Malaria, mosquitos and maps

Malaria

Malaria is a parasitic disease that can cause headaches, severe fevers and even death. There are over 100 species of the malaria disease, the majority of which affect birds and monkeys.

Only five species affect humans, of which two have notable health implications: Plasmodium falciparum (has a global distribution and the highest mortality rate) and Plasmodium vivax (also has a global distribution and causes lots of illness but is not generally fatal).

Plasmodium falciparum has an annual global death toll of 1 million. That’s one death every 30 seconds, 90% of which occur in Africa. Further to this, around 350-450 million people suffer from malaria each year.

The economic impacts of malaria are also sizeable. Individual families can suffer if a breadwinner becomes infected with malaria, or if they have to pay for treatment. This can tip some families over the edge, into a poverty trap that can be hard to recover from. On a national scale, it is estimated that the GDP of some countries has been reduced by 1.3% annually as a result of malaria. This costs around $12 Billion per annum for African economies alone.

But no matter how rich or famous you are, you can still contract malaria. Singer Cheryl Cole, actor George Clooney and footballer Didier Drogba are among those who have contracted the disease in recent years. However, it is relatively easy to protect yourself against any risk and the Malaria Global Action Plan ultimately aims to eradicate malaria across the world.

Aims of the Global Malaria Action Plan

• Reduce global malaria cases from 2000 levels by 50% in 2010 and by 75% in 2015

• Reduce global malaria deaths from 2000 levels by 50% in 2010 and to near zero preventable deaths in 2015

• Eliminate malaria in 8-10 countries by 2015

• In the long term, eradicate malaria world-wide through progressive elimination in countries.

Read the full Global Malaria Action Plan. You may also want to refer to Millennium Development Goal 6, which aims to reverse incidences of malaria worldwide.

The UK historically eradicated malaria through basic environmental control: draining of wetlands (where many mosquitos are found) and increasing urbanisation (where fewer mosquitos are found). Today, the first response is to provide people living in malaria hotspots with:

• An Insecticide-Treated Net (ITN): The insecticide treatment lasts for around three years and kills mosquitos attempting to bite people when they are sleeping under a net

• Indoor Residual Spray (IRS): Along with INTs, the World Health Organisation (WHO) recommends that sprays are used universally by everyone in a malaria hotspot. Any mosquito that lands on a spray-protected indoor surface is likely to be killed. The spray lasts for 3-6 months

These first responses are limited by the fact that, over time, mosquitos can develop resistance to some insecticides. A lot of research time is spent developing new insecticides.

Scientists are also developing a vaccine, which is beginning to show reasonable effectiveness. With two doses of the vaccine, one third of infants develop some degree of immunity to malaria. However, we are a long way from developing a highly effective vaccine that is viable for use at the global scale.

Diagnosis and treatment of malaria are also important in eradicating malaria. If you treat enough people in a community, you can quickly reduce transmission, limit the spread of the disease and prevent deaths.

Mosquitos

In recognition of his work into the life cycle of malaria, Sir Ronald Ross became the first Briton to win the Noble Prize for medicine in 1902. His discovery – that mosquitos transmit malaria between humans – remains an important starting point for understanding the disease today.

Not all mosquitos can carry malaria and pass it onto humans. Only the Anopheline genus (of which there are 512 species) can transmit malaria between humans. However, just 70 of those have actually been shown to transmit malaria, of which 41 can transmit malaria at an intensity whereby it is a hazard to public health.

Malaria-transmitting mosquitos follow particular spatial and temporal patterns. For example, malaria is relatively easy to eradicate in temperate regions because the mosquitos that live there tend to feed on animal rather than human blood. All Anopheles are most active during the night and many are often found near water and in rural areas – urban mosquitos are in the minority.

Maps

Maps are important in monitoring and evaluating progress made towards the worldwide reduction and eventual eradication of malaria. However, previous world maps of malaria tend to have three limitations:

• They don’t show you the data that was used to put the map together. This means that you can’t really tell why the information is represented as it is.

• They cannot reach the same level of accuracy that computer-based mapping can achieve today. They were generally hand-drawn before Geographical Information Systems(GIS) existed.

• They don’t give a confidence level. This means policy makers have no way of knowing about the accuracy of the data behind the maps.

Initiated in 1955, the Global Malaria Eradication Program led to the very specific measurement of:

• Annual Parasite Index: A measure of the number of malaria cases per annum in any given location

• Parasite Rate: A measure of the proportion of people that carry malaria i.e. prevalence per capita

Mapmakers today are fortunate that these global standardised measures have been in place for over half a century. This means there is a large amount of data across the world and dating back to the mid-20th century, which makes mapping and data analysis very effective.

How to create a Malaria Atlas Project map

• Divide the world into the areas that we need to worry about – in terms of malaria – and those we don’t. Discard those in which human health is not affected by malaria. Roughly 90 countries will remain

• Approach governments for data about malaria. Only take the most fine-grained data – that which goes down to a very low scale. Local borough data is more useful than national county data

• Map cases of malaria (Annual Parasite Index) or the proportion of people that carry malaria (Parasite rate). This will give you an understanding of how malaria is spatially distributed on a global scale

• Overlay temperature and humidity onto the map. Climatic factors affect the rate at which malaria spread. If it is too cold or arid, malaria cannot spread. This gives us even more regions that we can discard

• You have your map, in this case showing the spatial distribution of malaria

From this map, we can make a number of simple observations:

• The Americas have a lower rate of malaria than the rest of the tropics

• Sub-Saharan Africa is characterised by predominantly high rates of malaria

• Asia has predominantly low rates of malaria, with some pockets of high distribution

Using computer modeling, we can ask the hypothetical question: what happens if everyone in the tropics uses mosquito nets and repellent spray? This modeling tells us that if this occurs, then:

• In the areas where malaria is most dominant (e.g. parts of Africa), even universal coverage of nets and sprays will not get rid of malaria entirely. Complete eradication will require addition measures in these areas

• In the areas of middle concentration (e.g. parts of Asia), it is predicted that universal coverage of nets and sprays will eradicate malaria entirely

• In the areas of low concentration (e.g. parts of South America), malaria can be eradicated entirely, even without universal coverage of sprays and nets

Looking even further into the data, we find that two thirds of the people at risk from the Plasmodium falciparum (the potentially fatal species of malaria) are located in Asia. The risk of mortality to an individual is higher on average in Africa but there are a larger proportion of people at risk in Asia, because more people live there.

So, using these sophisticated computer modeling techniques, policy makers can theoretically eradicate the risk of malaria for two thirds of those currently at risk worldwide. Furthermore, this can be achieved simply through the provision of bed nets and repellent sprays.

Globally, there remain a number of challenges in eradicating malaria, including:

• Migrant populations: Cross-border movement has resulted in an increase in ‘imported malaria cases’ from neighbouring countries. International movement risks increasing the spread of malaria in particular countries.

• Agricultural land-use: Farming is extending towards urban areas, which brings malaria breeding sites (e.g. wet rice fields) closer to population centres.

• Political and financial commitments: If malaria is not perceived as a public health priority, eradication of the disease may not receive high levels of support from political leaders. In order to fight malaria, a number of players are involved, including: Non Governmental Organisations (NGOs), researchers and academics, businesses, MEDCs and malaria-endemic countries. Each player must fulfill their role.

Will climate change increase cases of malaria?

Researchers asking this question have modeled the spread of malaria under a warmer global climate. If you warm things up, you can speed up the rate at which malaria develops inside mosquitos. This, in turn, speeds up the rate of transmission, which spreads the distribution of malaria globally. Some researchers using this method have argued that malaria will spread to the USA and Europe by 2020. And, in some cases, this has filtered through into policy.

However, if we look at the world over the last 100 years, we can see that the area affected by malaria has shrunk – in spite of the earth getting warmer over that period. Malaria has gone from being a global disease, to just being a tropical disease. Furthermore, the intensity of infection in the affected areas has decreased. This runs counter to claims that malaria will inevitably spread in the future.

The reality is that public health successes have outweighed any potential negative effects associated with climate change. Climate change has not had any notable impact on the spread of malaria. Other factors have had more of an impact and will continue to if interventions remain successful in the future.

Key terms

Confidence level: Used to convey a degree of certainty about a statistical estimate. The more reliable a set of data, the more certain we can be about an estimate and the greater a confidence level will be.

Geographical Information Systems (GIS): Computer-based mapping that allows the representation and manipulation of geographical data. Data is stored as discrete layers (transport links, national boundaries, population distributions, incidences of malaria) which are then layered on top of one another. GIS can also be used to model potential scenarios, which can help to predict geographical phenomena into the future.

Parasitic disease: An infectious disease transmitted by a parasite. A parasite is an organism that makes contact with another living organism (host), to the benefit of the parasite but to the detriment of the host. This is a non-mutually beneficial relationship.

Activities 

• Evaluate the usefulness of the ‘Annual Parasite Index’ and ‘Parasite Rate’ as indicators of malaria worldwide. Which one is most appropriate for global policy makers to use and why? (4)

• Using the map of malaria distribution (above) and the analysis given, present an argument to suggest which region of the world should be a priority for the reduction or eradication of malaria. (15)