Biosecurity: Routes of Disease Transmission

Just-In-Time Training for Animal Health Emergencies Biosecurity: Routes of Disease Transmission

Multi-State Partnership for Security in Agriculture; Center for Food Security and Public Health

December 2015 1

Biosecurity

Routes of Disease

Transmission

December 2015

During an animal disease emergency, efforts to contain and control

the spread of disease will be essential. Responders need to have a

basic understanding of how diseases can move from animal to

animal, as well as location to location; these are called routes of

transmission. This Just-In-Time training presentation will overview

these routes of disease transmission as well as provide some

specific preventive measures that can be used to break the

transmission cycle.

Disease Transmission

● Sources

– Animal to animal

– Environment

 soil, water, feed

 vectors

– Animal to human

 Zoonotic

– Human to animal

Just In Time Training

Biosecurity: Disease Transmission

Animals can be exposed to diseases from a variety of sources. Most

occur between animals, but transfer can also occur from the

environment, such as soil, water, or feed. Some diseases can also

be transferred between animals and people. Diseases of animals

transferred to people are referred to as zoonotic diseases, while

diseases of humans transferred to animals are referred to as

reverse zoonoses. Zoonotic diseases of concern for responders

during animal health emergencies are addressed further in the

Health and Safety: Zoonoses Risks and Prevention Just-In-Time

training presentation.

[Photos: (Top) Cattleman herding cattle through a ravine; (Bottom)

oral examination of a dairy cow, Source: Danelle Bickett-Weddle,

Iowa State University]

Routes of Transmission

● Direct contact

● Inhalation (Aerosol)

● Oral/Ingestion

● Fomites

– Inanimate objects

– Equipment, boots, vehicles

● Vectors

– Mosquitoes, ticks,

biting midges

– Rodents or birds

Just In Time Training

Biosecurity: Overview

Regardless of the source, animal diseases, much like human

diseases, are then spread (or transmitted) through a variety of

ways. These can vary with the disease of concern.

Animal diseases can be spread by 5 main routes of transmission:

direct contact; inhalation of aerosols; ingestion; indirect transfer by

fomites, such as equipment, footwear or vehicles; or vector

transmission.

[Photos (Top): Feedlot cattle in close contact, Renee Dewell, Iowa

State University; (Bottom) mosquito and tick, Centers for Disease

Control and Prevention Public Health Image Library]

Direct Transmission

● Susceptible animal

comes in contact

with infected

animal

● Body fluids

– Urine, feces

– Saliva

– Blood, milk

● Tissues

– Lesions

– Carcass

● Breeding

● Mother-to-offspring

Just In Time Training

Biosecurity: Disease Transmission

Direct contact is one of the main methods of disease spread

between animals. It occurs when a susceptible animal comes in

direct contact with an infected animal, its body fluids or tissues.

Depending on the microorganism, it may be transferred directly by

blood, saliva, urine, or feces. It may also be spread through contact

with infected animal lesions or tissues. Entry into the susceptible

animal generally occurs through contact with the mucous

membranes, such as the eyes, nose, or mouth but can also enter

through open wounds or breaks in the skin. So, possible exposures

can occur from nose-to-nose contact, biting or rubbing against each

other. Some diseases of animals can also be spread during breeding

as well as from mother-to-offspring, during gestation or through

milk when nursing.

[Photo: A flock of turkeys, USDA]

Just-In-Time Training for Animal Health Emergencies Biosecurity: Routes of Disease Transmission

Multi-State Partnership for Security in Agriculture; Center for Food Security and Public Health

December 2015 2

Aerosol Transmission

● Disease agents contained

in droplets

– Pass through air

● Most agents not stable

in droplets

● Close proximity required

– Enclosed barns

– Coughing, sneezing

– Contaminated soil

 Birthing tissues

 Feces, urine

Just In Time Training

Biosecurity: Disease Transmission

Aerosol transmission is another means of disease spread. This

involves the transfer of disease agents in droplets spread through

the air, which are then inhaled by another animal. Most

microorganisms are not able to survive for extended periods of

time within the aerosol droplets, and as a result, close proximity of

infected and susceptible animals is required for disease

transmission. Aerosol transmission can also occur when infected

droplets from urine, feces, or birthing material get stirred up from

contaminated soil or dust and inhaled.

[Photo: Depiction of aerosol spread from a cow, Clint May, CFSPH,

Iowa State University]

Oral Transmission

● Ingestion of

contaminated

feed or water

– Feces, urine

– Saliva

– Milk

● Licking/chewing

contaminated

environment

● Shared feed or

water sources

Just In Time Training

Biosecurity: Disease Transmission

Oral transmission of disease causing organisms involves ingestion

through the consumption of contaminated feed or water, or by

licking/chewing on contaminated environmental objects. Feed and

water contaminated with feces, urine or saliva are frequently the

cause of oral transmission of disease agents. Fecal-oral

transmission of diseases is a common means of infection in animals

(and people). Shared feed and water sources can contribute to the

spread of the disease.

[Photos: (top): Cattle eating at a feedbunk, Danelle Bickett-Weddle,

CFSPH, Iowa State University; (bottom) cattle sharing a water tank,

Danelle Bickett-Weddle, CFSPH, Iowa State University]

Fomite Transmission

● Contaminated

inanimate object

● Carries pathogens

to other animals

– Needles, balling guns

– Buckets

– Bedding, shovels

– Vehicles, trailers

– Humans, clothing

Just In Time Training

Biosecurity: Disease Transmission

Indirect transmission may occur by fomites. These are inanimate

objects, such as equipment, clothing, footwear or vehicles, that can

transfer microorganisms from an infected animal to another animal

or person. Examples of fomites that may be present during a

response include needles, balling guns (used to dispense

medication to cattle), feed or water buckets, bedding and shovels.

Even items such as clothing or vehicles may become contaminated

and serve to spread pathogens.

[Photos: (top) Syringe and balling gun. Danelle Bickett-Weddle,

CFSPH, Iowa State University; (bottom): pickup and trailer, Bryan

Buss, CFSPH, Iowa State University]

Vector Transmission

● Living organism

transfers disease

between animals

– Mosquitoes

– Ticks

– Biting midges

– Flies

● Acquires pathogen

from one animal

● Transmits to

another animal

Just In Time Training

Biosecurity: Disease Transmission

Lastly, some diseases are spread by vectors – living organisms –

able to transfer microorganisms from an infected animal to

another. Mosquitoes, ticks, biting midges and flies are common

disease carrying vectors, but sometimes rodents or birds can serve

as disease vectors.

[Photos: (top): Calf with numerous face flies, USDA; (bottom):

mosquito (left) and tick (right), CDC Public Health Image Library]

Just-In-Time Training for Animal Health Emergencies Biosecurity: Routes of Disease Transmission

Multi-State Partnership for Security in Agriculture; Center for Food Security and Public Health

December 2015 3

Points to Keep in Mind

● Transmission

routes vary with

disease

– Multiple routes

– Single route

● Animals may not

show obvious

signs of disease

● Persistence in

environment

 Soil, manure, water

Just In Time Training

Biosecurity: Disease Transmission

It is important to remember that transmission varies with the

disease of concern. Multiple routes of transmission may be possible

for some diseases, while others may be limited to a single means of

transfer. Equally important is knowing that transmission may occur

without animals exhibiting obvious signs of disease. That is why

awareness of the various routes of transmission becomes so

essential when implementing a strategy to minimize disease spread

during a response. Finally, remain aware that many disease agents

can survive for extended periods of time in the environment or on

objects; therefore, environmental contamination should not be

ignored.

[Photo: Outdoor swine shed and pen, VDPAM, Iowa State

University]

Biosecurity Measures for

Transmission Routes

Route of

Transmission

Possible Biosecurity

Measures

Direct Contact

Isolation

of infected animals; personal

protective equipment

Fomites

leaning and disinfection procedures;

personal protective equipment

Aerosol

Isolation of infected animals; personal

protective equipment

Ingestion

Cleaning

and disinfection procedures

Vectors

(e.g., insects)

Pest management

procedures

Just In Time Training

Biosecurity: Overview

This table shows some of the possible biosecurity measures that

may be used to limit transmission of pathogenic agents based on

their routes of transmission. For pathogens spread by direct contact

and aerosols, the isolation of infected animals and use of personal

protective equipment, such as gloves, can limit and prevent

transmission by this route. For pathogens spread by fomites, such

as equipment or vehicles, or ingestion, cleaning and disinfection

measures can be effective in reducing contamination. Control of

vector-borne diseases will involve the use of pest management

procedures to limit transmission. Let’s talk about these biosecurity

measures a bit more.

Prevention: Direct Contact

● Isolation/quarantine

– Increase distance

between sick and

well animals

● Dedicated equipment

to prevent spread from

isolation area

● Cleaning and disinfection

Just In Time Training

Biosecurity: Disease Transmission

One of the first steps in preventing further spread of disease is

minimizing contact between susceptible and infected animals. This

is often accomplished by isolating the infected animal. In the case

of animal disease emergencies, often more than one animal is

involved; therefore the entire farm may be quarantined, in efforts

to prevent the further spread of the disease. When working with

animals in isolated or quarantined areas, dedicated equipment

should be used to prevent pathogen spread outside of the area.

Proper cleaning and disinfection procedures are also important for

preventing the spread of pathogens by fomites, such as equipment,

vehicles, or footwear. Keep the animal housing environment as

clean and dry as possible to minimize risk of environmental

exposure.

[Photos: (top) Bull in an isolation pen, Bryan Buss, CFSPH, Iowa

State University; (bottom) cleaning and disinfecting boots, Sandy

Amass, Purdue University]

Just-In-Time Training for Animal Health Emergencies Biosecurity: Routes of Disease Transmission

Multi-State Partnership for Security in Agriculture; Center for Food Security and Public Health

December 2015 4

Prevention: Aerosol

● Adequate ventilation

– Provide fresh air to

all animals

– Decrease humidity

and odor build up

● Control dust

– Wear respiratory

protection in

certain situations

Just In Time Training

Biosecurity: Disease Transmission

To minimize aerosol transmission, maximize ventilation so that

fresh air is provided to all animals and humidity and odors do not

build up. Control the amount of dust generated in animal housing

areas. This can damage the protective cells in the respiratory tract,

as well as result in exposure to contaminated particles that can

cause disease. Responders should wear respiratory protection,

especially when there is a zoonotic disease concern.

[Photos: (top) Ventilation fans in a poultry facility, USDA; (bottom)

stirred up dust, The Animal Photo Archive]

Prevention: Ingestion

● Keep feed and water clean

● Prevent rodent and

bird access

● Proper waste

management

– Keep environment clean

and dry

● Cleaning and disinfection

Just In Time Training

Biosecurity: Disease Transmission

Keeping feed and water clean by minimizing fecal and urine

contamination is extremely important. Prevent rodent and bird

access to feed and water to prevent contamination by these

vectors. Proper waste management procedures can help to keep

the environment clean and dry. Cleaning and disinfection

procedures for feed bunks or waterer can help minimize

transmission between animals.

[Photos: (top) Feedlot cow at a waterer, Renee Dewell, CFSPH, Iowa

State University; (bottom) cows at a feedbunk, Mykel Weding,

CFSPH Iowa State University]

Prevention: Vector Control

● Source reduction

– Habitat

reduction/elimination

– Parasitic or predatory

insects

● Control adults

– Insecticides

 Knockdown and residual

sprays

 Baits, fly traps

● Minimize interaction

– Sheltering of animals

Just In Time Training

Biosecurity: Disease Transmission

Vector control begins with an understanding of the insect’s life

cycle. Insect life stages vary and so do the specific, effective control

measures. For instance, the egg laying grounds for flies are

different than that of mosquitoes and midges, and one approach

will not necessarily work for all. Source reduction consists of

eliminating potential insect breeding areas and larval habitats.

Generally this involves removing standing water sources, such as

tree holes or old tires or agitating any water sources, such as stock

tanks or water troughs. Some insects require manure or organic

material for development, so cleaning animal feeding areas, yards

and barns can minimize these vectors. Sometimes, parasitic or

predatory insects may be used to control the larval stages of other

insects. Controlling adult insects, often involves the use of

insecticides, either as a knockdown or residual treatment. These

methods are often less effective compared to habitat reduction

methods. Baits and fly traps may aid efforts, but should not be used

as the sole method of control. Sheltering animals indoors, can

minimize the opportunities for insects to interact with animals.

Additional information on vector control can be found in the

corresponding Just-In-Time training presentation.

[Photo: A rodent bait trap, Danelle Bickett-Weddle, CFSPH, Iowa

State University]

Just-In-Time Training for Animal Health Emergencies Biosecurity: Routes of Disease Transmission

Multi-State Partnership for Security in Agriculture; Center for Food Security and Public Health

December 2015 5

Personal Protective Equipment

● Gloves

– Creates barrier between you and

pathogen

– Especially hands with cuts, abrasions,

chapped

– Wash hands after

removing gloves

● Coveralls, footwear

● Respiratory and

eye protection

Just In Time Training

Biosecurity: Disease Transmission

The use of personal protective equipment, such as gloves, coveralls,

and boots, can help reduce exposure and transfer of pathogens.

Gloves should be worn when working with sick animals and those

that you are unaware of their health status (remember that

infected animals do not always appear sick). This is especially

important if hands have cuts, abrasions or are severely chapped

because areas of broken skin provide an entrance for disease

agents. Wearing gloves does not replace good hand washing habits

– wash hands in warm water and soap after removing gloves.

Coveralls will help keep your clothes clean and cover your arms to

minimize disease exposure when handling tissues or animals.

Protective footwear (e.g., rubber boots) will protect your shoes

from contamination and minimize spread to other areas of the

farm. Wear masks in certain situations to prevent inhaling

contaminated particles. Additional information on PPE can be found

in the corresponding Just-In-Time training presentation.

[Photos: Responder in PPE, Travis Engelhaupt, CFSPH, Iowa State

University]

Additional Resources

● USDA Foreign Animal Disease

Preparedness (FAD PReP) Guidelines:

Biosecurity

– http://www.aphis.usda.gov/animal_health/emrs/nahems.shtm

● Just-In-Time training presentations

– http://www.cfsph.iastate.edu/Emergency-Response/just-in-

time-training.php

Just In Time Training

Biosecurity: Disease Transmission

For more information on biosecurity issues during an animal health

emergency response, consult the USDA FAD PReP Biosecurity

Guidelines. Additional training presentations, including a

biosecurity overview, personal protective equipment, cleaning and

disinfection, and wildlife and vector control, can be found on the

Just-in-Time training website.

Acknowledgments

Development of this presentation was by the

Center for Food Security and Public Health at

Iowa State University through funding from the

Multi-State Partnership for Security in Agriculture

Author: Glenda Dvorak, DVM, MPH, DACVPM

Information provided in this presentation was developed by the

Center for Food Security and Public Health at Iowa State University

College of Veterinary Medicine, through funding from the Multi-

State Partnership for Security in Agriculture.