Download Wildlife Diseases

Are you prepared to be grossed out?
• mortality factor in dense populations
• threat to endangered/restricted species
• human and domestic animal health
– rabies, brucellosis, Lyme disease, etc.
A definition of DISEASE…
•any departure from health
•disturbance of normal bodily function or
structure
•zoonosis– disease of animals transmissible
to humans
• Infectious/Parasitic
– microparasites-viruses, rickettsiae, bacteria, fungi,
protists
– macroparasites-worms, arthropods
– prion diseases
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Toxic substances
Physiological
Nutritional deficiency
Congenital
Degenerative
Trauma
• The study of the incidence and control of disease and
epidemics
Occurrence - pattern of disease in time and space
– prevalence: proportion (or %) infected at a given time/place
– incidence: number of new cases per unit time at a place
Susceptibility
– Susceptible
– Infected
– Infectious – capable of infecting other hosts
– Immune
Virulence – speed & severity of symptoms
Enzootic – constantly
present in the population at
some predictable rate
(usually low); usually low
morbidity.
Epizootic - occurs at
greater than normal level,
often with high morbidity
and/or mortality.
Transmission - spread from infectious to susceptible hosts
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vertical-from parent to offspring
horizontal-other than parent to offspring
direct-agent is spread via contact
indirect-agent is spread by contaminated food or water
vector-borne
Vector – animal that physically carries the disease agent
from host to host
– e.g., ticks are vectors of Lyme disease
– can you name others?
Reservoir – host that sustains a disease agent
– e.g., mice are reservoirs of Lyme disease
– often experience low morbidity/mortality themselves
• an infectious disease will only spread if each
infected individual (on average) infects > 1 other
individual in its lifetime
• highly virulent agents cause rapid death, so
there is less time to infect others, e.g. Ebola
• for most diseases transmission is densitydependent
Defined-the probability of becoming infected increases with
the density (#/area) of infectious animals
– increased number of contacts of individuals
– reduced immune system competence due to fewer resources &
more stress
Factors that cause animals to be concentrated in space
can increase opportunities for disease
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habitat fragmentation
concentrated food or water sources (e.g., artificial (bird) feeders)
overpopulation
captivity
breeding aggregations
Myxomatosis: used to try to control exotic
rabbits in Australia (start 1950)
– caused immediate crash in rabbit population
– but rabbit populations recovered somewhat
– rabbits evolved resistance
– virus evolved toward less-virulent form
Current research: genetically engineer herpes
– viruses to stimulate immune response to zona
pellucida proteins
– Brushtail possums in New Zealand
– Red Foxes in Australia
Infectious
Caused by pathogens
• Bacteria
• Viruses
• Rikettsiae
• Parasites
• Fungi
Bacterial Diseases
Avian Botulism
Clostridium botulinum, an anaerobic bacterium
Major Botulism Outbreaks in N.A.
Avian Botulism
1. Inability to fly—’steaming’
2. Paralyzed nictitating membrane
3. Paralysis of neck muscles; can’t
hold head erect; drowning
Rickettsia
• Bacterial, intracellular parasites
• All transmitted by arthropod vectors
• Humans are accidental/incidental hosts
Rickettsiae
Disease
Organism
Vector
Reservoir
Rocky Mountain
spotted fever
Rickettsia rickettsii
Ehrlichiosis
Ehrlichia chaffeensis
E. erwingii
Tick
Anaplasma
phagocytophilium
Deer
Deer
Small mammals
Rickettsialpox
R. akari
Mite
Mites, wild rodents
Scrub typhus
R. tsutsugamushi
Mite
Mites, wild rodents
Epidemic typhus
R. Prowazekii
Louse
Murine typhus
R. typhi
Flea
Wild rodents
Q fever
Coxiella Burnetii
None
Cattle, sheep,
goats, cats
Tick
Ticks, wild rodents
Humans, squirrel
fleas, flying
squirrels
Rocky Mountain Spotted Fever
American dog tick
(Dermacentor
variabilis)
Rocky Mountain Spotted Fever
•Most common rickettsial disease in US
•Principal reservoir is a hard tick
•Most cases April-September
•Inactive rickettsia are warmed by
blood meal, get into saliva; hence,
prolonged bite increases transmission
likelihood
•Wild rodents infected, but not main
reservoir host
The ‘spots’
•Symptoms: abrupt onset of fever,
chills headache and myalgia usually 212 days after the bite
•Mortality rate in untreated patients is
20%
Parasitic Diseases
Parasitic Life Cycles
• Several different kinds of hosts
– Definitive-where they reach sexual maturity
– Intermediate
• Reservoir
• Dead end
• May be endo- or ectoparasites
Ichthyophthirius
A ciliated protozoan
Black Spot/Black Grub
•complex life cycle requires fish-eating birds or mammals,
snails, and fish at different stages
•encysted larval stage of one of several flukes
•even heavy infestation does relatively little damage unless
on gills, eyes, or very young fish
•common in our creek
Botfly life cycle
Tapeworm
Taenia pisiformis
Taenia pisiformis
Cysticercosis
• In rabbits, appears as conspicuous spots on the liver (sometimes
confused with tularemia)
• Dogs and related carnivores are host to the adult tapeworm.
• Eggs are passed out of the body in the feces.
• Rabbits are the major intermediate host; become infected when the
eat vegetation contaminated with the eggs.
• In digestive tract eggs develop into parasites that penetrate the gut
wall and travel to liver via the blood stream.
• In the liver tissue for a number of days, they break into the
abdominal cavity where they attach to the surface abdominal organs
and complete development into cysts.
• The cyst stage is as far as these tapeworms develop in rabbits. If
eaten by a dog or other suitable carnivore, the tapeworms will then
continue their development to maturity.
Cysticercosis in Humans
Sarcoptic
Mange
Sarcoptes scabiei
•mite parasites of squirrels, rabbits,
foxes, dogs, humans, and many
other mammals
•larvae and adult mites eat skin cells
from their hosts
•mate on the surface of the host's
skin
•cause allergic reaction w/intense
itching and often bald spots
•often leads to secondary infections
Deer Liver Fluke
Fascioloides magna
•Often fatal in sheep
•In cervids, are encapsulated,
thus restricting migration
•Usually fairly well tolerated
in deer
Whirling Disease
• introduced from Europe
• serious problem in hatcheries
• pathogen is Myxobolus cerebralis, a metazoan
parasite
• penetrates the head and spinal cartilage of fingerling
trout where it multiplies very rapidly, putting pressure
on the organ of equilibrium
• causes the fish to swim erratically (whirl), and have
difficulty feeding and avoiding predators
Toxic Substances
• Pesticides
– Chlorinated hydrocarbons a.k.a. organochlorines
• Lipophilic, attack CNS, persistent, mobile, biomagnify; some may mimic
action of sex hormones
• Examples: DDT (banned), aldrin, dieldrin, endrin, chlordane, heptachlor,
toxaphene (banned)
• PCP (PolyChlorinated Biphenyls)-not a pesticide; banned in 1979
– Organophosphates
• Less persistent than organochlorines
• Associated with secondary poisoning, e.g., hawks die after eating poisoned
grasshoppers (the target species)
• Examples: malathion, parathion; inhibit acetylcholinesterase
– Carbamates
• Less persistent, hence less biomagnification; also inhibit Ach-ase
• Example: Fenoxycarb-inhibits insect metamorphosis; e.g., Temic, Sevin,
Furadan
– Bacillus thuringiensis (Bt)-not toxic to animals, but may affect their prey,
e.g. silkworm moths and Whip-poor-wills
Toxic Substances
• Herbicides
– Of course, animals are non-target species;
may have direct toxicity or indirect effects
such as defoliation
– Examples:
• Trifluralin (mallards)
• 2, 4-5 T-little effect on mallards
• Paraquat-very significant effects
Mercury Poisoning
• used in the past as the active ingredient in ointments,
parasiticidals, antiseptics, disinfectants, diuretics and
fungicides
• current major source is coal-burning power plant emissions
• bioaccumulates in fish and fish-eating animals. Inorganic
mercury is readily converted to methyl mercury by aquatic
microorganisms and accumulates in the tissues of fish. The
Common Loon, mink and otter have been poisoned by
mercury as a result of ingestion of mercury contaminated fish.
• reported to cause abnormal egg laying behavior, impaired
reproduction, slowed duckling growth, and altered duckling
behavior in mallard ducks. Occasionally seed eating birds are
affected by mercury toxicity after feeding on mercury
fungicide treated seed.
Lead Poisoning
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ingestion of spent lead shot or fishing sinkers and jig heads during normal feeding activities.
in the acidic environment of the gizzard (ducks, geese and swans) or the ventriculus (loons),
it is worn down, dissolved, and absorbed into body tissues.
also been noted in small mammals (raccoon) and raptors, presumably from the ingestion of
lead contaminated prey.
toxic levels in the tissues cause muscle paralysis and associated complications result in
death.
mimics the movement of calcium.
symptoms include lowered food intake, weakness, weight loss, drooping wings, inability to
fly, and green watery diarrhea.
secondary "non-lethal" effects of lead such as reproductive problems, increased
susceptibility to disease and infection, and increased predation due to anemia and weakened
muscles.
switch from lead to non-toxic shot has significantly reduced the number of birds dying from
lead poisoning in the U.S.
• #1 vector-borne disease of humans in North
America (13,000 – 18,000 U.S. cases / year)
• caused by spirochete, Borrelia burgdorferi
• transmitted by the blacklegged tick, Ixodes
scapularis
• White-tailed deer is the host for adult ticks
• White-footed mice is the host for juvenile ticks
and reservoir of B. burgdorferi
Lyme Disease Cycle
Gray Squirrels (Sciurus carolinensis)
• were introduced to UK in 1800s
• have spread over much of the country, with
matching declines in the native Red Squirrels (S.
vulgaris) (not the same as our Red Squirrel,
Tamiasciurus hudsonicus; see photo next slide)
• weak direct competition
– grays do better in deciduous woods
– reds do better in coniferous
European Red Squirrel, Sciurus vulgaris
Parapoxvirus is common in North American
squirrels
– Gray Squirrels are essentially unaffected
– European Red Squirrels highly susceptible
– severe lesions and >30% weight loss after 2-3
weeks
Antibodies to parapoxvirus never been
found in living wild Red Squirrels, only in
those already dead from the disease
Roundworms, Raccoons and Rats
Allegheney Woodrat, Neotoma magister
Raccon Roundworm, Baylisascaris procyonis
Roundworms, Raccoons and Rats
Allegheny Woodrat (Neotoma magister)
– once widely distributed in northeast
– have declined greatly in some areas
– are “pack rats”, collect & store, including raccoon
feces in food caches
– highly susceptible to Baylisascaris procyonis
– worm eggs can persist long time in cached feces
– woodrats tend to take over vacant dens
Raccoon roundworm (Baylisascaris procyonis)
– definitive host is raccoon, (Procyon lotor)
– lives in intestine
– eggs excreted with feces
Roundworms, Raccoons and Rats
LoGiudice, 2003
– reintroduced
Allegheny Woodrats
to four locations in
New York and New
Jersey
– survival was
negatively related to
abundance of
infected raccoon
latrines
– all reintroduced
populations failed
within 2 yrs.
…and now, it’s your turn!