Strongyloidiasis

What is Strongyloidiasis?

Strongyloides stercoralis, or threadworm, is a type of worm called a roundworm that lives in soil and can infect humans. This parasitic worm can be found almost everywhere around the world, except for the farthest northern and southern regions. However, we still don’t know just how much of the world’s population is affected by this parasite, as there’s not enough specific data from places where it’s most common. As a result, the threat of S. stercoralis is often overlooked among other less-known tropical diseases.

This particular worm, S. stercoralis, doesn’t just affect humans. It can also naturally occur in pets like dogs and cats, and even in primates. What sets it apart from other types of roundworms is its unique ability to produce offspring outside of its host’s body. It accomplishes this by shedding a type of larvae, or young worms, in the feces of the infected individual. These larvae continue to reproduce outside the body and can eventually grow into worms capable of penetrating human skin and causing infection. How this infection affects the individual can vary greatly. Some people may not show any symptoms at all, while others may experience a severe infection that spreads throughout the body.

The term used for an infection caused by Strongyloides stercoralis is strongyloidiasis. One of its unique characteristics is the potential to cause extreme infection in individuals with weakened immune systems. Moreover, S. stercoralis can continue to live within its host for their entire lifetime due to its ability to reinfect the same individual. This infection can span from showing no symptoms at all to causing a severe, life-threatening disease in those whose immune systems are compromised.

What Causes Strongyloidiasis?

Strongyloides stercoralis is a type of worm that lives in soil. It is part of a group called roundworms or nematodes. The majority of the 50 types of Strongyloides worms do not infect humans.

The disease in humans caused by S. stercoralis is called strongyloidiasis, and it’s caught mainly by the worm penetrating the skin. But it can also be caught from eating or drinking something contaminated with the worm’s eggs or through organ transplants from a donor who is infected.

Certain factors can increase your risk of getting strongyloidiasis; these include HIV infection, a viral infection known as human T-lymphotropic virus type 1 (HTLV-1), and alcoholism. If you have a condition that weakens your immune system—like diabetes, HIV, HTLV infection, or alcoholism—or if you’re on immune-suppressing drugs, you’re at a much higher risk of severe disease.

Poor sanitation in households and walking barefoot can also increase your risk of getting this worm infection. Interestingly, even though HIV weakens the immune system, it doesn’t seem to increase the risk of catching more worm infections. It’s thought that’s because being infected with HIV makes you more prone to bacterial and viral infections than worm infections.

Risk Factors and Frequency for Strongyloidiasis

Strongyloides stercoralis, a type of soil-transmitted worm, is found in almost every corner of the world, with the exception of Antarctica. This worm has been estimated to infect 370 million people globally, but is more commonly found in tropical and subtropical regions. In these areas, between 10 to 40% of the population is affected by it. According to a 2021 study, the Western Pacific region has the highest rate of infection. They reported that 9 to 21% of the population is infected. The Eastern Mediterranean Region has the highest number of people who test positive for the disease, with up to 40% of the population affected.

• It’s important to note that the real rate of Strongyloides stercoralis is likely much higher than reported, as the tests for it are not always accurate and it’s not always reported in countries where it’s common.
• This worm is often found in warm, moist locations with poor sanitation conditions.
• Of note, one study reported infection rates as high as 91% in Gabon and 75% in Peru, though results can vary widely due to different testing methods.
• Interestingly, studies on how frequently new cases occur are not available.
• In developed countries, this disease is most commonly seen in farmers, miners, immigrants, tourists, and military members returning from areas where the disease is common.
• In the United States, most afflicted individuals are immigrants from Africa and Asia, followed by those from Central and Latin America.
• It’s worth mentioning that refugees receive deworming treatment upon entering the United States.
• The disease slightly more commonly affects males, which researchers believe is due to greater exposure in these individuals through activities like farming and field work.

Signs and Symptoms of Strongyloidiasis

Strongyloidiasis is a type of infection that is typically symptom-free, especially in individuals with a healthy immune system. It’s often noticeable only through an unexplained increase in a certain type of white blood cell known as eosinophils. However, some people with the infection may display general symptoms.

The signs of the acute phase of the infection can include a skin rash that is itchy and serpent-like in appearance, usually where the larvae of the parasite entered through the skin. This could be anywhere on the body but is often found on feet or hands. The skin reaction is known as ground itch and is characterized by itching, swelling, and redness at the site of the infection. The itchiness can last up to three weeks. The skin rash, also known as larva currens or running larva, can progress rapidly in a few hours.

The larvae of the parasite can pass through the lungs, causing a dry cough, difficulty breathing, wheezing, increased eosinophils, and changeable lung conditions. This can result in bleeding in the lungs and cough, while the buildup of the eosinophils in the small air spaces often leads to a type of lung inflammation known as pneumonitis. Other symptoms can include diarrhea, vomiting, and upper abdominal pain.

A severe complication known as hyperinfection syndrome can occur, exhibiting signs such as fever, blood infection, and signs of damage to the end organs which may include hemoptysis (coughing up blood), gastrointestinal bleeding, obstruction in the intestines, and low sodium levels.

The Strongyloides stercoralis parasite can cause chronic infections that can persist for years and may present as cough, abnormal breath sounds, difficulty in breathing, abdominal pain, lack of appetite, diarrhea, and/or constipation. The symptoms linked with the respiratory and digestive systems are usually mild, and skin conditions such as hives or larva currents can still be seen.

Hyperinfection occurs when the parasite rapidly multiplies within the host, causing a high parasite burden and serious disease. The signs and symptoms of hyperinfection are similar to symptoms caused by increased larvae movement within the organs. A severe complication of hyperinfection syndrome is disseminated disease that leads to the spread of the larvae to distant organs like the liver, pancreas, kidneys, lymph nodes near the small intestine, brain, and muscles.

Testing for Strongyloidiasis

To definitely confirm a Strongyloides stercoralis infection, doctors need to find larvae, the immature form of the parasite, in a stool sample. However, this may be challenging because the parasite doesn’t always consistently produce a lot of larvae. Sometimes, if a tissue sample is taken from the intestines, parasites can be found in the stomach or small intestine tissues, along with a higher proportion of a type of white blood cell, called eosinophils.

However, it is important to note that an endoscopy, a procedure where a small camera is used to look inside your body, is not usually used to check for this type of infection. There are also tests that can detect the DNA of the parasite in urine samples. Laboratory tests can be done on sputum, the mixture of saliva and mucus coughed up from the lungs, to reveal the infection.

Another way to detect the disease is to use serologic tests that look for signs of an immune response to the infection in the patient’s blood. Unfortunately, the sensitivity (the ability to correctly identify those with the disease) and specificity (the ability to correctly identify those without the disease) of these tests are not very high.

The commonly used stool test can only find the disease 21% of the time. Stool concentration methods have a higher sensitivity, but can still miss the infection. The serologic tests tend to be more sensitive, but also have false positives due to cross-reactivity with other types of similar infections. Tests that can detect proteins released by the parasite in the stool are better at indicating an ongoing infection.

The gold standard, or most accurate, tests for S.stercoralis have not yet been developed. Typically, both stool and blood tests are done. While DNA tests that detect genetic material of the parasite show promise, they’re not widely available yet.

Eosinophilia, a higher than normal level of eosinophils, is common in chronic infections. However, it’s not very reliable in finding strongyloidiasis. Furthermore, in patients with a severe form of the disease, called hyperinfection syndrome, eosinophilia is usually absent.

Diagnosing chronic strongyloidiasis is difficult because of the low number of parasites in the body, making stool tests less sensitive and blood tests less specific.

Studies show that although stool tests and blood tests aren’t very sensitive, especially in acute or chronic infections, blood tests can still be useful because if the test is negative, it’s highly likely the patient doesn’t have strongyloidiasis. A study in 2019 revealed a link between immune control of strongyloidiasis and the strength of the immune response.

In patients with hyperinfection syndrome, the disease can be identified by testing stool, body fluids, or tissues, because of the high number of parasites.

Treatment Options for Strongyloidiasis

The aim of treating strongyloidiasis, a parasitic infection, is to get rid of the parasite completely. This applies to everyone whether they’re showing symptoms or not, and whether their immune system is strong or weakened.

The most common treatment for this condition is a course of specialized medication. Usually, these medications include ivermectin, thiabendazole, or albendazole. Your doctor will check how you’re responding to the treatment by conducting regular stool tests or blood tests to make sure the parasite is being eliminated. They may do this for one to two years.

For those with severe symptoms or infection, the drug ivermectin will likely be used along with broad-spectrum antibiotics. It’s important to note, if you’re from certain parts of Africa where a condition called loiasis is common, you will need to be screened for this illness before starting ivermectin treatment. This is because sometimes the combination of these conditions and this medication can cause serious brain conditions.

Of all the different available treatments, ivermectin is usually the preferred choice as it has shown the best results and its side effects are as common as with albendazole. Albendazole is often viewed as the second choice because it is less effective than ivermectin. Thiabendazole is used less often now due to its increased side effects, though it works as well as ivermectin.

If your immune system is weak, doctors might need to adjust your current immunosuppressive therapy and your strongyloidiasis treatment may be extended. In general, the treatment continues until tests show no signs of the parasites in your stool, urine, or phlegm for at least 14 days.

What else can Strongyloidiasis be?

If you’re experiencing breathing issues, it could be due to a variety of conditions, including:

• Acute respiratory distress syndrome (ARDS)
• Pneumonia
• Bronchial asthma
• Pneumonitis

Likewise, if you’re dealing with stomach discomfort, this could be from a range of issues like:

• Acute appendicitis
• Intestinal obstruction
• Inflammatory bowel syndrome
• Proctitis
• Loffler syndrome
• Peritonitis

Remember, these symptoms could point towards multiple conditions and it’s important to get evaluated by a medical professional to receive the correct diagnosis.

What to expect with Strongyloidiasis

The general outlook for both acute and chronic infections, with proper treatment, is usually good. However, in situations of hyperinfection syndrome and widespread infection, the death rate can skyrocket to a staggering 70 to 100%. This disease can prove to be more dangerous for patients with a weakened immune system (due to any existing illness and/or immunity-weakening treatment), alongside bacteremia (bacteria in the bloodstream), and a delay in diagnosis.

A study conducted in Hong Kong in 2006 reviewed the progression and outcome of disseminated strongyloidiasis, a severe parasitic infection, over a span of 10 years. The study identified seven patients, five of whom had lung involvement at the beginning of the illness and unfortunately passed away despite receiving anti-parasite drugs and intensive supportive care. Most of these patients experienced significant lung and bowel symptoms, and none of them showed any peripheral eosinophilia (a high level of specific white blood cells that fight infections and allergies).

Possible Complications When Diagnosed with Strongyloidiasis

The most feared outcome of an infection by the parasite Strongyloides stercoralis is a condition called hyperinfection syndrome. This syndrome involves a severe spread of the disease throughout the body, leading most often to multiple organ failure and, tragically, death. This happens despite treatment to eliminate parasitic worms (anthelmintic therapy). On top of that, patients with severe symptoms are also at risk of blood infection (gram-negative bacteremia) and severe bodily infection (sepsis). Therefore, broad-spectrum antibiotics, which kill a wide range of bacteria, are recommended in addition to the parasite-wiping therapy for patients with severe disease.

Possible Consequences:

• Severe spread of the disease throughout the body (Hyperinfection syndrome)
• Multiple organ failure
• Death
• Blood infection (Gram-negative bacteremia)
• Severe bodily infection (Sepsis)

Preventing Strongyloidiasis

Patients who stand a high risk for chronic and widespread strongyloidiasis, a type of parasitic infection, would benefit from taking preemptive measures to prevent the disease. This includes checking people who show no symptoms, especially if they’ve been in areas where the disease is common. It is useful to carry out blood tests in these individuals even if they don’t exhibit any symptoms:

• Patients who’ve been to areas where the disease is common and now need treatments that suppress their immune system.
• Those who’ve been exposed to relevant environmental conditions and are now becoming organ donors.
• Military personnel who’ve served in regions with the disease, no matter how long ago their exposure was.
• Immigrants and refugees coming from regions where the disease is prevalent.

Just like other diseases that are spread through the soil, controlling the occurrence of this illness in high-risk areas can be achieved by improving sanitation, providing clean water, promoting hand washing, and general cleanliness.