ZOONOTIC DISEASE HISTORY

Of the worlds’ new and emerging diseases, approximately 75% are zoonotic!!

These emerging infectious diseases make the role of the veterinary health care professional extremely important!

Veterinary health care professionals help prevent disease in animals and humans.

Besides producing diseases in humans, zoonotic diseases can affect the food chain – for example Brucellosis.

The environment may also affect zoonotic diseases. For example, changing ecosystems have resulted in an increase in tropical diseases.

With the domestication of animals, changing culture has played a role in the development of zoonotic diseases.

Human disease itself has played a role in the increase of zoonotic disease!!! With the increase of immunosuppressive conditions and drugs (chemotherapy and HIV) physicians are concerned that their patients with pets may be more susceptible to zoonotic disease.

There are more than 150 known zoonotic diseases, however fewer than ½ of them are clinically significant.

(Think ‘The Black Plague”, tuberculosis, Lyme disease)

Term: Sentinel

A domestic animal host for a particular disease that is placed at various locations to determine the potential for human exposure to a particular disease.

Chain of Infection

Pathogen

Susceptible Host Reservoir

Portal of Entry Portal of Exit

Mode of Transmission

Reservoir: an animate (living) or inanimate (non-living) object that serves as a long-term habitat and focus of dissemination for an infectious agent.

Living reservoirs include humans, animals and arthropods (insects, arachnids, crustaceans)

Vector: any live animal that transmits an infectious agent from one host to the next (typically used to describe arthropods)

Biological Vectors: actively participate in a pathogen’s life cycle, serving as a place where the pathogen multiplies or completes its life cycle.

Infectious agents are spread via injecting infected saliva into blood,

defecating around the wound, regurgitating blood into

the wound bite, aerosol formation or touch

Ex: mosquitoes, fleas, ticks

Mechanical Vectors: are not necessary for the life cycle of the pathogen

and are passive participants in the transmission

of disease.

Spread disease when their external body parts

become contaminated through contact with the

pathogen.

Transferred to human or animals indirectly by an

intermediate such as contaminated food or

directly by contact between the contaminated

body part and a mucous membrane or skin

surface

Ex: houseflies, cockroaches

Non living reservoirs :

air

soil

dust

food

milk

water

fomites (objects that are able to transfer disease organisms)

Transmission:

Direct transmission – the immediate transfer of an infectious

agent from a reservoir to a susceptible host

Ringworm

Indirect transmission: the transfer of an infectious agent carried from a

reservoir to a susceptible host.

West Nile Virus

Direct and Indirect transmission occurs by a variety of mechanisms:

* Contact: occurs through touch and may be either direct or indirect

Ex: a human touches the skin lesions of a ringworm positive cat

and then transfers the ringworm. (direct)

Ex: a person touches the skin of a ringworm-positive cat then

touches another cat transferring the fungal spores to the

second cat that then gets ringworm (indirect)

* Airborne droplets of respiratory secretions may contain pathogens

and have the ability to spread disease via aerosol.

Ex: sneeze or cough from the infected animal to an uninfected

animal (direct)

Ex: sneeze that contaminates a ventilation system that eventually

infects an animal/human (indirect)

* Placental transmission occurs from mother to offspring and is

form of direct transmission.

* Fomites (or vehicles) such as animal bedding that have become

contaminated by blood, saliva, urine, feces, vomit, exudates,

respiratory secretions, or milk may be a source of indirect transmission

* Arthropods such as fleas, mosquitoes, lice, ticks, mites and flies can indirectly transmit infectious agents.

Classification of Diseases

Acute: diseases that develop rapidly but last only a short time (common cold)

Chronic: diseases that develop slowly, usually with less severe clinical signs and are continual or recurrent 9tuberculosis)

Latent: diseases in which a pathogen remains inactive for along periods fo time before becoming active (herpes viral infections)

Infectious or communicable: a disease that is acquired from an infected host (flu)

Contagious: easily transmitted communicable diseases (chickenpox )

Noncommunicable: not spread from one host to another and diseased individuals do not serve as a source of contamination for others (tooth decay)

Epidemiology

The study of the effects of diseases on the community. The frequency and distribution of disease within a population is studied.

* microbe virulence* ports of entry and exit* course of disease

Epidemiologists are concerned with the who, what, where, when , why and how of infectious diseases.

They monitor statistics to determine the frequency of a particular disease in a given population.

Endemic: diseases that are always present within a population of a particular

geographic area.

Enzootic disease: conditions affecting animals of a specific geographic area – constantly present in a specific animal community, but only

occurs in a small number of cases. (plague in prairie dogs)

Sporadic: when there are a few isolated cases of a disease, such as the plague in

humans, seen in widespread areas in an unpredictable manner

Epidemic: a disease with a sudden onset and widespread outbreak within a group

Epizootic: widespread disease in populations of animals – spread rapidly,

simultaneously affecting a large number of animals in a region

Pandemic: disease that is a widespread epidemic and generally involves the spread across continents.

Panzootic: widespread epizootic disease.

Agencies

WHO: (World Health Organization) a specialized agency within the United Nations.

Missions: 1. to promote cooperation for health care among nations

2. carry out disease control and eradication programs

3. improve the quality of human/animal life

When epidemics occur, WHO sends out teams of epidemiologists to investigate the outbreak and to assist in bring the outbreak under control.

CDC: (Centers for Disease Control and Prevention: a United States federal agency under the control of the U.S. Department of Health and Human Services.

Function: to assist state and local health departments in all aspects of

epidemiology.

“to promote disease prevention and health promotion goals

that will foster a safe and healthful environment where

health is protected, nurtured, and promoted.”

One branch within the CDC is the National Center for Infectious

Disease (NCID) and its mission is “to prevent illness, disability,

and death caused by infectious disease in the United States and

around the world.”

NIH: National Institutes of Health – a division of the U.S. Department of Health and Human Services – the primary federal agency for conducting and supporting medical research.

Publishes guidelines for the care of animals in research facilities as well as the prevention of disease transmission among animals and between animals and humans.

NIH funds research on a variety of disease topics including zoonoses and ways to prevent their spread.

NIH also educates the public and physicians about the role of zoonoses and human health through providing information such as the role of pets and the immunocompromised person.

At the federal level, the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) requires licensed veterinary personnel to report diseases that pose a significant threat to human health.

All information taken directly from Understanding Zoonotic Diseases by Janet Amundson Romich. Thomson Delmar publishing