Parasitic Diseases of Wildlife
Helminths = worms
Arthropods (lice, mites, ticks)
Parasitic Diseases of Wildlife
Helminths - Multicellular eukaryotic animals w/
organ systems
Platyhelminthes = flatworms - flattened from front to back
Nematodes = roundworms – tapered at both ends
Helminths
Distinguishing characteristics of parasitic helminths
1.
2.
3.
4.
May lack a digestive system
Nervous system is reduced
Means of locomotion is reduced or completely lacking
Reproductive system is complex, produce large
numbers of fertilized eggs
Helminths
Generalized Life Cycle
Can be very complex, succession of intermediate hosts for
completion of each larval (developmental) stage of the
parasite and a definitive host for the adult parasite.
Adults may be dioecious – male and female reproductive
systems in separate individuals
Adults may be monoecious or hermaphroditic – male and
female systems in the same individual
Platyhelminthes = flatworms
Trematodes = flukes
Flat, leaf-shaped bodies,
ventral and oral suckers
Common names based on
tissue of the definitive
host where adult lives –
blood fluke, liver fluke,
lung fluke…
Platyhelminthes = flatworms
Cestodes = tapeworms
Head with suckers, flat body,
no digestive system
Nematodes = roundworms
Complete digestive systems
Most species dioecious
2 main categories
eggs are infective
larva are infective
Nematodes = roundworms
Meningeal (brain) worm - Parelaphostrongylus tenuis
Raccoon roundworm - Baylisascaris procyonis
Meningeal worm - Parelaphostrongylus tenuis
Meningeal worm - Parelaphostrongylus tenuis
Definitive Host
Meningeal worm - Parelaphostrongylus tenuis
A – Adult worms in
meninges lay eggs
Meningeal worm - Parelaphostrongylus tenuis
B - Eggs go into
circulation, reach
lungs (C), hatch into
larvae L1.
Meningeal worm - Parelaphostrongylus tenuis
The L1 migrate up
bronchial tree (D) to
pharynx, coughed,
swallowed  feces (E)
Meningeal worm - Parelaphostrongylus tenuis
L1 infects snails or
slugs thru foot  L3,
takes ~3 wks.
Intermediate Host
Meningeal worm - Parelaphostrongylus tenuis
F – S with L3 are
ingested 
abomasum
Intermediate Host
Meningeal worm - Parelaphostrongylus tenuis
Spinal nerves 
spinal cord 
mature 20-30 days
to adults
Intermediate Host
Meningeal worm - Parelaphostrongylus tenuis
Adults migrate to
subdural space 
brain
Intermediate Host
Meningeal worm - Parelaphostrongylus tenuis
From ingestion to
exit of eggs in
feces = prepatent
period
Intermediate Host
Meningeal worm - Parelaphostrongylus tenuis
•
•
•
If infected snails or slugs
are ingested by susceptible
incidental hosts, the L3 are
released in the digestive
tract.
L3 migrate to the spinal
cord and continue to
migrate aimlessly within the
CNS causing neurologic
disease.
Do not develop into adults.
Raccoon roundworm - Baylisascaris procyonis
Raccoon roundworm - Baylisascaris procyonis
Definitive host
Raccoon roundworm - Baylisascaris procyonis
Adults in intestines
lay eggs
Raccoon roundworm - Baylisascaris procyonis
Eggs are shed
with feces
Raccoon roundworm - Baylisascaris procyonis
Over 2-4 weeks the
eggs develop larvae
Raccoon roundworm - Baylisascaris procyonis
Embryonated egg
with larvae is
ingested by raccoon
Raccoon roundworm - Baylisascaris procyonis
Larvae in
intestines develop
into egg-laying
adults
Infection rates
in raccoons
are high – as
high as 70%
of adults and
over 90% of
juveniles
Raccoon roundworm - Baylisascaris procyonis
Embryonated
egg with larvae
are ingested by
intermediate
hosts
Raccoon roundworm - Baylisascaris procyonis
Eggs hatch and
release larvae
into intestines 
gut wall 
migrate thru the
various tissue
causing
considerable
damage and
then encyst
Raccoon roundworm - Baylisascaris procyonis
In the eye 
blindness
Raccoon roundworm - Baylisascaris procyonis
5-7% CNS disease
Raccoon roundworm - Baylisascaris procyonis
Dead
intermediate is
scavenged by
raccoon.
Raccoon roundworm - Baylisascaris procyonis
Emerging zoonotic disease
Dogs may be reservoir
hosts, can shed eggs.
Infective eggs found in
aging feces. Can remain in
the environment for years.
Resistant to all common
disinfectants
http://www.maniacworld.com/raccoon-encounter-with-dog-and-cat.html
Arthropds
Crustacea
Insecta - lice
Arachnids - mites and ticks