Managing water-related disease Revision Notes

Malaria is caused by Plasmodium parasites, which require two hosts to complete their life cycle: the female Anopheles mosquito and humans. When an infected mosquito bites a human, it injects sporozoites into the bloodstream. These travel to the liver, where they mature and multiply into merozoites. The merozoites then enter red blood cells, causing them to burst and releasing more parasites, which leads to the symptoms of malaria such as fever and chills.

Some parasites develop into sexual forms called gametocytes, which are taken up by another mosquito during a blood meal. Inside the mosquito, gametocytes mature into gametes, fuse to form zygotes, and develop into sporozoites that migrate to the mosquito’s salivary glands, ready to infect another human. This cycle allows the parasite to spread and persist in populations.

• Malaria parasite requires both mosquito and human hosts to complete its life cycle.
• Transmission occurs when infected mosquitoes bite humans, injecting sporozoites.
• Parasites multiply in the human liver and red blood cells, causing illness.
• Gametocytes taken up by mosquitoes continue the cycle within the vector.

Controlling malaria involves interrupting the parasite’s life cycle and reducing human exposure to infected mosquitoes. Antimalarial medications such as chloroquine and artemisinin-based combination therapies target parasite stages inside humans to treat infection and prevent disease progression. However, drug resistance can reduce effectiveness, requiring ongoing development of new treatments.

Vector control aims to reduce mosquito populations and prevent bites. Insecticide-treated bed nets (ITNs) provide a physical barrier and kill mosquitoes on contact, significantly lowering transmission risk. Indoor residual spraying (IRS) applies insecticides to walls where mosquitoes rest, reducing their lifespan. Environmental management includes draining stagnant water and clearing vegetation to eliminate breeding sites.

Eradication efforts combine these methods with surveillance to detect cases early and community education to promote protective behaviours. For example, the Global Malaria Eradication Programme in the mid-20th century used widespread spraying and treatment but faced challenges due to resistance and logistical issues, highlighting the complexity of eradication.

• Antimalarial drugs treat and prevent infection but face resistance challenges.
• Insecticide-treated nets and indoor spraying reduce mosquito bites and populations.
• Environmental management removes mosquito breeding habitats.
• Eradication requires integrated approaches including surveillance and education.

Cholera is a waterborne disease caused by the bacterium Vibrio cholerae, which spreads through contaminated water and food. Control focuses on providing safe drinking water to prevent ingestion of the bacteria. Boiling water kills pathogens effectively but requires fuel and time, which may limit use in some areas.

Chlorination is a chemical disinfection method that kills bacteria and viruses in water supplies. It is widely used in water treatment plants and emergency responses due to its effectiveness and ease of application. Maintaining proper chlorine levels is essential to ensure safety without harmful side effects.

Improving sanitation infrastructure to prevent sewage contamination of water sources and promoting hygiene practices such as handwashing are critical complementary strategies. These reduce the risk of cholera outbreaks by interrupting transmission pathways.

• Cholera spreads through contaminated water and food.
• Boiling water kills cholera bacteria but may be resource-intensive.
• Chlorination disinfects water efficiently and is widely used.
• Sanitation and hygiene improvements prevent contamination and outbreaks.

Multipurpose dams provide benefits such as water storage for irrigation, hydroelectric power, flood control, and domestic water supply. However, they also have environmental and social impacts that must be managed.

For example, the construction of a large dam can alter river flow, affecting aquatic ecosystems downstream and reducing sediment transport, which can degrade fertile floodplains. Reservoirs may submerge habitats and displace communities, leading to social disruption.

On the positive side, dams can improve water availability during dry seasons, support agriculture, and generate renewable energy. Effective management involves balancing these benefits with mitigation measures such as fish ladders, resettlement programs, and environmental flow releases to sustain ecosystems.

• Dams provide irrigation, power, flood control, and water supply.
• They can disrupt ecosystems and displace communities.
• Reduced sediment flow affects downstream fertility and habitats.
• Management requires balancing benefits with environmental and social mitigation.

Water bodies can become polluted from sources such as industrial discharge, agricultural runoff, sewage, and urban waste. For instance, a river receiving untreated sewage may experience eutrophication, where excess nutrients cause algal blooms that deplete oxygen and harm aquatic life.

Pollution affects water quality, making it unsafe for drinking, recreation, and harming biodiversity. It can also impact fisheries and local livelihoods dependent on clean water.

Management strategies include regulating pollutant discharge, treating wastewater before release, promoting sustainable agricultural practices to reduce fertilizer runoff, and community monitoring programs. Restoration efforts may involve aeration, removal of contaminants, and habitat rehabilitation to improve water quality.

• Pollution sources include industry, agriculture, sewage, and urban waste.
• Eutrophication from nutrient pollution harms aquatic ecosystems.
• Pollution reduces water safety and affects human and ecological health.
• Management involves regulation, treatment, sustainable practices, and restoration.