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I was sitting outside the other night, looking up at the crescent moon. Using just a pair of binoculars, the craters are clearly visible, pock-marking the surface and reminding me of the tremendous impacts that have occurred over the millennia. As most of us know, the same has happened to Earth, causing mass extinction events and ending the era of the dinosaurs 65 million years ago. Although 70% of life on Earth was destroyed, lower life forms survived and among them, the fungi. Largely ignored by biologists in the past, fungi are now being recognised for their importance in our ecosystems and increasingly for their role in medicine. One of the members of the Penecillium genus was made famous by Fleming (and also Howard Florey and Ernst Chain, who shared the Nobel prize for penicillin) but there are many not so helpful species in this ubiquitous group.
Mushrooms, yeasts and moulds are all fungi and are familiar to us, even though precise identification requires expertise, especially when foraging for something edible. Dogs are not very choosy when it comes to eating, as we all know, and vets spend a good deal of time treating the results of canine pica, sometimes due to ingestion of a poisonous mushroom or mould. The common names of our most toxic mushrooms leave no doubt about their nature, for example “death cap”, “destroying angel” (the Amanitas) and “funeral bell” (Galerina). If you visit the Woodland Trust website there are some excellent photos of these with notes on the habitats that they favour. Obviously to be avoided but try telling your dog who’s knowledge of mycology extends as far as ‘if I eat it and it makes me sick, it’s toxic’. Not as though they think in quite those terms!
Mushrooms are easy to spot but other fungi are far less visible, existing in the soil and on organic material, releasing invisible spores and toxins that can be inhaled and ingested. Our old ally Penecillium is often the mould found on food but these species are different to Fleming’s classic and secrete toxins not antibiotics. Our food recycle bins are picnic hampers for dogs and a Petri dish for fungi and bacteria. The simple handle-up locking device on the kerb-side recycle containers is no match for many dogs and many of us have seen the evidence strewn across the road. So what sort of harm can be caused by eating mouldy food or a poisonous mushroom? Well, fungal toxins usually cause gastro-intestinal and neurological signs, like many poisons and symptoms start a few hours after ingestion.
An example happened just the other day. One of the busiest breeds in the business, a young working Cocker spaniel, had been out with her owners exploring the countryside at great speed. As usual, nothing unusual was seen on the walk but a few hours later poor Olive was shaking like a leaf in a gale and was clearly ‘altered’ although still conscious. No sign of vomiting so low blood glucose (not uncommon in highly active breeds after excessive exercise) was also a possibility. However, Olive had not been out for long and had eaten that day so hypoglycaemia was not top of my list. As I was arranging an emergency referral to the on-call service, poor Olive went into a full-blown seizure. Luckily I had some diazepam (Valium) on hand and managed to give her an intra-venous dose despite all the tremours. The vet on-call took over the case management and Olive made a full recovery, although it took several days. This was a lucky escape as some more severe cases of fungal toxicity suffer permanent brain damage and of course, can die. As there is no specific antidote for these poisons, the outcome depends on the particular toxin, the dose ingested and the speed of treatment. We don’t know what Olive ate, as is usual in such cases, unless some material is vomited up for inspection. The delay in onset of symptoms makes this unlikely, adding further uncertainty but as we know, veterinary medicine and uncertainty go hand-in-hand.
So much for fungal toxicology. Important as they are often forgotten, are actual fungal infections that can affect the skin and the ear (quite common and caused by ringworm and a yeast called Malassezia) and much more rarely the nasal passages in long-nosed dogs (Aspergillus). This latter condition used to be almost incurable without radical surgery but the development of effective anti-fungal treatments has given us powerful weapons against those fungi who are not our friends, even though the vast majority are.