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

• 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 – not infected or immune– 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– 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

Reservoir – host that sustains a disease agent– e.g., mice are reservoirs of Lyme disease– often experiences low morbidity/mortality

• 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 density-dependent

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 spacecan increase opportunities for disease

– 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

http://upload.wikimedia.org/wikipedia/commons/4/49/Rabbits_MyxomatosisTrial_WardangIsland_1938.jpg

Infectious

Caused by pathogens

• Bacteria

• Viruses

• Rikettsiae

• Parasites

• Fungi

Bacterial Diseases

Avian BotulismClostridium 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 Tick Ticks, wild rodents

Ehrlichiosis Ehrlichia  chaffeensisE. erwingiiAnaplasma phagocytophilium

TickDeerDeerSmall mammals

Rickettsialpox R. akari Mite Mites, wild rodents

Scrub typhus R. tsutsugamushi Mite Mites, wild rodents

Epidemic typhus R. Prowazekii Louse Humans, squirrel fleas, flying squirrels

Murine typhus R. typhi Flea Wild rodents

Q fever Coxiella  Burnetii None Cattle, sheep, goats, cats 

Rocky Mountain Spotted Fever

American dog tick (Dermacentor variabilis)

Rocky Mountain Spotted Fever

The ‘spots’

•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

•Symptoms: abrupt onset of fever, chills headache and myalgia usually 2-12 days after the bite

•Mortality rate in untreated patients is 20%

Parasitic Diseases

Parasitic Life Cycles

• Several different kinds of hosts– Definitive– 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

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 FlukeFascioloides 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

http://upload.wikimedia.org/wikipedia/en/4/45/LifeCycle%28Myxobolus_cerebralis%29.jpg

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)

– 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

• 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

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.

Roundworms, Raccoons and Rats

…and now, it’s your turn!