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 • • • • • 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 • • • • 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 • • • • • 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