Infectious. Contagious. You have probably heard these words several times in your life, maybe even used them. While similar and related, they are often used interchangeably or incorrectly and there is a difference. The distinction between the two is this: all contagious diseases are infectious, but not all infectious diseases are contagious. 


The literal definition of infectious is “the process or state of being infected with a disease.” And to infect means “to affect or contaminate someone or something with pathogenic microbial agents.” Pathogenic meaning disease producing, and microbial referring to viruses, bacteria or other microorganisms. To simplify infectious, it basically means germs get into the body and spread, causing sickness. Contagious diseases are infectious diseases that can be transmitted through direct bodily (close) contact with an infected individual or their bodily discharges, or an object or surface they have contaminated (i.e. COVID-19). Other infectious diseases, however, are transmitted indirectly such as by mosquitoes (malaria) or ticks (Lyme disease).


The Big Picture

Contagious diseases are spread by contact, while infectious diseases are spread by infectious agents. So when something is contagious, it is also infectious because some contact exposed you or your animal to the infectious agent. Something infectious however is not always contagious.  Confused yet? You can be infected with food poisoning (you ate the potato salad that sat out in the sun), but food poisoning isn’t contagious (you aren’t going to pass your food poisoning to someone else or your animals with just a simple contact). Suppose you are near someone sneezing quite a bit and they have an obviously stuffy nose. Well, if you have contact with that person and then you develop the sniffles and sneezes, it was contagious. It was also infectious because the way sniffles and sneezes are contagious is usually through an agent such as a virus or bacteria. If that person’s symptoms were caused by allergies though, they aren’t contagious because you can’t catch allergies. 


Since disease is spread by pathogens such as viruses, bacteria, fungi, parasites and other microorganisms, biosecurity at your farm is key to prevention. Having a solid plan in place to keep pathogens away from your farm or property, animals and personnel is key. The major components for your program are (adapted from USDA-APHIS):


General Signs of Animal Diseases of Concern

• Sudden, unexplained deaths in the herd or flock

• Severe illness affecting a high percentage of animals

• Blistering around an animal’s mouth, nose, teats or hooves

• Unusual ticks, maggots or other insects

• Staggering, falling or central nervous system disorders

• Abortions or still births



Control Access to Your Property

• Have only one combined entrance and exit to your farm if possible.

• Keep property gates locked at all times.

• Make sure all visitors check with you prior to entering your property or visiting your animals.

• If you have a large number of visitors, keep track of who visits your farm. Make sure all

visitors sign in at arrival and sign out at departure.

• Only allow essential vehicles and visitors to enter the farm and keep these vehicles in a

separate area away from animals.


Biosecurity Precautions

• When a new animal moves onto a farm, be sure that the health status and the source of the

animal is known.

• New animals or animals returning to a farm should be separated from the rest of the herd for

approximately two weeks. This can be difficult in some cases. If you are unable to completely

isolate the animals, keep them in a pen or stall farthest from the rest of the stock, keep feed

and water buckets or bowls separate, avoid nose to nose contact with other stock. For

horses or stock that need to be exercised or worked, remove other animals from the pen,

arena or paddock and set up a time for the new stock to have access to the area.

• Keep vehicles, such as milk, feed and livestock trucks, from driving through areas where

animals are housed or feed is kept.

• Wash hands thoroughly before/after handling livestock.

• Ask visitors to provide information about recent farm and animal contacts; deny entry if they have been to an area or farm of concern.

• Clothing worn on farms in other locations/countries should be washed.

• All footwear should be disinfected before entering and after leaving an animal housing area.

• Discourage visitors from walking through feed mangers and having physical contact

with animals.

• Report morbidity and mortality events to your local veterinarian or to the state veterinarian’s



Provide Disposable Protective Clothing

• Make sure visitors entering your farm have clean clothes or you can keep a supply of

disposable clean coveralls and boot/shoe covers for visitors.

• If you haul your own animals, wash your truck, clean and disinfect boots and change

coveralls before returning to your farm.

• In general, don’t borrow or share equipment. In cases where there are no other options,

clean and disinfect the equipment prior to use and make sure to repeat these steps prior to

returning the items.

• If it is necessary to be around the animals of another farm, consider wearing protective

clothing such as coveralls, and boots that can be cleaned and disinfected before you enter

the property and removed when you leave.


Provide Disinfectant for Incoming Visitors

• Provide visitors with a tub of disinfectant and a brush for scrubbing shoes for use before they

enter your property, or provide shoe covers.

• Vehicles entering and leaving your property should be kept away from animal areas or have

their tires washed with disinfectant.


Additional Steps

• Control your companion animals and poultry.

• Control pests such as rodents and wild life.

• Keep garbage and other waste from supplies and animal housing.

• Evaluate feed purchased or brought onto the property and fed to animals.

• Practice security and cleanliness in feed storage.



The take home message.

With infectious diseases, it’s all about spreading germs. They can be spread in many ways, such as through direct contact with an infected person or animal or by direct contact with a contaminated object, consumption of contaminated food (salmonella) or water (cholera) or exposure to disease carrying insects (West Nile, numerous others).


With contagious disease, it’s all about contact. The bottom line: have a good biosecurity plan in place on your farm/veterinary practice. Good hygiene, solid insect and parasite controls as well as limiting contact with suspect or new animals/people can help cut down disease problems.  If any issues are noted or arise, don’t wait; call your veterinarian, state veterinarian or extension agent. USDA can be reached toll-free at 1-833-663-8732.



Jackie Smith, PhD, MSc, MACE, Dipl AVES, is an epidemiologist based at the University of Kentucky Veterinary Diagnostic Lab. Emma Adam DVM, PhD, DACVIM, DACVS, is based at the University of Kentucky Gluck Equine Research Center and Veterinary Diagnostic Laboratory, where she is responsible for research and serves as a veterinary industry liaison.