Ascariasis is not only the most common parasitic infection, it's also one of the worst parasitic infections to get. Though ascariasis is rare in the United States, it is still prevalent in many countries with poor sanitation systems.
Ascariasis is caused by a type of roundworm (or ascaris). Technically, two different types of roundworms lead to the infection - ascaris suum is a pig roundworm and ascaris lumbricoides is a human roundworm. Both can infect humans, though, and they are virtually indistinguishable from one another. Once an infection takes hold, it can be difficult to get rid of it.
In people, ascariasis may not present symptoms for a long time. In livestock, the parasite is so hard to get rid of that widespread infection is almost guaranteed. The infection can usually be cured with medication that is relatively low-cost. However, if the infection is advanced and there is a full-fledged infestation of worms, it can be fatal.
You can protect yourself with basic hygiene, but if you're traveling abroad to a remote area or an area known to have roundworms, it's important to avoid contaminated soil that could contain roundworm eggs. You can get ascariasis directly from soil, or from food that was exposed to the soil.
Turns out, hitting up that McDonald's while you're abroad may not be such a bad idea after all.
Once you've swallowed the roundworm eggs, you've set the parasitic lifecycle in motion. The eggs will hatch in your intestine, and the larvae will travel to your lungs via your bloodstream. When the larvae become full-fledged worms, they'll make their way from your lungs to your throat. You may cough up the worms, or you may swallow them again. If you swallow, they end up back in your intestines, where the mature worms will lay more eggs.
Mature roundworms can lay almost two million eggs per day, and the eggs are very hardy. They have thick shells that withstand most disinfectants. Eggs can only be destroyed via steam cleaning or sunlight. Because of their tenacity, the eggs can survive for up to 15 years outside the body. In water, they can live for at least 14 months. These two factors make ascariasis in livestock nearly impossible to get rid of or prevent.
If roundworms are present in your stool, then you most certainly have been infected. However, most people with ascariasis have no symptoms. If the infection is severe enough and the worms spread to your lungs and/or intestines, you will start to experience other signs of infection. Abdominal pain, nausea, vomiting, fatigue, and weight loss can all be indicative of ascariasis.
60,000 people die from ascariasis each year. Yet despite the prevalence of roundworm infections, physicians are typically not trained to look for the parasite prior to surgery or treatment. Testing for the parasite is cheap and easy, even in remote areas; today's CT technology makes it even easier. However, despite the relative ease and low cost, the vast majority of trauma victims are not tested or diagnosed until after surgery.
A study showed that those with prior roundworm infections suffered more from other ailments. For example, a child who inhaled smoke during a fire ended up dying, as the ascariasis infection worsened the lung injury.