CORAL REEF DISEASE, LINK TO HUMAN SERRATIA STRAINS
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Date: 23 Oct 2010
Source: Medical News Today [edited]
<http://www.medicalnewstoday.com/articles/205372.php>
Transmission of Human Pathogen to Coral Reefs to be Studied by UGA Researchers
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The spread of lethal diseases from animals to humans has long been an issue of great concern to public health officials. But what about diseases that spread in the other direction, from humans to wildlife?
A multidisciplinary team of researchers at the University of Georgia
(UGA) has just been awarded a 5-year USD 2 million Ecology of Infectious Diseases grant from the National Science Foundation and National Institutes of Health to study the first known case of such a "reverse zoonosis" that involves the transmission of a human pathogen to a marine invertebrate, elkhorn coral.
White pox disease has devastated coral reefs throughout the Caribbean and Florida Keys, and is believed to be responsible for much of the coral reef loss there since 1996. White pox disease is caused by a human strain of the common intestinal bacterium _Serratia marcescens_, which causes the hospital infection serratiosis.
Historically, many emerging human diseases, such as AIDS and Ebola, have come from the natural world. The researchers are concerned that the transmission of _Serratia marcescens_ from humans to elkhorn coral may indicate the beginning of a new phenomenon of diseases jumping from humans to wildlife.
The UGA team will investigate the mechanisms of transmission of white pox disease and the factors that drive its emergence in marine animals. "This bacterium has jumped from vertebrate to invertebrate, from terrestrial to marine, and from anaerobic to aerobic environments," said James W. Porter, associate dean of the Odum School of Ecology and the team's leader. "Triple jumps like this are rare." Understanding the modes of transmission will allow the scientists to attempt to predict future impacts of the disease and to begin to develop effective control strategies.
The scope of the team's research will extend beyond gaining an understanding of the impact of white pox disease on elkhorn coral and how to counter it. The most likely source of the pathogen for coral reefs is under-treated human sewage, so the study will also explore the intersection of public health practices and environmental health outcomes.
"This investigation addresses not only environmental protection, but also the socio-ecological determinants of coastal zone protection,"
said Porter. "This includes the cost of wastewater treatment infrastructure. Given a reliance on tourism by most Caribbean countries, this study addresses a disease system that is of great economic importance and public health concern to developing nations."
The complexity of the problem required assembling a team of researchers from different scientific disciplines. "The Odum School is extremely well-positioned to lead this study," said Dean John Gittleman. "Working effectively in collaboration with units from across campus is one of our strengths, and aquatic ecology, theoretical ecology and disease ecology are 3 of our areas of particular depth that facilitate such interdisciplinary team building."
Porter, who has spent decades studying coral reefs in the Florida Keys and the Caribbean, said that this is the most exciting and groundbreaking study of his career. "This is science in action to save an endangered species and a threatened ecosystem," he said. "We are linking good public health practices to effective environmental protection."
Microbiologist Erin K. Lipp, associate professor of environmental health science in the College of Public Health, will be looking at the genetic diversity of _Serratia marcescens_ to determine which of its different strains are pathogenic to corals, and why. She will collect and analyze samples to determine how the different strains of the bacterium are related, and will then conduct challenge experiments. "We'll inoculate fragments of corals with different strains and see which cause signs of disease," said Lipp. "If we can identify strains that do versus those that don't cause disease, we can then conduct genetic comparisons to isolate the genes that are responsible."
Assistant professor Andrew W. Park, who has a joint appointment in the School of Ecology and College of Veterinary Medicine department of infectious diseases, will use the data gathered by Porter and Lipp to create models to inform analysis of the spread of the disease. "My part of the project is about making sense of the data in terms of transmission," said Park. "We'll use the modeling to help test the hypothesis that there is variation for resistance to the bacteria and explore different candidate hypotheses for how the disease spreads.
The pathogen can be spread in different ways -- for instance, by predatory snails, or through water currents. We're trying to untangle all those competing explanations."
John Wares, assistant professor of genetics in the Franklin College of Arts and Sciences, will be looking into the interactions of the pathogen with the microbial environment of coral reefs in the Caribbean. Unlike humans, corals do not have classic immune systems, with white blood cells to take on and destroy invading bacteria.
Instead, they appear to rely primarily on external defense systems, such as beneficial bacteria that live on their surface. Wares will investigate this system to determine whether healthy bacterial communities can defend corals from disease. "This is essentially high-tech community ecology," said Wares. "I'll be looking at what organisms are living on the coral and what role they play in promoting coral immunity." He said he is excited about the opportunity to use next-generation genetic sequencing, through the Georgia Genomics Facility at UGA. "In the past, we might have been limited to looking at a sample of a few hundred microbes from a given sample!
of the community," he said. "For this study, we can study tens of thousands from each sample. It will be very powerful."
Understanding the transmission process is critical, but Porter said that the study has wider implications. "By incorporating the role of land use practices and water quality into our environmental models of disease prevalence and transmission, this project will have particular significance for sustainable development activities and coastal-zone carrying capacity studies worldwide," he said. "The modeling element of this study connects disease transmission with water quality, climate variability and patterns of human population density. We expect to show that if you upgrade land-based wastewater disposal systems you improve survival of economically important natural resources such as coral reefs."
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[This sounds like an exciting and worthwhile study. It may impact developing nations, but it seems likely that it could focus on better sanitation efforts in developed nations, if this does prove to be the cause of some of the coral diseases and die-offs.
While this article does not tell us, it would seem the researcher will need an "artificial ocean" or risk infecting areas in the ocean which would seem counter productive to what they are wishing to accomplish.
Hopefully the research and modeling will also provide methods of prevention and even cures for the ailing coral reefs. - Mod.TG]
[_Serratia marcescens_ is a Gram-negative bacillus in the family Enterobacteriaceae. Some strains produce a red-to-pink pigment that may have been the cause of the development of bloody discoloration of food as described as early as the 6th century BC by Pythagoras (1).
Until the middle of the 20th century, the organism was considered a harmless commensal (reasonable definition: an organism that eats with you, not eats you) but is now considered a potential cause of a variety of human infections, often nosocomial (hospital acquired) in origin.
The bacterium may be quite resistant to many antimicrobial agents.
During the time when it was considered to be a nonpathogen, it was reported to have been used as a biologic marker for biowarfare by the US military, having been released in the Pacific Ocean near San Francisco and followed in the environment (2). Whether the development of osteomyelitis and endocarditis in Bay Area intravenous drug users due to _S. marcescens_ [mostly in the mid-1970s but occurring as early as 1951 (3)] had anything to do with the military studies more than 2 decades before is not known. Yu (1) states that covert _S. marcescens_ aerosolization studies were also done in Alabama and Key West, Florida, at the same time as the San Francisco studies. Again, whether this release in 1951 is at all related to the white pox of elkhorn coral is pure speculation.
1.Yu VL: Serratia marcescens. Historical perspective and clinical review. NEngl J Med 1979; 300:887-93.
2.U.S. Army Activity in the United States:Biological warfare programs. Washington, DC, Department of the Army, February 24, 1977 (cited in reference (3)).
3. Wheat RP, Zuckerman A, Rantz LA: Infection due to Chromobacteria:
report of eleven cases. Arch Intern Med 1951; 88:461-6.
- Mod.LL]
[see also:
Coral reef bleaching - Caribbean: temperature related 20101020.3796 Montipora white syndrome, coral reef - USA (02): (HI) 20100415.1220 Montipora white syndrome, coral reef - USA: (HI) 20100403.1078
2007
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Vibrio, rare coral - UK 20070905.2933
Coral reef kill - Costa Rica 20070904.2915 Coral reef kill - Pacific Region 20070810.2600
2004
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Coral reef kills - USA (FL) (02) 20040327.0846 Coral reef kills - USA (FL) 20040320.0777
2002
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Coral reef kills, unknown etiology - Australia 20021023.5624 Coral reef kills, human waste suspected - Caribbean 20020627.4622 2000
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Coral reef kills - Belize 20000510.0713
1999
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Coral reef kills & potential human disease (02) 19990204.0161 Coral reef kills & potential human disease 19990124.0111
1998
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Coral reef bleaching & El Nino - Indian Ocean (02) 19981113.2187 Coral reef bleaching, El Nino effects - Indian Ocean 19980705.1246 Coral reef kills, etiology determined - USA 19980415.0693
1996
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White pox, coral reefs - Florida, USA (02) 19961231.2165 White Pox, coral reefs - Florida, USA 19961228.2160] ....................tg/ll/ejp/lm
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