Biosecurity 101: Disease Transmission
Rachael O’Brien, Manager Biosecurity & Extension, Queensland
A good biosecurity plan consists of sound practices, and is as individual as the property it protects.
The question I’m often asked is what is biosecurity, and how does this translate into a biosecurity plan?
Biosecurity describes good management practices that will minimise the risk of either bringing disease/pests onto your property or spreading them by sending them off.
To implement good biosecurity we first must understand what we are trying to achieve. The common goal of most biosecurity plans is to protect your livestock from pests and disease. The broader goal of biosecurity is to prevent the entry, establishment or spread of a disease. This is applicable to exotic diseases (diseases you don’t have in your region, state or even country) and endemic diseases (diseases that are already here and established so we now must manage their impacts).
The golden rule of biosecurity is segregation. If we keep a disease or pest away from a host there is little chance that the host will become infected. Our best biosecurity asset is our island status. Being segregated geographically from other countries is why we don’t have a lot of the nasties that other countries do. Sure, we have plenty of hosts (i.e. livestock), but our absence of land borders with other countries decreases the likelihood of an exotic disease just dropping in. It also means we can focus our preventative methods in the areas that we know something may enter (e.g. airports, sea ports), rather than managing an entire border. The Australian Government works to protect Australia from serious biosecurity threats every day, but if this isn’t enough you are our next line of defence.
You do this by having an on-farm biosecurity plan, with processes in place that in the event of a disease introduction you can play your part in detecting it and assisting with its eradication or management.
A lot of what we producers do every day is actually part of good biosecurity in terms of managing endemic disease. Even a day-to-day management practice such as vaccinating your animals starts to have an effect on that disease; because it’s unable to find a host the likelihood of it surviving starts to decrease. This is part of biosecurity 101. By implementing good biosecurity practices you are helping your neighbours, your region and your industry.
To apply adequate biosecurity measures to our properties that protect livestock from disease it’s important to have an understanding of what they are and how they are spread.
Disease is a word that we use to describe anything that negatively impacts on our animals that isn’t a physical injury. What causes that disease is then referred to as a pathogen and we break this word up into three major categories – viruses, bacteria and a fungus.
There are five main ways that an animal gets a disease:
- Direct Contact: when there has been physical contact between an infected animal and a susceptible host(s). This could be through tissues and or bodily fluids (e.g. saliva, blood, or faeces). Such contact would occur during breeding (sexually and mother-to-offspring), nose-to-nose contact, ingesting faeces whilst grazing or even when fighting. Disease generally enters the uninfected animal through orifices; the most common are sexually, orally, through the eyes or nose, or through open wounds.
- Inhalation (aerosol) (Indirect transmission): the animal inhales the disease as droplets carried through the air. Foot-and-mouth disease can be contracted via the inhalation of infection. (We don’t have FMD in Australia)
- Oral Ingestion (Indirect transmission): the animal eats or drinks the pathogens. This could be through feed or water contaminated with faeces, saliva, blood or urine. The faecal-oral pathway is the most common contributor to the spread of disease.
Fomites (Indirect transmission): an object that capable of spreading infection after coming into contact with the pathogen. This applies to inanimate objects such as equipment, clothing vehicles and footwear, needles, drench guns, dirty gloves, water buckets etc. Think of it like the cutting board on chicken dinner night. The cutting board isn’t going to make us sick but if we put raw chicken on the cutting board and then put the cooked chicken back on the cutting board we can transfer bacteria onto our dinner. This doesn’t mean we should never use a cutting board ever again, it just means we need to clean it between uses.
- Vectors (Indirect transmission): mosquitos, ticks, midges and flies can also carry diseases from animals to animals. For example, three day sickness is spread by biting insects that bite and feed off infected animals and then bite and feed off a non-infected animals thus infecting the second animal. 
Stay with me – I am explaining this because this is the most fundamental element of how you apply biosecurity. Knowing what you are up against means you know how to deal with the problem to solve it.
Pests is another broad category; pests are anything that has a negative impact on our animals or environment. Wild pigs are considered a pest to agriculture because they destroy things, muddy up water holes and can spread diseases. Cattle ticks are considered a pest because they have an economic impact on your profits by taking blood from your animals. This impacts on production rates, meaning instead of converting food to weight gain they are putting efforts into repairing body tissues and replacing blood cells, which starts to limit their growth and weight gain.
Both disease and pests have one thing in common: they negatively impact on livestock industries, whether that be through lost production or animal health. Preventing this impact or minimising the effect seems logical.
So how do we deal with both of these things, in order to minimise their impact? Using a biosecurity plan is how. Having an on-farm biosecurity plan helps you to play your part in the greater picture of biosecurity.
In my next article, I’m going to discuss how human activity and farm management can both create and mitigate biosecurity risks on-farm, and explain how to build those preventative measures into your biosecurity plan.
 University of Queensland Gatton, Animal Biosecurity 2008.