Diseases Flashcards
– Infectious diseases have many sources
• Viruses, bacteria, fungi, prions, and protozoans
Disease – Impairment to health
- Physiological or psychological imbalance
- Poor nutritional state
- Stressed state
- Infections
Zoonoses
• Infectious diseases transmitted between animals and
humans
• Wildlife may serve as hosts or vectors
• Constitute over 70% of emerging infectious diseases
– Human-wildlife contact more common
– Outdoor recreation and ecotourism are increasing
• Three factors must be present for any disease
to occur
– Host must be susceptible to disease agent
– Environmental conditions must promote pathogen
stability and viability
– Host and pathogen must come into contact
relatively frequently
• Parasites generally do not kill their hosts
• Parasitic diseases can lead to population
declines
• Parasite-caused extinctions
– Occur in multi-host parasites
– Groups with domestic mammals most susceptible
(Artiodactyla and Carnivora)
– Reducing contact between wild and domestic
mammals may minimize disease
Monkeypox Virus
• Member of orthopoxvirus family
– Creates skin lesions similar to smallpox
– Humans infected via direct contact with infected
animals
– Disease endemic to Central and West Africa
– Bushmeat may be important route of infection
– 2003 US outbreak
• Shipment of infected small mammals from Africa
distributed to pet stores
Ebola Virus
• Ebola hemorrhagic fever (EHF)– a Filovirus
– Rare but often fatal infectious disease
– Discovered in Central Africa in 1976 near Ebola
River
– Causes fever, vomiting, diarrhea, pain, and
internal and external bleeding
– Pteropodids believed to be primary reservoir
Nipah Virus
• Humans suffer neurological problems • Endemic to Malaysia • Viral reservoir includes pteropodids – Large bat roosts spread virus to pigs – Pig farmers contracted disease from sick pigs
Hantavirus
• Hantavirus family of viruses
• Originated in Korea and in western United States
(Sin Nombre virus)
• Muroid rodents reservoir for varieties infecting
humans
– Also found in shrews in United States, Asia, Africa
– Humans infected by aerosolized saliva, feces, urine, or
when bitten
– Most species that host hantavirus do not frequent
urban areas
Rabies
• RNA virus
• Infects endotherms (including humans)
– Infects bats, primates, cattle, and a wide range of
carnivores
– Domestic dogs and cats pick up rabies from
contact with wild animals
• Virus present in saliva of infected animal
– Typically contracted from a bite
Rabies
• Late-stage symptoms
– Acute pain – Uncontrolled movements – Aggressive behavior – Profuse salivation – Inability to swallow water • Eventually results in coma and death
Rabies
• 55,000 human deaths from rabies in 2006
• In Africa, Asia, and Latin America dogs are
primary reservoir
• Pattern of wildlife rabies in the United States
is regional and species-specific
– Raccoons in the mid-Atlantic and Northeast
– Skunks in the Midwest
– Insectivorous bats widespread
Prion Diseases
• Prions
– Misfolded proteins
– Cause neurodegenerative diseases
• Bovine spongiform encephalopathy (BSE)
– “Mad cow disease”
– Suspected link between BSE and human prion
disease
• Variant Creutzfeldt-Jakob Disease (vCJD)
• Outbreaks in Europe and North America
Prion Diseases
• Chronic Wasting Disease (CWD)
– Transmissible spongiform encephalopathy
– Infects deer, elk, moose
– Spreading across western and midwestern United
States since 1967
– Spreads via nose-to-nose contact or contact with
excrement
Bacterial Diseases
• Plague – Bacterium Yersinia pestis – Human infections have led to pandemics – Symptoms include fever, body ache, and nausea – Three clinical forms • Bubonic plague (most common) • Septicemic plague • Pneumatic plague
Plague
• Bubonic plague – Humans bitten by Yersiniainfected flea – Bacteria enter lymphatic system – Cause swellings of lymph nodes (bubos) – Treatable w/ antibiotics if recognized quickly
Plague
• Three major pandemics of plague
– Plague of Justinian in northeastern Africa in the 5th
century
• Killed approximately 25% of humans in the region
– Black Death in Eurasia in the 14th century
• Killed over 200 million people
– Plague pandemic beginning in China in 1855
• Over 15 million deaths
• Plague still exists in rodent populations
Toxoplasmosis
– Protozoan parasite Toxoplasma gondii – Felids primary host (infects most mammals) – Infected cats shed oocysts in feces – Oocysts consumed by new host • Cysts form in muscle and brain tissues • 60 million people in U.S. infected
Other Emerging Pathogens (Nonzoonotic)
• White-nose syndrome (WNS)
– Decimating bat colonies throughout the
northeastern United States
– Discovered in 2006 in caves near Albany, NY
– Characterized by patches of white fungal hyphae
on the face and wings
– Fungus Geomyces destructans grows optimally in
temperatures below 10ºC
• WNS now spread to eight additional states
• Estimated that 90% of bats have perished at
some hibernacula in the northeastern United
States
• Uncertain whether the fungus is the
pathogenic agent or a post-infection symptom
Devil Facial Tumor Disease
• Tasmanian Devil (Sarcophilus harrisii)
• Highly aggressive cancer
– Spreads by contact (devil bites another devil)
– Tumors and lesions spread rapidly
– Fatal within a few months
• First reported in 1996
• Led to 20% to 50% decline in devil populations
