Poverty - the neglected disease cause

Tropical diseases have been affecting people in the American South as long as humans have been living there. Drainage and sanitation projects in the 19th century eliminated many mosquito breeding grounds, but epidemics continued. The last yellow fever outbreak in the USA hit New Orleans in 1905, killing nearly 1,000 people. Malaria was even more difficult to eradicate, stubbornly remaining in pockets of the South into the 1940s and 1950s. The Centers for Disease Control and Prevention was founded in 1946 specifically to combat this problem, which is why their headquarters are in Atlanta: it was then the heart of malaria country.

Infectious diseases that were eradicated in America during the 20th century are now roaring back, thanks to growing poverty, failing sanitation, and underinvestment in science and health research and regulation. Chagas, hookworm disease, cysticercosis, and chikungunya -- just to name a few. They cluster in the American south and southwest, and disproportionately effect the poorest Americans. Chagas is caused by the parasite Trypanosoma cruzi and spread by a group of insects called Triatoma, or ‘kissing bugs’ (because they like to bite near the mouth). Most people with Chagas don’t know they’ve been infected but that doesn’t mean damage isn’t occurring. Over time, the T. cruzi parasite can chew through cardiac muscle and cause heart failure. Chagas is a major problem in Latin America, where an estimated 8 million people are infected. It’s also one of the leading causes of heart failure in the region and causes an estimated 11,000 deaths each year. Like mosquitoes, triatomine bugs drink blood from a variety of vertebrates, including humans. However, triatomine bugs don’t spread the Chagas parasite directly through their bite. After they finish feeding, some bugs might defecate, leaving parasite-laden faeces on their host’s skin. Scratching the bite can cause microscopic tears in the skin, through which the parasite can enter. In other cases, touching the bite can transfer the parasite to the fingers, which then spread it to the eyes and nose. The disease can also be transmitted from mother to fetus during pregnancy and through blood transfusions. Most triatomine bugs feed at night, which is why many people don’t know they have been bitten. And while some have flu-like symptoms several days after they were infected, or develop a swelling near the eye called a chagoma, many people have no symptoms at all. A 2014 study showed that one out of every 6,500 people who donated blood screened positive for Chagas – almost 50 times more than the CDC’s estimate that one in 300,000 Americans was infected.

 A little-known parasitic disease called toxocariasis (caused by roundworm) is another example and estimated to infect 2.8 million African Americans, most of them living in urban poverty. The disease can cause asthma and wheezing, as well as cognitive delays and behaviour problems. Poverty is a critical factor. In 2005, an outbreak of dengue (a virus carried by mosquitoes that causes headache, fever and severe joint pain) affected two cities on either side of the US–Mexico border: Brownsville in Texas and Matamoros. Although the mosquito that spread the virus was present in roughly equal numbers in both cities, the infection rate in Matamoros was nearly double that of Brownsville’s. The reason? Better housing and a higher standard of living in Brownsville meant the widespread use of air conditioning, which deters mosquitoes. Poverty matters, and it matters a lot.

“While we were calling them neglected tropical diseases, the ‘tropical’ part is probably a misnomer,” says Peter Hotez, who founded a school of tropical medicine at the Baylor College of Medicine in Houston, “Most of the world’s neglected tropical diseases are in wealthy countries. It’s the poor living among the wealthy. There’s been a gradual rise in the economies of all nations…but it’s leaving behind a bottom segment of society, and that bottom segment of society is who gets the neglected tropical diseases,” Hotez says. An estimated 45 million Americans live in poverty, including more than one in five children. Approximately 1.65 million live in extreme poverty, defined as living on less than $2 per day. Economists estimate that the disparity between rich and poor Americans now is greater than at any time since the Great Depression, and this includes the South. “Poverty is seldom evenly distributed across the country. Poverty clusters in pockets. It clusters in northeastern Brazil, it clusters in northern Argentina, it clusters in southern Mexico, it clusters in southwestern China,” Hotez says. “Well, it’s the same thing in the USA. Poverty is clustered in the American South.” Economists believe that a combination of low-paying jobs, inadequate social safety nets and systemic racism all contribute, while disease – as well as being a consequence of inequality – might also turn out to be a significant factor.

It is the nature of these diseases – neglected diseases, diseases of poverty, call them what you like – that they can go unnoticed for years, chewing away at the health of individuals and communities. As poverty, geography, climate and social factors combine to bring tropical diseases out of hiding once again in the US South, physicians, politicians and the general public have to take the warning signs seriously and recognise that the tools available for tackling tropical diseases are sorely lacking. With diseases like Chagas now known to be prevalent and transmissible within the USA, better awareness, better tests and better treatments are all urgently required. Otherwise, as Hotez says, the number of people affected and infected will only continue to rise as this perfect storm grows ever stronger.