Ecology of zoonotic diseases

Figuring out the what, where and when of disease outbreaks By Nadine Lymn, ESA director of public affairs Plague, Lyme disease, Hantavirus, West Nile Virus—these bacteria and viruses are zoonotic diseases that can be transmitted to people from animals like ticks, mosquitoes and rodents and were the subject of a recent Ecological Society of America (ESA) congressional briefing. Disease transmission is an environmental issue–understanding the ecological dynamics at play is crucial.  Ecology can help sleuth out the source of new diseases and help predict where and when new outbreaks are likely to occur. That was a key message Robert Parmenter and Gregory Glass had for the congressional, federal agency and scientific society staff attending ESA’s briefing on April 23, 2013. Parmenter directs the Scientific Services Division of the US Department of Agriculture’s Valles Caldera National Preserve in New Mexico.  He has years of experience with zoonoses, especially plague and Hantavirus. Glass is a professor at Johns Hopkins School of Public Health and directs the Global Biological Threat Reduction Program of the Southern Research Institute. His work has included a focus on Lyme disease and Anthrax, along with hantaviruses.  Between the two of them, Parmenter and Glass painted a vivid picture of the dynamics of these diseases and how collaborations between ecological and medical research can solve disease mysteries, such as that of the first hantavirus outbreak in the Four Corners region of the US. In May of 1993, people were coming down with flu-like symptoms that rapidly filled their lungs with fluid, killing some of them. Others just as quickly recovered. A sense of panic gripped the area and scientists from the Centers for Disease Control arrived and, within 19 days, identified the disease as Hantavirus Pulmonary Syndrome for which there is neither a vaccine nor a cure. But where had it come from and why now? Enter the ecologists who began field surveys and discovered that the source for the disease was the deer mouse, whose aerosolized urine and feces can infect humans with Hantavirus if inhaled. An unusually wet winter had led to a boom in the deer mouse population, which resulted in many of them descending from higher elevation forested areas to lower elevation areas where people tend to live, increasing the likelihood of mouse-human encounters. Since 1993, there have been other Hantavirus outbreaks, but now, with a much better understanding of the ecological factors in play, people can be notified ahead of time that conditions are right for increased chances of exposure and take appropriate precautionary steps. It turns out that different varieties of Hantavirus are present in a variety of rodents across North and...

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Global economic pressures trickle down to local landscape change, altering disease risk

by Liza Lester, ESA communications officer The pressures of global trade may heighten disease incidence by dictating changes in land use. A boom in disease-carrying ticks and chiggers has followed the abandonment of rice cultivation in Taiwanese paddies, say ecologist Chi-Chien Kuo and colleagues, demonstrating the potential for global commodities pricing to drive the spread of infections. Their work appears in the September issue of ESA’s journal Ecological Applications. After Taiwan joined the World Trade Organization in 2001, active cultivation of rice paddies fell from 80 percent to 55 percent in just three years. The government of Taiwan subsidized twice-yearly plowing of abandoned fields to reduce the spread of agricultural pests into adjacent fields still in cultivation. Compliance has been spotty. Kuo found that, while plowing did not suppress rodent populations, it did inadvertently reduce the presence of the ticks and chiggers that use rodents as their primary hosts. “The government considers only agricultural pests such as insects and rodents. They don’t think about the disease factors,” said Kuo. But land use policy can have complex and unexpected reverberations in the ecology of the landscape. Chiggers, the larval stage of trombiculid mites, spread scrub typhus (Orientia tsutsugamushi), a bacterium that gets its name from the scrubby, dense vegetation that often harbors its flesh-loving host. Scrub typhus is a common culprit underlying visits to Southeast Asian hospitals for flu-like symptoms. It is one of the rare bacterial infections that develop into hemorrhagic fever. Without antibiotics, the infection is often fatal. Ticks (Ixodidae) transmit bacteria spotted fever group rickettsiae, causing fever, aches and rash similar to Rocky Mountain spotted fever. Neither pest prefers to live underwater. Hualien, Kuo’s study area, is one of the least populous of Taiwan’s counties, yet had nearly the highest incidence of scrub typhus from 1998-2007. The county is a smattering of small villages surrounded by a patchwork of flooded, plowed, and abandoned rice paddies. Flooded paddies are poor habitat for ticks and chiggers, and so cultivation of rice, which locally means carefully managed flooding of fields to drown agricultural pests, likely suppresses ticks and chiggers as well. Even the seemingly unkillable ticks die after a few weeks of submersion, and chiggers are similarly terrestrial. Though studies are few, limited data indicate that most chiggers die after a month under water. This study did not assess flooded paddies due to the difficulty of finding and collecting rodents, ticks, and chiggers underwater. Instead, Kuo trapped rodents in fallow and plowed fields and examined their tick and chigger passengers, testing the arachnids for presence of disease-causing rickettsial bacteria. He found 6 times as many ticks on the rodents living...

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Chickenpox sweeties and the social ecology of infectious disease

This post contributed by Liza Lester, ESA communications officer   No one speaks for the endangered poliomyelitis. No one raises money to protect the last survivors, as health workers stalk the virus through its last redoubts in India, Pakistan, Nigeria and Afghanistan. On the contrary, the WHO spends billions on hunting it to extinction. But the virus has held out longer than expected. Joshua Michaud, policy analyst at the Kaiser Foundation, thinks the polio fighters are falling behind. Guinea worm will be the next scourge to fall, he said on an AAAS panel engaged to discuss Infectious Disease: Challenges to Eradication on Monday. Why have efforts with guinea worm been so successful? a precocious Georgetown student wanted to know. Biology was on our side. There is no vaccine for guinea worm, and no medicine to cure infection. To extract the worm, you must wind it slowly around a stick as it emerges through a sore in your leg (an oft-repeated story holds that the treatment has not changed since the Egyptians of the XVIII dynasty described it in 1550 BCE, though the source appears to have been exaggerated). The process is excruciating, and it takes weeks. But we know key details of the worm’s biology that the ancient Egyptians did not. Basic technology and careful hygiene can defeat the worm. Larvae harbor in the bodies of invisible copepods, “water flies” tiny enough to swallow. Once swallowed, female larvae nestle against the long limb bones of their hosts, growing up to a meter in length over the course of a year. They surface inside a burning ulceration that sends their victims running for a dip in a cool pond—and the next generation of larvae escape to start the cycle of life anew. The good news, said Michaud, is that guinea worm does not have another host. It has no environmental bolt hole to hide in while under siege, only to emerge when health forces are not looking. It needs humans. And affected people are visibly affected. Break the cycle for one year, and you can free a communal water source, and its community, from the worm. Copapods may be microscopic, but a simple nylon strainer on the end of a drinking tube saves you from swallowing them (although not bacterial and viral parasites that might also lurk there, interjected Dennis Carroll, in charge of avian flu and other emerging threats at USAID). Help the infected, persuade them to stay out of drinking water sources when their worm breaches, and you break the cycle. Success requires the help and good will of village elders. The Carter Foundation has been courting good...

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Pest control resources fell as anti-terrorism efforts rose

The United States “war on terrorism” mobilized the federal government to take action to prevent a recurrence of the events of 9/11/01. Ten years and just over a month later, efforts that span two presidential administrations have led to a country that is more secure against one of Earth’s most dangerous species: humans. Unfortunately, an unwanted side effect has been a jump in the infiltration into the U.S. of countless other species that pose an entirely different kind of threat. A recent analysis by the Associate Press (AP), found that in the years since 9/11, scientists that were once responsible for curbing the entry of invasive species at U.S. borders have been reassigned to anti-terrorism efforts after the formation of the Department of Homeland Security (DHS), established under the Homeland Security Act of 2002 (P.L. 107-296). In 2003, as laid out in the bill’s provisions, many APHIS agricultural border inspectors were transferred from the Department of Agriculture to U.S. Customs and Border Protection, a unit of the U.S. Department of Homeland Security. As a result, the number of pest cases intercepted at U.S. ports of entry fell from over 81,200 in 2002 to less than 58,500 in 2006. The numbers have since steadily risen again after complaints from farm industry and lawmakers. As highlighted in a recent EcoTone post, invasive species can be serious burden on the economy as clean up costs for individual species can number anywhere from hundreds of thousands to millions of dollars. The AP article notes that the most problematic overseas imports are fruits, vegetables and spices, which can carry insects, their larvae or contagions capable of decimating crops. The article states that crop-threatening species has spiked from eight in 1999 to at least 30 in 2010. The Center for Invasive Species Research (CISR) reports that since 1991, the silver-leaf whitefly has cost an estimated $500 million to California agriculture, translating to “roughly $774 million in private sector sales, 12,540 jobs and $112.5 million in personal income.” Nationally, the fly’s damage has been estimated to be in excess of $1 billion.  CISR also found that the red palm weevil, first identified in the United States in August 2010, poses a “serious threat” to ornamental palm tree sales, which contribute $70 million to the California economy and $127 million to the Florida economy each year. A recent study found that wood boring insects, such as the Asian long-horn beetle, reportedly cost more than $3.5 billion in losses, including $1.7 billion to local governments, $1.59 billion to homeowners, $130 million to forest landowners and $92 million to the federal government. The same study concluded there is a 32 percent...

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A look at agencies responsible for suppressing a real world ‘contagion’

Recent blockbuster films, including “Rise of the Planet of the Apes” and “Contagion” have featured zoonotic diseases that spread into (spoiler alert) deadly pandemics. If the respective films didn’t give you a case of hypochondria, statistics collected by the Centers for Disease Control (CDC) will: Approximately 75 percent of recently emerging infectious diseases affecting humans are diseases of animal origin and approximately 60 percent of all human pathogens are zoonotic, communicable from animals to people. But what current procedures are in place to prevent fiction from becoming fact? A recent article from the United States Geological Survey (USGS) details the work being done to monitor wildlife in efforts contain outbreaks and prevent spread to humans. Established in 1975 and headquartered in Madison, Wisconsin, the USGS National Wildlife Health Center (NWHC) collaborates with wildlife biologists from the Department of Agriculture and the U.S. Fish and Wildlife Service as well as state partners to provide immediate technical assistance to field personnel who find sick and dead wildlife. NWHC personnel provide instructions on collection, preservation, and shipment of specimens for laboratory examination and travel to problem areas to conduct field investigations and assist local personnel with disease control operations. While the NWHC is on the front lines in monitoring wildlife, the CDC’s  National Center for Emerging and Zoonotic Infectious Diseases focuses specifically on human impacts, with a complex network across six divisions to detect, prevent, and control infectious diseases from spreading in the United States and around the world, including the Division of Foodborne, Waterborne, and Environmental Diseases, the Division of Global Migration and Quarantine, the Division of Healthcare Quality Promotion, the Division of High-Consequence Pathogens and Pathology, the Division of Preparedness and Emerging Infections, the Division of Scientific Resources and Division of Vector-Borne Diseases. Established in early 2010, the center consists of a diverse workforce of “microbiologists, epidemiologists, educators, chemists, ecologists, demographers, statisticians, health economists, veterinarians, health communicators and information technology experts.” Read more at Preventing Pandemic: the Wildlife Forensics of New and Emerging Diseases and learn more about the CDC National Center for Emerging and Zoonotic Infectious Diseases here. Photo Credit: Rich Magahiz...

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New grants promote greater understanding of infectious disease

This post contributed by Lindsay Deel, a Ph.D. student in geography at West Virginia University and Intern with ESA’s journal Frontiers in Ecology and the Environment Infectious diseases won’t know what hit them. A massive new collaborative effort between funding sources in the United States (US) and United Kingdom (UK) takes aim at infectious diseases from ecological and social perspectives, reported the National Science Foundation (NSF) in a recent press release. The overall goal of the suite of eight projects is to improve understanding of the factors affecting disease transmission, said NSF, but a major focus will also be on building models to help predict and control outbreaks. Each of these projects examines different themes within the global context of infectious disease. For example, Tony Goldberg (Professor of Epidemiology, University of Wisconsin–Madison) and colleagues will investigate the spread of HIV from its origin in monkeys to humans by examining similar viruses that are currently impacting wild monkeys in Uganda. This project will also study human social factors – such as awareness, beliefs, and behaviors – surrounding the transmission of such diseases. Another project helmed by David Rizzo (Professor of Plant Pathology, University of California–Davis) will explore how interacting forest disturbances – such as fire and drought – may control the emergence, persistence, and spread of invasive pathogens using the case of sudden oak death – a disease caused by a non-native pathogen, Phytophthora ramorum. “Over the past 10 years, potentially millions of trees in California and Oregon coastal forests have died as a result of this emerging disease,” explains Rizzo. “The goal of this new grant is [to] link this new disturbance agent (sudden oak death) with pre-existing disturbance agents (fire, drought) in coastal forests.” Samantha Forde (Professor of Ecology and Evolutionary Biology, University of California – Santa Cruz) will lead a project using a simplified laboratory system of E. coli bacteria and its viruses as a model to study why some viruses have evolved the ability to infect multiple host species, while others can only infect one.  “This will further a general understanding of the dynamics of disease in natural systems and help to improve public health initiatives,” she says. From the modeling perspective, Armand Kuris (Professor of Biological Sciences, University of California at Santa Barbara) and colleagues will delve into the complexity of ecological systems and how the level of complexity might influence disease dynamics.  Kuris and colleagues hope to bring the role of infectious diseases into the core of ecological thinking, comparable to the roles of predation, competition, disturbance and resource quality. Joseph Tien (Professor of Mathematics, Ohio State University) will examine the recent cholera epidemic in Haiti. ...

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