The Global Fool

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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...

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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...

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Food-Borne Parasites: The “Top Ten” List
Jul01

Food-Borne Parasites: The “Top Ten” List

By Roberta Attanasio Food-born parasites affect the health of millions of people all around the world, causing huge social costs. However, we don’t know much about these parasites — where they come from, how they live in the human body, and how they make us sick. Today (July 1, 2014), the Food and Agriculture Organization of the United Nations (FAO) released, along with the World Health Organization (WHO), a report — Multicriteria-based ranking for risk management of food-borne parasites — as a first step in tackling the problem. Parasites are organisms that derive nourishment and protection from other living organisms known as hosts. Parasites that are present in food cause food-borne infectious diseases. They are classified biologically as protozoa (single-celled organisms) or helminths (better known as tapeworms, flatworms and roundworms).  Infectious diseases caused by food-borne parasites have not received the same level of attention as other food-borne biological and chemical hazards. Nevertheless, they cause a high burden of disease in humans, may have prolonged, severe, and sometimes fatal outcomes, and result in considerable hardship in terms of food safety, security, quality of life, and negative impacts on livelihoods. It is difficult to know how widespread these parasites are globally — in many countries it is not compulsory to notify public health authorities of their presence. In Europe, more than 2,500 people are affected by food borne parasitic infections each year. In 2011 there were 268 cases of trichinellosis and 781 cases of echinococcosis recorded in the EU. In Asia, there is no precise national data but parasitic diseases are known to be widely spread and are recognized as major public health problems in many countries. In most African nations there is no data at all on the prevalence of food borne parasites in humans because there of a general lack of surveillance systems. In the United States, Neurocysticercosis, caused by Taenia solium, is the single most common infectious cause of seizures in some areas of the US where 2 000 people are diagnosed with neurocysticercosis every year. Toxoplasmosis is a leading cause of food-borne illness and death. The FAO-WHO report was developed following a request by the global food standards body, the Codex Alimentarius Commission (Codex), to review the current status of knowledge on parasites in food and their public health and trade impacts. FAO’s food safety and quality unit and WHO responded by jointly organizing a global call for information on the problem. Twenty-two nations and one regional body responded, followed by an assessment and analysis by 21 experts on the impact of food-borne parasites. From this work, an initial list of 93 parasites was developed. The list was then narrowed down to the 24 most damaging parasites based on the...

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