Summary about Disease
Blood fluke infection, also known as schistosomiasis, is a parasitic disease caused by trematode worms of the genus Schistosoma. Humans become infected when larval forms of the parasite, released by freshwater snails, penetrate the skin during contact with infested water. The adult worms live in the blood vessels, where they lay eggs. Some of these eggs are passed out of the body in feces or urine to continue the parasite's life cycle, while others become trapped in body tissues, causing immune reactions and progressive damage to organs. Schistosomiasis is prevalent in many tropical and subtropical areas, especially in poor communities lacking access to safe drinking water and sanitation.
Symptoms
Symptoms can vary depending on the species of Schistosoma and the stage of infection. Many people, especially in early stages, have no symptoms. When symptoms do occur, they may include:
Acute schistosomiasis (Katayama fever): Fever, cough, abdominal pain, diarrhea, fatigue, muscle aches, and eosinophilia (increased eosinophils in the blood). This occurs a few weeks after initial infection.
Chronic schistosomiasis: Abdominal pain, enlarged liver or spleen, blood in urine or stool, problems passing urine, portal hypertension (increased pressure in the portal vein), ascites (fluid accumulation in the abdomen), and increased risk of bladder cancer (especially with S. haematobium infection). In rare cases, the parasite can affect the brain or spinal cord.
Causes
Schistosomiasis is caused by parasitic worms called schistosomes. People become infected when:
Contact with contaminated water: The most common route of infection is through skin contact with freshwater containing the infective larval stage (cercariae) released from specific types of freshwater snails.
Lack of sanitation and hygiene: Poor sanitation and hygiene practices, such as defecating or urinating in freshwater sources, allow the parasite's eggs to enter the water and infect snails, thus perpetuating the cycle.
Irrigation and agricultural practices: Irrigation projects can create ideal habitats for the snail hosts, increasing the risk of schistosomiasis transmission.
Medicine Used
The primary medication used to treat schistosomiasis is Praziquantel. It is effective against all species of Schistosoma. The drug works by paralyzing the worms, making them susceptible to attack by the host's immune system. Corticosteroids may be used in cases of severe Katayama fever or central nervous system involvement.
Is Communicable
Schistosomiasis is not directly communicable from person to person. The infection requires an intermediate snail host to complete its life cycle. Humans are infected through contact with contaminated water, not through contact with other infected individuals.
Precautions
Avoid swimming or wading in freshwater: Especially in areas where schistosomiasis is known to be present.
Boil or filter water: If freshwater contact is unavoidable, boil water for at least one minute or filter it to remove the parasite.
Vigorous towel drying: Thoroughly drying the skin after potential exposure to contaminated water may help prevent the parasite from penetrating.
Improve sanitation: Proper sanitation and waste disposal systems prevent the contamination of freshwater sources with human waste containing parasite eggs.
Snail control: Measures to control snail populations in infested water bodies can help reduce the risk of transmission.
Education: Educating communities about the risks of schistosomiasis and preventative measures is crucial.
How long does an outbreak last?
The duration of an outbreak depends on factors such as the extent of water contamination, the number of people exposed, and the implementation of control measures. Untreated individuals can harbor the infection for many years (even decades) if untreated. With widespread access to praziquantel, outbreaks can be controlled relatively quickly by targeting at-risk populations and infected individuals. Without intervention, endemic areas can experience ongoing transmission for extended periods.
How is it diagnosed?
Microscopic examination of stool or urine: Identifying parasite eggs in stool or urine samples is the most common diagnostic method. Multiple samples may be needed, as egg excretion can be intermittent.
Blood tests:
Eosinophil count: Elevated eosinophils can suggest parasitic infection.
Antibody tests: Serological tests (ELISA) can detect antibodies against Schistosoma, indicating past or present infection. However, these tests may not be able to distinguish between active and past infections.
Tissue biopsy: In some cases, a biopsy of the liver, rectum, or other tissues may be performed to look for parasite eggs.
Imaging: Ultrasound can detect liver or spleen damage due to chronic schistosomiasis.
Timeline of Symptoms
Penetration: Cercariae penetrate the skin - May cause a transient itchy rash (swimmer's itch) at the site of entry within days.
Migration and maturation: Worms migrate through the body and mature - asymptomatic
Acute schistosomiasis (Katayama fever): 3-8 weeks after infection. Symptoms: Fever, cough, abdominal pain, diarrhea, fatigue, muscle aches, eosinophilia. Can last for several weeks.
Chronic schistosomiasis: Months to years after initial infection. Symptoms vary depending on organ involvement: abdominal pain, enlarged liver or spleen, blood in urine or stool, problems passing urine, portal hypertension, ascites. Damage is progressive over time.
Important Considerations
Co-infections: Schistosomiasis can exacerbate other infections, such as HIV and hepatitis B/C.
Children: Children are particularly vulnerable to schistosomiasis due to their frequent contact with water.
Travelers: Travelers to endemic areas should be aware of the risks of schistosomiasis and take precautions to avoid exposure.
Public health: Schistosomiasis is a significant public health problem in many developing countries. Control efforts focus on mass drug administration, snail control, sanitation improvements, and health education.
Resistance: Resistance to praziquantel has been documented in some areas, highlighting the need for continued research and development of new treatments.