STRONGYLOIDES STERCORALIS

Strongyloidiasis was first described in French troops stationed in modern day Vietnam during the late 19th century who were suffering from severe, persistent diarrhea. It is a parasitic disease caused by nematodes, or roundworms, in the genus Strongyloides that enter the body through exposed skin, such as bare feet.  Strongyloides is most common in tropical or subtropical climates.

Most people who are infected with Strongyloides do not know they are infected and have no symptoms. Others may develop a severe form and, if untreated, become critically ill and potentially die.

FAQS

What is strongyloidiasis?

Strongyloidiasis  is a disease caused by a nematode, or a roundworm, in the genus Strongyloides. Though there are over 40  species within this genus that can infect birds, reptiles, amphibians, livestock  and other primates, Strongyloides  stercoralis is the primary species that accounts for human disease. The  larvae are small; the longest reach about 1.5mm in length -- the size of a  mustard seed or a large grain of sand.

How do people get infected with strongyloides?

Strongyloides is classified as a soil-transmitted helminth. This means that the primary mode of infection is through contact with soil that is contaminated with free-living larvae. When the larvae come in contact with skin, they are able to penetrate it and migrate through the body, eventually finding their way to the small intestine where they burrow and lay their eggs. Unlike other soil-transmitted helminths such as hookworm and whipworm whose eggs do not hatch until they are in the environment, the eggs of Strongyloides hatch into larvae in the intestine. Most of these larvae will be excreted in the stool, but some of the larvae may molt and immediately re-infect the host either by burrowing into the intestinal wall, or by penetrating the perianal skin. This characteristic of Strongyloides is termed auto-infection. The significance of auto-infection is that unless treated for Strongyloides, persons may remain infected throughout their lifetime. In addition to contact with soil and auto-infection, there have been rare cases of person-to-person transmission in:

• organ transplantation
• institutions for the developmentally disabled
• daycare centers.

Where do most cases of strongyloidiasis occur in the United States?

In the United States, Strongyloides has classically been associated with uniformed-service veterans who returned from  tropical regions such as Southeast Asia and the South Pacific during World War  II. Small domestic studies have shown locations of infection in rural  Appalachia. The highest rates in the United States have been documented in  immigrant populations.

Strongyloides is more commonly found in areas that are  relatively warm and moist, in rural areas, and areas associated with  agricultural activity, but it can occur anywhere. It is found more frequently  in socio-economically disadvantaged persons and in institutionalized  populations.

What are the signs and symptoms of strongyloidiasis?

The majority of people infected with Strongyloidesare without symptoms. Those who do develop symptoms  tend to have non-specific, or generalized complaints. Some people develop  abdominal pain, bloating, heartburn, intermittent episodes of diarrhea and  constipation, a dry cough, and rashes. Rarely people will develop arthritis,  kidney problems, and heart conditions. Strongyloidiasis can be severe and life-threatening in  persons who:

• are on oral or intravenous steroids -- such as those  with asthma or chronic obstructive pulmonary disease (COPD) exacerbations, lupus,  gout,  or in persons using steroids for  immunosuppression or symptomatic relief
• are infected with the virus HTLV-1
• have hematologic malignancies such as leukemia  or lymphoma
• are  transplant recipients.

How soon after the exposure do symptoms develop?

Most people do not know when their exposure occurred.  For those who do, a local rash can occur immediately. The cough usually occurs several days later. Abdominal symptoms typically occur approximately 2 weeks later, and larvae can be found in the stool about 3 to 4 weeks later.

What should I do if I think I might have strongyloidiasis?

See your health care provider.

How is infection with Strongyloides diagnosed?

Strongyloides is  classically diagnosed by visualization of larvae on microscopic stool examination.  This may require that you provide multiple stool samples to your doctor or the  laboratory. Some laboratories are capable of diagnosing Strongyloides with blood tests.

How is strongyloidiasis treated?

Safe and effective drugs are available to treat infection with Strongyloides.

How can strongyloidiasis be prevented?

The best way to prevent Strongyloides infection is to wear shoes when you are walking on soil, and to avoid contact with fecal matter or sewage. Proper sewage disposal and fecal management are keys to prevention.

EPIDEMIOLOGY & RISK FACTORS

Strongyloides is  known to exist on all continents except for Antarctica, but it is most common  in the tropics, subtropics, and in warm temperate regions. The global prevalence of Strongyloides is unknown, but experts estimate that there are  between 3 – 100 million infected persons worldwide.

In the United States, a series of small studies in select populations have shown that between 0-6.1% of persons sampled were infected. Studies in immigrant populations have shown a  much higher percentage of infected persons ranging from 0-46.1%.

Strongyloides is  found more frequently in the socioeconomically disadvantaged, in institutionalized  populations, and in rural areas. It is often associated with agricultural  activities.

The most common way of becoming infected with Strongyloides is by contacting soil that  is contaminated with Strongyloides larvae. Therefore, activities that increase contact with the soil increase the  risk of becoming infected, such as:

• walking with bare feet
• contact with human waste or sewage
• occupations that increase contact with  contaminated soil such as farming and coal mining.

Furthermore, many studies have shown an association with Strongyloides and infection with Human  T-Cell Lymphotropic Virus-1 (HTLV-1). These studies have shown that people infected  with HTLV-1 are more likely to become infected with Strongyloides, and that once infected, are more likely to develop  severe cases of strongyloidiasis.

Of note, being infected with HIV/AIDS has not been shown to  be a risk factor for developing Strongyloides or having a worse clinical course.

BIOLOGY

Causal Agent:

The nematode (roundworm) Strongyloides stercoralis.  Other Strongyloides include S. fülleborni, which infects chimpanzees and baboons and may produce limited infections in humans.

Life Cycle:

The Strongyloides life cycle is more complex than that of most nematodes with its alternation between free-living and parasitic cycles, and its potential for autoinfection and multiplication within the host. Two types of cycles exist:

Free-living cycle: The rhabditiform larvae passed in the stool  can either molt twice and become infective filariform larvae (direct development) or molt four times and become free living adult males and females  that mate and produce eggs  from which rhabditiform larvae hatch. The latter in turn can either develop into a new generation of free-living adults or into infective filariform larvae. The filariform larvae penetrate the human host skin to initiate the parasitic cycle.

Parasitic cycle: Filariform larvae in contaminated soil penetrate the human skin, and are transported to the lungs where they penetrate the alveolar spaces; they are carried through the bronchial tree to the pharynx, are swallowed and then reach the small intestine. In the small intestine they molt twice and become adult female worms. The females live threaded in the epithelium of the small intestine and by parthenogenesis produce eggs, which yield rhabditiform larvae. The rhabditiform larvae can either be passed in the stool. In autoinfection, the rhabditiform larvae become infective filariform larvae, which can penetrate either the intestinal mucosa (internal autoinfection) or the skin of the perianal area (external autoinfection); in either case, the filariform larvae may follow the previously described route, being carried successively to the lungs, the bronchial tree, the pharynx, and the small intestine where they mature into adults; or they may disseminate widely in the body. To date, occurrence of autoinfection in humans with helminthic infections is recognized only in Strongyloides stercoralis and Capillaria philippinensis infections. In the case of Strongyloides, autoinfection may explain the possibility of persistent infections for many years in persons who have not been in an endemic area and of hyperinfections in immunodepressed individuals.

Life cycle image and information courtesy of DPDx.

DISEASE

Most people infected with Strongyloidesdo not know they’re infected. If they do feel sick the most common  complaints are the following. Abdominal:   

• stomachache, bloating, and heartburn
• intermittent episodes of diarrhea and constipation
• nausea and loss of appetite

Respiratory:  

• dry cough
• throat irritation

Skin:  

• an itchy, red rash that occurs where the worm entered the skin
• recurrent raised red rash typically along the thighs and buttocks.

Rarely, severe life-threatening forms of the disease called hyperinfection syndrome and  disseminated strongyloidiasis can occur. These forms of the disease are more common in people who are on corticosteroids (prednisone for example) or other immunosuppressive therapies or who are infected with HTLV-1. In this situation, people become critically ill, and should be taken to the hospital immediately.

DIAGNOSIS

Strongyloides is usually  diagnosed by seeing  larvae in stool when  examined under the microscope. This may require that you provide multiple stool  samples to your doctor or the laboratory. Some laboratories are capable of  diagnosing Strongyloides with blood  tests.

PREVENTION AND CONTROL

The best way to prevent Strongyloidesinfection is to wear shoes when you are walking on soil, and to avoid contact  with fecal matter or sewage. Proper sewage disposal and fecal management are  keys to prevention.  Furthermore, if you believe that you may be infected, the  best way to prevent severe disease is to be tested and, if found to be positive  for disease, treated.  You should discuss testing with your doctor if you are:

• taking  steroids or other immunosuppressive therapies
• about to start taking steroids or other  immunosuppressive therapies
• a veteran who served in the South Pacific or  southeast Asia
• infected with Human T-cell Lymphotropic Virus-1  (HTLV-1)
• diagnosed with cancer
• going to donate or receive organ transplants.

For more information view the source:Center for Disease Control

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