The Brain, Intelligence, and Infections: Neglected Tropical Diseases

The world is a dangerous place.  Humans live in constant contact with a mixture of bacteria, viruses and parasites.  Evolution and modern hygiene have provided us with the means to coexist with those that are helpful and usually survive encounters with most of the ones that are not.  Unfortunately, victory in this conflict is unattainable because dangerous elements are constantly changing form.  Flu and the common cold are caused by viruses that are constantly mutating into different species.  By disturbing ecologies we encounter additional threats that must be dealt with.  Encounters with new diseases should be expected.

Harriet A. Washington has provided us with an indication of what we should expect in an article in The American Scholar: The Well Curve.  She focuses on diseases that can affect brain function and begins by providing a few recent discoveries as examples.

“In 1987, more than 100 Canadians developed….symptoms after dining on tainted mussels harvested off Prince Edward Island. Short-term memory loss accompanied vomiting and diarrhea. The victims also became disoriented and aggressive and finally were wracked by prolonged crying jags. This new disease, christened “amnesiac shellfish poisoning,” was caused by….several species of Pseudo-nitzschia algae. The algae produce domoic acid, a powerful neurotoxin that destroys the ability to make memories and thrives in algal blooms—popularly called red tides—that are incubated by warm weather.”

“Domoic acid resembles a form of the neurotransmitter glutamate so closely that sufferers’ brains could not discern the difference as it passed through the blood-brain barrier to cause confusion, disorientation, seizure, coma, and sometimes death. Monterey Bay National Marine Sanctuary scientists announced a red tide recurrence as recently as June, followed by a mass die-off of infected anchovies, which also threatened their mammalian predators, including man.”

A more recent discovery is even more troubling—a virus that affects algae that somehow learned how to infect humans.

“Investigators from Johns Hopkins, Baltimore’s Sheppard Pratt Health System, and the University of Nebraska–Lincoln were startled to find a previously unsuspected virus, Acanthocystis turfacea chlorella virus 1, or ATCV-1, lurking in the throats of two of every five of their Baltimore research subjects.”

The researchers who made this discovery were involved in investigating physical attributes that might affect mental processes.  They were deeply troubled by what they learned.

“But the study’s baseline cognitive tests unveiled the true shocker. When compared with those who did not harbor the virus, those infected were about 10 percent slower to make calculations and had a reduced attention span, suggesting that the virus compromised their ability to calculate, to focus, and to process visual information—disadvantages in the classroom, on the job, and in other familiar learning situations.”

“The lowered mental functioning was independent of potentially confounding factors, including age, socioeconomic status, education, place of birth, or smoking status. Gender and race made no difference. Repeating this experiment in a larger population yielded the same results, and when the research team tested mice before and after exposing them to the virus, they found 1,000 gene changes in brain regions known to be important to memory and learning. These infected mice also took 10 percent longer to navigate a maze and showed reduced attention spans, compared with the uninfected controls.”

These findings were newsworthy because they occurred in wealthy western countries.  Meanwhile, in poorer counties where health surveillance and treatment are inadequate, infection by pathogens thought to harm brain development or function are common.  It is these diseases that most concern the author.  In fact she begins her piece with this warning.

“Tropical diseases are undermining intellectual development in countries with poor health care—and they’re coming here next.”

Washington gathers evidence to support the notion that racial or ethnic differences in the measurement of what wealthy western countries refer to as IQ (not to be confused with intelligence itself) can be explained by socioeconomic and biomedical factors such as the frequency of infection by diseases known to affect cognitive performance.

“This take on race, intelligence, illness, and poverty is the exact opposite of hereditarian screeds, from Arthur Jensen’s ‘Thirty Years of Research on Black-White Differences in Cognitive Ability’ to Charles Murray and Richard J. Herrnstein’s The Bell Curve to J. Philippe Rushton’s musings on race, intelligence, and penis size. These broadsides and their refutation have dominated the public debate on race and intelligence. The authors’ theories rest on several articles of faith. One is that intelligence, measured by IQ tests, is largely genetic and varies in a racial hierarchy, with Asians or Caucasians usually occupying the apex and various African groups located at the bottom.”

Her choice of title, The Well Curve,’ is indicative of her disdain for the work of the mentioned writers.  Her faith is in the work of others.

“….pathogens that affect cognition have traditionally infected poor people of color in the developing world, so their ravages and long-term effects have been more likely to go unanalyzed and untreated. In developing countries, points out Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston, infection by such pathogens is the norm, not a headline-worthy exception.”

“Studies like a 2010 report from Randy Thornhill, an evolutionary biologist at the University of New Mexico, and a 2011 research study from Carleton University in Ottawa, have strongly correlated low average IQs from various nations with high rates of infectious disease. A 2011 article Thornhill published in the journal Intelligence calculated that, in the United States, allowing for education and wealth, “Infectious disease was the best predictor of average IQ.”

Thornhill provides an interesting explanation for how these diseases can affect brain development and function: these various bacteria, viruses, and parasites compete with the brain for meager nutritional resources.  Deficient nutrition in young children can lead to impaired brain development even without an infectious disease.

“Thornhill’s ‘parasite-stress’ theory maintains that parasites sap the brain’s energy in several ways. The newborn human brain uses fully 87 percent of the body’s “metabolic budget,” an amount that diminishes with age and maturity, and if a young brain cannot meet these initial high-energy requirements, its growth and development suffer. Microbes and larger parasites drain this energy by feeding on tissues and lodging in the digestive tract, where they siphon off nutrients and iron. Additionally, viruses divert energy from their hosts to crank out copies of themselves. This stolen energy normally would fuel brain building and other metabolic needs of the child.”

Washington refers to these diseases that afflict more than a billion people as NDTs (neglected tropical diseases). 

“….NTDs plague extremely poor denizens of the subtropics not only of sub-Saharan Africa, but also of Saudi Arabia, Brazil, India, China, Indonesia, and Mexico. They are, in the words of Peter Hotez, the dean at Baylor, ‘great disablers rather than killers’.”

The extent to which these NTDs affect cognitive performance may still be a bit controversial, but there is no arguing that they are physically and economically debilitating.  Young children who tend to be at least slightly malnourished in many of these countries can only be harmed by being required to compete with parasites for calories.

Perhaps the most interesting—and frightening— conclusion by Washington is that these types of diseases already exist in the United States.

“….tropical diseases—and their neglect—are not limited to the tropics any more. They’re now very much at home in the United States. The Big Five diseases—Chagas disease, cysticercosis, toxocariasis, toxoplasmosis, and trichomoniasis—are quite common here among the poor, Hotez says. ‘While sub-Saharan Africa accounts for many of the world’s NTDs, somewhat paradoxically, most of the world’s NTDs can be found among the poor living in wealthier countries, including the ‘Group of 20’ nations. Houston and Texas … represent ‘ground zero’ for many of America’s neglected tropical diseases’.”

Some explanation of a few of these will suffice to get one’s attention.  Cysticercosis describes what follows from an infestation of the brain by tapeworm larvae.  Tapeworms are usually associated with the digestive track, but in some cases the larvae manage to reach the brain.

“Tunneling into the brain, the larvae become encysted, cloaking themselves from the immune system with specialized tissues. Thus ensconced and unmolested by the immune system, they unleash the horribly versatile disease called cysticercosis.”

“Cases are more common than one might think. Ted Nash, chief of the gastrointestinal parasites section at the National Institutes of Health, told Discover magazine in 2012, “Minimally, there are 5 million cases of epilepsy [worldwide] from neurocysticercosis.” From 1,500 to 2,000 neurocysticercosis cases have been diagnosed in the United States when confused, unconscious, or epileptic patients are brought to the hospital and the detection of antibodies definitively identifies the disease. Cysts near the brain’s visual cortex can blind the carrier. Cysts near the language area can disrupt speech or comprehension. Cysts sometimes block the flow of cerebral fluid, causing hydrocephalus, which necessitates a shunt to relieve the pressure and prevent unconsciousness and death. All too frequently, a tapeworm cyst causes epilepsy.”

Chagas disease is a parasitic ailment that is usually delivered when the inappropriately named “kissing” bug (triatominae) defecates on the skin while sucking the blood of a person.  It is a disease whose home is in the Americas and is more prevalent in the Central American regions.

“Tropical medicine experts agree that at least 330,000 U.S. citizens have Chagas disease, the most common parasitic disease in the Americas, and estimates range as high as one million. It infects six million to seven million more people in Latin America. This chronic, silent parasitic infection leads to fatal heart or intestinal damage in two of every five sufferers, and it also causes intellectual slowing. It can be treated, but the lack of awareness by doctors in the United States means that it often isn’t.”

And then there is this summary statement.

“….taken altogether, the infections that ravage the developing world now imperil the bodies and minds of at least 14 million U.S. residents.”

It seems unavoidable that these NTDs would find a home in the United States.  Many are endemic in warm, tropical regions.  The United States is one of the few wealthy countries that possesses regions in which the climate is actually warm and tropical.  As mentioned earlier, Texas and Houston are ground zero for these types of infections.  Combine the climate with a healthcare system that has little training in recognizing these diseases, while at the same time providing subpar medical care to the poor blacks and Hispanics who are most at risk, and disease becomes inevitable.

Globalization and climate change are also at work.  Increasing temperatures encourage diseases to move northward.  Pathogens can even be carried by wind from distant continents.  The movement of people and large amounts of materials around the world in a globalized economy are not helpful in containing diseases.

Yes, the world is a dangerous place.  We should not expect that to change any time soon.