According to the WHO, the current registration of patients with strongyloidiasis is 30-100 million patients annually. The global distribution of strongyloidiasis is underestimated. The greatest risk factor for the occurrence of this parasitosis is unfavorable socioeconomic conditions: poverty, unsanitary conditions, open defecation, nomadic lifestyle, close contact with the soil in endemic areas.
What is Strongyloidiasis?
Strongyloidiasis is an infectious disease caused by Strongyloides stercoralis, a roundworm widespread in tropical and subtropical regions of the world. The adult male worm is not a tissue parasite. It is excreted after fertilization of the female worm. The adult female worm is very small and almost transparent. Its length is approximately 2.2-2.5 mm; it lives in the tunnels between enterocytes in the human small intestine.
Lifecycle of parasite
Strongyloides stercoralis has a unique and complex life cycle. It is more complex than that of most nematodes, due to the difference between the free-living and parasitic cycles, as well as due to the high ability for autoinvasion and reproduction in the host. There are two types of cycles:
- Free-living cycle;
- Parasitic cycle.
The free-living cycle means that rhabditiform larvae, excreted in the feces, can either molt twice and develop into infective filariform larvae (direct development), or molt four times and develop into free-living adult males and females, which mate and lay eggs from which rhabditiform larvae hatch. They can later develop into either a new generation of free-living adult larvae or infective filariform larvae that penetrate the skin of the human host, beginning the parasitic cycle.
During the parasitic cycle, filarial larvae penetrate human skin and lungs, move along the bronchial tree into the pharynx and, after ingestion, enter the small intestine. In the small intestine, the larvae molt twice and become adult female worms. Females live in the epithelium of the small intestine and produce eggs through parthenogenesis.
Rhabditiform larvae can either be excreted in the feces or cause autoinfestation, that is, transform into infective filamentous larvae that can penetrate both the intestinal mucosa (internal autoinvasion) or the skin of the perianal area (external autoinfection).
How infection occurs from larvae
Disseminated strongyloidiasis occurs when the larvae, having entered the body through the skin or with contaminated water and food, penetrate the blood or lymphatic vessels and are carried through the bloodstream into the lungs. Then they migrate along the airways to the oropharynx, enter the digestive tract (when swallowed), and reach the duodenum, where their maturation is completed.
Causes and Transmission
The paragraphs below describe the causes and transmission of strongyloidiasis infection. Try to carefully study the material to protect yourself and your loved ones from illness.
How the infection occurs
The main reason for the development of intestinal strongyloidiasis is infection with parasite larvae, which occurs upon contact with infected soil, domestic animals (dog, cat, etc.), or objects. This can happen when walking barefoot, lying on the grass, etc. The larvae enter the environment through the feces of a sick person, who is the source of infection strongyloides. Much less often, infection occurs through the consumption of contaminated food or water, as well as through direct contact with sick people.
Skin contact
The roundworm Strongyloides stercoralis most often enters the body through unprotected skin contact with helminth-contaminated soil. Therefore, it is recommended to avoid direct skin contact with soil to prevent strongyloidiasis hyperinfection.
Fecal-oral transmission
As stated above, the main mechanism of pathogen transmission is fecal-oral. That is, the larvae enter the environment through the feces of a sick person and infect the soil, which ultimately leads to infection of other people and the appearance of strongyloidiasis symptoms.
Symptoms of Strongyloidiasis
The clinical incubation period is 15-17 days. Strongyloides stercoralis has a mechanical effect on the mucous membranes, resulting in disruption of the gastrointestinal tract. The waste products of helminths have a toxicoallergic effect on the body. This can be manifested by periodic diarrhea, asthmatic bronchitis, dermatitis, urticaria, papular rashes, local edema, eosinophilic infiltrates in the lungs, and severe eosinophilia in peripheral blood.
External manifestations of strongyloidiasis vary and largely depend on the state of the person’s immune system. People with strong immunity usually have asymptomatic or mild illness. But people with weakened immunity and immunodeficiency conditions may encounter a disseminated form with the spread of helminths throughout the body.
Acute vs. chronic infection
The disease can occur in two forms:
- Acute;
- Chronic.
The acute stage lasts from the moment of infection and takes from 2-3 weeks to 2 (sometimes 4) months. Symptoms of acute strongyloidiasis are usually severe and include abdominal pain and diarrhea, rash, pulmonary symptoms (including cough and wheezing), and eosinophilia.
The chronic strongyloidiasis lasts several years. The symptoms are usually less pronounced but still bother the person.
Rashes, itching, swelling
The main symptom of the disease is a characteristic linear rash on the skin in the form of fluid-filled blisters, localized in a specific area (focus of infection). A specific strongyloidiasis rash on the skin spreads very quickly and is accompanied by severe itching and sometimes swelling.
Cough, wheezing, sore throat
Many patients experience pronounced clinical symptoms of bronchopulmonary system disorders: cough, wheezing, asthma attacks, fever, sore throat, and shortness of breath.
Gastrointestinal issues
The gastrointestinal tract is significantly affected by strongyloidiasis. Patients have nausea, vomiting, and acute pain in the epigastric region on an empty stomach, 2-2.5 hours after eating, sometimes at night. Some people complain of pain syndrome throughout the abdomen, in the right or left hypochondrium, in the right or left iliac region. Stools are often normal or mushy up to 1-2 times a day. Sometimes constipation alternating with diarrhea is observed. Mucus and blood can be found in the stool, which is often associated with duodenal ulcers.
How Strongyloidiasis is Diagnosed?
To date, there is no uniform standard for diagnosing strongyloidiasis. According to the CDC, the disease may remain undiagnosed for a long time due to the nonspecific clinical manifestations. Stool microscopy, stool culture, serologic tests, PCR, etc. may be required to confirm the strongyloidiasis diagnosis. Let’s consider several common diagnostics in more detail.
Microscopic stool examination
Microscopic stool examination is an effective method for examining stool to identify larvae. The stool can be examined directly, after concentration (formalin-ethyl citrate), after recovery of larvae using the Baermann funnel method, after culturing using the Harada-Mori filter paper method, and after culturing in an agar plate.
PCR stool tests
Polymerase chain reaction (PCR) is a molecular diagnostic method that allows the detection of genetic material (RNA) of an infectious agent in biological material.
Serologic blood tests
A serological blood test is a laboratory test used to diagnose infectious diseases and determine the stage of the infectious process. The analysis is carried out on the basis of blood serum obtained by removing fibrogen from the blood plasma – the component responsible for blood clotting.
Skin biopsy
A skin biopsy involves taking a piece of skin and conducting a histological examination to identify signs of a pathological process.
Strongyloidiasis Treatment Options
Strongyloidiasis in stool can be treated successfully. Specific drugs containing antiparasitic substances (Mintezon, Ivermectin, or Stromectol) are usually prescribed. Sometimes patients need to use allergy medications to reduce swelling and itching. The generalized form of the disease requires infusion therapy aimed at maintaining the functionality of the affected organs.
How to Prevent Strongyloidiasis While Traveling?
Disease exposure prevention involves following a few simple rules. You should avoid walking barefoot or lying on the ground without a cushion. You should also wash vegetables and fruits to remove dirt before eating. If you take care of your health and follow these simple steps, you will most likely be able to effectively prevent strongyloidiasis while traveling within the United States or abroad.
Summary
Итак, strongyloidiasis is an infection caused by Strongyloides stercoralis. The sensitivity of the human body to the pathogen is high. Symptoms include abdominal pain and diarrhea, rash, pulmonary disorders, etc. Antiparasitic drugs can quickly and effectively cure the infection, while ignoring symptoms, on the contrary, can lead to a chronic course of the disease.
FAQ
How can a person get strongyloidiasis?
The main route of infection for strongyloidiasis is the penetration of worm larvae through the skin when walking barefoot or through any other contact with the ground.
How do humans get rid of strongyloides fuelleborni?
The basis of treatment is broad-spectrum anthelmintic drugs that quickly destroy parasites in the human body.
What does strongyloides rash look like?
Skin strongyloides usually appears as pink-red, oval-shaped blisters that rise above the surface of the skin.
How common is strongyloidiasis in the US?
Strongyloidiasis is not common in the US, although endemic foci exist in rural areas of the southeastern states and Appalachia.