Strongyloidiasis is a disease caused by strongyloides stercoralis parasitic in the human small intestine, and is manifested by rash at the site invaded, pulmonary lesions during the migratory stage, and diarrhea during the intestinal parasitic stage.
Rhabditiform larvae of strongyloides stercoralis absorb organic matter in the soil for a living, and develop into free-living adults after 4 molts within 1 - 2 days. The male adults have two copulatory spicules. Mature females contain 4 - 16 eggs in the uterus, and the eggs can be hatched into rhabditiform larvae. If the environment is uncomfortable, rhabditiform larvae develop into infective filariform larvae after 2 molts, invading the human body through the skin or mucous membranes.
After invasion of the human body, filariform larvae enter the subcutaneous minute blood vessels, migrate from the right heart to the lungs through the bloodstream, and then penetrate the alveolar capillaries and enter the alveoli. Most larvae migrate upwards from the lower respiratory tract, are swallowed into the digestive tract through the throat, settle in the small intestine, mainly the duodenum and upper jejunum, where the larvae develop and mature. There are only females found in the human body, and they undergo parthenogenesis. The females are relatively slender, about 2.2mm × (0.03 - 0.074) mm in size. Females live and lay eggs in the intestinal mucosa. Each female can lay 50 eggs per day. Rhabditiform larvae are hatched out in several hours, escaped from the intestinal mucosa, and excreted outside the body through feces. Under special circumstances such as constipation, enteritis, malnutrition, and receiving immunosuppressive treatment, rhabditiform larvae can rapidly develop into filariform larvae in the human body, penetrate into the intestinal wall, and invade the blood circulation, causing endogenous autoinfection. After filariform larvae are excreted through feces, if they invade the perianal skin and enter the blood circulation, exogenous autoinfection can occur.
Signs and Symptoms
About 2/3 of patients are asymptomatic.
Larva migrans is the most common early manifestation. Maculopapular rash or creeping eruption occurs on the perianal skin or other areas in 66% - 84% of patients, and about 5% of patients present with cough, asthma, low-grade fever, or hypersensitivity pneumonitis caused by pulmonary infiltration. Few patients develop severe respiratory symptoms such as dyspnea, cyanosis, hemoptysis, and bronchopneumonia.
Moderate and severe patients often present with abdominal pain, diarrhea, vomiting, anorexia, or constipation. Burning sensation or cramping in the upper abdomen may be present. There are watery or loose stools, as well as bloody, mucoid stools. Paralytic ileus, abdominal distension, electrolyte imbalance, dehydration, and circulatory failure may occur in few patients.
Different organs invaded result in different symptoms, such as meningitis and urinary tract infection. Neurasthenic syndrome manifested by fever, general malaise, irritability, depression, and insomnia results from the disintegration or metabolites of the worms. Bacterial or fungal sepsis may occur in some patients. When patients are immunocompromised, the larvae can cause disseminated hyperinfection, resulting in multiple organ failure or death.
Complications such as shock, respiratory failure, bronchopneumonia, and sepsis occur in severely ill patients. The fatality rate is about 26%, up to 50% - 86% in patients with disseminated hyperinfection.
If the larvae are found in the feces, duodenal contents, sputum, or bronchoalveolar lavage fluid, or positive antibodies are detected in immunization, the disease can be diagnosed.
The treatment regimen is ivermectin 200mcg/kg orally once a day for 2 days, or albendazole 400mg orally twice a day for 7 days.