but* all three hosts happen to be dogs. so - in between each stage it 
will leave the host to molt, but then it goes back onto another dog. or 
the same dog, I guess, if that's the only dog there. these are not 
woodland ticks here in the US. almost exclusively found in inside areas. 
probably best thought of as a subtropical tick. does well outside in 
southern US, occurs in tropics worldwide and lives outside year round 
there. but here, it can't spend winter outside. it is found inside, 
instead. very important in homes, kennels, breeding establishments. 
anywhere dogs are kept in runs. populations of these ticks on a given 
host are much higher - multiple ticks/host. because dog is right in the 
infested environment. it lives there. so it gets multiple life stages on 
it. you'll see all three stages on the same dog if dog is living in 
infested environment.  this tick is a vector for ehrlichia canis (k9 
pancytopenia) and babesia canis, a protozoan parasite. now, this tick 
isn't moving enzootic diseases - it's just moving dz from dog to dog. 
this is a pest, annoyance, and blood-loss causing tick. 

boophilus, the 
cattle tick. one host tick. stays on cow for whole life cycle from larvae 
to adults. also a vector of babesia bovis. to transmit from cow to cow, 
you have to have transovarian transmission - an individual tick never 
leaves its cow, so it can't go cow to cow. it has to go cow to tick, tick 
to tick, tick to cow.   
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