Microbiology
Summary
Schistosoma species are trematodes found in aquatic environments, with larvae posing a risk to those exposed to infected water sources. Snails act as intermediate hosts for these species. Once inside the host, the Schistosoma trematodes mature in the liver and migrate against portal blood flow. Among them, Schistosoma mansoni has eggs with a lateral spine, Schistosoma japonicum eggs appear round due to a small spine, and Schistosoma haematobium eggs possess a large terminal spine. Infections can manifest as swimmer's itch, a rash commonly on the lower legs. Chronic infections with S. mansoni and S. japonicum can result in hepatic complications such as cirrhosis, periportal fibrosis leading to portal hypertension, and hepatitis presenting with jaundice. S. haematobium, specifically, is associated with urinary schistosomiasis with hematuria, and increased risk for squamous cell bladder cancer. Praziquantel is an effective treatment against Schistosoma infections.
Another trematode, Clonorchis sinensis, infects the biliary tree, including the gallbladder and bile ducts. Its infection is associated with sclerosing cholangitis, pigmented gallstones, and an elevated risk of cholangiocarcinoma. Snails are the intermediate hosts of C, sinensis, and praziquantel is effective against this infection. Paragonimus westermani is a trematode that affects the lungs, causing symptoms like chronic cough and hemoptysis. Its infection route is through the consumption of raw or undercooked seafood, with snails being its intermediate hosts and praziquantel being its treatment. Both Clonorchis sinensis and Paragonimus westermani produce operculated eggs (a lid-like structure on the egg that can open).
Lesson Outline
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FAQs
Trematodes, commonly known as flukes, are a type of parasitic flatworm. One prominent genus of trematodes is Schistosoma, which is known to cause a disease called schistosomiasis. This parasitic disease occurs mostly in tropical and subtropical regions, affecting millions of people worldwide. It's typically contracted when individuals come into contact with water that has been contaminated by the parasite.
Schistosoma species typically thrive in an aquatic environment. Their life cycle involves freshwater snails as an intermediate host. The parasite larvae infest the snails and then are released back into the water where they can penetrate the skin of humans who come into contact with the contaminated water. This is how humans become the primary host for the parasite.
Schistosomiasis can cause a variety of severe complications if left untreated. Over time, the bodyÕs reaction to the eggs of the parasite can lead to liver inflammation, portal hypertension (high blood pressure in the vein that goes to the liver), and cirrhosis (scarring of the liver). These conditions often result in liver failure, which can be life-threatening.
Infection with certain species of trematodes, particularly Schistosoma haematobium, is linked to bladder cancer. It's possible for infected individuals to experience hematuria, which is the presence of blood in urine, a common symptom in bladder cancer. The parasite causes chronic inflammation within the bladder lining, which can lead to abnormal cell growth and eventually cancer.
The most common treatment for diseases caused by trematodes, including Schistosoma and Clonorchis sinensis, is a medication called praziquantel. This drug is effective at killing the worms and helping the body excrete them. However, it's crucial to note that preventionÑprimarily by avoiding contact with contaminated water and consuming contaminated foodÑis the best approach against these diseases.
