----start----
parasit
11/12/97

note re: lab practical in a couple of 
weeks. it will be covering basically 80% of it will be the second half of 
the course. nematodes will only be about 20% of this lab. but you will 
need to know all the techniques we learned. study materials: AV slides in 
computer room, tick quiz on bobtail.upenn.edu under win95, cal project 
endoparasites of dog is finished, has quiz questions. if you have 
questions please see dr nolan or lok.

ok.
johnstone

pathophysiology of 
gastroenteritis

note re: final. it will be 200 points. if you look at 
last part of course, since last exam, it's about 10 points per lecture 
give or take. that means that as Dr J is writing the question for Dr G 
that he will have 80 points. he's going to allot about 10 points per 
lecture. anthelmintics 10, swine 10, horses (20), ruminant (20 - 10 
cattle, 10 sheep), pathophysiology (20 points - one on ostertagia 
diarrhea, one on hemonchus anemia).

so. pathophysiology of 
gastroenteritis:

pathophysiology describes morphological and 
physiological changes occuring in disease - here, with parasitic 
infections - ostertagia in cattle and haemonchus in sheep. it's the 
morphological and physiological effects parasite has on host.

3 
components of parasitic disease
-parasitic phase of life cycle

-morphological and physiological changes that come from parasite being 
there (both direct and indirect)
-clinical syndrome resulting from the 
pathophysiological changes. 

so these three components are interrelated. 
all pathophysiological changes aren't equal. just because a parasite is 
there doens't mean all possible changes will occur. degree to which 
normal state is altered is determined by numerous factors. 

most 
important - number of parasites present/weight of infection. usually, the 
more parasites, the more serious is the disease. this generally holds 
true, esp for today's examples.
it also depends on the species of 
parasite - worm for worm, some parasites are more pathogenic than others. 
strongylus vulgaris, haemonchus contortus in sheep, these are pathogenic 
worms. trichostrongylus axei or nematodirus are not as pathogenic, worm 
for worm. 
it also depends on the age of the host. physiology changes as 
animals age. there is some innate resistance as well as animals age.

sometimes immune status is linked with age. young animals are more 
susceptible because they are immunologically naive.
immune status itself 
is another factor affecting the degree of pathophysiological changes. 
older, more immune animals will have fewer problems because of parasites, 
will have lighter infections.
nutritional status also affects the degree 
of change. 

interrelationships of disease:
pathophysiologic changes- the 
greater they are, the more severe will be the clinical disease. the 
severity of clinical disease will be related to impairments to 
productivity and resulting economic losses. 
as you might expect, affects 
are most clearly seen in overt cases of parasitic infection, but even in 
subclinical infections (and this is more easily seen in production 
animals) we can often observe marked pathophysiological changes with 
marked effect on productivity, without any overt clinical signs.

the 
kinds of physiological changes we see in infections of the GI tract 
include:

both clinical and pathophysiological:

often we see animals 
anorexic, off feed, or reduced food intake. they stop eating or eat less.


may have pale mms which is often but not always associated with anemia

may have diarrhea
may exhibit weight loss
may have protein losses
may be 
hypoproteinemic and have edema
may have anemia
may have reduced digestion 
and absorption.

Ostertagia and Haemonchus are both abomasal nematodes. 
we're going to discuss them in detail now. 

Ostertagia ostertagi in 
cattle produces ostertagiasis as a clinical syndrome. development of 
parasitic phase takes place in gastric glands of abomasum. emergence of 
L5 onto abomasal mucosa occurs between 17-21 days after initial infection 
of the type seen in young animals grazing for the first time on 
contaminated pasture. 17-21 days later you will see eggs in their feces. 

clinical signs include:
diarrhea, anorexia, inappetance, weight loss or 
reduced weight gain. 
also we see several biochemical changes:
increased 
pH of contents of abomasum
increase in levels of plasma pepsinogen

hypoproteinemia - reduction in serum proteins, esp albumin
remember that 
growth and development of parasitic stages occur in gastric glands. it 
won't surprise you then to know that the effects we see are related to 
the changes in structure and function of the glands. 

a gastric gland 
has two important cell types lining it. parietal cells making HCl and 
zymogen or peptic cells making pepsinogen. pepsinogen is activated by HCl 
to pepsin, which is a functional hydrolytic enzyme in the abomasum. note 
that the normal gland has a closed epithelium. the integrity of this 
epithelium is maintained by things called "zonula occludens" or tight 
junctions between each cell. this is an area of fusion of the lipoprotein 
layers of two adjacent plasma membranes, which prevents flow of any kinds 
of molecules across that epithelial sheet in any direction.  all the 
important changes associated with ostertagiasis occur in the glands. it 
is here that larvae grow and molt twice to become immature adults (L5). 
this causes constant erosion of the epithelium lining the glands, which 
is replaced by rapidly dividing, immature, nonsecretory epithelial cells. 
this is due to compression by the larvae on the secretory epithelium, 
forcing it to be replaced too quickly by immature epithelium. 

slide: 
gland about 10 days after infection - note it is very very dilated, 
contains larva. the growing larva compresses the gland, the gland swells, 
the larva erodes the epithelium, the swelling gland also compresses 
adjacent glands causing erosion of their epithelium even if they aren't 
parasitized. 

slide: gland about 15 days after infection. gland is still 
bigger. 
slide: day 20 - immature adult is popping out of gland returning 
to surface of abomasal mucosa to mature, mate, and lay eggs. so for about 
17 days of the 21 day PPP, larva occupies gland, before returning to 
abomasal mucosa. 

note that you don't have to parasitize all the glands 
to seriously disrupt the epithlium in all the glands. the affected glands 
will press on neighboring glands.

so at this stage, the worms are 
compressing and eroding the glands they are in and the neighboring 
glands, so there is widespread erosion and loss of parietal and zymogen 
cells. you can see the swollen glands grossly as nodules with dark spot 
marking entrance of gastric pit. nodular appearance to heavily infected 
abomasal mucosa.

this causes increase in pH of abomasal contents, 
directly attributed to loss of parietal cells. if you measure the pH of 
abomasal contents, you see it rises rapidly from 2 to 7. so pepsinogen 
isn't activated, proteins aren't denatured, there is loss of 
bacteriostasis
second important change is reduced output of pepsinogen 
due to loss of zymogen cells. you see impaired protein digestion
third 
change - enhanced permeability of abomasal mucosa, which causes rise in 
plasma pepsinogen and hypoalbuminemia.

so, now, we speculate. how do we 
tie all these changes in to the functional changes that occur, and how to 
the functional changes become clinical signs?

a failure to convert 
pepsinogen to pepsin occurs due to rise in pH - it won't convert above pH 
of 5. also, proteins aren't denatured, due to rise in abomasal pH, and 
there is loss of bacteriostatic effect so that bacteria proliferate. this 
is also due to rise in pH.

the reduced output of pepsinogen adds to 
problem digesting protein.

the permeability of abomasal mucosa is 
enhanced because the tight junctions are lossed. molecules can cross the 
epithelial layer because normal epi is replaced by immature, rapidly 
dividing cells - and these cells have not yet formed their tight 
junctions.  therefore, molecules esp small proteins can cross in both 
directions. any pepsinogen that is produced (not 100% lost, some is still 
made) can pass through this epi into the circulation - and we'll see 
elevated levels of pepsinogen in blood. also, plasma proteins can enter 
abomasum. 

so if we make a chart, at about 19 days post inffection there 
is an abrupt rise in pH to about 7. if you look at changes in plasma 
pepsinogen, at about day 14 it starts to rise, it is near a peak at day 
20. these changes closely follow the morphological changes that occur.


clinical consequences - how can we explain clinical signs based on what 
we know about morphological and biochemical changes?

impaired digestion

anorexia/loss of appetite
diarrhea
dehydration (comes directly from 
diarrhea and animals not drinking)
weight loss or poor wt gain

impaired 
digestion occurs due to loss of peptic activity - loss of HCl and 
pepsinogen.

loss of appetite is more difficult. it is related to level 
of infection. it is hard to explain because explanations are obscure. 
ideas include one, we know that nematodes infecting the GI tract of 
ruminants seem to stimulate production of CCK, and that increased plasma 
levels of CCK act centrally to depress appetite. when you see animals 
infected heavily, they are miserable. they show evidence of abdominal 
pain, probably related to the parasites in the glands/erupting. pain may 
be another cause of inappetance but this is sort of conjecture since 
animals don't tell us. 

diarrhea has been reported in all GI nematode 
infections except haemonchus. onset and duration of diarrhea closely 
follows elevation of pH and increased bacterial numbers in abomasum. note 
that as pH rises, and bacteriostatic effect is lost, bacterial numbers 
just explode. additionally, we can fairly logically conclude that there 
are extra osmotically active particles in the GI lumen - the extra 
bacteria and undigested proteins. this will create an osmotic effect, 
moving water into the GI tract to produce diarrhea. note that anorexia 
generally occurs *after* the onset of diarrhea. signs are often acute. 
animal seems fine, then the next day has acute diarrhea, and is 
recumbent. 

this then leads to dehydration.

wt loss can be significant 
in heavy infections. over 7-10 days may see up to 20% wt loss! first, you 
see a loss of proteins through leaky mucosa. you see anorexia and 
impaired digestion. in this case, energy and proteins required to 
maintain vital functions are not coming from food intake or digestion 
which is impaired, they have to come from somewhere, and there is only 
one source of protein reserves in the body - muscle. so the animal will 
use the muscle protein to provide AAs needed to build proteins vital for 
life to continue. if protein mobilization from muscle occurs, weight is 
lost. this isn't news or anything. we know this stuff from other classes. 

note- animals over two years are quite immune. plasma pepsinogen levels 
are not a good indicator of level of infection in these animals. they may 
have a low level of infection, but an increased plasma pepsinogen level 
due to an immune response occuring in the abomasal mucosa. these animals 
only have loss of tight junctions, not loss of secretory epithelium


[he's going off on a philosophical tangent]
ok.

part II of the sermon...


Haemonchus contortus in sheep.

haemonchosis.

this mixture of possible 
clinical and biochemical changes we see includes:

unexpected death

weakness
anemia
pale mucous membranes
hypoproteinemia/edema "bottle jaw"

wt loss or poor wt gain

in situ - small reddish worms about 1 cm long, 
attached to abomasal mucosa, sticking their sharp lancets out of their 
buccal capsule to slit open capillaries which bleed. they secrete an 
anticoagulant to keep it bleeding,and they lap up the blood. they are 
voracious, wasteful blood feeders. sites continue to bleed after worm 
leaves. 

anemia is directly related to blood sucking activity
studies 
using radiolabelling of RBC and protein have shown that avg blood loss is 
0.05 mL/worm/day. labelled rbc's appear in feces 6-12 days after 
infection. this is within the PPP. this means that larvae can also blood 
feed. this is why in a heavy, acute infection, you may see unexpected 
death before finding eggs in feces. 

2000 worms = 100 mL blood loss/day


blood volume of an adult sheep is only about 2 L. so this is pretty 
significant.
it clearly puts a lot of stress on infected animals.


effects on red cells
animals are infected and within 2 weeks we see 
labelled red cells in feces, indicating that before patency, larvae are 
sucking blood. at the same time, we see a big drop in PCV, followed by 
stabilization at a lower plateau. in really heavy infections, animals 
will die without stabilizing the PCV - it will just keep dropping. so 
note the time lag - time needed for erythropoeitic system to make enough 
rbcs to replace those being lost. the plateau represents a state of 
balance. the animal is coping, but circumstances are not good. so, with 
the initial smaller amount of blood loss you get a big drop in PCV, then, 
with the mature infection and increased daily blood loss, PCV is 
maintained at the plateau. the large drop occurs during the time needed 
by erythropoietic system to kick in.

consider all the rbcs normally 
processed daily - a normal sheep replaces all red cells every 4 mos. the 
infected sheep would have to do it every 3 weeks to maintain normal 
hematological indices. this is a huge stress on the sheep. sheep normally 
have low iron reserves anyway. in the face of continual blood loss, iron 
reserves are rapidly depleted. 

so. during the first two weeks after 
infection we see a significant drop in PCV indicating sudden, severe loss 
of red cells. we see blood loss in prepatent period at lower levels than 
during patent infection but still significant. no eggs in feces at point 
of first blood loss. initial drop in PCV reflects a loss of blood, and 
also it reflects the fact that the body is not yet responding to the loss 
- it reflects a stage of unresponsiveness of the erythropoietic system 
during which the system is mobilizing to produce red cells in significant 
numbers to replace those being lost. assuming animal survives past the 
initial drop, it will eventually balance out. with heavy, acute 
infections, there can be sudden death before the erythropoietic system is 
able to kick in fully. 
so, although the sheep is in trouble, once the 
erythropoietic system kicks in it is coping.

after the initial PCV drop, 
when the blood loss increases and PCV plateaus, fecal egg count rises.  
if you then challenge the host with more L3, you activate the self cure 
response. egg counts drop suddenly, blood loss per day drops suddenly, 
PCV stays the same. But then, the second wave begins to mature. you see a 
new drop in PCV, a big leap in blood loss, and a big rise in egg counts. 
these animals may die because the PCV will start going down, but the 
erythropoietic system is exhausted. actually it is more subtle - the 
animal dies of an iron deficiency anemia due to acute shortage of iron. 
as second infection becomes established, blood loss becomes too severe, 
and sheep succumbs. sheep have low iron reserves. they must get iron in 
diet. if not getting enough to produce all these replacement RBCs they 
will die from iron deficiency anemia under these conditions. this is the 
primary reason they die under these second conditions. note with the 
first type, acute heavy infection, they will die due to the lag of the 
erythropoietic system being longer than they can handle. with chronic 
infections, they get the iron deficiency. also note that the self cure 
thing that we describe above occurs naturally when an infected host 
grazes and ingests new L3s. see notes from Farrell's lecture. 

so. in 
the field, we often see chronic haemonchosis 
these animals have 
hypoproteinemia - low albumin levels. initially, there is a large drop, 
and then they plateau at a lower level. the initial decline represents 
the moderate initial blood loss due to bloodfeeding larvae, and then the 
plateau occurs during the stage of increased blood loss with the patent 
infection. why is there a plateau of serum albumin levels? 
the only way 
to compensate for loss of albumin is to increase synthesis. this means 
the body needs to use dietary or muscle sources. so metabolism increases 
dramatically. infected animals have decreased weight gain, but increased 
dietary intake. this looks contradictory - they're eating more and 
gaining less weight. how can this be? reduced growth rates can't be 
accounted for by loss of appetite because they are eating more. it is 
physiological. to maintain needed levels of plasma proteins and 
hemoglobin in the face of massive blood losses, available AAs are 
diverted away from muscle and toward liver and bone marrow. so they are 
eating more but they are not gaining as much wt. all the protein in the 
diet is replacing blood components. these animals with chronic 
haemonchosis 
are not anorexic. they are eating. they are not losing wt - 
they just aren't gaining much, because they are diverting their protein 
intake towards synthesis of blood components instead of toward growth/wt 
gain.

similar things are seen in cases of hookworm in dogs,which also 
causes blood loss.

these sheep have pale mms. 
they have bottlejaw
how 
do you explain the edema? starling's principles, exchange of fluid at 
capillary levels, loss of protein, decreased colloid osmotic pressure, 
increased hydrostatic pressure... increased flow of fluid into ECF at 
arterial end, and not drawn in at venous end due to reduced colloid 
osmotic pressure
again - you can see these effects, you can relate it 
back to physiology. you can explain why you have edema b/c you know 
animal is hypoalbuminemic. 

ok.
----break---

REVIEW
we are now entering 
the review phase. quick ten minute review.

anthelmintics:

the ideal 
anthelmintic principles:
broad spectrum (for nematodes and arthropods)

nontoxic
wide safety margin
rapid metabolism and excretion (get out of 
the body ASAP)
zero/minimal meat/milk residues
easy to administer 
(otherwise people won't buy them)
cost effective (otherwise people won't 
buy them)

know these principles, be able to list them.  all seven of 
them.

all other things being equal, which two are most important from 
economic point of view? consider breeding sows maintained indoor on 
cement. must be *easy to administer* because a breeding sow is hard to 
handle. also must be *broad spectrum* because adult pigs on cement have 
the problem of *mange* which isn't seen as much outdoors. you'd want a 
wide safety margin in any case. residues don't matter, she's not a food 
animal. 

beef cattle on pasture in september in louisiana destined for 
slaughter within 6 weeks. need *minimal residues* and *easy to 
administer* (beef cows tough to catch when they're out on pasture) and 
also, could be *broad spectrum* since there are lots of flies and stuff 
at that time of year in louisiana.

he says a drug should always be cost 
effective, so you wouldn't choose that answer. you have to consider the 
question as "all other things being equal" what are the most important 
factors...apply it to the specific situation. cost effective applies to 
all cattle. 

remember  -  right tool, right time, right treatment

so 
there are general properties but when applying to specific situations, 
choose the ones that are most applicable to that situation. choose what 
is most important for your particular situation. 

a recent innovation in 
administration of anthelmintics in cattle are pour on avermectin products 
that are absorbed via the skin. this is a revolutionary step. what are 
three advantages to the use of these products?
-broad spectrum
-easy to 
administer
-very wide safety margin
they're convenient, safe, easy to 
use. that makes them good. 

what is one important factor that limits 
potential effectiveness of these preparations? -rain.

but, eprinomectin 
offers two advantages over the other two products - 
-gets absorbed 
rapidly so won't wash off
-zero milk and meat withdrawal time

so, there 
is much to know about these drugs, but this is the really important stuff 
leading you to make decisions about using them in large animals. you can 
create scenarios in small animals the same way. you can't just memorize 
stuff you have to USE it. transform your facts into knowledge.

briefly - 
swine parasites:

ascaris suum, isospora suis, trichuris suis, sarcoptes 
scabei, oesophagostomum dentatum, hematopinus suis, strongyloides 
ransomi, metastrongylus apri, hyostrongylus rubidus, trichostrongylus 
axei, stephanurus dentatus

which ones *increase* in prevalence when 
operation is moved from outdoors to indoors?

sarcoptes scabei, isospora 
suis, hematopinus suis, and strongyloides ransomi (s.ransomi: because 
neonates get patent infections from mom and then pass eggs into crowded 
environment and there is constant reinfection).


you should know enough 
about these to make this leap of judgement. 

think of breeding sows, 
outdoors, using the same list of parasites, which two have the highest 
prevalence in adult outdoor breeding sows?
ascaris suum and trichuris 
suis (both have larva develop in eggs that last years within soil) these 
are the most common parasites in pigs raised outdoors.

in treating pigs 
for parasites, there are several routes of delivery - injection, feed 
additives, oral pastes. which is best from producer's point of view? the 
feed. from a parasitological point of view, can you defend that? no. 
explain. well, it's dubious from a parasitological point of view, because 
when you deliver a drug in the feed you have potential underdosing or 
overdosing of individuals, and because from a veterinary point of view, a 
common clinical sign is inappetance, and if the pigs are sick and not 
eating, they're not going to get any of the drug. so delivery of 
anthelmintics in feed is only appropriate for prevention, never for 
treatment. if you look at past final exams, this is the sort of theme 
that he likes to ask. you shouldn't be purely memorizing things. you have 
to use the information to make choices, solve problems, give answers. 
that is how these questions on this exam will be written. 

one question 
about ostertagia pathophysiology
one about haemonchus
he likes to ask 
about the "paradox" of animals which eat more food but don't gain weight. 
be able to explain that. protein metabolism - protein intake diverted to 
synthesis.

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