cat-scratch fever

I am always enthralled with the panel-discussions on BBC Radio 4’s In Our Time whatever the topic, and this week’s episode on Parisitism was no exception and particularly enjoyed the sidebar about the curiously manipulative micro-organism called the Toxoplasma gondii, which punches way above its weight. Though it can infect any mammal, in most incidents the parasite infests its host by cloning itself and these incursions in turn are generally short-lived as the biological defences of the host can quickly adapt to wear down the infection.
Sexual reproduction—which accords the parasite the evolutionary advantage of diversity and subsequent generations propelling the better traits of the forebears—can also occur but only while dwelling in felines. I had heard of toxoplasmosis once before when the wife of a co-worker, apropos of nothing, shared with me the fact that she had been diagnosed with it at one point, but never knew of its prevalence nor the strange and circuitous path it takes to mate. Seemingly a disease of affluence, some half of the human population are estimated to have been exposed and carry the parasite though most cases are mild, asymptomatic and vary greatly according to culture. In order to get from the wilds into lions, tigers or house-cats and complete its lifestyle, T. gondii, picked up by rodents, has been seen to radically alter their instinctual behaviour. Uninfected rodents demonstrate a visceral aversion to the smell of cat urine out of self-preservation, but those infested will sacrifice themselves to their local mouser, like a Trojan horse. Studies are not terribly conclusive but research suggests that the parasite may induce some of the same neurologic disorders. No offense intended for cat-fanciers but this does make me wonder why so many self-identify with their affinity for either the canine or feline persuasion and if there’s not some underlying pathology.