The Global Fool

our planet is our village

Climate Change, Parasite Infections, and Immune Responses
Mar06

Climate Change, Parasite Infections, and Immune Responses

By Roberta Attanasio Global climate change noticeably impacts human health—safe drinking water, sufficient food, and secure shelter are threatened by rising sea levels and severe weather events. Heat waves dramatically increase death rates not only from heat strokes, but also from complications arising from cardiovascular, respiratory, and cerebrovascular diseases. Although global warming may bring some localized benefits, such as fewer winter deaths in temperate climates and increased food production in certain areas, the overall health effects of a changing climate are likely to be overwhelmingly negative. For example, climate warming is predicted to increase the transmission of parasite infections. Now, results from a recent study show that host immunity can influence the impact of warming on host–parasite interactions and mitigate its long-term effects. For the study (Host immunity shapes the impact of climate changes on the dynamics of parasite infections), researchers focused on soil-transmitted gastrointestinal helminths, also known as parasitic worms. In humans, these worms cause some of the most common parasitic infections worldwide. According to the World Health Organization (WHO), approximately 2 billion people are infected with soil-transmitted helminths globally, mostly in the poorest and most deprived communities. They are transmitted by eggs present in human feces, which in turn contaminate soil in areas where sanitation is poor. However, the researchers focused on two parasitic worms of rabbits, Trichostrongylus retortaeformis and Graphidum strigosum. In previous studies, the researchers found that, in rabbits, infections from one of the parasites are controlled by the immune response, whereas infections from the other parasite species are not controlled, even though the rabbits do mount an immune response to the parasite. Therefore, the researchers designed the new study to understand the contribution of climate change and immunity on the long-term and seasonal dynamics of infections caused by the two rabbit parasitic worms. They examined samples collected monthly between 1977 and 2002 in Scotland. The study results show that climate warming—rising temperature and humidity—increases the availability in pastures of the infective stages of both intestinal worms. The intensity of infection increases for the worm not regulated by immunity. In contrast, there is no significant long-term positive trend in the intensity for the immune-controlled worm. Specifically, G. strigosum infection is not controlled by the rabbit immune response. Therefore, the intensity of the parasite infection increases with warming, leading to significant accumulation of G. strigosum in rabbits, mostly in adult rabbits. Why? The rabbits aren’t able to clear the infection caused by G. strigosum with their immune response; therefore, the rabbits accumulate more and more parasites as they age—the result is that older individuals carry most of the infection in the population. However, because T. retortaeformis infection is...

Read More
The Global Travels of Chikungunya Virus: Is it Coming to You?
Mar30

The Global Travels of Chikungunya Virus: Is it Coming to You?

By Roberta Attanasio Chikungunya virus is spreading fast — worldwide. First described during an outbreak in southern Tanzania in 1952, it caused sporadic illness in Africa and large urban outbreaks in Thailand and India in the 1960s and 1970s. As of now, it has been identified in over 60 countries in Asia, Africa, Europe and Americas. The virus, which causes fever and severe joint pain, is transmitted to humans by the bites of infected female mosquitoes, most commonly by Aedes aegypti and Aedes albopictus — two species that can also transmit other mosquito-borne viruses, including dengue. There is no vaccine and no specific treatment for the infection. Gemma Handy aptly describes the onset of the disease in an Antiguan patient: “The acute ache started in her ankles before quickly spreading through her body, crippling her muscles, pounding her joints and leaving her hands and feet severely swollen.” The patient said: “”I was fine when I went to bed, but when I woke up in the morning and tried to get up my ankles hurt so much I couldn’t stand. It was very scary. After that I started getting different pains all over my body. Soon my hands were so swollen I couldn’t hold anything.” Indeed, “chikungunya” derives from a word in the Kimakonde language, which is spoken by the Makonde, an ethnic group in southeast Tanzania and northern Mozambique — it means “to become contorted”, and describes the stooped appearance of sufferers with joint pain. Most patients recover fully, but in some cases joint pain may persist for several months, or years — and even become a cause of chronic pain and disability. In 2007, disease transmission was reported for the first time in a localized outbreak in north-eastern Italy. Outbreaks have since been recorded in France and Croatia. According to the Centers for Disease Control and Prevention (CDC), the first local transmission of Chikungunya virus in the Americas was identified in Caribbean countries and territories in late 2013 — local transmission means that mosquitoes in the area have been infected with the virus and are spreading it to people. Beginning in 2014, Chikungunya virus disease cases were reported among U.S. travelers returning from affected areas in the Americas and local transmission was identified in Florida, Puerto Rico, and the U.S. Virgin Islands. The current numbers of people infected with the virus within the Americas are staggering: the Pan-American Health Organization reports that, as of the end of February 2015, the initial handful of cases had exploded to 1,247,400 suspected and confirmed cases, affecting almost every country in the hemisphere. After the first locally acquired case of Chikungunya was reported...

Read More
Small Predator Diversity Plays a Significant Role in the Spread of Infectious Diseases
Mar23

Small Predator Diversity Plays a Significant Role in the Spread of Infectious Diseases

By Roberta Attanasio Biodiversity is a term coined to describe the diversity of all living things, from human beings to microorganisms. A New York Times editorial published almost two decades ago aptly describes the importance of the biodiversity concept: “Biodiversity is a hugely important concept that stresses the coherence and interdependence of all forms of life on earth and a new willingness to appraise the meaning of that interdependence, not just for humans but for every one of life’s component parts.” The editorial goes on to illustrate the alarming effects of biodiversity loss: “Biodiversity is a way of talking about what scientists have long understood and a way of reminding the rest of us of a cardinal fact: that we are standing in the midst of the earth’s sixth great extinction of diverse species, that this extinction is driven by us and that we are not now and will never be immune to its effects.” One of these effects is the worldwide spike in infectious diseases, as suggested by a study recently published in the journal Proceedings of the National Academy of Sciences. The study (Predator diversity, intraguild predation, and indirect effects drive parasite transmission) explores how the diversity of small predators shapes the transmission of parasites in wetlands. Lead author Jason Rohr said in a press release by Penn State: “In the last century, there has been an unprecedented global increase in infectious diseases and a concomitant decline in and homogenization of biodiversity. The controversial ‘dilution effect hypothesis’ suggests that the two phenomena might be linked, or that biodiversity often decreases disease risk.” The study, which included a series of laboratory experiments, field surveys and mathematical modeling, shows that — in presence of various species of dragonfly larvae — there is a reduction of frog infections caused by trematodes, which are parasitic flatworms also known as flukes. The dragonfly larvae are small predators that eat trematodes. Val Beasley, senior author of the study, said in the press release that various species of trematodes penetrate tadpoles. The trematodes sometimes kill the tadpoles. In other instances, the trematodes weaken them by causing tissue damage, kidney failure, or severe limb deformities while the tadpoles develop into frogs. He added that other vertebrate species commonly catch trematode infections from bodies of water. These vertebrate species include wildlife, domestic animals and humans — mostly children — who are commonly affected by schistosomiasis in tropical parts of the world. Schistosomiasis is a parasitic disease carried by freshwater snails infected with one of the five varieties of the parasite Schistosoma, a type of trematode. Although the worms that cause schistosomiasis are not found in the...

Read More
TB Unmasked: Healthcare Workers and the Global Tuberculosis Epidemic
Mar21

TB Unmasked: Healthcare Workers and the Global Tuberculosis Epidemic

By Roberta Attanasio World TB Day, falling on March 24th each year, is approaching — it reminds us that tuberculosis (TB) is a massive global health problem. Indeed, according to the World Health Organization (WHO), tuberculosis is one of the world’s deadliest communicable diseases. It is second only to HIV/AIDS as the greatest killer worldwide due to a single infectious agent. In 2013, an estimated 9.0 million people developed TB and 1.5 million died from it — mostly in developing countries. However, TB is curable and preventable. The WHO estimates that 37 million lives were saved between 2000 and 2013 through effective diagnosis and treatment. Despite the many saved lives, the death toll is still unacceptably high. Last month, Anthony S. Fauci, Director of National Institute of Allergy and Infectious Diseases, said: “Progress is being made in the international fight against TB; however, the disease remains entrenched in many countries, especially those in Sub-Saharan Africa.”   TB is caused by bacteria (Mycobacterium tuberculosis) that most often affect the lungs. It spreads from person to person through the air. When people with lung TB cough, sneeze or spit, they propel the TB bacteria into the air. A person needs to inhale only a few of these bacteria to become infected. About one-third of the world’s population has latent TB — people have been infected by TB bacteria but are not (yet) ill with the disease and cannot spread the bacteria. When a person develops active TB (disease), the symptoms (cough, fever, night sweats, weight loss and others) may be mild for many months. For this reason, people with active TB may delay seeking care, and bacteria can spread to others. People ill with TB can infect up to 10-15 other people through close contact over the course of a year. Without proper treatment, up to two thirds of people ill with TB will die. Unfortunately, the vaccine currently available to prevent TB has limited efficacy. Healthcare workers who come into contact with patients affected by active TB are at considerable risk of contracting the disease. Indeed, every day, millions of healthcare workers around the world put their lives at risk as they combat tuberculosis. They’re vulnerable to TB exposure and infection. And they deserve to be protected. Therefore, Aeras — a nonprofit biotech advancing the development of new tuberculosis vaccines for the world — launched the TB UNMASKED campaign on September 24, 2014. TB UNMASKED supports and empowers people who put themselves at risk of tuberculosis infection through caring for patients, and gives healthcare workers on the front lines of the TB epidemic the opportunity to tell their stories using photographs,...

Read More
Tasmanian Devils: Contagious Cancer Drives the Risk of Extinction
Dec05

Tasmanian Devils: Contagious Cancer Drives the Risk of Extinction

By Roberta Attanasio In November 2013, a team of biologists scattered 15 plastic cylinders in the fields of Maria Island, three miles off the east coast of the Australian island state of Tasmania. Each cylinder contained a healthy Tasmanian devil, a marsupial  species that until then lived only in Tasmania. Soon, the 15 devils emerged from the containers, becoming the first ever to inhabit Maria Island. The biologists were planning to take more devils to the island. Why? To establish a healthy colony, needed for the survival of the entire species. The Tasmanian devil is on the brink of extinction because of an unusual disease — a contagious cancer that is spreading very quickly. In some areas, more than 90% of the population has been wiped out. The disease is called Devil Facial Tumor Disease, or DFTD for short, and is characterized by malignant tumors — around the mouth and head — that behave as parasites and have caused an epidemic of cancer. The tumors are directly transmitted when the devils bite each other faces during fights — sometimes they bite off little pieces of tumor. When this happens, the cells reach the attacker’s bloodstream and, from there, its face. Once in the face, they start growing, producing a new tumor. Because the growth of tumors is not controlled by the devils’ immune system, the disease causes 100% mortality among infected devils. Tasmanian devils (Sarcophilus harrisii) are dog-sized carnivorous marsupials known for their black color, spine-chilling screeches and bad temper — they look and sound fierce. Today, the devil is a Tasmanian icon set to disappear. However, if the devils become extinct in Tasmania, the disease will disappear with them, as they are the only animals affected by this type of contagious cancer. At that point, the healthy devils from Maria Island could be introduced back in the wild.  Carl Zimmer wrote that when the tumor disease was first discovered in 1996, many scientists assumed it was caused by a rapidly spreading virus. Instead, in 2006, Anne-Maree Pearse and Kate Swift (Department of Primary Industries, Water and Environment in Tasmania), discovered something strange about the tumor cells. The chromosomes looked less like those in the animal’s normal cells and more like those in the tumors growing in other Tasmanian devils. Pearse and Swift proposed that the disease is transmitted when an infectious cell line is passed directly between the animals through bites they inflict on one another. They thought that the low genetic diversity and high degree of kinship among devils might help to reduce their immune response to cancer cells implanted during biting. In 2007, Katherine Belov and her collaborators published a study showing that the tumor DNA was similar in different animals,...

Read More