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CDC targets five Neglected Parasitic Infections in the US

The triatomine bug is the vector for T. cruzi, the parasite that causes Chagas disease
Rachel Curtis/Hamer Labs

When you think of Neglected Tropical Diseases (NTD), you think of diseases occurring in poor and developing countries. NTDs perpetuate a cycle of poverty that continues from generation to generation.

The World Health Organization (WHO) says Neglected Tropical Diseases are a medically diverse group of infections caused by a variety of pathogens such as viruses, bacteria, protozoa and helminths. The 17 neglected tropical diseases prioritized by WHO affect more than 1 billion people worldwide and are endemic in 149 countries.

The 17 NTDs according to the WHO include Dengue/Severe dengue, Rabies, Chagas disease, Human African trypanosomiasis (sleeping sickness), Leishmaniases, Cysticercosis/Taeniasis, Dracunculiasis (guinea-worm disease), Echinococcosis, Foodborne trematodiases, Lymphatic filariasis, Onchocerciasis (river blindness), Schistosomiasis, Soil-transmitted helminthiases, Buruli ulcer, Leprosy (Hansen disease), Trachoma and Yaws.

Despite many Americans believing that neglected diseases only occur in the poorest of the poor nations, in March the Centers for Disease Control and Prevention (CDC) named the five Neglected Parasitic Infections (NPI) that the federal health agency has targeted as priorities for public health action, based on the following three factors: Number of people infected, severity of the illnesses and the ability to prevent and treat them.

The five NPI are Chagas disease, cysticercosis, toxocariasis, toxoplasmosis, and trichomoniasis. These five parasitic infections are considered neglected because relatively little attention has been devoted to their surveillance, prevention, and/or treatment.

Chagas disease
Chagas disease CDC

Chagas disease

According to the CDC, Chagas disease is caused by the parasite Trypanosoma cruzi, which is transmitted to animals and people by insect vectors that are found only in the Americas (mainly, in rural areas of Latin America where poverty is widespread). Chagas disease (T. cruzi infection) is also referred to as American trypanosomiasis.

Estimates say that upwards around 8 million people in Central and South America and Mexico are infected, with many unaware of their infection.

It is estimated that there are over 300,000 people living in the United States who are infected with the parasite that causes Chagas disease. More than 300 infected babies are born every year in the United States.

Most people are infected with the parasite via insect vectors called triatomine bugs. Others ways people can become infected are through congenital transmission (from a pregnant woman to her baby); blood transfusion; organ transplantation; consumption of uncooked food contaminated with feces from infected bugs; and accidental laboratory exposure.

If untreated, infection is lifelong and can be life threatening and can cause heart failure and death.

Cysticercosis CDC


Cysticercosis is a parasitic tissue infection caused by larval cysts of the pork tapeworm, Taenia solium.

Human cysticercosis occurs either by the direct transfer of Taenia solium eggs from the feces of people harboring an adult worm to their own mouth (autoinfection) or to the mouth of another individual, or indirectly by ingestion of food or water contaminated with the eggs.

When the person ingests the eggs, the embryo escape from the shell and penetrates the intestinal wall, gets into the blood vessels, where they spread to muscle, or more seriously, the eyes, heart or brain.

The severity of cystercercosis depends on which organs are infected and the number of cysticerci. An infection consisting of a few small cysticerci in the liver or muscles would likely result in no obvious disease and go unnoticed.

Those that form in voluntary muscle tend to be asymptomatic, but may cause some pain. On the other hand, a few cysticerci, if located in a particularly "sensitive" area of the body, might result in irreparable damage.

For instance, a cysticercus in the eye might lead to blindness, or a cysticercus in the brain (neurocysticercosis) could lead to traumatic neurological damage, epileptic seizures or brain swelling that can kill.

The CDC notes that neurocysticercosis is the single most common infectious cause of seizures in some areas of the United States. 2,000 people are diagnosed with neurocysticercosis every year.

Toxocara CDC


In the United States, most puppies and many adult dogs are infected with the roundworm, Toxocara canis.

Infection of the adult dog with this parasite happens when they ingest eggs from the contaminated environment. The puppies usually get this parasite from the mother before birth through her milk. The puppies will start passing eggs in their feces by 3 weeks of age.

This parasite can be spread to humans by ingestions of eggs from the soil or from contaminated hands. Most at risk are young children under 5 years of age, especially those with a history of eating dirt and exposure to puppies.

One study showed that 20-60% of soil samples from backyard residences, public parks and children’s sandboxes were contaminated with Toxocara canis eggs. Though it is found throughout the U.S., diagnosis of disease in children is made most frequently in the south.

Light infections in humans are usually asymptomatic, and probably occur quite frequently.

Human infection with Toxocara usually takes one of two forms; visceral larval migrans (VLM), this is where the larvae migrate aimlessly. They usually end up migrating to the liver, but almost any tissue can be invaded.

The other rarer manifestation is ocular larval migrans (OLM), where the larvae enter the eye where permanent vision loss is possible.

The CDC says At least 14% of the U.S. population has been exposed to Toxocara. Every year an estimated 70 people, most of them children, are blinded by toxocariasis. The true numbers are believed to be even higher.

Toxoplasma CDC


Toxoplasmosis is a protozoan parasite that’s found worldwide. According to the Centers of Disease Control and Prevention (CDC) there are approximately 23% of adults and adolescents infected with the parasite. They also mention that in certain populations around the world the prevalence may be as high as 95%. It is believed that the infection is acquired throughout life.

For the person with a healthy immune system who picks up this parasite, Toxoplasma gondii, the symptoms are mild or totally asymptomatic and the acute infection passes unnoticed. The immune system keeps the parasite in check in the tissues. If at a later time the immune system is compromised, the disease can be reactivated.

This parasite infects almost all warm-blooded animals, but the domestic cat is the final host. Cats may excrete millions of these parasites in their feces on a daily basis. Cats usually pick up this organism through eating mice, rats, birds and by grooming themselves.

There are several conditions in which the organism Toxoplasma can cause lethal infection; people with AIDS, cancer patients on chemotherapy and transplacentally transmitted between mother and child are the main groups of patients most at risk. Serious disease manifestations may include brain abscesses, eye infections and pneumonia.

In the pregnant woman, the risk is if she gets a primary (new) infection during her pregnancy. The infection may be passed to the unborn child with devastating outcomes.

Human infection with Toxoplasma typically occur by one of the following routes; eating undercooked or raw meat, changing cat litter boxes and getting exposed to cat feces while gardening or other activities.

The CDC says more than 60 million people in the United States are chronically infected with toxoplasmosis.

Trichomonas vaginalis
Trichomonas vaginalis CDC

Trichomonas vaginalis

Trichomonas vaginalis is the most common pathogenic protozoan infection in humans in developed countries. In North America alone it is estimated that in excess of 8 million new cases are reported annually. The World Health Organization (WHO) estimated that 180 million infections are acquired annually worldwide.

It is spread through contact with vaginal and urethral discharges during sexual intercourse. It is highly unlikely to catch this parasite by means of sitting on a toilet seat as many believe; Trichomonas just does not withstand drying and do not survive very long in the environment outside of the host.

In women, though sometimes asymptomatic, when symptoms are present it is characterized by a profuse, thin greenish-yellow discharge with a foul odor. Other signs of trichomoniasis are small hemorrhages causing reddening on the cervix known as “strawberry cervix”, vaginal itching and an urge to urinate.

In men, most show no symptoms, however it may invade the prostate and seminal vesicles.

Rarely, babies born to infected mothers may contract infection during delivery.

The CDC says Trichomoniasis is a major cause of infertility and preterm labor in women, and low birthweight in babies

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