April 19, 2017

A recent study has found a connection between hereditary sickle cell disease and malaria, a dangerous parasitic disease transmitted by mosquitoes. The study determined that genetic mutation responsible for sickle cell disease, a serious blood disorder, rapidly spread through human populations in Africa more than 40,000 years ago mainly because it provides protection from malaria. Genetic scientists used computer-based models to understand the conditions that spread the sickle cell mutation among certain human populations. The scientists learned that this mutation was among the most important factors affecting survival over the last 40,000 years for people living in malaria-affected regions. The study’s results were published on March 10, 2017, in the scientific journal PLOS Genetics.

A new study has shown that people carrying the sickling gene that can cause sickle cell disease have a higher natural resistance to malaria parasites, shown here in pink and blue. Credit: © CNRI/SPL from Photo Researchers

Sickle cell disease, also called sickle cell anemia, is a hereditary blood disease. In the United States, it occurs chiefly among African Americans. It also affects other groups, including people of Central African, Mediterranean, Middle Eastern, and South Asian origin. Sickle cell patients have an abnormal type of hemoglobin, the oxygen-carrying protein that gives red blood cells their color. This abnormal protein, called sickle hemoglobin, or hemoglobin S, forms crystals in red blood cells. This causes the normally round red blood cells to change into twisted, rigid sickle-shaped forms. The sickle cells can get trapped and block the normal flow of blood through blood vessels. This disruption of blood flow causes periodic crises (attacks of severe pain and fever) and related problems including strokes, lung or kidney damage, and sudden death.

This magnified blood sample shows the red blood cells of a person with sickle cell anemia. Normal red blood cells appear round in the image. But, abnormal, sickle hemoglobin causes many red blood cells to change into twisted, rigid sickle forms. Credit: © Bruce Coleman Inc./Alamy Images

Scientists know that harmful mutations, such as the one responsible for the abnormal sickle hemoglobin, should become less common in populations over time because of the process of natural selection. Natural selection sorts out these random changes according to their value in enhancing the individual’s reproduction and survival. In the past, people with sickle cell disease rarely survived long enough to have children. Today, modern medicine has improved the health and life span of people with the condition.

Scientists have lately learned that carriers of the sickling gene—that is, people who have only one copy of the mutated gene instead of two—not only have normal blood cells, but they also have a higher natural resistance than noncarriers to malaria. Sickle cell anemia is a rare disorder, but it occurs most often among populations that live in areas threatened by malaria. Thus, the sickling gene—despite its negative effects for some—represented an important advantage for other people in these tropical and subtropical regions. The new research shows that the sickle cell mutation had a rapid and dramatic effect in shaping the genetic makeup of certain human populations in the past. Such dramatic changes are also possible in the future, as human populations continue to adapt to a constantly changing global environment.

Oct. 5, 2015

The Nobel Prize is awarded each year in the categories of physiology and medicine, chemistry, physics, literature, peace, and economics. Winners receive a gold medal, a diploma, and money. (Credit: Nobel Foundation)

Officials at the Nobel Assembly at the Karolinska Institute in Stockholm, Sweden, announced today that three scientists will share the 2015 Nobel Prize in physiology or medicine  for discoveries that led to new treatments for parasitic diseases. William C. Campbell, an Irish-born American of Drew University in Madison, New Jersey, and Satoshi Omura of Kitasato University in Tokyo, Japan, will share half of the prize for their research on treatments for roundworm parasites. The Chinese scientist Youyou Tu of the China Academy of Traditional Medicine in Beijing, China, was also honored for her work in developing treatments for malaria.

Working independently, Campbell and Omura studied chemical compounds that are effective against roundworms. At least 14 species of roundworms cause serious infection in millions of humans worldwide. Omura identified certain compounds produced by Streptomyces, a microbe that grows in soil, which acted against bacteria and other infections. In the U.S., Campbell further studied the compounds and found that one component was remarkably efficient in fighting roundworm parasites in animals. The compound, called Avermectin, has been developed into drugs that protect people and animals from a wide variety of diseases caused by roundworm parasites. These diseases include ascariasis, lymphatic filariasis, River blindness, and trichuriasis.

Dr. Tu used her background in Chinese traditional medicine to identify compounds in plants that could be used to treat malaria. Malaria is one of the most widespread and threatening parasitic diseases that affect human beings. The disease is caused by infection with parasites called Plasmodia (in the singular, Plasmodium). They are transmitted to human beings through the bite of the female Anopheles mosquito. Scientists estimate that about 500 million people are infected by malaria parasites and 1 million to 3 million people die from malaria each year.

In the 1980’s, Tu isolated a compound from Artemisia annua, a plant commonly used in traditional herbal medicine. This compound was developed into a drug, called artemesinin, that is highly effective for treating malaria and preventing the development of varieties of Plasmodia that resist the effects of other drugs.

Other World Book articles

• Nobel Prize
• The Timeless Scourge of Malaria (a Special report)

August 15, 2014

The Panama Canal, a waterway that cuts across the Isthmus of Panama and links the Atlantic Ocean and the Pacific Ocean,  opened 100 years ago today. When the canal was completed in 1914, it shortened a ship’s voyage between New York City and San Francisco to less than 5,200 miles (8,370 kilometers). Previously, ships making the trip had to travel around South America—a distance of more than 13,000 miles (20,900 kilometers).

The Panama Canal cuts the trip from New York City to San Francisco by about 9,000 miles (14,400 kilometers). (World Book map)

Work on the Panama Canal was begun by the French in the 1880′s. After a few years, however, they stopped the project. They had lost nearly 20,000 workers to endemic diseases, mostly yellow fever and malaria.

Teddy Roosevelt became president in 1901 and immediately wanted to start building a canal across Panama. The political and engineering challenges were still formidable, but the timing was better for disease control. Since the 1880′s, scientists had learned that both yellow fever and malaria were transmitted by mosquitoes.

President Theodore Roosevelt visited the construction site of the Panama Canal in 1906. He wrote his son about the Gaillard Cut, saying, "They are eating steadily into the mountain ... ." (Bettmann Archive.)

Steps taken to defeat these two dread diseases in Panama included draining standing water or covering standing water with kerosene to prevent mosquitoes from laying eggs; and heavily spraying areas with insecticide to kill adult mosquitoes.

Work began on the canal in 1904 and it was completed in 1914. Worker deaths on the project the second time around were still very high—6,000 Americans died building the canal.

When the canal opened, approximately 1,000 ships a year passed through it. Today, some 15,000 ships a year pass through the canal.

Additional World Book articles:

• Building and Construction 2012 (a Back in Time article)
• Panama 2009 (a Back in Time article)
  

March 7, 2014

Warmer temperatures, associated with global warming, are causing malaria to become more common at higher altitudes, according to a report in the latest issue of the journal Science. A study of malaria in the highlands of Africa and South America by an international team of scientists found that generally higher temperatures in the future may well lead to millions of additional people exposed to the mosquito-borne disease.

Malaria, a disease common in tropical and subtropical regions, is caused by infection with parasites called Plasmodia. The parasites are one-celled organisms called protozoans. They are transmitted to human beings through the bite of the female Anopheles mosquito.

“The impact in terms of increasing the risk of exposure to disease is very large,” stated the lead author of the study, Mercedes Pascual of the University of Michigan. Pascual noted that in the past, higher altitudes provided  protection against this devastating disease because both the malaria parasite and the mosquito that carries it do not thrive in cooler air.

Malaria parasites appear in pink and blue in a false-color image. (c) CNRI/SPL from Photo Researchers

Pascual and her team studied densely populated areas in the highlands of Colombia and Ethiopia, where scientists have kept detailed records of both temperature and malaria cases from the 1990’s to 2005. The team found that malaria shifted higher into the mountains in warmer years and stayed at lower elevations in cooler years. “We have estimated that, based on the distribution of malaria with altitude, a 1-Celsius-degree (1.8-Fahrenheit-degree) rise in temperature could lead to an additional 3 million cases in people under 15 years old,” stated Pascual. Climatologists predict that Earth’s surface temperature could rise by as much as 1 Celsius degree by 2030.

The World Health Organization estimates that there were about 207 million cases of malaria in 2012 leading to approximately 627,000 deaths. Children living in Africa are particularly hard hit by the disease.

Additional World Book articles:

• Charles Louis Alphonse Laveran
• Sir Ronald Ross
• Blood Feeders: Real-Life Vampires (a Special Report)
• The Timeless Scourge of Malaria (a Special Report)