Biosecurity-Infectious Agents


Biosecurity is a relatively new word in the language of livestock production. It is not found in many English dictionaries and as a result has come to have a large number of meanings. For the sake of this discussion, biosecurity will be defined as the protection of a swine herd from the introduction of infectious agents (viral, bacterial, fungal, parasitic, etc.) It should be noted that this definition addresses the introduction of infectious agents and not necessarily the introduction of disease. Infectious agents do not always cause serious infections in pigs but can be important to keep out of swine herds for other reasons.

Types Of Infectious Agents

Many different types of organisms cause infections. From roundworms that can be 20 to 40 cm in length to microscopic bacteria and viruses, a large variety of bugs infect pigs. There are a number of ways to classify these infectious agents: microscopic and macroscopic, pathogenic (disease causing) and nonpathogenic to pigs, zoonotic (transmissible from animals to people) and non-zoonotic, and others. There are only two categories of infectious agents that are a concern in biosecurity: agents that can cause disease in pigs (pathogenic) and agents that are zoonotic.

Infectious agents that are potentially pathogenic to pigs

There are hundreds of infectious agents that can cause disease in pigs. Often producers are heard to say that they don't worry about biosecurity because their pigs already have every disease that exists. This is true if all of the producer's pigs are dead. Death is the true indicator of a pig that has every disease available in Ontario. Therefore, biosecurity is important to every swine producer whose pigs are still breathing.

Most infectious agents can be managed to minimize or eliminate their effects on the health of a swine herd. Few infectious agents are capable of causing disease by themselves. However, the cost of managing some infectious agents so that they do not cause disease can be prohibitive.

Although many infectious agents can be managed to limit their effects on the health and productivity of a swine herd, multiple infectious agents will overwhelm the best efforts at disease management. Biosecurity, therefore, is crucial for high health, as well as, conventional health herds. Disease in pigs is not inevitable as some producers believe. Many producers have maintained high health herds for decades by utilizing relatively unobtrusive biosecurity protocols.

Infectious agents that are zoonotic

Infectious agents that can be transmitted from animals to people or vice versa are termed zoonotic. Zoonotic agents may or may not be pathogenic to pigs. For example, Toxoplasma organisms almost never cause disease in pigs. In people, however, they cause fetal injury or death if consumed by pregnant women. On the other hand Salmonella infection in swine can cause diarrhea problems in both people and pigs. Both Toxoplasma and Salmonella are zoonotic but only Salmonella is likely to be pathogenic in swine.

Fortunately, very few zoonotic agents are found in pigs under modern swine husbandry conditions. This fact, together with a tradition of cooking pork thoroughly has, to a large degree, eliminated food borne illnesses associated with pork production. The potential for zoonotic infections from pork however remains real. Good husbandry practices, attention to biosecurity and good food handling and cooking practices will continue to maintain pork's excellent reputation in the marketplace.

Three Reasons To Keep Infectious Agents Out of Swine Herds

We have discussed two of the three reasons to maintain adequate biosecurity on a swine farm. One is the increase in the cost of production associated with swine diseases. Another is ensuring a safe and wholesome product for the consumer. A third reason, and a very important one, is producer enthusiasm. It takes more time, more work, and more money to raise pigs that are infected with a large number of infectious agents compared to pigs free of these bugs. It is dramatic to see the change in attitude that results when a sick herd is depopulated and repopulated with clean breeding stock. There is neither profit nor pride in treating sick animals. A producer working 70 hour weeks producing 17 pigs per sow per year with a $10.00 per pig "disease management cost" suddenly begins working 50 hour weeks, producing 23 pigs per sow per year and has a $2.00 per pig disease management cost. Same producer, same expertise, same barn---whole new world. The producer, the feed salesman, the veterinarian, the banker - everyone shares in the success. But the good times only last as long as the biosecurity holds.

It should also be noted here that if the trend towards restricting the use of antimicrobial agents in swine production continues, it will become ever more important to prevent new diseases from entering a swine herd. If access to livestock medicines becomes more restrictive, the ability to treat new infections in a swine herd may become more difficult. This then is a potential fourth reason to maintain tight control over biosecurity.

Avoiding The Entry Of Infectious Agents

The easiest way to infect a swine herd with a new infectious agent is with an already infected pig or pigs. Pig bugs are pig bugs because they live in pigs. Therefore, pigs are the best source of these infectious agents. This leads to two important principles of biosecurity:

  1. Make sure the health status of the herd (and hopefully not herds) that supply breeding stock to a farm is equal to or higher than the health status of the recipient herd.
  2. Quarantine all incoming breeding stock for a minimum of 30 days off-site or at least separate from the main herd. This quarantine period ensures that there is not a change in the supplier's health status before introducing the new animals to the existing herd or, that the new arrivals do not themselves begin to demonstrate signs of disease.

After considering the introduction of live pigs, the next most important cause for concern is summed up in the real estate matra; "location, location, location." Area spread is a term for the transmission of diseases from one farm to another farm in close proximity. Area spread was very significant during the foot and mouth disease outbreak in Britain last year. Although scientists debate whether area spread is the result of airborne transmission, insect carriers, rodent and bird carriers, free ranging domestic dogs and cats, or other factors, the indisputable fact is that the closer healthy animals are to sick animals, the more likely it is that the healthy animals will become infected. One, two and three kilometers have all been suggested as safe separation distances between farms but it is difficult to verify any of these distances. Most consultants suggest somewhere between two and three kilometers, if possible.

After live pigs and area spread, the sources of infectious agents for a pig farm become more diverse. Anything that has recently been in contact with pigs then comes under suspicion. This can include semen for artificial insemination, veterinarians, salespeople, feed trucks, deadstock and livestock trucks, manure wagons, etc.


No drugs, no barn design, no manager's expertise can compensate for an overload of infectious agents on a farm. Biosecurity is not just an issue for high health herds. Regardless of the health status of a swineherd, biosecurity is key to maintaining productivity and profitability.

Every infectious agent that enters a swine farm potentially increases the cost of production, the time spent in the barn, and can decrease productivity and producer enthusiasm. The introduction of zoonotic agents may cause diseases in the pigs but even more importantly can damage the excellent reputation of pork in the marketplace. For productivity, profitability, producer enthusiasm and food safety, biosecurity is the key.

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