The Hack In The Cat

Blog Author: Professor Adrian Thomas, CSO, Animal Dynamics

Cyber security is becoming increasingly critical – computer systems are a valuable resource, ripe for exploitation, and vulnerable to infection by hostile actors. The terminology around trojans, ransomware and viruses is not entirely accidental – biology has suffered similar issues since cells first evolved. Some of the techniques biological parasites use to spread themselves are spectacularly sophisticated.

Obviously, just as with computer security, the first step is to keep the bad-guys out. That is why skin is so tough, and heals so quickly if it is damaged. It is probably also why we are disgusted by dirt – to avoid infection. Air-gaps work in software and wetware. However, animals have to eat, and lots of parasites have evolved to manipulate the behaviour of an intermediate host to make it more likely to get eaten. A bit like the trick of leaving USB sticks laying around outside a company in the hope someone takes them through the airgap and plugs them in.

Perhaps one of the most spectacular is in the brain-worm Toxoplasma gondii. Toxoplasma gondii’s primary host is the cat, and Toxoplasma oocytes are shed in cat faeces, where they can be picked up by mice, rats, and other animals (including pigs, sheep and cows). In the secondary host, particularly mice and rats, Toxoplasma changes the hosts behaviour, making them more risk prone, more likely to explore, less scared of open spaces and less scared of cats. That means infected rats and mice get caught and eaten by cats, and the life-cycle continues.

Humans can also pick up Toxoplasma either from cat faeces (wear gloves when gardening), or more likely from contaminated meat (don’t eat raw meat). In humans Toxoplasma infection is short lived, with flu-like symptoms, and the immune system usually clears it up within weeks. However, there is some evidence that infection with Toxoplasma also leads to increased risk taking in humans. Strikingly, students who tested positive for Toxoplasma antibodies (salivary test) were 1.4x more likely to major in business and 1.7x more likely to have an emphasis in ‘management and entrepreneurship’. It’s not just students – among professionals attendees at entrepreneurship events, Toxoplasma gondii-positive individuals were 1.8x more likely to have started their own business than other attendees. The correlation seems to be global – Toxoplasma gondii prevalence in a nation is positively correlated with level of entrepreneurial activity in that nation in the Global Entrepreneurship Monitor. These are all correlations, but they hint that even in humans parasite infection can have strong impact on complex behaviours, including those linked to business, productivity and economics.

Preventing Toxoplasma infection is not too tricky – avoid cat-poo and raw meat, but if those fail the immune system can mop it up – most people produce antibodies to Toxoplasma and clear it up in a few weeks. Antibodies are part of the Adaptive Immune System, as opposed to the Innate Immune System. The Innate Immune System is the older of the two, in evolutionary terms, being present in plants, funghi and invertebrate animals.

The Innate Immune System recruits immune cells to sites of infection through chemical signals, identifies bacteria through the complement cascade and clears dead cells, and identifies and removes foreign substances using white blood cells. It is essentially pre-programmed, based on information in the genome, to recognise self- and other-.

The adaptive immune system is evolutionarily; much more recent (vertebrates) and much more sophisticated than just a pre-programmed genetically-determined self-other comparison. The adaptive or acquired immune system can develop an immunological memory to a novel pathogen and retain that memory and associated immunity for long periods, sometimes a lifespan. It is called the adaptive, or acquired immune system because it adapts to new pathogens by acquiring pathogen-specific receptors through an adaptive (evolutionary) process involving mutations in antibody-coding genes, which allow antibodies to evolve within the body with an almost infinite repertoire of specificity – i.e. able to recognise almost any novel pathogen protein. That specificity is retained by being passed down the line of lymphocytes as they reproduce – all the progeny retain the new mutation and its associated specificity. This allows the adaptive immune system to generate antibodies to pathogens that have never before been encountered. Triggering this process is how immunisation works.

Johnson SK, Fitza MA, Lerner DA, Calhoun DM, Beldon MA, Chan ET, Johnson PTJ. 2018 Risky business: linking Toxoplasma gondii infection and entrepreneurship behaviours across individuals and countries. Proc. R. Soc. B 285: 20180822. 11, 2021