Biology · Ch 7 — Human Health and Diseases
Parasitic Diseases: Malaria, Filariasis, Ascariasis, and Amoebiasis
Parasitic Diseases: Malaria, Filariasis, Ascariasis, and Amoebiasis
A large share of the disease burden covered in the WBCHSE syllabus for this chapter comes from parasites — organisms, either single-celled protozoans or multicellular worms, that live in or on a human host and cause disease. Four such diseases are discussed here: malaria, filariasis, ascariasis, and amoebiasis.
Malaria is caused by protozoan parasites of the genus Plasmodium (chiefly P. vivax and P. falciparum in India), and is transmitted exclusively through the bite of an infected female Anopheles mosquito. Once inside the human body, the parasite invades and multiplies inside red blood cells; when large numbers of infected red blood cells rupture together and release the parasite (along with a toxic pigment called haemozoin) into the bloodstream, the patient experiences a sudden, sharp bout of high fever accompanied by chills and shivering (rigor). Because the parasite's life cycle inside red blood cells runs on a fairly fixed schedule, this fever tends to recur periodically — classically every 48 or 72 hours, depending on the Plasmodium species involved. Prevention centres on breaking the mosquito's access to people: insecticide-treated bed nets, indoor residual spraying, window screens, and eliminating stagnant water where the mosquito breeds, alongside prompt diagnosis and antimalarial treatment of confirmed cases.
Amoebiasis is caused by the protozoan Entamoeba histolytica, spread through food or water contaminated with faecal matter containing its cysts (a hardy, resistant stage of the parasite). Once swallowed, the cysts release amoebae that colonise the large intestine, where they can cause abdominal pain and cramps, constipation alternating with stools containing excess mucus and blood-tinged clots. Prevention relies on safe drinking water, thorough hand-washing, properly cooked food, and sanitary disposal of human waste.
Filariasis (also called elephantiasis in its advanced form) is caused by thread-like nematode worms, Wuchereria bancrofti and W. malayi, transmitted through the bite of an infected Culex mosquito. The worms lodge in the lymphatic vessels and lymph nodes, mainly of the legs and the external genital organs, where chronic inflammation over years causes the affected tissue to swell dramatically. Because this vector is a night-biting mosquito that breeds in polluted water, prevention again centres on mosquito control, personal protection against bites, and mass drug administration programmes using anti-filarial medicine in affected regions. …
| Disease | Causative Agent | Type of Pathogen | Mode of Transmission | Key Symptoms | Preventive Measures |
|---|---|---|---|---|---|
| Malaria | Plasmodium vivax, P. falciparum, and related species | Protozoan | Bite of infected female Anopheles mosquito | Recurring cycles of high fever with chill and rigor, headache, sweating | Insecticide-treated mosquito nets, removing stagnant water, indoor spraying, prompt antimalarial treatment |
| Filariasis | Wuchereria bancrofti and W. malayi | Nematode (roundworm) | Bite of infected Culex mosquito | Chronic inflammation and swelling of the lymphatic vessels, especially of the legs and external genitals (elephantiasis in advanced cases) | Vector control, avoiding mosquito bites, mass drug administration with anti-filarial medicine |
| Chikungunya | Chikungunya virus (CHIKV) | Virus | Bite of infected Aedes aegypti mosquito | Sudden high fever with severe, often persistent, joint pain and swelling, headache, rash | Eliminating mosquito breeding sites, using repellents, protective clothing |
| Dengue | Dengue virus (DENV) | Virus | Bite of infected Aedes aegypti mosquito | High fever, severe headache, pain behind the eyes, muscle and joint pain ("breakbone fever"), sometimes a fall in platelet count | Eliminating stagnant water where Aedes breeds, mosquito nets/repellents, prompt medical care for warning signs |
| Ascariasis | Ascaris lumbricoides | Nematode (roundworm) | Ingestion of contaminated food, water, or soil carrying eggs (faecal-oral route) | Internal bleeding, muscular pain, fever, blockage of the intestinal passage in heavy infections | Personal hygiene, washing vegetables and hands, safe drinking water, proper sanitation |
| Typhoid | Salmonella typhi | Bacterium | Contaminated food or water (faecal-oral route) | Sustained high fever, weakness, abdominal pain, headache, loss of appetite, constipation | Safe drinking water, food hygiene, hand-washing, typhoid vaccination |
| Pneumonia | Commonly Streptococcus pneumoniae (also other bacteria/viruses) | Bacterium (mainly) | Respiratory droplets from an infected person; also spreads by sharing utensils/glasses used by a patient | Fever with chills, cough with mucus, difficulty in breathing, chest pain; alveoli fill with fluid | Vaccination (pneumococcal), covering mouth while coughing/sneezing, avoiding overcrowding |
| Common Cold | Rhinovirus | Virus | Airborne droplets and contact with contaminated surfaces | Nasal congestion, sore throat, mild cough, sneezing, watery eyes; usually resolves in 3-7 days | Hand hygiene, avoiding close contact with infected persons, adequate rest and fluids |
| Amoebiasis | Entamoeba histolytica | Protozoan | Contaminated food and water (faecal-oral route) | Abdominal pain and cramps, constipation, stools with excess mucus and blood clots | Safe drinking water, hand hygiene, proper disposal of sewage |