Wednesday, October 1, 2014

CDC for Wildlife Diseases

Fig.1. Little brown bats (Myotis lucifugus) are especially vulnerable to White Nose Syndrome, with 90%-100% mortality during an outbreak (Photographer: Merlin Tuttle)

Last week, the U.S. Fish & Wildlife Service awarded more than $1.2 million to 30 states in an effort to combat White Nose Syndrome, a deadly disease affecting many bat species. Since its appearance in 2006, this disease has spread fast with greater than 90 percent mortality in some bat species. A 2009 study done by researchers at the National Wildlife Health Center in Madison, WI, determined that the fatal epizootic was caused by the fungus Pseudogymonoascus destructans. Although the White Nose Syndrome is only known to infect bats, declines in bat populations affect ecosystems and agriculture.

Monitoring White Nose Syndrome is only one of many duties performed by the National Wildlife Health Center (NWHC), a research branch of the U.S. Geological Survey. The center’s director Dr. Jonathan Sleeman jokingly referred to his organization as the “CDC for wildlife.” Although NWHC is only about 120 strong, it aims to give the same type of support for wildlife health that the Centers for Disease Control and Prevention does for public health.

Diseases that cross borders

The NWHC provides valuable diagnostic, epidemiological, and surveillance research. In addition to pathogen discovery, such as that behind the White Nose Syndrome, its duties stretch to provide assistance in outbreak mitigation and response. The NWHC studies avian influenza, chronic wasting disease, foot and mouth disease, and the sylvatic plague, among others. Though most of its research focuses on wildlife diseases, such as White Nose Syndrome, others, including avian influenza, have significant public health implications.

“These diseases cross borders,” Sleeman said. “These diseases don’t respect anyone’s species.”

Like the FDA’s CORE Network the NWHC collaborates with agencies such as the Fish & Wildlife Service, the National Park Service, the U.S. Department of Agriculture, local wildlife management centers, and the CDC. Wildlife agencies, local and federal, constantly monitor animal disease prevalence and work together to address outbreaks. The NWHC and human health agencies contact each other when zoonotic diseases -- the plague, avian influenza, or rabies, to name a few -- jump from animals to humans. Partnerships like these help them emphasize predictive modeling to inform preventative measures.

“Can we anticipate and predict where a disease is going to emerge and focus our resources on those hot-spots where diseases are emerging?” Sleeman asked.

The key, Sleeman stressed, was to understand the driving factors of the disease, from human population density to agricultural intensification and climate change. 

“By looking at these variables and factors, we can start to build maps and build models of areas where there are high risk factors,” Sleeman said.

For example, wild birds in close contact with poultry increases the risk for avian influenza to go from wild species to domesticated species and into humans. Unfortunately, cases are rarely this simple in real life. In addition to dealing with any number of wildlife species, coordination with partner organizations and agencies remains difficult. For wildlife outbreaks, it is not always clear who can respond to which disease and to what extent.

New way to study collections

Despite challenges with coordination, recent developments in data distribution have made it easier to connect with researchers. NWHC diseased tissue collections, such as their chronic wasting disease samples, are used in comparison studies and to create better diagnostic tests to identify the disease more quickly. Their reference strain repositories are also useful to compare outbreak samples to known pathogens.

Increasingly, scientists are sequencing and analyzing the phylogeny of biological collections kept by the NWHC. Sequencing -- or mapping out the complete DNA arrangement of an organism’s genome -- has become much more cost effective in the past couple of years, allowing more researchers in wildlife and human health to utilize this technique.

“Historically, [sequencing] is not common in an outbreak investigation,” Sleeman said. “Now it’s standard technique. You identify a novel virus, you sequence it, and you look at where it fits in the phylogenetic tree.”

To create a phylogenetic tree is to track the evolutionary history of that organism. Sequencing the collections held by NWHC allows scientists to understand to potential origin and epidemiology of diseases. This process requires good collection management and an accessible and online database. One of Sleeman’s long-term goals is to digitize all of NWHC’s collections.

“We use them to map the distribution of diseases, historical trends, developing an online system to make this information more readily retrievable by our partners,” Sleeman said.

References:

Blehert, D.S., Hicks, A.C., Behr, M., Meteyer, C.U., Berlowski-Zier, B.M., Buckles, E.L., Coleman, J.T.H., Darling, S.R., Gargas, A., Niver, R., Okoniewski, J.C., Rudd, R.J., & Stone, W.B. (2008). Bat White-Nose Syndrome: An Emerging Fungal Pathogen? Science, 323 (5911), 227. doi: 10.1126/science.1163874.

Coleman, J., & Hibbard, C. (August 25, 2014). U.S. Fish & Wildlife Service News Release. Retrieved from https://www.whitenosesyndrome.org/sites/default/files/files/2014_wns_state_grants_final.pdf.

Disease Information. (May 22, 2013). USGS National Wildlife Health Center online. Retrieved from http://www.nwhc.usgs.gov/disease_information/.

Tuttle, M. (Photographer). [Untitled photograph of a little brown bat]. Retrieved Sept. 19, 2014, from: http://www.batsaboutourtown.com/pages/LittleBrownBat.htm.




Glossary

epidemiology
A branch of medicine that deals with incidence, distribution, and control of diseases and health factors
epizootic
An outbreak of a disease in an animal population.

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