International demand for goods contributes to malaria risk

Previous studies have shown that deforestation and disturbance of tropical forests lead to increased transmission of malaria. The destruction of the jungle generates new environmental and ecological conditions in which mosquitoes thrive better. A new study links global demand for goods with deforestation and the risk of malaria.

The work is the first to directly relate global consumption to the increase in malaria cases in some regions. It is estimated that in these regions where cases are increasing, a fifth of deforestation is driven by international trade. Coffee, wood, soy, cocoa, palm oil, tobacco, calf meat and cotton are the main products demanded globally that stimulate deforestation.

Despite the fact that globally it seems that the number of cases has been decreasing since 2000, its increase is worrying in some regions. In 2018 there were 228 million cases worldwide and 405,000 deaths, of which seven out of ten were children under the age of five.

7 out of 10 deaths from malaria worldwide are children under the age of 5

90% of malaria cases occur in three tropical forest regions: the Congo Basin, the Amazon Basin, and the Greater Mekong Basin in Asia (Fig. 1). In these regions, the main mosquitoes that transmit malaria are: Anopheles gambiae, Anopheles funestus, Anopheles dirus, Anopheles minimus and Nyssorhynchus darlingi. All of them associated with deforestation, land use changes and human migration.

Distribución malaria Africa America asia

Fig. 1. Map of the regions with populations at risk of contracting malaria in yellow. Striped areas represent the areas that are suffering the most deforestation. Simplified map of Chaves et al. 2020. Nature Communications 11: 1258. Source: Mosquito Alert (CC-BY-NC-2.0)

Demand for basic products from rich countries increases the risk of malaria in other countries

The link between deforestation and the increase in malaria cases has been demonstrated in Indonesia, Nigeria and the Amazon. A work carried out in 795 municipalities of the Amazon during 13 years, concluded that clearing the forests by 10% leads to a 3.3% increase in malaria cases.

The new study reconnects the incidence of malaria with deforestation, but also establish a relationship between deforestation with the consumption of products globally. For this they used a detailed international database with the entry and exit of products by country. With it they were able to establish the global network of supplies, from the deforested area to produce, to the countries that consume the product.

Countries with an increased risk of malaria associated with deforestation are Nigeria, Tanzania, Cameroon, Uganda, the Democratic Republic of the Congo, India, Zambia, Burma, the Central African Republic and Burundi. Part of the increased risk in these areas is due to the demand for products from the richest countries, with Germany, the United States, Japan, China, the United Kingdom, France, Italy, Spain, the Netherlands and Belgium leading the list. The demand for wood, cocoa, tobacco and cotton are among the main causes of deforestation.

Populations most exposed to malaria are those that benefit the least economically from forest exploitation

The work is new evidence of the close relationship between the health of human populations and the environment, and shows, with numbers, that the problem is global. The authors hope that their results can be used to mitigate malaria cases, either by regulating supply chains or by labeling and certifying products.

Communities that are facing a greater transformation of their landscape to meet international demands are at the same time the most at risk as they are more exposed to mosquitoes that transmit malaria. In addition, the populations most exposed to the disease are those that benefit least from the exploitation of forests.


Austin K, Bellinger M, Rana P. 2017. Anthropogenic forest loss and malaria prevalence: a comparative examination of the causes and disease consequences of deforestation in developing nations. AIMS Environmental Science 4: 217-231

Berazneva J, Byker TS. 2017. Does forest loss increase human disease? Evidence from Nigeria. American Economic Review 107: 516-521

Chaves LSM, Fry J, Malik A, Geschke A, Salud MAM, Lenzen M. 2020. Global consumption and international trade in deforestation-associated commodities could influence malaria risk. Nature Communications 11: 1258

Garg T. 2019. Ecosystems and human health: the local benefits of forest cover in Indonesia. Journal of Environmental Economics and Management 98: 102271

MacDonald AJ, Mordecai EA. 2019. Amazon deforestation drives malaria transmission, and malaria burden reduces forest clearing. PNAS 116: 22212-22218


A mosquito could kill Alexander the Great

As he approached Babylon, Nearch, who had returned to the Euphrates by the great sea, said that some Chaldeans had spoken to him, urging him not to enter Babylon; but this one did not pay attention, but continued his march, and when he was already touching the walls, he saw many crows fluttering and pecking at each other, of which some fell in front of him.

This is how, in the late 1st century, Plutarch described the arrival of Alexander the Great in Babylon. This small fragment of volume V of his “Parallel Lives” took a few years ago to the epidemiologist, John Marr, and to the expert in infectious diseases, Charles Calisher, has announced that they had found the cause of death of the Macedonian conqueror.

After seizing the Macedonian throne, Alexander overthrew the Persian Empire and looked east, eventually invading much of India. It gave rise to the largest empire of the time, but it died suddenly in 323 BC. A. In the mesopotámica city of Babylon, located near the present Baghdad. His death has intrigued historians for years, the chroniclers of the time did not mention any of the endemic diseases in the region, making his death a mystery. Modern authors have suggested different types of poisonings, influenza, malaria and typhoid fever as possible causes. All of them based on the different documents that describe the illness that affected him for two weeks until his death.

A few years ago, Marr and Calisher came up with a new suggestion: Alexander the Great was the victim of encephalitis caused by the West Nile virus. A fever, which is now common in parts of Africa, Western Asia and the Middle East, although more and more cases are detected in Europe and the United States. The virus is mainly housed by birds, with mosquitoes transmitting it from one individual to another, or from one species to another, sometimes being able to transmit it to humans or horses and other equines.

Dead crows: bad omen or symptom of West Nile fever?

His death took place in late spring. Babylon, located on the Euphrates River, bordered on the east by a swamp. Birds and mosquitoes had to be abundant, as they are in other swampy areas.

Plutarch’s text is the one that gave the lead to both investigators, to suggest West Nile fever as the cause of their death. The scene of crows flying frantically, with collisions and individuals falling dead, led them to think of the West Nile virus (Fig. 1). Among the birds, the virus mainly affects corvids. The family of birds to which crows belong are particularly susceptible to the pathogen, with some of their species being responsible for their spread. The virus is transmitted from one bird to another and, from time to time, some mosquitoes can transmit it to people and horses (Fig. 2). Humans and horses can get sick, but they cannot transmit the virus, unlike birds. From the point of view of the virus, infecting a person is a dead end, unlike infecting birds.

Alejandro Magno virus Nilo Occidental mosquito muerte

Fig. 1. The scene of the crows at the entrance to Babylon is the one that suggests that these birds could be infected with the West Nile virus and end up infecting Alexander the Great.


In addition to the crows text, Marr and Calisher tested their idea using an online diagnostic program: GIDEON (Global Infectious Diseases and Epidemiology Network). When introducing the symptoms described in the texts of the time about Alexander’s death (respiratory infection, liver disorder, skin rashes, etc …) along with that of the birds, the response obtained by the program was only one: West Nile fever.

Obviously, not all authors have accepted this version. Some argue that symptoms of West Nile virus infection are generally mild, similar to the flu, and most people recover within a few days. The disease can be complicated for the elderly and people with a weakened immune system, requirements that a 32-year-old Alexander the Great who had conquered such a vast empire does not seem to meet.

But regardless of whether or not Alexander could have been weakened enough to complicate the infection, other researchers provided other data to doubt West Nile fever as the cause of his death.

Was there West Nile virus in Alexander’s time?

The authors, Marr and Calisher, assumed that the virus, endemic in the Middle East, had to circulate between the Tigris and the Euphrates, not only centuries, but millennia, and just as the birds were affected by the virus, Alejandro He was able to contract the disease from a mosquito bite.

ciclo del virus del Nilo Occidental

Fig. 2. West Nile virus cycle that is maintained by transmission between birds through mosquitoes, mainly Culex. Sometimes infected mosquitoes can transmit the virus to people and horses.


But this hypothesis does not seem to be fulfilled in view of genetic studies on these viruses. A study on the analysis of the time of divergence between different flaviviruses (the group to which the West Nile virus and dengue belongs), estimates that the virus, which supposedly killed Alexander, appeared 1043-1274 years ago, that is, more a thousand years after his death. Other work suggests that some of the modern lines of the virus emerged 300-400 years ago.

Viruses evolve quickly, it not only makes it difficult for us, based on the effects of current viruses, to infer what viruses or symptoms suffered from ancestors thousands of years ago. But also, that they can be dated correctly at what time some viruses diverged from each other. Substitution rates are reliable for the most recent divergence events, but they lose reliability as you go back in time. It is possible that in the Babylon of Alexander the Great 2,500 years ago, an ancient flavivirus was already circulating, but can it be said that it was the same as the current West Nile virus?

The death of Alexander the Great will remain a mystery unless one day his remains were found, another mystery as great as that of his death for archaeologists and historians. But the debate unleashed from the work of Marr and Calisher added an important point to the topic: attending to the details of the environment when diagnosing a disease, wondering what the climate, fauna and behavior were like, if there are descriptions of it. Today we know that our health is intimately linked with that of other animals and ecosystems.



Cunha BA. 2004. Alexander the Great and West Nile Virus Encephalitis. Emerging Infectious Diseases 10: 1328-1333

Galli M, Bernini F, Zehender G. 2004. Alexander the Great and West Nile Virus Encephalitis. Emerging Infectious Diseases 10: 1328-1333

Mackenzie JS, Gubler DJ, Petersen LR. 2004. Emerging flaviviruses: the spread and resurgence of Japanese encephalitis, West Nile and dengue viruses. Nature Medicine 10: S98-S109

Marr JS, Calisher CH. 2003. Alexander the Great and West Nile Virus Encephalitis. Emerging Infectious Diseases 9: 1599-1603

May FJ, Davis CT, Tesh RB, Barrett. 2011. Phylogeography of West Nile virus: from the Cradle of Evolution in Africa to Eurasia, Australia, and the Americas.

McMullen A, Albayrak H, May FJ, Davis CT, Beasley DWC, Barrett ADT. 2013. Molecular evolution of lineage 2 West Nile virus. Journal of General Virology 94: 318-325

Pearson H. 2003. West Nile Virus may have felled Alexander the Great. Nature news031124-11

Simmonds P, Aiewsakun P, Katzourakis A. 2018. Prisoners of war – host adaptation and its constraints on virus evolution. Nature Reviews Microbiology 17: 321-328

Pioneering UN Backed, Citizen Led Alliance against Mosquito Borne Diseases Joins Global Fight to Save 2.7 Million Lives Every Year

Initiative Empowers National Networks, Stakeholders and Governments to Generate and Access Real-time Data and Tools through UN Electronic Platform ‘Environment Live”.

Miembros participantes de la reunión a la sede de las Naciones Unidas (Ginebra).

Participants of the meeting at United Nations in Geneva. Frederic Bartumeus, John Palmer and Roger Eritja assisted as members of Mosquito Alert.


A new alliance of citizen-science organisations and UN Environment will be launched, Monday, in an effort to escalate the global fight against mosquito-borne diseases, responsible for killing close to 2.7 million people annually, mostly in Africa and Latin America. Overall mosquito borne cases are estimated at 500 million every year.

The new initiative, launched under the name ‘Global Mosquito Alert’, brings together thousands of scientists and volunteers from around the world to track and control mosquito borne viruses, including Zika, yellow fever, Chikungunya, dengue, malaria and the West Nile virus. It is the first global platform dedicated to citizen science techniques to tackle the monitoring of mosquito populations. The programme is expected to move forward as a collaboration involving the European, Australian and American Citizen Science Associations as well as the developing citizen science community in Southeast Asia.

Agreement to launch the initiative was reached at a two-day workshop that took place in Geneva earlier this month, organised by UN Environment, the Wilson Center’s Science and Technology Innovation Program (STIP), and the European Citizen Science Association (ECSA).

Director of Science at UN Environment, Jacqueline McGlade, said, “The Global Mosquito Alert will offer for the first time a shared platform to leverage citizen science for the global surveillance and control of disease-carrying mosquitos. It is a unique infrastructure that is open for all to use and may be augmented with modular components and implemented on a range of scales to meet local and global research and management needs.”

She added, “The programme will offer the benefit of the millions spent in developing existing mosquito monitoring projects to local citizen science groups around the world.  Opportunities to keep these citizen-led initiatives at the cutting edge of science will now depend on securing major funding to support the ongoing programme development and its promotion to millions of people world-wide.”

Los miembros de la iniciativa se reunieron durante dos días en Ginebra.

The members of the initiative were on a two-days meeting, lead by the Mosquito Task & Finish Group from ECSA.


The Global Mosquito Alert will be supported by a consortium of data and information providers, coordinated through Environment Live, the dynamic UN knowledge platform, designed to collect, process and share the world’s best environmental science and research. Built and maintained by UN Environment, the platform provides real-time open data access to policy makers and the general public, using distributed networks, cloud computing, big data and improved search functions.

The consortium includes: Mosquito Alert, Spain; MosquitoWEB Portugal; Zanzamapp in Italy; Muggenradar in the Netherlands; the Globe Observer Mosquito Habitat Mapper, USA/International and the Invasive Mosquito Project USA.

The information displayed on Environment Live will allow managers to mitigate risk and reduce health threats while opening up an opportunity for concerned citizens to contribute their mosquito observations and possible solutions.  Citizen data will augment information already available from Government public health sources.

The new consortium has agreed to share current approaches to monitor the spread of key mosquito species and their breeding sites, and to measure the nuisance value of the citizen mosquito experience to support health risk management.  The group also agreed to pool knowledge and experience on citizen science programmes to monitor mosquito species using the latest DNA identification techniques.

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