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Wildlife Biology
Updated 26 August 2009
Bolen and Robinson (2003) Ch. 8 – Wildlife Diseases
pathogens – infectious, disease-producing agents (e.g., bacteria, viruses, rickettsias,
parasites, fungi)
disease – any prolonged, serious deviation from the normal condition; an abnormality
that prevents an animal from living and reproducing in a normal manner
etiology – study of the cause of disease; natural history of the disease; mainly causative
studies
epidemiology – study of epidemics – cause and spread; study of outbreaks of disease,
statistics of spread and devastation
endemic –localized; inherent to a local population (i. e., it is usually in that area all the
time)
parasitic disease – host and parasite usually have a long evolutionary history; parasite
lives off host (but host usually lives an almost-normal life)
reservoir –population where a disease is either dormant or active, but it can serve as a
place to infect or reinfect other animals (sort of a “storage” place for the disease)
vector – any organism that carries and transmits pathogenic microorganisms from one
host to another; commonly an insect or arthropod
disease/parasites – can often weaken an animal or get a foothold because the animal is
already weak from something else
This chapter largely addresses epizootiology, the “how” and “why” of diseases in either
their enzootic (chronic) or epizootic (eruptive) states in wildlife populations.
Enzootic – the chronic level of disease frequency, that is, a low but constant occurrence
of a disease in a population.
Epizootic – outbreak of disease in an animal population; large numbers of animals die in
a short period.
Why Study Wildlife Disease? - read this section – very interesting; mentioned
many diseases including the following:
- 22,000 mule deer shot when outbreak of foot-and-mouth disease (in 1925-26 in
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California)
brucellosis – and the Yellowstone herd
tsetse flies – carrying sleeping sickness in Africa – hooved wildlife killed to try
and control the flies
avian cholera
kill mosquitoes in sensitive wetlands
Know Table 8-1 --- “Selected Diseases of Wildlife” excellent table that lists diseases,
main target species, and characteristics of the disease
Parasitic Diseases:
sarcoptic mange – see table
liver fluke (Fascioloidea magna) – found in deer; not usually fatal; quite noticeable in
northern tier states – Minnesota, Michigan; can affect cattle – more serious in them;
deer serve as reservoirs for flukes that infect livestock
- clay soils hold water; this allows a snail (which is the intermediate host) to
live and perpetuate the disease; sandy soils are better – harder for the
parasites to survive
brainworm – (Pneumostrongylus tenuis) – parasitic nematode that matures in meninges
of the brain; in deer, it causes little harm; however, in moose, it is usually fatal (it
damages the CNS, paralysis, death)
duck malaria – (Leucocytozoon simondi) – blood parasite transmitted by blackflies;
waterfowl are carriers; it often kills young birds – it attacks the blood cells, causing
anemia
Bacterial Diseases:
Brucellosis – (Brucella abortus) – see Table 8-1; cattle can pick it up and transmit it to
humans by milk; it is called undulant fever in humans
Leptospirosis – similar to brucellosis; in ungulates; can infect cattle
Tularemia – (Francisella tularensis) – “rabbit fever” – can be passed to humans by body
fluids or blood; passes from rabbit to rabbit by ticks (hunting seasons are set for later in
the year when most vectors have died; this lessens the chance of infection of humans)
Botulism – (Clostridium botulinium) – read in book; know life cycle in Fig. 8-5; dead
invertebrates and maggots harbor the toxin; ducks ingest it and die; make more
carcasses for maggots to infect – keeps the cycle going
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Viral Diseases:
Epizootic hemorrhagic disease (EHD) – (found in white-tailed deer in 1955)
- lesions throughout body, especially in the GI tract, also heart, lungs, liver,
kidneys, spleen
- terminal signs – bloody urine, labored breathing
- they think it has an arthropod vector (midge)
- animal usually dies within 3-4 days
- external symptoms – loss of appetite, weakness, salivation, fever,
hemorrhages of oral cavity; coma and death follow 3-36 hours of these
symptoms
- especially affects deer – up to 90% mortality of infected animals;
- read in book
Encephalitis –
- arthropod vector – mosquito
- equine encephalitis – can cause death and illness in children- can cause
permanent damage to nervous system – not as severe in adults (usually) –
drowsiness, GI tract disturbances
- often large areas are sprayed for mosquitos
rabies – virus is transmitted in saliva; most common in skunks, foxes, bats, raccoons
- 3-8 weeks incubation in dogs, less in smaller animals; more in humans (30-60
days)
- 3 phases of rabies:
o prodromal phase –
 incubation period
 subtle changes in behavior – not very noticeable
o excitative phase –
 “furious” phase (not all animals show this phase)
 dogs roam, fight, attack
 close to death
o paralytic phase –
 ends in death; laryngeal musculature is paralyzed, cannot
swallow oral secretions (hence the saying “foaming at the
mouth”
- some animals show no clinical signs – just crawl into a hole and die
- there is no cure for rabies once the pathogens have begun to grow (i.e., after
the incubation period)
- in the recent past, humans could get rabies shots in the abdomen; however, a
recent article about the human case of rabies in Oct 2000 said that humans can
now get the shots in the arm (however, the shots must be given very soon after the
person has been exposed to rabies or they do not work)
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Diseases and Biological Controls
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European rabbit (Oryctolagus cuniculus) was introduced into Australia in
1859. (They actually tried several times before this to introduce this species,
but efforts failed.) Populations exploded- helped “overgraze” the range,
contributed to erosion; competed with sheep for food
myxomatosis (a pox-virus) was introduced in 1950 to control the rabbits; it
killed off many rabbits while having little impact on native marsupials
myxomatosis – is spread by a variety of arthropods, especially mosquitos
the natural host for myxomatosis is Sylvilagus sp. – the pathogenic effects are
“self-limiting”
right now, rabbits and the disease seem to be “co-evolving”; some rabbits
survived and developed resistance; current strains of disease seem to be less
virulent
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another disease, rabbit calicivirus disease (RCD), is currently killing
rabbits in Australia; it appeared mysteriously in China in 1984, and then
spread in Asia and into Europe
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RCD causes extensive internal blood clotting, lapsing into a coma, and death
within 36 hours
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in 1995, RCD was undergoing host-specificity tests on an island off Australia;
disease escaped accidentally and hit the rabbits on the Australian mainland
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so far, disease seems only to be killing the rabbits, but wholesale killing of
rabbits might cause other ecological problems --food base gone for some
predators, lots of decaying carcasses; might cause more sheep grazing if
rabbits are gone (more erosion and overgrazing); on the other hand, some
native plants that have been suppressed by the rabbits might recover when the
rabbits are gone
2.
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Bighorn sheep are susceptible to bluetongue or “soremuzzle” – also infects
a variety of wild and domestic ruminants (e.g., white-tailed deer, elk,
pronghorn, sheep, goats)
they think domestic sheep flocks carry it to bighorn sheep
they tried using gnats as “mobile syringes” to vaccinate bighorn sheep- they
give the gnats a blood meal of bluetongue vaccine before they release them
(this species of gnat is the natural vector of the disease)
“New” Diseases
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Hantaviral pulmonary syndrome (HPS)– outbreak in New Mexico a few years ago;
hantavirus is carried by small rodents, mainly deer mice, but also by pinon mice, cotton
rats, and cliff chipmunks
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humans can get it by inhaling or ingesting dust contaminated with urine or
feces from infected mice; often fatal in humans; lungs and other organs stop
working; when humans get it, it is often indoors where the urine/feces are in a
more enclosed area and concentrations can get high
Conjunctivitis in songbirds – caused by the microorganism, Mycoplasma gallisepticum,
not found until recently in wildlife populations; the infection causes respiratory disease
in domestic poultry and other pen-reared birds
- in house finches, it produces conjunctivitis characterized by crusty, swollen
eyes; first found in house finches in mid-Atlantic states in 1994; has now
spread across eastern half of North America (might be spread at birdfeeders)
- has now also been recently detected in American goldfinches (but do not yet
know the extent of the disease)
West Nile Virus – gets its name from the region in Uganda where it was initially in
1937. In 1999, cases suddenly appeared in humans in New York City and the disease has
since spread. They think it got carried to the US by an infected migrating bird or a
imported bird. Transmitted by mosquitoes from bird to bird or from birds to humans.
Can cause encephalitis in humans.
Mad Cow Disease – or bovine spongioform encephalopathy (BSE) – is one form of a
group of infections known collectively as TSE, transmissible spongioform
encephalopathies. Pathogens responsible for TSE are prions – short for proteinaceous
infectious particles – lack DNA and thus do no reproduce genetically as do bacteria or
viruses- destroys brain tissue.
Chronic Wasting Disease (CWD) – is a type of TSE – spreading in elk and deer. See
notes from talk.
Lyme Disease – is now the most commonly reported arthropod-borne disease of
humans in US
- 89,000 cases in 49 states and DC between 1992 and 1998, with an increase
from 9896 cases in 1992 to 16,802 in 1998.
- pathogen is a spirochete bacterium, Borrelia burgdorferi, which is transmitted
in the NE US by the deer tick, although other vectors are known
- the disease gained national attention in 1975 when an unusually high
incidence of “juvenile rheumatoid arthritis” was mistakenly diagnosed in
Lyme, Connecticut
o causes bulls-eye rash around site of bite (but not always)
o joint pain
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o in advanced stages, attacks of arthritis, abnormal heart rhythm, and
neurological difficulties
o symptoms might not appear for several weeks or months
o treated with antibiotics
deer are the hosts for adult deer ticks; but deer are not reservoirs for the
spirochetes
deer ticks are often carried on white-footed mice and deer mice and they
serve as reservoirs for the spirochetes; they think that ear tags may have
increased the incidence of deer ticks because the mice have a harder time
grooming their ears when they have tags and/or the tagged ears attract the
ticks
read about more details of tick life cycle in book
Wildlife Diseases and Humans
Plague:
- about 20 million people died of the “Black Death” (bubonic plague) in the
14th century (about 1/3 of the population of Europe died)
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sylvatic plague in animals is caused by the same pathogen that causes
bubonic plague, i.e., Yersinia pestis (a type of bacterium)
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sylvatic plague is carried by fleas and is often found in communal rodents like
prairie dogs or certain kinds of ground squirrels (although many other animals
can carry the fleas also)
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burrows of these rodents can sometimes harbor the fleas; entire prairie dog
towns are sometimes treated for fleas (but as you can imagine, this is hard on
the whole ecosystem)
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people can get the sylvatic plague from prairie dogs or other animals;
however, if caught early enough, it can be treated with antibiotics
Tularemia - humans can get it from skinning rabbits – see above
(some rabbits found in West Fargo a few week ago were believed to have had
tularemia)
Rabies – see above -- read more in your book – lots of interesting details and
implications for wildlife management