Finding evidence of liver flukes in a stool sample indicates a parasitic infection known as fascioliasis, clonorchiasis, or opisthorchiasis. Liver flukes are parasitic flatworms, specifically trematodes, that infect the biliary system, including the liver and bile ducts, of mammals. The infection is often contracted through the consumption of contaminated food or water. The discovery of the parasite’s microscopic eggs in human waste confirms an active infection is present.
Biological Profile of Liver Flukes
Liver flukes are parasitic trematodes with flattened, leaf-like bodies. They are obligate parasites requiring at least one intermediate host, typically a freshwater snail, to complete their life cycle. Human infections generally involve two distinct groups of these parasites.
One group includes smaller flukes, such as Clonorchis sinensis (Chinese liver fluke) and Opisthorchis spp. (East and Southeast Asian liver flukes). These species measure 10 to 25 millimeters in length and primarily reside and mature within the smaller bile ducts of the liver.
The second type is Fasciola hepatica, known as the sheep or cattle liver fluke, which is significantly larger. Adult F. hepatica can reach lengths of up to 30 millimeters and widths of 15 millimeters. Unlike the smaller species, Fasciola adults migrate and reside in the larger bile ducts and the liver parenchyma, where they cause damage.
The Infection Cycle and Passage in Stool
The liver fluke life cycle begins outside the human body, involving intermediate hosts, typically freshwater snails. Larval forms, known as miracidia, hatch from eggs passed in the stool and penetrate the snail, developing through several stages. They eventually emerge from the snail as cercariae, ready to infect the next host.
Human infection occurs through the ingestion of the infective stage, the metacercariae. For Clonorchis and Opisthorchis, the cercariae encyst in freshwater fish, and humans are infected by consuming raw or undercooked fish. Fasciola hepatica cercariae encyst on aquatic vegetation, such as watercress, leading to infection when these plants are eaten.
Once ingested, the metacercariae excyst within the duodenum. The young flukes then actively migrate through the abdominal cavity to the liver. They mature into adult flukes in the bile ducts, continually producing thousands of microscopic eggs.
The eggs are flushed from the bile ducts into the small intestine and then excreted with the feces, providing diagnostic evidence of an established infection. Adult flukes are only rarely passed in stool.
Health Consequences and Diagnosis
The health impact of liver fluke infection varies based on the parasite species, infection intensity, and duration. During the initial, or acute, phase, patients may experience fever, fatigue, and right upper quadrant abdominal pain as young flukes migrate through the liver tissue. Blood tests often show eosinophilia, an elevated count of white blood cells responding to parasitic invasion.
As the infection progresses into the chronic phase, adult flukes in the bile ducts cause mechanical irritation and toxic damage to the epithelial lining. This chronic inflammation, known as cholangitis, can lead to the thickening of bile duct walls and fibrosis. Duct blockage can occur, potentially causing jaundice due to impaired bile flow.
The long-term presence of flukes can also lead to gallstones and recurrent bacterial infections within the biliary system. The most severe consequence associated with chronic infection by Clonorchis sinensis and Opisthorchis spp. is cholangiocarcinoma. This bile duct cancer develops as a result of years of chronic inflammation and cellular damage induced by the parasites.
Diagnosis
Confirming a liver fluke infection relies primarily on the microscopic examination of stool samples to identify the characteristic eggs. This standard diagnostic procedure uses the distinctive sizes and shapes of the eggs to differentiate between the various species. Multiple stool samples may need examination over several days to increase the probability of detection, especially in low-intensity infections.
Supplementary diagnostic tools are employed to assess the extent of damage within the liver and bile ducts. Blood tests can measure levels of liver enzymes. Imaging techniques, such as abdominal ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI), can visualize bile duct dilation, thickening, or abscesses within the liver parenchyma.
Treatment
Medical treatment for liver fluke infection is generally highly effective, relying on specific antiparasitic medications that target the adult worms. For infections caused by Clonorchis or Opisthorchis, the drug of choice is typically Praziquantel, which paralyzes the parasites. Infections involving Fasciola hepatica are treated with Triclabendazole, a medication highly effective against both immature and mature forms of that species.