Contaminants and Disease

Anthropogenic stressors, including contaminants, can interact with natural stressors to negatively affect wildlife health and productivity. Our lab is particularly interested in how natural and anthropogenic stressors may impact disease dynamics. Typically, the combined effects of a pollutant and parasitic infection are greater than either effect alone. We have several studies underway investigating how exposure to contaminants may alter susceptibility to disease and disease ecology. Currently these studies include amphibian (chytrid and ranavirus) and avian (malaria) diseases and will likely soon include wild hogs.

Ranavirus and Batrachochytrium dendrobatidis

SREL Collaborators: Stacey Lance, Cara Love, David Scott, Megan Winzeler

Many amphibian species’ populations are declining globally due to anthropogenic causes and recent amphibian extinction rates are higher than those for any other vertebrate species. There are many potential causes of amphibian declines but among the most often cited are exposure to environmental contaminants and emerging infectious diseases. In particular, both the chytrid fungus, Batrachochytrium dendrobatidis (Bd), and viruses within the genus Ranavirus have been implicated in mass mortality events involving amphibians. A variety of natural and anthropogenic stressors have been hypothesized to increase the emergence of wildlife diseases in amphibians via increased host susceptibility. To look at this more closely we undertook a preliminary assessment of the prevalence of ranavirus and chytrid within three contaminated (Tim’s Branch, A-01 system, H-02 constructed wetlands) and two uncontaminated (Castor Bay, Fire Pond) wetlands sites on the SRS. The A-01 wetland treatment system was designed to remediate elevated metal levels [primarily Cu, Zn, and lead (Pb)]. The H-02 wetlands are modeled after the A-01 wetlands and were constructed in 2007 to remediate elevated levels of Cu and Zn and a high pH. The Tim’s Branch system is quite different and is extensively contaminated by uranium and nickel from historical inputs from the M-Area facility, but it is hydrologicaly linked to the A-01 system and the potential for connectivity of amphibians and their pathogens exists. Our two reference sites on the SRS, Castor Bay and Fire Pond, represent uncontaminated isolated and permanent wetlands, respectively. So far we have seen higher incidence of both diseases in the constructed wetlands on site that are contaminated with copper and zinc. Now Cara, Megan, David and I are expanding the study to include more wetlands, more species and to use quantitative pcr. Megan will also be doing experimental studies to directly assess the impact of contaminant exposure on susceptibility to ranavirus.

Avian malaria in wading birds

SREL Collaborators: Larry Bryan, Stacey Lance, Cara Love, Gary Mills

Outside Collaborators: Rena Borkhataria, University of Florida

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Avian malaria (Plasmodium and/or Haemoproteus sp.) is a global pandemic which can result in multiple fitness effects on its hosts.higher parasite risks for avian populations are predicted in the future due to global climate changes, with predicted higher ambient temperatures resulting in greater distribution of vectors and extended breeding season for vectors. At the same time, Hg is a ubiquitous environmental contaminant that is transferred trophically through aquatic and terrestrial food webs. Atmospheric deposition of Hg has led to measureable Hg in most freshwater wetlands, where it converts to its bioavailable organic form (methylmercury).Mercury is a well-documented immune suppressor across vertebrate taxa and in all avian species studied to date. This is of special concern in fish-eating bird species due to the potential for bioaccumulation. As a result wading birds may be exposed to two, sublethal yet chronic stressors which could result in costs affecting productivity and survival making them ideal species to examine for potential inter-relationships between infection by avian malaria and Hg uptake. We've been undertaking a study with three main objectives:

1. Establish a baseline of the occurrence/prevalence of avian malaria in wading bird nestlings of multiple species from coastal and inland colonies in South Carolina and Georgia, and document the genera associated with the infection, given that this could change in future years with predicted temperature increases.

2. Document mercury levels in wading bird nestlings of multiple species from multiple coastal and inland colonies in South Carolina and Georgia.

3. Examine species-specific and landscape-specific trends (coastal vs. inland) in avian malaria occurrence/prevalence and mercury uptake, and assess whether the disease occurrence is linked to contaminant uptake.

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The content and opinions expressed on this web page do not necessarily reflect the views of nor are they endorsed by the University of Georgia or the University System of Georgia. Jason O'Bryhim & Stacey Lance 2013