Name 2 diseases caused by parasitic worms and for each mention the;
i) causative agent
ii) mode of transmission
iii)life cycle of the parasite
iv) effect of the parasite on the host
v) adaptive characteristics of the parasite
1) Ascariasis:
i) Causative agent: The causative agent of ascariasis is the parasitic roundworm called Ascaris lumbricoides.
ii) Mode of transmission: Ascariasis is usually transmitted through ingestion of Ascaris eggs present in contaminated soil, food, or water.
iii) Life cycle of the parasite: The life cycle begins when Ascaris eggs are ingested by a human host. The eggs hatch in the intestines, and the larvae migrate through the bloodstream to the lungs. The larvae are then coughed up and swallowed, returning to the intestines where they mature into adult worms. The adult worms produce eggs that are passed in the host's feces, completing the life cycle.
iv) Effect on the host: Ascaris lumbricoides can cause abdominal pain, malnutrition, and obstruction of the intestines if a heavy infestation occurs. In severe cases, the worm can migrate to other organs like the bile duct, appendix, or pancreas, leading to complications.
v) Adaptive characteristics of the parasite: Ascaris lumbricoides has a durable and resistant outer layer on its eggs, allowing it to survive harsh environmental conditions and remain infective for a long period of time. The adult worms can also grow up to 30 cm in length, enabling them to absorb nutrients from the host's intestines efficiently.
2) Schistosomiasis:
i) Causative agent: Schistosomiasis is caused by different species of parasitic trematodes (flukes) belonging to the genus Schistosoma.
ii) Mode of transmission: Schistosomiasis is transmitted when humans come into contact with freshwater contaminated with the larvae of Schistosoma, which are released from infected snails.
iii) Life cycle of the parasite: The life cycle of Schistosoma involves two hosts - humans and snails. The eggs released by adult female Schistosoma in the human host's bloodstream are excreted in feces or urine. When the eggs reach freshwater, they hatch, releasing larvae called cercariae. The cercariae infect specific species of snails, where they develop into infective larvae called cercariae. These cercariae are then released from the snails into freshwater, where they can penetrate the human skin, entering the bloodstream to complete the life cycle.
iv) Effect on the host: Schistosomiasis can cause a variety of symptoms depending on the species of Schistosoma involved. Symptoms can range from mild itching and rash (during the penetration of cercariae through the skin) to chronic infections that lead to damage of the liver, spleen, bladder, and intestines. Long-term complications include anemia, organ failure, and increased susceptibility to other infections.
v) Adaptive characteristics of the parasite: Schistosoma parasites have a complex life cycle involving snail hosts that provides them with protection and a suitable environment for development. The parasites have evolved mechanisms to evade the host's immune system, including antigenic variation and altering the host's immune response. Additionally, the cercariae possess enzymes to help them penetrate and migrate through the skin, ensuring successful entry into the human host.
Disease 1: Schistosomiasis
i) Causative agent: Schistosoma parasites, specifically Schistosoma mansoni, Schistosoma haematobium, and Schistosoma japonicum.
ii) Mode of transmission: The parasite is transmitted to humans through contact with freshwater contaminated with specific intermediate host snails that release infective cercariae (a larval stage). The cercariae penetrate the human skin during activities like swimming, bathing, or wading in infested water.
iii) Life cycle of the parasite: After penetrating the skin, the cercariae travel through the bloodstream to reach specific organs such as the liver (S. mansoni and S. japonicum) or the bladder and urinary tract (S. haematobium) where they develop into adult worms. The adult male and female worms mate and produce thousands of eggs, which are then released into the environment through the urine or feces of the infected individual. The eggs hatch in water, releasing miracidia (another larval stage) that infect the intermediate snail host. Inside the snail, the parasite undergoes further development and eventually produces infectious cercariae, completing the cycle.
iv) Effect of the parasite on the host: Schistosoma worms reside in the blood vessels of the affected organs. The immune response to the eggs trapped in the tissues causes inflammation and damage, leading to various symptoms depending on the specific species involved. Symptoms may include fever, cough, abdominal pain, bloody stool/urine, liver enlargement, bladder dysfunction, anemia, and developmental disorders in children. If left untreated, chronic infections can lead to severe complications like liver and kidney damage and an increased risk of bladder cancer.
v) Adaptive characteristics of the parasite: Schistosoma parasites exhibit several adaptive characteristics that contribute to their survival and transmission. These include the ability to penetrate the human skin efficiently, their complex life cycle involving an intermediate snail host, and the production of thousands of eggs that can be shed into the environment through human excreta, allowing the cycle to continue.
Disease 2: Onchocerciasis (River blindness)
i) Causative agent: Onchocerca volvulus, a parasitic filarial worm.
ii) Mode of transmission: The disease is transmitted through the bites of infected blackflies (Simulium species), which deposit the parasite's larvae (microfilariae) into the human skin during feeding.
iii) Life cycle of the parasite: After entering the human host, microfilariae migrate to the subcutaneous tissues, where they mature into adult worms. The adult female worms then produce thousands of microfilariae that can live in the skin or migrate through the body. The blackfly takes up the microfilariae while feeding on an infected individual, where they develop into infective larvae. When an infected blackfly subsequently bites a new human host, the infective larvae enter the skin and continue the cycle.
iv) Effect of the parasite on the host: Onchocerca volvulus worms cause a range of symptoms and complications. The adult worms often form tangled masses within subcutaneous nodules, causing itching and skin lesions. However, the most severe consequence is the eye damage caused by the microfilariae. These microfilariae can migrate to the eyes, leading to inflammation, intense itching, and in some cases, visual impairment or blindness. Skin changes, including depigmentation and thickening, are also common among those affected by the disease.
v) Adaptive characteristics of the parasite: Onchocerca volvulus exhibits several adaptive characteristics, including a complex life cycle involving both human and blackfly hosts, the ability of the microfilariae to migrate throughout the body, and the susceptibility of blackflies to become infected during their feeding process. The parasite's ability to cause prolonged infections and evade the host immune response also contributes to its long-term survival.