Ebola: new study models a deadly epidemic


February 12, 2015

On Dec. 26, 2013, a two-year-old boy living in the Guinean village of Meliandou, Guéckédou Prefecture, was stricken with a rare disease, caused by the filament-shaped Ebola virus.

The child is believed to be the first case in what soon became a flood-tide of contagion, ravaging the West African countries of Guinea, Sierra Leone and Liberia, infecting over 21,000 cases as of Jan. 21, according to the World Health Organization, with nearly 9,000 confirmed deaths – the actual toll likely much higher. Ebola map of Africa Download Full Image

Now, researchers from Arizona State University and Georgia State University are trying to better understand the epidemiology of the Ebola virus disease in order to alleviate suffering and prevent future disease outbreaks from reaching the catastrophic proportions of the current crisis.

In a report appearing in the February 2015 issue of the prestigious British medical journal The Lancet Infectious Diseases, ASU researchers present the study "Modelling the effect of early detection of Ebola," which examines the levels of detection and patient isolation required to shut down transmission of Ebola and reports on new efforts to model the impact of timely diagnostic testing on the spread of Ebola across populations.

A better understanding of viral dissemination and techniques for disease management are vital if a similar calamity is to be avoided in the future.

Wave of destruction

The Ebola virus has become notorious, not only for its highly contagious and lethal nature, but for the nightmarish assortment of symptoms collectively known as hemorrhagic fever. These may include vomiting of blood, bleeding from the eyes, ears, nose, mouth, rectum, internal bleeding,excruciating pain and the liquidization of internal organs.

The three West African nations centrally affected by the epidemic were acutely unprepared for the crisis. Treatment centers were rapidly swamped with severely ill patients. Resources for proper care, isolation of infected patients and even basic means of sterilization were soon depleted. Health care workers were especially vulnerable to infection.

A number of exacerbating factors contributed to the outbreak and rapid spread of Ebola in the region. Timber and mining activities have impacted densely forested regions and brought fruit bats – believed to be a natural reservoir for the virus – in closer contact with humans. Infected animals consumed as bush meat may also have planted early seeds of the disease in the vulnerable population. Long periods of civil unrest have left the area deeply impoverished and the health infrastructure fractured.

Meliandou, the town identified as ground zero, is situated in a forested area at the convergence point of Guinea, Liberia and Sierra Leone. Populations move fluidly across these porous borders, as impoverished residents are often on the move in search of work. These conditions created a perfect storm for the aggressive virus.

An additional factor fueling the explosive spread of Ebola in West Africa was the delayed and inadequate response to the crisis on the part of developed countries and global health organizations.

Time is the enemy

As the authors of the current study emphasize, breaking the chain of Ebola transmission presents intimidating challenges. After the development of symptoms, the virus is highly contagious, and each new contact presents an opportunity for further spread of the disease.

Tracking all contacts of infected individuals can be a daunting effort, even in first-world settings, with low case numbers. In the absence of a vaccine or reliable therapeutic for Ebola, diagnosis of the disease at a pre-symptomatic stage and rapid isolation of infected individuals are the surest means for arresting further disease transmission.

“Early detection of Ebola infection provides the opportunity and time to safely isolate and treat individuals before they become contagious," said Karen Anderson, Biodesign Institute researcher and professor in ASU's School of Life Sciences. "Our findings show two key things: first, that the predicted impact of early diagnostic tests depends on existing public health measures. Second, there appears to be a tipping point, where early diagnosis of high-risk individuals, combined with adequate isolation, can markedly decrease the predicted number of infected individuals.”

Stopping an epidemic in its tracks requires a reduction in a critical value known as the reproductive ratio – a measure of new infections generated by a single case over the course of the infectious period. The higher the number for the reproductive ratio, the more difficult an epidemic is to contain.

A technique known as polymerase chain reaction (PCR) can be used for pre-symptomatic identification of the Ebola virus. The current study models the expected outcomes on viral transmission of Ebola using PCR-based pre-symptomatic diagnosis and isolation of infected patients within three days of the onset of symptoms.

“Our results underscore the dramatic impact that diagnostic capacity can bring about during an Ebola epidemic to quickly identify Ebola cases before these start new chains of transmission in the community or health care settings,” said Diego Chowell, lead author of the study.

Carlos Castillo-Chavez, director of the Simon A. Levin Mathematical, Computational and Modeling Sciences Center, emphasizes the power of mathematical modeling for understanding and limiting the scale of epidemics: "Finding that small differences in isolation effectiveness may have a large impact on epidemic size highlights the importance of evaluating novel diagnostic technologies at the population level using mathematical models,” he says. “An intervention may not work or be effective unless it is effectively used beyond a tipping point."

The authors urge the implementation of the strategy of pre-symptomatic diagnosis and rapid isolation, targeting high-risk individuals, including care givers and health care workers.

The desperate need for early diagnosis of Ebola is clear. During the West African epidemic, most Ebola patients remained undiagnosed in their communities. Among those who were diagnosed, the average time from symptom onset to positive diagnosis was about five days – a prescription for rapid, far-flung transmission of the disease.

End game

According to the latest reports from the World Health Organization, the Ebola epidemic appears to be weakening its grip on the region. For the first time since June 2014, there have been fewer than 100 new weekly cases reported in the three countries most affected, signaling what health care workers hope is the final phase of Ebola’s devastating reign.

Increased vigilance and new tools at both the epidemiological and therapeutic ends of the spectrum are vitally needed if another epidemic – perhaps of even greater scale – is to be prevented.

Richard Harth

Science writer, Biodesign Institute at ASU

480-727-0378

ASU researcher uses new tools to explore ancient life


February 12, 2015

Mummies excavated nearly a century ago are yielding new information about past lifeways through work conducted in Arizona State University’s Archaeological Chemistry Laboratory.

Using new techniques in bioarchaeology and biogeochemistry, a team of bioarchaeologists and archaeologists have been able to study the diets of 14 individuals dating back almost 2,000 years. textile from the Wari Kayan Necropolis Download Full Image

The findings were recently published in the Journal of Archaeological Science.

The mummies were unearthed from one of the most famous sites in Peru: the Paracas Necropolis of Wari Kayan, two densely populated collections of burials off the southern coast. The region has a rich archaeological history that includes intricate textiles and enormous geoglyphs, yet it has been relatively overlooked for bioarchaeological research.

With support from the National Science Foundation, ASU associate professor Kelly Knudson and her colleagues are attempting to rectify that.

In addition to Knudson, the team was made up by Ann H. Peters, of the University of Pennsylvania Museum of Archaeology and Anthropology, and Elsa Tomasto Cagigao, of the Pontifical Catholic University of Peru.

The researchers used hair samples – between two and 10 sequential samples for each mummy, in addition to two hair artifacts – to investigate the diets of Paracas’ ancient people. They focused on carbon and nitrogen isotope analysis of keratin to determine what these individuals ate in the final stages of their lives.

Diet not only provides insight into health, but can also indicate where people lived and traveled, as well as offer clues about their daily lives by pointing to whether their foods were sourced from farming, fishing, hunting or gathering.

During the last months of their lives, the Paracas individuals appear to have eaten primarily marine products and C4 and C3 plants, such as maize and beans. Also, they were either geographically stable or, if they traveled between the inland highlands and coastal regions, continued to consume marine products.

“What is exciting to me about this research is that we are using new scientific techniques to learn more about mummies that were excavated almost 100 years ago. It is a great application of new science to older museum collections,” says Knudson, who is in ASU's School of Human Evolution and Social Change in the College of Liberal Arts and Sciences.

Knudson, who is affiliated with the school’s Center for Bioarchaeological Research, explained why it is so important to learn about the lived experiences of people who existed long ago.

“By using small samples of hair from these mummies, we can learn what they ate in the months and weeks before they died, which is a very intimate look at the past,” Knudson said.

When first discovered in 1927 by Peruvian archaeologist Julio Tello, each mummy was bound in a seated position; found with burial items, like baskets or weapons; and wrapped in a cone-shaped bundle of textiles, including finely embroidered garments.

Since the sampled individuals were mostly male, Knudson and her colleagues suggest that future research may involve more females and youths. The researchers also plan to further examine artifacts and mortuary evidence to build context for their isotopic data.

More information on the Necropolis of Wari Kayan can be found at the Paracas Archaeology Research site.

Rebecca Howe

Communications Specialist, School of Human Evolution and Social Change

480-727-6577