Strongyloides are not true strongyles - an interesting and strange quirk of naming. Because they lack a copulatory bursa on the males, they are technically not in the same genus. But, they got named before this was found out. So Strongyloides they shall remain!
Many people mistake these wormies for hookworms. They are not, though they do at times have very similar presentations. To complicate things further, their geographic distributions are quite similar - they both enjoy tropical and subtropical humid areas. Their L1 larva even look extremely similar to hookworm L1 larva! However, strongyloides have a large genital prominence in the L1 stage, while hookworms have a small one.
These worms tend to infect less people than hookworms, with only 100-200 million people infected worldwide. They live in areas where sanitation is poor. (Another worm that could be prevented with a flush toilet, shoes, or a deep shaft toilet!) Like the hookworms, they transmit though the soil, entering out pores as infective larva. They also go through the blood and lymph streams to the lungs, where they grow, are coughed up, and eventually enter the small intestine. They tend to cause less irritation to the lungs than other worms with this cycle, likely because one is more likely to have a chronic ongoing Strongyloides infection. People have been shown to carry Strongyloides infections for several decades, for reasons I'm about to go into.
Strongyloides can have a method of entry into the host that is very similar to hookworms, in that they are passed with feces, grow up in the ground, and then re-enter the body through pores. However, a key difference is that the eggs hatch while still inside the body. This is important for diagnosis, as it means you will almost never find Strongyloides eggs in a stool sample. It also means that sometimes, the larvae will progress to their infective stage while still inside the body, allowing for a constant source of re-infection. They also have a very strange trait in the soil - while most helminths who follow the host->soil->larvae->reinfection pattern cannot live in the soil longer than 1 generation, Strongyloides can. They will become free-living adults (known as Rhabditiform adults), who can then mate and lay their own eggs in the soil, meaning that the ground can stay infected for a much longer time than with most helminths.
While most people living with Strongyloides will have few symptoms (perhaps some vague intestinal pain or some wheezing, or alternating diarrhea and constipation), problems occur when the outbreak becomes more severe. This can happen in two ways - disseminated infection or hyperinfection. While most literature will use these two interchangeably, there are symptoms that really apply more to one than the other.
With a hyperinfection, the worms have become too prolific within the gut. Most of the time, parasites have an innate sense of how many of them can survive in the host at any given time, and will plan accordingly. They don't want to kill the host, because then they would most likely die as well. However, hyperinfection can occur. This will often result in severe diarrhea, malabsorption, and weight loss. It can be fatal.
With a disseminated infection, the larvae start fleeing to other parts of the body that they would not normally be found in. This is often the result of steroids - either ones that have been given to a patients, or ones that the body makes naturally, such as in cases of extreme malnutrition. Diagnosis can be made by finding larvae in organs through biopsies and finding rhabditiform larva in sputum (normally never found inside the body). This is typically only seen in previously immunocompromised patients. In these cases, it is very important NOT to administer more steroids, even though that is what would usually be done in a case where larvae were being found in places that they normally would not be. This is because the steroids actually act as a signal for them to go wandering about the body, and will exacerbate the problem. Interestingly, even though this is found in immunocompromised patients, it is not associated with AIDS. Researchers think that the immune system factors associated with keeping levels of Strongyoides down are not the same as those affected by AIDS, and as such the patients have no greater chance of getting one of these worse infections.
Disseminated infections can also be diagnosed when a condition called Larva Currens happens. Larva currens shows up similarly to cutaneous larva migrans, in that it is a long red streak left in the wake of the larva. However, these move much faster - they can sometimes go several mm in an hour! These tend to show up near the chest and butt areas, and it is important to seek anti-helminthic treatment for these.
Photo Credit: Institute of Tropical Medicine, Antwerp
Diagnosis with a Strongyoides infection can be very difficult, as the symptoms in infections that are not severe include atypical bronchitis, followed a few weeks later with some diarrhea and epi-gastric pain. L1 larva may be found in the feces, but it can also be confused with hookworm, as a stool sample with hookworm eggs will hatch if not attended to quickly enough. However, if a patient has a history of being in an area where these helminths are prevalent, it is important for doctors to check and treat them before preforming surgeries such as organ transplants, where steroids would normally be given.
