SWA MP CA NCER Honey's Journey
M
y son, Tully owns “Honey”, a 10-year-old 9hh mini-pony he drives in harness. Tully was awarded the 2019 Junior Driver of the Year by the Australian Carriage Driving Society. The February 2020 rains brought grass back to our farm in Northern NSW, and filled the back swamp that had been bone dry. On the 11 March I noticed a small, weeping sore on Honey’s offside pastern. I knew it was Pythium Insidiosum. Often, the initial lesion is mistaken for pastern dermatitis, a small cut, proudflesh or many other common, skin conditions. Pythium is confined to tropical and subtropical regions, with most infections occurring when temperatures are between 30C and 40C. From past experience with this disease I knew it to be true to its name, it is insidious. Think water borne mould, on steroids with a cloak of immunological invisibility. To understand what Honey was facing, I need to give a quick biology lesson. Pythium insidiosum is an oomycete, a “water mold”, having fungal characteristics but not a true fungus. Oomycetes are found in standing or stagnant water, hence the common name “swamp cancer” for Pythium infections. Pythium usually lives in aquatic vegetation, but at certain stages it develops zoospores that have motile flagella. These swimming zoospores seek out vegetation, or if present, horse hair or skin. The zoospore cannot pierce skin but finds an entry point of broken skin, an insect bite is sufficient, and enters the animal. Once inside, 12 EQUINE NEWS.COM.AU
it sheds its flagella and starts colonizing the flesh by sending out hyphae (think microscopic roots), which tear the flesh apart, starting a cascade of biological reactions. The body identifies Pythium as an allergen, not a killer, and starts a normal allergic response resulting in itching and exudate. This is the “Th2” immune response. However, Pythium is smart (if an oomycete can be smart), and makes the body create a concrete like substance around the hyphae termed “kunkers”. Even though Pythium infects dogs, cats and even humans, kunkers are only found in equine pythiosis. Unfortunately, the Th2 response is the wrong response. The body needs to recognize the threat and send its “Th1” immune response to kill it, however, the kunkers cloak the hyphae and the body stays locked in its ineffective Th2 immune response. What results is a weeping, mushy wound with microabcesses and draining tracts, growing rapidly every day, with an itch so severe it causes self-mutilation. I spent the next day calling up vets to get an appointment so we could start treatment. Time is precious; the best prognosis requires treatment within 20 days of infection. The vets returned my calls; one wasn’t interested in treating Honey, (due to such poor prognosis), another was prepared to take her on but did not have the facilities to treat a horse. My usual vet, Dr Oliver Liyou specialises in equine dentistry and reproduction. As a rule, he doesn’t do emergency work, but as a long-standing client, he agreed to see Honey at 8am the next day for a diagnosis, but not necessarily for ongoing
Lesion when it was first noticed
treatment. That evening I noticed a kunker and the lesion had spread, any hope I was dealing with a simple infection was gone. At the appointment, the diagnosis was obvious. Dr Oliver and I both knew it was Pythium; treatment would be expensive and likely futile. Dr Oliver and I had been down this road a decade earlier, with my stockhorse, Tommy (euthanised after unsuccessful treatment). Two things were different now; I had a disposable income and new treatment options existed; both surgical and pharmacological. We formed a war plan, essentially throwing every scientific treatment that had ever shown experimental success against this organism. Excision of the lesion, IV treatment with sodium iodide, topical treatment with DSMO and Immaverol, and a course of painful immunotherapy injections. Dr. Oliver knew an excellent equine surgeon, Dr David Ahearn, skilled in electrocautery surgery, practicing in Queensland that day. So, we loaded Honey and the children up SPRING 2021
