As Strongyloides stercoralis is called a dwarf nematode. The parasite can cause illness in humans.
The Strongyloides stercoralis is a dwarf threadworm that belongs to the genus Strongyloides. The parasite occurs in the ground, but also affects humans. In medicine, dwarf threadworm infestation is also called strongyloidiasis.
A dwarf threadworm 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. Sometimes the dwarf threadworm can also be found in moderate climates. Doctors estimate that around 80 million people worldwide are infected with Strongyloides stercoralis.
Strongyloides stercoralis is mainly found in warm, humid areas such as the tropics. However, it can also occur in Europe in the warm zones of tunnels or mines. In Germany and Western Europe, however, the dwarf threadworm is rarely found.
Female dwarf threadworms 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 around a third smaller. The maximum size of the males is about one centimeter.
The life cycle of Strongyloides stercoralis can be divided into two phases. So there are larvae and adult worms. The parasites get into the human intestines by entering the body through the skin and through the bloodstream to the lungs. After the parasites have emerged from the tissue, they continue towards the stomach via the windpipe and esophagus. Finally they reach the small intestine, in whose mucous membrane the worm larvae nest. There they grow until they are sexually mature.
Only female dwarf threadworms develop from the larvae in the small intestine. Each day they lay several thousand eggs, from which the next generation of worms then develop. After moulting, the Strongyloides stercoralis is able to penetrate the intestinal wall or to move further into the intestine. From there it penetrates into the anal mucosa or adjacent areas. Doctors refer to this process as an exo-auto-invasion.
As the disease progresses, Strongyloides stercoralis is excreted in the stool. Thereby dwarf threadworms of different sexes form. They reach a smaller size than specimens that are located in the intestine. The worms produce eggs from which new infectious larvae emerge. Each egg contains an embryo of Strongyloides stercoralis, which matures into a larva. The development of the dwarf threadworm only takes a few days. The exact mechanisms of the reproductive process have not yet been clarified.
If the parasites remain in the human body, there can always be renewed infection. In some cases, however, humans remain unaffected by dwarf threadworms. In other cases, the Strongyloides stercoralis pierces the affected person's intestines and enters the bloodstream. This occurs preferentially in the appendix, in the ileum and in the main area of the colon.
The risk of infection is particularly high when people walk barefoot. People who suffer from an immunodeficiency are also at risk of dwarf threadworm infestation.
An infestation with Strongyloides stercoralis is known as Strongyloides stercoralis infection or dwarf threadworm infection. In some cases the infection is chronic and lasts for decades without the affected person feeling any discomfort.
Symptoms can show up as worm larvae migrate through the skin. They are called larva migrans cutaneous complaints and cause mechanical skin damage. Inflammatory reactions occur within the migration area. This process is noticeable through redness and itching.
The dwarf threadworm larvae move quickly and cover about ten centimeters an hour. If the Strongyloides stercoralis reaches the human lungs, there is a risk of acute breathing difficulties, bronchitis or even pneumonia.
The extent to which the intestines are affected by the dwarf threadworms depends on the patient's immune system. If this person suffers from an immunodeficiency disease such as AIDS or cancer, there is a risk of complications that can be fatal in the worst case. A chronic worm infestation threatens further infections with other pathogens.
In addition, intestinal bacteria can spread throughout the body as the larvae migrate, which in turn leads to infections. In women, Strongyloides stercoralis can also be transmitted through breast milk during breastfeeding if the parasites have penetrated the milk ducts.
The first symptoms of an infestation with dwarf threadworms appear in the digestive tract about 3 to 4 weeks after the infection. Those affected then suffer from bloody diarrhea, nausea and vomiting.
In around 30 percent of the people affected, however, there are no symptoms at all. A diagnosis of dwarf threadworm infestation is possible through a microscopic examination of stool and sputum.
Drug therapy is used to combat Strongyloides stercoralis. 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. Then the body is freed from Strongyloides stercoralis again.