Fellow Travellers

Symbiosis and Sustainability – ‘the problem with pets’
As Suzie ventures into the unknown, the possibility that he will pick up unwanted visitors along his travels haunts.  Him catching fleas preoccupies Angela, an occasional scratching cat provoking the dread of an infestation. Of course there are remedies: collars, powders and so on, the paraphernalia of cat consumerism, not only expensive but risky, as the environmental lobby points out.

So many products on the market are comprised of toxic, harmful chemicals, terrible for the pet and dangerous if you have young children. They can even create resistant generations of fleas that are no longer killed by the treatments and weaken your animal to become vulnerable to further infestations. What are we to do?

A sustainable pets movement is possible, according to Southern Fried Science. ‘The Problem with Pets’ is that

pets have a real and lasting impact on both social and natural ecosystems,their position in society is problematic,and when talking about living sustainably,the choices we make with regards to our pets matter

The first step in becoming a sustainable pet owner is asking yourself,“do I really need a pet?”Remember,the lowest environmental impact you can have regarding your pets is none at all. Take the money you’ll save from not owning a pet and donate to local organizations that help reduce feral animal populations. Beyond that,there are three guidelines that will help you define what is and is not a sustainable pet…

The word ‘symbiotic‘ (meaning together-alive) describes a close, mutual relationship between life forms, “the living together of unlike organisms”.

The cat/human bond, one of many symbioses, multifaceted with benefits and compromises, goes back thousands of years. Anecdotal evidence of humans love for cats is widespread. But there seems to be a need to explain, simply or definitively, why this is so. Maia Szalavitz, writing in TIME Healthland, speculates a third life form may be responsible, a clever yet tiny ‘parasitic infection’, Toxoplasma gondii.

A parasitic relationship is one type of symbiosis, and the term ‘parasites’ covers both life forms that kill their hosts and those that need their hosts alive. Toxoplasma gondii, or T.gondii for short, infects mammals but can only sexually reproduce in cats, so needs to infect cats to continue its life cycle. Thus the cat is known as the ‘definitive host’.

t.gondi life cycle
the life cycle of T.gondii

In increasing its chances of getting into cats, T.gondiihas achieved something rare for such a simple organism – it can affect the minds of infected rodents.

Rats and mice, cleverly enough, normally flee from the mere hint of cat odour knowing it means trouble. But when infected with T.gondiithey become attracted to cats natural smells.

t.gondi life cycle
another view of the cycle

T.gondii seems to raise dopamine in just the right parts of the brain to fool the rodent the cat’s a potential mate. The cat can then easily catch and eat the rodent and the parasite easily crosses over into the cat. The cat gets a free rodent and T.gondii gets a free ride to a new spawning generation.

In the TIME piece, Szalavitz asks, referencing one study that suggests

infected women were warmer and friendlier than non-infected women…does T. gondii also cause cat ladies to collect furry felines? No research appears to have been done directly on this subject, though one study did find a connection between the bug and obsessive-compulsive disorder, of which animal hoarding is one form

This is tenuous in the extreme; we can’t say T. gondii affects humans in the same way. Why would it? There’s no evolutionary advantage to it, since cats do not routinely ingest humans. Suzie would have thought it far more interesting to look at what the risks to the cat are, and how to minimise the general risks for cats and humans alike. This blog will report on this soon, but cats are very unlikely to catch T.gondii from humans, as the life-cycle diagrams above indicate.

But let us first look deeper at the clever little critter, investigated ‘scientifically’ for years, which with something like this means animal experiments.

Foreground -T.gondii at work. Background - T.gondii cyst in the brain

A 1998 paper observes T.gondii build tiny cysts ‘in the neural and muscular tissues, including the brain, eyes, and skeletal and cardiac muscles”. Reassuringly, if indolently, the researchers reckon “tissue cysts probably do not cause any harm and can persist for the life of the host without causing…inflammatory response”.

News of the mind-control effect the organism has on rodents was published as long ago as 2000 by the Royal Society:

Fatal attraction in rats infected with Toxoplasma gondii (Abstract).
T. gondii’s manipulation appears to alter the rat’s perception of cat risk, in some cases turning their innate aversion into an imprudent attraction…this ubiquitous parasite subtly alters the brain of its intermediate host to enhance predation rate whilst leaving other behavioural categories and general health intact. This is in contrast to the gross impediments frequently characteristic of many other host–parasite systems.

Note the emphasis on the health of the intermediate host, and not the cats. In 2006 researchers in America also found mice and rats with T. gondii lost their fear of cats, and that “such loss of fear is remarkably specific, because infection did not diminish learned fear, anxiety-like behavior, olfaction, or nonaversive learning”. This 2011 research, which has caught Szalavitz’s eye, seems further confirmation of the effect, finding:

rats infected with the brain parasite approach the cat odors they typically avoid…this change in host behavior is thought to be a remarkable example of a parasite manipulating a mammalian host for its own benefit.

Suzie Bubbs will not say. He’s yet to catch a rat or mouse, and when he does he will let the humans know, sure they will be entertained by the spectacle. For now, parasites can take their own chances.


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