Ticks, botulism blamed for deaths of 22 horses November 3, 2011 Scrub tick infestation or botulism most likely caused the deaths of 22 horses at Kooralbyn, in Queensland, authorities say. Chief Biosecurity Officer Jim Thompson said both conditions caused progressive muscular paralysis, as was seen with these horses, and it was often hard to differentiate between the two. "Botulism is a bacteria that lives in soil and produces a toxin that affects the nervous system if ingested," he said. "The other likely scenario is scrub tick poisoning. "Witnesses have reported that the horses first noticed to be in distress on Thursday, October 6, had been carrying large numbers of ticks. "Fatal infestations of scrub tick on adult horses have been recorded in the past. "This has been an unusual and complex case. Biosecurity Queensland worked closely with the attending private veterinarian and Queensland Health to test a range of samples from the horses and the paddock where they were kept. "Despite carrying out such a thorough investigation, we know from experience that test results don't always pinpoint an exact cause of death. "However based on the circumstances, Biosecurity Queensland believes scrub ticks or botulism were most likely responsible in this case." The department said its conclusions were reached after three weeks of comprehensive laboratory testing. It said test results excluded Hendra virus, pesticides, heavy metals (arsenic, lead, cyanide, nitrate), toxic plants, water contamination and deliberate poisoning.