8.8: Malaria

Malaria

Malaria is another infectious disease that kills at least a million people worldwide every year. It sickens millions more, and by doing so, creates huge burdens on the developmental potential of many regions in Africa and Asia. Malaria is a parasitic infestation of the blood. Malaria is transmitted when female mosquitoes inject parasites into the blood through their saliva as they take a blood meal. Mosquitoes carry around the parasite, so mosquitos are called the disease vector because they transport the infectious parasites between hosts. Flies, ticks, fleas, and lice are other common disease vectors. Malaria is a very complex disease because the parasite that harms people goes through a large number of life stages. The parasite can also lay dormant for long periods, living part of its life in a human host, and some of its life in the mosquito. The parasite can invade multiple parts of the body. Sometimes the parasite is hosted by an animal (monkeys, e.g.) Mosquitos, hosts and parasites all have different spatial behaviors and environmental needs, which contributes to the difficulty of controlling malaria. Solutions require spatial methods and geographic tools.

Cool Map:

Malaria Atlas Project A significant malaria research tool with data, maps and research links.

Malaria has been around for thousands of years, and likely contributed to the fall of the Roman Empire, but it was nearly eradicated in the 1950s. Or so it was believed. After World War II, effective drugs and massive insecticide spraying campaigns appeared to be working miracles against this age-old scourge. However, both the mosquitoes that carry malaria and the disease-causing pathogen evolved over the last few decades, rendering many drugs and pesticides largely useless in the fight against today’s version of malaria.

Malaria in the United States:

English colonist who came to the region thought North America to be free of malaria. They didn’t yet understand the source of the disease. They mistakenly thought that it, like cholera, was a product of miasma. Because both European and African settlers brought with them reservoirs of malarial blood within their bodies across the Atlantic Ocean, the disease had only to find a suitable mosquito vector (i.e., Anopheles quadrimaculatus) to begin spreading. Within a generation, malaria had become a serious problem in the American colonies, especially where rice plantations created ideal breeding grounds for mosquitoes. Africans had some measure of resistance to malaria, contributing to their desirability as slaves in the plantation system that grew in during the 1800s.

Figure : US Map - Malaria killed and sickened many thousands in the United States prior to the 20th century. The US Census produced this map from 1880 data. Source: Wikimedia.

By the mid-1800s, malaria was out of control in the United States. A series of changes in American society nearly eradicated malaria within 100 years. The remarkable turnaround was created by several changes in the American economy. The demise of wet-rice culture in the Deep South was the first change. During the 1800s, thousands of mosquito-infested, wet rice paddies were drained all over the southern US as cotton and corn crops became more profitable. The profitability of these new crops also encouraged farmers to drain thousands of acres of swamps and wetlands for use farmland, thus destroying ideal mosquito habitats. By the mid-1800s railroads also began to replace river and canal transportation across the US, thereby redirecting many thousands of travelers away from the places where they were most likely to be bitten by mosquitos. At the same time, steam power began replacing waterpower, eliminating the need for thousands of mill ponds all over the country. People also became more prosperous, moved to cities, built houses with windows and screens and generally got healthier. Eventually the anti-malarial drug quinine became widely available in the United States, helping deplete the blood reservoir of the disease. Another important moment in the battle against malaria came in the early 1900s when scientists discovered that mosquitos transmitted malaria. Slowly, health officials in the US took steps toward mosquito eradication. Government workers drained swamps and manipulated water levels in lakes by constantly raising and lowering dams. They removed vegetation from lakes at the shoreline and provided houses within a mile or so of lakes or ponds window and door screens.

Figure Atlanta, Georgia - The Center for Disease Control headquarters includes several emergency management command and control centers featuring GIS displays of data on outbreaks, resources and threats. Source: CDC, press release.

After World War II thousands of soldiers returned from Asia carrying the malaria pathogen in their blood. The government took steps to prevent malaria from spreading once again. The biggest effort was in the US South where the military already had practice preventing malaria on southern military bases. The secret weapon in this post-war campaign was a new, highly effective insecticide called DDT. The government launched a massive effort spraying DDT on millions of acres across the US. By 1949, the government declared the US free of malaria. The headquarters of the anti-malaria effort was chosen to house the CDC.

Other countries copied America’s strategy for fighting malaria. Unfortunately, the widespread and indiscriminate application of DDT across the globe created a different crisis of interest to biogeographers. After about 10 years of widespread use of DDT in the US, it became apparent to wildlife biologists and birdwatchers that DDT and related insect poisons were harming animals other than just insects. Anything that ate insects regularly, like birds and fish were at risk. Alarmed by the unusual number of bird deaths in areas sprayed with DDT, environmentalist Rachel Carson wrote the book, Silent Spring, detailing the numerous ecological dangers posed by the overuse of chemical pesticides. In addition to pointing out how chemicals could be responsible for human cancers, and the near inevitability of pesticide resistance, the book also detailed how the toxic effects of pesticides grew slowly over time in the bodies of predators (like birds) through a process called bioaccumulation. Carson’s book also condemned chemical companies for misleading the public about pesticides, which of course drew scathing rebuttals from chemical companies and their allies in Congress. Nevertheless, the book became a best seller and is widely regarded today as a significant milestone in the American environmental movement. The US government banned DDT for agricultural use in the US in 1972, though it is still used in Mexico. Scientists credit the ban on DDT for helping Bald Eagles and other birds-of-prey return from the brink of extinction.