1990s’ Island health scare: Were babies at risk?
It could have been from an infected cougar or maybe a handful of house cats. What’s certain is that in the spring of 1995, heavy rain washed feline feces laced with millions of parasitic eggs into the Humpback Reservoir.
Within weeks, more than 100 Victoria residents fell ill with toxoplasmosis in the largest outbreak of its kind ever recorded.
On the lookout for fever, eye problems and brain swelling, health officials tested at least 5,000 pregnant women for the parasitic infection.
“Babies at risk? Testing will tell,” read one Times Colonist headline as health officials scrambled for answers.
“Health scare turns cats into pariahs,” read another.
In the wake of the outbreak, the Humpback Reservoir was closed for good and a disinfection plant was added to the water-supply system that used ultraviolet light to neutralize micro-organisms not killed by chlorine.
A protozoic parasite smaller than the width of a human hair, toxoplasma gondii are found virtually everywhere you look.
“It is so pervasive — it is the most successful life form on the planet,” said Kevin Lafferty, a senior ecologist studying parasites with the U.S. Geological Survey. “It’s 8,000 feet up in the air in geese. It’s 8,000 feet below the surface of the ocean in sperm whales. It’s on every continent, including Antarctica.”
At once neglected and endemic, the parasite could have already infected up to half of humanity, researchers say.
Yet without cats, toxoplasma (or T. gondii) would face an evolutionary dead-end. That’s because its life cycle depends on making it back to the cells that line a feline’s intestine.
The oocysts, or eggs, are shed into the soil with cat feces. From there, the parasite passes through water or onto plants where any warm-blooded animal, including humans, ingests it. That could put some gardeners at risk. But infection can also spread through what you eat, and a slice of medium-rare pork or undercooked chicken could end up transmitting the parasite across your dinner plate.
In the U.S., toxoplasma is estimated to lead to eight per cent of all hospitalizations due to food illness, costing the country an estimated $3 billion US every year. In Canada, its prevalence is not as apparent, though some estimates in Indigenous communities suggest up to a 65 per cent infection rate.
In one 2018 Health Canada study, the parasite was found in 4.3 per cent of fresh ground beef, chicken breast and ground pork bought in supermarkets in B.C., Alberta and Ontario.
Once someone is infected, the parasite can lead to flu-like symptoms, cause damage to eyes and internal organs and lead to encephalitis. People with compromised immune systems and pregnant women and their fetuses are especially at risk of severe illness and even death.
Those clinical symptoms alone are enough for doctors to recommend pregnant women stay away from a domestic cat’s litter box. But like the thousands of Victoria residents thought to have become infected in the 1995 outbreak, many will never notice they have caught the bug.
That’s where things get weird.
In the early 1990s, scientists in the Czech Republic started testing how the parasite might be affecting human personality through a form of gene manipulation in the amygdala, which, among other things, regulates emotion, memory and the fight-or-flight response.
A decade after the outbreak in Victoria, Lafferty joined a growing number of parasitologists obsessed with toxoplasma, asking: Could it be influencing entire cultures?
In 2006, Lafferty published a study examining infection data on the parasite in dozens of countries. He found some striking correlations between infected people and their behaviour: infected women showed increased levels of intelligence, were more likely to follow rules and were more compassionate; infected men, on the other hand, showed lower levels of intelligence, were more frugal and mild-tempered. Infected people of both genders appeared to be more prone to feelings of anxiety, guilt and self-doubt.
Since then, Lafferty says other research has suggested a person’s blood type (particularly those who are Rh+) could offer protection from the parasite’s worst effects.
A wave of research followed. In 2018, a study found entrepreneurs who tested positive for the parasite were 1.8 times more likely to have started their own business. At a global level, nations with higher rates of parasitic infection had higher rates of entrepreneurial activity and were less likely to cite “fear of failure” when starting a new business venture.
A few months later, a group of Polish researchers dissecting the brains of 102 recently deceased cadavers found that the more toxoplasma DNA in a person’s brain, the more likely they had taken a big risk and died because of it.
“T. gondii may contribute to hundreds of thousands of deaths worldwide, including deaths in road accidents, accidents at work and suicides,” concluded the paper.
The idea that tiny organisms at a massive scale are controlling our minds has provided thought-provoking fodder for several media outlets over the years. Despite the number of studies on toxoplasma, Lafferty and other scientists interviewed for this story warn that more work needs to be done to understand the extent to which the parasite is manipulating human behaviour.
“All the stuff we have on humans are basically statistical associations, which we need to take with a grain of salt,” said Lafferty. “However, they are fairly consistent with well-controlled experimental studies in rodents.”