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parasit.lec.09.11.97
dr johnstone
lecture 10

ASCARIDS AND 
OXYURIS OF EQUINES AND SWINES

superfamily ASACRIDOIDEA (non bursate 
nematodes
large nematodes 
direct and indirect life cycles
predilection 
site: small intestine
Egg+L2 is infective stage
no bursa
male tails often 
coiled, female tails blunt
no buccal capsule

species: 

ascaris suum and 
parascaris equorum

a.suum: si of pigs
p.equorum: si of horses and 
donkeys

a. suum is largest parasite of pigs. females 25-40 cm.
it's very 
common in pigs. it is relatively  non pathogenic compared to other 
nematodes. It can cause serious disease when animals have a heavy worm 
burden, but this is a rarity these days. ascaris infections can be source 
of serious dz in young pigs, though.

live cycle
direct preparasitic 
phase and migratory parasitic phase
preparasitic phase: eggs passed in 
feces. L1 and L2 develop inside the egg (only one molt in the egg). pig 
eats egg+L2. Now, beetles or earthworms can also eat the infective eggs, 
in which case eggs will hatch, and L2 will migrate to the tissue of the 
paratenic host, but will not develop further. so pig could eat infected 
worm or bug as well as just eating egg. then, egg hatches in intestine, 
L2 migrates through wall, when it reaches liver molts to L3, goes on to 
heart, lungs. reaches lungs about 4-6 d post infection. tracheal 
migration, swallowing, bam they're in the small intestine. L3-->L4-->L5. 
females lay eggs - prepatent period 6-8 wks. egg surface is rough and 
thick shelled and ovoid.

parasitic phase: ingestion of L2 in egg, hatch 
in small int, gets to liver via portal vein, to liver, molts to L3, 
lungs, swallow, yada yada, PPP 6-8 wks

PATHOGENESIS:

liver: "milk spot" 
lesions. inflammatory rxn/immune response. necrosis/fibrosis with 
inflammatory infiltrate, eosinophils. liver lesions due to migrating and 
molting larvae. will regress in 4-6 wks so they indicate recent 
infection. 

lungs: migrating L3s cause hemorrhage, intense inflammatory 
infiltrate w/eosinophils. pneumonia. "thumps" or "heaves". also 
predisposition to secondary infections eg swine influenza

signs usually 
seen in young animals 2-5 mos old. older animals develop resistance.


intestinal obstruction (rare): mass of adults and larvae in intestine. 
when pigs were raised outside more, it was more of a problem.

slide: 
normal pig liver.
slide: milk spot lesions. milky white round lesions. 
intense inflammation.
slide: lungs w/intense pneumonia
slide: intestinal 
obstruction w/masses of spaghettilike worms. fairly unusual to see.


EPIDEMIOLOGY:
thick shell, sticky egg - resistant, find it all over

prolific females
eggs highly resistant to drying, can live 5-10 yrs

development to L2 is temperature dependent. there is a visceral larva 
migrans in ruminants that graze pig pastures. a.suum is also zoonotic but 
doesn't usually produce patent infxn.

DIAGNOSIS: young coughing pigs. 
eggs in feces. clinical signs are respiratory. necropsy: milk spots, 
pneumonia, adults in small intestine.

PARASCARIS EQUORUM: the only 
really important ascarid of horses/donkeys.
large worm, can't miss it. up 
to 40 cm long. slide: small intestine of foal that died of colic and 
peritonitis. resulted from rupture of intestine along line of mesenteric 
attachment, due to huge worm mass.

preparasitic phase is direct. thick 
shelled spherical eggs. eggs do not hatch. one molt L1-->L2 in egg. egg + 
L2 is infective stage. earthworms not involved. horses do not eat 
earthworms. eggs resistant, can live long time outside. only susceptible 
to dessication. eggs hatch in small intestine. L2-->portal vein, --> 
liver, becomes L3...heart, lungs, small intestine. just like the other 
one but PPP is a bit longer at ten wks.

PATHOGENESIS

Liver: migrating 
larvae cause milk lesions, no clinical signs

Lungs, bronchi: migrating 
larvae cause pneumonia, nasal d/c, coughing
these signs in young foals 
really indicate parascaris equorum infection. 

small intestine: adults 
can obstruct it and cause impaction rupture, peritonitis, and death. a 
colicking foal would definitely have this on the differential diagnosis 
list.

fecal egg counts do not necessarily correlate with the number of 
adults in the host.

foal A	300 eggs	1120 adults		diarrhea, impaction, 
death
foal B	1100 eggs	562 adults		impaction and death
foal C	6100 eggs	
212	adults		some debilitation

so the egg counts do not correlate with 
the number of adult worms. the number of adults does correlate to the 
clinical signs, at least more than the egg count does.

EPIDEMIOLOGY:

females very fecund/prolific - up to 200,000 eggs/day. long lived eggs 
that survive for years and will stick to everything including mare's 
teats. preparasitic development again is temperature dependent. infective 
stage may develop in less than 2 weeks.

note that you might have a 
coughing foal and no eggs in feces...

OXYUROIDEA (in order oxyurida)


oxyuris equi aka "pinworms"
direct life cycles
predilection site: lg 
intestine of horses.

female has pointy tail - hence "pinworm". 
characteristic double bulbed esophagus characteristic of all oxyurids.


preparasitic part of life cycle is direct. female migrates to anus of 
horse, pokes out, and lays eggs (waving to assembled multitudes...". eggs 
are flattened on one side and are packed together with a fluid secreted 
by the female. to find eggs, do a perineal scraping or take a sample from 
the ground. L1-->L2-->L3 occurs inside egg. L3+egg is infective stage. 
development to infective stage takes 4-5 days in warm, wet conditions.

parasitic phase - no migration. eggs hatch in small intestine, L3 pass 
into lg intestine, migrate to crypts of cecum and colon, hatch to L4, 
then L5, which emerges from crypt. PPP about 5 mos. 

egg is thinshelled 
with mucoid plug at one end and is slightly flattened at one side - very 
subtle, that. 

pathogenesis: mucosal feeding of L4s - erosions, ulcers. 
really this is just a nuisance - causes itchy butt. perineal irritation 
is caused by egg masses - mucous is very irrited to the horse. horses rub 
tails, have intense pruritis. horse develops "rough" appearance to top of 
tail from rubbing on things.  oxyuris infections are much less common 
than they used to be. dx is based on clinical signs. if butt itches, 
probably has it. egg masses on perineum and the diagnostic egg are 
diagnostic.  can treat with any one of many antihelmintics. if you treat 
for strongyles, you'll get this one too. but if you do see this, you need 
to pay a little more attention - wash the perineal areas and treat and be 
careful about hygeine.

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