Case Study: Malaria (AQA A-Level Geography): Revision Notes

Case Study: Malaria

What is malaria?

Malaria is a tropical disease transmitted biologically through insect vectors. The disease has a devastating impact on people's health and their livelihoods across the world.

The disease is caused by a single-celled parasite from the Plasmodium family. When a female Anopheles mosquito bites a person, the parasite can be transferred into their bloodstream. Once inside, the parasites multiply in the liver before infecting red blood cells.

Symptoms and progression

The disease manifests through several characteristic symptoms:

• Fever
• Headache
• Vomiting

These symptoms typically appear 10-15 days after the mosquito bite. If malaria is not treated, it can rapidly become life-threatening by disrupting blood supply to vital organs. The disease can either kill a person directly or weaken their immune system, making them vulnerable to other illnesses.

Global distribution and prevalence

Although malaria was once common in many more places around the world, it has been eliminated in numerous populous regions over the course of the twentieth century, including many parts of the USA and Europe. This has saved millions of lives.

Current global statistics (WHO, 2018)

• 3.6 billion people (nearly half the world's population) across 91 countries live in areas at risk of malaria transmission
• An estimated 228 million cases occurred, resulting in around 405,000 deaths
• Children under five years of age are the most vulnerable group, accounting for 67% (272,000) of all malaria deaths worldwide

Geographic concentration

Sub-Saharan Africa carries a disproportionately high share of the global malaria burden. In 2018:

• The region was home to 93% of malaria cases
• It accounted for 94% of malaria deaths

Countries most affected

Specific countries bear the heaviest burden:

• 19 countries in sub-Saharan Africa plus India carried almost 85% of the global malaria burden
• Six countries accounted for more than half of all malaria deaths worldwide:
  • Nigeria (25%)
  • Democratic Republic of the Congo (12%)
  • Uganda (5%)
  • Côte d'Ivoire, Mozambique and Niger (4% each)

Environmental factors influencing malaria transmission

Physical environment and seasonal patterns

Malaria is strongly linked to the natural environment. The transmission of the disease is greatest in areas where both the rainy season and temperatures are suitable for mosquito breeding.

Mosquitoes breed in stagnant water, which means transmission is enhanced in areas with standing water after the rainy season. The length of the malaria transmission season is directly related to the length of the rainy season.

Temperature requirements

Temperature plays a crucial role in malaria transmission:

• At altitudes above 1,500m and where rainfall is below 1,000mm, malaria transmissions fall
• The parasites require temperatures between 16°C and 32°C to develop inside the mosquito
• This is one reason why the disease is largely concentrated in the tropics and subtropics

Altitude and rainfall patterns

Areas at high altitude with low rainfall typically experience reduced transmission. This is because cooler temperatures at higher elevations fall outside the optimal range for parasite development.

Seasonal variations

Climate change will gradually alter the pattern of the transmission season in all areas over time:

• Areas receiving more flood events may show higher incidence of transmission over a longer period
• Regions that become more prone to drought may have shorter transmission seasons but will face other health challenges

Coastal areas

On a smaller scale, coastal areas have much less seasonal variation in temperature. These areas are:

• Lower in altitude
• Have higher relative humidity
• Temperatures lie within the transmission vector's range of tolerance

This means coastal areas often show a higher prevalence of the disease throughout the year.

Land use factors

Land use is another important factor determining malaria risk. Studies in India have shown that those living in proximity to forested areas (with higher humidity) are more susceptible to infection.

Socio-economic factors influencing malaria risk

While environmental variables are the overriding determinant of malarial mosquito presence, socio-economic factors also influence the level of risk of contracting the disease. Malaria is often referred to as a disease of poverty.

Malaria is a common cause of morbidity in many countries but is concentrated in the world's poorest continents. This is due to the lack of investment in projects for developing new drugs and vaccines, and the limited availability of existing programmes to control the disease.

Studies undertaken in Africa, Asia and South America have identified a number of prevailing socio-economic variables that increase the incidence of malarial infection:

Poor housing quality

Homes with earth or sand floors using materials such as mud, bamboo cane or wooden trunks for walls, and grass or palm leaves to provide a roof face higher risk. Those with:

• Poorly-fitted windows or doors
• Windows without glass, screens, curtains or shutters

are particularly vulnerable to mosquito entry.

High density occupancy

Densely clustered built-up areas and overcrowded rooms (for sleeping) represent another important risk factor. High malaria incidence is associated with:

• High infant mortality rates
• Subsequently high fertility rates

A consequence is that children (and sometimes parents) often share a room with at least five occupants.

Unsanitary conditions

Studies of malaria 'hotspots' in Chennai identified that although individual houses were clean, surrounding areas were dirty and polluted by:

• Rubbish and waste outflows
• Spitting and open defecation

These practices are also commonly associated with attracting mosquitoes.

Occupation

Agricultural workers are more exposed to the mosquito vector. This particularly applies to:

• Those living near to stores of irrigation water
• Migrant workers who may sleep outdoors at night

Rural vs urban environments

Generally, those in rural areas are seen to be more at risk. However, contamination rates in urban slums and poorer settlements are high due to:

• Building density
• Unsanitary conditions
• Stagnant water being retained in rubbish

Age and gender

These are not significantly associated with the risk of infection, though children aged under 5 are more likely to suffer the extreme consequences of the disease. However, studies in both The Gambia and Tanzania indicate a shift in malaria burden from the under-fives to older children aged 5 to 14 years. This is thought to be as a result of the focus on prevention in the younger age groups through better education, awareness and provision of nets.

Poverty and prevention

It is important to distinguish between the overall risk of infection (determined by the mix of physical and socio-economic environmental factors listed above) and the utilisation of prevention and treatment methods. These have a much clearer association with poverty and socio-economic status, such as the level of income and educational attainment, as well as accessibility to intervention methods.

There is more convincing evidence that vulnerability to the consequences of malaria is higher among lower socio-economic groups:

Income

There is a strong positive correlation between income and the use of prevention methods. Those with higher incomes spend more on:

• Repellents
• Insecticide-treated nets (ITNs)
• Mosquito coils

This reduces their risk of infection. Higher income is associated with better nourishment, and studies show that cerebral malaria is less common in well-nourished children. This disproportionately affects agricultural workers, many of whom receive seasonal incomes at harvest time and cannot afford nets or treatment during the main malaria season.

Education

Those with a clearer understanding of the link between malaria and surrounding environmental conditions (including hygiene and sanitation) are more likely to use prevention strategies. For example, studies in Malawi found that net ownership was largely absent in homes where the head of the household had not completed primary education.

Distance and accessibility

Greater distance to the nearest clinics or hospitals is associated with:

• Fewer people seeking treatment for symptoms
• Less expenditure on prevention methods

For example, repellents and coils are less available and so used less in rural areas. Instead, there is a reliance on burning medicinal plants as a repellent.

The poverty-malaria connection

Most of the variables listed are proxies for poverty. The evidence suggests that malaria infection, and particularly death resulting from malaria, is strongly associated with low socio-economic status. It is children from the poorest income groups living in poor housing who are most at risk.

Impacts of malaria

Health and well-being impacts

Mortality statistics

Malaria kills a child somewhere in the world every two minutes. Ninety-four per cent of malaria deaths occur in Africa, where malaria accounts for about one in six of all childhood deaths.

Symptoms and disease progression

Malaria causes the patient to develop a high fever, which comes and goes. The pattern of fevers varies according to the species of malaria. Initially, it feels like the flu: high fever, fatigue, and body aches, with hot and cold stages.

Signs and symptoms in children may be nonspecific, leading to delays in diagnosis. People also may have:

• Headache
• Nausea
• Shaking chills (rigors)
• Sweating
• Weakness

Anaemia is common in patients with malaria, partly due to the effects of the Plasmodium parasite on the red cells.

Severe malaria (Plasmodium falciparum)

Plasmodium falciparum causes a particularly severe form of malaria. In addition to fever, patients may experience complications such as:

• Destruction of red blood cells
• Yellow skin discolouration
• Kidney failure
• Fluid in the lungs
• Cerebral malaria
• Convulsions
• Coma
• Death

Partial immunity

People who have lived for years in areas with malaria may develop a partial immunity to new infections.

Impacts on women and children

The disease also contributes greatly to anaemia among women and children. Infection during pregnancy is associated with:

• Severe anaemia and other illness in the mother
• Low birth weight among newborn babies (one of the leading risk factors for infant mortality)
• Sub-optimal growth and development

Economic impacts

Malaria has serious and far-reaching impacts, slowing economic growth and development and prolonging the vicious cycle of poverty. While it is true that poverty and lack of development may be key causes of the presence of malaria, there is a strong argument that malaria causes underdevelopment.

Costs to individuals and families

These include:

• Travel to and treatment at clinics
• Purchase of drugs to treat malaria
• Lost income from absence from work
• Reduction in crop production
• Absence from school
• Purchase of preventative measures
• Burial expenses in cases of death

Costs to government

Government expenditure includes:

• Building, staffing and maintaining healthcare facilities
• Purchase of drugs and public health intervention equipment such as insecticides and nets
• Loss of production and revenue from taxes during absences
• Loss of tourism revenue

Healthcare burden statistics

It has been estimated that in many parts of west and central Africa, malaria accounts for:

• Up to 40% of public health expenditure
• 30-50% of inpatient hospital admissions
• 60% of outpatient hospital clinic visits

Direct and indirect costs

The direct costs of malaria resulting from the provision of healthcare are thought to be around US$15-18 billion each year globally. In addition, there are many indirect costs resulting from:

• Lost economic growth
• Lost productivity
• The lack of foreign investment in industry, commerce or tourism

Management and mitigation strategies

Globally, the elimination net is widening, with more countries moving towards the goal of zero cases of malaria each year.

Vector control

This is the main way to prevent and reduce malaria transmission. When malaria was more prevalent and widespread globally, many countries eliminated the disease by removing mosquito habitat and breeding sites. This was done by:

• Changing land use
• Draining swamplands containing stagnant water
• Regular, extensive fumigation of areas using insecticides such as DDT

Fumigation using DDT is still carried out in many tropical and sub-tropical countries and can be effective in reducing mosquito numbers.

Environmental consequences

Both of these methods have environmental consequences:

• Changing habitat impacts on other species
• The application of insecticides kills honey bees and other pollinators
• Affects human health

For example, it is thought that DDT can be ingested and passed through the food chain. WHO recommends the following methods of vector control:

Insecticide-treated mosquito bed nets (ITN)

Sleeping under an ITN is seen as a particularly effective low-cost strategy as it provides a physical barrier with an insecticide effect.

The insecticide woven into the net kills mosquitoes so they cannot go on to bite others who may not be protected. Bed nets can reduce transmission by as much as 90% in areas with high coverage.

In 2018, about half of all people at risk of malaria in Africa were protected by ITNs, though this proportion has not increased significantly in recent years.

Indoor residual spraying (IRS)

Spraying indoor surfaces with pyrethroid insecticides can also reduce malaria transmission. To gain significant community protection, IRS should be implemented at a high level of coverage. However, usage has declined across most WHO regions. This is partly because there is evidence of Anopheles mosquitoes developing an increasing resistance to pyrethroid insecticides. Many countries are switching to more expensive alternatives to mitigate mosquito resistance to pyrethroids.

Mosquito coils

Mosquito coils are used in some parts of the world. They are burned to emit a repellent smoke that controls mosquito invasion, but studies have shown they are only between 24% and 64% effective. Their use has also been discouraged by WHO because they emit other pollutants such as:

• Sulphur dioxide
• Nitrogen dioxide
• Volatile organic compounds (VOCs)

Medical interventions

Anti-malarial drugs

Some medicines can be used to prevent malaria by suppressing the blood stage of the infection. WHO has recommended intermittent preventative treatment for:

• Pregnant women
• Infants living in moderate to high transmission areas

Additional seasonal doses of medicine in areas of sub-Saharan Africa are also recommended. Unfortunately, Plasmodium resistance to anti-malarial drugs, such as chloroquine, is a recurring problem.

Vaccines

Until the last few years, there were no vaccines available to prevent malaria. The first and only one to be developed shows that it can significantly reduce malaria in young African children. It is RTS,S/AS01 (RTS,S), sold under the trade name Mosquirix, which acts against Plasmodium falciparum. In large scale clinical trials, the vaccine prevented approximately four in ten cases of malaria over a four-year period.

Treatment

Early diagnosis and treatment of malaria reduces disease, contributes to reducing transmission and prevents deaths. The most effective treatment for malaria sufferers is artemisinin-based combination therapy (ACT).

Global management strategies

To follow up the progress made by the Roll Back Malaria programme (part of the Millennium Development Goals), WHO has launched a global technical strategy for malaria from 2016-2030 as part of all the SDGs. The strategy sets ambitious but achievable global targets, including:

• Reducing both malaria case incidence and mortality rates by 90% by 2030
• Eliminating malaria in at least 35 countries by 2030
• Preventing a resurgence of malaria in all countries that are malaria free

The Global Malaria Programme

The programme co-ordinates WHO's global efforts to control and eliminate malaria. The programme is supported by an Advisory Committee (MPAC) that is made up of a panel of malaria experts.

High burden, high impact approach

In 2018, WHO called for an aggressive new approach to make faster progress in tackling malaria. The approach is being driven by 11 countries that carry a high burden of the disease, including:

• Burkina Faso
• Cameroon
• DRC
• Ghana
• India
• Mali
• Mozambique
• Niger
• Nigeria
• Uganda
• Tanzania

The approach builds on the principle that no one should die from a disease that can be diagnosed and prevented. Key elements include:

• Political will to reduce malaria burden
• Measures taken based on strategic information
• Better guidance and a co-ordinated national response