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parasit
9.16.97
Dr Schad

Trichuroidea: Genera are 
trichuris, capillaria, trichinella

Trichocephalidae: whipworms and 
relatives

this is an isolated group with evolutionary roots different 
from those already discussed. they stand apart. they are different in 
many respects. why is it inserted here? well it is soil transmitted, so 
we tend to run it in behind ascaridoids, probably for ease of learning.


they're not related to ascaridoid nematodes, but they do also have an egg 
that does not hatch outside in the environment. Egg + L1 is infective.


trichuris spp - long, with straighter tail == female. highly coiled tails 
== male. they have whiplike shape, with anterior elongation that is 
narrower, and posterior handle-like broadening. trichuris means 
"filamentous." trichocephalus would be more descriptive, because the head 
is the filamentous part. the long filamentous head weaves into the 
intestinal mucosa.

the anterior ends of the worms actually thread into 
the mucosa. the worms will spear a line of enterocytes, puncturing one 
after another. 

egg - oval, with plugs at either end.

all trichuroidea 
have a bipolar plugs on the eggs, with trichinella being the only 
exception. trichinella also has no freeliving stages at all, and has no 
intermediate host. adult worm lives in intestine, makes larvae that 
encyst in muscle, so adult and infective larvae are both found in the 
same host, and infection is by ingestion of infected meat.

Trichuris 
spp: 

* t.ovis, common in sheep and small ruminants, not very 
pathogenic. eggs often seen in sheep/goat feces. that doesn't mean that 
trichuris is causing whatever the problem is. can contribute to diarrhea, 
but not usually the main problem. 
*t.suis, -important! is cause of 
mucohemorrhagic dz in swine, along with some other things.  it opens the 
way for secondary microbial invaders. on its own, it can also cause 
diarrhea in heavy infestations.

* t.vulpis, - occurs in dogs. Important! 
also occurs in fox. all trichuris spp are parasites of cecum and lg 
intestine, btw. heavy infestations will cause bloody diarrhea - frank 
blood in feces, because they occur low down in the gut.
won't see a tarry 
diarrhea, but will see red color in feces.

* t.trichiura- important in 
zoo and wildlife medicine. primates commonly have this. including humans! 
this is a parasite of some importance - can cause mental and physical 
retardation in children, or a prolapse of the rectum which is rather 
gross.

LIFE CYCLES

direct and simple. no intermediate hosts. few 
complications. L1 develops in egg in environment (except trichinella)


see back page of handout. adults live in cecum/lg intestine, host passes 
eggs in feces, L1 develops in egg in environment, infective egg +L1 is 
eaten by new host, eggs hatch, larvae develop to adult stage in cecum.


trichuris suis has a more complex life cycle: worms in cecum, lay eggs, 
egg is passed in feces. long period of development outside. in warm 
weather it takes a month for eggs to become infective. direct fecal oral 
transmission. larvae spear a row of intestinal epithelial cells,move 
along them into the crypts, puncture crypt, get out through base of 
crypt, then eventually back into the lumen, leaving their anterior ends 
embedded in the mucosa. PPP 41-47 days. diarrhea may occur well before 
eggs appear in feces.

if t.suis is very abundant, can undermine mucosal 
surface and cause it to slough off.

see handout for details of t.vulpis 
life cycle.
there is no vertical/prenatal/transmammary transmission. 
trichuriasis is not a disease of the neonate.

PATHOGENESIS:

the result 
of the undermining of the mucosa depends on number of worms. if not that 
abundant, there may be frequent soft mucoid stools +/- blood specks. in 
severe infections, there may be marked bloody diarrhea with mucosal 
sloughing.

in young, but not newborn, pigs, we may see "21 day diarrhea" 
which appears about 3 weeks after pigs are first put out on pasture or 
wherever. this implies relatively sudden ingestion of a large number of 
eggs and poor management practices in a heavily contaminated environment.


DIAGNOSIS: 
trichuris type

clinical signs: profuse diarrhea day 17-21 
("21 day scours"), anorexia, growth retardation, dehydration, emaciation, 
death

really think of these as spectral diseases, with intensity of 
signs varying with level of infestation.

slide: trichuris eggs with 
bipolar plugs.
in human and dog, endoscopy is sometimes done. why would 
you do that if you can see so many eggs in the feces? Well, females 
aren't very prolific, so you won't see eggs in the feces all the time. so 
you might not see eggs, and you would need to do further diagnostics. in 
endoscopic exam, you see tails of worms sticking out of mucosa of lg 
intestine. if there are a lot of developing worms, during the prepatent 
period, that's another case where you might need to do endoscopy. but 
USUALLY with clinically significant infections, there will be eggs in 
feces.

tx: standard antihelmintics. milbemycin of HW prophylactic will 
also kill these worms.

with swine, they are treated as a matter of 
routine, presented in the handout. 

move on to CAPILLARIA:

egg is 
narrower than trichuris egg, but still has bipolar plugs. has rough 
shell, not smooth like trichuris. the worm is  long thin worm without the 
broadening at the posterior end. males have a single spicule. no bursa. 
there is a row of single cells lying across the esophagus (all trichuroid 
nematodes have this) and it's called the _stichosome_. a series of 
cuboidal cells running along esophagus, filled with enzymes used to 
penetrate tissue

spp: c. aerophila, with direct life cycle, lives in 
lungs; and c. plica, which lives in bladder and sheds eggs into urine. 
wrt life cycle of aerophila, it's direct, no vertical transmission, no 
infection of neonates, is transmitted only by fecal oral route, L1+egg is 
infective stage. 

pathogenesis: parasite c.aerophila occurs in lungs, 
eggs pass up airway, irritate trachea, cause trachitis and bronchitis. 
dogs present coughing, wheezing, +/- nasal d/c. anorexia w/heavy 
infestation. 

dx: eggs in feces. notice in comparison with trichuris egg 
- plugs don't protrude as much, and exterior of shell is not smooth. 
capillaria eggs are sort of asymmetrical longitudinally as well.

c.plica 
- as handout indicates, they need an earthworm as intermediate host. 
animals have to live around soil to get this infection, because of the 
earthworm host. we've had at least one group of animals seen at Penn 
where all animals in kennels were infected - whippets from Chester Co, 
which were raised in large grass kennels. that was kind of surprising, 
dogs don't usually eat earthworms. Dr. Bovee will probably tell us more 
about these dogs, which came in with hematuria, dysuria, and so forth. 
this was surprising. this parasite is not supposed to be a pathogen. so 
when it comes to differential diagnosis, based on these eggs, we have 
plica eggs in urine, never in feces, so you can tell it apart :)


c.aerophila eggs can be found in sputum, transtracheal wash, and feces. 
look for pitted egg as opposed to smooth egg, with less prominent plugs 
than in trichuris.

prevention/control: remember a few lectures back we 
discussed control of geohelminths already. no point doing it again. this 
is a very useful condensed review in the handout, though.

some years ago 
a hookworm vaccine came out that was a live vaccine with a short shelf 
life. vets got refrigerator inserts that kept the vaccine at a particular 
temperature (higher than normal fridge temp). vet would inject living, 
irradiated larvae with reduced pathogenic potential into the animal. this 
protected them against hookworm anemia, but not against infection. so 
sometimes eggs would appear in the feces which confused techs and 
clients, and clients got annoyed that their dogs got worms after being 
vaccinated. sales people didn't explain to vets that dogs who were older 
weren't vaccine candidates because of hypersensitivity potential. was 
only good in naive - young- animals. so it wasn't useful really outside 
of the greyhound industry. was a commercial failure and is no longer 
around.

this is all he has to say about prevention and control of 
geohelminths.

so, these species above are geohelminths.

trichinella 
spiralis: first of the meat borne parasites. occurs worldwide in 
mammalian carnivores (and recently reported in a crocodile!). (is really 
a group of say 5 species)
adults occur in small intestine and if abundant 
can cause enteritis, diarrhea, usually not though, usually this part of 
infection isn't noticed. trichinellosis usually considered to be when 
larvae migrate to muscles, which can be very painful, can cause fever, 
eosinophilia, and so forth. we're talking about an organism with adult 
worm in gut, larvae in muscle - transmission is by predation, 
cannibalism, or scavenging. 

trichinosis is a reportable disease - 
should be reported to CDC - very few cases reported in US but still large 
problem for pork industry because there is always the risk of a major 
outbreak of disease, which is usually a single source outbreak. what 
usually happens is that someone goes and buys a pig and has a roast or a 
barbeque or somethign as a big social function. then, a whole group of 
people become infected from that animal if it isn't well cooked or 
something. or, if pig is used for sausage...

this kind of thing gets 
into press and causes problems for pork industry.

there is also 
trichinella pseudospiralis
occurs in birds, humans, relatively poorly 
known, probably global in distribution. doesn't make cysts.

life cycle: 


adult worm occurs in small intestine. will penetrate villi. is an 
intracellular parasite at least in part. 

so start with L1 larvae 
encysted in striated muscle (meat). infected meat is eaten by man, wild 
game, pig - mammalian carnivores or omnivores - L1 will penetrate 
epithelial lining of small intestine in host, undergoes 4 molts, adult 
worms stick tails into lumen of intestine. newborn larvae (subL1) pass 
through lymphatics and are distributed throughout muscle, and then encyst 
in skeletal muscle. they alter the myocytes to support their own growth. 
they recruit capillaries to make little cysts around them and stuff. life 
cycle is very unusual in many ways.

re: pathogenesis: in handout it says 
swine must be very heavily infected before they show any signs (eg, over 
900 larvae per gram) - and even then it will just be muscle 
soreness/stiffness, so will see unusual gate, lameness, reluctance to 
move, resistance to handling. so treatment dealing with trichinus pig is 
a rare issue - infection is usually discovered at postmortem, too late to 
treat :)

now, in the US we do not inspect meat for trichinosis. a few 
plants which ship pork overseas might have some inspection. this involves 
digestion of tissue samples (?). so mostly this disease is a problem in 
humans. the intestinal part of infection is usually not noticed. but when 
a human ingests a lot of larvae (and you can eat a LOT if you eat 
infected meat that is cooked rare...) you can have a problem with the 
migratory phase of the infection, which causes muscle pain, periorbital 
edema as a result of larvae moving through muscles around the eye, 
discoloration around eyes, fever, and eosinophilia. low grade infections 
may appear flulike and be overlooked. 

slide: plump lebanese woman with 
periorbital edema and bluish discoloration around eyes. appears to be in 
pain :(

diagnosis: dog wearing plaid baseball cap, holding a magnifying 
glass, inspecting ground meat. :) this is not an american dog. we do not 
do this kind of inspection here.

you take a pinch of meat, and look 
under microscope for larvae - "pressed preparation" of meat.

in certain 
small slaughterhouse conditions, peptic digestion of small samples of 
muscle may be performed. 

prevention and control: see handout. self 
explanatory. prevent pig from eating infected meat! do not feed raw meat 
to pigs. end of story. COOK the garbage before you feed it to pigs! if 
any pigs die on farm, REMOVE THEM right away before they can be 
cannibalized! detection at the slaughterhouse is a good idea too but not 
used here. inactivation by the processor - say, hotdogs, are cooked. any 
cooking or freezing done will prevent transmission of US strains, except 
for alaskan strains. consumer can also cook or freeze pork to prevent 
infection.

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