May 8, 2019

Measles is making a comeback. The highly contagious disease is characterized by the spotty pink rash it causes over the body. Once rare, measles has come roaring back in the United States, as more than 750 cases were officially recorded in the first four months of 2019. That number is more than twice the amount of U.S. cases typically recorded in a full year. The new measles cases were primarily recorded in large outbreaks in the states of New York and Washington, but the disease has also appeared in 21 other states.

A health worker gives a measles vaccine to a young girl in Peshawar, Pakistan. Credit: © Asianet-Pakistan/Shutterstock

Measles chiefly strikes young children, but it is increasingly affecting adolescents and young adults. People who have the disease pass the virus by coughing and sneezing. People can spread the disease long before they realize they are ill. Three to five days after the first symptoms appear, faint pink spots break out over the body. Few people in the United States die of measles. But the disease is dangerous to those with a weakened immune system, and measles kills many undernourished children in other countries.

A child with measles shows the characteristic pink rash that spreads over the body. Credit: © Lowell Georgia, Photo Researchers

Public health experts are dismayed that measles has regained a foothold in the United States, where it was once eradicated. In 2000, the U.S. Centers for Disease Control and Prevention (CDC) announced that measles had been completely eliminated. This was an important public health achievement made possible by the widespread use of the highly effective measles vaccine. Of course, that did not mean that measles was completely gone. CDC officials still recorded a number of cases brought in from travelers—mostly from parts of Asia and Europe where measles is less well controlled. But, until recently, measles transmission in the United States had ended.

In recent years, however, a misinformed yet highly visible anti-vaccination (anti-vaxx for short) movement has led to fewer vaccinations, which has in turn led to the current measles outbreak. Anti-vaxx activists in the United States have launched a coordinated effort to convince parents not to vaccinate their children. They falsely claim that childhood vaccinations can cause a variety of health complications, autism, or even death. This disinformation is spread through websites, Facebook, and other social media. Medical professionals point out that anti-vaxx claims are often misleading and lack any credible or relevant evidence.

The anti-vaxx movement has spearheaded efforts to allow parents to opt out of mandatory vaccinations previously require to enroll their children in public schools. The latest measles outbreak is spread primarily though such unvaccinated students, who expose other children to measles and other preventable diseases, such as whooping cough.

Unvaccinated people, including those who may have a weakened immune system from chemotherapy, can be protected from measles through herd immunity. This term describes a population protected from a disease because high rates of vaccination make it impossible for the virus to spread. Although the measles virus can remain infectious for two or more hours outside the human body, the virus ultimately requires a human host to reproduce. If enough people in a population are vaccinated, the cycle of transmission is disrupted, and the virus will become extinct.

However, herd immunity does not work unless a great majority of the population is vaccinated. To achieve herd immunity for measles, at least 90 to 95 percent of the population needs to be vaccinated. In the past, this was achieved through mandatory vaccinations for school children. In recent years, however, increasing numbers of parents have requested vaccine exemptions for their children on ethical or religious grounds. Many states, cities, and school districts are now reconsidering allowing such exemptions.

November 15, 2017

Since 2015, civil war and famine have killed more than 10,000 people in Yemen, a country on the southwestern tip of the Arabian Peninsula. To make matters worse, an outbreak of cholera, an infectious disorder of the intestines, has killed thousands more in the past year. Fighting between Sunni Muslim government forces and Shī`ite Muslim rebels has destroyed much of Yemen’s already poor infrastructure and displaced millions of citizens. Sewage systems in urban areas have collapsed, as have Yemen’s health services. Throughout the country, people have crowded into temporary camps. Unsanitary conditions and shortages of food, clean water, and medicine led to the cholera outbreak. Cholera is transmitted by water or food that has been contaminated with the feces (solid body wastes) of people who have the disease.

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Yemen. Credit: WORLD BOOK map

The World Health Organization (WHO), a specialized agency of the United Nations, estimates that more than 800,000 Yemenis have fallen ill with cholera since late 2016, and more than 2,100 people have died from the disease. More than 25 percent of the cholera deaths have been among young children already weakened by malnutrition. The cholera epidemic in Yemen is the largest and fastest-spreading outbreak of the disease in modern history. Cholera cases in Yemen are expected to exceed 1 million by the end of 2017, and deaths too are expected to rise.

Cholera occurs when the comma-shaped bacterium Vibrio cholerae enters the intestines and releases cholera toxin. The toxin causes the intestines to secrete large amounts of water and salt. Because the intestines cannot absorb the water and salt at the rate they are secreted, the victim suffers severe diarrhea. This loss of fluid causes severe dehydration and changes in the body chemistry. If untreated, the illness can lead to shock and eventually death. With proper medical treatment, cholera lasts only a few days.

Heavy fighting in Yemen, as well as a naval blockade and an extensive aerial bombing campaign, have prevented health workers and medicine from reaching many cholera victims, resulting in high numbers of otherwise preventable deaths. Such international relief agencies as Médecins Sans Frontières (Doctors Without Borders), the international Red Cross and Red Crescent, Save the Children, WHO, and UNICEF (United Nations Children’s Fund) are doing all they can to help, organizing Yemeni health workers and volunteers from other countries and setting up temporary hospitals and oral rehydration and intravenous therapy centers. Until the fighting stops, however, cholera will continue to add to Yemen’s miseries.

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.

April 25, 2014

The world’s $5-billion banana crop is being threatened by a devastating fungal disease that has already spread from Asia to Africa and the Middle East and is menacing Latin America, according to the United Nations Food and Agriculture Organization (FAO). The fungus, Tropical Race 4 (TR4), causes a variety of a well-known banana disease called Fulsarium wilt, also known as Panama disease. Although exact figures are unavailable, scientists estimate that TR4 has already caused tens of millions of dollars in damage. According to the FAO, bananas are the eighth most important food crop in the world and the fourth most important in developing nations. “Countries need to act now if we are to avoid the worst-case scenario, which is massive destruction of much of the world’s banana crop,” warned a FAO plant pathologist. FAO officials are strongly urging countries to improve their efforts to detect and report cases of the disease as well as their preventive measures.

The fruit produced by banana trees infected with TR4 is still edible. But the trees turn a sickly yellow as they wither and die. Current methods of fighting fungal diseases, including fungicides, cannot eliminate TR4, which lives in the soil and can last for decades. For this reason, agricultural officials are emphasizing the need for stricter preventive efforts.

Bananas overflow a stall at an outdoor market in Jamaica. Bananas are the fourth most important food crop in developing countries. (© Marilyn Martin, Index Stock)

TR4 is not new to agriculture. But it has become increasingly dangerous because of changes in the banana industry. Until recent decades, Asian planters cultivated various banana varieties. On such plantations, the appearance of any one fungus, including TR4, caused relatively little damage. However, the TR4-susceptible Dwarf Cavendish now dominates the international banana trade. Banana growers turned to the Dwarf Cavendish in the 1900′s after the then-popular Gros Michel banana became susceptible to two other races (varieties) of the fungus that causes Fulsarium wilt. Planters embraced the Dwarf Cavendish because in addition to being resistant to races 1 and 2, it does not bruise easily or ripen quickly—advantages for bananas being shipped internationally. With the widespread cultivation of Dwarf Cavendish bananas, TR4 has now become a serious threat.

So far, agricultural scientists have been unable to produce a hybrid or genetically modified variety of the Dwarf Cavendish that resists TR4. Many experts argue that the only way to save the banana industry is by cultivating a greater number of the more than 1,000 known varieties of the fruit.