Health Wanted Show Notes: Neglected Tropical Diseases
World Neglected Tropical Disease Day was January 30.
What are neglected tropical diseases? They are a diverse collection of conditions that can be caused by viruses, bacteria, fungi, parasites, or even toxins.
They tend to affect the poorest communities in tropical areas.
They’re difficult to control from a public health perspective because their epidemiology and spread is impacted by things like environmental conditions, the insects that spread them, and their animal reservoirs animal reservoirs, all of which make eradication difficult.
But, most importantly, they don’t get a lot of attention (hence the “neglected” part) because much of the world doesn’t even know they exist.
And if you’re part of that cohort that’s been blissfully unaware, get ready. Because it’s time to learn.
We’re starting with trachoma.
Trachoma is a persistent infection in the eye that’s caused by the bacteria Chlamydia trachomatis.
It’s thought to be responsible for blindness or vision impairment in 9 million people globally.
This is because repeated infections in the eyes cause scar tissue to form inside the lid, which causes the bottom of the lid to start pulling inward, causing the lashes to rub against the cornea and scratch it, which is obviously incredibly painful.
If left untreated the scarring can create irreversible damage to the eye.
In areas where trachoma is endemic, women are blinded up to four times as often as men. This is likely due to the fact that preschool aged children, who women are typically in closer contact with, are significant carriers of the bacteria.
Flies then pick the bacteria up when they make contact with the tears or snot of an infected person and pass it on to others when they land on their faces.
It can also be spread through personal contact with hands, bedding and hard surfaces.
Preventative efforts include improving access to sanitation to keep hands and faces clean, and mass administration of the antibiotic azithromycin to kill bacterial infections.
Leprosy is another bacterial infection that you may have thought was a disease of yore.
It is actually still very much a problem, causing about 200,000 cases a year.
The disease is caused by infection with the bacteria Mycobacterium leprae, which is passed by droplets from the nose or mouth of an infected person by close, prolonged contact.
Once infected, the bacteria can affect a person’s skin, eyes, mucous membranes, and nerves, causing disfiguring sores and nerve damage.
This is actually what leads to the myth that leprosy causes flesh and limbs to fall off. In reality, it can damage nerves, causing people to lose sensation and not realize they’ve injured themselves. With enough damage, sometimes those extremities need to be amputated.
These days the disease can be effectively treated with multidrug therapy. And interestingly, it’s estimated about 95% of people who get infected will simply clear the bacterial infection on their own without any treatment at all.
There’s actually a debate about if you should call the disease “leprosy” or “Hansen’s disease” after Gerhard Hansen, a Norwegian physician who discovered the bacteria responsible for the disease in 1874.
The problem with calling it leprosy is that there is now such a strong stigma around the name. Leper colonies used to exist as places to banish the ill to keep them away from, and out of sight of, civilized society. For a long time, thanks to the Bible, the term leprosy has conjured images of everything impure, unholy, or bad.
The problem with calling it Hansen's disease is that Hansen was a jerk. At one point he locked one of his patients who had a form of leprosy in his office and poked her in the eye with a needle that contained matter from a patient who had a different kind of leprosy, against her will and while she actively protested, just to see what would happen.
Even though he lost his position at the hospital as a result of this experiment, he showed no remorse, stating it was worth it for the science, and besides, she already had
There are fewer than 200 cases of leprosy in the U.S. every year, and it’s suspected that one way people become infected is through contact with the nine-banded armadillo, which can carry the bacteria.
Vector-borne parasites move around in the bodies of other bugs or animals, only to burst forth to infect humans and continue their life cycles.
For example, there are two types of trypanosomiasis: American and African
American trypanosomiasis comes from infection with the parasite Trypanosoma cruzi and is more commonly called Chagas.
It’s estimated that 6 to 7 million people worldwide are infected with the T. cruzi parasite, resulting in 12,000 deaths a year.
People get infected when they come into contact with the parasites found in the urine or feces of the kissing bug, so named because they come out at night and bite exposed parts of the skin, usually on the face, to feed on blood.
And then, rather rudely, the bugs defecate or urinate next to the bite. The sleeping person or animal reflexively swipes at the bug, smearing the parasite-containing matter into their open wound, mouth, or eyes.
cruzi can also be transmitted through contaminated food, blood products, or from mother to child during pregnancy or childbirth.
Though Chagas had mainly affected countries in Latin America, there is now concern that climate change is contributing to an expanded range for kissing bugs and therefore Chagas disease.
Symptoms come in two phases:
The first phase is usually mild as the parasites circulate in blood. This is the best time to treat Chagas with antiparasitics.
If an acute phase goes untreated, we move into a chronic phase, in which parasites mainly collect in the heart and digestive tract. As you can imagine, having a bunch of parasites in your heart is not great. And untreated infection can result in things like the destruction of the nervous system, cardiac arrhythmias, progressive heart failure, stroke, and sudden death.
The other trypanosomiasis is human African trypanosomiasis.
It is caused of two types of the Trypanosoma brucei
The parasite is mainly transmitted through the bite of the tsetse fly in rural areas of sub-Saharan Africa.
The first phase of infection includes symptoms like fever, rash, skin lesions, and swelling. If left untreated, the parasites will accumulate and cross the blood-brain barrier, causing symptoms like severe headache, personality changes, slurred speech, and progressive confusion.
It can also impact sleep cycles, causing daytime drowsiness and insomnia at night, which is what gives it the common name “African sleeping sickness.”
If left untreated, death will occur in weeks to months.
While we have made great strides in controlling T. brucei (new cases have been reduced by 97% over the last 20 years), the fact that it predominantly occurs in rural areas and requires skilled professionals to diagnose and treat it makes eradication difficult.
Both types of trypanosomiases also have animal reservoirs. For T. cruzi it’s many animals, but the common opossum is the most important. For T. brucei it’s cattle. This can make it extremely difficult to control because you need to remove it from the animal population as well.
Schistosomiasis, or “schisto,” is another neglected tropical disease.
The disease is caused by infection with blood flukes, tiny parasites whose larval form can penetrate the skin of unsuspecting humans who come into contact with infested waters.
And how are those waters infested? One, by people who have a schisto infection and urinate or defecate into freshwater sources, releasing eggs, and two, by infected snails who shed the larva.
The larva inside a human body develops into adult worms, which like to live in the blood vessels where the females lay eggs. Some of the eggs are expelled to continue the life cycle, and some stay in tissues to grow into more adults which cause immune reactions and progressive damage to organs.
When Napoleon’s troops came to Egypt in 1798, they called it “the land of men who menstruate” because of the high rate of schisto infections of the bladder and kidney that caused blood in the urine.
Other symptoms depend on where the eggs are laid, and most are a direct result of the body’s reaction to those foreign objects. Some people experience things like pain, diarrhea, and liver and spleen enlargement. Kids can experience anemia and growth disorder, or stunting.
The economic impacts are considerable, because the disease disables more than it kills.
The current strategy for control involves things like improving access to safe water and sanitation, hygiene education, behavior change, and snail control.
At-risk communities are often prophylactically treated with the anti-parasitic praziquantel, meaning all members are given the medication without bothering to do diagnostic tests, but the environmental aspects of transmission make control difficult.
Schisto isn’t the only kind of trematodiases—there are also versions that infect humans through contaminated foods
These other versions of flukes get more niche, but unless you’re working on treating them, the information is largely the same.
It starts with a snail, then the larva move into a second host—in some cases a fish, in some cases a crustacean, in some cases just attaching to freshwater vegetation. The last stage is to get into a human body.
Getting your fish, crustaceans, and vegetation from areas that have good water sanitation and then fully cooking or cleaning them is going to do wonders to reduce the risk of infection.
Let’s end with Dracunculiasis, or Guinea worm.
People become infected by drinking unsafe water that contains near-microscopic crustaceans called copepods which themselves are infected with guinea worm larvae.
The larvae become worms who use your body to reproduce for about a year until adults are ready to come out.
And how do they get out? By creating a blister on the skin, typically on the legs or feet, from which to emerge.
And given that adult worms can reach lengths of 3 feet, emerging takes a while.
In fact, the common method to remove Guinea worms was to wait for the worm’s head to appear and then continue to wrap it around a stick or piece of gauze and slowly, painfully, extract it over a period of several weeks.
Guinea worms have kind of a genius design, in that their exit causes a burning sensation, which often results in people submerging their leg in water to help with pain. The second the pregnant worm touches water, she releases her eggs, starting the cycle again.
Eradication efforts are going very well!
In the mid-80s there were approximately 5 million cases. In 2024, there were 13. Not 13 million. Just 13.
This has been accomplished by work done through the World Health Assembly and the Carter Center through activities like increased access to safe water, education about keeping affected limbs out of water sources, not letting animals contaminate water, and regularly treating stagnant water to kill copepods.
Without a vaccine or a cure, guinea worm is close to being only the second human disease to ever be eradicated.
