Schistosomiasis Overview and Lifecycle

Study Notes

Schistosomiasis

Schistosomiasis is a chronic parasitic disease caused by flatworms known as schistosomes.
Schistosomiasis is caused by five species of schistosomes, but the most common are Schistosoma mansoni, Schistosoma japonicum, and Schistosoma haematobium.

Types of Schistosomiasis

Schistosoma mansoni and Schistosoma japonicum affect the liver and intestines, causing hepatosplenic schistosomiasis.
Schistosoma haematobium infects the bladder and reproductive organs, causing genitourinary schistosomiasis.

Schistosome Lifecycle and Transmission

Schistosomiasis is acquired through contact with contaminated water containing the larvae of the parasite.
Schistosomes require certain species of snails as intermediate hosts.
Swimming or bathing in infested bodies of water is a major risk factor.

Schistosome Larvae: Cercariae and Schistosomula

Free-swimming larvae known as cercariae penetrate the skin of humans.
Cercariae lose their tails after entering the skin, transforming into schistosomula.
Schistosomula travel through the bloodstream to the lungs, heart, and eventually to their target organs.

Schistosomiasis Symptoms

Schistosomes can cause a skin rash known as "swimmer's itch" when they penetrate the skin but are unable to mature.
Schistosomes can remain silent in the body, producing no symptoms.
Schistosomiasis symptoms often appear 4-8 weeks after infection, and they can range from mild to severe, depending on factors such as parasite load.

Schistosome Maturation

Schistosomula mature into sexually mature male and female worms in the blood vessels.
Male schistosomes have a ventral groove called the gynecophoral canal, which carries the female.
Schistosomes remain together in a permanent copulation for years, feeding on blood and laying eggs.

Schistosome Eggs: A Major Cause of Disease

Schistosome eggs are released into the bloodstream and spread to the liver or bladder.
Schistosome eggs can penetrate the intestines or bladder walls, but many fail to reach there and become trapped, causing inflammation.
Inflammation caused by trapped eggs can lead to fibrosis, granulomas, and other problems.

Liver Damage

Schistosome eggs often become trapped in the liver, leading to fibrosis around the portal vein branches.
This fibrosis can block the flow of blood through the liver, causing portal hypertension.
Portal hypertension can lead to abdominal fluid buildup (ascites), varices, and splenomegaly.

Bladder Damage

Schistosome eggs can cause bladder inflammation, granulomas, and urethral obstruction.
Bladder damage can lead to kidney damage, urinary tract infections, and hematuria.

Reproductive System Damage

Schistosoma haematobium can cause genital inflammation, granulomas, and hematospermia in males.
Schistosoma haematobium can cause vaginal inflammation and infertility in females.
Genital inflammation predisposes females to acquiring HIV.

Treatment and Control

Schistosomiasis can be treated with a single dose of praziquantel.
Glucocorticoids can manage severe inflammation.
Control measures include improving sanitation, educating the public, and reducing snail populations.

Schistosomiasis in South America

Schistosomiasis in South America is believed to be a consequence of the slave trade.
The presence of similar snail species in South America and Africa suggests that schistosomiasis was introduced through historical migration.

Description

This quiz explores the chronic parasitic disease schistosomiasis, its causative agents, and types. You will learn about the lifecycle of schistosomes, their transmission through contaminated water, and the role of snails as intermediate hosts. Gain insights into the symptoms and impacts of this disease on human health.