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parasit
10/15
dr lok

two handouts: Mites and Ticks

a 
quick review.
we finished all the insects already and, as is his wont, dr 
lok is now going through the previous lecture material in an outline 
form,telling us what we already went over. I already wrote all that 
information down when he discussed it the first time. yada yada fleas, 
yada yada lice, yada yada flies. see previous lectures for information on 
these creatures.

now we're going to go into something else. moving away 
from insects/hexapods and going into the arachnid arthropods. first, the 
mites.

the arachnida are a class of arthropoda, which includes orders 
comprising scorpions, spiders, and the acarina - mites and ticks. so the 
order acarina contains the family of mites. most are freeliving - some 
are microherbivores, some predate other arthropods - some are parasites 
on other arthropods - relatively few bother animals. now we know some 
tapeworm life cycles - enoplacephalidae -> use mites as one of their 
intermediate hosts. those are freeliving mites. 

mites have a wide range 
of habitat from aquatic (many of these parasitize mosquitoes et al) to 
terrestrial (plant feeders, microherbivores, animal parasites). all mites 
are geared strictly for fluid feeding. they penetrate the tissue of some 
material or whatever and suck out fluid. they are not particulate 
feeders. the basis of their vet/med importance is blood loss. some mites 
are particularly damaging to poultry causing severe blood loss in 
nestlings. others cause dermatitis/tissue damage - mange. mange is caused 
by some groups of parasitic mites. we also know that mites or their 
products are very7 potent household allergens. the cuticles, feces, etc 
of freeliving mites eg "housedust mites" are potent allergens.  I for one 
am extremely allergic to them and got shots for years because of them.  
lastly, we'll look at a group of mites which transmits pathogens among 
vertebrates. some freeliving mites are also intermediate hosts of 
helminth parasites.

generalized arachnid body:

the body is more or less 
segmented - think scorpion - as we move through different orders in class 
arachnida there is loss of segmentation esp through the abdomen. aranida, 
spiders, don't have overt abdominal segmentation like the scorpions do. 
as we get into acarina, we see that the body is really not segmented, but 
rather is more sac like. so we see loss of superficial segmentation. 


generalized acarine - mite:

the body is laid out with these gross 
morphological features that we can use as aids in speciating these 
suckers. they have a basic two segmented body with saclike legbearing 
segment which bears legs, repro organs, openings to repro and GI tract 
(anus), in adult stage there are 4 pairs of jointed legs. the head part 
is the "capitulum" and it bears mouthparts which include paired palpi, 
which are multisegmented, which are sensory structures - mechano and 
chemo receptors present here. used to find host and feeding site. just 
medial to those are the paired chelicerae. these are the organs that do 
the dirty work - they are columnar structures bearing armature -> 
pincers, claws, or stylets -> these are used to penetrate skin of host. 
the biting part. medial to those is the single hypostome. the hypostome 
in the mites does not function in feeding. in the tick, it acts as a 
holdfast organ. so that's the layout of parts.
the legs are 
multisegmented like the insect legs. there is an additional patellar 
segment in these legs that isn't in insect legs. in lab we will see the 
distal "pretarsus" composed of a caruncle and some terminal armature eg 
claw, suction cup, whatever. this part of the leg is highly variable from 
one species to another and is good taxonomic tool to speciate these guys. 


mites and ticks have single openings to resp tract -> spiracles. you can 
see leading internally from the opening is a peritreme -> large tracheal 
trunk that hooks up with the rest of the system. the form and placement 
of spiracles is also useful taxonomic feature.

the scheme of organizing 
discussion of mites -> we're not getting into rigorous mite taxonomy. 
we're just going to practically divide them up ito burrowing and 
nonburrowing mites. the burrowing mites are sarcoptes, notoedres, 
knemidocoptes, and demodex, which all cause mange. demodex do not 
actively penetrate skin - they are normal fauna, hang out in follicles. 
the nonburrowing mites include psoroptes, otodectes, dermanysus, 
ornynithonyssus, chyletiella and trombiculidae. these all stay on the 
surface of the host skin. 

alright. 
real mites.

first group to discuss 
is the burrowing mites. 
the family sarcoptidae contains some important 
veterinary pathogens. these mites are all fairly globular in shape. 
scabies mite, s.scabei, is nearly spherical in shape. we see no external 
openings to respiratory tract- respiration is transcuticular. the pairs 
of coxae one and two (basal segments of legs) are widely separated on the 
body from 3 and 4. 1 and 2 are in anterior half of body, and 3 and 4 in 
posterior section. 

we'll also see some ridgelike structures leading 
back from the legs. also in family sarcoptidae, the pretarsal terminal 
segment has a little suction cup on it. 

life cycle: behind what they do 
to the host, pathology wise. male mites and immature mites move freely on 
skin surface .adult females secrete a potent proteolytic enzyme with 
which they burrow through skin in torturous pattern and lay eggs in these 
canals or channels. this is basis for the pathology - sarcoptic mange. 
what happens when female mites burrow in is we get localized inflammatory 
response around the channels, and we see a copious serous exudate in the 
area of burrowing. this can cover a large part of the host body. 

sarcoptic mange is esp problematic in pigs. pigs very susceptible. we see 
a good illustration on this pig slide - serous exudate, many scabs over 
lesions, dried exudate, etc. the other thing about sarcoptic mange, is 
that it is highly pruritic. these animals will scratch, rub, etc. it's 
realyl bad. this pig is unhappy. the agent we see here is sarcoptes 
scabei. s.scabei is a large complex of subspecies. they *can* interbreed 
and yeild fertile offspring. best to consider them physiologic races. 
this is variety suis on this pig. we also see var equi on horses, var 
bovis on cows in area of body w/less hair, var ovis causing black muzzle 
on sheep, var canis causing scabies or common mange in dogs. lesions in 
dogs are very similar to these in pigs. mainly in areas of sparser hair. 
scab encrusted and highly pruritic. there is a variety which is a 
parasite of humans. var scabei is the one that infests people. the big 
question is are any varieties cross contagious between species? you will 
hear common wisdom that canine sarcoptic mange is transmissible to 
humans. but, if you take sarcoptes mites from canine to human host, the 
mites on the human host can cause a transient dermatitis, but they 
cannot,if on wrong species of host, set up a self perpetuating life 
cycle. they can't reproduce there. so s.scabei canis can cause transient 
dermatitis in people, but that infestation is not self perpetuating. so 
we can get clinical dermatitis in people who contact infested dogs, but 
you can't incriminate dogs as point sources of outbreaks of human 
scabies. you may have to adjudicate this point at some time. frequently 
human outbreaks of scabies end up causing people to erroneously 
incriminate dogs. 

dx: skin scraping and microscopic evaluation. these 
mites are located deep in epidermis, so you have to scrape vigorously to 
the point of drawing a little blood. use mineral oil on skin  and smear 
this onto a slide and check it out. you will see mites and sometimes 
eggs. these mites may be moving around on the slide, too.

a couple of 
other sarcoptes like mites: we don't see s.scabie in cats, but we see 
notoedres cati. looks very similar to s.scabei, with cuticular ridges, 
suction cups on pretarsi. another way to recognize this species is that 
in sarcoptes, anal pore is terminal on body, in this species, it is 
dorsal. notoedres causes sarcoptic like mange in cats and some wildlife 
eg var canicula in rabbits, a variety in squirrels, etc. it causes the 
similar mange lesions in cats.

a sarcoptiform mite we see in domestic 
fowl is knemidokoptes. similar life history. seen on chicken legs, other 
poultry. cause a kind of hypertrophy of cells underlying the scales. 
there is swelling, edema, serous exudate, causing scales to lift up and 
look gross. this is called "scaly leg" in domestic fowl. very globular 
mite. obviously sarcoptiform. there is a knemidokoptes mite that affects 
parakeets and other caged birds as well. 

last group of burrowing mites: 
demodex - the follicle mites. they look like cigars. d.folliculorum - 
human version. they are elongate with legs all in anterior half of body. 
fusiform posterior end is covered with annular striations or rings. 
mouthparts are very short. these mites will be moving around, are seen in 
skin scrapings. if any of us took a coverslip and scraped our face, we'd 
probably see some of thes emites. these are part of natural skin fauna of 
many animals. really are commensals in the baseline situation. but can 
also be pathogenic. almost all mammals have their own species of demodex. 
in almost all cases are passed from mom to offspring at birth. the 
species of demodex we see most is d.canis. you will find this on normal 
dog skin. you aren't concerned about the route of transmission because 
all dogs have them. BUT for reasons that are not well understood, some 
local immune deficiency or change in skin physiology sometimes allows 
populations of mites in local area to increase to the point where they 
cause a mangelike condition. demodex mange can really have two possible 
outcomes. mostly, demodecosis remains localized around a few small 
patches, usually face, forepaws. usually about 1 cm patches. this is 
localized demodecosis, and these lesions are usually self limiting and 
don't require tx, will go away on their own. there is also a serious 
version in dogs with underlying systemic immunodeficiency which allows 
these lesions to become generalized. we see lesions moving to trunk, 
hindlimgs, and will cover the whole dog if not treated. this underlying 
immunodeficiency can be innate, inbred, most often seen in purebred dogs, 
or can be as a result of drugs or something. eg, iatrogenic from 
prednisolone or something. demodectic mange presents clinically 
differently from sarcoptic mange. lesions are not pruritic. they are 
frequently associated with secondary bacterial infxn that makes skin 
smelly and reddish. smells kinda mousy and is erythematous. so this is 
often called "red mange" in dogs. in generalized demodecosis, prognosis 
is bad w/o tx. in sarcoptic mange, route of transmission is from one 
infested animal to another via direct contact. those mites do not survive 
in environment. kind of louselike epidemiology. with demodecosis, mites 
are there to start out with and some underlying problem allows them to 
proliferate. there are three possible outcomes of demodex infestation. 
one: no problem. two: localized lesions. three: generalized demodecosis. 
we see some demodex in livestock: sheep, goats, cattle. these larger 
species get pustular nodules under the skin which are teeming with mites. 
can decrease value of hide in cows.

non-burrowing mites:
suborder 
mesostigmata
these are mites that stay on surface of host skin, feed on 
tissue fluids, blood, other stuff. first group is this mesostigmata sub 
order. this refers to location of spiracle - located between legs three 
and four. morphology unlike sarcoptiform or demodex mites. kinda 
spiderlike in appareance. legs are closely grouped on body unlike 
sarcoptiform mites. anterior mouthpart bearing segment is distinctly 
separate from the saclike body. spiderlike/ticklike appearance. the 
armatures on the piercing parts of mouth parts may have pincers, claws, 
or stylets. they are used to penetrate the skin of the host. the 
important thing to recall about these mesostigmatid mites is that there 
are some immature stages that feed on blood, and that they feed only 
temporarily on host. between feedings, they get off, and hide down in 
host bedding. so these mites are parasites of nesting birds and mammals. 
are only briefly on host, to feed, then hide in nest. these mites will 
often feed at night, or during times when host is nesting or roosting. so 
in birds, we see them feeding at night on roosting birds, or on nestlings 
which are the preferred blood source. also babies of mammals that are 
nestlings. we have an entymological term that refers to parasites with 
this kind of life history - "lair ectoparasite" -> remember that. this 
refers to the fact that they hide in the lair or bedding of the host 
between feedings. 

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Curtis sings "I live on the legs of a 
lot of little chickies, the name of my order is knemidokiptes, heeeeeeey, 
acarina..."

one thing re: generalized demodecosis - there is another 
aspect to it. once started, the mites themselves secrete some 
immunosuppressive factors. the underlying immune deficiency is then 
augmented by this factor and it becomes a vicious cycle.

so we're 
talking about this suborder mesostigmatidae. one of the best known most 
important memebers of this group is dermanyssus gallinae, the chicken 
mite. this parasite bothers domestic fowl, chickens, turkeys, pigeons. 
typical lair ectoparasites. once done feeding they hide back in nest. 
they cause decreased production in poultry, decreased egg laying, 
decreased wt gain, and can exsanguinate hatchlings. can cause annoyance 
to people who have to handgather eggs or handle birds with infestations 
but seldom bite people. 

ornithonyssus sylvarium looks like the chicken 
mite. this is the northern fowl mite - problem of domestic poultry. mites 
feed around vent area of bird. difference between this and dermonyssus is 
that the dermanyssus are transmitted from nest to nest by bird movement, 
whereas ornithonyssus can be spread by migrating perching birds like 
sparrows, chickadees, etc. those birds carry infestations from one region 
to another. o.sylviarum can survive 60 or more days in abscence of host. 
the longer they are w/o host, the more aggressive they are when they get 
a host. this is a feature of lair ectoparasites in general - some of 
them, anyway. some ticks are like this. another thing about northern fowl 
mite is that not only will they annoy bird handlers, they will actually 
blood feed on people fairly voraciously. when dr lok was a grad student 
he worked with infested chickens and when they went in to collect the 
eggs you would get bitten by the mites. 

another interesting mite you 
can see that falls into this suborder is the nasal and bronchial mite of 
dogs - pneumonyssoides caninum. lives in nasal passages and paranasal 
sinuses of dogs. clinical signs include chronic sneezing and epistaxis. 
that's about all about them. 

another group of nonburrowing mites that 
cause a mangelike condition in livestock - mites of the family 
psoroptidae: they appear superficially sarcoptiform with globular body, 
but the legs are longer than the sarcoptiform mites. main functional 
difference between families is that these mites feed only on outer 
surface of skin - never burrow in. they secrete some anticoagulants and 
proteolytic enzymes, so can cause erythema, irritation, itchy lesions, 
scabs, serous exudate - resembles sarcoptic mange but caused by these 
surface feeders.


chorioptes bovis - causes mange in cows that is 
sometimes called hock mange b/c this mite is often found on extremities - 
tail, neck, hocks, heels, feet. not found around trunk or heavily furred 
areas. 

the next genus of these psoroptidae mites is psoroptes, which 
typifies the family with globular shape, long legs with suction cups on 
ends
again, surface feeders. most important as agent of psoroptic mange 
or "scab" in sheep. you see wool falling off in tags, clumps. typical of 
this mite. these mites are found all over the trunk especially in wooly 
or hairy areas. cause erythema, scabs, wet lesions.

otodectes cynotis: 
auricular mites of cats, dogs, ferrets, and foxes. cause a lot of 
discomfort when they swarm in ears. typically psoroptiform in shape. "ear 
mites". sometimes when populations of these mites builds up to certain 
level, you  can see them moving out over the rest of the haircoat and get 
generalized infestations of otodectes. these mites also cause a typical 
brown flaky d/c - coffee-ground discharge. 

next: family of mites called 
chyletidae. genus: chyletiella - fur mites or itch mites. important in 
rabbits. also a sp called chyletiella something else that happens in 
cats. these mites have large claws on their palpi which hook onto skin. 
they cause a very irritating feeding lesion, tend to be quick feeders and 
they are kind of lair ectoparasites which survive well off the host. 
chyletiella mites tend to be particularly problematic in lab rabbit 
colonies. they survive well off host so have to really clean the 
cages/nest boxes, etc.
have a typical hourglass shape to them..kind of a 
waist. very shapely mite.

another thing about them if you look closely 
you can see the little tarsal claw is in the shape of a delicate comb 
instead of claw or cup. probably the easiest way to identify this genus.


family trombiculiidae: chiggers. these are funky. trombiculid mites are 
only parasitic in larval stage, which has 6 legs instead of 8 legs. so 
you can ID them this way. chiggers stay on host for a short period during 
which they secrete a stable proteolytic enzyme which causes itchy, 
erythematous, papular lesion with necrotic center to it. because, see, 
mites have to liquefy host tissue and ingest it - can't chew. 
liquefaction = necrosis. these are very pruritic lesions. sometimes you 
see mite in lesion, but more often larva has left by the time you see it. 
kind of a lucky find to see oe of these attached. the adult stages and 
other life stages are free living. if you look in grass in warm climates, 
the harvest mite is a trombiculid, and adults are covered iwth bright 
orange hairs, so you might see them. sometimes the larvae are also orange 
or yellow. larvae are usually associated in nature with scrub vegetation. 
free living part of life cycle takes place with low lying scrub 
vegetation. if you grew up in deep south you probably got chigger bites 
on lower legs that really itched. in vet med there is one significant 
species in cats - neotrombicula whartoni. red papular lesions in cats. 
esp ears, facial areas. in warm climates. very pruritic wheal-like, 
pustular lesions. 
tromboculids like this in people vector a rickettsia 
which causes scrub typhus. the dz got the name b/c before we knew about 
the mite, we knew the dz cropped up in people who went to scrub 
vegetation areas. it's a disease that was first described among troops in 
WWII in pacific theatre. btw, transmission of that rickettsia depends on 
transstadial (transmission from one life stage to another), and from the 
female parent to her offspring (transovarial)

with chicken mites - 
northern fowl mite, etc - consider treating both infested birds with 
topical tx eg sprays of organophosphates AND the environment, realizing 
these mites are lair ectoparasites. 

chorioptes bovis: topical ciodrin 
dips (organophosphate) 
toxaphene is used to tx sarcoptic mange in many 
spp, although ivermectin has really supplanted the organophosphates. 
ivermectin or ivomec as marketed is probably the agent of choice for 
psoroptic an sarcoptic mange in livestock. also good for otodectes. in 
dogs, dose level of ivermectin required to tx sarcoptic mange is not 
licensed for dogs. so tx in dogs with ivermectin is an offlabel use of 
drug - 200 mcg/kg. but it's used commonly.

generalized demodecosis - 
amitraz/Mitaban dips. works on sarcoptic and demodectic mange, but is tx 
of choice for demodex.

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the TICKS
moving on to the ticks...

also 
in order acarina
two groups - hard and soft ticks
ticks are really highly 
specialized mites - but from a functional standpoint there are some very 
practical differences.

argasidae: soft ticks- argas, otobius, 
ornithodoros
ixodidae: hard ticks- dermacentor, rhipicephalus, ixodes, 
boophilus, amblyomma

general discussion of ticks as a group: 
slide of 
cow ear with a LOT of ticks in it - rhipicephalus sp. occurs in 
equatorial zone of africa esp east coast. vectors a protozoa. this slide 
illustrates that ticks can cause severe blood loss and annoyance. another 
consequence is that the ticks are secreting saliva and anchoring 
substance into feeding lesion. the saliva also contains some 
pharmocologically active neurotoxins that can cause paralysis etc. 
intoxication is another consequence of tick feeding. tissue damage - 
these suckers can produce lesions that are then subject to myiasis or 
secondary infection. 

big red spot: lyme dz "bullseye". ticks are 
vectors of some important dz in humans and animals. vector protozoan 
pathogens eg babesia, viruses - colorado tick virus - bacteria,eg lyme 
spirochete, and helminths, eg filarial worms. 

what constitutes the 
reasons why ticks are good vectors? they are very persistent blood 
feeders. if you go look at that cow ear, those hard ticks will remain on 
host 5-7 days and are very hard to dislodge. they are cemented on, and 
host can't dislodge them. this increases chance of picking up blood borne 
pathogens. also good opportunity to incubate pathogens to infectious 
stage, and pass them on. also they have wide host ranges. may parasitize 
multiple individuals and/or species during one life cycle. very good 
zoonotic vectors. lyme spirochete enzootic in fieldmice and chipmunks. 
transferred to people by ticks which may transfer from one host sp to 
another during life cycle. ticks are long lived. soft ticks esp can live 
up to 2+ yrs w/o host! can be stable reservoir of pathogens. life cycle 
of deer tick encompasses 2+ years. finally we see a high frequency of 
transovarial transmission. many tick associated pathogens esp viruses and 
protozoa are passed from female to offspring, giving way for pathogen to 
traverse generations and go on to infect other hosts. 

morphology: 
generalized tick
you'll see a lot of morphological landmarks from mite - 
body is saclike or teardrop shaped, with four pairs of legs on adult. 
larvae have 6 legs, 3 pairs. anchord to body by basal segment called 
coxa. anus is on ventral abdomen. genital opening is more anterior and 
also ventral. mouthpart bearing segment is anterior either thrust out or 
recessed and is composed of same subsegments seen in mites. we have 
lateral palpi, which are segmented and which serve same function - 
sensory - help locate site to feed. then medially are the  chelicerae 
which go in and penetrate host skin- teeth on the end, with muscles on it 
to tear skin, and the most medial hypostome which is unpaired. external 
surface of hypostome has  rows of curved teeth. it's a tonguelike 
structure which anchors tick to host before it secretes the cement stuff.


why are we going over this? well, in lab next week, we'll get a pictorial 
key to help us id these ticks at the genus level  using shapes of these 
structures. 

how to tell apart soft and hard ticks:

morphological 
distinctions: hard ticks have dorsal surface covered by a hard shell or 
scutum. in soft ticks, the integument is more leathery, pliable. no hard 
shell. it has a  different texture. another feature we see in hard ticks 
is a high degree of sexual dimorphism. very different males and females. 
male and female soft ticks are virtually identical. no gross 
morphological characteristics to tell them apart. the capitulum (head) in 
hard ticks is placed out in front of the body. looking from above, down 
on tick, you can see the capitulum sticking out in front of the body. in 
soft ticks, the capitulum is recessed ventrally - you can't see it from 
the dorsal view. the front part of the body kind of forms a hood over it. 


biologies of these groups: the hard ticks stay on the host for a long 
long time. some ticks remain on there 5-7 days, to become fully engorged. 
feeding is slow and deliberate and the hard ticks are cemented on there 
the whole time - not moving host to host during this time. when they 
finish feeding they drop off host. the soft ticks on the other hand are 
very quick feeders. they feed within minutes and get off the host right 
away (most soft ticks do this, not all). as far as resistance to 
starvation or dessication - hard ticks are susceptible to environmental 
extremes, don't overwinter well, need to be around host. soft ticks can 
live years in abandoned host area waiting for new host. can also 
withstand dessication well. tend to be denizens of arid climates ,seen in 
arid or desert climes.  






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