---start----

parasit
10/22/97
farrell

flagellates
protozoa of the 
intestinal and reproductive tracts

today we're going to discuss two of 
these suckers
in the group mastigophora
trichomonas and giardia


trichomonads are flagellated, are surrounded by unit membrane. about 25 
microns in size. single nucleus, three anterior flagellae and one curved 
back to produce undulating membrane, and has an axostyle. these do not 
form cysts, are only surrounded by unit membrane. are not resistant to 
environment. slide: stained specimen. can see nucleus and membrane, he 
says, but all I see is something looking kinda like a demodex mite with a 
red dot in it. 
in cattle, this is a venereal disease. in males it lives 
in folds of the penis and sheath. is not generally an invasive organism. 
it hangs out on the surface. transmission is venereal like t.vaginalis in 
humans. same thing occurs in cattle (funny slides of mating cattle and 
people kissing). so it's transmitted to the female cow in this way, 
during coitus. in the bull,the organism produces virtually no signs. it's 
basically clinically undetected. once infected, the bull probably remains 
infected for life. there are some suggestions that young bulls may clear 
infections if a treatment is used - eg ointment on penis - but bulls do 
not like treatment, and it doesn't always work, so you may as well not 
treat. there are no approved drugs for this in the US either. in the 
bull, the organism lives in epithelial crypts of penis and prepuce. 
slide: cross section of epithelium with shallow crypts. as bull ages, 
crypts get markedly deeper. there is considerable evidence that 
infections are lighter in young than old bulls. the reason is, the 
protozoa live in the crypts, and if deeper, more room for them to live. 
older bull = over 4 or 5 yrs old. is more common in older bulls than 
younger bulls - this may be wrong in handout. infections less common in 
young bulls. bull transmits infection to cow, where it lives on surface 
tissues of vagina and uterus primarily. usually there are no clinical 
signs. sometimes there may be a mild vaginal discharge which is hard to 
recognize in the cow. most are asymptomatic, though. the primary 
pathology of trichomonas in cattle is abortion. usually this isn't 
clincal abortion where you see the fetus. generally, it is very early 
abortion, in first 90 days, where you have no visible signs, and you 
think cow simply didn't conceive. pyometra (2%), visible abortion, can 
occur occasionally.  clinical outcome is generally that after mating with 
infected bull, 10% are not infected at all, 20% show no signs but are 
infected, 60% display infertility, recycling, etc, 5% show post-coital 
pyometra, and 5% have late abortion after 70-125 days. so mainly you see 
a lot of "open" cows who look like they failed to conceive. most 
developing fetuses are lost early with no clinical signs. after a cow has 
aborted, usually they can go into estrus in a normal manner 1-2 cycles 
after the abortion. so about 3-4 weeks is cycling time, so they may miss 
one cycle and then cycle again a month later. it all depends on when the 
fetus is lost. if very early, in first two weeks, may cycle again 
immediately. if later, at 50-60 days, may cycle irregularly for a couple 
of months before normal estrus. if animal remains infected, it will abort 
again, but most trichomonad infections in cows spontaneously resolve in 
2-4 mos or so, so during the next cycle cows generally can conceive in 
normal manner, so there is no permanent infertility. usually one sees 
infertility during one season, then cows normal during next season. 

how 
prevalent is this dz? we don't know. there was a survey in 1988 in CA 
where half of the 25 herds checked had positive bulls on their property. 
generally this occurs in western US, where cattle are bred on the range, 
through natural means. the organism can potentially be transmitted during 
AI but any reputable purveyor of bull semen will screen for this. 


control: 
breed virgin bulls to virgin cows
clean artificial insemination

test and remove infected bulls - you see dz when new bulls are introduced 
w/o testing or cows are introduced and spread it to bull. in nonimmune 
herd you can see 60-70% reduction of births in first year after 
introduction. 
cull open cows
maintain young bull battery (sounds 
bizarre). use young bulls for breeding.
vaccinate - there is a ft. dodge 
killed vaccine. it reduces levels of infection. it's given to cows 
immediately before breeding season and is fairly effective at reducing 
levels of abortion in a herd but not totally so and doesn't prevent 
infection- will reduce infection rate- reduces level of infection eg 
number of organisms... but it's a useful adjunct.

cows do develop 
immunity. hard to test. in bull, take prepucial washes, in cow take 
vaginal washes, and culture the organisms. fairly efficient in bulls, 
less so in cow - may have to do 4-5washes over a week in cow to ensure 
negative result. 

in terms of actual pathogenicity little is known. we 
think organisms on mucosal surface of uterus lead to some altered 
physiology which causes rejection of fetus. mild, mild inflammation. no 
severe disease. we don't really know why early fetuses are rejected but 
they are.

there are trichomonads in other animals. in humans it is 
pretty common and produces mild clinical dz (t.vaginalis). t. gingivalis 
in humans sometimes occurs in mouth. dogs may harbor intestinal 
trichomonads which aren't considered pathogenic. you do not detect them 
on your fecal exams except on fresh smear of diarrhea. seen most often in 
dogs. doesn't cause dz, as far as we know. probably multiplies when 
bacterial flora are altered for some reason. 
occasionally  people treat 
these because they can't find a cause of the diarrhea. there is a 
correlation indicating this may help, but no studies show that you can 
infect an animal with these and cause disease. 

they are natural flora 
of a bunch of animals. more commensals than pathogens

giardia 

the 
other common flagellate. this is an intestinal parasite with two nuclei 
in trophozooite stage. does produce a cyst that passes in feces. the cyst 
is seen on fecal exam. cyst is infective to another host. we already went 
over structure in detail so I won't get into that now. they're piriform, 
with two nuclei, and look like faces to me. cyst is almost as large as 
trophozooite, can see axostyle and nuclei in it. these are tiny compared 
to toxocara eggs. they also occur in other animals like cows. eimeria 
oocysts are seen in cow feces
and are larger than giardia cysts. are 
often overlooked.
on the SEM these look like horseshoe crabs to me :)

ventral side has a disclike depression of the membrane. the flagellae are 
clearly seen. organisms reside on intestinal villi. possibly bound by 
interactions with surface receptors, with epithelial glycoproteins, 
probably enhanced by beating of flagellae keeping them pressed against 
villi. 

in heavy infection you can get massive numbers of them covering 
the entire surface in the middle of the small intestine. they live mainly 
in the jejunum, don't like acid so not in duodenum, and is incapable of 
making many lipids, so needs to be in jejunum where cholesterol is high. 


disease: compared to normal intestinal mucosa, affected mucosa has 
flattened villi, short crypts and blunted villi. 

where do we see 
giardia? in this hospital we see it in dogs and cats. it varies year to 
year, but about 5% of the fecals here are positive for giardia cysts. the 
presence of the infection does not mean there is disease. disease usually 
occurs in young animals, puppies and kittens. parasite is noninvasive, is 
on surface of epithelium, causes simple diarrhea, no dysentery, no blood. 
so, a kitten or puppy might come in w/mild diarrhea and steatorrhea is 
also common with giardiasis. the animals generally recover over a few 
months, and it's uncommon to find adult animals exhibiting signs of 
clinical disease, although they may still host giardia parasites. how do 
organisms cause dz? we don't know. there are many possibilities. since 
they live attached to intestinal epithelial villi, they can damage villi, 
and we see blunted villi, so...by adhering to surface may cause 
mechanical damage. there is a lot of evidence that disaccharidase 
activity in intestinal villi is reduced by giardia, so that could lead to 
malabsorption syndrome. one feature that is less common is a stunting of 
growth, failure to gain wt. if young animal has severe giardiasis it will 
not thrive. it may remain stunted. bile salts which are present in 
jejunum in high levels can be used as nutrient source by giardia at least 
in vitro. so it's possible that altered levels of bile salts or 
deconjugation of bile salts could play a role in altered fat metabolism 
resulting in steatorrhea. 

finally, there is some evidence from studies 
in mice that immunodeficient mice w/o T cells have more severe giardia 
infections in terms of numbers of giardia, but do not exhibit the signs, 
including villous blunting, so there may be immune mediated pathogenesis 
of disease as well. eg, cytokines causing dz or whatever. basically we 
have high level of infection in young, non immune animals, causing soft 
stools or frank diarrhea, and a malabsorption syndrome of monosaccharides 
and lipids. animals will often spontaneously recover, or others will show 
continuing signs. dx is by fecal exam and id of cysts. cysts are easily 
distorted by salt and sugar so we use zinc sulfate for floatation. often 
you have to do multiple exams to find these suckers. ten years ago they 
brought some naturally infected cats in and did fecals q 2 days for 40-50 
days and one day the cat would have 100,000 cysts/grm feces, and five 
days later none, and so forth. it varies trememndously from day to day. 
the reason is totally unclear but recent reports say that the organisms 
require cholesterol to form cysts, so it may have something to do with 
that.

tx: metronidazole, quinocrine. tx usually short, 4-5 days, clears 
up most infxns, but there are many reports of animals exhibiting cysts 
within a week of tx. so you have to retest to check on that. and you have 
to test multiple times to be sure. 

where else do we see giardia? in 
kennels and catteries. also, the cysts of giardia are highly susceptible 
to dessication. they are fairly short lived. under optimum conditions 
only survive a couple of weeks. on soil, probably 24 hrs. this is a water 
borne disease. unless cysts are IN water, they die soon. they can be 
killed by bleach. we see dz in kennels/catteries where multiple cats live 
in enclosed area and concrete gets hosed down but leaves puddles. also, 
people will treat a few animals in a group housing situation - you have 
to treat them ALL. also have to have adequate sanitation and dry 
surfaces. 
also, giardia is probably a zoonotic infxn. right now there 
are multiple species, one in rodents, a couple in birds, and one that 
used to be called giardia lamblia but is now called giardia intestinalis, 
which infects dogs, cattle, horses, and humans. not a lot of tranmission 
studies between animals/humans have been done. but giardia cysts from 
humans are infective to dogs/cats...so one should assume until proven 
otherwise that cysts passed by animals are infective to humans.  final 
point - we talked about dogs/cats but it's been shown to cause protracted 
diarrhea in cattle where it is probably missed because people don't do 
fecals on cattle and if one does they will see parasite eggs or coccidian 
oocysts and will overlook giardia. also horses, sheep, goats. probably 
other spp too that we don't know. 

---end----