FERAL pigs cause major headaches for farmers each year - destroying crops, preying on livestock, as well as having and spreading exotic diseases.
Given they are known 'super spreaders' of virus - could wild boars exacerbate a foot and mouth (FMD) outbreak in Western Australia?
According to the National Feral Pig Management co-ordinator Heather Channon, studies have shown the destructive pest are unlikely to play a significant role or maintain a reservoir of FMD infection.
Dr Channon said in temperate countries, feral pigs were most likely to contract FMD by the ingestion of uncooked meat scraps.
At a global scale, swill feeding - or feeding food scraps which contain meat or have been in contact with meat to pigs - is one of the most common ways of disease transmission.
So much so, swill feeding was banned in Australia, after it initiated FMD outbreaks in the United Kingdom (1976 and 2001) and South Africa (2000).
"There's no evidence showing feral pigs, which are present in low densities in the wild rather than large congregations (such as intensive piggeries), would be capable of generating a significant level of aerosolised virus to be considered epidemiologically important," Dr Channon said.
"FMD can be spread by direct contact between animals.
"Contact between feral pigs and infected ruminants, including cattle, sheep and goats, is a risk factor, which may complicate control in Australia."
FMD virus can be found in blister fluid, exhaled air, saliva, milk, semen, manure and urine from infected animals.
It also survives in straw, and on boots and clothes contaminated with manure, and can be spread by air under cool, moist conditions.
This requires high concentrations of infected pigs to generate a plume of virus-containing aerosols.
The potential role of feral pigs in FMD outbreaks has been explored in the Kimberley region's pastoral settings.
A study looked at how feral pigs and domestic cattle may interact.
Modelling indicated feral pigs, at a density of one pig per square kilometre of suitable habitat, would not be able to sustain a FMD epidemic on their own.
Instead, the model showed higher concentrations and movements of cattle were more significant at maintaining an outbreak.
Dr Channon said while feral pigs were shown to exacerbate FMD outbreaks slightly, it was much less important than domestic cattle.
She said usually the disease died out in feral pigs without further action, as FMD was controlled in cattle.
However, smaller and shorter outbreaks resulted when FMD was controlled in feral pigs concurrently with cattle.
"Ideally, the response strategy to manage an exotic disease incursion involving feral pigs will require the distribution and abundance of the feral pig population to be determined," Dr Channon said.
"Proactive control and surveillance in feral pigs may also be important to give confidence to industry and overseas markets that the outbreak could be dealt with competently.
"There are potential risks from feral pigs that can't be dismissed."
So what factors come into play in a pig's ability to spread FMD?
According to Dr Channon it comes down to factors including their distribution and abundance, climatic conditions, contact rates with other susceptible animals and habitat suitability.
The strain of disease can also determine the ability of a feral pig to spread it.
"Pigs, both feral and domestic, usually become infected with the virus by eating FMD virus-contaminated products, or by direct contact with other FMD-infected animals or contaminated fomites.
"For example - clothes, shoes, wool, soil or other materials that can carry viruses."
Pigs are amplifying hosts and can expel large quantities of virus in exhaled breath.
Transmission occurs most readily when animals are close to one another, such as at watering points, feeding troughs, stockyards and milking sheds.
Dr Channon said these spreads may contribute to FMD transmission from feral animals to domestic animals and visa-versa.
She said feral populations would present difficulties in the control of FMD, and may complicate and prolong the period to establish proof of freedom and market access.
"In some areas - where feral pigs may have a role in FMD transmission - the modelling has indicated an outbreak could be controlled using humane, integrated best practice management techniques (including aerial shooting, baiting and trapping), particularly when done in conjunction with cattle control measures.
"Keeping Australia's feral animal populations FMD-free is a key priority.
"Onfarm biosecurity practices to exclude contact between susceptible domestic and feral livestock by Australian livestock producers - in conjunction with feral animal control activities - are important risk mitigation activities and should be considered by any producers who farm susceptible species."
So if FMD was detected in feral pig populations could anything be done to mitigate the risk?
Dr Channon said the best measure was prevention, followed by early detection and reporting of disease.
She said if an outbreak of FMD occurred in feral pigs it was likely risk assessment and surveillance would occur to determine whether feral pigs were important to the epidemiology of the outbreak.
"Integrated control strategies could then be implemented to reduce the density of feral pigs in the outbreak area," Dr Channon said.
"This would ensure they cannot transmit the virus or be a reservoir of infection.
"Actions by land managers that reduce potential risks of contact between feral pigs and other susceptible animals are being encouraged."
Dr Channon added, the National Feral Pig Action Plan aimed to lead and support all land managers to work together and effectively control feral pig populations over the long-term and reduce their many impacts.
She said this would limit the contact rate between individual feral pigs from different groups, thus reducing the chance of disease transmission.
"Awareness of the risks of swill feeding and actions to mitigate access of feral pigs to food waste left by recreational and other users of land inhabited by feral pigs are important.
"All livestock producers are encouraged to be vigilant with onfarm biosecurity practices and be familiar with - and on the lookout for - signs of FMD.
"Reporting using the emergency animal disease hotline of any signs suggestive of FMD should be undertaken as a priority."
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