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The devastating impact the mouse plague has had on the rural community has been well documented, but it has also taken a massive toll on domestic animals and those whose job it is to care for them, writes Tracey Porter.
Scores of domestic animals came close to being euthanised unnecessarily after veterinarians at the coalface of Australia’s unprecedented mouse plague ran out of supplies of the antidote used to treat poisoned pets.
Frontline rural practitioners say they were left high and dry as numbers of dogs, cats and chickens arriving at clinics with rodenticide poisoning skyrocketed as a result of being exposed to baited rodents.
The problem was compounded by medication shortages, particularly that of vitamin K1, a supplement used to counteract the effects of anticoagulant rodent bait on domestic pets.
Dr Jo Hoad, co-owner of Uralla Vet Clinic, runs a small two-vet practice in a town of 2500 people. She says at the peak of the crisis she was seeing 10 to 15 rat bait cases a week when normally her clinic would see around 10 cases a year.
Toowoomba Family Vets co-owner Dr Louis Gilshenan is also in the thick of the impacted area. He says his team’s workload increased significantly as a result of farmers and graziers using baits containing the anticoagulant brodifacoum to help stem the waves of mice making their way across the region.
Dr Gilshenan says the number of domestic animals presenting at his clinic showing signs of toxicity after being exposed to baits has quadrupled in recent months.
“In normal periods, you wouldn’t even see one case a week. Now, it wouldn’t be unusual for us to see three to five cases of rodenticide toxicity each day. It’s literally gone from zero to 100.”
Dr Lisa Nivison of Greencross Vets South Tamworth tells a similar tale.
“In some cases, pets were poisoned from mice coming from neighbours where baits were being used. We were seeing on average six-plus cases per day during the peak of the plague. Despite our best treatment efforts, some animals were not able to be saved and succumbed to the effects of these baits.”
CSIRO research officer Steve Henry says the secondary poisoning is associated with people impacted by the mouse plague trying to bait mice around their house by using the second-generation anticoagulants in bait stations or wax blocks.
Henry says that when rats or mice eat the bait, the anticoagulant accumulates in the fatty tissues around the organs but takes a while to take effect.
“In the lead up to the rodents dying they actually become quite weak, sick and disorientated and they become easy pickings for other animals,” he says.
Dr Gilshenan says 95 per cent of the rodenticide cases his clinic is seeing is in domestic pets presenting with haemorrhagic shock, resulting in dogs “bleeding into all different sorts of spots”.
While the signs of poisoning can vary greatly depending on the amounts ingested and time frames involved, other symptoms include lethargy, loss of appetite, coughing, swollen joints, discoloured gums and increased heart rate.
Currently the most effective course of treatment sees sick domestic animals receive canine plasma which is used to replace the clotting factors within the blood. While blood transfusions help, vitamin K is critical to helping to restore the clotting process.
When such treatment is followed most poisoned pets can be saved.
Vitamin K shortage
However, in recent months the unparalleled demand for vitamin K led to the exhaustion of much of the country’s supplies.
In fact, supplies were so scarce some clinicians were forced to set up group chats across their veterinary networks and beg colleagues to forward their personal supplies.
With vitamin K wholesalers unable to source enough stock to meet demand, many vets feared being left with no option but to euthanise active cases.
Dr Hoad says she was one of many vets who ran into serious problems sourcing vitamin K to treat affected patients. Twice she was told by her drug wholesaler there was no vitamin K available anywhere in the country, forcing her to supply a quarter of the total recommended course to clients at a time, in the hope she could source more in her next delivery.
“Sometimes we were able to source bottles from online chemists and pet supply stores and even eBay, but eventually we could not source from anywhere. In May, we were in the situation where we did not have quite enough vitamin K to treat our current patients for their full course, there was no vitamin K available anywhere in Australia, and we were being given an ETA of availability for further supplies of up to a month.
“We were faced with having to euthanise any further cases that came in as we had nothing to treat patients with and neither did any of the clinics in neighbouring towns.”
Dr Alex Keough of Lake Road Veterinary Hospital in Wagga Wagga admits the situation got “pretty grim. We couldn’t source any more, and we were just divvying up the meagre amount of vitamin K we had. Sadly, many of the poisoned pets died. But it got to the point where we had to ask ourselves, ‘Are they going to die of rat bait or are they going to die because we are skimping on our doses?’”
Mavlab national product and export manager Paul Ross says his Queensland-based company manufactures vitamin K doses in two tablet sizes under the K-Mav label.
He says demand for the K-Mav Tablets increased three to fourfold over normal sales during the period of the mouse plague. He concedes this did have an impact on supply.
“This increased demand did lead to some supply issues despite considerably increased production levels. The long lead times for sourcing raw materials from overseas contributed to this.”
Dr Hoad believes she was one of the lucky ones because at the 11th hour her clinic was able to source some supplies preventing her from having to euthanise any animals. But, she says, “it was a very close thing. This scenario was extremely stressful for our vets and nursing staff, we spent considerable time trying to source vitamin K by any means we could and the uncertainty and potentially having to tell clients we were unable to treat their loved pets and working dogs due to a lack of normally readily available medication was very difficult.”
Dr Hoad says another major problem she faced was that supplies of anticoagulant rodenticides also ran short. This resulted in stockists selling other less familiar rodenticides such as cholecalciferol-based products and zinc phosphide products, marketed as a ‘pet safe’ alternative.
While there is a very low risk of secondary toxicities with Selontra-type products, if the baits themselves are ingested the impact on animals is disastrous, she says.
“I haven’t personally dealt with any zinc phosphide toxicities however we have dealt with several cholecalciferol toxicities. Even with rapid presentation to a vet clinic and inducing vomiting of the baits in their entirety, case survival after eating these baits is very low. These cases have been heartbreaking as there is no real antidote, just supportive treatment.”
The impact on vets
The Lincoln Institute co-director and industry advocate Dr Michael Powell says aside from the unnecessary loss of much loved pets, what is most concerning about this situation is the devastating impact scenarios such as this have on vets.
Dr Powell says compounding the emotional distress being felt by these vets was the fact that even before the arrival of the mouse plague, many rural animal health specialists were already stretched to capacity owing to the well-publicised vet shortage.
“What we do know anecdotally is that most clinics have had a surge in demand for their services through the COVID-19 period of about 20 per cent. Most are trying to accommodate that demand whilst operating in an environment where there is a shortage of vets to fill vacant positions.
“Watching a patient suffering a horrific illness and potentially dying from it is tough enough of a challenge on its own for a medical profession hardwired to relieve suffering. But vets having to euthanise animals that could otherwise be saved due to a lack of access to basic medication is equally devastating. You can see that many vets are operating on a knife’s edge.”
However, there could be some light at the end of the tunnel with signs that, for now at least, the K1 shortage appears to be over.
While reluctant to discuss numbers, Ross says most wholesalers should now have cleared any backorders for the tablets and all should have stock available in their warehouses.
Mavlab have been in constant contact with wholesalers and veterinary clinics over recent months to monitor likely future demand for the product and will continue to do so until the plague has been contained, he says.
When will it end?
The problem remains that no-one knows when the mouse plague is likely to be over.
CSIRO research officer Steve Henry says there’s usually a one-year trajectory during which the mice get to such high numbers, they all become quite stressed because of the high level of interaction. This then facilitates the spread of disease through the population and food becomes scarce.
Typically, they then start to turn on each other and eat the weak ones and the population shrinks away to nothing.
The problem, says Henry, is this is not what has happened with this current plague.
“We saw about three or four months in that the mice had started to eat each other and that was a sign that the plague was about to end. We don’t think that we have seen a crash though because in some areas, people are still reporting relatively high areas of mice.
“About eight to 10 weeks ago mice stopped breeding because of the onset of shorter days and winter. The population will plateau through the wintertime and a fair proportion of them will die through the winter as well. But what is difficult to predict is the level of over winter survival you get because that determines the starting population next spring. When they start to breed again, and there’s a lot of them who have survived through winter, the rate of increase is really high. That’s a cause for some concern for us.”