Strongyloides stercoralis is the name given to a dwarf nematode. The parasite can cause disease in humans.
What is Strongyloides stercoralis?
Strongyloides stercoralis is a dwarf nematode that belongs to the genus Strongyloides. The parasite is found in soil, but also affects humans. In medicine, a dwarf nematode infestation is also called strongyloidiasis. Dwarf nematode infection is one of the most common worm diseases. The larvae are able to settle in the entire organism. People in tropical regions are particularly affected. However, the dwarf nematode can also be found in temperate climates. Doctors believe that approximately 80 million people worldwide are infected with Strongyloides stercoralis.
Occurrence, distribution, and characteristics
Native to Strongyloides stercoralis is mainly in warm, humid areas such as the tropics. However, it can also be found in Europe in the warm zones of tunnel constructions or mines. In Germany and Western Europe, however, the dwarf nematode is rarely found. Dwarf nematode females that settle in the human intestine reach a maximum size of 2.7 centimeters. Specimens of Strongyloides stercoralis that live outside the human body are about a third smaller. The maximum size of males is about one centimeter. The life cycle of Strongyloides stercoralis can be divided into two phases. Thus, there are larvae and adult worms. The parasites enter the human intestine by penetrating the body through the skin and travel through the bloodstream to the lungs. After exiting the tissues, the parasites continue their journey toward the stomach via the trachea and esophagus. Finally, they reach the small intestine, in whose mucous membrane the worm larvae settle. There they grow until they are sexually mature. The larvae in the small intestine develop into exclusively female dwarf threadworms. They lay several thousand eggs per day, from which the next generation of worms is formed. Following molting, Strongyloides stercoralis is able to penetrate the intestinal wall or travel further into the intestine. From there, it invades the anal mucosa or adjacent areas. Medical experts refer to this process as exo-autoinvasion. In the further course, Strongyloides stercoralis is excreted in the stool. In the process, dwarf threadworms of different sexes are formed. They reach a smaller size than specimens that are established in the intestine. The worms produce eggs from which new infective larvae emerge. Each egg contains an embryo of Strongyloides stercoralis, which matures into a larva. Further development of the dwarf nematode takes only a few days. However, the exact mechanisms of the reproductive process have not yet been clarified. If the parasites remain in the human body, they can be re-infected again and again. In some cases, however, the human remains unaffected by the dwarf threadworms. In other cases, Strongyloides stercoralis pierces the intestine of the affected person and enters the bloodstream. This occurs preferentially in the appendix, the scrotum, and the main area of the colon. The risk of infection is considered particularly high when people walk barefoot. Also at risk for dwarf nematode infestation are people who suffer from immunodeficiency.
Diseases and complaints
An infestation of Strongyloides stercoralis is called a Strongyloides stercoralis infection or dwarf nematode infection. In some cases, the infection is chronic and persists for decades without the affected person experiencing symptoms. Symptoms may be seen as the worm larvae migrate through the skin. They are called larva migrans cutanea symptoms and cause mechanical skin damage. Inflammatory reactions occur within the migratory area. This process is noticeable by redness and itching. The dwarf nematode larvae move quickly and cover about ten centimeters per hour. If the Strongyloides stercoralis reaches the human lungs, acute respiratory problems, bronchitis or even pneumonia threaten. The extent to which the intestine is affected by the dwarf threadworms depends on the state of the patient’s immune system.If the patient suffers from an immunodeficiency disease such as AIDS or cancer, there is a risk of complications, which in the worst case can be fatal. In the case of chronic worm infestation, there is a risk of further infections with other pathogens. In addition, intestinal bacteria can spread within the body during the migration of the larvae, which in turn results in infections. In women, transmission of Strongyloides stercoralis via breast milk is also possible during lactation if the parasites have reached the milk ducts. The first symptoms of an infestation with dwarf threadworms sometimes appear about 3 to 4 weeks after infection in the digestive tract. Those affected then suffer from bloody diarrhea, nausea and vomiting. However, about 30 percent of infected individuals do not experience any symptoms at all. Diagnosis of dwarf nematode infestation is possible by microscopic examination of stool and sputum. To combat Strongyloides stercoralis, drug therapy is used. Here, the patient receives anthelmintics such as mebendazole, albendazole or ivermectin, which kill the parasites. Treatment with the broad-spectrum drug mebendazole usually lasts three days. Following this, the body is once again free of Strongyloides stercoralis.
