Malaria is a disease that is almost exclusively restricted to tropical climates. This is largely due to the life cycle and the optimal growing conditions for its vector (mosquito). Of the nearly 3000 species of mosquitoes, only a few dozen from the Anaphoeles genus are capable of carrying the plasmodium parasite to humans.
A fairly wide band across the center of the globe dominates the path of spread. From Brazil to Subharan Africa and across to southeast Asia, Malaria transmission rates in these tropical areas dwarf the rates seen elsewhere across the globe. A figure from the US Centers for Disease Control makes it easier to see. What makes these areas more fertile for malaria spread? One would think its because mosquitos cannot breed in cold weather. Surprisingly it’s not just climate.
Even within tropical climates, malaria rates vary widely. Urban centers have relatively few cases, and poorer, rural areas have much higher rates of transmission and death. Researchers in Gabon conducted a cross sectional study to compare the rates in urban, semi-urban and rural areas. The prevalence of plasmodium infection was nearly 80% in rural areas vs only 20% in the urban areas, a nearly 4 fold difference (Maghendji-Nzondo et al. 2016). A similar pattern was found during a study conducted in Ghana (Gardiner et al. 1984).
If malaria transmission rates were exclusively due to temperature cycles alone, then the prevalence should be equal across all areas with the same climate. But additional data that I recently found from the World Economic Forum seems to dispute this. Data from the World Economic Forum on Malaria incidence is available on Google Public Data for easy access.
Through this online tool, it is quite simple to plot malaria transmission rates by a number of variables. It gets interesting when plotting by income. In advanced economies, malaria incidence rates are almost zero. But in lower middle income and low income countries, the rates are considerably higher. Nearly 10 fold difference. A sharp rise was seen in 2008 to 2009, perhaps owing to the global recession. But rates have not come down since.
In conclusion, it seems obvious that more needs to be done to address the disparity between poor and rich in malaria transmission. Since malaria is a vector borne disease, it will continue to spread for decades in poor rural areas unless we do something. More coordinated outreach needs to be created to address these inequities. Perhaps we should look back to the massively successful smallpox eradication programs in the 1970s. The smallpox movement and its outreach into rural communities was a grassroots efforts, supported by virtually every nation on earth. It’s time for malaria to rise to the same challenge.
Gardiner, C., R. J. Biggar, W. E. Collins, and F. K. Nkrumah. 1984. “Malaria in Urban and Rural Areas of Southern Ghana: A Survey of Parasitaemia, Antibodies, and Antimalarial Practices.” Bulletin of the World Health Organization 62 (4). World Health Organization:607.
Maghendji-Nzondo, Sydney, Lady-Charlène Kouna, Gaël Mourembou, Larson Boundenga, Romeo-Karl Imboumy-Limoukou, Pierre-Blaise Matsiegui, Rella Manego-Zoleko, et al. 2016. “Malaria in Urban, Semi-Urban and Rural Areas of Southern of Gabon: Comparison of the Pfmdr 1 and Pfcrt Genotypes from Symptomatic Children.” Malaria Journal 15 (1). BioMed Central:420.