The zoonotic disease burden in Australia.

The COVID-19 coronavirus is a zoonotic disease — meaning it arose in animals, jumped the species barrier to humans, and then spread via human-to-human transmission.

Many, and arguably all, zoonotic diseases arise because of the ways humans treat animals — both directly, as is the case in ‘wet markets’ and factory farms, and indirectly, for example through land clearing, which leads to habitat destruction and increased contact between people, wildlife and the diseases they can carry.

Right now, millions are infected with COVID-19 — and hundreds of thousands of people have tragically died. Our collective sense of self and security has been shaken to the core, and many of us will never be the same.

It’s no overstatement to say the coronavirus has brought the world to a standstill — but it’s only the latest in a series of zoonotic disasters. From bird and swine flu, to SARS, MERS and anthrax among others, as you’ll see below — there is a strong case that the treatment of animals in our broken food systems is a major factor in the spread of new diseases on a global scale.

We’ve been given a collective ‘wake up’ call, and we must take this time to pay attention to the lessons of the past, to learn and, most importantly, to change — if not, we risk ‘inviting’ another, likely even more devastating, pandemic to wreak havoc on humanity.

We’ve compiled a list of the most well-known and prevalent zoonotic diseases in Australia. Believe it or not, we’re not just trying to scare you! Our aim is simply to kick-start the conversation about how the human-animal relationship is well overdue for change — for the good of us all.

Bird Flu

Avian influenza viruses may be introduced to Australian commercial poultry farms through contact with wild birds and ducks (the natural reservoirs). The viruses then circulate within poultry populations, mutating on-farm and occasionally becoming highly pathogenic due to the large numbers of birds living within a shed or row of sheds.

From there, the virus may be spread off the farm by workers; when the poultry are transported in trucks to a slaughterhouse; in the poultry’s waste products which may be sprayed across land or dumped in a water body; by wild birds, flies and other insects; and by high-volume fans that are necessary to ventilate the densely packed sheds.[1]

A schematic representation (not to scale) of multiple potential pathways for exposure to and transfer of pathogens within the environs of concentrated animal feeding operations:[1]

At least seven highly pathogenic avian influenza (HPAI) outbreaks and fifteen low pathogenic avian influenza (LPAI) outbreaks have occurred in Australian poultry farms since 1976.[2]–[3] Poor conditions on-farm were identified in at least three of the seven HPAI outbreaks.

Outbreaks of Highly Pathogenic Avian Influenza in Australian poultry farms:

• 2013: In Young (NSW), an outbreak of H7N2 occurred on an egg farm housing over 400,000 layer hens across 8 free range and 6 caged sheds.[4]The outbreak spread to another egg farm 35km away, which housed 40,000 layer hens. All birds were destroyed.[5]
• 2012: In Maitland (NSW), an outbreak of H7N7 occurred on an egg farm and some 50,000 layer hens were destroyed.[6]
• 1997: In Tamworth (NSW), an outbreak of H7N4 occurred on two broiler chicken breeding farms and an Emu farm. The first farm housed 128,000 chickens across 15 sheds, ranging in age from 23 to 93 weeks. The second farm had 32,000 63-week old chickens across 6 sheds. Subsequent surveillance of nearby properties detected the same virus in a flock of 3-month old emus on a contract grower farm, though they were asymptomatic. Following confirmation of HPAI, all three farms were ‘depopulated’; a total of 310,565 chickens, 261 emus, over 1.2 million fertile chicken eggs and 261 emu eggs were destroyed. Transmission of the virus among the chicken farms was attributed to a dead bird pick-up truck and worker.[7]
• 1994: In Lowood (Qld), an outbreak of H7N3 occurred on an egg farm housing approximately 22,000 layer hens aged from 6 to 40 weeks. The source of the outbreak was suspected to be river water heavily populated with wild ducks due to the drought, though this was never proven.[8]
• 1992: Near Bendigo (Vic), an outbreak of H7N3 occurred on a ‘meat’ chicken breeding farm. The source of the outbreak was believed to be a neighbouring, poorly managed duck farm housing 5,700 ‘meat’ ducks. The owner of the duck farm worked periodically on the affected chicken farm and may have inadvertently spread the virus to (or from) the chickens. All of the birds were slaughtered.[9]

• 1985: Near Bendigo (Vic), an outbreak of H7N7 occurred on a chicken farm housing 120,000 chickens across 12 sheds. The chickens comprised ‘meat’ chickens and breeders, egg-laying hens and started pullets. The property also incorporated a small abattoir. The farm had a continuous history of various low-grade disease problems. The source was suspected to be wild ducks using a lake on the farm, though this was never proven.[10]
• 1976: In Keysborough (Vic), an outbreak of H7N7 occurred on a combined ‘meat’ chicken and egg-laying hen farm. Subsequent surveillance identified an H7 virus present in the duck farm opposite, and this was believed to be the source of the chicken farm outbreak. The duck farm was in a disgraceful condition with dilapidated sheds and poor oversight of the animals.[11]

Swine flu

The Swine Influenza H1N1 pandemic of 2009 is estimated to have caused as many as 575,400 human deaths worldwide.[12] The virus emerged in California in April among people who had direct contact with pigs. By May, it had infected people in Australia, and by August, it had caused outbreaks in three commercial piggeries across NSW [13], Victoria [14] and Queensland [15]. The H1N1 pandemic virus has been circulating in commercial Australian piggeries with sporadic outbreaks ever since.[16]

This trend of human influenza pandemic viruses entering pig farms is a global one, and not limited to the 2009 H1N1 pandemic. Genetic analysis of tissue samples collected from sick pigs at commercial piggeries in WA and Queensland revealed the transmission of multiple H1N1 and H3N2 influenza A viruses, including some derived from the 1977, 1995, 2003 and 2009 human outbreaks. [17]

Novel swine influenza viruses have also been detected in Australian people and piggeries. In 2012, an outbreak of respiratory illness and deaths occurred in a piggery near Perth and was accompanied by a mild respiratory illness reported by several of the workers. Analysis of the pig samples taken revealed an unidentified swine influenza A virus containing genes of human origin.[ 18] More recently, in September 2018, a 15-year old girl from a semi-rural area in South Australia became infected with Swine Influenza variant H3N2 after exposure to pigs at a livestock exhibition. The virus was detected during routine screening of influenza positive samples. [19]–[20]

Q Fever

Q Fever is caused by the highly pathogenic bacteria Coxiella burnetti, and symptoms can vary from a mild influenza-like illness to a fatal acute condition.

The bacteria are found in birthing fluids, milk, urine and faeces, and can become airborne, spreading over wide areas in the wind and in air conditioning systems. Cattle, sheep and goats are the main reservoirs, and human infections typically result from slaughtering animals or assisting with animal births. A study of Q Fever cases across a decade in South Australia found that the disease primarily affected men aged 21-40 years old, with most cases occurring through occupation (livestock farmers or slaughterhouse workers) or residence (living in a suburb with a slaughterhouse).[21]

Q Fever was first described in Australian slaughterhouse workers in the 1930s, though it occurs across the globe. Since 1990, there have been 300-800 confirmed human cases of Q Fever in Australia each year.[22] However, seroprevalence studies reveal 30-70% of slaughterhouse workers have been exposed to the bacteria, suggesting the burden of Q Fever is much larger than the number of annual case notifications.[23]

Outbreaks of Q Fever in Australia, including cases where the bacteria has become airborne, have been traced to saleyards[24], intensive dairy farms[25] and slaughterhouses, including facilities that process cattle placentas[26]. Q fever has the potential to cause large epidemics, as demonstrated in The Netherlands from 2007-2010. Some thirty intensive dairy goat and sheep farms became infected, and more than 4,000 people were confirmed Q Fever cases (though the number of people infected was likely over 40,000). The disease spread to people living within 5 kilometers of an infected farm, and to people visiting and interacting with the young goats and lambs.[27]–[28]

Anthrax

Anthrax is an ancient disease caused by the bacteria Bacillus anthracis, which lives in soil and primarily infects herbivores like cattle, sheep, goats and deer. People become sick through contact with infected animals, and the type of illness a person develops depends on how the anthrax spores enter the body. Anthrax can be fatal if not treated with antibiotics and is notoriously known as a potential bioweapon.

Anthrax in Australian farmed animals was first recorded in 1847 at Leppington (NSW), spreading through cattle and sheep stock routes to Victoria, where it was first recorded around the Warrnambool area in 1886. From 1900 to the 1920s, there were approximately 80 outbreaks in NSW and 40 outbreaks in Victoria. Cases continued to be reported in NSW, with around 347 outbreaks from 1930-1962. Major outbreaks in Victorian cattle and sheep have occurred across 27 farms in the Yarrawonga/Shepparton area during 1968; across 83 dairy farms in the Stanhope/Tatura area during 1997; and across 10 farms in the Goulburn Valley area during 2007. Another large outbreak occurred simultaneously in NSW in 2007, involving 10 dairy farms across the Hunter Valley.[29]

More recently, anthrax outbreaks on sheep or cattle farms in NSW have occurred in the Parkes area (2015), Rankins Springs district (2016), Cumnock district of the Central Tablelands (2016 and 2018), Forbes district (2017), the Central West region (two outbreaks in 2018), and the Nyngan district (2019).[30] There have also been reported anthrax cases on sheep farms around the Swan Hill area of Victoria in 2017 (5 farms) and 2018 (two properties).[31]

Food-borne disease

Two of the most common and costly gastrointestinal diseases in Australia — Campylobacteriosis and Salmonellosis[32],[33] — are primarily caused by eating contaminated animal-based foods. Chicken meat has been implicated in 85% of foodborne Campylobacter outbreaks where a source was identified.[34] Thousands of non-typhoidal Salmonella cases from numerous outbreaks have been traced to eggs — a trend that is increasing.[35] Eggs have been implicated in 71% of Salmonella Typhimurium outbreaks where a source was identified. Furthermore, the burden of Salmonellosis in Australia is suspected to be seven times greater than the number of yearly case notifications.[36]

Scientific publications also reveal the routine detection of numerous pathogenic bacteria and parasites in farms, saleyards and slaughterhouses across the country.[37] From Listeria monocytogenes to Escherichia coli, Yersinia enterocolitica, Clostridium, Bacillus cereus, Cryptosporidium and Toxoplasma gondii — all of them (and many more!) can be found in places where Australian farm animals are raised and killed. Other studies reveal the presence of these harmful pathogens in animal-based foods available from Australian shops.[38]

The widespread use of antibiotics on farms to combat these bacteria is contributing to the evolution of antimicrobial resistance and ‘superbugs’ that pose significant risks to public human health.

Importantly, this is all to be expected because farmed animals are the hosts for many micro-organisms, which may live in their digestive systems or be found on their skin, hair, wool and feathers. The presence and concentration of many pathogenic micro-organisms are directly influenced by the animals’ living conditions. Stocking density, weather, poor handling practices as well as dirty farm and transportation conditions all contribute to the presence of harmful pathogens in farm animals, while stress increases the concentration of pathogens in their faeces.[39]–[40]

These pathogens readily contaminate meat products through contact with the animals’ faeces and entrails as the carcass is being skinned or de-feathered, eviscerated and processed; from the slaughterhouse environment or workers along the slaughterhouse processing line.[41]–[42] Bacteria that contaminate milk may come from the lactating mothers’ body (especially if she has developed mastitis), from faeces, contaminated feed, housing and water — and, importantly, some harmful bacteria can survive pasteurization.[43]

Finally, Salmonella bacteria can colonize the inside of an egg while it is developing within a layer hen, or the shell surface when it is laid in a contaminated environment or moved through contaminated equipment. And though most eggs are washed prior to being sold, this does not reduce the concentration of bacteria living within pores along the eggshell surface. [44], [45]:

Psittacosis

Psittacosis (also known as Ornithosis) is a lung infection that may be asymptomatic or cause pneumonia. Small epidemics have been reported worldwide for over 100 years, with some involving >700 cases and 20-30% fatality rates.[46] In Australia, there are up to 230 cases diagnosed each year, though this is expected to be a substantial underestimate of Psittacosis prevalence.[47],[48]

The disease is caused by inhaling the excrement or other aerosols generated by birds infected with Chlamydia psittaci bacteria.

This pathogen has been found in over 450 bird species[49], though recent evidence from Australia suggests that C. psittaci infection is ten times higher in captive birds than wild birds[50]. Other Australian research suggests that wild birds entering the pet trade experience a stress-induced ‘shedding’ of various pathogens, meaning captive birds have a greater concentration of pathogenic bacteria and viruses in their faeces because they are stressed.[51]

Many psittacosis outbreaks have been traced to newly exported/imported sick birds within the wildlife trade. It was first demonstrated that Australian parrots in export shipments were harboring and spreading the disease in the early 1930s.[52] The export of native Australian birds is still a thriving trade — both legally and illegally.[53],[54]

Other outbreaks in Australia have been traced to birds in pet shops[55], duck farms and slaughterhouses,[56],[57],[58] a game bird processing facility[59] and, most recently, a thoroughbred horse in a veterinary clinic[60].

Menangle Virus

Menangle Virus emerged during a single outbreak among intensively farmed pigs and piggery workers in Menangle (NSW) during 1997. This virus circulates naturally among flying foxes (fruit bats) and it is likely pigs became infected from exposure to bat urine or other bodily fluids. Infected pigs primarily suffered reproductive losses — stillborn and mummified piglets — while human infection results in a severe influenza-like illness.[64]

The piggery had 2,600 sows and comprised four sets of sheds, located immediately alongside a forested flying fox roosting area. Young females selected for breeding were housed in units 1 and 2, while units 3 and 4 were the farrowing areas and where sows spent the majority of their pregnancies. These units were closest to the bat roosting area. Between 8-24 pregnant sows were kept together throughout their pregnancies. Piglets were weaned at 18-24 days old and moved to growing sheds either on-site or several hundred kilometers away in Trunkey Creek and Young. Each week, a group of 125 piglets were moved among the shed units.[64b]

Development Applications (DA) for intensive ‘factory’ farms, such as the piggery above, currently (in theory) require comprehensive environmental impact statements. As a matter of urgency these DAs ought also to require a thorough analysis of the local wildlife and if any flying foxes or other potential viral hosts are detected the DA must be denied, in the interests of public health and safety.

Brucellosis

A recent global review of diseases at the wildlife-livestock interface ranked brucellosis amongst the top ten diseases.[65] Symptoms in people are typically non-specific and flu-like, sometimes including severe depression, and have an overall case fatality rate of 2%.

In Australia, brucellosis is caused by Brucella suis bacteria that live in wild pigs across Queensland and NSW.[66] Transmission to people and dogs occurs during pig hunting and eating uncooked wild pig meat, by direct contact with infected pig blood or bodily fluids, or by aerosol spread.[67] Infected pig hunting dogs can also pass the disease to breeders, handlers and veterinarians exposed to birthing fluids.[68]

Pig hunters hold ‘weigh in’ competitions whereby potentially infected pig carcasses are transported to the event, handled by numerous people from different towns and left for hours under the sun alongside people eating, drinking and so on.[69] Such events may pose additional outbreak risks to the broader community.

Brucellosis caused by Brucella abortus bacteria was once a common disease among slaughterhouse workers in Australia but has been eradicated from the local cattle herd since 1989.[70]

Where to from here?

In the midst of this global calamity, there is a powerful opportunity for us to demand and enact real change that will benefit all who share this planet.

In his compelling presentation — Pandemics: History & Prevention — Dr Michael Greger, M.D. FACLM, tells us how we can treat the cause by preventing the emergence of pandemic viruses in the first place.

It’s time to change them back. ‘Modern’ agricultural methods such as factory farming represent the most profound alteration of the human-animal relationship in thousands of years, and far from providing food security and abundance — in reality, it’s killing us.

For our own health, and the health of our planet, we are being compelled to rethink and change the way animals are treated in our current, broken food systems. We must consider animals as the unique individuals they are, who deserve a life worth living — free from the horrors of ‘wet markets’, factory farms and slaughterhouses.

Then, and only then, will we have a real chance of emerging from this ‘Age of Emerging Plagues’ — into a new and evolved Age of Compassion, which will only be of benefit to humans and animals alike.

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