PHA 520 - L4 Zoonoses

What is a zoonotic disease?

An infectious disease that can be transmitted or spread between animals and humans.

What types of infectious organisms can cause zoonoses?

Parasites, bacteria, fungi, viruses, and prions.

What are the major routes of zoonotic disease transmission?

Direct contact, indirect contact, vector-borne transmission, and foodborne transmission.

What is direct transmission of a zoonotic disease?

Contact with an infected animal or its saliva, blood, urine, mucus, feces, or other body fluids; includes petting/touching animals and bites or scratches.

What is indirect transmission of a zoonotic disease?

Contact with contaminated environments, objects, or surfaces where animals live or roam, such as pet habitats, aquarium water, chicken coops, soil, and food/water dishes.

What is vector-borne transmission?

Transmission through the bite of a vector such as a tick, mosquito, or flea.

What is foodborne zoonotic transmission?

Infection from eating or drinking contaminated products, such as unpasteurized milk, undercooked meat/eggs, or produce contaminated with infected animal feces.

Why are zoonotic diseases an important public health concern?

They are common, can cause serious illness, permanent disability, or death, and emerging zoonoses are a growing global health threat.

What is One Health?

A worldwide strategy recognizing that human, animal, and environmental health are interconnected and requiring collaboration among disciplines such as medicine, veterinary medicine, pharmacy, public health, ecology, and others.

What are examples of parasitic zoonoses and their animal sources?

Cryptosporidium = cows; Trichinella = pigs/wild game; Baylisascaris = raccoons; hookworms, roundworms, and tapeworms = cats/dogs/wildlife.

How can Cryptosporidium be transmitted to humans?

By accidentally swallowing food or water contaminated with stool from infected animals.

How can Trichinella be transmitted to humans?

By eating raw or undercooked infected meat, especially bear, wild boar, or domestic pig containing Trichinella larval cysts.

How does canine hookworm infection manifest in humans?

Hookworm larvae penetrate bare skin, usually after contact with moist contaminated soil or sand, causing cutaneous larva migrans ("creeping eruption") with red, intensely itchy lines under the skin.

How does roundworm infection manifest in humans?

Ingested eggs can hatch and larvae can migrate through tissues, causing visceral larva migrans; invasion of the eye causes ocular larva migrans and may cause blindness, while invasion of the brain causes neural larva migrans.

What human manifestations are associated with roundworms and Baylisascaris?

Ocular larva migrans (eye; may cause blindness), visceral larva migrans (organs), and neural larva migrans (brain).

How can humans acquire roundworm infections from pets?

Usually by ingesting eggs from contaminated soil, dog/cat feces, or other contaminated substances; children are particularly susceptible.

How can humans acquire Baylisascaris?

By accidentally swallowing soil contaminated with infected raccoon feces.

How are canine tapeworms transmitted to humans?

Human infection is extremely rare and requires ingestion of an infected flea; the flea is the intermediate host.

What are general manifestations of parasitic zoonoses in humans?

Manifestations vary by parasite and person; patients may be asymptomatic or develop symptoms such as diarrhea, muscle aches, and fever, while some parasites can cause skin, eye, organ, or neurologic disease.

What are major routes of bacterial zoonotic transmission?

Animal bites/scratches, fecal-oral transmission, contaminated animal food products, improper food handling/inadequate cooking, vectors, and contaminated soil or water.

What is the most common way zoonotic bacterial infections from pets are transmitted to humans?

Animal bites and scratches.

What causes cat-scratch disease (bartonellosis)?

Bartonella henselae; transmission can occur through cat scratches/bites or contact of cat saliva with broken skin or the sclera.

How can cat-scratch disease manifest in humans?

Papules or pustules at the injury site that may progress to a chronic non-healing wound, fever, and abscess; systemic treatment may be needed in immunosuppressed people.

Which bacteria causing infectious diarrhea in companion animals can be transmitted by the fecal-oral route?

Salmonella, Escherichia coli, Shigella, and Campylobacter.

What are two frequent foodborne bacterial zoonoses?

Salmonellosis and campylobacteriosis.

What is important about Salmonella and non-traditional pets (NTPs)?

Salmonella is the most common bacterial zoonotic infection passed by non-traditional pets; sources include rodents/small mammals, reptiles, fish/amphibians, and backyard poultry.

How is leptospirosis transmitted?

Through contact with contaminated urine, especially in moist environments.

What are examples of vector-borne bacterial zoonoses?

Rocky Mountain spotted fever = Rickettsiae via ticks; ehrlichiosis = Anaplasma phagocytophilum via ticks; Lyme disease = Borrelia burgdorferi via ticks; bartonellosis = Bartonella spp. via flies/lice/sand flies; tularemia = Francisella tularensis via ticks.

What causes plague and what is its zoonotic significance?

Yersinia pestis; it is an important re-emergent wild rodent-borne bacterial disease.

How can zoonotic viruses be transmitted directly?

Through direct contact with an infected animal, such as an animal bite (rabies), or by handling infected animal tissues/materials.

How can zoonotic viruses be transmitted indirectly?

Through vectors such as blood-sucking arthropods that acquire the virus from a reservoir animal and transmit it to another host.

What are examples of viral zoonoses and their transmission?

Rabies = animal bite; Hantavirus = contact with rodent excreta; West Nile/equine encephalitis and other viral diseases may be transmitted by insect vectors; avian influenza is associated with infected birds/animals and contaminated environments.

What role does wildlife play in viral zoonoses?

Wildlife is a major reservoir for zoonotic viruses and can transmit pathogens through insect vectors, animal bites, excreta, or initial spillover into humans.

What is a zoonotic spillover event?

The movement of a pathogen from its primary animal host/reservoir into a new species, such as humans.

What conditions promote a spillover event?

The pathogen does not rapidly kill its primary reservoir host, there is close contact between primary and secondary hosts, the pathogen overcomes species barriers through mutation, and further mutation/evolution occurs.

What is the general progression of zoonotic disease emergence?

Spillover event → repeated small outbreaks in humans → pathogen adaptation for human-to-human transmission.

What factors can contribute to emerging and re-emerging zoonoses?

Global population growth, population mobility, urbanization, human behavior, food preferences/production, companion animals, trade, environmental changes, deforestation, habitat fragmentation, human encroachment, and climate change.

What are examples of common zoonoses transmitted from companion animals?

Rabies, ringworm (dermatophytosis), cat-scratch disease (bartonellosis), scabies, Lyme disease, toxoplasmosis, leptospirosis, intestinal parasites, and Giardia.

What are examples of manifestations of pet-transmitted zoonoses in humans?

Hookworm → cutaneous larva migrans/itchy creeping eruption; roundworm → ocular, visceral, or neural larva migrans; Bartonella → papules/pustules, fever, non-healing wound or abscess; intestinal bacterial infections → diarrhea; ringworm → skin lesions; rabies → severe neurologic disease.

What is the most important general prevention measure for zoonotic diseases?

Wash hands with soap and clean running water immediately after being around animals, even if you did not directly touch them.

What should be used if soap and water are unavailable?

Alcohol-based hand sanitizer containing at least 60% alcohol; wash with soap and water as soon as they become available because sanitizer does not eliminate all types of germs.

What are the major measures for preventing zoonotic disease?

Good hand hygiene; avoid animal bites/scratches; prevent mosquito, tick, and flea bites; safely handle food; wash produce; cook meat appropriately; avoid contact with animal feces; maintain veterinary care, vaccination, deworming, and parasite prevention for pets.

What are the "Four P's" for parasite prevention?

Pick up Pet Poop Promptly, dispose of it properly, and wash hands after handling pet waste.

How can pet care help prevent zoonotic disease?

Keep pets under veterinary care, keep vaccinations current, use regular deworming/parasite prevention, and control vectors such as ticks and fleas.

How can vector-borne zoonoses be prevented?

Use insect repellents, perform routine tick checks after outdoor activity, promptly and properly remove ticks, wear long sleeves and light-colored trousers, and use routine insecticide/parasite treatment for pets.

Who should take extra precautions around animals that may transmit zoonotic infections?

People with weakened immune systems.

What are key companion-animal prevention strategies for rabies, leptospirosis, intestinal parasites, Lyme disease, Giardia, and toxoplasmosis?

Vaccinate pets against rabies and leptospirosis when appropriate; use routine deworming and parasite/tick prevention; and practice good hygiene.

What is the overall take-home message for zoonoses?

Prevention is key: recognize that infections can move between animals and humans, understand the major transmission routes and possible human disease manifestations, and reduce risk through hygiene, safe food handling, vector control, responsible pet care, vaccination, and parasite prevention.