Countdown to Hallowe'en 2017: Latent Feline Infection

This meme dates from 2010. Image Source: Know Your Meme.

Today's post concerns how cats influence human health, based on the article: Influence of latent Toxoplasma infection on human personality, physiology and morphology: pros and cons of the Toxoplasma–human model in studying the manipulation hypothesis. That article concerns the often asymptomatic or latent disease, toxoplasmosis, caused by an intercellular parasite which is passed through cats to humans and is related to human depression, autism, cerebral calcification, sex addiction, and schizophrenia. It is a disease that affects rodents and makes them lose all fear of cats; this has allowed the parasitic protozoan to return to feline systems, where it can complete its life cycle. The parasite also affects the rodent brain's sexual impulses and reward centres.

Toxoplasma gondii parasitic protozoa. Image Source: Ke Hu and John Murray via Business Insider.

Scientists believe that toxoplasmosis infection similarly makes humans attracted to cats. The disease affects an enormous number of people, which may incidentally ensure the survival of the domestic cat, while also safeguarding the protozoan. Wiki:

"Up to half of the world's population are infected by toxoplasmosis but have no symptoms. In the United States about 23% are affected and in some areas of the world this is up to 95%. About 200,000 cases of congenital toxoplasmosis occur a year. Charles Nicolle and Louis Manceaux first described the organism in 1908. In 1941 transmission during pregnancy from a mother to a child was confirmed."

Perhaps those Walking Dead zombie stories are telling you the truth about a reality you suspect, but cannot see. If you think everyone around you is infected by some mysterious bug that makes them crazy, you may not be paranoid. You may be right. From Florence Robert-Gangneux and Marie-Laure Dardé in American Society for Microbiology (2012):

"Low seroprevalences (10 to 30%) have been observed in North America, in South East Asia, in Northern Europe, and in Sahelian countries of Africa. Moderate prevalences (30 to 50%) have been found in countries of Central and Southern Europe, and high prevalences have been found Latin America and in tropical African countries."

Approximate rates of infection by country below are almost all based on tests of pregnant women. Some studies only focus on particular regions, and the numbers change from year to year. Follow the links for years and details; not all countries conduct studies or keep statistics. Note that these statistics tend to show infection passed from mother to child in the womb. They do not include post-natal infection, in which people are infected directly by handling cats or eating raw or rare meat:

• Argentina: sources for Buenos Aires 45.6%-57.2% infected
• Australia: 28% infected; 23% found infected in pregnant women from Melbourne
• Bahrain: 22.3% tested positive, from pregnant women in Manama only
• Belgium: 48.7% infected
• Brazil: 66.9% infected; other sources range 55.6%-77.8%, depending on region
• Canada: unknown; extrapolated estimate 14%-22% infected
• Chile: 40%-90% of the population, depending on region
• China: Changchun only, 10.6% infected among pregnant women
• Colombia: 43.1%-66.7%, different sources, depending on region
• Costa Rica: approximately 55%, increases in rural areas and with poverty
• Croatia: 38.1% infected
• Cuba: different studies from Havana areas, 44%-66.3%
• Czech Republic: 30%-40% infected; in Prague, 19.8% infected
• Denmark: statistics for Copenhagen, 27.8% infected
• Egypt: measured in women only, 46.5% in urban areas, 57.6% in rural areas
• France: 45% infected
• Germany: Western Pomeranian statistics only, 63.2% infected
• Greece: depending on different studies and different regions, 20%-36.4% infected
• Grenada: 57% infected, nationwide estimate
• India: 11.6%-45%, depending on class and region
• Iran: 29.4%-63.9%, depending on class and region
• Iraq: 49.2% infected, statistics for pregnant women tested in Basra
• Italy: 17.5%-34.4%, a range of averages, from different studies and different regions
• Ivory Coast: 60% infected among pregnant women from Abidjan
• Jordan: 47.1% infected in Amman
• Kuwait: 45.7% infected among pregnant women
• Malaysia: 49% infected among pregnant women from Kuala Lumpur
• Mexico: extrapolated estimate 22% infected; another source found 6.1% of pregnant women infected in Durango
• Morocco: Rabat statistics only, among pregnant women, 50.6% infected
• Netherlands: 35.2% nationwide
• New Zealand: statistics for pregnant women from Auckland, 35.4% infected
• Poland: 35.8%-43.7% infected, based on pregnant women only in three cities, Warsaw, Lodz, Poznan
• Romania: 57.6% infected in women of child-bearing age, Timisoara only
• Serbia: 33% infected nationwide
• Singapore: 17.2% infected among pregnant women
• Slovakia: 22.1% among pregnant women, Bratislava data only
• Slovenia: 34% infected nationwide
• South Korea: 4.3% infected; other sources range 0.8%-3.7% infected in Daejeon and Suwon
• Spain: 18.8%-43.8% infected, averages from certain regions only
• Sudan: Khartoum and Omdurman only, pregnant women tested, 34.1% infected
• Sweden: 18% infected from Stockholm and Skane only
• Switzerland: 8.2%-35% infected, based on data from Lausanne, Geneva, Basel only
• Thailand: 5.3%-21.5% infected among pregnant women from different regions
• Turkey: 30.1%-60.4% average infected among pregnant women, from different classes and regions, impacted by regional culinary traditions (consumption of raw meat)
• United Kingdom: 31% infected, 20 million people in 2012, with 80% of these asymptomatic; East Kent statistics for pregnant women showed 9.1% infected
• USA: 15%-22.5% of the population, depending on demographic, 60 million+ infected; another source states 11% nationwide, with 7.76% for US-born and 28.1% for foreign born
• Venezuela: 38% infected among pregnant women from Lara State
• Vietnam: from Nha Trang only, 11.2% of pregnant women infected

In humans, the disease can remain latent until adulthood, or until the body experiences weakened immunity due to other causes. The non-latent form of the disease can feel like the 'flu' and spreads to the brain, eyes, and other organs; it creates cysts in the amygdala and nucleus accumbens, and changes the connections inside the brain which deal with fear responses, sexual attraction, decision-making and memory. The parasite also increases dopamine production, altering brain chemistry in the same ways cocaine - and schizophrenia - do. Those who are infected post-natally and directly through handling cats after birth are affected more severely than those who are infected congenitally.

Image Source: Twitter.

A low index-to-ring-finger ratio, especially on the left hand, can be caused by congenital toxoplasmosis; a low ratio also alters facial appearance, making a toxo-infected individual resemble the face on the far right. If the parasite is acquired post-natally, the decreased asymmetry can also appear in the left hand as the infected individual responds to changed testosterone levels over time. Czech researchers further found that these facial differences, derived from hormonal differences, relate to perceived intelligence in social interactions. Image Source: Postironic Distillation.

Composite photographs of 18 toxoplasma-free (left) and 18 toxoplasma-infected students (right)." (2007 article) Image Source: Neuroendocrinology News.

Equally long index and ring fingers, often on the left hand, may be a sign of toxoplasmic infection. Image Source: Zombie Hunters.

In questionable findings, scientists go so far as to claim that high levels of toxoplasma infection in a society can change its political evolution and governmental history, based on the general population's disposition toward certain behaviours. Video Source: CBC via Youtube.

The parasite affects face and body shape. Both males and females infected with the parasite have a lower index finger to ring finger ratio, especially on the left hand (see articles here, here and here) because infection changes testosterone levels. Compared to the non-infected, they have shorter index fingers and longer ring fingers, making those fingers of equal length. The waist-to-hip ratio of infected people is also lower than in non-infected individuals. Directed assymetry in infected individuals further affects facial appearance and attractiveness, which I previously discussed in this post. Frozen Evolution:

"As always, our lovely Toxoplasma had a surprise in store. It turned out that Toxo positives and negatives exhibited minimal differences in fluctuating asymmetry, but significant differences in specific anthropometric measurements. If there was any asymmetry, then it was likely directional – in several anthropometric measurements, all the Toxo positives were asymmetrical to [the] same side. Toxo positives had a wider forehead, a wider left ear, wider and longer palms, longer fingers on both hands and wider ankles. The most obvious difference that we noted in men had to do with body height – Toxo positive men were an average 3 cm taller than Toxo negatives.

Another difference that stood out was the length ratio of the pointer and ring fingers on the left hand. This was interesting, because scientists think that the ratio correlates negatively with the concentration of testosterone which the embryo is exposed to during intrauterine development. Men usually have a shorter pointer than ring finger, which means that the length ratio of the 2nd to 4th finger is less than one. In women, this difference isn’t as distinct – they often even have a longer pointer than ring finger, so the ratio is greater than one. For each gender, the ratio correlates with a number of characteristics – in men, with sexual orientation, and mathematical and musical talent; in women, with things like fertility."

Image Source: Funny Animal Archive.

Wiki summarizes the behavioural changes the parasitic protozoan creates in the human mind:

"Once healthy humans are infected with Toxoplasma gondii, it may lead to altered behavioral differences like psychomotor performance and neurological disorders like depression and/or suicide and even schizophrenia. ... 

Differences in behaviour observed in infected hosts compared to non-infected individuals have been shown to be sex dependent. Looking at humans, studies using the Cattell’s 16 Personality Factor questionnaire, found that infected men scored lower on Factor G (superego strength/rule consciousness) and higher on Factor L (vigilance) while the opposite pattern was observed for infected women. This means that men were more likely to disregard rule[s] and were more expedient, suspicious and jealous. On the other hand, women were more warm hearted, outgoing, conscientious and moralistic. ...

It was found that the infected adults performed much more poorly and lost their concentration more quickly than the control group. But, the effect of the infection only explains less than 10% of the variability in performance. (i.e. could be other confounding factors) Correlation has also been observed between seroprevalence of T. gondii in humans and increased risk of traffic accidents. Infected subjects have a 2.65 times higher risk of getting into a traffic accident. A similar study done in Turkey showed that there is a higher incidence of Toxoplasma gondii antibodies among drivers who have been involved in traffic accidents. Furthermore, this parasite has been associated with many neurological disorders such as schizophrenia. In a meta-analysis, 23 studies met inclusion criteria. The results demonstrate that the seroprevalence of antibodies to T.gondii in people with schizophrenia is significantly higher than in control populations (OR=2.73, P < 0.000001). In more recent studies, it was found that suicide attempters ha[ve] significantly higher IgG antibody levels to T. gondii as compared with patients without a suicide attempt. Infection was also shown to be associated with suicide in women over the age of 60. (P < 0.005) As mentioned before, these results of increased proportions of people seropositive for the parasite in cases of these neurological disorders does not indicate a causal relationship between the infection and disorder. It is important to mention that in 2016 a population-representative birth cohort study which was done, to test a hypothesis that toxoplasmosis is related to impairment in brain and behaviour measured by a range of phenotypes including neuropsychiatric disorders, poor impulse control, personality and neurocognitive deficits. ...

There definitely is a link/association however, the evidence is still very conflicting. In order to fully establish the extent of Toxoplasma gondii’s influence on human behaviour, better research designs and larger sample sizes are needed."

There are data here on how the disease may or may not affect behaviour and health, in terms of self-inflicted injuries, unintended injuries, traffic accidents, shortened lifespans due to related diseases, including cancer, heart disease, addictions and MS, and several neuro-psychiatric conditions. However, there are so many complicating factors that it is difficult to determine how the parasite is directly or indirectly responsible.

Toxo-positivity is associated with higher incidents of traffic accidents, which are coincidentally, statistically dominated by men. Image Source: The Mirror.

Toxo-positivity is linked to schizophrenia, a disease which affects more men than women. On males, a low index-to-ring finger length ratio on the left hand is a sign of toxoplasmosis infection; and equally-long (low ratio) left index and ring fingers similarly may be a sign of male schizophrenia: "[R]esearchers found that men with schizophrenia had a higher digit ratio for the right hand than men without the disorder. In other words, schizophrenic men were more likely to have longer right index fingers and shorter ring fingers. On the left hand, however, schizophrenic men had lower digit ratios than healthy men." Image Source: Boomer to Boomer.

English artist Louis Wain (1860-1939), may have suffered from schizophrenia. Cats featured in many of his paintings and drawings, and he may also have been toxo-positive. Above is a famous series of his increasingly-abstract cat paintings; their style was possibly affected by the progress of his mental illness. But it is not confirmed that they were painted in the presented order. Because we cannot confirm the correlation between illness and art - as opposed to artistic experimentation and art - in these works, psychiatrist Dr. David O'Flynn deemed Wain's paintings, "the Mona Lisa of asylum art." Image Source: reliawire.

Louis Wain Exhibition, Bethlem Archive and Museum, SLaM, London, UK (December 2012): "Gallery talk by Dr. David O'Flynn, Consultant Psychiatrist, Lambeth and the Maudsley Hospitals, South London and Maudsley NHS Foundation trust." Video Source: NHS via Youtube.

Toxo-posivity is associated with male love of cats as well as increased risk of suicide. In 2015, a New York high school senior, Draven Rodriguez, whose yearbook lasercat photo went viral on the Internet, tragically committed suicide. Image Source: Lol Cat Research.

Analyses of toxoplasmosis symptoms are controversial and easily challenged because correlation does not imply causation. A 2013 article in the Journal of Experimental Biology found that men infected with the parasite are taller, look more masculine, and are dominant; the parasite may lower male IQ, although one gauge for that was lower probability of attending higher education. That gauge could have been influenced by toxoplasmosis' tendency to make infected males break rules. However, another study assessed personality, neuroses and intelligence of toxo-positive as compared to toxo-negative subjects through the NEO Personality Inventory; the Wiener Matrizen Test of Intelligence; and the OTIS Intelligence Test. Infected males may be more appealing to women because they have higher levels of testosterone. Stanford neuroendocrinologist Robert Sapolsky believes that there is a military interest in toxo-positive personnel, because they show increased risk-taking, rage disorder, and lower fear thresholds (some studies peripherally connect military personnel and toxoplasmosis infection; see here, here, here, here, here and here).

Image Source: Hollywood Subliminals.

How one measures behavioural symptoms related to toxoplasma infection can be questioned for the gender stereotypes the conclusions confirm. Neuroscientists and epidemiologists may love evolutionary psychology. But one wonders how well they know social anthropology; they reach conclusions which smack of gender essentialism and age-old feline-human myths. For females, according to researchers, toxo-positivity is associated with neuroses, promiscuity, and extroversion, due to the parasite's impact of dopamine levels in the brain. Jaroslav Flegr of Prague's Charles University, a well-known researcher on this topic, has been quoted as saying that toxo-positive women might be "sex-kittens" who suffer from bipolar disorder. But do they age into suicide-prone crazy cat lady spinsters? No, Flegr believes that toxo-positive men are more attracted to owning cats, while toxo-positive women are not; but his reasoning sounds nebulous. Infected females are shorter than non-infected females, and on average display higher intelligence alongside their (supposed) nymphomania, lower proneness to guilt, and lower testosterone.

Image Source: What Would Jack Do.

Image Source: Relatably.

For males and females (at least in the supposed sex-kitten phase) alike, these symptoms increase the chances that infected hosts will mate with people, infected or not, and have children. The parasite passes from mother to child in the womb, with the mother having greater likelihood of giving birth to a boy with dominating traits, and so the protozoan ensures its survival. This is why pregnant women are advised not to keep or handle cats, or at the very least not to clean their litter - and not to eat raw or rare meat. Diagnostic advisories are here, here, here and here.

If you want to know more, google 'latent toxoplasmosis.' The disease could be influencing the behaviour of 2 to 3 billion people. Articles and reports:

• Parasitology Today (1985): Tox[o]plasmosis in Developing Countries
• American Journal of Epidemology (26 February 2001): Toxoplasma gondii Infection in the United States: Seroprevalence and Risk Factors
• Emerging Infectious Diseases (November 2003): Toxoplasma gondii Infection in the United States, 1999–2000
• Right Diagnosis (based on 2004 statistics; very rough extrapolated estimates): Statistics by Country for Toxoplasmosis
• Cross-Cultural Research (February 2004): Personality and Culture Revisited: Linking Traits and Dimensions of Culture
• Discover (1 August 2006): A Nation of Neurotics? Blame the Puppet Masters?
• Neuroendocrinology Letters (2007): Higher perceived dominance in Toxoplasma infected men – a new evidence for role of increased level of testosterone in toxoplasmosis associated changes in human behavior
• Schizophrenia Bulletin (2007): Effects of Toxoplasma on Human Behavior
• American Journal of Physical Anthropology (2008): Brief Communication: Latent toxoplasmosis and salivary testosterone concentration—Important confounding factors in second to fourth digit ratio studies
• Discover (5 October 2008): Toxoplasma – the brain parasite that influences human culture
• International Journal for Parasitology (17 February 2009): Toxoplasmosis snapshots: Global status of Toxoplasma gondii seroprevalence and implications for pregnancy and congenital toxoplasmosis
• The Economist (3 June 2010): A game of cat and mouse
• Psychology Today (25 July 2010): Research Suggests a Link between Toxoplasmosis and Mental Illness
• Journal of Global Infectious Diseases (July-September 2011): Toxoplasmosis: A Global Threat
• Time (18 August 2011): Crazy Cat Love: Caused By Parasitic Infection?
• The Atlantic (March 2012): How Your Cat Is Making You Crazy
• Clinical Microbiology Reviews (1 April 2012): Epidemiology of and Diagnostic Strategies for Toxoplasmosis
• Scientific American (1 September 2012): Common Parasite Linked to Personality Changes
• The Independent (3 September 2012): How toxoplasma spreads... and spreads
• The Independent (4 September 2012): Beware of the cat: Britain's hidden toxoplasma problem
• The Independent (4 September 2012): Professor Joanne Webster: The scientist who uncovered 'fatal feline attraction'
• The Week (4 September 2012): What is toxoplasmosis? How your cat could make you suicidal
• World Health Organization (3 May 2013): The global burden of congenital toxoplasmosis: a systematic review
• Evolutionary Behavioral Sciences (2013): The Relationship between Sex-Typical Body Shape and Quality Indicators
• Advances in Bioresearch (2014): Latent Toxoplasmosis and Testosterone level affect second to fourth digit ratio in Human
• PLOS One (24 March 2014): Toxoplasmosis – A Global Threat. Correlation of Latent Toxoplasmosis with Specific Disease Burden in a Set of 88 Countries
• Frontiers in Behavioral Neuroscience (2014): Are there any relationships between latent Toxoplasma gondii infection, testosterone elevation, and risk of autism spectrum disorder?

The crazy cat lady is a favourite, cheap, easy, and comfy Millennial Hallowe'en costume. Image Source: Coolest Homemade Costumes.

The crazy cat lady meme inspired a famous scene in the horror movie, Jeepers Creepers (2001). Image Source: pinterest.

Image Source: Ellen.

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