Appearing on a late night talk show, Depp described Nationals leader and Agriculture Minister Barnaby Joyce as an “inbred tomato”, while Joyce fired back by declaring himself Depp’s “Hannibal Lecter”.

The feud between the two was sparked by Depp and partner Amber Heard’s failure to declare their two Yorkshire Terriers to Australian customs officials during a visit last year.

It was exacerbated by Depp mocking the couple’s now-famous, wooden apology for failing to declare the dogs, joking with reporters at a recent news conference in London that he was sorry for not having smuggled his dogs into England.

We’ve all bemoaned the prospect of a quarantine inspection after a long-haul flight, but experts say Depp’s offhand remarks belie the real risks to Australia posed by introduced diseases and rogue species.

David Jones, a molecular plant biologist at the ANU College of Medicine, Biology and Environment, says few people understand what’s at stake.

“I think, underneath, they don’t really appreciate the fact that there are real concerns and real threats to the Australian environment, and agriculture and human health,” he said.

Had Johnny Depp and Amber Heard chosen to bring their canine buddies in through the right channels, the process would have taken about seven months.

The biggest threat that domestic dogs from the US pose to Australian biosecurity is the introduction of rabies – and ruling it out takes time.

The dogs must be microchipped, have a rabies vaccination and then have a blood test. The minimum waiting period after the blood test is six months.

On arrival in Australia, all pets are quarantined at a facility in Melbourne for 10 days, where officials look for any signs of ill-health and for the presence of ticks, which can also introduce disease.

People in the industry say it’s very rare that dogs are smuggled into the country in similar fashion to Pistol and Boo.

“This is the first case we’ve heard of,” conceded Narelle Hammond, from pet transport company Animal Travel.

But she also thinks the dogs might have been able to stay incognito in Australia had their groomers not unwittingly notified the authorities by posting pictures of themselves with the terriers online.

“Unless someone alerts someone else to the fact that they’ve falsified their documentation and made a false declaration, I suppose it could happen,” said Ms Hammond.

Simon Jackson, the chief executive of pet transport company Dogtainers, and the treasurer of the International Pet and Animal Transport Association, says he knows of only two other cases of undeclared pets entering Australia in the past 20 years. Both were accidental.

“An animal got in a container as the house was being packed, and they found it, and the second time the animal got in the suitcase . . .  It’s certainly a very rare occasion,” said Mr Jackson.

2. So, what is rabies?

Rabies is a viral disease that affects the central nervous system. It’s deadly; and it’s expensive to control.

“If rabies came into Australia, it would radically change the way that we interact with our natural world,” said Andrew Robinson, the deputy director of the Centre of Excellence for Biosecurity Risk Analysis at the University of Melbourne.

The World Health Organisation estimates rabies kills up to 59,000 people a year. While it can be prevented by vaccines, many deaths occur in areas where the vaccine isn’t readily available or where victims cannot afford it. Symptoms can include hallucination, insomnia, difficulty in swallowing and frothing at the mouth.

“There’s a point at which you can still treat the disease, but after that point it’s incurable and a very painful and lengthy death,” said Associate Professor Robinson.

Rabies deaths in North America are rare, according to the US Centre for Disease Control, and have been declining steadily since the 1970s to average just one or two per year.

That’s mainly due to better control programs and more effective treatments for the disease, but the low death rate doesn’t come cheaply. The centre estimates that the costs of detection, prevention and control of rabies exceeds $US300 million a year.

Australia and close neighbours New Zealand and Papua New Guinea are rabies-free. While an outbreak in Australia might not carry with it a high death toll, Associate Professor Robinson says it would have a profound effect on the way Australians interacted with the great outdoors.

“Right now, we can feel some confidence that we are safe out in bush areas. But imagine if a dingo contracted rabies and started attacking humans.”

That, in turn, would almost certainly have an impact on Australia’s quintessential brand of outback tourism.

It is an expensive undertaking to manage a rabies outbreak – and it’s one that would never end.

“Once it’s in, it’s in; there’s nothing you can do. It would be very difficult to eradicate,” said Associate Professor Robinson.

However, strict standards remain in place for bringing animals into Australia, meaning a rabies outbreak remains unlikely.

“If people obey the laws, then the likelihood of rabies entering the country is very slim,” he added.

3. A tiny army of invaders . . . 

But not every pest or disease is as easy to stop. Some are small, hidden and already here.

The red imported fire ant – Solenopsis Invicta – was first detected in Brisbane in 2001 and is already threatening to undermine the Aussie way of life.

“This is an ant that swarms and its stings are extremely painful and can be fatal if you have enough of them,” Associate Professor Robinson said.

He added: “The vernacular description for its effect on life in places that it has infested, like Texas, is that you can’t have a barbeque in your back garden.”

The ants are simply too aggressive when they’re swarming. Family pets also need to be kept inside.

More seriously, the red imported fire ant poses a threat to Australia’s biodiversity.

In appraising the effect of the species in the US, the Australian Department of Environment notes that in areas where the ant is present “the diversity and abundance of native arthropods and even vertebrates have been greatly reduced.”

Besides the fire ant, an invasive ant from Argentina is playing havoc with our electronics. The tawny crazy ant – nylanderia fulva– was introduced to northern Australia and Christmas Island. They don’t bite, but they can infest electronics, chewing on the wires and even causing appliances to short circuit. 

4. Biosecurity = food security

And then there are the threats to agriculture.

One of the next big things on the radar of Australian biosecurity experts is not an animal, but a fungus.

Wheat blast – magnaporthe tritici – has just made its way to Asia, detected in Bangladesh for the first time in February and confirmed in late April.

The fungus attacks the heads of wheat, where it’s hard for fungicides to reach, and the outbreak has already led to the loss of more than 15,000 hectares of crops.

“They just look white because they’re bleached,” said ANU’s Dr Jones of the effect on the heads. “They have no seeds because the fungus has affected the seed heads. Yield is negligible after a major outbreak.”

Wheat blast is a major threat to food security as wheat is the second major food source in South Asia.

To try to combat the problem, researchers are using rapid data sharing – a technique more often seen in medical emergencies like the spread of the Zika virus.

The website Open Wheat blast publishes real-time genetic sequencing data without any restrictions, making the information available for analysis by the scientific community at large. Researchers can, in turn, publish their findings on the site to help find ways to prevent the spread of the fungus.

Wheat blast is not the only threat to Australia’s multi-billion-dollar grain industry.

UG-99, named after its origin country Uganda and the year in which it was discovered, is another fungal threat for which Australia is already preparing.

“Researchers from Australia have gone and trialled Australian varieties of wheat in the areas which have UG-99 to see whether any resistance existed in that material. They found some resistance, so they are using that in breeding programs to prepare for a possible eventual incursion of UG-99,” said Dr Jones.

He added: “To control that sort of fungal incursion, if you don’t have resistant varieties, you have to apply pesticides and that would be in the order of hundreds of millions of dollars to protect our industry. So it would have a very major economic impact on an important Australian industry.”

5. Bringing in animals . . .  the wrong way

Thankfully for Australia’s biosecurity, a saga like that surrounding Johnny Depp’s hapless Pistol and Boo is a rarity.

That’s because, among other reasons, people aren’t willing to risk having their pet sent back to where it came from — or put down — because they hadn’t met quarantine conditions.

Animal smuggling is mostly reserved for species that aren’t allowed into Australia – usually because they’re on the international list of endangered species.

Australia is a signatory to the Convention on International Trade in Endangered Species of Wild Fauna and Flora, known as CITES, meaning people need permission to import or export anything protected by the convention.

For certain animals and animal parts, that permission would only be granted under special circumstances, such as a zoo importing an endangered animal. Private individuals would not be granted such permission. 

Last year, Australian Customs disrupted an exotic fish-smuggling network after officers discovered 20 plastic bags full of endangered fish estimated to be worth almost $300,000 on the black market, hidden in the suitcase of a man arriving from Singapore.

That led them to two addresses in Adelaide, where more fish were found, including an Asian arowana valued at $30,000.

In 2014, a Czech national was charged with attempting to bring into Australia 16 Monk and Quaker parakeet eggs by concealing them in his underwear.

The illegal wildlife trade endangers both species at risk of extinction and also Australia’s biosecurity, because flora and fauna smuggled into the country bypass quarantine checks.

Smuggled animals often die on the journey because of cramped conditions and the stress of travel.