Zoonotic Diseases
Zoonotic diseases:
– Synanthropic: urban or domestic animal life cycle
• Leptospirosis
• Toxoplasmosis
• Plague
– Exoanthropic: feral or wild animal cycle
• Rabies
• Plague
• Tularemia
Zoonotic diseases:
• Infectious diseases naturally transmitted from
non-human animals to humans
• >250 etiologic agents are known to cause
zoonotic infections
• 40+ involve companion animals
Vector transmitted diseases
• Mechanical vectors
• Biological vectors
• Arboviruses
Vector transmitted diseases
• Changes in geographic distribution
– Introduction or natural migration of vectors
– Altered distribution of natural hosts
– Aberrant feeding patterns of vector, i.e. due to habitat
disruption or destruction
– Introduction of etiologic agent to region with endemic
competent vectors
• Complex life cycles may involve one or more animal
reservoirs
• Confluence of reservoirs, vectors, etiologic agents,
and hosts may be sporadic, stable, or evolving
• biological vector an arthropod vector in
whose body the infecting organism develops
or multiplies before becoming infective to the
recipient individual.
• mechanical vector an arthropod vector which
transmits an infective organism from one host
to another but which is not essential to the
life cycle of the parasite.
Sapronoses = environmentally
acquired infections
• Infections affecting humans and other animals
in which the agent is maintained in nature
(replication in soil, water, feces, decaying
vegetation or flesh)
• Humans and animals acquire infection
independently
• Companion animals can serve as sentinels
Sapronoses
• Fungal infections:
– Cryptococcosis, blastomycosis, histoplasmosis,
coccidiodomycosis
• Anthrax
• Phythiosis
Anthropozoonoses
• Disease agent found primarily in humans, with
animals acquiring infection via human-animal
contact or contact with fomites contaminated by
infected humans:
– Mycobacterium tuberculosis: elephants; non-human
primates; rarely dogs
– Methicillin-resistant Staphylococcus aureus
– Entamoeba histolytica: non-human primates
– Herpes viruses (non-human primates)
Routes of transmission
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Bite or saliva: rabies, tularemia
Aerosol: plague, Q fever
Fecal-oral: toxoplasmosis, salmonellosis
Urine: leptospirosis
Vector borne-diseases: tularemia, plague, Rocky
Mountain spotted fever, equine encephalitis
viruses (EEE, WEE, VEE)
• Consumption of infected meat: toxoplasmosis,
trichinellosis,
Rabies
Rabies
• Rabdovirus family (Rabdoviridae)
• Receptors used for binding, entry, trafficking
in neurons are highly conserved
• Reservoir in many countries = feral dogs
• Reservoir in US: depends on region
– Bat
– Skunk
– Raccoon
Rabies: terrestrial reservoirs in the U.S.
Rabies virus: entry & exit strategies?
Tularemia
• Francisella tularensis
– Gram negative, non-spore-forming, non-saprophytic
coccobacillus/small bacillus
– Disease in humans:
– Normal life cycle (complex, diverse)
• Type A: primarily tick-rabbit
• Type B: complex (ticks, rodents, mosquitos, mud, beavers…)
– Intracellular pathogen
– Very sensitive to dessication, but can survive for weeks in
infected carcass if not desiccated
• Reportable disease: immediate
– classified as catergory A select agent due to potential use as
bioterrorism agent
Q fever: Coxiella burnettii
• Primary reservoir = goats & sheep
– Subclinical infection is common
– Organism is shed in urine, milk, feces
– Causes abortion, high # of organisms in placenta & amniotic
fluid
• Disease in people usually = fever, headache, myalgia, +/vomiting, diarrhea
• More severe cases: pneumonia, myocarditis, hepatitis,
meningitis, encephalitis
• Can cause pre-term delivery or miscarriage in pregnant
women
• Chronic disease: endocarditis, orchitis, osteomyelitis
Coxiella burnetti
• Small Gram-negative rod
• Intracellular pathogen: survives in the
phagolysozome
• Extremely hardy organism – survives for long
periods in environment, resistant to
desiccation, many detergents
Plaque: Yersinia pestis
• Prokaryote = Gram negative rod;
Enterobacteriaceae family, facultative
anaerobe
• Vector = flea; or direct transmission
• Endemic in rodent populations
Yersinia pestis: Black Death
Toxoplasma gondii
Domain: Eukarya
Kingdom: Protista
Apicomplexan
Etiologic agent of
toxoplasmosis
Life cycle of
Toxoplasma gondii
Int. hosts
Definitive
host
Arboviral encephalitis
• Eastern equine encephalitis
• Western EE
• West Nile Virus
Arboviral encephalitis: natural history
Anthropozoonosis
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Methicillin-resistant Staphylococcus aureus
Primary human pathogen
Infections identified in dogs, cats, horses
Risk factor: exposure to infected humans or human medical
health workers
• Canine & feline staph isolates:
– Staphylococcus pseudintermedius
– Staphylococcus schleiferi
Anthropozoonosis
• Mycobacterium tuberculosis
– Acid fast bacterial rod
– Live in macrophages
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Primary human pathogen: reservoir = people
Elephants and non-human primates esp. susceptible
Rare cases in dogs living with infected person
Risk factor: exposure to infected humans
Treatment: financial & ethical dilemmas