----start-----

parasitology
9.24.97
dr nolan

CESTODA - tapeworms

note: EXAM FORMAT is similar to the ones in the computer. will be mix of 
multiple choice, matching, columns, use more than one answer, essays, 
short answers, etc. A veritable potpourri, if you will. LAB EXAM goes 
through tomorrow's lab. material for study is out in the bottles in the 
lab. slides are in computer room. videos are there. notes, lab book, etc. 
minilab review can be Friday at noon or tomorrow at 4....for the 
practical you have two hours. unlimited time at the stations but if lines 
build up people will get very annoyed. you can go back and forth between 
things.

CESTODES

remember we're in phylum PLATYHELMINTHES. we learned about trematodes 
already now we're doing cestodes. flat, tapelike worms. anterior scolex 
is the hold fast organ. this is an anchor. these worms live in small 
intestine. body of worm is called strobilla and is broken into proglottid 
segments, each containing full set of reproductive organs. they are 
hermaphrodites. proglottids are formed anteriorly and old ones are pushed 
back. anterior ones are immature. midworm are mature proglottids, 
functional. at the end you have gravid proglottids packed full of eggs. 
eggs are released or proglottid drops off host. realize it isn't a colony 
of individuals. it is ONE individual worm. nerves start at anterior end 
and run whole length as do muscles and gut. moves as one individual. has 
many reproductive segments, is all. the rat tapeworm will start at 
anterior duodenum. as food comes in it will follow the food bolus. at the 
end of the day it's in the large intestine. while rat is asleep, it moves 
up close to the stomach again.

slide: scolex anteriorly. can see hooks - rostellum, only on some worms. 
all have either suckers or slits to grab villi. hooks are optional. worms 
with hooks are "armed", without are "unarmed". neck region - new 
proglottids form here. dark lines running down sides are nerves.

although these are hermaphrodites, they are protandrous, meaning male 
organs develop first. in early mature proglottids, there are only 
functioning testes - worm can mate with other worms having functional 
ovaries. favors crossfertilization. can mate with other proglottids on 
same worm, too, or within itself after ova develop. there is a genital 
pore on the proglottid. can see uterus. in gravid proglottid, testes 
degenerate, and uterus is packed full of eggs. these gravid ones break 
off and go out in feces. still has some nerve and muscle so can kinda 
move.

so. gutless wonders sitting in host. no mouth. how do they feed? 
absorption through skin. really, they are sitting in digested food so 
they don't need to digest anything. their outer layer is a syncytium, one 
giant cell. surface microthrix are like microvilli - increase surface 
area. active and passive transfer of nutrients. there is a glycocalyx on 
the microthrix, made of sugar residues which protect worm from proteases 
in the gut. all tapeworms live in GI tract of host. they are mostly in 
small intestine of definitive host. a few in large intestine, a few in 
bile or pancreatic ducts. but most in small intestine. 

GENERAL LIFE CYCLE

indirect (except one rat tapeworm we don't have to know)

Adult in gut of host-->egg goes out with feces-->ingested by intermediate 
host. hexacanth larva hatches in gut of intermediate host (in all but two 
we'll discuss. in a few they hatch outside the int.host). goes to 
predilection site and becomes a metacestode (larval cestode)--->can be 
eaten by definitive host, and adult develops, OR-->eaten by second int 
host-->2nd metacestode grows------>eaten by definitive host OR-->by 
transport host which is then eaten by definitive host.

pediagenesis: asexual reproduction in larval stage. 
some metacestodes are single - become one adult. others undergo 
pediogenesis and you end up with a whole bunch of infective stages. so 
one egg can produce thousands of infective stages.

EGGS: at some point during developmnt of egg, have onchosphere inside 
which is also called hexacanth larvae (6 hooks==hexacanth). the hooks are 
these little lines you see. 

slide: tapeworm egg - can see 6 hooks inside the egg in the middle. just 
some linse runnign across the inside, really. inside the hexacanth larva. 
so, this hatches out eventually, the larva does, and it migrates to the 
predilection site, using the hooks to hang on or something like that. 
didn't quite catch it.

two orders of tapeworms: CYCLOPHYLLIDEA (most of 'em), and 
PSEUDOPHYLLIDIA (a couple). 

CYCLOPHYLLIDIA:

4 suckers on scolex, two on either side. the genital pore is marginal, 
lateral. intermediate host may be aquatic or terrestrial, and usually 
only one int host. proglottids are shed in feces, rather than releasing 
eggs.

first one is in the family DILEPIDIDAE which has two sets of repro organs 
in each proglottid, and retractable hooks in scolex. we're going to 
discuss

DIPYLIDIUM CANINUM: most common tapeworm in dogs and cats, worldwide 
distribution.

gravid proglottids come out of host, eggs inside proglottid are eaten by 
biting or chewing louse (lice live on host for whole life cycle) or by 
flea larvae. the cysticercoid (tapeworm larva, aka metacestoid) develops 
within the flea or louse. Dog/cat eats flea or louse. cysticercoid is 
mature at about the same time as the flea. flea finds dog so this is a 
good host for the tapeworm. 
scolex of dipylidium has the rostrellum and has hooks on it, and has four 
suckers, two on each side. the mature proglottids have testes and 
ovaries. ovaries are the darker brown blotches. testes are the more 
diffuse pale spots. two of both in each proglottid. 

eggs come out in packets. if you crush a gravid proglottid, the eggs come 
out in packets, 10-20 eggs per packet. can see the hooks inside each egg 
inside the packet.

disease: none. these are nonpathogenic. if you have a LOT LOT LOT of 
worms, maybe some soft stools. but really these are NOT pathogenic. these 
proglottids are motile and can move out on their own and cause the butt 
of the dog to itch and cause it to lick the anal region or to drag its 
butt on the floor as it would with impacted anal glands. HOWEVER these 
things do move out on their own, are about 1/4-1/2 inch long, look like 
rice, will find them on your lap, on the feces, etc. owners see them and 
get VERY UPSET. they don't want to know that the animal has worms. of 
course, if you treat them, you get rid of the worm but not the fleas so 2 
wks later (PPP=2 wk) it will pass segments again. so you HAVE to get rid 
of the fleas. otherwise the owner will call you in 2 wks and say the meds 
didn't work. it can be VERY hard to convince cat owners that their cats 
have fleas, since cats groom the fleas off so efficiently.

when you see tapeworm segments, you SHOULD speciate them. 99% will be 
dipylidium, but rarely in cats will be other kind, not from fleas.
(note: don't have to know about anthelmentics yet)


next family 

MESOCESTOIDIDAE- not like others. has four suckers but they are atypical 
looking, each sucker has four lobes so looks like 16 suckers. genital 
pore is median, not marginal/lateral. gravid proglottid has a paruterine 
organ - specialized egg sac at end of uterus, which stores eggs. 

life cycle: has two intermediate hosts, two different larval stages.
so proglottid drops off host, paruterine organ full of eggs, releases 
eggs onto soil. freeliving mite eats the eggs, larva migrates out into 
mite and becomes cysticercoid. this mite is then ingested by another int 
host, a bird, amphibian, reptile, or mammal, and the tetrathyridium 
develops from the cysticercoid. there are paratenic hosts which will eat 
the second intermediate host, as well, if the definitive host doesn't get 
it. definiteive host is dog/man/cat. so, the tetrathyridium are found in 
the peritoneal cavity of the intermediate host, and when they get in 
definitive host they become adults. the tetrathyridia are sluglike with 
four suckers and can bud off and reproduce asexually. this can lead to a 
parasitic peritonitis. odd thing about this tapeworm is it isn't sure 
what the definitive host is. if eaten by dog, will either mature, or 
possibly stay as tetrathyridium and multiply. sometimes in dogs you have 
both adults and tetrathyridia. this is odd. also adult tapeworm retains 
ability to bud at the neck and produce new worms. the scolex is most 
resistant to drugs so this is important. this wouldn't be too bad if it 
was nonpathogenic, but it can cause a severe mucoid diarrhea in man, a 
moderate mucoid diarrhea in dogs. (Men infected via raw frogs??)

TAENIIDAE: most important family. rostellum usually present with four 
suckers present on scolex. segments are longer than they are wide. single 
pair of repro organs in segment, eggs have striated shell, all taenia spp 
have same kind of eggs. intermediate and definitive hosts are mammalian

t.taeniaformis: in cats. eggs eaten by mouse, larvae (strobilocercus) 
grow in mouse liver, , cat eats mouse, larvae attach to intestine and 
grow to adult. can grow to about 60 cm and live about two years. just 
like the dipylidium, the gravid proglottids are shed. large enough to be 
seen by owners, etc.

note: cysticercoids are found in arthropod hosts. in mammalian hosts many 
diff types of metacestodes (larval stages) are found. 

t. pisiformis - def host= dog. int host rabbit. larval stage is a 
cysticercus which lives in rabbit peritoneum- looks like cysticercoid 
with inside out scolex. PPP about 8 wks from ingestion. adult worm about 
6 feet long!
disease-wise- little if any signs are seen. in rabbit, may sap strength 
and slow it down so dog can catch it more easily.

t. multiceps: dog/sheep life cycle. dog=def host. proglottids eaten by 
sheep. hexacanth larvae reach brain of sheep and mature into coenurus. 
coenurus asexually multiplies. form cysts which are fully developed in 
7-8 mos and may be > 5 cm in diameter. adult worms are a meter in length. 
larvae seen in brains of sheep, cattle, goats - or other organs of goats. 
common in sheep raising areas where sheep and dogs hang out. dog has to 
eat infected sheep brain. definitive dx in ruminant only possible on 
necropsy. btw- sheep brains are small. 2 inch cyst in there can compress 
it. first sheep will circle to one side, maybe go blind in one eye, may 
see convulsions, paralysis (one sided). called "true gid" or "staggers" - 
sheep acts drunk. if this is growing against the top of brain, can grow 
against skull and you can feel it - it creates a soft spot in skull (?)

no dz in dog, but will kill sheep. 
other tapeworms of dogs are also found in sheep, but we do not have to 
know their names so I am not going to write them down, because I might 
accidentally learn them :) just know there is a relationship between 
taenia spp in dogs and sheep. if you do not feed your dogs raw sheep, you 
aren't going to have a problem.

taenia spp do not cause dz in dogs/cats. perhaps a few GI upsets, some 
scooting. in RARE RARE cases you get so many worms in a small dog that 
you have intestinal obstruction or rupture. but you need a HUGE worm 
burden here, and a small host. 

echinococcus is another genus of taeniidae.

e.granulosus: dog is definitive host. eggs eaten by sheep, hexacanth 
migrates through intestine gets into venous blood and is carried to 
liver. most are filtered out there and grow as hydatid cysts in the liver 
(another larval type) or can be carried to heart and go to lungs. if they 
somehow get past lungs, end up in brain. but 80-90% in liver, and less 
than 1% not in lung, liver, or brain.
grows to  maybe 5 cm in diameter. no problem in liver. problem in brain. 
adults are only 4 segments long. are small and only in the crypts of 
lieberkuhn so hard to see. dogs have thousands of worms, no problem - 
shedding hundreds of thousands of eggs/day onto pasture

PPP 4-6 wks

in USA seen in utah, montana, etc - wherever sheep and dogs hang out and 
dogs eat sheep. e.granulosus also can affect horses, pigs, camels, 
antelopes, etc.  in USA pretty much only have the sheep strain. but the 
sheep strain can infect deer and moose, and they are eaten by coyotes and 
wolves, so...

so you can have deer/coyote or moose/wolf "sylvanic cycles" out in the 
wild. these will contaminate pastures to perpetuate the domestic cycles. 
for our purposes, can consider deer/coyote and moose wolf as reservoirs. 


in PA we have seen echinococcus in horses, usually from england. dead 
horses are fed to dogs, too. humans can also be infected by hydatid 
cysts. they take years to grow large, but they can get big.  they have 
nice solid outer acellular layer, fibrous deposition by host, lined by 
germinal layer. in sheep, these cysts rarely get more than 10 cm b/c 
sheep die. but in humans can get huge. if they rupture, usually see 
anaphylaxis due to highly antigenic fluid inside them. 

slide: liver with huge cysts in it. you wonder why someone would feed 
this to a dog. no one would. but usually only smaller cysts, not these 
huge softball sized ones.  
slide: infected woman. she looks pregnant. from goat raising family. 

the hydatid cyst is full of "protoscolices" and each protoscolex grows 
into an adult worm. so one dog eating one cyst gets hundreds or thousands 
of worms. 

humans are dead end host except for these african goat people who get 
eaten by hyenas. there, humans are intermediate hosts. 

there may be drugs to chemosterilize these cysts, but they don't cause 
them to regress. you need surgery to remove it.

dx of echinococcus in dogs: taeniid eggs in stool, brown striated shell - 
looks like all taeniid eggs, so not diagnostic for echinococcus. 
proglottid is about 1 mm long, hard to see if it comes out, usually 
releases eggs in intestine anyway. if you see taenia eggs and no 
segments, you probably have echinococcus - but dog can have BOTH taenia 
spp. so there are tests for echinococcus antigen in stool and serum. 
those tests are about 70% good. miss 30% of infxns.

in sheep/goats - meat inspection, postmortem exam, u/s or serology.
in the african goat area they're using u/s to screen the goats. 50-60% of 
goats are infected.  you have to train the people not to feed the viscera 
to the dogs, but really it's hard to do that. cooking might help. 

control: 

how to dx dog - give special drug causing him to purge gut via 
defecation. everything comes out. sieve through feces and look for the 
adult worm segments. not too fun for the dog. good way to ID infected 
dogs, though. 

hydatid dz has been a problem for a long time. they were using arecoline 
hydrobromide (this purging drug) to get rid of this tapeworm for a while 
in NZ, for about 30 yrs. would purge dogs til they were clear and then 
let them go back to farm. now they are echinococcus granulosus free. 

Cypress also instituded a control program. they shot all stray dogs, 
licensed own dogs with very high fees that most people couldn't pay, and 
said any slaughter of sheep had to occur in special facility with 
inspector there. they got rid of dz also.

both islands, no reservoir hosts.

in argentina they are now registering all dogs, visiting the dogs q 2 mos 
and treating them all with praziquantel dog biscuits. PPP 6-8 wks. so 
they catch them before they can seed environment. also they're educating 
people not to feed raw sheep to dogs. human cases have dropped from 6% of 
kids infected to under 1% of kids infected.

in USA we have reservoir hosts so can't get it out of sheep population. 
but we can prevent dog infections and human infections. we give coloring 
books to kids on farms. kids get educated about it and then yell at their 
parents not to feed raw sheep to dogs (like some of us may have yelled at 
parents about recycling)

e. multilocularis: smaller than granulosus. def host is arctic fox, red 
fox. int host is meadow vole, mouse, muskrat. cats, dogs, coyotes also 
def host. dead end host = man. forms hydatid cyst that is multilocular- 
budding mass - multiple chambers...grapelike mass. if dog eats one mouse 
will get a couple thousand worms. nonpathogenic in definitive host. 
number of eggs shed is huge. in humans this is invariably fatal if not 
treated. sx not an option. too thinwalled, rupture can seed other areas 
and start other cysts elsewhere. must tx with albendazole daily for say 
3-5 yrs to sterilize them, then maybe try to remove them. 

distribution of multilocularis is northern hemisphere, found formerly 
only in arctic fox range- was real problem in eskimos where sled dogs 
hunted voles. still problem in some areas of aleutians. in 1960s, a focus 
was found in foxes in north dakota. never seen in foxes there before. 
they do see it there now though. probably got into red fox from arctic 
fox...as of 1991, it's gotten as far south as N MO, and as far W as the 
rockies, and east into central Ohio. probably spreading all through ohio 
and into PA by now. fortunately, it's pretty much stayed in the red 
foxes. a few barn cats in minnesota, a human in minnesota and a human in 
alberta, but that's about it. but it CAN enter domestic/human spp. 

so, we're not doing anything to stop the spread of e.multilocularis. we 
may be encouraging it by shipping foxes around the country for hunting! 
one illegal shipment of foxes into s.carolina had e.multilocularis and 
rabies!! they stopped that shipment, but who knows when the next shipment 
will sneak in.

Tapeworms of larger animals. 
life cycle of beef tapeworm of humans - human = definitive host, int host 
= cow.
cysticercus are about pea sized, in muscles of cow. person eats raw beef 
and gets tapeworm. this is t.saginata, which is rare in the USA. this is 
probably biggest taenia problem in humans - people get upset when they 
see segments crawling out of their butts. it's really pretty 
nonpathogenic. 

we find t.saginata by meat inspection. inspectors look at tongue, heart, 
masseter, outside of carcass - want to look for it without ruining 
carcass.

test was done. they took a kg of beef from a carcass and sliced it every 
5 mm. it turns out if you have 1-10 cysts per kg, only 27% is detected by 
inspection. when you have over 20 cysts per kg, you still only get about 
77% of infected cows by inspection.

in this country there is a problem with immigrants who come in and bring 
the tapeworm in their gut. mexico, africa, eastern europe - it is in 
human population, people are eating raw beef, and getting this. so in 
feedlots in AZ, TX, etc, where mexican immigrants work the cattle 
feedlots, they get infected at home, bring the worm up north, and can 
shed eggs into feedlot- proglottids are crawling out of worker butts, 
dropping to ground, getting into cows. so there are these posters that 
are posted in feedlots. feedlot owner is supposed to screen and treat 
workers before they work but people are scum and they don't do it. so 
they try to educate people. 

t.solium - pork is the host of cysticercus this time. otherwise similar. 
not a problem in US. worms do come in from people in endemic areas. pigs 
here usually not raised by migrant labor so unlikely to get infected. 
t.solium, though, can do something - if eggs are passed from a human host 
and ingested by another human, the egg will think you are a pig and will 
develop into cysticercus - if it does this in the muscles, not a huge 
problem. BUT if they go to the brain, you have neurocysticercosis. space 
filling lesions in brain. this can be a major problem. this is number one 
cause of epilepsy in central america and a large part of africa. in USA 
is also a problem. in NY a nicaraguan nanny infected kosher jewish kids 
and they were having seizures, etc. so this is a problem, a public health 
hazard, and it is on the International Task Force for Disease 
Eradication's "eradicable" list.

these two can be 23 feet long

ANOPLOCEPHALIDAE: no rostellum, segments broader than long, double repro 
organs

moniezia spp - proglottids shed from host, eggs picked up by mite which 
develops cysticercoid, sheep eat grass with mites on it, get adult 
tapeworms. fairly large

m. expansa in sheep, m.benedeni in cattle usually but can switch. older 
animals get immune.

anoplocephala in horses. 3 spp. same life cycle as above.
a. magna 6-8 inches long, in sm int of horses- nonpathogenic
a. perfoliata- in sm and lg intestine of horses. eggs triangular, unique. 
these worms are pathogenic- like the ileocecal junction, instead of 
loosely hanging on, will burrow in a little into the mucosa. you can get 
this inflammation around them, leading to a number of problems which 
increase with worm burden. can get intussusception of small intestine 
into lg intestine since ileocecal valve weakens due to worms burrowing. 
worse, can get hemorrhage in intestine, bleeding, lots of problems. this 
is an important pathogen. it used to be pooh-poohed because strongyles 
killed horses before these built up. now strongyles are all killed with 
drugs and this worm is more important. is seen worldwide, most common 
tapeworm in PA horses. 
paranoplecephala mammillana - all equines. nonpathogenic

PSEUDOPHYLLIDIA: no suckers. has two slits on scolex. genital pore in 
middle not on edge. two intermediate hosts, aquatic. sheds eggs - spit 
out by proglottid. when proglottid empties will break off and come out.

spirometra mansonoides - dog, cat raccoon. eggs washed into water, hatch, 
ciliated coracidium swims to water flea, which develops the procercoid 
stage, water flea eaten by any vertebrate other than fish or def host and 
grows into plerocercoid. can then have transport host or go directly to 
def host. plerocercoid is fairly long, usually wound up subcutaneously.  


diphyllobothrium latum - cycle similar to above. plerocercoid stage eaten 
by fish. fish eating mammal eats fish. def host dog, mink, etc. 

big worms, meters long, causing minor problems. the spirometra may cause 
diarrhea and anorexia. other one may cause pernicious anemia in humans 
b/c it likes B12 and can outcompete you for it. not usually in dog/cat 
though.

READ HANDOUT. he sped through this last part like crazy.
----end-----